Matthew Sanders 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.
>
> 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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Matthew,

You may use the following to correlate the field and test cycling.

N test = N field x ( delta T field/delta T test) *2

Example:  product operates between 25 deg. C and 65 deg. C
          test cycling is between  0 deg. C and 100 deg. C
          product on/off cycles are 250/yr and 1250 for 5 Yr. life.

N test = 1250 (40/100)*2
        = 200

This can be used to comapre different test cycling environment for a
given field application. The exponent varies depending upon product and
test variables and can range from 1.9 to 2.1.

hope it helps.

pratap.

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