With the rapid update of electronic products, the printing of PCBs has expanded from the previous single-layer boards to double-layer boards and multi-layer boards with more complex high-precision requirements. Therefore, there are more and more processing requirements for circuit board holes, such as: the hole diameter is getting smaller and smaller, and the spacing between holes is getting smaller and smaller. It is understood that most of the board factories use epoxy resin-based composite materials. The definition of the hole size is that the diameter below 0.6mm is a small hole, and the diameter below 0.3mm is a micro hole. Today I will introduce the processing method of tiny holes: mechanical drilling.
In order to ensure high processing efficiency and hole quality, we reduce the proportion of defective products. In the process of mechanical drilling, two factors, axial force and cutting torque, should be considered, which may directly or indirectly affect the quality of the hole. The axial force and torque will also increase with the feed rate and the thickness of the cutting layer, so the cutting speed will increase, so that the number of cutting fibers per unit time will increase, and the tool wear will also increase rapidly. Therefore, the life of the drill is different for holes of different sizes. The operator should be familiar with the performance of the equipment and replace the drill in time. This is also the reason why the processing cost of tiny holes is higher.
In the axial force, the static component force FS affects the chisel edge Beton cutting, while the dynamic component force FD mainly affects the cutting of the main cutting edge. The dynamic component force FD has a greater impact on the surface roughness than the static component force FS. Generally, when the diameter of the prefabricated hole is less than 0.4mm, the static component force FS decreases sharply with the increase of the hole diameter, while the decreasing trend of the dynamic component force FD is relatively flat.
The wear of the PCB drill is related to the cutting speed, the feed rate, and the size of the slot. The ratio of the drill bit radius to the glass fiber width has a great influence on the tool life. The larger the ratio is, the larger the cutting fiber bundle width of the tool is, and the tool wear also increases. In practical application, 0.3mm drill life can drill 3000 holes. The larger the drill, the fewer holes it will drill.
In order to prevent the problems of delamination, hole wall damage, stains and burrs during drilling, we can put a 2.5mm thick backing plate under the layering, put the copper clad laminate on the backing plate, and then Put an aluminum sheet on top of the copper clad laminate. The function of the aluminum sheet is to:
- Protect the surface of the board from scratching.
- Good heat dissipation, the drill bit will generate heat when drilling.
- Buffer action/drilling action to prevent partial hole.
The way to reduce the burr is to use the technology of vibration drilling, use the carbide drill to drill, the hardness is good, and the size and structure of the tool also need to be adjusted.
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