In a message dated 10/05/1999 7:34:38 AM Central Daylight Time,
[log in to unmask] writes:

<< And anyway, what on earth generates cold solder in the waving process?

 Ioan >>

Hi Loan!

I was gonna ask the same question...I always thought that the "cold solder"
defect was exclusive to solder paste, not molten solder from a wave soldering
machine...hmmmm, ya' learn something new everyday! I would hazard a guess
that it was real grainy looking solder, not cold. Which would tend to point
to some sort of contamination on the leads or in the barrels...

I did have a weird cold solder defect happen to me one time in the past. We
were using water soluble paste, and I had a QA inspector let me know we were
getting cold solder on some boards. I asked to see one of the boards so I
could tell how cold it was...sometimes by looking at it you can see that just
slowing the belt speed down, or bumping up the spike zone a tad will be
enough to correct the problem. But when I looked at the board, it was only a
few random pins on some DRAM (we were building memory SIMM's). Hmmmm, I
thought to myself, how can this be? Why would one pin exhibit cold solder,
and the pin next to it look fine? Convection heat don't work that way...

Come to find out, the operator had been using a damp rag to wipe the
underside of the stencil...actually the rag was pretty soaking wet. Water
would remain in a few of the apertures and it was enough to upset the flux
chemistry on the following prints enough to where there would be this thin
layer of solderballs over the surface of the fillet that hadn't coalesced
into the main fillet. You could take your tweezers and scrape away the layer
of solderballs and there would be a reflowed fillet of solder
underneath...weird huh?

Anyway, enough of my "sea-stories:...

-Steve Gregory-

P.S. I took the rag away from the operator...

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