Carl,

The only way to really tell is to attach thermocouples to the circuit card
and get a time-temperature profile.  The condition you described could occur
if the temperatures are too low and the micro balls don't fuse together.
The same condition can occur if the preheat time is too long and the flux
de-activates prior to reaching melt temperatures.  In this case the solder
melts but there is not enough flux activator left to allow the micro balls
to wet together.

Jim Kittel

 -----Original Message-----
From:   Carl Barnes [mailto:[log in to unmask]]
Sent:   Monday, October 02, 2000 4:51 PM
To:     [log in to unmask]
Subject:        [TN] Soldering Question??

        Technetters,

Need some help from all the soldering experts out there. We have a group of
boards that show evidence of poor solder quality throughout the board. To
the novice eye, it looks like the solder paste did not reflow completely.
There appears to be small balls of unreflowed solder and small pin holes in
some of the joints. Most of the quality group thinks that the profile was
not hot enough. However, when the engineering group came to examine the
joints, they stated, "Why No, these joints were just the opposite, they were
liquidous too long!" Can I get some opinions on this? Any one out there with
examples of solder joints that reflect these two scenarios would be
appreciated. Please send them directly to me. We are having these joints
cross sectioned, once the pictures come in I will forward to anyone
interested. Thanks in advance of any help anyone can give.

Carl Barnes
Production Process Analyst

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