Kelly, et. al.
Thanks for the information so far! I'm going to look into the C-SAM and
chemical analysis Michael suggested.
We're currently using adhesiveless base material on the parts due to some
low yield problems we'd seen in the past. Unfortunately, the delamination
we're seeing is coverlay to copper where we're using the acrylic adhesive.
Does anyone have experience with epoxys or other adhesives for that
component?
As for the tweezer method, that's similar to what we've been doing as a
check; I feel pretty good about the method, but I'm worried about the
possibility of this discoloration, even if it doesn't give me the tactile
delam feedback, having some problems later in life. I worried that even the
C-SAM, while it can verify the parts as-is, won't necessarily tell me if
I'll see any future problems (or if it's ok now, will it be ok in the
future?). Does testing the bond strength between the cover and the copper
help?
This is something of a separate thread, but for adhesiveless flex materials,
is there any practical functional difference between cast polyimide and
sputtered copper (/11 and /12 I think). Is it a difference I should worry
about when specifying materials?
Thanks for the information so far!
Matt
Matthew Sanders
PCB/Metal Procurement Engineer, Trimble Navigation Ltd.
[log in to unmask]
Phone: (408) 481-7817
Fax: (408) 481-8590
-----Original Message-----
From: KELLY M SCHRIVER [mailto:[log in to unmask]]
Sent: Tuesday, May 11, 1999 6:00 AM
To: [log in to unmask]
Subject: Re: [TN] Flex circuit - discolored copper, delam?
Matt -
From your description of the dark vs. light areas of copper, I suspect you
are
correct about a delaminated or debonded condition.
The acrylic adhesive used in your flex has a glass transition (Tg)
temperature
of about 45C, as opposed to a Tg of 240-250C for the polyimide materials in
the structure. This means your process temperatures can temporarily turn
the
acrylic adhesive to something rather like grease. In this state, it is
subject to debonding/delaminating rather easily from any form of stress.
I would suggest the following as a quick check to confirm: Place the
specimen
under low magnification (10-20X) and gently squeeze the suspect area with
tweezers or similar. If debonded/delaminated you should be able to observe
movement in the structure between the cover film and the circuit.
Several years ago, DuPont, Sheldahl and others standardized and commenced
marketing "all polyimide", "adhesiveless flex" or "bondable polyimide", or
whatever you want to call it. This material has a Tg in the 230C or above
range, which is much more durable. We have switched over most of our
designs
and have seen improved product yields at the fab houses and in our own
assembly operations, as well. In our case, this has pretty well turned out
to
be a true "drop in replacement". All of our government sector customers, to
date, have agreed that it is a class 2 change..
Good luck - I'm at 256.882.4536 if you need to talk.
Regards - Kelly
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