In former incarnations, we always preheated the ceramic. I agree that 
     you can get good solder joints without preheat, but it sure makes it 
     much easier with the preheat. The problem I have seen is when you 
     don't have the preheat, people feel under the gun and are forced to 
     not do a good job (gotta ship and/or need to make my numbers). I 
     strongly suggest that either keep the preheat or make it impossible to 
     "cheat."


______________________________ Reply Separator _________________________________
Subject: Preheating of Ceramic Chip Capacitors
Author:  [log in to unmask] at Internet
Date:    10/10/96 9:45 AM


Dear Technet,
     
We are a military assembly house that employs preheating 
plates for ceramic chip rework to reduce the risk of 
internal chip delamination from thermal shock. 
This has been done per IPC recommendations.   However, this step in the 
rework process is time consuming and cumbersome.  We have done 
minor and informal tests to determine the real value of this 
practice and found that it really is not needed if the operators take 
care in their soldering.  If the tip size and heating time is 
controlled, there doesn't seem to be an immediate effect or a 
temperature cycling effect on the chips.
     
I am interested to see how widespread the use of preheating 
plates actually is.  I would like to hear from anyone having
any experience indicating that the process is actually necessary. 
(or not necessary)
     
Thank you in advance for any input.
     
Jason Spera
Manufacturing Engineering
General Atronics Corporation
     
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