I am sorry if I upset you over what you think I meant to imply.
I suppose you are refering to my remark
"... 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...." ??
What I meant by this is best illustrated by example. Suppose I were to write
:
"outstanding thermal performance" in a data sheet entitled "unfilled acrylic
adhesive".
This would be a true statement if say the thermal conductivity or
temperature withstand were significantly better than the norm for unfilled
acrylics. However it would not mean that the user should automatically
expect outstanding thermal performance in whatever aspect his application
happened to be or specifically need. It's a relative claim in the context of
the data sheet not an objective statment of fact. A lawyer would point this
out (for a small fee).
Specifications have to be objective verifiable statements and can be
compared. Finally it would seem prudent to base expectations on the minimums
claimed/stated rather than hoping you would always hit the maximums.
I hope this makes things clearer as it wasn't my intention to suggest that
suppliers set out to deliberately mislead users. I suppose this all goes to
show how careful you have to be with words rather than numbers.....
Mike Fenner
BSP, OX15 4JQ, England
T:+44 1295 722 992
F: +44 1295 720 937
-----Original Message-----
From: Andy Magee <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Cc: [log in to unmask] <[log in to unmask]>
Date: 06 July 1999 13:28
Subject: Re: Acrylic adhesive resistance to temp
>
>
>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
>>
>
>
>
>
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