The maximum warpage or twist of IPC-6012, SMB–SMT circuit board is 0.75%, and the warpage of other boards generally does not exceed 1.5%. The warpage allowed by the electronic assembly factory (double-sided/multi-layer) is usually 0.70 —0.75%, (1.6mm board thickness) In fact, many boards such as SMB and BGA boards require warpage less than 0.5%. Some factories are even less than 0.3%. PC-TM-650 2.4.22B.
Warpage calculation method = warpage height/curved edge length
Prevention of circuit board warpage:
The prepreg arrangement between layers should correspond. The core board and prepreg of the multilayer board should use the same supplier’s products. The outer layer C/S surface graphics area should be as close as possible, and independent grids can be used.
Generally at 150 degrees for 6-10 hours, the water vapor in the board is removed, and the resin is further cured completely, eliminating the stress in the board. Baking the board before cutting, no matter the inner layer or both sides are required!
The warp and weft shrinkage ratios are different. Before laminating the prepreg, pay attention to the warp and weft directions. When cutting the core board, you should also pay attention to the warp and weft directions. The general direction of the cured sheet is the warp direction. The long direction of the copper clad laminate is the warp direction.
Warped Plate Treatment:
150 degrees or hot pressing for 3-6 hours, press with a flat and smooth steel plate, and bake 2-3 times.
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