Hi Steve,
You may be on to something here. I have received a lot of great responses
already, but my experience seems to relate well with your own. Since I can
create the balls on bare boards, I don't see an issue with my solder paste.
I have also run bare laminate through the oven w/o solder balling, so it
shouldn't be an oven issue. The relative humidity in the factory is around
55% right now, so I don't see an environmental issue. I believe that the
solder balls do originate from vias. Although the solder balls can be
anywhere on the board and not necessarily near a via, I have seen solder
mask breakout from a few via (.013") holes. Also, we have a 50 mil BGA in
the middle of the board with vias between the pads. These vias are plugged
on one side of the board, not both sides like you encountered, but I have
been wondering if this operation could have trapped some HASL solder in the
mask, which then later erupted when exposed to reflow temperatures. Someone
else also mentioned a possible incompatibility between the solder mask (Toyo
matte) and the flux, by which I assume he meant the flux used in the HASL
process. Has anyone seen this occur? Could the via plugging on one side of
the board cause the problem?
Thank you,
Paul Black
Manufacturing Engineer
Kronos
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Wednesday, September 24, 2003 9:13 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Balls
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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