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How to prevent PCB board warping?

PCB information network: PCB warping can cause inaccurate component positioning; When bending in SMT and THT, the uneven pins of the components will bring many difficulties to assembly and installation work. The maximum warpage or twisting degree of IPC-6012 and SMB-SMT circuit boards is 0.75%, and the warpage degree of other boards generally does not exceed 1.5%; The allowable warpage (double-sided/multi-layer) for electronic assembly plants is usually 0.70-0.75%, (1.6mm board thickness). In fact, many boards such as SMB and BGA require a warpage of less than 0.5%; Some factories are even less than 0.3%; PC-TM-650 2.4.22B Warpage Calculation Method=Warpage Height/Edge Length: Prevention of PCB Warpage:

1. Engineering design: The arrangement of interlayer semi cured sheets should correspond; Multi layer core boards and semi cured sheets should use the same supplier's products; The area of the outer C/S surface graphics should be as close as possible, and independent grids can be used;

2. Before cutting, the board is usually dried at 150 ° C for 6-10 hours to eliminate moisture inside the board, further solidifying the resin and eliminating stress inside the board; Bake the board before cutting, whether it is the inner layer or both sides!

3. Before laminating multi-layer boards, attention should be paid to the warp and weft directions of the cured sheets: the shrinkage ratio in the warp and weft directions is different, and before cutting and stacking the semi cured sheets, attention should be paid to distinguishing the warp and weft directions; When cutting the core board, attention should also be paid to the warp and weft directions; The general direction of the cured sheet roll is in the warp direction; The length direction of the copper clad plate is in the longitudinal direction;

4. Cold press the laminated thick stress relieving pressure plate and trim the burrs;

5. Drying plate before drilling: 150 degrees for 4 hours;

6. It is recommended to use chemical cleaning instead of mechanical grinding and brushing for thin plates; Special fixtures are used during electroplating to prevent bending and folding of the board

7. After tin spraying, cool naturally on a flat marble or steel plate to room temperature or clean with an air flotation bed after cooling; Warping plate treatment: 150 degrees or hot pressing for 3-6 hours, using flat and smooth steel plates for heavy pressing, 2-3 times baking!