Multiple-image Production Master

A production master used in the process of making two or more printed boars simultaneously.

Multimeter

A portable test instrument which can be used to measure voltage, current and resistance.

Multi-layer PCB

Printed circuit boards consisting of three or more conducting circuit planes separated by insulating material and boned together with internal and external connections of the circuitry as required.

Muffle

An enclosure that is located between the heating elements and the parts being processed that contains the atmosphere required for the re-flow soldering process.

Mounting Hole

A hole used for the mechanical mounting of a printed board or for the mechanical attachment of components to the printed board .

Mother Board

Also called back plane, or matrix board. A relatively large printed circuit board on which modules, connectors, sub-assemblies or other printed circuit boards are mounted and inter connections made by means of traces on the board.

Module

A separable unit in a packaging scheme displaying regularity of dimensions.

Modifier

A chemically inert substance added to a resin to change its properties.

Mixed Component-Mounting Technology

A component mounting technology that uses both through-hole and surface-mounting technologies on the same packaging and interconnecting structure.

Mis-registration

The lack of dimensional conformity between successively produced features or terns.

Minor Defect

A defect which is not likely to reduce the usability of the unit for its intended purpose, It may be a departure from established standard having no significant bearing on the effective use or operation of the unit.

Minimum Electrical Spacing

The minimum allowable distance between adjacent conductors that is sufficient to prevent dielectric breakdown, between the conductors at any given voltage.

Mil

One thousandth (0.001) of an inch. Not to be confused with Mil (short for millimetre).1Inch=25.4mm; 1mil=0.0254mm.

Micro-strip

A type of transmission line configuration which consists of a conductor over a parallel ground plane, and separated by a dielectric.

Micro-sectioning

 A destructive test procedure in which a section of specimen it cut and removed for close examination.

Metallization

A deposited or plated thin metallic film used for its protective or electrical properties.

Metal Clad Base Material

Base material covered with metal on one or both of its sides.

Meniscus

The contour or shape of molten solder as formed by surface tension forces in turn controlled by wetting.

Melting Range

The temperature range over which the solder alloy melts .An alloy with a single melting point, rather than a melting range, is known as a eutectic alloy .

MELF

A metal electrode leadless face surface mount component that is round with metallic cap terminations.

Measling

A condition existing in the base laminate in the form of discrete white sports or crosses below the surface of the base laminate, reflecting a separation of fibres in the glass cloth at the weave intersection.

Mean Time between Failure (MTBF)

The statistical mean average time interval, usually in hours, that may be expected between failures of an operating unit. Results should be designated actual. Predicted or calculated.

MCR

Moulded Carrier Ring. A tape of fine-pitch chip package named for the method of supporting and protecting the leads. The leads are left straight; the ends of the leads are embedded in a strip of plastic, which is the Moulded Carrier Ring.

Maximum, Plated Through-hole Size

A hole size equal to the specified hole size before plating, plus the manufacturing tolerance, less twice the minimum plating thickness.

Master Pattern

An accurately scaled pattern which is used to produce the printed circuit within the accuracy specified on the master drawing.

Master Drawing

A document that shows the dimensional limits or grid locations applicable to any or all parts of a printed board(rigid or flexible),including the arrangement of conductive and non-conductive patterns or elements; size, type and location of holes.

Master Artwork

A document showing dimensional limits and grid locations for all parts of  an assembly to be fabricated. It includes the arrangement of conductors and non-conductive patterns and the size, type and location of holes.

Mass Soldering

Methods of soldering in which many joints are made in the same operation.

Mask

A material applied to enable selective etching, plating or the application of solder to a printed circuit board.

Margin

The distance between the reference edge of a flat cable and the nearest edge of the first conductor.(See also Edge Spacing)

MAR(Minimum Annular Ring)

The minimum metal width, at the narrowest point between the circumference of the hole and the outer circumference of the land. This measurement is made to the drilled hole on internal layers of multi-layer printed circuit board to the edge of the plating on outside layers of multi-layer boards and double-sided boards.

Manhattan Distance

The orthogonal distance between two points.

Major Defect

 A defect that could result in failure or significantly reduce the usability of the part for its intended purpose.