Nowadays, with the rapid update of electronic products, the printing of PCB has expanded from single-layer board to double-layer board and multi-layer board with more complicated requirements for high precision. Therefore, there are more and more processing requirements for PCB holes, for example, the hole diameter is getting smaller and smaller, and the distance between holes is getting smaller and smaller. It is known that epoxy resin matrix composites are widely used in circuit board manufacturers at present, and the definition of hole size is that the diameter below 0.6mm is a small hole, and the diameter below 0.3mm is a micropore. Machining method of tiny holes: mechanical drilling.
In order to ensure high production efficiency and hole quality, we reduce the proportion of defective products. In the process of mechanical drilling, axial force and cutting torque should be considered, which may directly or indirectly affect the quality of holes. The axial force and torque will also increase with the feed rate and the thickness of cutting layer, and then 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 service life of drill knives is different for holes of different sizes. Operators should be familiar with the performance of equipment and change the drill knives in time. This is also the reason why the processing cost of micro-holes is higher.
In the axial force, the static component FS affects the cutting of the horizontal edge, while the dynamic component FD mainly affects the cutting of the main cutting edge. The dynamic component FD has a greater influence on the surface roughness than the static component FS. Generally, when the diameter of prefabricated hole is less than 0.4mm, the static component FS decreases sharply with the increase of the diameter, while the dynamic component FD decreases relatively flat.
The wear of PCB drill bit is related to cutting speed, feed rate and slot size. The ratio of drill bit radius to glass fiber width has great influence on tool life. The larger the ratio, the larger the cutting fiber bundle width of the tool and the greater the tool wear. In practical application, the life of 0.3mm drill tool can drill 3000 holes. The bigger the drill, the fewer holes it will drill.
In order to prevent problems such as delamination, hole wall damage, stain and burr 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 the copper clad laminate. The function of the aluminum sheet is 1. Protect the board surface from scratching. 2. Good heat dissipation. The drill bit will generate heat when drilling. 3. Buffering effect/drilling effect to prevent deviation of hole. The method to reduce burr is to adopt vibration drilling technology, which uses cemented carbide bit to drill, and the hardness is good, and the size and structure of the cutter also need to be adjusted.
