Matthew-

A less destructive, or non-destructive, method of checking for delam is
scanning acoustic microscopy (SAM). You might contact the Bay Area Sonoscan,
Inc., office about C-SAM evaluation of your rigid flexes, at(408) 456-5020.

Also, have you tried chemical analysis for detection of plating solutions,
or other contaminants, in the sectioned delam parts? Robisan, or one of the
board fabricators might have some advice in this area.

Michael Alderete


Matthew Sanders wrote...
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Date:    Mon, 10 May 1999 18:54:47 -0700
From:    Matthew Sanders <[log in to unmask]>
Subject: Flex circuit - discolored copper, delam?

Hello all,

I have some 6 layer rigid flex boards with discolored copper in the flex
area. If I look at the flex (after 2.5 hour bake and 2 reflow cycles), I see
a uniform amber area for most of the circuit along a .250" trace; however,
there are some areas that are significantly lighter and some that are
significantly darker than the majority of the area. I'm not sure if I should
be concerned with this state of being, so I guess I have a few questions.

- What is this? One of the darker ones appeared to have the coverlay
delaminated (2 mil acrylic adhesive over 1 oz copper), but the lighter ones
seem to have no problems.

- How can I tell if it's a problem or if it'll cause any end-use
difficulties (or delaminate during use)? I've taken some samples and run
them through our reflow oven 24 times, soaked them in water for 3 hours, and
run them through reflow 4 more times. So far, the dark ones look like
there's delam (as shown by cross section), and the light ones look ok.

- What can my fabricator do to avoid it (assuming it is a problem)? Are
there better adhesives to use (epoxies, etc.)?

- Would cross-hatching the .250" trace reduce the liklihood of occurance?
Should I need to do this, or should a fully in control fab process not cause
this?

Ok, thank you all for your kind assistance. I'm never sure if I'm alone out
there in my rigid-flex woes, so I'm interested to see responses.

Thanks,
Matt Sanders

Matthew Sanders
PCB/Metal Procurement Engineer, Trimble Navigation Ltd.
[log in to unmask]
Phone: (408) 481-7817
Fax: (408) 481-8590

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