Hi Tom - there hasn't been much published on this topic in the last 5-10 
years as most folks wave solder processes are reasonably controlled, the 
SMT capacitor manufacturers have better/more consistent fabrication 
processes and the preheat capacity of modern wave solder equipment is much 
better than in the past. A "general" industry consensus was reached that 
SMT capacitors temperature had to be within 100C-125C of the wave solder 
temperature. A combination of adequate preheat parameters, use of the chip 
wave, the physical distance between the chip wave and the laminar wave, 
and the wave solder pot temperature all came into play to avoid thermal 
shocking the components. We conducted an number of investigations looking 
at the process/parameters and found we could get a heating rate of 
5-6C/second and not have any thermal shock issues. Lead-free solder 
processing is going to have everyone probably giving the thermal shock 
issue a second look as there have been some suggestions that we may need 
controlled cooling of our assembles as they exit solder process equipment. 
If controlled cooling becomes necessary, then the thermal shock concern 
that Werner detailed could be an ugly balancing act to achieve. There were 
some good papers on the whole SMT capacitor/wave solder thermal shock 
topic published in the early 1990s.

Dave Hillman
Rockwell Collins
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"Gervascio, Thomas L" <[log in to unmask]> 
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[TN] Wave soldering SMT capacitors






A friend of mine asked a good question, why is that most SMT capacitor 
specs call out for a maximum heating rate at SMT of 2-4 C/sec but the same 
specs allow a temperature delta at wave soldering of 100-125 C? In case of 
wave, the time between preheat and soldering causes a heating rate in 
excess of the SMT heating rates. But it is OK to subject the part to the 
wave solder but not SMT using those heating and cooling rates?

I never could recall a logical explanation. Called several capacitor 
manufacturer's and they seemed to dance around the question.

Any information would be helpful




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