Paul:
 
There have been some studies done, in the early nineties, that suggested that matte versus semi-gloss and gloss solder masks reduced the number of solder balls. However, these studies were not reproducible and tests in other sites showed that the biggest effect on solder balling was the preclean cycle.
 
We did some studies on the surface tension of the various masks and found that  lower the surface tension of the mask in dynes/cm2, the lower the number of solder balls. I would like to see that study repeated, since it was not done in an experimental design format. Matte masks  seemed to have lower surface tension which makes it more difficult for solder to stick, however, they also are more polar and attracted more moisture. That could have affected the readings.
 
In the end, all theory aside, we found the best cure for minimizing the solder balls was the preclean cycle.
 
Leo Roos 
----- Original Message -----
From: [log in to unmask] href="mailto:[log in to unmask]">Black, Paul
To: [log in to unmask] href="mailto:[log in to unmask]">[log in to unmask]
Sent: Wednesday, September 24, 2003 4:57 AM
Subject: [TN] Solder Balls

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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