Selection of pads for PCB drilling technique
Printed circuit board drilling, use the up and down pads to prevent circuit board surface and bottom of foil flowers produce burrs, circuit board drilling surface smooth and improve the quality and yield of printed circuit boards. Due to the use of this material have a certain cost, but due to the above reasons are in fact required to use, can greatly improve the qualification rate of products to reduce costs.
Pads on the circuit board drilling requirements are: there is a certain hardness to prevent drilling burrs on the upper surface. But not too hard and wearing drill bit. Requirements of the pad itself resin constituents not to expect too much, otherwise the drill will form when the molten resin ball sticking in the wall. Bigger is better thermal conductivity, heat away, so you can quickly drill, reducing the temperature of drill hole drills to prevent drill annealing. Must be rigid to prevent drill plates vibrate, but also have some degree of flexibility when a drill drill variants immediately contacts an instant, drill precise alignment is drilling location and ensure the drill position. Material should be uniform no impurities produce both soft and hard not nodes, or easy to broken drill bit. If backing plate on the surface is hard and slippery, small-diameter bit may slip away from the drilled holes in the circuit board out of the oval hole.
Domestic use the plate on the main 0.2~0.5mm thick paper plastic epoxy-phenolic glass cloth laminated board and foil thickness 0.3mm LF2Y2 (2nd, rust-proof aluminum semi cold work hardening or LF21Y (21st, rust-proof aluminum cold work hardening condition) as ordinary two-panel drilling pads better achieve suitable hardness prevents drilling burrs on the upper surface. Because of the good thermal conductivity of aluminum rigid-elastic, the bit has some cooling effect, aluminium foil material more phenolic panels evenly free of impurities caused by broken drill bit and hole much less than the rate of phenolic plate. Lower temperature and is an environmentally friendly material, widely used on many of the factory has been using aluminum foil as a plate, while comparing with plate, epoxy-phenolic panels, not because of the resin and may make contaminated with resin, thickness of aluminum foil in the process of using the chosen to be 0.15, 0.20, 0.30 mm in actual use, the three kinds of 0.15 and surface contact best but in cutting-cutting and delivery process and the use of technology is not easy to control, 0.30 higher prices generally compromise using 0.20 mm aluminum foil, the actual thickness of 0.18 mm.
Abroad there is a composite plate, upper and lower layer is 0.06mm of aluminum foil, the middle layer is pure fiber core, total thickness is 0.35mm. It is easy to see, this kind of structure and materials to meet the requirements of printed circuit board drilling pads, used on a high quality plywood plate, and foil their advantages are: drilling of high quality, high hole position accuracy, due to wear and tear little bit increase in life expectancy, while plates outside back to the original shape much better than aluminum foil, are much lighter in weight, is particularly suitable for drilling small holes.
Domestic use pads under the phenolic paper board, cardboard, sawdust Board. Cardboard is soft and prone to glitches, broken bits and bites but homogeneous hard to drill, but the price is cheap, can be used in thin copper foil or single-sided. Particle boards poor uniformity of texture and hardness better than paper plates such as drilling Burr on the circuit board copper foil is greater than 35 microns is, I tried to use the drill 70 µm copper foil double panel, results cannot be passed. Phenolic paper board best hardness uniformity between the former two, works best but more expensive and environmentally unfriendly.
Under the same abroad have a composite plate, upper and lower layer is 0.06mm of aluminum foil, the middle layer is pure fiber core, total thickness is 1.50mm. Of course performance is remarkable and environmentally friendly, well over the phenolic paper board, especially the drill when MLB and the small diameter hole can fully show its advantages, disadvantage is of course more expensive.