Those would require the carrier for the device -- in some applications it is a viable way to go -- in others where there is not room for the device carriers one must go with underfill and corners method, or look at other approaches -- these also have a bit more lead inductance than a solid ball, and thus affect signal and power integrity in some cases. One may even be left with the choice of mounting bare die on a hybrid package for some appliations (Very high temperature / High vibration - like the engines)
Another very real aspect is the reduction in total solder joints to have as potential failure points with modern VLSI and FPGA packages in BGA and other high density devices. This is partly also addressed via X-ray laminography and conventional X-ray inspection techniques. Some aspects of an aircraft just do not permit BGA's in those locations however.
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.
Blog Make a Frequency Plan Tom Burke 17 comments When designing a printed circuit board, you should develop a frequency plan, something that can be easily overlooked. A frequency plan should be one of your first steps ...