hi,

assuming this was a vacuum bagging operation, was there protection of the leads from the collapsing vacuum bag?  if not, the force of the vacuum bag against the leads could cause the leads and solder to be disturbed.  frankly, i don't understand the oxidation part. do you mount thermocouples on the component during this process?  if not, you should.

phil

-----Original Message-----
From: Linda Woody [mailto:[log in to unmask]]
Sent: Thursday, July 25, 2002 5:49 AM
To: [log in to unmask]
Subject: [TN] Disturbed solder joints


Hi Technet,
I currently have a solder anamoly I need to understand. The component in
question is a very large ceramic leaded (glass bead seals on leads)device
with leads on two sides only. The leads are gold and have been pretinned.
After reflow the solder joints look great (so I believe the thermal profile
is good). The problem is seen after a vacuum thermal bond to a heatsink.
The temperature is 250 degrees F. for 5 hrs. at 26 inches of mercury. Also
the component is being stacked to the PWB (polyimide material) using a bead
of Hysol 151 epoxy on both ends.

Post bond the solder joints look disturbed and oxidized. I understand the
oxidation and am not concerned over this. The disturbed look concerns me.
Is this due to a CTE mismatch? Could there be some other explaination? The
joints aren't fractured but the lead foot appears to have shifted in the
solder. Any theories or possible explainations would be greatly appreciated.

Thanks all,

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