Bill,

You didn't mention whether the joints were on SMT components glued to the
wave side of the PCB or through hole components.  If they are through hole
components one thing I'd suggest checking is whether you're getting some
component movement during the critical time when the solder is "freezing"
or going into it's solid phase.  This movement can be due to conveyor
problems causing shake, rattle, and roll or even due to leads dragging on
the solder wave nozzle which tends to incline them, then they reposition
after the board leaves the wave.

If component movement is the culprit, the grainy joints will often occur on
both (or all) leads of the same component, but not always.

Methods of verifying the actual cause really depend on the occurance rate
of the grainy joints, but if it's fairly high this movement can often be
detected by simply watching the board as it exits the molten wave.
Hope this helps,

Larry Morse
Celwave RF

 ------------------------ INTERNET MAIL ------------------------
From:   	"BROMLEY, Bill" <[log in to unmask]>
Subject:	ASSY:Grainy wave solder joints
Date:   	Tue, 18 Mar 97 16:05 EST

---------------------------------------------------------------------------

We are currently experiencing random grainular solder joints on double
sided rigid PWB assemblies after wave solder. Our wave solder machine is an
Electrovert Econopak 229, and we are using Alpha 615-25 (RMA-type) flux
with Sn6337 solder per QQ-S-571. The PWB is GHN type per Mil-P-13949/5 with
"C" type copper, and solder coated, with a dry film soldermask. We have
made many process adjustments, including speed, top-side board temperature,
wave bath temperature, etc. We have very recently verified that solder
purity is within specifications. The graininess we are seeing in the solder
joint (including the fillet area) is randomly distributed, and in some
cases located one pad from a perfect solder joint. There is no consistent
pattern from board to board. Can anyone offer some advice?

Bill Bromley/Mike Polifrone
Lucas Aerospace PSA
777 Lena Dr.
Aurora OH 44202 USA
voice: 216-995-1000 ex 7036
email: [log in to unmask]



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