Once a full accounting has been done of how the part is designed|
and constructed and insight is provided, through the FEA about
where and under what conditions to expect thermal and mechanical
stress concentration, a final validation test plan can be generated.
If the FEA describes high levels of stress at maximum application
temperatures, at a particular lead or chip interface, then a test can be
performed that thermally exercises that interface to show the durability
or life expectancy for the lot intended for use. The same would
be done to show the capability of the part to withstand a mechanical
test which is particularly stressful to it. ER qualification programs
do not make many design specific assumptions about how the part may
fail in use. It classifies parts in a broad way, usually based on
their electrical functionality. As noted above, a great number of part
failures occur due to assembly or package design deficiencies.
The ER approach requires a battery of mechanical "shake, rattle and
roll" tests, in an attempt to loosen, break or fail a faulty
mechanical member or interface. To cover all possible problems, based
on failure history, the battery of tests destroys 30 to 50 parts.
This is simply not economical to the user or the manufacturer for complex
constructions such as multi-chip modules and memory stacks
which cost several thousands of dollars each. The TVA test process will
subject parts to what may be a destructive test on samples of
two to ten pieces. Lot Acceptance and qualification testing such as 100%
burn-in and box level vibration and shock, are carried out by
"Shaking" Fiber Optic Connections
Here are some references that may get you started:
311-INST-001: Instructions for EEE Parts Selection, Screening, and Qualification, August 1996, NASA GSFC
311-INST-001 is a guidebook that provides the user with part screening and qualification testing requirements for active and passive parts for three different reliability levels. Standard test methods and specific condition letters are noted. Accept/Reject values, such as leakage current and lengths of allowed intermittents, are given in some cases. In most cases, the user is directed to procurement specifications for part specific accept/reject values.
The following pages can be referenced to view more information about the types of testing named in the title. These will be used as a repository of information, so we welcome your inputs and lessons learned. Please contact Jeannette Plante through email or by phone (301-902-4310) if you would like to contribute information to these pages.
Radiation and Other Environmental Effects Testing