Hi Paul!

You said that you've run bare boards through the reflow oven and are getting
the solder balls, so to me that would eliminate any issues with solder paste.

I've had this happen to me before. It was with a board that was HASL'ed, then
as a secondary operation the vias were capped, or tented, on both sides of
the fab. During reflow the HASL would of course become liquidous, and pressure
would build inside the via, then squirt a little solder ball up on the surface
when the pressure would break the mask cap...does it look like the solder
balls are coming from via's?

In our case when we had that problem, we rejected the fabs. Too much of a
risk for a solder ball to come out beneath a part and cause all kinds of
problems...

-Steve Gregory-


> Hi TechNet Gurus,
>
> Has anyone experienced solder balls resulting from the board fabrication
> process? We have been getting them from our offshore supplier for a few months
> now and have had to add a wash step to our no-clean process. We know that it's
> fro the board because we have run bare boards through the reflow oven using
> the normal reflow recipe from that board and we are seeing 25-60 random
> solder balls on our 9" x 7", 8 layer, .062", HASL FR4  board. We believe the
> problem is caused by uncured solder mask that erupts when exposed to reflow
> temperatures but have been unsuccessful trying to eliminate the problem. We have
> tried baking the board @ 320 F for anywhere from 1.5 - 6 hours. This has
> reduced the number of solder balls to maybe a dozen or less. Anyone have a
> suggestion?
> Thank you,
> Paul Black
> Manufacturing Engineer
> Kronos
>
>
>


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