With the rapid development of electronic products, PCB printing has been expanded from single-layer to double-layer and high-precision multi-layer boards. Therefore, the circuit board hole processing requirements are more and more, such as aperture is smaller and smaller, hole and hole spacing is smaller and smaller. It is understood that epoxy resin matrix composites are more commonly used in plate factories now. The hole size is defined as small holes with a diameter of less than 0.6mm and micro-holes with a diameter of less than 0.3mm. Today I will introduce the micro-hole processing method: mechanical drilling.
In order to ensure high processing efficiency and hole quality, we reduce the proportion of defective products. During 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 increase with the feed and the thickness of the cutting layer, and then the cutting speed will increase, thus the number of cutting fibers per unit time will increase, and the tool wear will also increase rapidly. So different size of the hole, the life of the drill tool is not the same, operators should be familiar with the performance of the equipment to replace the drill tool in time. This is why tiny holes are more expensive to process.
In the axial force, the static component FS affects the broadside cutting, while the dynamic component FD mainly affects the cutting of the main cutting edge. The dynamic component FD has a greater impact on the surface roughness than the static component FS. In general, when the diameter of a precast hole is less than 0.4mm, the static component FS decreases sharply with the increase of the aperture, while the dynamic component FD decreases in a relatively flat trend.
The wear of PCB bit is related to cutting speed, feed rate, and slot size. The ratio of the bit radius to fiberglass width has a great influence on tool life. The larger the ratio is, the larger the width of the cutting fiber bundle will be, and the greater the tool wear will be. In practice, the 0.3mm drill tool life can drill 3000 holes. The bigger the drill, the fewer holes.
In order to prevent the problems of stratification, hole wall damage, dirt, burring, we can put a 2.5mm thickness of the pad below the first layering, put the copper-clad plate on the top of the plate, and then put the aluminum sheet on the copper-clad plate, the role of aluminum sheet is:
1.Protect the board from chafing.
2. Heat dissipation is good. The drill will generate heat when drilling.
3. Buffering effect/drilling-out effect to prevent hole deviation.
The way to reduce burr is to use vibration drilling technology, using carbide bit drilling, good hardness, tool size, and structure also need to be adjusted.
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