Major defect

A defect likely to result in failure of a unit or product by materially reducing its usability.

Master Drawing

A document showing dimensional limits or grid locations for all parts on a PCB. It includes the arrangement of conductors and nonconductive material of  a PCB, e.g. dielectric, resist, etc.

Mealing

A condition at the interface of the conformal coating and base material, in the form of discrete spots or patches, which reveals a separation of the conformal coating from the surface of the printed board, or from the surfaces of attached components, or from both.

Measling

An internal condition that occurs in laminated base material in which the glass fibers are separated from the resin at the weave intersection. This condition manifests itself in the form of discrete white spots or “crosses”  below the surface of the base material, and is usually related to thermally induced stress.

MELF, Metal  Electrode Leadless Face

A component  package that is cylindrical and has metalized terminations on its two ends for surface mounting. The package is commonly used for diodes, capacitors, and resistors.

Metallization

A metallic deposited on  substrates and component terminations by itself, or over a base metal, to enable electrical and mechanical interconnections.

Mixed Mounting Technology

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

Multilayer Board

A printed wiring board that uses more than two layers for conductor routing. Internal layers are connected to the outer layers by way of plated via holes.

Neutralizer

An alkaline chemical added to water to improve its ability to dissolve organic acid flux residues.

Nonwetting`

A condition whereby a surface has contacted molten solder, but the solder has not adhered to all of the surface. The base metal remains exposed. Nonwetting is caused by physical barrier (intermetallic or oxide) between surfaces to be joined.

Open

Two electrically connected points that are separated due either to overetching  or fabrication-related problems, by insufficient solder from wicking or gross nonplanarity of the leads at the point of connection.

Outgassing

De-aeration or other gaseous emission from a printed circuit board or solder joint.