We are having a problem with popcorning of a plastic BGA that has been under careful humidity control. We have had problems in the past and some have been related to too much trapped internal solvents from the die attach epoxy. We did a life time buy of these parts. I am wondering if any one has experience in doing a slow long term vacuum bake out of the parts ramping up from 25 to 125C over 4 days (or more)to outgass potential solvents rather than just 48 hours at 125C to drive out moisture. Will vacuum down to 1 torr do more harm than good? Our solder profile for this and many other parts has been verified to be as good as it can, only this one package type from a certain vendor is failiing. Thanks, Gary
With plastic BGAs it is more difficult to remove the trapped moisture because of ground planes in the substrate. If your parts have been sitting around for a long time they may be soaked with moisture and in some cases the 48 hours bake cycle is not sufficient to dry them below the safe level for reflow.
The best solution is to bake them for a longer period of time. The upcoming revision of J-STD-033 will propose an extended bake cycle of 96 hours at 125C for PBGAs. The real effect of vacuum on component drying is still a subject of controversy in the industry and it is not endorsed by the technical committee in charge of the IPC/JEDEC standard.
I hope this is helpful. Feel free to call or e-mail if you need more information.