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PCB Glossary

Active Components: Semiconductor devices, such as transistors and diodes, that can change its basic characteristics in an powered electrical circuit, such as amplifiers and rectifiers.

Analog Circuit: An electrical circuit that provides a continuous quantitative output as a response from its input.
Annular Ring: The width of the conductor pad surrounding a drilled hole.
Artwork: Printed circuit design.
Aspect Ratio: The ratio of the board thickness to the smallest-hole diameter of the printed circuit board.
Assembly File: A drawing describing the locations of components on a PCB.
Automated Test Equipment (ATE): Equipment that automatically tests and analyzes functional parameters to evaluate performance of the tested electronic devices.
Ball Grid Array (BGA): A SMD package in which solder ball interconnects cover the bottom surface of the package.
Bare Board: An unpopulated PCB.
Base Copper Weight: see Copper Foil
BBT: Bare Board Test.
Bill of materials (BOM): A comprehensive listing of all subassemblies, components, and raw materials that go into a parent assembly, showing the quantity of each required to make the assembly.
Built-In Self Test: An electrical testing method that allows the tested devices to test itself with specific added-on hardware.
CAD: Computer Aided Design.
CAM: Computer Aided Manufacturing.
CAM Files: The files used for manufacturing PCB including Gerber file, NC Drill file and Assembly Drawings.
Ceramic Ball Grid Array (CBGA): A ball grid array package with a ceramic substrate.
Chip-on-Board (COB): A configuration in which a chip is directly attached to a printed circuit board or substrate by solder or conductive adhesives.
Chip: The individual circuit or component of a silicon wafer, the leadless form of an electronic component.
Component Side: The Side of a PCB on which most of components are mounted.
Coating: A thin layer of material, conductive, magnetic or dielectric, deposited on a substance surface.
Coefficient of Thermal Expansion (CTE): The ratio of dimensional change of an object to the original dimension when temperature changes, expressed in %/ºC or ppm/ºC.
Contact Angle (Wetting Angle): The angle between the contact surfaces of two objects when bonding. The contact angle is determined by the physical and chemical properties of these two materials.
Copper Foil (Base Copper Weight): Coated copper layer on the board. It can either be characterized by weight or thickness of the coated copper layer. For instance, 0.5, 1 and 2 ounces per square foot are equivalent to 18, 35 and 70 um-thick copper layers.
Corrosive Flux: A flux that contains corrosive chemicals such as halides, amines, inorganic or organic acids that can cause oxidation of copper or tin conductors.
Curing: The irreversible process of polymerizing a thermosetting epoxy in a temperature-time profile.
Curing Time: The time needed to complete curing of an epoxy at a certain temperature.
DFSM: Dry Film Solder Mask.
Die: Integrated circuit chip as diced or cut from a finished wafer.
Die Bonder: The placement machine bonding IC chips onto achip-on-board substrate.
Die Bonding: The attachment of an IC chip to a substrate.
Dielectric: An insulating medium between conductors.
DIP: Dual in-line package with two rows of leads from the base in standard spacing between the leads and row. DIP is a through-hole mounting package.
Double-Sided Assembly: PCB assembly with components on both sides of the substrate.
DRC: Design rule check.
Dry – Film Resists: Coated photosensitive film on the copper foil of PCB using photographic methods. They are resistant to electroplating and etching processes in the manufacturing process of PCB.
Edge Connector: A connector on the circuit-board edge in the form of gold plated pads or lines of coated holes used to connect other circuit board or electronic device.
Edge Clearance: The smallest distance from any conductors or components to the edge of the PCB.
Electroless Deposition: The chemical coating of a conductive material onto a base material surface by reduction of metal ions in a chemical solution without using electrodes compared to electroplating.
Electroplating: The electrochemical deposition of reduced metal ions from an electrolytic solution onto the cathode by applying a DC current through the electrolytic solution between two electrodes, cathode and anode, respectively.
ESR: Electro-statically applied Solder Resist.
Fine Pitch: Fine pitch is more commonly referred to surface-mount components with a lead pitch of 25 mils or less.
Finger —A gold-plated terminal of a card-edge connector. Also see Gold Finger.
Flux: The material used to remove oxides from metal surfaces and enable wetting of the metal with solder.
FR4: Flame Retardent laminate made from woven glass fiber material impregnated with epoxy resin.
Functional Test: The electrical testing of an assembled electronic device with simulated function generated by the test hardware and software.
Gerber File: Data file used to control a photoplotter.
Ground Plane: A conductive plane as a common ground reference in a multilayer PCB for current returns of the circuit elements and shielding.
GI: The woven glass fiber laminate impregnated with polyimide resin.
Gold Finger —The gold-plated terminal of a card-edge connector. Also see Finger.
HDI: High Density Interconnect.
Hermetic: Airtight sealing of an object.
In-Circuit Test: Electrical test of individual component or part of the circuit in a PCB assembly instead of testing the whole circuit.
Hole Density: The number of holes per unit area on a PCB.
Interstitial Via Hole: An embedded through-hole with connection of two or more conductor layers in a multilayer PCB.
Laminate: A composite material made by bonding together several layers of same or different materials.
Lamination: The process manufacturing a laminate using pressure and heat.
Leakage Current: A small amount of current that flows across a dielectric area between two adjacent conductors.
Legend: A format of printed letters or symbols on the PCB, such as part numbers and product number or logos.
LPI: Liquid Photo-Imageable solder mask that uses photographic imaging to control a thinner mask deposition than the dry film solder mask.
Minimum Conductor Width: The smallest width of any conductors, such as traces, on a PCB.
Minimum Conductor Space: The smallest distance between any two adjacent conductors, such as traces, in a PCB.
Multilayer PCB: Circuit boards consisting three or more layers of printed circuits separated by laminate layers and bonded together with internal and external interconnections.
NC Drill: Numeric Control drill machine used to drill holes at exact locations of a PCB specified in NC Drill File.
Netlist: List of parts and their connection points which are connected in each net of a circuit.
Node: A pin or lead to which at least two components are connected through condcutors.
NPTH: Non-plated trough-hole.
Pad: The portion of a conductive pattern for connection and attachment of electronic components on the PCB. Also called Land.
PCB: Printed Circuit Board. Also called Printed Wiring Board (PWB).
PCMCIA: Personal Computer Memory Card International Association.
PEC: Printed Electronic Component.
Pick-and-Place: A manufacturing operation of assembly process in which components are selected and placed onto specific locations according to the assembly file of the circuit.
Pitch: The center-to-center spacing between conductors, such as pads and pins, on a PCB.
Plastic Leaded Chip Carrier (PLCC): A component package with J-leads.
PTH (plated-through Hole): A plated hole used as a conducting interconnection between different layers or sides of a PCB either used as connection for through-hole component or as a via.
Plating Resist: Material deposited as a covering film on an area to prevent plating on this area.
Reflow Soldering: Melting, joining and solidification of two coated metal layers by application of heat to the surface and predeposited solder paste.
Resist: Coating material used to mask or to protect selected areas of a pattern from the action of an etchant, solder, or plating.
Route (or Track): A layout or wiring of an electrical connection.
RF (radio frequency) and wireless design: A circuit design that operates in a range of electromagnetic frequencies above the audio range and below visible light. All broadcast transmission, from AM radio to satellites, falls into this range, which is between 30KHz and 300GHz.
Screen Printing: A process for transferring an image from a patterned screen to a substrate through a paste forced by a squeegee of a screen printer.
Silk Screen (Silk Legend): Epoxy-ink Legend printed on PCB. The most common colors used are white and yellow.
Small Outline Integrated Circuit (SOIC): An integrated circuit with two parallel rows of pins in surface mount package.
SMOBC: Solder mask over bare copper.
SMD: Surface Mount Device.
SMT: Surface Mount Technology.
Solder Bridging: Solder connecting, in most cases, misconnecting, two or more adjacent pads that come into contact to form a conductive path.
Solder Bumps: Round solder balls bonded to the pads of components used in face-down bonding techniques.
Solder Mask or Solder resist: Coating to prevent solder to deposit on.
Solder Wick: A band of wire removes molten solder away from a solder joining or a solder bridge or just for desoldering.
Temperature Coefficient (TC): The ratio of a quantity change of an electrical parameter, such as resistance or capacitance, of an electronic component to the original value when temperature changes, expressed in %/ºC or ppm/ºC.
Test Point: A specific point in a circuit board used for specific testing for functional adjustment or quality test in the circuit-based device.
Testing : A method for determining whether sub-assemblies, assemblies and/or a finished product conform to a set of parameter and functional specifications. Test types include: in-circuit, functional, system-level, reliability, environmental.
Turnkey: A type of outsourcing method that turns over to the subcontractor all aspects of manufacturing including material acquisition, assembly and testing. Its opposite is consignment, where the outsourcing company provides all materials required for the products and the subcontractor provides only assembly equipment and labor.
UL: Underwriter’s Laboratories. A popular safety standard for electrical devices supported by many underwriters.
Via: A plated-through hole used for interconnection of conductors on different sides or layers of a PCB.
Wave Soldering: A manufacturing operation in which solder joints are soldered simultaneously using a wave of molten solder.


