In the PCBA processing process, the choice of PCBA tin penetration is very important. In the through-hole plug-in process, the PCB board has poor tin penetration, which can easily cause problems such as false soldering, tin cracks and even dropouts. We should understand these two points about pcba through tin:

1. pcba tin penetration requirements

According to the IPC standard, the PCB tin penetration requirement of through-hole solder joints is generally more than 75%. That is to say, the tin penetration standard for the appearance inspection of the panel surface is not less than 75% of the hole diameter (board thickness). The tin penetration is suitable at 75%-100%. The plated through hole is connected to the heat dissipation layer or the heat conduction layer for heat dissipation, and the PCB tin penetration requires more than 50%.

2. Factors affecting PCB tin penetration

The pcba tin penetration is mainly affected by factors such as material, wave soldering process, flux, and manual soldering.

Specific analysis on the factors affecting pcba tin penetration:

2.1. Material, tin melted at high temperature has strong permeability, but not all metals to be welded (PCB, components) can penetrate in, such as aluminum metal, whose surface generally automatically forms a dense protective layer. Moreover, the difference in the internal molecular structure makes it difficult for other molecules to penetrate. Second, if there is an oxide layer on the surface of the welded metal, it will also prevent the penetration of molecules. We generally use flux to treat it or brush it with gauze.

2.2. Flux, flux is also an important factor affecting PCB tin penetration. Flux mainly plays a role in removing surface oxides of PCB and components and preventing re-oxidation during soldering process. Flux selection is not good and coating is not good. Uniformity and too little amount will cause poor tin penetration. A well-known brand of flux can be selected, which will have higher activation and wetting effects, and can effectively remove difficult-to-remove oxides; check the flux nozzle, and the damaged nozzle should be replaced in time to ensure that the PCB surface is coated with a proper amount of flux. Play the flux effect of flux.

2.3. Wave soldering, PCB poor tin penetration is directly related to the wave soldering process, re-optimize the poor solder penetration parameters, such as wave height, temperature, welding time or moving speed. First, reduce the orbital angle appropriately and increase the height of the wave crest to increase the contact amount of liquid tin with the soldering end; then, increase the temperature of wave soldering. Generally speaking, the higher the temperature, the stronger the permeability of tin, but this should be considered. The components can withstand the temperature; finally, the speed of the conveyor belt can be reduced, and the preheating and soldering time can be increased, so that the flux can fully remove oxides, infiltrate the solder ends, and increase the amount of tin consumed.

2.4. Manual soldering. In the actual plug-in soldering quality inspection, a considerable part of the weldment only has a taper on the surface of the solder, but there is no tin penetration in the via. The function test confirms that many of this part are soldered. It is more common in manual plug-in welding, which is caused by improper soldering iron temperature and too short welding time. Poor solder penetration of pcba can easily lead to false soldering and increase the cost of repair. If the requirements for pcba tin penetration are relatively high and the welding quality requirements are stricter, selective wave soldering can be used, which can effectively reduce the problem of poor pcba tin penetration.