PCB CNC Drilling Machine: Use of Backing Plate
The requirement for drilling the upper plate of the circuit board is that it has a certain surface hardness to prevent burrs on the upper surface of the drilled hole. But not too hard and wear the drill bit. It is required that the resin composition of the upper and lower pads should not be too high, otherwise a molten resin ball will be adhered to the wall of the hole during drilling. The larger the thermal conductivity, the better, so that the heat generated during drilling can be quickly taken away, the temperature of the drill bit when the hole is drilled, and the drill bit annealed. It must have a certain rigidity to prevent the plate from vibrating during the lifting, and it must have a certain elasticity. When the drill bit is touched, the deformation immediately deforms, so that the drill bit is precisely aligned with the position to be drilled, and the drilling position accuracy is ensured. The material should be uniform and there should be no impurities to produce soft and hard nodes, otherwise it is easy to break the drill bit. If the surface of the upper pad is hard and slippery, the small diameter drill bit may slip away from the original hole position and drill an elliptical oblique hole on the circuit board.
The upper backing plate used in China is mainly 0.2~0.5mm thick phenolic paper rubber sheet epoxy glass cloth board and aluminum foil such as LF2Y2 with thickness of 0.3mm (No. 2 anti-rust aluminum semi-cold hardening state or LF21Y (No. 21 anti-rust aluminum) Cold work hardening state) As a common double-panel drilled upper plate, the effect is better, and the hardness is suitable to prevent the upper surface of the drilled surface from burr. Because aluminum has good thermal conductivity and rigidity, it has a certain heat dissipation effect on the drill bit, and the material of the aluminum foil Compared with the phenolic plate, no impurity causes the probability of breaking the drill bit and the partial hole is much smaller than that of the phenolic plate. It can reduce the drilling temperature and is an environmentally friendly material. The application is increasingly wide. Many factories have used aluminum foil as the upper backing plate, and the phenolic plate and ring. Compared with the oxygen plate, the hole may not be contaminated by the resin. The thickness of the commonly used aluminum foil is 0.15, 0.20, 0.30 mm during use. In actual use, the contact with the surface of the plate is preferably 0.15. However, during the cutting process and during the transportation process and during use, the process is not easy to control, and the price of 0.30 is a little higher. Generally, 0.20 mm of aluminum foil is used, and the actual thickness is generally 0.18 mm.
There is a composite upper pad in foreign countries. The upper and lower layers are 0.06mm aluminum alloy foil, and the middle layer is pure fiber core with a total thickness of 0.35mm. It is not difficult to see that this structure and material can meet the requirements of the PCB on the PCB printed circuit board, and it is used for the upper pad of the high quality multi-layer board. Compared with the aluminum foil, the advantages are: high drilling quality, hole The position accuracy is high, and the life of the drill bit is improved due to wear and tear. At the same time, the original shape of the plate is much better than that of the aluminum foil after being subjected to external force, and the weight is also much lighter, and it is particularly suitable for drilling small holes.
The underlying plates used in China are phenolic paperboard, cardboard, and wood chipboard. The cardboard is soft and easy to produce burrs, but the texture is uniform and it is not easy to break the drill bit and bite the drill bit, but it is cheap and can be used in thin copper foil or single panel. The chipboard has poor texture uniformity and hardness is better than paperboard. However, if the copper foil of the drilled circuit board is larger than 35 microns, it will produce burrs. I tried to use the double-panel of 70-micron copper foil to pass the board. . The hardness of the phenolic paper board is preferably between the first two, and the effect is best but expensive and not environmentally friendly.