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Make Before Break (MBB) Selected contacts in a connector that make an electrical circuit before breaking (open circuiting) other contacts.
male connectors consist of an insulated plastic moulding (sometimes called a housing) fitted with plug contacts.
manual pin routing See board routing process.
manufacturer’s data specification sheet It provides electrical and mechanical data about a part and is used as a source of information for library inputs, design activities, and material procurement.
manufacturing data Information consisting of photoplotting files, drill files, pick-and-place files, bare and loaded board testing files, support drawings, and bills of materials required to do the actual fabrication, assembly and test of a PCA.
manufacturing engineering The technical organization that is usually responsible for planning and implementing PCA production activities.
markings Information imprinted on parts and circuit boards, such as reference designations, part or serial numbers, revision level, orientation or polarization symbols, bar codes, and electrostatic discharge (ESD) sensitivity.
mask A chrome and glass pattern for a layer of the wafer used in the photolithography process for silicon device manufacture.
mass soldering The process of forming all solder joints on a PCA simultaneously (wave soldering, dip soldering, oven reflow, vapour phase soldering).
master pattern drawing A document that shows the dimensional limits or grid locations applicable to any or all parts of the circuit board. This also includes the arrangements of conductive and nonconductive patterns or elements, the size, type, and location of holes, and other information necessary to describe the product for fabrication.
maximum/least material concept Used in geometric dimensioning and tolerancing, maximum material describes the condition of a mechanical feature within a stated limit of size (minimum hole size, maximum shaft diameter). Least material describes the minimum size of a feature (maximum hole size, minimum shaft diameter).
MCM = Multi-Chip Module A chip package within which more than one bare semiconductor die is bonded directly to a substrate by flip-chip, TAB or wire bonding. MCMs can also contain sealed components and chip components. The most complex are really encapsulated PCBs.
MCR = Moulded Carrier Ring A type of fine-pitch package named from the method of supporting and protecting the leads. The leads are left straight, with their ends embedded in a strip of plastic, the ‘Moulded Carrier Ring’. The MCR is cut off, and the leads formed, only immediately before assembly, thus protecting them against handling damage.
measling An internal defect in laminated base material in which the internal weave becomes visible, which takes the form of discrete white spots or crosses below the surface of the base laminate, reflecting a separation of glass fibres from the resin at weave intersections. Measling is usually due to thermally induced stress and indicates a weakened and unreliable substrate. (Also see ‘ crazing’)
mechanical shock and vibration External forces imposed on an assembly by cyclical energy inputs (vibration) or a single, sudden high-energy input (shock).
media The type of material used for product data and documentation, such as electronic (tape, CD disk) and drawings (paper, Mylar, film).
megabit One million binary pieces (bits) of information.
MELF =Metal Electrode Leadless Face bonded A (usually cylindrical) surface mount component package that has a metallic cap termination at each end instead of metallisation. Commonly used for diodes, capacitors and resistors.
meniscus That part of the insulation coating on a dipped component which has flowed up onto the lead, such as on a dipped capacitor.
metal foil See copper foil.
metallisation A metallic layer deposited on substrates and component terminations, either by itself or over a base metal, which makes it possible to create electrical and mechanical interconnections.
MIC = Microwave Integrated Circuit module A circuit assembly designed to function in the microwave frequency range. It usually contains a substrate with stripline circuitry and active chip devices, all sealed in a metal case for shielding purposes.
microstripline A type of high-frequency transmission line configuration that has a specific, characteristic impedance value. It consists of a conductor placed in a precise relationship with a ground or reference plane and surrounded by dielectric materials.
microwave Circuitry that operates at frequencies between 3 GHz and 300 GHz. See RF.
misregistration Nonconformity of the position of a pattern (or a portion of the pattern), a hole, or other feature to its intended position on a printed board.
mixed analogue/digital An integrated circuit or PCA that contains both analogue and digital circuitry.
moulded-in contacts Connector contacts that are encapsulated during the moulding process and cannot be removed. They are normally only used where a fully-sealed connector is required.
mounting hole A hole used for mechanical mounting of a printed board (e.g. to the chassis) or for mechanical attachment of components to the board. (also known as an ‘access hole’)
MTBF = Mean Time Between Failures The statistical average time interval, based on the probability of failure of a product, to be expected between operating unit failures. Usually quoted in hours.
multilayer (printed circuit board) A PCB manufactured from (normally rigid) base material upon which completely processed printed wiring has been formed on more than two layers, each separated by insulating materials, and bonded together. Internal layers are connected to the outer layers by plated via holes.
multilayer lamination See lamination.
multimeter A portable test instrument which can be used to measure voltage, current, and resistance.
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