Wireless Glossary

1X or 1XRTT: A high speed data protocol that is used with CDMA phones and devices for wireless internet.

2G: The most common type of phone in North America today. 2G phones deliver both voice and data transmissions, but primarily focus on voice communications. Data connections using the wireless phone are similar to dial-up connections using a older modem and speeds are quite slow. Okay for simple text messages (SMS) and email, but not much else.

2.5G: An intermediate bridging standard between 2G and 3G phones. 2G phones are purely digital and can transmit wireless data at about the same rate as a dial-up connection with a fast modem. Good for email and simple web browsing.

3G: A third-generation high-speed mobile phone that will eventually provide data at rates similar to cable or ADSL. At present, very limited availability and data transfer speeds are limited to about 144 Kbps.

3G: 3G stands for the third generation of wireless communication technology. It refers to pending improvements in wireless data and voice communications through any of a variety of proposed standards. The immediate goal is to raise transmission speeds to 2Mbit/sec.

802.11: A group of wireless specifications developed by the IEEE. It details a wireless interface between devices to manage packet traffic (to avoid collisions, etc.) Some common specifications and their distinctive attributes include the following:

802.11a — Operates in the 5-GHz frequency range (5.125 to 5.85 GHz) with a maximum 54Mbit/sec. signaling rate. The 5-GHz frequency band isn’t as crowded as the 2.4-GHz frequency because it offers significantly more radio channels than the 802.11b and is used by fewer applications. It has a shorter range than 802.11g, is actually newer than 802.11b and isn’t compatible with 802.11b.

802.11b — Operates in the 2.4-GHz Industrial, Scientific and Measurement (ISM) band (2.4 to 2.4835 GHz) and provides signaling rates of up to 11Mbit/sec. This is a very commonly used frequency. Microwave ovens, cordless phones, medical and scientific equipment, as well as Bluetooth devices, all work within the 2.4-GHz ISM band.

802.11e — Due to be ratified by the IEEE in June, the 802.11e quality-of-service specification is designed to guarantee the quality of voice and video traffic. It will be particularly important for companies interested in using Wi-Fi phones.

802.11g — Similar to 802.11b, but this standard supports signaling rates of up to 54Mbit/sec. It also operates in the heavily used 2.4-GHz ISM band but uses a different radio technology to boost overall throughput. Compatible with older 802.11b.

802.11i — Also called Wi-Fi Protected Access 2 (WPA 2), 802.11i was ratified in June 2004. WPA 2 supports the 128-bit Advanced Encryption Standard, along with 802.1x authentication and key management features.

802.11k — The 802.11k Radio Resource Management standard will provide measurement information for access points and switches to make wireless LANs run more efficiently. It may, for example, better distribute traffic loads across access points or allow dynamic adjustments of transmission power to minimize interference.

802.11n — The Standard for Enhancements for Higher Throughput is designed to raise effective WLAN throughput to 100Mbit/sec. But the group handling this task is still in the very early stages of its work.

Access point: A WLAN transceiver or “base station” that can connect a network to one or many wireless devices. APs can also bridge to one another.

Ad hoc mode: A wireless network framework in which devices can communicate directly with one another without using an AP or a connection to a regular network. Contrasts with an infrastructure network, in which all devices communicate through an AP.

Airtime: Actual time spent talking on your cellular telephone. In general most cellular phone companies charge you from the time you hit the SEND button until you hit the END button (i.e., you pay to listen to a ringing signal, but only if someone answers). GSM phone companies generally charge actual talk time and not time listening to ringing signals. You are not charged for listening to busy signals or if your call is not answered.

AMPS: Advanced Mobile Phone Service; commonly known as analog cellular that uses the 800 MHz spectrum. AMPS service has been available in North America since the mid 80’s and it is also available in Central and South America. AMPS is quickly being phased out as more energy is needed to make and monitor for calls from a handset plus providers rather use the newer digital technologies that allow them to squeeze several callers onto one channel.

Base Station: A transmission and reception station for handling cellular traffic. Usually consists of one or more receive/transmit antenna, microwave dish, and electronic circuitry. Also referred to as a cell site, since it holds one or more tx/rx cells. Base stations are constructed and placed on high buildings, hydro towers, monopoles, or other structures with a good elevation above the area to be covered. Several base stations within an area form a wireless network. On average, 800 MHz sites are spaced about 10-12 km (6-8 mi) apart and 1900 MHz sites are spaced about 3-4 km (2-2.5 mi) apart. In high network traffic areas base stations are placed much closer together. Base stations may also be placed closer together to deal with interference from adjacent buildings and other geographic irregularities. Even a Simpsons episode featured a cellular base station above their house. Mind you, real base stations don’t look like this!

BlueTooth: Bluetooth is a specification for providing links between mobile computers, mobile phones and other portable handheld devices, and connectivity to the Internet. It enables users to connect a wide range of computing and telecommunications devices easily and simply without the need to buy, carry, or connect cables.

CDMA: Code Division Multiple Access. One of the newer digital technologies in use in Canada, the US, Australia, and some southeastern Asian countries (e.g. Hong Kong and South Korea). CDMA differs from GSM and TDMA by its use of spread spectrum techniques for transmitting voice or data over the air. Rather than dividing the radio frequency spectrum into separate user channels by frequency slices or time slots, spread spectrum technology separates users by assigning them digital codes within the same broad spectrum. Advantages of CDMA include higher user capacity and immunity from interference by other signals. Available in either 800 or 1900 MHz frequencies.

CDPD: Cellular Digital Packet Data technology is used by telecommunications carriers to transfer data to users via unused analog cellular networks. If one part of the network — a specific geographic area or “cell” — is overused, CDPD can automatically reallocate network resources to handle extra traffic.

Cell: The basic geographic unit of a cellular system and the basis for the generic industry term “cellular.” A city is divided into small “cells”, each of which is equipped with a low-powered radio transmitter/receiver or base station. The cells can vary in size depending on terrain and capacity demands. By controlling the transmission power and the radio frequencies assigned from one cell to another, a computer at the MTSO monitors the movement and transfers or hands off the phone call to another cell and another radio frequency as needed.

Codec: Short for “compressor/decompressor”; refers to the hardware in a cell phone and in the cell network that compresses digitized voice prior to transmission AND takes received compressed voice and decompresses it prior to passing it to either a cell phone speaker or into a wireline system. Codec allows the cell network to essentially pass a lot of data in compressed form to permit additional users on the system and to save bandwidth. The idea behind codec is that human voices are highly lossy and a significant amount of the conversation can be removed since human ears can fill in the removed gaps at the other end. Each technology has different codec algorithms — for CDMA there is 13K and 8K.

Control Channel: A channel used for transmission of digital control information from a base station to a cellular phone (forward control channel) or from a cellular phone to a base station (reverse control channel).

CTIA: The Cellular Telecommunications & Internet Association is the international organization that aims to represent all elements of wireless communication — cellular, personal communications services, enhanced specialized mobile radio and mobile satellite services — and serve the interests of service providers, manufacturers and others.

Dual Band: Dual band phones are capable of using two different frequencies of the same technologies. For example a TDMA or CDMA phone that can use either the 800 or 1900 MHz band. There are also Triple Band phones in the GSM market that support 900, 1800, and 1900 MHz. Dual band phones allow you to access different frequencies in the same or different geographic regions, essentially giving your phone a wider coverage area.

