1.The influence of temperature on PCB
High temperature will cause the stress release of the PCB circuit board and eventually cause deformation, and it will also cause embrittlement of some PCB product materials that are not resistant to high temperatures. In addition, the speed of heating and cooling will cause different stress pulling effects on products with different expansion coefficients.
In addition to oxidizing metal parts, humidity is also a catalyst for electron ionization (electromigration).
For some fine-grained or high-density BGA parts, high temperature and high humidity combined with the volatilization of flux will cause a short circuit phenomenon, which may consume the power of the backup battery, and may cause misoperation of some parts.
Therefore, it is necessary to control high temperature and high humidity in SMT chip processing.
Now, as the precision of products is getting higher and higher, some aerospace technology and military products also have great requirements for the material storage of components, so it is not just the PCBA link, all quality control links must be extended forward .
2. Processing method
High heat-generating device plus radiator and thermal board
When a small number of components in the PCB generate a large amount of heat (less than 3), a heat sink or heat pipe can be added to the heating device. When the temperature cannot be lowered, a heat sink with a fan can be used to enhance heat dissipation effect. When the number of heating devices is large (more than 3), a large heat sink (board) can be used, which is a special radiator customized according to the position and height of the heating device on the PCB or a large flat radiator Cut out different component height positions. The heat dissipation cover is integrally buckled on the surface of the component, and it contacts each component to dissipate heat. However, the heat dissipation effect is not good due to the poor consistency of height during assembly and welding of components. Usually, a soft thermal phase change thermal pad is added on the component surface to improve the heat dissipation effect.
Heat dissipation through the PCB board itself
At present, the widely used PCB boards are copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, and a small amount of paper-based copper-clad boards are used. Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation. As a heat dissipation method for high-heating components, it is almost impossible to expect heat to be conducted by the resin of the PCB itself, but to dissipate heat from the surface of the component to the surrounding air. However, as electronic products have entered the era of miniaturization of components, high-density mounting, and high-heating assembly, it is not enough to rely on the surface of a component with a very small surface area to dissipate heat. At the same time, due to the extensive use of surface mount components such as QFP and BGA, a large amount of heat generated by the components is transferred to the PCB board. Therefore, the best way to solve the heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heating element. To be transmitted or emitted.