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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