In a message dated 9/11/98 8:12:38 AM Pacific Daylight Time,
[log in to unmask] writes:

<< Here's a basic question, I'm routinely getting soft solder on fine pitch
connections (15-25 mils), the solder looks good but is just plain soft.  A
probe can pop the leads very easily.  The boards are almost exclusively
surface mount and are built and reflowed with a heat sink covering the entire
board attached.  I believe the profile to be good or very close.  I am washing
and baking all boards to lessen contamination issues yet I still see soft
solder.  Any ideas OK >>

Hello There!

     I've got a lot of ideas, but it would be better to understand your
situation a little more to be able to give you any good advice. First, is this
"soft solder" problem something that just started happening? Have you built
these same boards in the past without any problems? If so, has something
changed in your process? Solder paste perhaps?

     Now when you say the leads pop very easily, I've got to ask, are you
using a orange stick or some similar probe and gently applying pressure on a
suspect connection to check the bond, or are you using some sort of metal pick
and raking it across the leads to see what comes loose? I ask this because if
you're doing the latter, it's really not something you should be doing. At a
past company, that was the method a customers source inspector used to check
the fine pitch. Unfortunately, he damaged more solder connections than he
found actually bad. It doesn't take a heck of a lot of force to "pop" a fine
pitch lead even when it's soldered well.

        Does the board get waved at all?...and what alloy solder paste are you
using? You also mentioned a large heat sink attached to the board, it that
something that has to be, or can the heat sink remain off the board during
surface mount assembly and be attached later? Having that going into reflow
along with with your board has to complicate things quite a bit...

Regards


-Steve Gregory-

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