I have seen this before with larger PBGA components. When installed using a rework system, I would advise Convective rather thn IR. In my experience having high power (not high temp) convection is the only way to deal with these problematic devices when mounting at a rework station. I have watched a number of companies struggle using IR in this capacity with these particular devices, and also have completed successful mounting of these type devices in front of those same companies using forced air convection type rework stations with low (relative) temperatures and high power capacity.
That was some time ago and I am no longer in that particular business, but it is interesting to see the same old problems still resurfacing...
If you are already using Covective heating, you will need to control the temps carefully and not be in a hurry. Get some long lasting flux paste and ramp slowly up to reflow in a straight shot at about 1.5degC/min. That will help the different substrates of the BGA to stay closer in temperature and help mitigate the TCE problems with the part. Make sure the site is perfectly clean, skip the slolder paste, use tacky flux and control the ramp rate, especially from Flux activation to reflow. That part has to be slow. I counsel patience....
These things look like they are flapping wings sometimes LOL
Best of Luck
'hege
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