Bill, old & well documented. We may seemingly have to do with 'farting
chps' .Many  finish processes (in fact ALL) leave built-in gas e.g.
hydrogen. Normally the main part of voids in solder joints are from the
chemistry of the solder paste, and the addition of voids from termination
gas is negligable, but the opposite can happen if the component maker
doesn't have good control on the plating process, in fact, the outgassing
can be so violent that the slder looks like whipped cream, which is also
what we call it. A blowhole, even large ones, do not affect the solder
joint strength, but depending on what customer you have, it can be seen as
bad workmanship. What to do then? we simply performed single point
soldering of the bad joints or, if the bad guys were many, fluxed the board
and let it go through the soldering once more. You know, the gas generation
from the terminations can't fart a second time.

Inge

On 8 February 2013 03:56, <[log in to unmask]> wrote:

> Fellow TechNetters:  Recently having a problem with solder fillets on
> various SMT assemblies, we
> are observing an outgassing in the concave portion of the solder fillet of
> various resistor package
> sizes.  Specifically, 0603, 0805, and 2010 packages.  The outgassing is
> either a slight, hollow bump
> or a "blowhole" and always in the center of the fillet.  If we observe the
> condition, we switch the reel,
> and the problem generally goes away.
>
> It is only happening with resistors, not any other SMT package.  The
> observations have now occurred
> in two separate facilities, with the reels of resistors having date codes
> from 2009 thru 2011.  We have not
> changed solder paste, using a no-clean paste from a major manufacturer.
>
> Is anybody having issues with SMT resistors?  Can anyone shed any light on
> this absolutely random issue?
>
> Your thoughts and comments are greatly appreciated.
>
> THANK YOU,
> Bill
>
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