Extra Fine Pitch BGA pads
One of the annoyances of the world of trade secrets and proprietariness is that we can't all learn from each others' experiences. That is important and even generally necessary in a competitive world. If you put in some hard work, you should get the first right to profit from it. Otherwise what incentive would you have to put in that hard work?
There are times, however, when it would be helpful for the industry or the economy in general if we can all learn from someone else's challenges. Times when, for example, the entire auto industry and therefor the safety of the general public would benefit if all companies shared what they have learned about the reliability of electronic throttle systems.
Here's another chance for open source hardware to shine. Take the Beagleboard. The Ti folks who designed it pushed technology in a number of areas and by presenting what they have created as open source, we can all benefit from it. Even stepping outside of the great work in the schematic, they have done great service in the areas of manufacturing complex devices as well.
A while back, I wrote about soldermask defined (SMD pads) vs non-soldermask defined (NSMD) pads on .4mm pitch BGAs. The basic idea is that while with most BGAs, you want NSMD pads for better mechanical strength, with the really small BGAs, like the .4mm pitch OMAP processor, you want SMD pads to prevent shorts.
The messages that the Beagleboard team learned here are, first, it's true that you want SMD pads and second, make sure that your PCB fab house follows your instructions in that regard.
Many fab houses have their own rules and will set the soldermask up based on what they feel is best. They may have never used your part though. Make sure the board house does what you need. By insisting on closing up the soldermask, the Beagleboard team went from 90% failure with the NSMD pads to 96% good and no BGA shorts with the SMD pads. (This info and the photos come from the Beagleboard ESC presentation by Gerald Coley).
The worms do.