Shabtay,
an old Siemens spec once called for a delta Tg of max 3 deg C. Today's difunctional FR4 base material should have delta Tgs of max 2 deg C,
otherwise it is undercured. However your test method should be verified with your base material supplier (type of equipment, heat rise rate,
midpoint value, etc.).
For multilayers it is somewhat different, because you can only measure a composite Tg/delta Tg of already cured base material and prepreg
which you are curing in your press. As a rule of thumb, your 1 - 2 degrees should be ok for this composite.
If you really want to be more accurate, you should put a few plies of prepreg (approx. 1 mm total pressed thickness) between 2 sheets of
copper foil (prepreg in contact with the shiny side, so that you can peel off the copper foil afterwards), and place this sandwich in the
centre of a multilayer stack during a normal press cycle. Then you have a piece of pressed "laminate", bonded using the lowest heat rise rate,
etc., basically under the worst conditions. If the delta Tg of this "laminate" is similar to that of your inner layers, your press cycle is
ok., and your customers should be happy.
regards
Manfred Huschka
Taconic Advanced Dielectric Division
--- On Sun, 20 Dec 1998 09:04:12 +0200 "Eltek Ltd. - Process Engineering" <[log in to unmask]> wrote:
HI all
We are testing the Tg values in laminated panels randomly twice a week
as a process control off lamination process, One of our customers demanding
to establish testing of "Delta Tg", We have started with it & We are
receiving values about 1-2 centigrade (I think that it is O.K.), We would
like to know what should be the highest rate for "Delta Tq" in laminated
boards according to other PCB manufacturers experience. (The IPC is no
giving any recommendation for maximum rates of "Delta Tg").
Shabtay Shalev
Eltek Ltd - Israel
e-mail : [log in to unmask]
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--------------------------------------------------------
Name: Manfred Huschka
Taconic Advanced Dielectric Division, Mullingar Business Park,
Mullingar, Co. Westmeath, Republic of Ireland
Office: PF 1275, D-51676 Wipperfuerth, Germany
Tel.: +49 2267 888004
Fax: +49 2267 888005
E-mail: Manfred Huschka <[log in to unmask]>
Web: http:\\www.taconic-add.com
Date: 12/22/98
Time: 16:45:35
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