Hello,

I'm in the process of doing some thermal cycling tests to aid in determining
the reliability of rigid-flex circuit boards. I'm following the
"MIL-T-CYCLE" outlined in IPC-TR-579, the round robin reliability document
for small diameter vias. This is a -65 C to 125 C, 30 minute dwell, 38
minute transfer test. I'm facing the fundamental dilemma of trying to
correlate results to actual real life reliability. I have results from tests
done by one of my vendors, and they claim they can pass 400 cycles. I'm
seeing boards from one other source fail after only 50 cycles, though - only
from one source... the other 2 are still going at 100 cycles. While I'm
concerned about the discrepancy between the vendors, should I be concerned
with boards failing at 50 cycles. Are there correlations between cycling and
actual reliability? When do I get concerned?

Any help would greatly be appreciated.

Thanks,
Matt Sanders

Matthew Sanders
PWB Procurement Engineer, Trimble Navigation Limited
[log in to unmask]
Phone: (408) 481-7817
Fax: (408) 481-8590

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