Although the development of PCB technology is changing with each passing day, many PCB manufacturers focus on the HDI board, rigid flex board, backplane and other difficult parts.However, the existing market still has some relatively simple lines, unit size is very small, complex shape of the PCB, part of the smallest size of PCB even 3-4mm.The plate unit size is too small, unable to design the positioning hole in front design, using the way of positioning processing is easy to produce edge convex points, small PCB will be sucked by dust in the process, tolerance is not controllable, low production efficiency etc.. In this paper, the ultra small size PCB production has been deeply studied and experimentally optimized, and the shape machining method has achieved twice the result with half the effort in the actual production process.
Status analysis
The selection of the shape processing method is related to the shape tolerance control, the contour processing cost, the shape processing efficiency and so on in the contour processing. At present, the common shape processing methods are milling and punching.
Milling
Generally speaking, the machined surface of the milling workpiece has good appearance quality and high dimensional accuracy, but the size of the workpiece is difficult to control because of its small size.In the milling process, due to internal routing arc, internal routing angle and milling groove width restrictions, has great limitations of cutter size selection, often only 1.2mm, 1.0mm, 0.8mm, because the tool is too small, cutting speed is limited, resulting in inefficient production and processing. The cost is relatively high, so it is only suitable for small, simple shape, PCB shape processing without complex internal slot.
Punching
When processing large quantities of small size PCB, the effect of low production efficiency is much higher than that of the contour milling machine. In this case, only punching can be adopted.At the same time for internal slot PCB, some customers are processed by the right angle, drilling and milling is difficult to meet the requirements, especially for those who require a higher dimension tolerance and shape consistency of the PCB, should use punching outline. Punching outline process will increase manufacturing cost.
Experimental Design
According to our company’s experience in making such PCB, we carry out in-depth research and experiment from milling form processing method, stamping die, V-CUT and other aspects, the specific experimental plan is as follows in table 1:
Experiment process
Solution 1—> Outline by milling
Such small size PCB products have no internal positioning, and need additional positioning holes in the unit (Figure 2). When the three side are finished milling, there are open areas around the board, the tooling point not by force, the whole cutter drilling with refined offset direction, so that the finished tooling in forming obvious convex point.Because the 4 sides around have been milling into a suspended state, can not get support, so increased the incidence of bumps and burrs. In order to avoid this abnormal quality, the routing file must be optimized and divided into two milling plates. First, milling the parts of each unit to ensure that there is still a connecting position after processing to make the overall connection profile file (Figure 3).
Figure 2 Figure 3
The influence of milling machine processing experiment on the convex point: according to the above two kinds of routing processing, under each condition randomly selected 10pcs finished product board, using the two dimension for convex point measurement. The size of the finished product board of the original routing is larger and needs manual processing; the processing of the optimized routing can effectively avoid the protruding point, and the product board has a convex size of <0.1mm, which meets the quality requirements.
Solution 2 —> Outlineby CNC engraving and milling
Because the carved equipment cannot pause in the process, the figure 3 cannot be used with milling. The production according to figure 2 routing file, for processing small size, in order to prevent in the process of the finished plate by the dust sucking off dust in the processing process, and with the use of cover plate fixed with the minimum ash, reducing the occurrence of bumps.
The effect of processing on the carved bump: processed according to the processing method, can reduce the size of bump, bump size are shown, the bump can not meet the quality requirements, the need for manual processing.
Solution 3—> Outline by laser machine
Select the product of online contour size 1x3mm to test, make laser profile file along the contour line, according to the parameters, close the dust (to prevent the process of being sucked out of the plate), double sided laser appearance.
The experimental results of laser shape processing of finished plate without convex point, processing size can meet the requirements, but the shape of the finished product by laser laser black pollution surface, and such pollution because the size is too small, can not be used in plasma cleaning, wipe with alcohol can not be effectively treated, the processing effect can not meet customer demand.
Solution 4 —> Outline by punching
The punching process guarantees the size and shape accuracy of the stamping parts, without protruding points. However, it is easy to produce abnormal plate angle injury during processing, and this kind of abnormal defect is not accepted.
Conclusion
According to the shape of precision tolerances for +/-0.1mm high precision and small size PCB in milling, as long as make reasonable design in dealing with engineering data, and choose the suitable processing method based on PCB material and customer demand, a lot of problems will be smoothly done or easily solved.
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