In the PCBA production process, the choice of PCBA tin penetration is also crucial. In the plug-in process, and it is easy for the PCB board with bad tin penetration to cause problems such as void welding, tin cracking and even dropping parts.
1、 PCBA tin requirement
According to the IPC standard, the PCBA penetration requirement of the through-hole welding point is generally above 75%. That is to say, the tin standard of the surface inspection of the face is not less than 75% of the height of the aperture (plate thickness), and the PCBA penetration is appropriate in the 75%-100%. The plated through hole is connected to the heat dissipating layer or the heat conducting layer with heat dissipation, and PCBA passes through tin for more than 50%.
2、 Factors affecting PCBA tin penetration
The poor tin penetration of PCBA is mainly affected by factors such as materials, wave soldering process, flux, manual welding and so on.
The high temperature thawing tin has strong permeability, but not all the welded metal (PCB plate, component) can be penetrated, such as aluminum metal, its surface generally automatically forms a compact protective layer, and the internal molecular structure makes other molecules difficult to penetrate into. Second, if there are oxides on the surface of the welded metal, it will also prevent the penetration of molecules. We usually use flux treatment or gauze to clean them.
2. Wave soldering process
Poor PCBA tin penetration has a direct relationship with the process of wave peak welding. It can reoptimize the welding parameters, such as wave height, temperature, welding time or moving speed. First, the orbit angle is appropriately reduced, and the height of the wave peak is added to increase the contact amount of the liquid tin and welding end. Then, the temperature of the wave peak welding is increased. Generally, the higher the temperature, the stronger the penetration of tin, but this should take into account the temperature of the components. Finally, the speed of the conveyor belt can be reduced and the preheating can be increased. The welding time can make the flux fully remove oxide, infiltrate the welding end and increase the quantity of tin.
Welding flux is also an important factor affecting the poor tin penetration of PCBA. The flux mainly plays the role of removing the oxide of PCB and the surface of the components and preventing the reoxidation of the welding process. The poor selection of the flux, the inhomogeneous coating and the low quantity will lead to the poor tin penetration. The welding flux of famous brands can be used to improve the activation and infiltration effect. It can effectively remove the oxide that is difficult to remove. Check the flux nozzle and the damaged spray head in time to ensure the application of the welding flux on the surface of the PCB plate, and the welding effect of the flux.
4. Manual welding
In the inspection of the welding quality of the actual plug-in, a considerable part of the solder is formed only after the surface of the solder is conical, and there is no tin penetration in the hole. The function test confirms that many of the parts are welded, which is caused by the improper temperature of the soldering iron and the too short welding time in the manual plug-in welding. Poor penetration of PCBA leads to solder joint problem and increases cost of rework. If the requirements for PCBA tin penetration are relatively high, the welding quality is strict and the selective wave soldering can be used, which can effectively reduce the problem of PCBA tin penetration.