Dual Mode: Dual mode phones that support more that one technology. For example a 800 MHz CDMA phone that also supports 800 MHz AMPS. You can also have phones that support dual band/dual mode such as the Nokia 6185 which is 800, 1900 MHz CDMA and 800 MHz AMPS. Dual mode phones allow you to access different technologies in the same or different geographic regions, essentially giving your phone a wider coverage area.

ESN: Each cellular phone is assigned an unique ESN or Electronic Serial Number, which is automatically transmitted to the cellular base station every time a call is placed. The MTSO validates the ESN with each call. Cloned cellular phones transmit a stolen ESN and charges are made to the real cellular phone account.

Frequency reuse: The ability to use the same frequencies repeatedly across a cellular system, made possible by the basic design approach for cellular. Since each cell is designed to use radio frequencies only within its boundaries, the same frequencies can be reused in other cells not far away with little potential for interference. The reuse of frequencies is what enables a cellular system to handle a huge number of calls with a limited number of channels.

GPS: The Global Positioning System is a “constellation” of 24 satellites that orbit the Earth at a height of 10,900 miles, making it possible for people using ground receivers to determine their geographic location within 10 to 100 meters. The satellites use simple mathematical calculations to broadcast information that is translated as longitude, latitude and altitude by Earth-based receivers.

GPRS: General Packet Radio Service technology runs at speeds up to 115Kbit/sec., compared with the 9.6Kbit/sec. of older GSM systems. It enables high-speed wireless Internet and other communications such as e-mail, games and applications. It supports a wide range of bandwidths and is an efficient use of limited bandwidth. It’s particularly suited for sending and receiving small amounts of data, such as e-mail and Web browsing, as well as large volumes of data.

GSM: Global System for Mobile communications. The most common digital cellular system in the world. GSM is used all over Europe, plus many countries in the Middle East, Asia, Africa, South America, Australia, and North America. GSM’s air interface is based on narrowband TDMA technology, where available frequency bands are divided into time slots, with each user having access to one time slot at regular intervals. Narrow band TDMA allows eight simultaneous communications on a single radio multiplexor and is designed to support 16 half-rate channels. GSM also is the only technology that provides incoming and outgoing data services, such as email, fax, and internet surfing. GSM makes use of a SIM card that allows memory portability between dumb GSM phones.

Handoff: The process by which the MTSO passes a cellular phone conversation from one radio frequency in one cell to another radio frequency in another. The handoff is performed so quickly that users usually never notice.

Hertz: A unit for expressing frequency which is the number of times a wave-like radio signal changes from maximum positive to maximum negative and then back to maximum positive again. 1 Hz = 1 cycle per second. 1 kilohertz (kHz) = 1,000 Hz; 1 megahertz (MHz) = 1,000 kHz or 1,000,000 Hz; 1 gigahertz (GHz) = 1,000 MHz or 1 million kHz or 1 billion Hz. AMPS (analog) cellular phones in Canada and the US use the 800 MHz band. Digital phones use either the 800 MHz or 1900 MHz (or 1.9 GHz) frequencies. Specifically, CDMA and TDMA use either 800 or 1900 MHz; iDEN uses only 800 MHz; GSM uses either the 850 or the 1900 MHz spectrum in North America. GSM uses 900, 1800, and/or 1900 MHz on other continents.

Hot spot: A place, such as a hotel, restaurant or airport, that offers Wi-Fi access, either free or for a fee.

iDEN: A modified TDMA technology used by Motorola. iDEN phones operate at 800 MHz and are offered by Telus Mobility in Canada and by Nextel in the US. Some of the newer iDEN phones also are hybrid with GSM technology and may roam overseas.

I-Mode: A popular wireless Internet service rolled out in 1999 by NTT DoCoMo Inc. in Japan. It’s based on a simplified form of HTML and delivers packet-based information — such as games, e-mail and even business applications — to handheld devices.

IEEE: Institute of Electrical and Electronics Engineers Inc. is a nonprofit, technical professional association of more than 360,000 individual members in approximately 175 countries that is an authority in technical areas such as computer engineering and telecommunications. It developed the 802.11 specifications.

MAC: Every wireless 802.11 device has its own specific Media Access Control address hard-coded into it. This unique identifier can be used to provide security for wireless networks. When a network uses a MAC table, only the 802.11 radios that have had their MAC addresses added to that network’s MAC table are able to get onto the network.

MTSO: Mobile Telephone Switching Office. The central switch that controls the entire operation of a cellular system. It is a sophisticated computer that monitors all cellular calls, tracks the location of all cellular-equipped vehicles traveling in the system, arranges handoffs, keeps track of billing information, etc.

NAM: The NAM or Number Assignment Module is the electronic memory in the cellular phone that stores the telephone number. Phones with dual- or multi-NAM features offer users the option of registering the phone with a local number in more than one market.

Paging: The act of seeking a cellular phone when an incoming call is trying to reach the phone.

PCS: Personal Communication Services. Essentially the same as cellular, but indicating a digital phone. See this FAQ for a more detailed description.

PRL: Referred Roaming List. A list of SID’s kept inside a phone to permit roaming on other wireless networks. A service provider may set up roaming agreements with other service providers in different geographic regions and the PRL will try to locate one of these service providers’ networks first when the home service provider is unavailable. PRL’s do change so it’s a good idea to ask for a PRL upgrade every 6 months or so if you do a lot of roaming outside your home service area.

Registration: The procedure that a cellular phone initiates to a base station to indicate that it is now active.

RFID: Radio frequency identification uses low-powered radio transmitters to read data stored in a transponder (tag) at distances ranging from one inch to 100 feet. RFID tags are used to track assets, manage inventory and authorize payments, and they increasingly serve as electronic keys for everything from autos to secure facilities.

Roaming: The ability to use your cellular phone outside your providers’ home service area. Providers often set up Roaming Agreements with other providers in different geographic locations. A roaming agreement lets you seemlessly make calls in the other provider’s geographic service area without operator intervention. Roaming agreements save customers money and time. Airtime incurred while roaming shows up on your monthly statement as an additional charge, unless your monthly plan includes roaming.

Roaming is never as cheap as your home airtime rates, but is provided as a short-term convience for a provider’s customers. Sometimes a roaming agreement may not be in place and operator intervention is required to obtain a credit card number. This is usually much more expensive than a roaming agreement (up to $5/min compared to $1/min). Always contact your provider before roaming. Sometimes phones require roaming to be enabled to prevent fraudulent activity (e.g., anyone traveling to New York must have their provider unlock roaming restrictions for the duration of the trip); sometimes you need to know special codes to allow calls to be delivered to your phone; some roaming agreements allow the host provider to charge a daily roaming fee just to have the phone accessing their network; and some other providers charge airtime for the phone ringing even though you choose not to answer it.

SID: System Identification. A five digit number that indicates which service area the phone is in. Most carriers have one SID assigned to their service area.

SIM card: A small memory card not much bigger than half the length of your thumb. Used in GSM phones to hold your phone numbers and other information. Can be removed and inserted into other GSM phones, allowing you to keep your numbers and to place and receive phone calls.

Site survey: Done at the location for a new WLAN in an effort to avoid what could be time-consuming and costly problems down the road. It involves diagramming the network, checking the building and testing the equipment.

Smart phone: A wireless phone with text and Internet capabilities. Smart phones can handle wireless phone calls, hold addresses and take voice mail and can also access information on the Internet and send and receive e-mail and fax transmissions.

SMS: Short Message Service. A method of delivering a short (120-200 character) message to your digital cellular phone. GSM phones can also send SMS. A nice way to send a short message to someone without calling them. Private SMS services include weather and sports reports, stock quotes, and more. Usually people can either visit a SMS web page and type a short message which is sent to your phone or email your phone (e.g., 2509999999@telusmobilty.com). Some providers change additional monthly fees for the reception or transmission of SMS. See my Links page for a list of SMS services.

SP-lock: A lock placed on a cellular phone by some service providers to ensure that you can only use the phone with their services. More Information.

