is the ripping apart or
severing of the lead
in the lateral direction,
usually at one of its
bended portions. It
often manifests as a moderately ductile fracture of the lead propagated
by mechanical stresses acting on it. It is
often due to a problem in the raw material, i.e., the leadframe used is
defective or inherently weak.
tearing problems due to raw material issues can not be detected by the incoming QC's
prior to assembly,
mainly because most lead tearing cases manifest only after the leads have been
stresses, such as those imparted by the
trim/form/singulation steps of the assembly
Lead integrity tests, which apply stresses to the leads to
test their reliability, would therefore have a better chance of
detecting potential lead tearing issues.
Failure analysis on samples
that exhibit lead tearing
SEM inspection of the fracture surface, the topography
of which may indicate metallographic 'weaknesses' or abnormalities in
the lead. The failure analyst tasked with determining the distinguishing
anomaly of affected samples from normal ones must therefore have a
working knowledge of how the microstructure of a metal affects its
tearing damage is
generally occurs at the bended portion(s) of the lead, initiating at the
the lead. The tearing at
both sides of the lead propagates inward as the lead is subjected to more mechanical
stresses, until the cracks meet in the middle, at which time the lead
breaks into two.
Lead tearing is very rarely seen in production,
but needs serious attention if encountered.
Failure Mechanisms; Wirebonding; Failure Analysis
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