All drill bits are METRIC!
We drill with a late model mechanical Air-Bearing Spindle Drill Machine which carries a 300+ tool drum, auto-senses breakages & incorrect tool size, manages drill runout and even blows swarf from the drill tip. Holes sizes are available in 0.05mm increments from 0.25mm to 3.0mm and 0.1mm increments from 3.1mm to 6.0mm. Holes requiring tools larger than 6.0mm are routed in a separate process using router bits in the same way as plated slots.
BTW, whatever their function, HOLES (Vias, PTH or NPTH) are ROUND. If you need a long hole, a slotted hole or a square hole, with or without plating, these are SLOTS. Slots are NEVER drilled, they are routed. Click here for routing and slot info.
Here are some tips:
- Always specify the finished size for vias, PTH & NPTH.
- PTH need a pad minimum 0.3mm larger than their size to allow for plating. This means a 0.6mm via needs a pad that is 0.9mm or larger.
- Vias need a pad minimum 0.2mm larger than their size to allow for plating.
- Minimum drill to copper clearance on internal layers is 0.45mm.
- Don’t use holes smaller than you have to. Drill time, handling and therefore cost increases and reliability can decrease.
- Do try and consolidate your tool sizes. As drill bits are metric, specifying finished sizes in thou/mil will result in rounding to the next appropriate metric size, allowing for the size of the tool available. For example if you specify 31 thou, 32 thou and 33 thou holes, they will all be drilled at 0.95mm for a 0.8mm finish PTH.
- Don’t overdo it on the vias. Small holes drill fast but have a shorter tool life than larger holes and can therefore increase cost.
- Do indicate clearly which holes you need non-plated through (NPTH). These are usually drilled at the same time as the plated holes but rely on tented plating resist film to protect them during the plating process.
- Where possible do not have vias and PTH the same size. In Gerber, they are listed simply as a tool size and will have the same over drill rules applied, possibly leading to tight component holes.