>8/8 mil is quite unusefull for 0.65 mm pitch BGA package.

Ah, well then you are into specialised territory, for that size pitch.

>My question was a precise one, based on my last work. 4/4 mil,
>5 mil stacked microvia in least three layers (better four) and
>6 mil mechanical drilling (blind vias) is a must.

Any time stacked visa get involved, then AIUI there are a limited number of 
board houses that do it.

>Do you now any US PCB board house doing currently such boards ?

No, not being in the US, but rather in the UK. The only board house I 
personally know of doing stacked vias is in Sweden, but I am sure there are 
others in Europe.

For US suppliers, I suspect you may need to be looking at military qualified 
suppliers. I do not know if cell phones, pagers and similar miniature 
consumer devices use stacked vias (seeing as how they tend to use the size 
and style of chip you refer to) but I assume they all get the PCB 
manufactured and assembled in Asia. 

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