Being in the line of BGA rework and having performed much rework on boards that go into military planes, I can give you an opinion from a practical background rather than an in depth study.
Basically BGA's have caused many of my customers big headaches. Especially on military boards that need the PCB's to be glued to a heavy heat sink. It's hard to rework or upgrade a component that has a peak temperature rating of 220C whne you need to heat a board to 300C to overcome the amount of heat the heat sink is dissapating. It would be much easier to remove and hand solder a QFP to this type of assembly. Not to mention the cost of exchanging a BGA around $100.00 and a QFP $10.00. Equipment to rework BGA's start at around $35000.00 and for a QFP it starts at around $1500.00.
In the production stage BGA's appear to be pretty reliable. But in the prototype stage they have been causing many of my customer time to market issues. Mainly by assembly houses or rework houses lacking experience and assmeblying boards with poor profiles, not baking chips, not cleaning water soluble fluxes out from under the package well enough.
BGA's also appear to be more sensitive to black pad or plating contamination on the circuit board or even the BGA substrate itself. We find many BGA's that look acceptable visually and through X ray inspection. Black pad contamination is not visually or X ray detectable. It causes the connection to appear as an open during electrical test. Many people misdiagnose it as a defective BGA component. You can only diagnose this problem by removing the BGA and inspecting the PCB & BGA substrates.
I suggest that if you can use a QFP rather than a BGA, then do so. If you must use a BGA and have problems. Well, more business for me. http://www.repair-pcb.com
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