To make the circuit of each layer connected, the boards need to go through the drilling process to make the corresponding holes according to the specifications in the drill files. For single and double-sided boards, drilling process follows directly after board cutting, while multi-layered boards are drilled after lamination. And we can generally divide the PCB drilling process into the following four steps:
Drilling Location Holes
Location holes serve as the positioning points in the PCB production and testing processes. Before drilling, the back-up board, the substrate and the aluminum sheet are first put on the high-speed drilling machine table from bottom to up. According to the manufacturing instruction, three to four around 3.2 millimeter location holes are drilled on the edge of the board.
Inserting Pins
In order to increase production efficiency, several boards are stacked for drilling. But these boards need first to be taped on the drilling machine table through the pins with the backing board and the covering plate together to avoid shift and dislocation.
Drilling Holes
The drilling process is controlled by a computer program, so it simply requires to input the CAM-converted drilling parameter files to drill the corresponding holes. Mechanical drilling is a commonly used method to drill holes in the PCB manufacturing process. The drill bit is rotated at a high speed through spindle and create a cutting force to drill a number of different types of holes, including Plated Through Holes (PTH), Non-Plated Through Holes (NPTH) and Via Holes. Before drilling, a backing board is placed underneath the board to protect the surface of the drilling machine, and an aluminum sheet is also laid on the top to make the holes in the copper foil flatter and prevent the bit from overheating.
Hole Inspection
After drilling, the hole location and aperture of the first sample of board should be inspected. After making sure that there are no problems such as extra holes, missing holes, or hole shift, then it is ready for the next production process.
