External package contamination
is the presence of a
whether attached or unattached,
anywhere on the external
portions of the package body and/or its interconnection features (e.g., leads,
solder balls, etc.). Since
certain contaminants can affect the performance and reliability of the
contaminants need to be
promptly and, if necessary, traced to their root cause. Corrective
actions may then be implemented to prevent recurrence.
for rejecting external contamination depends on its location, extent,
and composition. Some contaminants are rejected because it results in
cosmetic failure, while others are rejected because of the reliability
risk involved, mainly with regard to lead corrosion and solderability
issues, as well as electrical leakage between pins.
contaminants can come from
anywhere. If all the units are affected, it is likely that it has come from
an equipment used in the process, or a bad batch of raw material has
been used. If the contaminated units are isolated, it may have been
produced by a random or non-repeating event.
contaminants, depending on their identity, can lead to
including excessive current leakage, pin-to-pin shorts, corrosion,
solderability failures, and visual-mechanical failures.
Lead contamination in PDIP (left) and metal can (right)
external contaminants include but are not limited to the following :
grease or oil from equipment; flux or solder on package; oxides on
leads; human contaminants such as spittle and fingerprint residues; and organic contaminants on package or leads.
used for identifying external contaminants include:
EDX Analysis, FTIR Analysis, and
Ion Chromatography. The corrosive
effects of contaminants may be
by PCT and HAST.
Failure Mechanisms; Failure Analysis
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