IPC-6012, SMB-SMT Printed circuit boards have a maximum warpage or twist of 0.75%, and other boards generally do not exceed 1.5%; the allowable warpage (double-sided/multi-layer) of the electronic assembly plant is usually 0.70 ---0.75%, (1.6mm thickness) In fact, many boards such as SMB and BGA boards require warpage less than 0.5%; some factories even less than 0.3%; PC-TM-650 2.4.22B

Warpage calculation method = warpage height/curved edge length
The battery circuit board factory teaches you how to prevent circuit board warpage:

1. Engineering design: the arrangement of the interlayer prepreg should correspond; the multi-layer core board and the prepreg should use the same supplier's product; the outer C/S surface graphics area should be as close as possible, and independent grids can be used;

2. Baking board before cutting
Generally 150 degrees for 6-10 hours, remove the moisture in the board, further make the resin cure completely, and eliminate the stress in the board; baking the board before cutting, whether the inner layer or both sides are required!

3. Pay attention to the warp and weft direction of the cured sheet before stacking the multilayer board:
The warp and weft shrinkage ratio is different. Pay attention to the warp and weft direction before cutting the prepreg sheet; pay attention to the warp and weft direction when cutting the core board; generally the curing sheet roll direction is the warp direction; the long direction of the copper clad laminate is the warp direction; 10 layers 4OZ Power thick copper plate

4. Laminating thick to eliminate stress, cold pressing after pressing the board, trim the burrs;

5. Baking board before drilling: 150 degrees for 4 hours;

6. It is best not to mechanically brush the thin plate, and chemical cleaning is recommended; special fixtures are used during electroplating to prevent the plate from bending and folding

7. After spraying tin, cool naturally to room temperature on a flat marble or steel plate or clean after cooling on an air-floating bed;