Chris Byrne asked:

>Presently we are seeing accurrances of solder splashes in our wave solder
>process. We have PCB's that are less then three months old and our storage
>process is inside of a ziplock bag with desiccant. Our present environment
>has a higher than normal humidity level of 40 to 50%.  We have attempted
>many adjustments to the proces such as speed, flux gravity(foamer), etc..
>The only thing that appears to eliminate or reduce the splashes is baking
>the assembly for 1 hour at 50 degrees 'C' and doing the wave process while
>the assembly is still hot.
>
>Does anyone out there have any ideas of what could cause this problem or
>things we should try that could eliminate them?

Your "solder splash" problem lacks details, but I'll guess anyway...
  [(?) means my S.W.A.G.]

You are using a water soluble flux (?)

Your problem is reduced by reducing the flux vehicle (solvent) by way of
having the board "hot" as it enters the fluxer (?)

I would suggest that you determine whether your flux vehicle has any water
in it. If you have a foam fluxer, you will probably have a flux which is
largely IPA. Your IPA can absorb water vapor from the air. If this is so,
the water content of the thinned flux will bias your S.G. reading (water
has a higher S.G.) and will also make it much more difficult for your
preheaters to evaporate the carrier. This is based on the guess that the
"splashing" is due to explosive evaporation of liquid hitting the wave.

Do you hear any "spattering" sound when the boards hit the wave? IMO, if
you do, you instantly know there is a problem!

Make sure you are getting good flux solvent (or IPA) and that the flux is
changed often enough to avoid picking up a few percent water from the
ambient air. You may have gotten a bad batch of IPA or flux, too. Get
technical grade or better, and you might consider having a batch of flux
and/or solvent analyzed for water content and dissolved or suspended
solids. In my experience, solder will tend to stick to contaminants on the
board surface, and I have seen such contaminants dissolved in flux before.

Also, in the past I found that when a board is very much above room
temperature, it would collapse the foam fluxer head (watch under the board
as it hits the fluxer to see if the foam is maintaining its surface
tension) and we would therefore let all prebaked boards cool back to room
temp before going into the wavesolder machine. When we did not, the fluxer
head would collapse and patches of the boards were getting little or no
flux.

Interesting this is NOT what you are doing, and it seems to _help_ you...


regards,

Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com/