PCB warping will cause inaccurate positioning of PCB components; When the plate is bent in SMT and THT, the pins of components are not complete, whICh will bring many difficulties to the assembly and installation. The maximum warpage or twist of IPC-6012 and SMB-SMT boards is 0.75%, and the warpage of other boards generally does not exceed

Warpage of the circuit board will cause inaccurate positioning of components; When the plate is bent in SMT and THT, the pins of components are not complete, which will bring many difficulties to the assembly and installation.

The maximum warpage or twist of IPC-6012 and SMB-SMT boards is 0.75%, and the warpage of other boards generally does not exceed 1.5%; The allowable warpage (double-sided/multi-layer) of the electronic assembly plant is usually 0.70-0.75%. In fact, many boards, such as SMB and BGA, are required to have a warpage of less than 0.5%; Some factories are even less than 0.3%; PC-TM-650 2.4.22B

Calculation method of warpage=warpage height/edge length

Prevention of PCB warping:

1. PCB engineering design: the arrangement of interlayer prepreg should correspond;

multilayer PCB core board and sEMI solidified sheet shall use the same PCB supplier's products;

The graphic area of the outer C/S surface should be as close as possible, and independent grids can be used;

2. Drying plate before blanking

Generally, the temperature is 150 ℃ for 6-10 hours, so as to eliminate the water vapor in the board, further make the resin cure completely, and eliminate the stress in the board; Bake the board before opening, both the inner layer and both sides need!

3. Attention shall be paid to the longitude and latitude directions of the curing sheet before the multilayer laminate:

The shrinkage ratio in longitude and latitude is different. Pay attention to distinguish the longitude and latitude directions before cutting and laminating the prepreg; Pay attention to the longitude and latitude direction when blanking the core plate; Generally, the roll direction of plate curing film is longitudinal; The long direction of CCL is longitudinal direction;

4. After the laminated stress relief platen is cold pressed, trim the burrs;

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

6. It is better to use chemical cleaning for the thin plate without mechanical grinding and brushing; Special clamps shall be used for electroplating to prevent bending and folding of plates;

7. After tin spraying, it shall be naturally cooLED to room temperature on flat marble or steel plate or cleaned after cooling in air floating bed;

Treatment of pcb warped plate:

150 ° C or hot pressing for 3-6 hours, use flat and smooth steel plate for heavy pressing, and bake for 2-3 tiMES.