Date: Fri, 21 Mar 1997 06:25:53
To: "Ron Hollandsworth"<[log in to unmask]>
From: Poh Kong Hui <[log in to unmask]>
Subject: Re: Assy:  QFP Reflow
Cc: Technet@ipc@org

It seems that you have the heat transfer thru' the via. Try plugging the
vias. 
However, do take the temperature of the via to ensure it is due to 
heat transfer thru' via..

I have ever tried to wave-solder at 220 degree C (solder pot) as to fix this
issue, but not too sure whether it works for yours, as it works for our
 boards.


Good Luck..

Poh..

............................................................................
.......................................................
>At 08:24 AM 3/20/97 -0500, you wrote:
>>
>>     Hello TechNet:
>>     
>>     We have a .062", board with a top side QFP (SMT) that is reflowing as 
>>     the board crosses the wave.  Our top side preheat temps have been 
>>     checked and double checked and is in the 230 degree "F" range.  Peak 
>>     temps shown as the board crosses the wave are well below the 361 
>>     degree "F" mark.  We have vias in the pads on some of the leads.  The 
>>     QFP is plastic.  The board is approximately 3"x5" in size.  Density is 
>>     maybe a little over average.
>>     
>>     Has anyone out there experienced the same thing with some of your 
>>     products?  We are not seeing a blatant open solder situation, but 
>>     suttle fractures that will eventually turn to a open situation.
>>     
>>     Supposedly the SMT guys profiles are ok.  They are pretty reliable.  
>>     The boards are inspected after SMT reflow.
>>     
>>     What do you think?  Is the reflow caused by the solder coming up 
>>     through the vias?  
>>     
>>     R. Hollandsworth
>>     [log in to unmask]
>>
>>
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