Microwave Tech - Causes and preventive methods of Printed Circuit Board warping

One of the causes of printed circuit board warpage is that the substrate used (copper-clad plate) may warpage, but in the process of printed circuit board processing, because of thermal stress, chemical factors, and improper production process will also cause printed circuit board warpage.

A, To prevent the printed circuit board from warping in the process of processing

1., To prevent improper inventory caused by or increase the substrate warpage

(1) Because of the copper-clad plate in the storage process, because moisture absorption will increase warping, the moisture absorption area of the single copper clad plate is very large, if the storage environment humidity is high, the single copper clad plate will significantly increase warping. The moisture of a double-sided copper-clad plate can only penetrate from the end face of the product, with a small moisture absorption area and slow warpage change. Therefore, for the copper-clad plate without moisture-proof packaging, we should pay attention to the warehouse conditions, try to reduce the humidity of the warehouse, and avoid the naked copper-clad plate, to avoid the storage of the copper-clad plate increased warpage.

(2) Improper placement of copper-clad plate will increase warpage. Such as vertical or copper plate pressure heavy, poor placement will increase the warping deformation of the copper plate.

2, Avoid warpage caused by improper design of printed circuit board or improper processing technology. For example, the conductive circuit graph of the PCB board is not balanced or the circuit on both sides of the PCB board is asymmetrical, and there is a large area of copper skin on one side, which forms large stress and causes the PCB board to warpage. The PCB board will warpage when the processing temperature is high or the thermal shock is large in the PCB manufacturing process. For the impact caused by the improper stock mode of covering board, PCB factory is better to solve, improve the storage environment and put an end to vertical, avoid heavy pressure. For PCB board with copper skin in the large area of the circuit pattern, it is best to grid copper foil to reduce stress.

3, Eliminate substrate stress, reduce the process of PCB warpage

Because in the PCB processing process, the substrate should be subjected to heat and chemical substances many times. Such as substrate etching to water, drying, and heat, graphic electroplating is hot, printing green oil and printing identification characters to use heating drying or UV light drying, hot air spray tin substrate by the thermal impact is also very large and so on. These processes can warp the PCB.

4., Wave soldering or dip welding, solder temperature is too high, the operation time is too long, will also increase the substrate warpage. For the improvement of the wave soldering process, electronic assembly plants need to cooperate.

Since stress is the main cause of substrate warping, many PCB manufacturers believe that drying the board (also known as the baking board) before putting the copper-clad board into use is beneficial to reduce the warping of the PCB board.

The role of the drying board is to relax the stress of the substrate sufficiently, thus reducing the warpage deformation of the substrate in the PCB manufacturing process.

B, Printed Circuit Board warpage leveling method

1. The warped board will be leveled in time in the PCB manufacturing process

In the PCB manufacturing process, the board with relatively large warpage is picked out and leveled by a roller leveling machine, and then put into the next process. Many PCB manufacturers believe that this approach is effective in reducing the warpage ratio of finished PCB boards.

2. PCB finished board warpage leveling method

Some PCB manufacturers put it into a small press (or similar fixtures) and press the warped PCB board for several hours to more than ten hours for cold flattening. From the observation of practical application, the effect of this method is not very obvious. One is that the leveling effect is not large, and the other is that the board is easy to rebound after leveling (that is, to restore warpage).