Printed circuit board micro hole mechanical drilling considerations

Nowadays, with the rapid update of electronic products, PCB printing has expanded from the previous single-layer board to the double-layer board and the more complicated multi-layer board required for high precision. Therefore, the processing requirements of the board hole are more and more, for example, the aperture is getting smaller and smaller, and the distance between the hole and the hole is getting smaller and smaller. It is understood that the more used in the board factory is the epoxy resin-based composite material. The aperture size is defined as a small hole with a diameter of 0.6 mm or less and a micropore with a diameter of 0.3 mm or less. Today I will introduce the processing method of tiny holes: mechanical drilling.

In order to ensure high processing efficiency and quality of the holes, reduce the ratio of defective products. In the mechanical drilling process, two factors, axial force and cutting torque, are considered, which may directly or indirectly affect the quality of the hole. The axial force and torque increase with the feed amount and the thickness of the cutting layer, and the cutting speed is further increased, so that the number of cutting fibers per unit time increases, and the amount of tool wear increases rapidly. Therefore, the life of the drill is different for different sizes of holes. The operator should be familiar with the performance of the equipment and replace the drill in time. This is why the cost of processing tiny holes is higher.

The static component force FS in the axial force affects the transverse blade Guangde cutting, while the dynamic component force FD mainly affects the cutting of the main cutting edge. The dynamic component force FD has a greater influence on the surface roughness than the static component force FS. Generally, when the pre-made hole diameter is less than 0.4 mm, the static component force FS decreases sharply with the increase of the aperture, and the dynamic component force FD decreases with a flattening tendency.

The wear of the PCB drill bit is related to the cutting speed, the feed rate, and the size of the slot. The ratio of the radius of the drill bit to the width of the glass fiber has a great influence on the tool life. The larger the ratio, the larger the fiber bundle width of the cutter and the larger the tool wear. In practical applications, a 0.3mm drill can drill 3000 holes. The larger the drill, the fewer holes are drilled.

In order to prevent problems such as delamination, hole wall damage, stains and burrs during drilling, we can place a 2.5mm thick subplate under the layer and place the CCL(copper-clad plate) on the subplate. The aluminum sheet is placed on the copper clad plate, and the function of the aluminum sheet is :

1. The surface of the board is not rubbed.

2. The heat dissipation is good, and the drill will generate heat when drilling.

3. Buffering effect/drilling action to prevent partial holes. The method of reducing burrs is to use vibration drilling technology. Drilling with hard alloy drill bits, hardness is good, and the size and structure of the tools need to be adjusted.