PCB Tech - The hazards of PCB circuit board deformation and treatment measures

The hazards of PCB circuit board deformation and treatment measures

According to incomplete statistics, in 2018 alone, the scale of domestic PCB output value reached a dominant position of tens of billions, and the domestic PCB industry has become more and more mature and continues to extend to the mid-to-high-end market. In recent years, the complexity of PCB layout design is significantly higher than in the past. In order to manufacture smaller and more portable electronic devices, the density and quality of the design must continue to increase. In addition to ensuring the quality of PCB boards, PCB factories will inevitably encounter distortions during PCB processing during PCB processing. The reasons for this are very complex. The causes of deformation during PCB processing are very complex and diverse. It can be divided into thermal stress and mechanical stress caused by two kinds of stress. Among them, the thermal stress is mainly generated during the pressing process, and the mechanical stress is mainly generated during the accumulation, transportation and baking process. If the quality of the plate used is not up to standard and the distribution of the copper skin is not uniform, it will cause warping and deformation after pressing. There are many reasons for this. Here I will only list some of the reasons for your reference.

How to judge a qualified PCB circuit board? We then look down:

1. The shape is not deformed, so as to avoid deformation of the housing and dislocation of the screw holes after installation. Now it is all mechanized installation, the hole position of the circuit board and the deformation error of the circuit and the design should be controlled within the allowable range

2. The line width, line thickness and line distance of the line meet the requirements to avoid problems such as line heating, open circuit, and short circuit.

3. The copper surface is not easy to be oxidized and does not affect the service life

4. The mechanical properties of the surface must meet the installation requirements

5. The copper skin is not easy to fall off under high temperature

We have just analyzed the reasons for the deformation, and then we are going to see what the hazards are; the first is that on the placement line of the input equipment, the overall circuit board is uneven, and the components will be misaligned and cannot be accurately attached. Mounting on the designated pad on the surface of the circuit board will also damage the automatic insertion equipment; the circuit board with the components mounted on it will bend after welding, and it is difficult to cut the component feet neatly. The entire circuit board cannot be installed in the specified product. Therefore, most PCB manufacturers need to go through a leveling process before shipment, and will pass a strict flatness inspection during the final inspection. It can be effectively improved by mechanical leveling or thermal bake leveling before shipment. Affected by the heat resistance of the solder mask and the surface coating, the general baking temperature is below 150 degree Celsius, which just exceeds the Tg temperature of ordinary materials, which has great benefits for the leveling of ordinary boards, and the leveling effect for high Tg materials It is not so obvious, so the temperature of the baking sheet can be appropriately increased on the high Tg boards with serious board warpage, and a series of measures can be improved to reduce the defective rate of finished products.

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