3.2 FAILURE MODES AND
In developing an effective part screening sequence, one must understand the
device’s construction, function, and potential manufacturing flaws with
consequent failure modes and failure mechanisms of the devices to be
screened. For example, Integrated Circuit (IC) failures can be
attributed to chip or die related failure mechanisms that are largely
dependent on the IC fabrication process and technology, and package
related failure mechanisms that generally result from the assembly
It is important to realize that no single screen is effective in
precipitating all defects. However, a series of screens can be
developed to significantly reduce the probability of these defects
escaping detection. Thus the selection of a screen depends on:
- The device technology, chip design, maturity, and user history.
- The expected failure modes and mechanisms.
- The supplier history (previous experience withthe same part
Additionally, when considering a part screening policy, one must be willing
to accept the following conditions:
- Defective devices are to be expected in the
- The screening stress and electrical tests
must eliminate or significantly reduce the population of these
- Handling and testing must not introduce degradation or damage and must
not jeopardize part life span.
- Screening procedures must be standardized and routine. New or
innovative screens at the part level may end up being either
noneffective to bad parts or damaging to good parts.
To achieve the requisite level of reliability, it is essential to
understand the failure modes and mechanisms inherent in these
devices, and then develop effective means of detecting or
screening parts that exhibit these failure