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B-stage A stage of resin polymerisation later than A-stage, at which the resin has a higher molecular weight, so is more viscous and insoluble, but still plastic and fusible. B-stage resin is still only partially polymerised, so retains the ability to adhere to other materials and to form further cross-links. Prepreg, used for making multilayer constructions, consists of reinforcing sheets impregnated with resin and cured to this intermediate stage.
ball grid array See BGA
bare board test(ing) Tests of electrical connectivity and isolation carried out by the manufacturer on the unassembled (unpopulated) circuit board. In the case of high frequency boards, can sometimes include impedance control measurements.
base (or basis) metal (or material) A metal or material upon which coatings are deposited.
base laminate The insulating support material (most usually epoxy-glass) used in the fabrication of printed wiring boards. (Also see ‘substrate’)
base substrate The insulating material that forms the support for conductor patterns and components.
BAT: Best Available Techniques, defined under Integrated Pollution Prevention and Control (IPPC). Note that BAT has many more cost and implementation issues than its predecessor BATNEEC.
BATNEEC: Best Available Techniques Not Entailing Excessive Cost, defined under Integrated Pollution Control (IPC).
bed of nails test fixture A fixture consisting of a frame and a holder containing an array of spring-loaded contact probes that make electrical contact with conductors at specific points on the surface(s) of a circuit. Used, primarily in volume manufacture, for bare board and in-circuit testing to identify defective parts.
bevel A sloping surface or line. The angle on the leading edge of a printed circuit board (the gold finger) to provide easier insertion into a connector. (Also see ‘ chamfer’)
BGA = Ball Grid Array A leadless IC package with a large number of terminations arranged in a matrix on the bottom of the package. Connections are made through solder terminations on the underside of the array , either in the form of solder balls (most common) or pillars. These are reflowed onto the board, forming pillars between the board and component.
bifurcated contacts Stamped and formed contacts, in components such as connectors, which are split into a pair of springs so giving two independent spring movements.
bilateral dimensioning Linear dimensioning (as opposed to geometric dimensioning) that defines tolerances allowing variations from the specified dimension in both directions.
bill of material(s) (‘BOM’) A document that lists all electronic, electrical, and mechanical components, and supporting materials that are required to manufacture an assembly, and gives the quantities used. The BOM will use reference designators that uniquely identify each component and material, including associated part/find numbers. A BOM is used for part procurement and, in conjunction with the assembly drawing(s), shows which parts are positioned where on the assembly.
binary Numbering system using two as a base and requiring only two symbols: 0 and 1.
biodiversity: The range of plant and animal species and communities associated with terrestrial, aquatic and marine habitats.
biological treatment: Any biological process that changes the properties of waste (for example, anaerobic digestion, composting). Biological treatment includes landspreading activities that are licensed.
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.
blistering (blister) A localised swelling and separation between any of the layers of a laminated base material or between base material and the metal cladding. (A form of ‘delamination’)
blowhole A large void in the solder connection created by outgassing during the soldering process. Volatile contaminants, air or gas trapped in the solder expand with the application of heat, leaving holes in the solder joint.
board construction Defines the types and dimensions of materials, the layering sequence of the cross-sectional structure of a circuit board, and its finished thickness.
board detail drawing A drawing that provides and describes all the requirements for fabricating a bare circuit board.
board extractor A device that is used as a means of extracting a PCA from its mating connector without damage to its electrical components. It can be permanently mounted on the circuit board or provided as external tool.
board profiling (also board routing process) A machining process for defining the outline of a circuit board. Pin routing uses a pin-guided template for manually profiling boards; NC routing utilizes programmable equipment to define a board profile. Both methods use cutters similar to end mills.
board-to-board stacking height The distance between the two inside faces of parallel mounted PCBs.
board thickness The overall thickness of the base laminate and the conductive pattern, usually measured at the gold fingers.
body The central portion of an electronic component, excluding its pins or leads.
BOM [pronounced ‘bomb’] see Bill of Materials.
bond strength The force required to separate a layer of material from the adjoining base. It is a measure of the structural effectiveness of adhesives, welds, solders, glues, or of the chemical bond formed between materials, when subjected to stress loading (shear, tension, or compression).
bonding agent An adhesive for bonding individual layers to form a multilayer laminate.
bonding layer An adhesive layer for laminating the separate substrates of a multilayer board.
bottom side The secondary side of a PCA, opposite the primary side. The bottom side of a PCA having some or all through-hole components (Assembly Types II and III) is the side accepting solder on the component leads. (Also referred to as ‘solder side’, ‘circuitry side’ or ‘conductor side’)
boundary scan A diagnostic test method that uses circuitry integrated in an IC component to facilitate testing or to monitor the performance of the component and its surrounding interfaces.
bow and twist Deviations from flatness requirements of a circuit board. Bow is measured from the top of a smooth arc to the same surface of the board if it were flat; twist is a helical divergence from flatness. See also warp.
BPEO: Best Practicable Environmental Option, a procedure that takes into account the total impact of a process and the technical possibilities for dealing with it. BPEO establishes the waste management option, or mix of options, that provides the most benefits or the least damage to the environment as a whole, at acceptable cost, in the long-term as well as in the short-term.
breadboarding ‘Quick and dirty’ assembly and test of a circuit to validate its performance before committing it to implementation as a PCA.
breakaway panels PCBs held together with breakaway tabs to make handling, placement and soldering easier and more efficient. Boards are snapped apart at the end of processing.
bridge ( bridging) A formation of solder that connects (bridges) adjacent conductors, such as two leads, completing an unwanted connection, causing short. One of the causes of an electrical short.
bulk resistance The resistivity (in ohm-cm or ohm-inch) through the cross-section of a conductive material.
burn-in The process of running an assembly at elevated voltage and temperature. This accelerates failure mechanisms, and makes it possible to remove assemblies which would otherwise be seen as early-life failures (‘infant mortality’). Burn-in can also be used on individual components before assembly in order to detect and remove potential failures.
burr A thin, ragged piece of metal produced during a machining operation which has been left on the edge of a piece of metal.
bus bar A mechanical means of providing power and ground interconnections using conductive metal (usually copper) bars rather than etched conductors.
bus structure A routed conductor pattern, usually used for point-to-point interconnection of power and ground.
butt joint A surface mount device lead that is sheared so that the end of the lead contacts the board land pattern without any hooks or bends; also called an ‘I-lead’.
byte A number of binary bits, usually eight, that represent one numeric or alphabetic character.
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