source:Industry News release time:2022-09-27 Article author:yu Popular:pcb
The deformation of the PCB board during the production process is a problem encountered in the mass production of PCBA. The deformation of the pcb circuit board will have a considerable impact on the patch and test, so it should be avoided as much as possible in the PCBA processing and production. There was a problem.
The smt workshop technical engineer of Shenzhen smt chip processing factory analyzed the reasons for PCB deformation as follows:
1. Improper selection of pcb raw materials, such as low T of pcb, especially paper-based pcb, because the processing temperature is too high, it will lead to PCB bending;
2. The unreasonable design of the pcb circuit board and the uneven distribution of components will cause excessive thermal stress to the PCB. Large-shaped connectors and sockets can also affect the expansion and contraction of the PCB circuit board, resulting in a permanent appearance of the PCB circuit board. distortion;
3. PCB circuit board design problems, such as double-sided PCB circuit boards, if the copper foil on one side is too large, such as the ground wire, and the copper foil on the other side is too small, in this case, it will also cause uneven shrinkage on both sides. pcb distortion;
4. Improper use of fixtures or too small distance between fixtures during patch processing in the smt process workshop, such as the middle finger of wave soldering is too tightly clamped, the PCB will expand due to the soldering temperature, and the pcb will be twisted and deformed;
5. Excessive temperature during reflow soldering will also cause PCB deformation.
For the above reasons, the smt technical engineer of Shenzhen smt Shiyan Patch Factory has put forward corresponding solutions based on rich experience:
(1) When the price and space of the pcb circuit board allow, choose a PCB with a high Tg or increase the thickness of the PCB to obtain the best aspect ratio;
(2) The smt technical engineering designer of the pcb board manufacturer needs to design the PCB reasonably. The area of the two sides of the steel foil should be balanced, and the copper layer should be covered where there is no circuit, and it will appear in the form of a grid to increase the hardness of the PCB;
(3) The smt technicians of the patch processing factory pre-bake the PCB before the PCBA patch, on the condition that it needs to reach the standard 125℃/4h;
(4) smt technicians adjust the fixture or clamping distance before PCBA processing to ensure the space for PCB thermal expansion;
(5) The welding process temperature during PCBA processing should be reduced as much as possible. If the PCBA circuit board is slightly deformed, it can be placed in the positioning fixture to heat and reset to relieve the stress. Generally speaking, that's it. This processing method will also achieve satisfactory PCBA quality results.
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