Hi TechNet -
     
     I would suggest reviewing and verifying (with thermal couples) your 
     total thermal profile of the caps as they go through the wave solder 
     process (machine entrance to exit!). I suspect that if you compare 
     your thermal profile data with the component suppliers data sheet that 
     you are exceeding a maximum temperature limit during the wave 
     soldering process. You may also have a process temperature/flux 
     chemistry interaction. Good Luck.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: Bowing off Tantulam Caps
Author:  [log in to unmask] at ccmgw1
Date:    6/9/97 10:40 AM


     
We are facing acute problem on blowing off caps . Specifically, these caps 
are tantulam caps with high capacitance range of 220 MICROFARADS , rated at 
10 voltage and tolerance in capacitance value is 20%.We have tried more than 
one vendor: one vendor was worse than the present one--however failures are 
always there.
     
These caps are processed ( assembled) alongwith other tantulum caps and 
 usually go through two heat cycles: first one on gluecure  and second one 
at wave. The standards (temp profiles) followed at reflow and wave are as 
per process guidelines .
     
These caps when tested after wave pass 100% at 5v test. Fails 20 to 25% for 
voltages above 7v . Dwell between wave and ATE does not matter much. Tried 
with and without wash -- it does not make significant difference.
     
It is expected that the cap should pass 100% at rated voltage. Clearly there 
is deterioration after assembly process. we ran DOE and observed caps 
failing after wave. however our wave process does not seem to out of 
control.
     
any one having experience on such a behaviour of Tantulum Caps -- we will 
appreciate your technical advise on this problem as we are running out of 
ideas and thinking to change process  to bypass wave solder operation 
altogether.But that is not easy to do in short time.
     
Please send your advise on this mail or email directly to me.
     
[log in to unmask]
Tel: 204-257-9199
     
     
     
     
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