In the process of PCBA processing, the choice of PCBA tin penetration is also very important. In the through-hole plug-in process, poor tin penetration of PCB board can easily lead to problems such as solder joint, tin crack and even dropping.
We should know these two points about PCBA tin penetration
1、 Requirements of PCBA tin penetration
According to IPC standard, the requirement of PCBA tin penetration of through-hole solder joint is generally more than 75%. That is to say, the standard of solder penetration of PCBA is no less than 75% of the aperture height (plate thickness) in the visual inspection of the welded surface, and the penetration of PCBA is appropriate in the range of 75% - 100%. However, when the through-hole is connected to the heat dissipation layer or the heat conducting layer, more than 50% of PCBA tin penetration is required.
2、 Factors affecting tin permeation of PCBA
The poor tin penetration of PCBA is mainly affected by material, wave soldering process, flux and manual welding.
The factors influencing the tin permeation of PCBA were analyzed
1. Materials
High temperature molten tin has a strong permeability, but not all the soldered metals (PCB board, components) can penetrate into, such as aluminum, its surface will generally automatically form a dense protective layer, and the internal molecular structure also makes it difficult for other molecules to penetrate. Second, if there is an oxide layer on the surface of the metal to be welded, it will also prevent the penetration of molecules. We usually use flux treatment, or gauze brush clean.
2. Wave soldering process
The poor tin penetration of PCBA is directly related to the wave soldering process. Re optimize the welding parameters such as wave height, temperature, welding time or moving speed. First of all, the rail angle should be properly reduced, and the height of wave crest should be increased to improve the contact amount between liquid tin and solder end; then, the temperature of wave soldering should be increased. Generally speaking, the higher the temperature is, the stronger the permeability of tin is. However, the bearing temperature of components should be taken into account. Finally, the speed of conveyor belt can be reduced and preheating and welding time can be increased to make the flux fully remove oxidation The solder joint is wetted and the tin consumption is increased.
3. Flux
Flux is also an important factor affecting the poor tin penetration of PCBA. Flux mainly plays the role of removing surface oxide of PCB and components and preventing reoxidation during welding process. Poor selection of flux, uneven coating and too little amount of flux will lead to poor tin penetration. The flux of well-known brand can be selected, the activation and wetting effect will be higher, which can effectively remove the oxide that is difficult to remove; check the flux nozzle, the damaged nozzle needs to be replaced in time, to ensure that the PCB board surface is coated with appropriate amount of flux, so as to play the soldering effect of flux.
4. Manual welding
In the actual plug-in welding quality inspection, a considerable part of the weldments only have the surface solder forming a cone, but there is no tin penetration in the through hole. In the function test, it is confirmed that many of these parts are false soldering, which is more common in the manual plug-in welding, because the soldering iron temperature is not appropriate and the welding time is too short. It is easy to increase the cost of solder repair due to poor penetration of PCBA. If the requirement of PCBA tin penetration is high and the welding quality is strict, selective wave soldering can be used, which can effectively reduce the problem of poor solder penetration of PCBA.
