Q: What drill sizes can I use in my design? Can I use inch sizes?
A: Yes, you can use inch sizes, but note that we work in metric units and we have drill sizes from 0.6 mm to 5.0 mm in 0.1 mm steps. This means that if we receive your drill sizes in inch units we’ll convert to metric and round to 0.1 mm. For instance if you are using 27 mils, 28 mils and 29 mils drill sizes they all will be rounded to 0.7 mm. To convert from IMPERIAL to METRIC you should divide your IMPERIAL drill size to 39.37 i.e. 130 mils / 39.37 = 3.3 mm and vice versa 1.0 mm = 39.37 mils after rounding = 39 mils. If this rounding is not taken into consideration you can easily make DRC violations – for instance you can use 34 mils drill with 50 mils pad/via which should pass the annular ring copper check as the pad-drill is 16 mils, but 34 mils drill = 0.86 mm will be rounded to 0.9 mm and the 1.27 mm pad/via will fail on the DRC check.