PCB distortion is a common problem in PCBA batch production, which will bring considerable influence to assembly and testing. How to avoid this problem, please see below.
The causes of PCB distortion are as follows:
1. Improper selection of PCB raw materials, such as low T of PCB, especially paper-based PCB, whose processing temperature is too high, PCB becomes bent.
2. Improper PCB design, uneven distribution of components will lead to excessive thermal stress of PCB, and connectors and sockets with larger shapes will also affect PCB expansion and contraction, resulting in permanent distortion.
3. PCB design problems, such as double-sided PCB, if the copper foil on one side is too large, such as ground wire, and the copper foil on the other side is too small, it will also cause uneven shrinkage and deformation on both sides.
4. Improper use of fixture or fixture distance is too small, such as wave soldering machine finger claw clamping too tight, PCB will expand and deformation due to welding temperature.
5. High temperature in reflow oven welding will also cause distortion of PCB.
In view of the above reasons, the solutions are as follows:
1. If the price and space allow, choose PCB with high Tg or increase PCB thickness to obtain the best aspect ratio.
2. Design PCB reasonably, the area of double-sided steel foil should be balanced, and copper layer should be covered where there is no circuit, and appear in the form of grid to increase the stiffness of PCB.
3. PCB is pre-baked before SMT machine at 125℃/4h.
4. Adjust the fixture or clamping distance to ensure the space for PCB heating expansion.
5. Welding process temperature as low as possible, mild distortion has appeared, can be placed in the positioning fixture, temperature reset, to release the stress, generally satisfactory results will be achieved.
Post time: Nov-30-2021