SSI: A Service Set Identifier is a sequence of characters unique to a specific network or network segment that’s used by the network and all attached devices to identify themselves and allow devices to connect to the correct network when more than one independent network is operating in nearby areas.

Standby time: The amount of time you can leave your fully charged cellular phone turned on before the phone will completely discharge the batteries.

Symbian Ltd.: A joint venture among LM Ericsson Telephone Co., Motorola Inc., Nokia Corp. and Psion PLC to develop new operating systems based on Psion’s EPOC32 platform for small mobile devices for wireless devices such as phones and handhelds.

Talk time: The length of time you can talk on your cellular phone without recharging the battery. The battery capacity of a cellular phone is usually expressed in terms of so many minutes of talk time OR so many hours of standby time. When you’re talking, the phone draws additional power from the battery.

TDMA: Time Division Multiple Access. TDMA divides frequency bands available to the network into time slots, with each user having access to one time slot at regular intervals. TDMA thereby makes more efficient use of available bandwidth than the previous generation AMPS technology. Available in either 800 or 1900 MHz frequencies.

UWB: Ultrawideband, also called digital pulse, is a wireless technology for transmitting digital data over a wide swath of the radio frequency spectrum with very low power. Because of the low power requirement, it can carry signals through doors and other obstacles that tend to reflect signals at more limited bandwidths and a higher power. It can carry large amounts of data and is used for ground-penetrating radar and radio locations systems.

Voice Channel: A channel used for transmission of voice data from a base station to a cellular phone (forward voice channel) or from a cellular phone to a base station (reverse voice channel)

WAP: The Wireless Application Protocol is a set of specifications, developed by the WAP Forum, that lets developers using Wireless Markup Language build networked applications designed for handheld wireless devices. WAP was designed to work within the constraints of these devices: a limited memory and CPU size, small, monochrome screens, low bandwidth and erratic connections. WAP is a de facto standard, with support from more than 200 vendors.

War driving: Typically refers to driving around with a wireless-enabled laptop and antenna to find places where it’s possible to access exposed wireless networks. These are usually company networks that extend beyond the physical infrastructure of the company and are left unprotected.

War chalking: Marking buildings or sidewalks with chalk to show others where it’s possible to access an exposed company wireless network. These access points are typically found through war driving (see above).

WEP: Wired-Equivalent Privacy protocol was specified in the IEEE 802.11 standard to provide a WLAN with a minimal level of security and privacy comparable to a typical wired LAN, using data encryption. It’s now widely recognized as flawed because of an insufficient key length and other problems and can be cracked in a short time with readily available tools.

Wi-Fi: Wireless fidelity is the generic term for 802.11 technology (see 802.11 above).

Wi-Fi Alliance: A nonprofit international association formed in 1999 to certify interoperability of WLAN products based on the IEEE 802.11 specification. Currently, the Wi-Fi Alliance has over 200 member companies from around the world, and over 1,000 products have received Wi-Fi certification since certification began in March of 2000. The goal of the Wi-Fi Alliance’s members is to enhance the user experience through product interoperability.

WiMax: Popular name of the 802.16 wireless metropolitan-area network standard that’s currently being developed. WiMax, which will have a range of up to 31 miles, is primarily aimed at making broadband network access widely available without the expense of stringing wires (as in cable-access broadband) or the distance limitations of Digital Subscriber Line.

Wireless Data: A service that allows you to send digital data over a cellular phone. Analog phones require a cellular modem; digital phones do not. Not offered by all providers.

WLAN: Wireless local-area networks use radio waves instead of a cable to connect a user device, such as a laptop computer, to a LAN. They provide Ethernet connections over the air and operate under the 802.11 family of specifications developed by the IEEE.

WML: Wireless Markup Language is like the Internet programming language HTML. It delivers Internet content to small wireless devices, such as browser-equipped cellular phones and handheld devices, which typically have very small displays, slow CPUs, limited memory capacity, low bandwidth and restricted user-input capabilities.

WPA: Wi-Fi Protected Access is a data encryption specification for 802.11 wireless networks that replaces the weaker WEP. It improves on WEP by using dynamic keys, Extensible Authentication Protocol to secure network access, and an encryption method called Temporal Key Integrity Protocol to secure data transmissions.


Semiconductor Glossary

Access Time: Time interval between the instant that a piece of information is sent to the memory device and the instant it returns.Alternating Current (AC): A type of electrical current in which the direction of the flow of electrons switches back and forth. In the US, the current that comes from a wall outlet is alternating; it cycles back and forth sixty times each second. The current that flows in a flashlight, on the other hand, is direct current (DC), which does not alternate.

Ambient: Room temperature.

Amplifier: A device which takes in a weak electric signal and sends out a stronger one. Amplifiers are used to boost electrical signals in many electronic devices, including radios, televisions, and telephones. Both vacuum tubes and transistors can be amplifiers, though today vacuum tubes are rarely used for this purpose.

Atoms: The smallest possible piece of any pure element that still has the properties of that element. Atoms are made of smaller particles including electrons, protons, and neutrons. Differences in the numbers of these particles create the differences between the elements. An atom is about 500-billionths of an inch, or a hundred millionths of a centimeter across.

Audion: A special kind of vacuum tube which can be used to amplify weak electric signals. The audion was used in the Bell phone system, as well as in early radios and computers. It was eventually replaced in most applications by the transistor.

Bit (Memory Bit) Short for ‘Binary Digit.’: The smallest piece of data (a ‘1’ or ‘0’) that a computer recognizes. Combinations of 1s and 0s are used to represent characters and numbers.

Byte: A number of binary bits, usually eight, that represent one numeric or alphabetic character.

Capacitor: A device that stores electrical charge, using a positively charged surface and a negatively charged surface with a gap between them. The Leyden jar, used by early electrical experimenters (including Benjamin Franklin) was a form of capacitor. A smaller kind of capacitor is often used in electrical circuits.

Cat’s Whisker: A tiny metal wire used in early home radio kits. Radio listeners carefully moved the wire tips around on the surface of a crystal to just the right spot to allow an electrical signal to travel down one wire, through the crystal and out the other wire. If the wires were positioned on the right spot, and it was often tough to find the right spot, the radio signal could be heard through the earphones.

Charge: An electrical property of particles, such as electrons and protons, which causes them to attract and repel each other. A material with an excess of electrons is defined to have a “negative” charge; material with an absence of electrons (or an excess of protons) is defined as “positive.” Materials with a balanced number of electrons and protons are called “neutral.” Positive and negative charges attract each other. That attraction can cause interesting effects at the junction between positive and negative semiconductors. This special junction is what makes the right configuration of semiconductors work as a transistor.

Circuit: A string of electronic devices such as transistors, resistors, capacitors, and diodes connected by wires so that current can run through it in a complete loop. Circuits can be simple or complex. The wiring connecting a switch to a light to the power source and back to the switch is a simple circuit; opening the switch breaks the circuit and stops the current flow. Even a computer chip is simply an extremely complicated network of circuits.

Cleanroom: The super clean environment in which semiconductors are manufactured. The lower the rating, the cleaner the facility. These rooms typically have hundreds of thousands of particles less per cubic foot than the normal environment.

Conductor: Any material that easily allows the flow of electricity. Metals are good conductors. Such materials conduct electricity because electrons can move from one atom of a conductor to the next, forming an electric current.

CPU (Central Processing Unit): The computer module in charge of retrieving, decoding, and executing instructions.

Crystal: A chunk of solid material in which all the atoms are lined up in an orderly pattern like rows of oranges in a grocery store. Transistors are made out of semiconductor crystals. Growing perfect germanium and silicon crystals with no defects or unwanted impurities is key to building a working transistor.

Current: The flow of charge carriers (holes or electrons) through a conducting wire or crystal.

Die: A single rectangular piece of semiconductor material onto which specific electrical circuits have been fabricated; refers to a semiconductor which has not yet been packaged.

Diffusion: The standard procedure for doping silicon by heating wafers in a furnace from 400 to 1,150 degrees C in an atmosphere of dopant atoms.

Diode: Rectifier. An electronic device with two wires or terminals. A rectifier allows electrical current to flow through in only one direction and is used for converting alternating current into direct current. Rectifiers were important for use in radios, which required direct current to power the amplifiers driving speakers or headphones.

