The distortion of circuit board can lead to inaccurate positioning of components.When the plate is bent in SMT and THT, the pins of the components are not straight, which will bring a lot of difficulties to the assembly and installation work.
Ipc-6012, SMB-- the PCB of SMT has the maximum warpage degree or warpage degree of 0.75%, and the warpage degree of other boards generally does not exceed 1.5%.The warp (double-sided/multi-layer) allowed by the electronic assembly plant is usually 0.70---0.75% (1.6mm thickness). Actually, many boards, such as SMB, require the warp of BGA boards to be less than 0.5%.Some factories are even less than 0.3%.PC - TM - 650 2.4.22 B
Warping calculation method = warping height/warping length
Prevention of circuit board warping:
1. Engineering design
Multi-layer core board and semi-cured sheet shall use the same supplier product;
The figure area of outer C/S surface is as close as possible, and independent grid can be adopted.
2. Dry plate before blanking
Generally 150 degrees 6 to 10 hours, remove the moisture in the plate, further solidify the resin completely, eliminate the stress in the plate;Before starting the material, both inner layer and double side are needed!
3. Attention should be paid to the longitudinal and latitudinal direction of the plate curing plate before laminated laminated plate:
The percentage of warp and weft contraction is different.The direction of warp and weft should also be paid attention to when feeding the core plate.Generally, the winding direction of plate curing sheet is meridional.The long direction of copper clad plate is meridional.
4. Cold pressing and trimming of the rough edges after removing the stress due to the thickness of laminate;
5. Dry plate before drilling: 150 degrees for 4 hours;
6. It is better to use chemical cleaning without mechanical brush.Special clamp is used for plating to prevent plate bending and folding
7. Spray tin on the flat marble or steel plate after cooling to room temperature or air float bed;
Warping plate treatment:
At 150 degrees or 3 to 6 hours of hot pressure, use smooth and flat steel and bake 2 to 3 times