Ralph,
This is just an aside and not an explanation to your problem. I laid out a board with 3 BGAs are 0.75 mm and one 256 pin BGA at 1 mm spacing. Using .004" tracks with .004" spacing I was able to route the whole board on two signal layers with two power layers and no special vias, meaning all were through hole, .018" pad .010" hole. It did take some time and careful planing but at a huge PCB cost savings. Any time you go over 4 layers and start using fancy vias the cost accelerates geometrically. I your case that may not be an issue but in mine I had no choice. Don't forget to use gold flash for the BGAs (for the whole board is easier) to reduce manufacturing problems with soldering BGAs.
Cheers, Tom
Ralph Effinger wrote:
I am haveing trouble laying put an 8 layer board. I have a schematic,
board with chips, resistor,caps and one 256 bga. The bga has a 1mm
pitch. I have setup the layer stack mang. and the desing rules the best
I know how,{this is my first bga}. I layed out the board using blind or
buried vias. I am using protell 99se. after auto routing the board, the
vias all go from the top layer to the bottom not useing any blind or
buried vias. I,ve looked at the tutorials and book, and can find nothing to help me. thank you!
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