Greg, The best advice that I can give you is a PBGA will respond just like any other surface mount package. There may be a 5 degree delta between a PBGA 356 and a QFP208 but the two respond very similarly in the convection reflow environment. CBGAs suck a lot more heat so you have to be careful with them. Don't worry about not being able to see the interconnections. The key to BGA processing lies in the printing process. Be sure your prints are well aligned and the apertures remain free of "held up" paste. I have processed PBGAs, CBGAs, EBGAs, and TBGAs for about 2 years now with a variety of ovens on over 100 different assemblies. No joke. Profile the board just as you would any other fab. The "nay sayers" are going to tell you to drill through the fab and insert a thermocouple into one of the balls of the BGA to get a rock solid profile. I believe this is overkill. I do not tweek my BGA profiles. I just profile the board as any other and shoot for 215 to 220 for a Max temperature and things always work out fine.
Regards, Justin Medernach
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