Bernhard Kuemel wrote:
>
> Firstly, isn't silicone "highly" permeable to gas? Does it really
> protect from oxygen?
Yes, it is highly permeable to gases.
>
> Secondly, is oxygen really a problem? I guess the semiconductor is
> immune, cause oxygen forms a highly stable and protective silicon oxide
> passivation layer. But there's also contact fingers and bus bars made of
> silver paste and other materials and solder connections.
Silicones are commonly used as "glob top" encapsulants
for chip-on-board packaging, i.e. where a chip is glued
to a circuit board and then wire-bonded. Silicone is
extremely hydrophobic, so it keeps the water out.
>
> Is Sylgard 184 silicone really a suitably protective encapsulant? I also
> found POLASTOSIL M-2000 which is supposed to be like SYLGARD 184:
>
http://www.ebay.com/itm/271079655104 . Do you think that's good, too?
If it's a platinum-catalyzed addition cure silicone,
that's good. Other cure systems may produce corrosive
byproducts, such as ammonia. Some materials can
inhibit the platinum catalyst, so you have to watch out
what materials the silicone will be in contact with.