Can any one tell what is the minimum aspect ratio required for PCB fabrication?
We have done 30:1 with a .4mm multisite design on a .188 thick board using mech drills with both DDI and R&D a few years back.. Yields were not that great, but it was doable. R&D actually did a better job at it with boards in 10 days and that was back 2007.
Now most customers would be prefer an HDI process for reliability purposes.
I try to maintain 9:1 but I have gone to 11:1 on thick boards with .8mm pitch BGA.