The best way to find a post separation is to look at the large holes by
cross sectioning them, if your coupon has smallest holes, smallest pads you
do not see the worst case for post separation, if you have a large hole like
in the e coupon, solder float the coupon, cross section it and look at the
hole before microetch, a dark line is a separated post. Heated electrical
test does not simulate assembly, particularly if you are soldering to the
rigid flex. A poorly bonded inner layer to hole separates when thermal
shocked so IMO heated electrical test probably will not do the job for you.
Post separation is usually a lot related problem, if one board in the lot
has it then they all may.
> -----Original Message-----
> From: Matthew Sanders [SMTP:[log in to unmask]]
> Sent: Tuesday, November 03, 1998 11:53 AM
> To: [log in to unmask]
> Subject: [TN] Heated ET
>
> 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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