I wouldn't be surprised if either solder is going up the barrel or if
the via is acting as a heat transfer conduit and reflowing the via.
I've seen this with vias near pads on BGA footprints.
You might consider covering/plugging the wave side of theses vias with
a secondary soldermask. This would reduce heat transfer up the via at
wave. Talk to your bare board supplier about this.
Density permitting the best option is to move the via out of the pad.
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Assy: QFP Reflow
Author: [log in to unmask] at dell_unix
Date: 3/20/97 7:17 AM
Hello TechNet:
We have a .062", board with a top side QFP (SMT) that is reflowing as
the board crosses the wave. Our top side preheat temps have been
checked and double checked and is in the 230 degree "F" range. Peak
temps shown as the board crosses the wave are well below the 361
degree "F" mark. We have vias in the pads on some of the leads. The
QFP is plastic. The board is approximately 3"x5" in size. Density is
maybe a little over average.
Has anyone out there experienced the same thing with some of your
products? We are not seeing a blatant open solder situation, but
suttle fractures that will eventually turn to a open situation.
Supposedly the SMT guys profiles are ok. They are pretty reliable.
The boards are inspected after SMT reflow.
What do you think? Is the reflow caused by the solder coming up
through the vias?
R. Hollandsworth
[log in to unmask]
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