Matt ,
If you got postseparation after assembly , you do have a real problem.
Do you have in your position control coupons ? If so , pass them several
times ( say 3 ) through thermal shock and make crossections .
Pre-baking can help , if the boards themself are suffering from excess
absorbed humidity , but to the the best of my knowledge it will not help you
to find defected boards .
Try to pass the boards through reflow and then re-check them by ET .


At 10:52 03/11/98 -0800, you wrote:
>Hello folks,
>
>Happy election day to those in the States!
>
>We've had problems with rigid flex boards failing for separation between the
>innerlayer trace and the PTH barrel after assembly (they passed ET before
>assembly, but they have an open due to this defect after). To try and catch
>them before assembling them, our board supplier suggested a heated
>electrical test. We've done this once before, and we were able to catch some
>of the problems. I feel the need to do it again (same vendor, we need the
>boards) before running a batch, but now I'm starting to wonder if this test
>will have the potential to induce failures.
>
>Here are the parameters:
>250 F
>2 hours
>test hot
>
>The temperature is the same temp we use for pre-bake during assembly (to
>drive off moisture for delamination). Does this test have the potential to
>cause any additional problems? Anybody have any suggestions for how to check
>these boards before use?
>
>Thanks,
>Matt
>
>Matthew Sanders
>PWB Procurement Engineer, Trimble Navigation Limited
>[log in to unmask]
>Phone: (408) 481-7817
>Fax: (408) 481-8590
>
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Edward Szpruch
Eltek Ltd - Israel
Tel  972 3 9395050
Fax 972 3 9309581
E-mail :  [log in to unmask]

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