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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