Daan,

I'd agree with Edward Szpruch, in that your flex supplier needs to tell
you more about his process and materials. It is very likely that the
same condition is buried under your rigid section too.

From my experience this sort of thing was related to the micro-etch
chemicals used just prior to application of the coverlay. For example,
it just takes the smallest of sodium persulfate crystals to cause what
you're seeing. Darkening of the spots with the application of heat, when
there is no apparent blister or bubble is a dead giveaway for chemical
contamination.

All the best,
Andy Magee - Flex Guru
Senior Consultant - Bourton Group
(317) 818-8148
[log in to unmask]
www.bourtongroup.com



Date:    Mon, 30 Jul 2001 15:47:00 +0200
From:    "d. terstegge" <[log in to unmask]>
Subject: Re: Flex delamination?

Thanks Steve,

Here's some extra info about the picture:

Before my destructive experiments with removing the coverlayer (always a
=
pleasure! ) this discoloration showed through as dark spots, some about
1 =
cm diameter. The material still looked flat, unlike most delaminations =
that I've seen, and that's why I'm not sure if this really is a
delaminatio=
n. After cutting the flex with scissors I found out that at these spots
=
there is very bad adhesion between copperplane and coverlayer.=20
Although the copper has a greenish color, it looks smooth and shiny.
This =
was already somewhat visible before assembly, but it became worse during
=
reflow soldering.

Daan

>>> <[log in to unmask]> 07/30 3:32 pm >>>
Hi Everyone!


Daan's asked me to post a picture for him up on our web site. Go to:

http://stevezeva.homestead.com/index.html=20

I've got a picture of a flex-rigid board with a greenish spot on the=20
copperplane, under the coverlayer. I would like to know what this is,
and =
if=20
it we should reject it or not.

Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net=20

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