The key to realize high-precision deep milling of PCB is that the grating ruler on each axis can sense the board surface, so that the descending depth of each Z axis can be controlled separately, and the axes can work independently in coordination to realize mass production processing. Here, the main influencing factors are analyzed:
1. The required thickness tolerance of PCB is 12±0.1mm from the factory, and the relationship between the Z-direction depth accuracy and the horizontal distance is 0.2/770=0.00026mm, which can be ignored when the actual size of the figure to be machined and milled is small. Similarly, for the thickness error of the base plate, we use melamine wood base plate with good flatness as the base plate, instead of milling the wood pulp board.
2. Because the presser foot pad presses the board surface, in order to prevent the sliding of the presser foot pad from scratching the board surface after surface treatment, a hard cover plate is usually placed on the upper surface of the processed product. We choose a copper-free substrate with a good flatness and a thickness of about 1.0mm as the cover plate. The thickness and flatness of the upper cover plate have a great influence on the depth accuracy, so it is advisable to choose a substrate with a smooth and flat surface. The thickness error can be compensated by the first pre-processing method. Long-term use of the plastic presser foot will cause wear and unevenness of the contact surface. In this case, the end face should be polished with sandpaper or a new presser foot pad should be used.
3. The measuring needle group can detect the effective cutter length of the upper ring rear milling cutter, and the cutter length deviation of different milling cutters can also be compensated by the first pre-machining method. The influence of changing the effective cutter length of the auxiliary claw on the depth accuracy can not be ignored, because this deviation occurs after compensation and adjustment, and it is not easy to be found. In order to avoid this kind of error, general depth milling should try to use a milling cutter for processing, and within the acceptable size range, the cutter withdrawal action will not be performed after each processing.
