The tiniest required or chosen diameter of the drill as per client specifications is called the minimum diameter of the drill. The drill has special significance in the manufacturing of a PCB because it is the second highest cost of all costs of manufacturing a board. The relevance of the drill includes not only the drill itself but also the number of times the drill pierces the board, the height of the stack and the number of drill types used by the PCB manufacturing facility. The stack height determines the amount of PCBs that can be drilled at one time. It is calculated by referring to the lowest diameter of the drill, tolerances of registration and the thickness of the PCB.
Guidelines for Avoiding Class 4
? To drill a finished and plated hole with a tolerance of plus 0.00 and minus 0.2, you should use a drill diameter no tinier than 0.20 mm.
? The hole size should never be larger than 6.75 mm.
? If you have a hole with a diameter of 4 mm or wider, you will need to do a pilot drill technique.
Important Limitations
The plating capability of the PCB fabrication facility determine the minimum drill diameter. Refer to the Aspect Ratio for more relevant information on this topic.
When you are drilling via-type of holes after HASL, you will most likely need to keep them plugged. In addition there will not be a required minus-tolerance.
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