Direct Current (DC): Current which moves in a single direction in a steady flow. Normal household electricity is alternating current (AC) which repeatedly reverses its direction. However, many electronics devices require DC, and therefore must convert the current into DC before using it. Diodes are used to convert AC to DC.

Doping: Deliberately adding a very small amount of foreign substance to an otherwise very pure semiconductor crystal. These added impurities give the semiconductor an excess of conducting electrons or an excess of conducting holes (the absence of conducting electrons) which is crucial for making a working transistor.

Electric Field: The region around any electrically charged material contains an electric field that affects other charged objects. The field around a negatively charged material pulls positively-charged objects in toward the material, while negatively-charged objects are pushed away. Around a positively charged material, on the contrary, negative objects are attracted and positive objects are repelled. The strength of the field gets rapidly weaker as one moves further away from the charged material.

Electric Signal: Information expressed through changes in an electric current. Information can be encoded in on-and-off switches of current, in the amplitude of the current, or in other easily-detectable changes. Sound waves, for example, can be converted to electricity by a microphone and sent as an electrical signal through the wires of a stereo to the speakers.

Electrode: An electrical lead or wire attached to any electronic device or circuit through which current may flow in or out.

Electron: Electrons are one of the particles that makes up an atom and particles that, in motion, can form an electric current. An electron is 2000 times lighter than the lightest atom.

Element: Any of over a hundred fundamental materials containing only one kind of atom. Some common elements are oxygen, gold, hydrogen, and silicon. All other materials are made of compounds or mixtures of elements. Water, for example, is made of two hydrogen atoms attached to one oxygen atom.

Etch: Removal of specific material (such as portions of a given layer) through a chemical reaction.

Field-effect transistor: The most common type of modern transistor, and the type of transistor used in integrated circuits. The field-effect transistor is so named because an incoming weak electrical signal creates an electrical field across a section of semiconductor. This field causes a second electrical current to flow across the semiconductor, identical to the first weak signal, but stronger.

Flat Pack: A flat, rectangular IC package type with the necessary leads projecting from the sides of the package.

Four-layer diode: A semiconductor device which can take alternating current and turn it into direct current but which also stops letting any current through once a certain voltage is reached. The diode is made of four layers of alternating types of semiconductor.

Germanium: A chemical element that acts as a semiconductor, meaning sometimes it conducts electricity and sometimes it doesn’t. The first transistors were all made out of germanium.

Holes: When an array of atoms in a crystal is missing a conducting electron, it’s said to have a “hole.” Since conducting electrons are negative, holes are positive. Even though holes are an absence of a conducting electron, scientists often talk about holes flowing as if they were real particles.

IC (Integrated Circuit): A tiny complex of electronic components and their connections produced on a slice of material such as silicon. Commonly referred to as a die or chip.

Insulator: Any material that does not conduct electricity. Glass and rubber are common insulators. These materials are made of atoms which don’t allow electrons to move freely, which means there can be no electric current.

Integrated Circuit: A collection of transistors and electrical circuits all built onto a single crystal. Today’s integrated circuits are no more than a centimeter long, and they can carry millions of microscopic transistors. All computers have integrated circuits inside.

KGD (Known Good Die): Fully tested chips that are ready for bonding into multi-chip modules.

Junction Transistor: The second type of transistor built, and a direct ancestor of modern day transistors. It consists of two sections of one type of semiconductor (N- or P-) around a middle slab of the other type. The junctions between the semiconductor sections cause an incoming weak electrical signal to be amplified.

Logic:The circuits used to control operation of IC devices.

Megabit: One million binary pieces (bits) of information.

Microprocessor: A circuit of transistors and other electrical components on a chip that can process programs, remember information, or perform calculations.

Mil: One-thousandth of an inch, equal to 25.4 microns.

N-type semiconductor: A semiconductor which has an excess of conduction electrons. A semiconductor can be made into N-type by adding trace amounts of another element to the original semiconductor crystal. Today’s transistors all require sections of both N-type and P-type semiconductors.

P-type semiconductor: A semiconductor which has an excess of conducting holes. It is created by adding trace amounts of other elements to the original pure semiconductor crystal. Today’s transistors all require sections of both N- type and P-type semiconductors.

PC Board Printed circuit board.: The board(s) used in a computer system onto which semiconductor components are connected.

Photoresist: A material that prevents etching or plating of the area it covers

Planar: A simple flat capacitor built between silicon and polysilicon layers.

Point-contact transistor: The very first type of transistor ever made, invented by John Bardeen and William Brattain. So-called because it consists of two metal points making light contact with the surface of a germanium crystal.

Rectifier: See Diode

Reticle: A piece of glass with a chrome pattern for several die, used in the photolithography process.

Semiconductor: A material that conducts more than an insulator but less than a conductor. Some semiconductors conduct at some times but not at others. Some common semiconductors are silicon and germanium. Transistors are made out of semiconductor crystals.

Shrink: Reduction in die (chip) size.

Silicon: Silicon is one of the most common elements on Earth in the Earth’s crust, it’s second in mass only to oxygen and can be found in any quartz crystal. Beach sand is largely silicon. Silicon is also the semiconductor material out of which almost all modern transistors are made.

SIMM (Single In-line Memory Module): A high-density DRAM package alternative consisting of several plastic leaded chip carriers (PLCC) connected to a single printed circuit board (PC board). SIMMs provide an upgrade vehicle for future generations of DRAMs without having to redesign the PC board.

Solid State: Relating to the properties of solid, usually crystalline, materials including semiconductors. Solid state science is often a mixture of physics, and chemistry, and materials science.

Subassemblies: Two or more individually replaceable items integrated to form a system.

Transistor: Transistors are tiny electrical devices that can be found in everything from radios to robots. They have two key properties: 1) they can amplify an electrical signal and 2) they can switch on and off, letting current through or blocking it as necessary.

Type-A transistor: What Bell called the first point-contact transistors they built. These were installed into the Bell Phone system, and given to the military and scientists for other purposes as well -­ but the Type-A transistor was never widely used.

Voltage: Voltage is a measure of the energy required to move a charge from one point to another. A difference in the amount of electric charge between two points creates a difference in potential energy, measured in “volts,” which causes electrons to flow from an area with more electrons to an area with fewer, producing an electric current.


Rapid Prototyping Glossary

3-Dimensional Printing (3DP): A rapid prototyping process developed at the Massachusetts Institute of Technology (MIT). Layers of powder are bonded by inkjet to form a part. The term is also used generically as synonym for rapid prototyping.

3D printer / 3D printing: Refers generally to the low-cost segment of the rapid prototyping machine market. The output of these systems is typically considered adequate for concept and appearance modeling, but may lack the accuracy or other attributes of more costly systems. This terminology is used extensively in the Wohlers Report, but others may not draw as fine a distinction.

Absolute Accuracy: Defined as the difference between an intended final dimension and the actual dimension as determined by a physical measurement of the part. In addition to those for linear dimensions, there are accuracy specifications for such features as hole sizes and flatness.

Adaptive Slicing: The use of variable layer thickness in an additive fabrication process, generally thinner layers being used where part detail is greatest.

Additive Fabrication: Fabrication of a part by adding materials to a substrate or previously formed portions of a part. The most common additive fabrication methods utilize a layered approach, but other geometries are possible. The term is also used generically as a synonym for rapid prototyping.

Advanced Digital Manufacturing (ADM): 3D Systems’ trade name for direct manufacturing or direct fabrication. Often used in conjunction with the company’s OptoForm technology.

Anisotropic: Refers to the fact that parts may have different physical properties depending on which direction measurements are made, and such differences can also arise if the exact same part is made in a different way. This can happen if the building orientation of the part in the machine is changed, and also from the sequence in which the part’s elements are fabricated.

Ballistic Particle Manufacturing (BPM): A rapid prototyping process which deposits materials by means of inkjet technology. At one time the term was used to refer to a specific company’s technology, BPM, Inc., now defunct, but prior to that it was an early generic term for inkjet-based RP. The term is not often used at present.

Bridge Tooling: Tooling which is typically capable of producing quantities of several tens to several hundreds of parts. That is to say, it “bridges” the quantity between very low volume prototype tooling and full production tooling. In some cases bridge tooling may offer sufficient volume to meet production requirements.

