Drill
Our drilling is performed by 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. It can reliably drill microvias at 0.2mm, right through to mounting holes at 6.3mm.
Drill bits are available in tool sizes with 0.05mm increments from 0.2mm to 3.0mm and 0.1mm increments from 3.1mm to 6.3mm. Drill tool size is typically 0.05mm to 0.15mm larger than the finished hole size to allow for plating on hole walls.
Holes requiring tools larger than 6.3mm 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:
- Don’t use holes smaller than you have to. It can increase cost, through drill time and handling, and 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.
- Don’t use blind or buried vias unless you absolutely have no other choice. Contrary to popular belief, it’s not easier. Blind/buried vias require multiple plating processes, multiple drilling processes and multiple lamination processes and therefore cost a great deal more than standard through vias.
- 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.