[Tinkerphones] Status GTA04A5

joerg Reisenweber joerg at openmoko.org
Mon Mar 27 07:32:52 CEST 2017


For the alternatives to PoP stacking one-reflow procedure I suggested:

*- Mount and reflow OMAP to PCB using standard SMD291SNL Sn96.5/Ag3.0/Cu0.5 or 
similar, should sit flat on PCB without warp thanks to solder adhesion.
*- Then in a second process step mount and reflow the RAM PoP chip to OMAP, 
using lowtemp solderpaste like  
http://www.chipquik.com/datasheets/SMDLTLFP.pdf and a relatively long top 
reflow profile temperature of 170°C, after sufficient preheating at 125°C

Thanks to lower temperature the OMAP bottom solderjoints can't snap open again 
during RAM PoP reflow. 

Unclear, but likely to be fine: will the Sn42/Bi57.6/Ag0.4 lowtemp solderpaste 
solder the Sn96.5/Ag3.0/Cu0.5 RAM BGA balls reliably?


This is just an untested idea that somehow feels like it's worth to give it a 
try.

cheers
jOERG
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