Hi Stephen - for additional info on grainy joints take a look at the
following reference:

"The Rough or Grainy Solder Phenomenon", R. Bulwith, PC Fab, October 1986,
pages 23-35.

In many cases a grainy solder joint is a cosmetic problem only. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




KELLY M SCHRIVER <[log in to unmask]> on 04/01/99 07:54:00 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to KELLY M SCHRIVER <[log in to unmask]>

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cc:
Subject:  Re: [TN] GRAINY JOINTS




Stephen -

The condition you describe suggests a localized "hot spot" which kept the
solder in a liquified state for a prolonged period of time following
reflow,
rather than a contaminant.  Eutectic solder which cools rapidly generally
has
a "bright/shiney" appearance.  (Excuse me, All, for using this phrase.)
The
same solder, cooled at a very slow rate has the tendency to form
crystalline
clumps, for lack of a better description, which give a highly textured
appearance to the solder surface.

The "hot spot" I mentioned can be the product of anything which produces a
high thermal mass area on the object being soldered, ie., heavy circuitry,
ground plane areas, a larger than normal component, a part which has a
higher
IR absorbtion rate than the others around it, etc.

Fine tuning the profile will probably help this condition.  Recommend you
instrument this part location and compare it to other areas on the board to
confirm that the cooling rate is slower.   I have also seen small pieces of
foil placed on top of parts prior to reflow to reduce IR absorbtance.


Good luck - Kelly

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