3.4.4 CONSTANT ACCELERATION
Mechanical stresses are difficult to apply directly to circuit materials
for stress screening.A centrifuge can be used to impose a constant
acceleration on circuit materials such that their inertial mass
essentially tugs on a wire bond or a die attachment.High acceleration
and inertial forces can be produced using transient mechanical shock
techniques. However, due to the low density of aluminum, the forces on
aluminum wires associated with reasonable values of constant
acceleration are usually too small to serve as an effective screen for
poor wire bonding.
Constant acceleration was effective when gold wire bonding systems were
widely used for hermetic devices. With the change to aluminum wire
bonding systems for most semiconductor and IC devices, the value of
this screen in precipitating wire bonding problems is less effective.
The screen can be effective in locating die lifting and package
defects. Some devices still use gold wire bonds and can benefit from this