In a message dated 7/9/98 15:09:16, Matthew Sanders, Trimble Navigation
Limited wrote:
>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.
Hi Matt,
I would definitely be concerned with PCBs with PTVs failing after only 50 MIL-
T-CYCLES, even though you don not give any details of the PCB design. And,
yes, there is a direct correlation between the numbers of cycles to failure in
an accelerated test and the life of those PCBs in the field.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]
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