Sounds like he needs to turn down the temp and turn down the conveyor speed?
In other words decrease the thermal ramp rate so he can equalise the
temperatures.

Sounds like an issue I had with a large BGA surrounded by BGA memory devices
which had to be kept close because of signal speed, but in my case the kind
design engineer also assembled more BGA memory on the same footprint on the
other side of the board (mirror image BGA footprint 26 layer board 20 inches
by 17 ish)).

Don't recall that this was a particular issue to set up sucessfully for
assembly BUT re-work was painful due to partial secondary reflow.

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Macko, Joe @ IEC
Sent: Friday, January 05, 2007 4:21 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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