1. Engineering design: Precautions for printed circuit board design:

A. The arrangement of interlayer semi cured sheets should be symmetrical, for example, for a six layer board, the thickness and number of semi cured sheets between layers 1-2 and 5-6 should be consistent, otherwise it is easy to warp after lamination.

B. Multi layer core boards and semi cured sheets should use products from the same supplier.

C. The area of the circuit diagram on the outer A and B sides should be as close as possible. If side A is a large copper surface and side B only runs a few wires, this type of printed circuit board is prone to warping after etching. If the area difference between the two sides of the circuit is too large, independent grids can be added to the sparse side for balance.

2. Drying board before cutting:

The purpose of drying the copper-clad board before cutting (150 degrees Celsius, time 8 ± 2 hours) is to remove moisture from the board and completely cure the resin inside the board, further eliminating residual stress in the board, which is helpful in preventing board warping. At present, many double-sided and multi-layer boards still adhere to the step of drying the boards before or after cutting. But there are also some exceptions to this in some PCB factories. Currently, the drying time for PCB boards varies among different factories, ranging from 4-10 hours. It is recommended to decide based on the grade of the printed boards produced and the customer's requirements for warpage. Both methods are feasible: cutting into panels and baking, or cutting into large pieces and baking before cutting. It is recommended to cut and bake the panels. The inner layer board should also be baked.

3. The warp and weft directions of the semi cured film:

The longitudinal and latitudinal shrinkage rates of the semi cured film after lamination are different. When cutting and layering, it is necessary to distinguish between the longitudinal and latitudinal directions. Otherwise, it is easy to cause warping of the finished board after lamination, and even with pressure drying, it is difficult to correct. The reason for the warping of multi-layer boards is often due to the unclear warp and weft directions of the semi cured sheets during lamination, resulting in disorderly stacking.