PCB Tech - Discussion on the outline processing of small size PCB

Although the current development of circuit board technology is changing with each passing day, many circuit board manufacturers have devoted their main energy to the production of high-difficulty boards such as HDI boards, rigid-flex boards, and backplanes. However, there are still some circuits in the existing market that are relatively simple. The unit size is very small, and the circuit board with complex appearance, the minimum size of some circuit boards is even as small as 3-4mm. Therefore, the unit size of the board is too small, the positioning hole cannot be designed in the front-end design, the use of external positioning method is easy to produce board edge bumps, the dust is sucked out of the circuit board during the processing, the shape tolerance is uncontrollable, and the production efficiency is low. problem. This article has conducted in-depth research and experiments on the production of ultra-small size circuit boards, optimized the shape processing method, and achieved a multiplier effect in the actual production process.

The choice of the shape processing method is related to the shape tolerance control, the shape processing cost, and the shape processing efficiency during the shape processing. At present, the commonly used shape processing methods include milling shape and die.

1.1 Milling profile

Generally speaking, the plate parts processed by the milling profile have good appearance quality and high dimensional accuracy. However, due to the small dimensions of such plates, the dimensional accuracy of the milling profile is difficult to control. In the shape of milling, due to the limitation of the arc of the inner gong, the size of the inner gong and the width of the milling groove, the choice of milling cutter size has great limitations. In many cases, you can only choose 1.2mm, 1.0mm, or even 0.8mm. The milling cutter is used for processing. Due to the small tool size and the limited cutting speed, the production efficiency is low and the processing cost is relatively high. Therefore, it is only suitable for small volume, simple appearance, and no complicated inner grooves for PCB appearance processing.

1.2 Die

When processing large quantities of small-size PCBs, the impact of low production efficiency is much higher than the impact of the cost of shape milling. In this case, only the method of punching can be used. At the same time, for the internal gong groove in the PCB, some customers require it to be processed into a right angle, and it is difficult to meet the requirements by drilling and milling. Especially for those PCBs with high requirements for shape tolerance and shape consistency, punching is required. The use of die forming process alone will increase manufacturing costs.

2 Experimental Design

According to our company’s experience in the production of such PCBs, we have carried out in-depth research and experiments in terms of milling profile processing methods, die, V-CUT, etc.

3 Experimental process

3.1 Scheme one-gong machine milling shape

This kind of small-size PCB products often have no internal positioning, and positioning holes need to be added outside the unit (Figure 2). When the three-sided gong is finished, when the last gong is finished, there will be open areas around the board, so that the cutting point cannot be stressed. The entire finished product is offset with the direction of the cutter cutting, so that the finished product is closed after being formed. The dots have obvious bumps. Because the surroundings have been milled into a suspended state and cannot be supported, the probability of bumps and burrs is increased. In order to avoid this quality abnormality, the gongs need to be optimized, and the milling is divided into two times, and part of each unit area is milled first to ensure that there is still a connection position after processing to make the overall connection profile file

The influence of gong machining experiment on bumps: According to the above-mentioned two gong belts, 10pcs finished boards are randomly selected under each condition, and the bumps are measured using the second element. The size of the bumps of the original gongs processing finished board is large, and manual processing is required; the optimized gongs processing can effectively avoid the bumps, and the size of the bumps of the finished board is<0.1mm, which meets the quality requirements

3.2 Scheme Two-Precision Engraving Machine Milling Shape

Because the precision carving equipment cannot be suspended during processing, the gongs in Figure 3 cannot be applied. It is produced according to the inner gongs in Figure 2. Due to the small processing size, in order to prevent the finished board from being vacuumed away during the processing, the vacuum must be closed during the processing, supplemented by a cover plate, and fixed with board dust to minimize Reduce the production of bumps.

The effect of fine carving processing experiment on bumps: processing according to the above-mentioned processing method can reduce the size of bumps

3.3 Scheme Three-Laser Shape Effect Verification

Choose the product with the online outline size of 1*3mm for testing, and make the laser outline file along the outline line. According to the parameters in Table 4, turn off the vacuum (to prevent the board from being sucked away during the processing), and perform the double-sided laser outline.

Experimental results: No bumps are produced on the finished board processed by laser contour, and the processing size can meet the requirements, but the finished product after laser contour will contaminate the surface of the board due to laser carbon black, and this type of pollution is too small to be plasma cleaned, and alcohol is used. Wiping cannot be effectively processed (as shown in Figure 7), and this type of processing effect cannot meet customer needs.

3.4 Scheme Four-Die Effect Verification

The die processing ensures the size and shape accuracy of the stamping parts, and no bumps are generated (as shown in Figure 8). However, abnormal board corner crushing is easy to occur during processing, and such abnormal defects are not accepted.

4 Conclusion

This article is aimed at the problems that occur in the high-precision small-size circuit board with a tolerance of +/-0.1mm, as long as a reasonable design is made when processing the engineering data, and the appropriate processing method is selected according to the circuit board material and customer needs, Many problems will be solved.