PCBFast

All drill bits are METRIC!

We drill with a late model Pluritec Multistation 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 0.2mm 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.

That sounds great, but what does it mean for a designer?  Here are some tips:

• Always specify holes/vias in your design as the finished size – we will adjust the actual drill size to accomodate plating.
• Minimum pad size is 0.4mm larger than the the hole/via size to allow for the overdrill required for plating in the PTH.  eg 0.35mm via + 0.4mm = 0.75mm pad
• Don’t use holes smaller than you have to. It can increase drill time and handling and therefore cost as well as decreases reliability.
• 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.
• From a fabrication point of view, there is no difference between vias and through holes, they are all just holes to us and are drilled at the same time and use the same plating process.  Where possible do not have vias and holes the same size as the overdrill used is different.