PCB board is bent and warped

In actual work, there will be virtual welding or air welding on PCB board. There are various reasons for this situation. This problem is eliminated in time and countermeasures are given, which will have little impact. However, if the problem is not found in time, sometimes even during the testing process, it will affect the production cycle. Here is one reason: PCB board bent board warped.

Then what causes PCB board bending and warping?

Causes of plate bending and warping:

1. In the production process of PCB board, copper foil, resin, glass cloth and other materials need to be pressed together. Because the physical and chemical properties of each material are different, the thermal stress residual generated in the pressing process will also lead to the deformation of PCB circuit board and the phenomenon of bending and warping.

2. Limited by products or institutions with special needs, there will be some PCB board shapes that are not regular or even very strange, but the interface components should be placed in narrow places. In the process of punching, it is easy to cause the phenomenon of PCB board bending board warping.

3. In the design process of printed circuit board, the unreasonable layout planning results in a large distribution deviation of copper foil, which is an important heat absorption and dispersion hot spot of PCB board. A large distribution deviation will cause uneven force and deformation of PCB board during thermal expansion; if the temperature rises very high, it will reach the Tg value of PCB board material. At this point, the PCB board will soften and be easier to deform.

Since PCB board bending will occur, what is the standard of PCB board bending and warping?

Standard for plate bending and warping:

The warpage degree of PCB board can be obtained by calculating the percentage of the ratio of the height warped relative to the plane and the length of the long side of PCB board. The formula is as follows:

As for the warpage degree of circuit boards, the industry standard specification IPC-6012 gives the standard: the warpage and distortion range of production circuit boards is 0.75%~1.5%. This specification standard, the general PCB board factory can meet. For PCB boards with surface mounting requirements or high BGA density, many PCB factories have control requirements below 0.5%. Sometimes, in order to meet the need for higher accuracy and mounting, some even achieve 0.3%.

Some sources give an individual formula for calculating the percentage of the ratio of the height of the plane to the diagonal length of the PCB board, but this standard gives a ratio of less than 0.7%.

The cause of PCB board bending and the standard of bending degree are known, then how can we avoid PCB board bending?

How to avoid bending and warping:

1.PCB board shape should be as square as possible, and device placement should comply with specifications

2.PCB board layers should be symmetrical

3. Lay copper surface as evenly as possible and add balanced copper

4. Bake the plate before production and remove the stress after lamination

5.PCB board materials should be of the same grade or manufacturer to reduce the problem of material matching

summarize

There are many reasons for PCB board bending and warping, and there are many measures to avoid it. There are factors such as water absorption and mechanical strength of the material, as well as factors such as baking and handling in the process of PCB processing, and even some human factors. Many situations will cause PCB warping. None of this matters. What matters is how to prevent it. Just as the quality of products is not controlled, but designed. If there is a problem, it is not afraid to know where the problem is.