In the PCBA processing phase, the selection of PCBA tin penetration is crucial. During the through-hole insertion process, inadequate tin penetration on the PCB can lead to issues such as false soldering, tin cracks, and even component dropouts. When considering PCBA tin penetration, keep in mind the following two points:

1. PCBA tin penetration requirements

According to IPC standards, the tin penetration requirement for through-hole solder joints is typically over 75%. This means that for visual inspection of the panel surface, the standard for tin penetration should not be less than 75% of the hole height (board thickness). Ideally, PCBA tin penetration should range between 75% and 100%. Additionally, for plated through holes connected to heat dissipation or conduction layers, a tin penetration of over 50% is required.

2. Factors affecting PCBA tin penetration


PCBA tin penetration is primarily influenced by several factors, including material type, wave soldering process, flux, and manual soldering techniques.

Specific analysis of the factors affecting tin penetration in PCBA processing:

1. **Material**: High-temperature melting tin exhibits strong permeability; however, not all metals (such as PCB boards and components) can be effectively penetrated. For instance, aluminum typically forms a dense protective layer on its surface, which, along with molecular differences in its internal structure, hinders penetration by other molecules. Additionally, if the metal surface has an oxide layer, this can also obstruct molecular penetration, often requiring treatment with flux or cleaning with a cloth.

2. **Flux**: The choice of flux plays a crucial role in the tin permeability of PCBA. Its primary function is to eliminate surface oxides from the PCB and components while preventing re-oxidation during soldering. Poor flux selection or uneven application can lead to inadequate tin permeability. Opting for a high-quality flux with enhanced activation and wetting properties can effectively remove stubborn oxides. Regularly check the flux nozzle and replace any damaged ones promptly to ensure proper flux coverage on the PCB surface, maximizing the flux’s effectiveness.

3. **Wave Soldering**: The rate of tin penetration during PCBA processing is directly tied to the wave soldering parameters. It’s essential to re-optimize welding parameters, such as wave height, temperature, welding time, and conveyor speed. Start by slightly reducing the track angle and increasing the wave crest height to enhance the contact area of liquid tin with the soldering end. Additionally, raising the wave soldering temperature generally improves tin permeability, provided that the components can withstand the heat. Slowing the conveyor belt speed and increasing preheating and soldering times allow the flux to fully remove oxides, better immerse the solder ends, and improve tin usage.

4. **Manual Soldering**: In practical inspections of plug-in soldering quality, many solder joints exhibit only a thin layer of solder on the surface, with no tin penetration in the through holes. Function tests have confirmed that many components are inadequately soldered. This issue is prevalent in manual soldering, often due to incorrect soldering iron temperatures or insufficient soldering times. Inadequate tin penetration can lead to soldering errors and increased rework costs. For applications where tin penetration requirements are stringent and high-quality soldering is essential, selective wave soldering is recommended, as it effectively addresses the problem of poor tin penetration in PCBA.

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