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July 1998

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Mon, 13 Jul 1998 15:49:20 +0800
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Hi all,

Delamination, another posibble cause.....:

Poor cleaning of glass fabric... (glass fabric facility)

Glass fabric does not combine with epoxy. It need to be 'coated' with
parafin or some amino stuff (I forgot the details). If this is not removed
completely (in an oven at 1000+ C.) delamination can habben. We had this
with 7628 fabric from Russia.

...but in you case...

Since you used PCBs from different manufacturers I just presume your
customers solders too hot, too slow or both.

If you have a good profit margin, sell them some Hi-TG material. Polyclad
has some FR4 with an TG of 170C (compare to 130C.). This should help too.

regards

Jens

PS: If I remember correctly. Wave solder is about 250C +/-10C



At 09:16 13.07.98 +0100, you wrote:
>Just one possible clue for you. Plastics hold on to moisture quite well
>below Tg. Only above or plausibly close to Tg is moisture free to move
>about or even out. 100 C is the boiling point of liquid water. Absorbed
>water is not in liquid form. 100C is irrelevent.
>David Heywood.
>
> << File: ENVELOPE.TXT >>
> --------------------------------------------------------------------------
> --
>We have been having a reoccurring problem with PCB delamination.  At
>first we were thinking that it was a moisture problem. The boards were
>being stored in our store room open to the ambient air. Once, after
>two boards in a run delaminated, the assembly house flagged the entire
>run, and I actually personally took the rest of the boards home to my
>electric oven to bake. I then re-packed them (warm) in some ammo cans
>that I have with a desiccant pack in each. None of the baked boards
>delaminated. We thought that we would solve our problems if we
>specified for the assembly house to bake the boards and handle them
>post-bake per IPC-PE-740, (as per a similar discussion here that I
>found in the archives). All this was with boards from two PCB
>manufacturers (call them PCHouseA and PCHouseB).
>
>Well just recently we got some boards in from a third manufacturer
>(call them PCHouseC) that we have never used before. (The board is for
>a product line that we bought from another company so we are still
>using their resources for purchasing.) We received the boards from
>them, opened them enough to make a quick visual inspection and
>immediately sent the boards to our assembly house. Unfortunately, due
>to communications lags, the board baking didn't happen for that run
>and we had delamination problems with those boards. Our QC inspector,
>(thinking that moisture may not be the problem because of the lack of
>storage time in our stock-room), talked to PCHouseC about this and
>their thoughts were about wave solder temperature and FR-4 temperature
>maximums.
>
>My questions are:
> 1. About how long does it take for FR-4 (0.062" thick) boards to
>    absorb moisture? (Any one got (or can point me towards) graphs for
>    this? If so, please use private E-Mail to MIME attach the
>    message.)
>
> 2. How would approaching (meeting, or exceeding) the Tg affect the
>    board at the solder wave in such a way as to produce delamination?
>    Is there another critical temperature that I should be aware of
>    here?
>
> 3. What wave solder temperature profile is considered 'standard' or
>    'average'?
>
>
>Many apologizes if any of the above questions are too vague for a
>concise answer, but I'm learning this stuff as I go... (definite
>trialby-fire here...)
>
>TIA for any help.
>
>
>Pax
> --
>     Member: Team AMIGA                       --} WatchDog
>Fingerprint: 2C 8A 03 3C D6 D3 32 7F         (Chris Elliott)
>             66 0F 9B 9F 03 77 1D 85      PGP Key ID: A6A79259
><tsb>
>Experience is directly proportional to the value of equipment destroyed.
> -- Carolyn Scheppner
>
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