Thanks Werner,
I really do appreciate your response, so often people don't respond to
requests for information on this net.
The use of square pads for BGA intersests me. I had thought that the reason
for this was to provide an irregular outline which would be useful for X -
ray inspection purposes.
Solder resist has quite a large tolerance for defined windows. (A border of
3 thou (mil) is normal and PCB fabs are telling us 1.5 is possible.) So +/-
1.5 to 3 thou.
What are the reasons for this tolerance?
How do different resist types perform?
Are there any improvements forth coming?

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