gas-tight joint The joint between
male and female contacts, or a termination to a
cable, which excludes air. This results in the
connector maintaining good electrical continuity
even under severe industrial atmospheric conditions.
geometric dimensioning A method
that defines the location and associated tolerances
of a mechanical feature in terms of its allowable
position with relation to its theoretical (true)
position.
(device) geometries Sizes within
a silicon device (e.g. 0.25µm) which refer to the
layout of components and interconnects on the die.
Gerber data (Gerber file) Named
after Gerber Scientific Co., who made the original
vector photoplotter. A data format that converts
physical feature information (location, shape etc.)
into data used to control a numerically controlled
photoplotter that produces printed circuit artwork.
glass transition temperature (Tg)
(pronounced “T sub g”) The temperature at which
a polymer changes from a hard and relatively brittle
condition to a viscous or rubber condition. This
transition generally occurs over a relatively narrow
temperature range. Although there is no phase
transition, in this temperature region many physical
properties (such as hardness, brittleness, thermal
expansion and specific heat) undergo significant and
rapid changes. Glass transition temperature is also
used as a shorthand way of indicating the
temperature at which the mechanical and electrical
properties of a laminate begin to degrade
glob top A blob of
non-conductive plastic, often black in colour, which
protects the chip and wire bonds on some kinds of
packages, particularly
Chip-On-Board constructions. This specialized
plastic has a low
coefficient of thermal expansion so that ambient
temperature changes will not rip loose the wire
bonds it is designed to protect.
gold finger A portion of a
conductive pattern (usually gold plated) on or near
any edge of a printed board that is intended for
mating with an edge board connector. Also see
printed contact.
gold plate removal Thick gold
plating is sometimes applied to leads as a
protective measure, usually as a throwback to
earlier Military Specification requirements.
Unfortunately, tin and gold can form a brittle
intermetallic interface, which will eventually cause
the joint to fail – in fact, it is not unknown for
gold-plated wires apparently firmly fixed in a solid
joint to be able to pulled straight out of the
joint! In order to get round this problem, the gold
plating is usually stripped before assembly by a
process of double dipping to ensure no possible
build-up of gold
gold(en) board A component or
assembly already tested as functional to spec and
used, via comparisons, to test similar units. Also
referred to as a ‘known good board’.
granular solder Solder
appearance with a coarse, large grain structure,
lacking in metallic lustre. Usually due to unclean
conditions of the joining members, contaminated
solder, or excessively high temperature of the
molten solder. (Similar to
cold solder)
grid origin See
datum intersection (origin).
gridless (shape-based) router
The type of CAD autorouting program that has the
flexibility to find paths for conductors based on
the shape of surrounding geometric features (such as
conductor widths and spacings), instead of being
restricted to a predefined grid.
ground plane A conductor layer
that covers all or a large portion of a board (with
suitable clearances around through-holes and vias),
and which is used as a common reference point for
circuit returns, shielding or heat sinks. The
similar power plane distributes
power to circuitry on the board. Both ground and
power planes may also be used as an electromagnetic
shield and as a reference plane for high-frequency (stripline)
circuitry.
grounding As used by the
connector industry, sending current flow to earth in
the case of a short circuit.
gull-wing A lead configuration
typically used on
small outline packages where the leads extend
horizontally out of the package for a short
distance, then drop to the pad level, then extend
horizontally again away from the component to make
attachment surfaces that rest on the pads. An end
view of the package resembles a gull in flight.
