The PQFP and similar packages are better for this but still have limits to the thermal cycling issue -- This can be partly addressed with underfills for All the different types of packages -- When thinking of the ROHS aspects to the underfill -- remember that half as many boards will need to be built -- providing a much bigger impact in this Aspect of Underfill vs No Underfill -- also not using the corner three balls enhances life by at least a factor of two -- with underfill and no corner BGA ball use one can get 5-10x the life out of a BGA in an aerospace application.
@betajet: Aren't there issues with maintaining column stiffness under stress? :-)
They are formed from a stiffer mix in the middle and a softer (more meltable) mix at the ends. My understanding is that they are very rugged and reliable and are used in things like military applications.
I haven't had experience with column grid arrays. I would think you'd still have the concern that solder doesn't flex as reliably as copper or aluminum. Aren't there issues with maintaining column stiffness under stress? :-)
@betajet: My chief worry is stresses on the balls caused by thermal mis-match between a BGA package and its underlying PC board.
Being a string man, I'm going to totally ignore the opertunity to make jokes about stresses on your balls due to thermal management and instead ask if you've had any experiance with column grid arrays (CGAs) in which the solder balls are replaces with solder columns that mitigate against thermal stress (much like wearing looser undergarments :-)
FYI: Disadvantages of BGAs. My chief worry is stresses on the balls caused by thermal mis-match between a BGA package and its underlying PC board. Those tiny solder balls don't flex like proper metal leads -- they crack. And who knows whether those mechanical stresses are causing tin whiskers, since that phenomenon is not well understood. "Oh my ears and whiskers!"
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