Tippit, Jack wrote:
> 
> What is the smallest acceptable plated through hole diameter in a .063"
> thick FR4 board without running into barrel-cracking problems?
> 
> Our suppliers are saying that a .010" drill dia. is acceptable for vias, but
> this exceeds the 3 to 4 aspect ratio (hole diameter to board thickness) that
> many books specify.  Are our books out of date?
> 
> Thanks in advance
> Jack Tippit
> [log in to unmask]
> 
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There are companies that have produced plated through holes with Aspect 
Ratio (A/R)of 10-12 in FR4 boards without via reliability problems. It is 
the process technology that is the limiting factor and not the A/R of via 
for a given board thickness. 

For any size via, the via drilling, seeding of via walls, copper plating 
uniformity and copper adhesion to barrel walls and type of plated copper 
is more critical than a rule of thumb.
-- 
Pratap Singh
Tel./Fax: 512-255-6820
e-mail: [log in to unmask]

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