I'm just following along on this exchange which is interesting, but Brian in this scenario
wouldn't the "middle" start a very short distance from the edge? I wouldn't have thought the
extra outlet path provided by the thickness of material would be significant over any great
distance compared to the surface area of the two faces of the sheet..

Mike

----- Original Message -----
From: Brian Ellis <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, June 09, 2000 9:21 AM
Subject: Re: [TN] Baking of boards


Tim

Thanks for this info. Interesting. First time I've heard of non-aqueous solvents
having the same effect, although it is not unreasonable. However, this leads me
to another question. To make the prepreg, the glass cloth is run through a
solution of resin, which is then dried in the treater ovens. There is always
some solvent (I think ca. 1%) left in the prepreg. During pressing, this will
certainly vapourise, but it has nowhere to go, especially in the middle of the
sheets. Does this mean that samples taken from the middle of a sheet of laminate
will have a lower Tg than from the extreme edge????

The 5 deg C Tg range measured seems very small. I would opt for 10 or more being
more typical, as this is a function of the MW of each molecule, which is very
variable. A small range implies that the average MW is quite small, which may
not offer the best electrical properties, as I understand it.

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