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From: "Andy Magee" <[log in to unmask]>
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Date: Tue, 6 Jul 1999 08:31:33 -0400
Subject: Re: Acrylic adhesive resistance to temp
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Mike,

I can't speak for the other materials manufacturers, but during the time I
worked at Rogers they actually went to extremes to avoid what you imply.
Performance testing was carried out very rigorously, and then we would
under-report the results (i.e. a one year rating after passing three years of
testing). There were basically two reasons for this approach. First, they were
very conservative, and they didn't want to leave any warranty questions hanging
out there. Second, if they had tried to make things look better just to improve
marketing it would have had the opposite effect when reality reared its' ugly
head.

An example of the second reason was an old UL flammability rating for R/flex
1000. The rating attracted some customers, but then turned them off when they
found out how difficult it actually was to get the material to pass the UL
testing. It could still pass the test, and the hard drive industry depended
quite heavily on it so they maintained the rating, but it drove several
potential new users nuts trying to get UL qualified. Even knowing all the
tricks, it took me two tries (and inventing a new trick) to get qualified when I
was with Mound Flexible Circuits.

Andy Magee
Flex Guru - Consulting
[log in to unmask]
(937) 435-3629



Michael Fenner wrote,


All polymer based materials have a maximum temperature to which they can be
exposed before they start to breakdown. This temperatue will vary from
polymer to polymer  and is also subject to being modified by conditions
of exposure and other materials present. For example it will be lower in
oxygen rich environments.This breakdown is cumulative and irreversible.
Think of it as invisible
charring to understand its effects. The adhesive properties of charcoal are
not usually regarded as outstanding.

As a general rule you would not expect "Acrylate" adhesives to have good
high temperatue withstand, high in this context would certainly include the
temperatures expected during pcb assembly processes,and acrylates are
generally not as good as epoxies which usually have a max continuous rating
in the 150C - 200C  max range.
However the problem with adhesives and general rules is that there is a huge
number of
proprietary formulations and the candidate materials that the suppliers can
use as bases for their blends is also large, notwithstanding the
combinations in their final blends.

So the first thing to do is read the data
sheet on your particular one as if you were a lawyer. See just what is
specifically stated on performance and not what the words leave you to
expect. Match the minimum specifications expected in this way with what you
actually anticipate the most severe in-service environment (including heat,
moisture, mechanical stress, chemical exposure etc) will be to form an
opinion as to suitability. Do the same for your processing  options and
limitations imposed by substrates to be joined. Then from the range of
candidate products you can narrow down your choice based on ease of use,
availability and so on. You may or may not end up with an acrylic based
material.

Mike Fenner
BSP, OX15 4JQ, England
T:+44 1295 722 992
F: +44 1295 720 937
-----Original Message-----
From: Matthew Sanders <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 01 July 1999 21:30
Subject: [TN] Acrylic adhesive resistance to temp


>Hello all,
>
>Thanks to all, by the way, for help on my last delamination problem on flex
>circuits - we think we've licked it. Here's my next question:
>
>I'm wondering about the degradation of performance of acrylic adhesives
with
>exposure to temperature. I think I've seen a lot of people mention that the
>adhesive becomes brittle over time at exposure to heat. Does anyone have
any
>data they can share? Also, are there other properties that are affected?
>Does the bond strength suffer?
>
>Thanks for any info!
>Matt Sanders
>
>Matthew Sanders
>PCB/Metal Procurement Engineer, Trimble Navigation Ltd.
>[log in to unmask]
>Phone: (408) 481-7817
>Fax: (408) 481-8590
>