drill size

[jasmine]

hi
I am using micro via in my design that size is 18.6 mils dia so what type of drill size is select ie 10mils drill or 12 mils drill? which is best?pls give me the reply .

Regards
jasmine

[varora]

8 mils would be better

[robert Tarzwell]

to keep your cost down the larger the drill bit the better, as the manufacture drills with decreasing drill size it gets very difficult and expensive very quickly. a 8 mil drill is quite hard to drill, not imposible but hard, a 10 is significantly better and 12 is more a normal size,. you did not mention the board thickness or layer configeration , as the board thickness increases so does the drillling difficulty with small bits.a 3-4 to one ratio is about all a bit can do easly.