Brown Part: A part which has been sintered or had other secondary operations performed on it to bring it from the loosely-bonded, as-formed “green” state. Parts in the brown state are generally dimensionally stable, but are often porous and usually must be infiltrated with another material before use.

Computer Numerical Control (CNC): Refers to a machine tool which is operated under automatic control, as opposed to manually by an operator.

Computer-Aided Design (CAD): Also sometimes called computer-aided drafting, is a computer program which implements the functions of geometric design, drafting and documentation.

Computer-Aided Engineering (CAE): A computer program which automates one or more engineering analysis functions to determine the mechanical, thermal, magnetic or other characteristics or state of a system. CAE programs may use a geometry definition from a CAD program as a starting point, and usually utilize some form of finite element analysis (FEA) as the means to perform the analysis.

Computer-Aided Manufacturing (CAM): A computer program that generates tool paths or other manufacturing data to fabricate tooling, usually by subtractive means. CAM programs may use a geometry definition from a CAD program as a starting point.

Concept Model / Conceptual Model: A part intended primarily for form or appearance study, but which typically cannot be used to either check fit to other parts, or provide functionality of the final part in an application.

Conformal Cooling: Cooling lines in an injection molding tool that closely follow the geometry of the part to be produced.

Desktop Manufacturing (DTM): An early synonym for rapid prototyping, but no longer in current usage. DTM Corp., now incorporated into 3D Systems, was named after this terminology. Use of DTM as a company name became more common usage than the prior technical definition itself.

Direct (Fabrication) Processes: Generally refers to tooling which is made directly by a rapid prototyping system, as opposed to using the RP part as a pattern in a secondary process.

Direct AIM tooling: 3D Systems’ trade name for a process of producing injection-mold tooling directly by stereolithography. AIM stands for ACES Injection Molding, where ACES stands for Accurate Clear Epoxy Solid, another 3D trade name.

Direct Composite Manufacturing: 3D Systems’ trade name for OptoForm technology, a stereolithography process which utilizes paste-like photopolymers to fabricate useable parts.

Direct Manufacturing: A synonym for rapid manufacturing. It refers to parts made directly for end-use by an additive rapid prototyping process.

Direct Metal Deposition (DMD):A rapid laser powder forming process commercialized by POM Group and based on research done at the University of Michigan.

Directed Metal Deposition System (DMDS): Optomec’s trade name for the LENS ® (Reg. trademark of Sandia National Labs. and Sandia Corp.) process.

Direct Shell Production Casting (DSPC): Soligen is the exclusive supplier for this specialized version of MIT’s three dimensional printing process (3DP). It is used exclusively for investment casting applications.

Directed Light Fabrication (DLF): A laser powder forming rapid prototyping process developed by Los Alamos National Laboratory.

Dots Per Inch (DPI): A measure of the resolution of a printer. The number of discrete and distinct printed marks that an instrument is capable of producing in a linear inch. Also sometimes used in RP to describe the ability of an RP system to produce discrete voxels in the X-Y axial directions.

Electron Beam Melting (EBM): The Electron Beam Melting (EBM) process from Arcam is a powder-based process having a lot in common with selective laser sintering, but replaces the laser with a scanned electron beam to produce fully-dense metal parts.

Electronic Marketplace: A virtual market for buyers and sellers implemented through the Internet or World Wide Web. Also known as a web exchange.

Final Machining: A secondary operation in which parts formed by a rapid prototyping method are brought to acceptable final finishes and tolerances typically by subtractive CNC technology.

Finish (Part Finish): A qualitative term for the appearance of a part. For example, technologies based on powders have a sandy or diffuse finish; some inkjet technologies produce a smooth finish due to use of extremely thin layers; sheet-based methods might be considered poorer in finish because stairstepping is more pronounced.

Freeform Fabrication (FFF): A synonym for rapid prototyping. The term is more precise and wider in scope, and somewhat favored by the academic community. One variant is freeform manufacturing (FFM), but a more common one is solid freeform fabrication (SFF).

Fused Deposition Modeling (FDM): A thermoplastic extrusion-based rapid prototyping technology provided by Stratasys.

Fused Deposition of Ceramics (FDC): Fused deposition modeling using a composite material of thermoplastic or other binder containing ceramic particles or fibers.

Green Part: A part that has been formed by a rapid prototyping process, but is in a loosely-bonded state. For example, metal or ceramic parts formed by some selective laser sintering systems are in a “green” state when removed from the machine. They are then sintered by a secondary operation to a “brown” state.

Indirect (Fabrication) Processes: Generally refers to tooling which is made by using an RP-generated part as a pattern for a secondary process as opposed to directly fabricating a tool using the RP process itself.

Initial Graphic Exchange Specification (IGES): A standard neutral format for the exchange of 2D and 3D CAD data. STEP is a follow-on to IGES and stands for Standard for the Exchange of Product Model Data.

Laminated Object Manufacturing (LOM): Helisys, now defunct and succeeded by Cubic Technologies, was the first producer but also several other manufacturers provide this technology. :Layers of paper or other materials are cut and bonded to form a part.

Laser Additive Manufacturing (LAM): A laser powder forming rapid prototyping process developed by AeroMet Corporation. It’s mainly aimed at producing large parts from reactive materials such as titanium for aerospace applications.

Laser Engineered Net-Shaping (TM) (LENS ®): A rapid prototyping process which deposits metal powder into a pool of molten metal or other build material formed by a focused laser beam. There are several variants either commercially available or under development. LENS ® was developed by Sandia National Laboratories and commercialized by Optomec. It can also be used for repairing and modifying existing parts and tools. (LENS ® and Laser Engineered Net-Shaping (TM) are registered trademarks of Sandia National Labs. and Sandia Corp.)

Liquid Metal Jet Printing (LMJP): Similar to inkjet printing where individual molten droplets are controlled and printed to specific locations.

Mass Customization: A process whereby small lots of individualized parts or products are produced. The opposite of mass production whereby large numbers of identical parts or products are produced.

Mesoscopic Integrated Conformal Electronics (MICE): This DARPA program is aimed at simplifying the manufacture of electronic devices and systems, and providing greater flexibility than is possible using existing technologies. In size, mesoscale devices fall between integrated circuits and surface-mount components.

Minimum Feature Size: Refers to the smallest detail of a part that can faithfully be reproduced. Mathematical definitions are usually based on a minimum curvature as a limit, but anecdotal values based on experience are more commonly utilized.

ModelMaker: This is an inkjet RP method produced by Solidscape (formerly Sanders Prototypes), and the related company, Sanders International. It produces the highest accuracy and resolution of all RP methods, but is slow and has limited material choices.

MultiJet Modeling: This is an inkjet RP method produced by 3D Systems, Inc. It uses a wide area head and is most often used for generating quick concept models. The materials available are wax-like plastics and accuracy is lower than that available from stereolithography.

Paper Lamination Technology (PLT): A variant on laminated object manufacturing RP technology from Kira Corp. of Japan.

Pattern: An object or part which possesses the mechanical geometry of a final object or part, but which may not possess the desired mechanical, thermal or other attributes of the final parts. Patterns are used in secondary processes to form tools to make parts for end-uses.

Photopolymer: Material systems which change from a liquid to a solid state upon application of light (actinic) radiation. Light sources can be a laser or lamp, but related radiation-curable materials may be made solid by application of microwave or heat-based radiation sources. Photopolymers are typically complex mixtures of compounds rather than consisting of a single component.

Precision: See absolute accuracy.

ProMetal: An application of MIT’s Three Dimensional Printing Process to the fabrication of injection molds. Steel powder layers are bonded by photopolymer selectively applied by a wide area inkjet head.

QuickCast: 3D Systems’ trade name for a stereolithography build style used to make investment casting patterns.

Rapid Manufacturing: Refers to the process of fabricating parts directly for end-use from a rapid prototyping machine. A synonym is direct manufacturing.

Rapid Prototyping: Computer-controlled additive fabrication. Commonly used synonyms for RP are: 3-Dimensional Printing, additive fabrication, freeform fabrication, solid freeform fabrication, stereolithography. Note that most of these synonyms are imprecise.

