How to reduce PCB warpage

How to reduce PCB warpage

With the development of electronic devices to chip-scale packaging technology, more difficult requirements have been placed on the flatness of the PCB surface. How to effectively control the warpage of PCB has become a problem that we are more concerned about now.

1. Press plate structure

The laminate structure mainly includes the copper foil required for the laminate, the inner sheet, the prepreg that connects the inner sheet to the copper foil as a dielectric layer, and the thermal expansion coefficient of the copper foil and resin will affect the warpage of the PCB. The thicker the copper foil , The greater the difference in thermal expansion, The greater the impact on PCB warpage..

2 The line distribution of different layers in the platen structure is as symmetrical as possible

The circuit distribution of different layers in the platen structure is asymmetrical, that is, the copper foil area of each layer is not the same, and the copper foil thickness is asymmetrical. These factors have differences in the degree of thermal expansion in different areas of the production board in the press board, and ultimately affect the warpage of the PCB board. Therefore, add copper blocks to the wireless circuit area under the premise of the customer's permission, so that the distribution of different layers of copper is as even and symmetrical as possible. Try to choose a thinner copper foil under the premise of meeting the signal transmission, which can reduce the problem of copper foil and substrate. The difference in the coefficient of thermal expansion affects the warpage of the PCB, so that the warpage of the PCB can be better controlled.

3. The impact of PCB process production

In order to improve the efficiency of PCB production and save production costs, each process production board generally contains a finished PCB with several or even dozens of units. The puzzle method is different, and the degree of PCB bending is also different. A reasonable way of puzzles not only considers production efficiency and production costs, but also considers product quality. Although the effect of the puzzle method on PCB warpage is the main factor, in tracking and solving the problem of PCB warpage beyond the control range, we unexpectedly found that when the length of the long side of the finished PCB is twice or more than the length of the short side, When the thickness of the PCB is less than 40mil, the long side of the PCB is the same as the length of the production board, and the area of the production board is more than 2 square feet, the puzzle method has a certain influence on the warpage of the PCB, and its influence is more obvious. The impact is mainly due to human factors in the production (the operator uses improper force when picking up the board) and the imperfect production method of some processes (after printing the green oil, inserting the skeleton drying board). These factors are sometimes inevitable,When only making similar PCBs, it is necessary to slightly change the puzzle of the production board, put the long side of the PCB and the short side of the production board together, and it is best to control the length of the long side and the short side of the production board at 121 Within, the area of the production board should not be too large, so as to reduce the chance of excessive board curvature caused by human factors and imperfect production methods in some processes.

4 Conclusion

Understanding PCB bending and twisting provides us with acceptable standard parameters and key prevention methods. Understanding the main causes of bending and bending of printed circuit boards is very important for manufacturers, an effective way to improve industry competitiveness.