PCB Technical - What factors affect PCBA processing through tin

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. Regarding PCBA processing through tin, you should understand these two points:

One, PCBA tin penetration requirements

According to the IPC standard, the PCBA 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 height (board thickness). PCBA 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 PCBA tin penetration requires more than 50%.

2. Factors affecting PCBA tin penetration

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

Specific analysis of factors affecting PCBA processing tin penetration:

1. Material, high-temperature melting tin has strong permeability, but not all metals (PCB boards, components) to be soldered can be penetrated, such as aluminum metal, which usually automatically forms a dense protective layer on the surface, while the internal Molecular differences in this structure also make it difficult for other molecules to penetrate into it. Secondly, if there is an oxide layer on the surface of the metal to be welded, it will also prevent molecular penetration. It is usually treated with flux or brushed with gauze.

2. Flux, flux is also an important factor affecting the poor tin permeability of PCBA. The main function of the flux is to remove the surface oxides of the PCB and components and prevent re-oxidation during the soldering process. The choice of flux is not good, and the coating is not good. Too low uniformity will result in poor tin permeability. You can choose a good flux, which has a higher activation and wetting effect, and can effectively remove difficult-to-remove oxides. Check the flux nozzle and replace the damaged nozzle in time to ensure that the PCB surface is coated with the proper amount of flux. Give full play to the flux function of the flux.

3. Wave soldering, the penetration rate of poor solder in PCBA processing is directly related to the wave soldering process. Re-optimize the welding parameters with poor welding parameters, such as wave height, temperature, welding time or moving speed. First, appropriately reduce the track angle 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; then the speed of the conveyor belt can be reduced, and the preheating and soldering time can be increased, so that the flux can completely remove oxides, immerse the solder ends and increase the consumption of tin.

4. Manual welding. In the actual plug-in soldering quality inspection, a considerable part of the soldering pieces only have a taper on the solder surface, and there is no tin penetration in the through holes. In the function test, it has been confirmed that many parts have been welded. This situation is more common in manual plunge soldering, because the temperature of the soldering iron is not appropriate and the soldering time is too short. Poor solder penetration of PCBA can easily lead to erroneous soldering problems and increase rework costs. If the requirements for tin penetration in PCBA processing are relatively high, and the requirements for soldering quality are more stringent, selective wave soldering can be used, which can effectively reduce the problem of poor tin penetration in PCBA.