Rapid Tooling: Most often refers to the process of fabricating tools from a rapid prototyping process. Rapid tooling may utilize direct or indirect methods: In direct methods, the part fabricated by the RP machine itself is used as the tool. In indirect methods, the part fabricated by the RP machine is used as a pattern in a secondary process. The resulting part from the secondary process is then used as the tool. In recent years, the term rapid tooling has been borrowed by practitioners of industry-standard methods such as subtractive CNC to refer to the ability to streamline these processes to compete with additive technologies.

Resolution: Refers to the minimum increment in dimensions that a system achieve. It’s one of the main determining factors for finish, appearance and accuracy, but certainly not the only one.

Reverse Engineering: The process of measuring an existing part to create a geometric CAD data definition of the part. In common non-technical usage, reverse engineering may also refer to measuring or analyzing a part or a product for the purpose of copying it.

Secondary operations: Manual or machine-based operations which must be carried out on a part fabricated by a rapid prototyping system before use. Secondary operations may include, post curing, support-removal, sanding, machining, etc.

Secondary process: Any one of a large number of processes such as rubber molding. Sprayform, EcoTool, etc., that utilize a rapid prototyping-fabricated part as pattern to create a final tool or part.

Selective laser sintering (SLS): A rapid prototyping technology in which powders are fused laser fused layerwise by a laser. The technology produces accurate parts and models in engineering polymers, metals and polymer-coated sand for casting applications. Speed is similar to stereolithography, but material selection is wider.

Solid freeform fabrication (SFF): A synonym for rapid prototyping. The term is more precise and wider in scope, and somewhat favored by the academic community. A variant is freeform fabrication (FFF).

Solid ground curing (SGC): This photopolymer-based technology was provided by Cubital. The company has been dissolved, but the process may still be available from a very few companies. A xerographically-generated mask is used to cure an entire layer of photopolymer at one time. It offers good accuracy coupled with high throughput, but is considered quite expensive.

Stairstepping: A type of inaccuracy, as well as a visual appearance artifact It refers to the stepped appearance of the edges of a part, a consequence of additive fabricating a part in layers of necesarily finite thickness.

STEP: A follow-on to the IGES neutral file exchange format. The acronym stands for Standard for the Exchange of Product Model Data.

Stereolithography (SL) (SLA): A rapid prototyping process that fabricates a part layerwise by hardening a photopolymer with a guided laser beam. Stereolithography is frequently used as a general term for “rapid prototyping,” but this is neither precise nor correct.

STL: A file format used in RP to define the geometry of the part to be made. STL files are created by CAD programs by translating their native or neutral files into the STL format. The STL file defines the coordinates of numerous triangular facets that approximate the shape of an object or part.

Subtractive Machining: The fabrication of a part by removing material from a stock shape of material. The stock shape may be a prismatic solid, cylinder, plate, etc. The removal of material may by cutting, turning, electro-discharge or other means. Common machinery such as millers, lathes and drills are subtractive tools.

Support Structure:Many rapid prototyping machines need a means to hold in place unsupported geometries during fabrication, such as the top of a part in the shape of the letter “T.” These supports are usually calculated and added to the part by the system’s software and may be formed of the same material as the part, or from a different material entirely. Support structures are either mechanically removed or dissolved away in secondary operations before the part can be used.

Virtual Prototyping: Computer-based prototyping without recourse to a physical part or object.

Voxel: The three dimensional equivalent of a pixel. A pixel is a “picture element,” and a voxel is a “volume element.” A voxel may also be defined as the minimum volume that a rapid prototyping system can fabricate.

Web Exchange: A virtual market for buyers and sellers implemented through the Internet or World Wide Web. Also known as an electronic marketplace.


RF Terms Glossary

2G – second generation of wireless communications systems
3G – third generation
A/D – analog-to-digital
AC – alternating current
ACPR – adjacent-channel power ratio
ADC – analog-to-digital converter
AGC – automatic gain control
AMPS – advanced mobile phone system
ASIC – application-specific integrated circuit
ASK – amplifier shift keying
ASP – application service provider
ATM – asynchronous transfer mode
AWGN – additive white gaussian noise
BER – bit error rate
BPSK – binary phase shift keying
CCRR – co-channel rejection ratio
CDMA – code-division multiple access
CDPD – cellular digital packet data
CMOS – complementary metal-oxide semiconductor
CMRR – common-mode rejection ratio
CPU – central processing unit system
CW – continuous wave
DC – direct current
dBc – dB relative to the carrier power
DCS – distributed communications system or digital cellular system
DDS – direct digital synthesis
DECT – digital european cordless telephone
DSP – digital signal processor
DUT – device under test
EEPROM – electrically erasable programmable read-only memory
EMC – electromagnetic compatibility
EMI – electromagnetic interference
ESD – electrostatic discharge
ETSI – european telecommunications standards institute
FCC – federal communications commission
FDD – frequency division duplex
FEC – forward error corrections
FER – frame error rate
FET – field-effect transistor
FHSS – frequency-hopping, spread spectrum
FIFO – first-in, first-out
FIR – finite impulse response
FM – frequency modulation
FSK – frequency shift keying
GaAs – gallium arsenide
GaN – gallium nitride
GFSK – gaussian filtered frequency shift keying
GHz – gigahertz
GMSK – gaussian minimum shift keying
GPIB – general-purpose interface bus
GPRS – general packet radio service
GPS – global positioning system
GSM – global system for mobile communications
HBT – heterojunction bipolar transistor
HEMT – high electron mobility transistor
Hz – Hertz
HSCSD – high-speed circuit-switched data
HTTP – hypertext transfer protocol
I and Q – in-phase and quadrature
I/O – input/output
IC – integrated circuit
IF – intermediate frequency
IM – intermodulation
IMD – intermodulation distortion
InGaP – indium gallium phosphide
InP – indium phosphide
IP – internet protocol
IR – infrared
ISM – industrial, scientific, and medical
kB – kilobyte
LDMOS – laterally diffused metal oxide silicon
LMDS – local multipoint distribution service
LNA – low-noise amplifier
LO – local oscillator
LOS – line of sight
LPF – low-pass filter
LSI – large scale integration
LTCC – low-temperature co-fired ceramic
MDS – multipoint distribution systems
MHZ – megahertz
MMDS – multichannel multipoint distribution service
MMIC – monolithic microwave integrated circuit
MOSFET – metal-oxide semiconductor field-effect transistor
MS/s – million of samples per second
NTC – negative temperature coefficient
OEM – original equipment manufacturer
OXCO – oven controlled crystal oscillator
PA – power amplifier
PAE – power added efficiency
PAR – peak-to-average ratio
PCB – printed circuit board
PCM – pulse-code modulation
PCN – personal communications network
PCS – personal communications system
PDA – personal digital assistant
PDC – pacific digital cellular
PECL – positive emitter-coupled logic
PHEMT – pseudomorphic high-electron-mobility transistor
PLL – phase-locked loop
PSK – phase shift keying
QAM – quadrature amplitude modulation
QASK – quadrature amplitude shift keying
QPSK – quadrature phase shift keying
RFI – radio frequency interference
RFIC – radio frequency integrated circuit
RISC – reduced instruction set computing
ROM – read-only memory
SDH – synchronous digital hierarchy
SCM – signal code modulation
SiGe – silicon-germanium
SMR – specialized mobile radio
SMS – short messaging service
SMT – surface-mount technology or surface-mount toroidal
SNR – signal-to-noise ratio
SOIC – small-outline integrated circuit
SONET – synchronous optical network
SPDT – single-pole double-throw
SSB – single side band
SSPA – solid state power amplifiers
TCP – transmission control protocol
TDD – time division duplex
TDMA – time-division multiple access
TETRA – trans european trunked radio
TTL – transistor – transistor logic
TXCO – temperature-compensated crystal oscillator
UART – universal asynchronous receiver transmitter
UHF – ultra high frequency
UMTS – universal mobile telecommunications service
PVCO – voltage-controlled oscillator
VCXO – voltage-controlled crystal oscillator
VOFDM – vector orthogonal frequency division multiplexing
VSAT – very small aperture terminal (satellite service)
VSB – vestigial side band
VSWR – voltage standing wave ratio
WAP – wireless application protocol
W-CDMA – wideband code-division multiple access
WLAN – wireless local area network


Electrical Engineering Terms Glossary

AC Signal: The time variant portion of a voltage or current.

