When the temperature difference between the center area and the edge area of the board is different, the board will have different degrees of expansion and contraction. This problem may cause damage to solder joints and components in the PCB, thus affecting the performance of the entire pcb. The shrinkage problem refers to the size change caused by the change of moisture content or the uneven distribution of heat during the manufacturing process of the PCB. Under normal circumstances, the PCB will shrink after processing, which is caused by the evaporation of its internal water. However, when the board encounters a humid environment or heating, the water will re-enter the inside of the board, causing its size to expand and shrink. The problem of compression expansion and shrinkage of PCB is mainly related to the coefficient of thermal expansion of materials. The coefficient of thermal expansion of different materials is different, and when the PCB is heated, different parts will have different degrees of expansion and contraction. Under normal circumstances, the PCB is composed of glass fiber and epoxy resin, and its coefficient of thermal expansion is about 16-18 ppm/℃, while the coefficient of thermal expansion of copper foil is about 17 ppm/℃. !Brown oxide Picture:Brown oxideThe expansion and contraction of PCB will have the following impacts on the product1. Causes a decrease in the electrical performance of the PCB If the problem of expansion and contraction of PCB is not solved in time, it can cause interlayer separation of materials, insulation layer rupture, etc., leading to a decrease in electrical performance. This not only reduces the performance of the entire circuit, but also increases the safety hazards of electronic products during operation. 2. Impact on product reliability The problem of PCB expansion and contraction can increase the internal stress of electronic products, leading to issues such as device looseness and solder joint cracks, and reducing product reliability. In order to solve the problem of compression expansion and contraction of the PCB, the following measures are usually taken: 1. Choose the right materials. Engineers can choose materials with a smaller coefficient of thermal expansion to manufacture PCB, such as polyimide (PI) and polytetrafluoroethylene (PTFE). These materials have excellent high temperature resistance and mechanical properties, which can effectively reduce the expansion and shrinkage of the PCB. 2. Adjust the solder joint layout. Correct solder joint layout can reduce the stress concentration problem caused by PCB expansion and contraction. The solder joint spacing should be as uniform as possible and as far away from the edge of the board as possible. This can effectively reduce the stress of the pcb solder joints and reduce the risk of solder joints cracking. 3. Control the temperature. In the manufacturing process of the pcb, the pressing temperature and pressing time should be controlled and optimized according to the characteristics of the material and the process environment. A reasonable pressing process can reduce the expansion and shrinkage of the pcb and ensure the electrical performance of the PCB. PCB compaction and shrinkage is a common but serious problem that can affect the performance and service life of the PCB. The above measures can effectively reduce the occurrence of expansion and contraction problems and improve the reliability and stability of the PCB.
