Cor, blimey! Some people know the books better than the author!!! Shows
what senility does to one!
I had forgotten that I'd put the water-containing side in a
thermostatted bath.
I know I did an acrylic as part of the same experiment, but I think the
result was quasi-zero diffusion through it and I didn't really believe
it was that good. This is probably why it is not mentioned. I also did a
phenol-formaldehyde lacquer, which was what had been used up to then, as
an internal reference. Its electrical characteristics at high
frequencies was hopeless and was the reason for the experiment as it had
to be replaced. For reference purposes, it was checked (it took several
days to build it up to 5 mm!) and was about as bad as the silicone (I
think a little worse, if my memory still serves me).
As I said earlier, I'm enthusiastic about acrylics in non-chemical, cool
environments but do not recommend them if the board temp (including
components) is likely to exceed ~60°C at any time. I used acrylics very
successfully for apps going up to 1E14 ohms, where I'm sure that others
may have failed.
Brian
Steve Gregory wrote:
> In a message dated 09/05/2003 2:03:30 AM Central Daylight Time,
> [log in to unmask] writes:
>
>
>> I thought I had reported the details of this in
>> my book, but could not find them today. Must have been somewhere else.
>
>
>
> Hi Brian!
>
> It is in your book, on page 329, at the bottom of the section where you
> talk about Silicone Elastomers.
>
> In your book you state that you made a diaphram of silicone that was 5mm
> thick, and 100mm in diameter. On one side the air was held at 40 degrees
> C., and 95% RH, the other side at 5% RH. There was 1g of water vapor per
> day allowed to pass through the silicone diaphram. You stated that is 40
> times worse than epoxies, and 20 times worse than polyurethanes.
>
> Do you have any idea about arcylics?
>
> Regards,
>
> -Steve Gregory-
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