[time-nuts] RoHS crap

[Didier Juges]

I forgot to mention that in our products, we use 100% MIL-SPEC conformal 
coating, which seems to slow the growth of tin wiskers to the point of 
not being a significant concern (at least from the people knowledgeable 
in the process,) and our customers are buying it.

As Chuck pointed out, simply using SnPb solder will not prevent wiskers 
from growing on the upper parts of the component leads which are not 
immersed in the Pb solder and therefore remain plated with 100% tin. It 
is less of a problem with surface mount parts simply because many don't 
really have leads, but still too many have enough of the leads exposed 
that if left unprotected could grow wiskers. For commercial 
applications, where conformal coating is too expensive, I am not sure 
what the fix will be.

Didier KO4BB

Didier Juges wrote:
> For those interested, google "tin wiskers" and look up the NASA web site 
> that has lots of good pictures. It is scary to think people actually 
> build equipment with that stuff.
>
> Needless to say, in my business (military electronics), nobody wants to 
> hear about lead free solder. The prime contractors and the military 
> customers simply don't want it in their planes/ships. They don't care if 
> it's the law or what not. But, as an equipment manufacturer, we are 
> stuck very often with lead-free parts, simply because most part 
> manufacturers and distributors don't want to carry two product lines, 
> and for those few that still do, they make it very non-attractive to buy 
> SnPb parts (price and lead time goes up), but that's OK, we get lead 
> free parts which we solder with SnPb after adjusting the profile. That 
> seems to work. Interestingly, none of our customers has asked (yet) to 
> requalify any product because we now use Pb free parts... I expect a 
> different ball game if we go to Pb free soldering.
>