Peter,
It will depend on the weight of the two parts of the PoP compared to the surface tension of the solder joints and the vibration or lack of vibration of your conveyor system. Also check how much cumulative heat the component supplier recommends. 
Bev
RIM

----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Thu Apr 23 20:00:12 2009
Subject: [TN] Second time reflow of PoP on bottom side of PCBA

Hello technet

I am reviewing an application involving PoP (14mm package on package) 
placed on the side A of the board, side B involves placement of multiple SMT 
connectors (USB etc) therefore it's necessary to process them last. 

My question is whether anyone sees a problem with the PoP device on side A 
going through a 2nd time reflow during side B processing? Would I need to 
utilize a reflow carrier to shield side A to avoid secondary reflow of the PoP 
device?

Any input is appreciated. Thanks.

Peter

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