trace recommendations fbga
hi
it depends on what kind of board,
a 0.8mm bga is a bad idea for any design
expect,
1. a shit load of cross-talk
2. DFM and DFA issues
3. High price tag for manufacturing
you cannot place a 0402 package between those pins,
you can do that provided,
1. use blind and burried via
2. drill over the bga pad, upto certain layer.
3. use drill size from 6-8 (be careful if your board is more than 100 mil thick this won't work, the aspect ration is 1:8 for tight design and 1:10 for high yield FAB)
its going to cost you dearly and a lot of trouble.
Intel dsicontinued their 0.8mm flash just for that reason.
but if you are ready for spending lot of money and you are ok with high-end fab process, you should use the above said recommendation.
use 20mil/20mil pad and 20 mil airgap between the 2 pads for the land-pattern of 0402
even doing all these, it is very tight low-yield FAB process and absolutely no rework.
ask your FAB vendor and have a meeting with them
discuss with them the all the options and design your board with an OKAY from them,
it will be very painful to know that your FAB vendor cannot do the board when it is too late, that is after you complete ur board
best of luck
regards