B-stage The condition of resin polymer when it is more viscous, with higher molecular weight, and insoluble, but plastic and fusible.

B-stage material Sheet material impregnated with a resin cured to an intermediate stage. Also referred to as prepreg.

back bonding Bonding active chips to the substrate using the back of the chip, leaving the face with its circuitry face up. The opposite process is face down bonding.

backplanes and panels Interconnection panels into or onto which printed circuits, other panels, or integrated circuit packages can be plugged or mounted.

ball grid array (BGA) Integrated circuit package in which the input and output points are solder bumps arranged in a grid pattern. Also known as bumped grid array.

bare board A printed circuit board that has all lines, pads, and layers completed but that has no components installed.

bare board testing Testing procedure in which printed circuit boards are tested prior to assembly of components.

base (1) A substance dissolved in water that produces hydroxyl ions comprised of an oxygen atom and a hydrogen atom. (2) Insulating layer of a printed circuit board.

base copper The thin copper foil portion of a copper-clad laminate for PCBs that can be present on one or both sides of the board.

base material The material (rigid, rigid-flex, or flexible) that serves as the substrate or foundation of the conductive pattern of the PCB.

bed-of-nails technique A method of testing production volume PCBs based on the theory that most failures that are the result of manufacturing defects (e.g., solder bridges, reversed components, etc.) or defective components can be caught and identified during in-circuit component testing. A test fixture, heavily laden with nail-type contact probes, contacts points on the board allowing the devices to be powered up. Then, using active guarding techniques, the system quickly determines the faulty devices or connections.

bed-of-nails test fixture A vacuum-activated or mechanically activated test fixture comprised of a frame, holder, and a field of spring-loaded probes designed to make electrical contact with the assigned PCB nodes.

BGA Abbreviation for ball grid array or bumped grid array.

blackbody A body that absorbs all radiation incident upon its surface.

blade attack angle The angle formed between the stencil and squeegee blade during squeegee travel.

bleeding A condition in which a plated hole discharges process material or solution from crevices or voids.

blind via A via that connects an outer layer of a printed circuit board to an inner layer but does not continue through to the other side. Also known as a buried via.

blister Delamination that occurs in localized areas of the PCB.

blistering The lifting of a copper track from a printed circuit board surface after soldering.

blow hole A void caused by outgassing.

board The unpopulated printed circuit board. The foil and base from which a printed circuit is fabricated.

board thickness The thickness of the metal-clad base material, including conductive layer or layers. May include additional platings and coatings depending on when the measurement is made.

bond liftoff The failure mode whereby the bonded lead separates from the surface to which it was bonded.

bond strength Strength of adhesion between two joined materials. Also known as peel strength.

bonding agent The adhesive used to bond individual layers into a laminate.

bonding layer An adhesive layer used in bonding together other discrete layers of a multi-layer PCB during lamination.

bonding pad A metallized area at the end of a thin metallic strip to which a connection is to be made. Also called a bonding island.

bonding time The time from the commencement of hot bar heat-up (moment of hot bar contact) until the reflow profile is completed.

bonding wire Fine gold or aluminum wire between bonding pads on a semiconductor and base lands.

bootstrap A feedback technique that tends to improve linearity and input impedance of circuits operating over a wide range of input signals.

boss On a printed circuit, it is the conductive area to which components or separate circuits are attached. A plated-through hole land is the conductor surrounding the hole through the conductive pattern and the base material. Also called land, pad, terminal point, tab, spot, or donut.

boundary scan A self test designed into components at the silicon level that allows testing by means of a built-in four or five pin test bus accessing input and output pins.

bow The deviation from flatness of a board characterized by a roughly cylindrical or spherical curvature such that if the board is rectangular, its four corners are in the same plane.

branched conductor Any conductor on a PCB that connects electrically to more than two leads.

breadboard model An assembly designed to prove the feasibility of a circuit, system, or principle.

breakaway panels Hardboards held together in a grouping with breakaway tabs. The panels make handling and processing easier for automatic placement and soldering; the boards can be separated by snapping apart.

bridge Solder that “bridges” across two conductors that should not be electrically connected, i.e., causing an electrical short.

brush fluxing A specialized wave solder technique in which a 360° bristled brush rotates in a foaming flux head to transfer the flux to the board.

bumped grid array Integrated circuit package in which the input and output points are solder bumps arranged in a grid pattern. Also known as ball grid array and abbreviated BGA.

bumps Inner terminations of a tape automated bonded and flip-chip integrated circuit.

buried via A via that connects two inner layers of a printed circuit board and hence is not visible from the outer layers. Also known as a blind via.

burn-in The operation of items prior to their ultimate application. Intended to stabilize their characteristics and to identify early failures. The process is designed to accelerate the aging of a device.

burn-in testing A method used to detect mortality in devices prior to their being put in subassemblies or into actual service. Usually occurs before the devices are potted or connected to a permanent heat sink.

bus A circuit over which data or power is transmitted from any of several sources to any of several destinations between circuits.

bus bars Power distribution components, many of which consist of two or more conductive layers electrically insulated from one another and from other components by thin dielectric layers.

butt joint A solder joint formed with a “footless” lead also known as an I-lead.