220°C seems pretty low for the max temp of a BGA. Is it a special part?  

I don't think tape will get the 10°C they're looking for. 
I agree with John, generally this means you have to go slower. 

Turning up the convection fans may help if it doesn't move the parts, it can
improve thermal transfer efficiency. Doesn't the 9 zone Heller have low, med
and high settings?  . . . I wonder if the oven blowers are working properly.


Another option is to increase the bottom side heaters and transfer heat
through the board rather than fight with the heat sink on the large BGA. If
there are heat sensitive parts on the back, they might have to consider
doing the primary side first with corner bonder on the BGA and other heavy
parts.




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Macko, Joe @ IEC
Sent: Friday, January 05, 2007 7:21 PM
To: [log in to unmask]
Subject: [TN] Reflowing different sized BGAs without exceeding
manufacturer's p eak body temperatures?

Hello Fellow techs,

 

One of our CMs is having great difficulty developing a thermal profile for a
small, double sided, densely populated board with different  sized BGAs on
one side.  One of the BGAs is rather large and higher in thermal mass than
the surrounding smaller BGAs. The issue is that when he gets the solder ball
temperature of the larger BGA up to at least 205 C, the peak body
temperature of 2 adjacent but much smaller and thinner BGAs exceeds their
manufacturer's recommended peak body temperature of only 220 C by ~ 10 C.
The CM does not think he can make any more adjustments to the 9-heating zone
Heller oven to accomplish this task.

 

Does anyone have any suggestions/ideas on how to heat the larger BGA
sufficiently without over heating the smaller adjacent BGA components?.
Possibly, he can insulate the smaller BGAs with a piece(s) of tape on the
top (prior to assembly) to lower the body temperature - has anyone tried
this? 

 

Look forward to reading anyone's idea. thanks

Joe 

 


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