Precision control skills and methods for PCB board milling

The milling technology of the circuit board CNC milling machine includes the selection of the direction of the cutting tool, the compensation method, the positioning method, the structure of the frame, and the cutting point, all of which are important aspects to ensure the precision of the milling process. The following is the precision control technique of the PCB board milling process summarized by pcb and methods.

     Tool direction, compensation method:
     When the milling cutter cuts into the plate, one side to be cut always faces the cutting edge of the milling cutter, and the other side always faces the cutting edge of the milling cutter. The former has a smooth surface to be processed and high dimensional accuracy. The spindle always turns clockwise. Therefore, whether it is a CNC milling machine with a fixed spindle movement or a fixed spindle movement, when milling the outer contour of the printed board, the tool should be moved in a counterclockwise direction.

     This is what is commonly referred to as up milling. The down milling method is used when milling frames or slots inside the circuit board. Milling compensation is when the machine tool automatically adjusts to the set value when milling, so that the milling cutter automatically offsets half of the set milling cutter diameter from the center of the milling line, that is, the radius distance, so that the shape of the milling is consistent with the program setting be consistent. At the same time, if the machine tool has a compensation function, it is necessary to pay attention to the direction of compensation and the command of the program. If the compensation command is used incorrectly, the shape of the circuit board will be more or less equivalent to the length and width of the milling cutter diameter.

     Positioning method and cutting point:
     Positioning methods can be divided into two types; one is internal positioning and the other is external positioning. Positioning is also very important for process planners. Generally, the positioning plan should be determined during the pre-production of the circuit board.

     Inner positioning is a common method. The so-called internal positioning is to select the mounting holes, plug-in holes or other non-metallized holes in the printed board as the positioning holes. The relative position of the holes strives to be on the diagonal and choose a hole with a large diameter as much as possible. Metallized holes cannot be used. Because the difference in the thickness of the coating in the hole will affect the consistency of the positioning hole you selected, and at the same time, it is easy to cause damage to the coating in the hole and the edge of the hole surface when taking the board. Under the condition of ensuring the positioning of the printed board, the fewer the number of pins the better.

     Generally, 2 pins are used for small boards, and 3 pins are used for large boards. The advantages are accurate positioning, small board shape deformation, high precision, good shape, and fast milling speed. Its disadvantage is that there are many types of hole diameters in the board, and pins of various diameters must be prepared. If there are no positioning holes available in the board, it is more cumbersome to discuss with the customer during the pre-production. At the same time, the management of different milling templates for each type of board is troublesome and expensive.

     External positioning is another positioning method, which uses positioning holes on the outside of the board as positioning holes for milling boards. Its advantage is that it is easy to manage. If the pre-production specifications are good, there are generally about fifteen types of milling templates. Due to the use of external positioning, the board cannot be milled and cut off at one time, otherwise the circuit board is very easy to damage, especially when the board is assembled, the board will be taken out by the milling cutter and the vacuum device, resulting in damage to the circuit board and the breakage of the milling cutter.

     And adopt the method of segmental milling to leave joint points, mill the board first, when the milling is finished, the program pauses and then fix the board with tape, execute the second section of the program, and use a 3mm to 4mm drill to drill out the joint points. Its advantages are less templates, less cost, and easy management. It can mill and cut all circuit boards without installation holes and positioning holes in the board. It is convenient for small craftsmen to manage, especially the production of pre-production personnel such as CAM can be simplified, and the substrate can be optimized at the same time. utilization rate. The disadvantage is that due to the use of drill bits, there are at least 2-3 raised points on the circuit board, which are not beautiful, which may not meet customer requirements, and the milling time is long, and the labor intensity of workers is slightly higher.

     Frame and cutting point:
     The production of the frame belongs to the early production of the circuit board. The frame design not only affects the uniformity of the electroplating, but also affects the milling board. If the design is not good, the frame is easy to deform or some small pieces are produced during the milling board. Small waste blocks, the generated waste blocks will block the vacuum pipe or break the high-speed rotating milling cutter. The deformation of the frame, especially when the milling plate is positioned externally, will cause the deformation of the finished plate. In addition, the choice of the cutting point and the processing sequence can make the frame Maintain maximum intensity and maximum speed. If the choice is not good, the frame is easily deformed and the printed board is scrapped.

     Milling process parameters:
     The shape of the printed board is milled with a cemented carbide milling cutter, and the cutting speed of the milling cutter is generally 180-270m/min. The calculation formula is as follows (for reference only):


     Where: p: PI (3.1415927)

     d: milling cutter diameter, mm

     n; milling cutter speed, r/min

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