The Prevention of PCB bow and twist:
1. Engineering design:
The inter-layer prepreg arrangement should correspond. Multi-layer PCB core material and prepregs should be used the same supplier's products. The outer layer C/S surface copper area is as close as possible, and a separate grid can be used.
2. Baking before cut material
Generally 150 degrees 6 to 10 hours, remove the moisture inside the board, further make the resin solidified completely, eliminate the stress in the board; before cut the material drying board, whether inner layer or both sides are required!
3. Pay attention to the warp and weft direction of the sheet material before laminating the pcb boards layer stack up.
The ratio of warp and weft shrinkage is different. Before the lamination of the prepreg, pay attention to the warp and weft direction; when the core board is cut, pay attention to the warp and weft direction too; the direction of the solid sheet is the warp direction; the long direction of the copper clad is the warp direction.
In addition to the above PCB bow and twist tips, please pay attention below points too:
1. Eliminate stress after lamination, cool press after pressing material, trim edge;
2. Drying board before drilling: 150 degrees and 4 hours;
3. To the thin boards, it is best not to be mechanically brushed, using chemical cleaning; special fixtures are used during plating to prevent the board from bending and folding.
4. After surface finish HASL, place the board on a flat steel plate and naturally cool it to room temperature or after the air floating bed is cooled and cleaned;
5. Treatment to boards with bow and twist: 150 degrees or hot pressing 3 to 6 hours, heavy pressure using smooth steel plate, 2-3 times baking.
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