Mike

Yes: that is why I used the term "extreme edge" because I have no idea how much diffusion
through the material could be expected in the pressing time.

Brian

Mike Fenner wrote:

> 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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