Alternate Sweep: A vertical mode of operation for a dual-trace oscilloscope. The signal from the second channel is displayed after the signal from the first channel. Each trace has a complete trace, and the display continues to alternate. This mode is used for SEC/DIV settings of less than 1 ms/div (faster than 1 kHz).

Alternating Current (AC): An electric current whose instantaneous value and direction change periodically. The term usually refers to sinusoidally shaped current or voltage waves.

Amplitude: Height of a waveform above ground (1/2 peak-peak value)

Attenuation: The decrease in signal amplitude during its transmission from one point to another.

Bandwidth: The oscilloscope frequency range within which performance of a particular characteristic falls within specified limits, commonly defined as the difference between the upper and lower frequency at which the response is .707 (-3dB) of the response at the reference frequency.

Blanking: The process of making the trace, or parts of a trace, invisible.

Bypass: A capacitor placed from a dc signal to ground will remove any ac component of the signal by creating an ac short circuit to ground.

Calibration: The process of comparing an instrument or device against a standard to determine instrument accuracy or to make a correction.

Capacitance: The property of a system of conductors to and dielectrics which enables the system to store electricity when a voltage is applied between the conductors, expressed as a ratio of the electrical charge stored and the voltage across the conductors. The basic unit is the Farad .

Capacitor: A device consisting of two conducting materials separated by an insulating material (dielectric), which can store an electrical charge when a potential difference exists between the two conductors.

Cathode-ray-tube: An electron-beam tube in which the beam can be focused to a small cross-section on a luminescent screen and varied in both position and intensity to produce a visible pattern.

Chop: A vertical mode of operation for dual-trace oscilloscopes in which the display is switched between the two channels at some fixed rate. This mode should be used for slow sweep rates.

Common: The potential level serving as ground for the entire circuit.

Comparator: A component which satisfies, for input Vin and reference voltage Vr the equations

if Vin > Vr then Vout = Vcc.
if Vin < Vr then Vout = -Vcc.

Compensation: The controlling elements that compensate, or, offset the undesirable characteristics of the process being controlled in a system.
Coupling: The association of two or more circuits or systems in such a way that power or information may be transferred from one to the other.
Crosstalk: “Leakage” of signal from one source into another.
Current: The rate of change of charge (electrons) or flow of charge/second (dQ/dt) through a circuit.
Detent: A stop or other device (such as a pin or lever) on a ratchet wheel. Switch action is typified by a gradual increase in force to a position at which there is an immediate and marked reduction in force.
Diode: The diode is the simplest and most fundamental non-linear circuit element. It is a two terminal device which only allows current to flow in one direction.
Direct Current (DC): An electric current that flows in only one direction with essentially constant value.
Display: The visual representation of a signal on a CRT screen.
Distortion: An undesired change in waveform.
Dual Channel (Dual-trace) Oscilloscope: An oscilloscope that has two independent input connectors and vertical sections and can display them simultaneously.
Dual-sweep (Dual-timebase) Oscilloscope: An oscilloscope that can display a signal with two independent SEC/DIV settings.
Duty Cycle: The ratio of the lengths of the positive to negative halves of a waveform expressed in percentages.
Farad” Unit of measure of capacitance. Named after Farad.
Feedbac: Voltage from the output of a circuit is channeled (or “fed”) back into the input of the circuit.
Focus: The oscilloscope control that converges the CRT electron beams to produce a sharp display.
Freerunning Trace: A trace that is displayed without being triggered and either with or without an applied signal.
Frequency: The inverse of time (1/seconds). How often an event occurs within a second.
Graticule: The CRT grid lines that facilitate the location and measurement of oscilloscope traces.
Ground: 1. A conducting connection that by which an electric circuit or equipment is connected to the earth to establish and maintain a reference potential level. 2. The voltage reference point in a circuit.
Hertz: Unit of frequency, one cycle per second.
Hysteresis: An output voltage Vcc does not change to -Vcc until the input increases above B*Vcc, B being a constant value. Conversely, -Vcc does not change to Vcc until the input decreases below -B*Vcc.
Impedance: The total apparent opposition a circuit offers to the flow of alternating current in an electrical circuit.
Inductance: The voltage across an inductor is directly proportional to the rate of change of the current through it divided by the rate of change of time (difference current/difference time = di/dt). The proportionality constant which makes this true is L, the inductance of the inductor component. It is denoted by L and its units are the Henry (H). Therefore, the voltage v across an inductor is given by v = L*(di/dt).
Inductor: Circuit element which is a conductor wrapped into a coil to create a magnetic field.
LED: Light Emitting Diode, emits light when current is passed through it.
Megahertz (MHz): A frequency of one-million Hertz, or 106 cycles per second.
Microphone (Condenser): An electromechanical transducer that converts sound pressure into an electrical signal. Condenser mics require power to charge a capacitor used to sense changes in sound pressure levels (SPL).
Noise: An unwanted voltage or curent in an electrical circuit.
Oscilloscope: An instrument for making visible the instantaneous values of one or more rapidly varying electrical quantities as a function of time or of another electrical or mechanical quantity.
Period: Duration between repetitions of a waveform cycle. (1/frequency).
Potentiometer: A three terminal device with a wiper that is positioned along a resistive element; effectively making a voltage divider.
Probe: An oscilloscope input device, usually having a pointed metal tip for making electrical contact with a circuit element and a flexible cable for transmitting the signal to the oscilloscope.
Rise Time: The time taken for the leading edge of a pulse to rise from 10% to 90% of its final value.
Resistance: A measurement of the impedence of a substance to charge movement.
Schmitt Trigger: A circuit devised of an op-amp configured as a comparator and given a positive feedback. The Schmitt trigger employs hysteresis in order to create a switching voltage which is less susceptible to noise than a straight switch.
Scope: Short for oscilloscope.
Screen: The surface of the CRT upon which the visible pattern is produced; the display area.
Sensitivity: The ratio of the output value to the input value.
Short Circuit: Include a wire or other component into a circuit which effectively nullifies a component of that circuit, or leaves the voltage across the component unchanged in its AC or DC signal.
Signal: A visual, audible, electrical or other indication used to convey information.
Single Sweep: The ability of an oscilloscope to display just one window of time, thus preventing unwanted multiple displays. Useful for trace photography.
Slope: The ratio of change in the vertical quantity (Y) to the change in the horizontal quantity (X).
Spot: The illuminated area that appears where the electron beam strikes the screen of a CRT.
Sweep: Time-dependent information created by the electron beam moving across a CRT screen.
Time Base: Oscilloscope circuitry that controls the time dependence for the sweep. Time dependence is set by the SEC/DIV control.
Trace: The visual representation of an individual signal on a CRT.
Transducer: A device that provides a usable output in response to a specific physical quantity, property, or condition which is measured.
Transient: A phenomenon caused by a sudden change in conditions that persist for relatively short time after the change.
Trigger: The signal used to initiate a sweep on an oscilloscope and determine the beginning point of the trace.
Trigger Holdoff: A front-panel control that inhibits the trigger circuit from looking for a trigger for some specified time after the end of the trace.
Trigger Level: The instantaneous level that a trigger source signal must reach before a sweep is initiated by the trigger circuit.
URL: Universal resource locator. This is the address of something on the web. Examples include http//ece.wpi.edu/~frontier, ftp//ftp.wpi.edu, mailtonatalie@wpi.edu.
Volt: The unit of electric potential difference that and electromotive force equal to the difference of potential between two points on a conductor carrying a constant one-ampere current when the power dissipated between these two points is equal to one watt.
Voltage: The difference in electric potential, expressed in volts, between two points.
Watt: The SI unit of power, it stands for 1 Joule/sec.
Waveform: Graphic representation of the variation of a quantity (such as volts) as a function of some variable, usually time.
X-Y: A graphic representation of the relationship of the X signal, which controls the horizontal position of the beam in time, and the Y signal, which controls the vertical position of the beam in time.
Z-axis: Refers to the signal in an oscilloscope that controls electron-beam brightness as the trace is formed.

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