Homebrew PCBs

On Mon, 08 May 2006 02:05:10 +0200, Adam Seychell  
<a_seychell@...> wrote:

> Interesting. I've had the "24hr" epoxy continuously immersed in CuCl for
>
> 8+ months and I can't detect any physical change except that it has gone
>
> more yellow. But it went yellow in the first month, and hadn't changed
>
> further since. I think not all epoxy is the same. I've always avoided
>
> the 5 minute stuff, as it never set as hard or durable as the others.
>
> I'm using low viscosity epoxy (http://www.westsystem.com) sold for fiber
>
> glass work to glue/seal various items permanently immersed in 20%
>
> sulfuric acid copper plating solutions, and my CuCl etching tanks. No
>
> problems after 1 year. In other parts I've used a structural type
>
> adhesive non flowing gel epoxy and find it stands up equally well
>
> permanently immersed. The color changes to yellow over time.
>
>
> Adam


Yes, the longer curing epoxy is much better. You only need to look at the  
mixing proportions, the 5 minute stuff uses 1:1 while the better stuff  
uses much less hardener. That additional hardener is material that doesn't  
do any favours to strength and chemical properties i guess.

It turned yellow first as well. Then brown, and then soft.

24h curing is a lot of time though (with my patience ;-) ), so i'll stick  
to 5-minute epoxy for most stuff. I like the long shelf life of epoxy  
compared to other glues.
For example that neutral curing silicone i bought not that long ago for  
the silicone paper tests - it's dead already. Doesn't cure any more. The  
acidic silicone just hardens up and you immediately see it is no good any  
more. But the neutral curing one will not harden, it stays a paste (though  
thicker and less shiny), but will not harden any more at all. So that's no  
fun at all, noticing a day after that the work was for nothing and you  
have to remove the gunk again. Learned my lesson - if it appears not as  
sticky as it used to try if it will still cure before using it!

ST