The smallest required or chosen diameter of holes to be drilled on a printed circuit board, as specified by the client’s files, is called the minimum drill size. Technical limitations in the manufacturing process, including plating and available drill bits, limit the minimum size a drilled hole can be through a PCB. At Bittele Electronics, our minimum drill hole diameter is 0.15mm for standard holes and 0.1mm for laser drilled holes. This means that we cannot manufacture boards with holes smaller than these sizes.
The leads of through hole components are always above the minimum drill size, thus only when choosing a size for your vias should the minimum drill size be considered. Most PCB designers should not need to worry about these minimums. However, if your design has a high density and you require the smallest possible via holes, then you may specify your holes down to our minimum size.
Another design parameter to consider is the aspect ratio of your holes. For thick boards with numerous layers or holes with very small diameters, there is a limit on the ratio between a hole’s depth and its diameter. At Bittele Electronics we permit a maximum aspect ratio of 10:1 for regular holes and 1:1 for laser drilling. This limitation is the reason why micro vias are drilled one layer at a time and cannot go through a multi-layer board in one drill.
One more specification to keep in mind when designing your board is the minimum clearance between your drilled holes and other copper features which it is not meant to connect to. This clearance varies based on the number of layers as follows:
Minimum clearance between the hole to other copper feature