Hi Thomas, 
What high rates of temperature change do, is set up transient internal thermal gradients causing differential thermal expansion [on heating] and contraction [on cooling]—and by the way, rapid cooling is worse than rapid heationg, because now you have the solidifying solder involved as well together with the interaction between warping components and PCBs.
Werner

 


 

 

-----Original Message-----
From: Gervascio, Thomas L <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Feb 11, 2011 3:58 pm
Subject: [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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