OSP vs Immersion Tin PCB Finish: Which One Suits You Better?

As a PCB designer, the choice of the right finish material shouldn't be your Achilles heel. If you don't know which finish will provide the most effective and durable solution, you've come to the right place. Get to know OSP and immersion tin PCB finish in this comparison guide.

OSP - What It Is and Whether It's Right for You

OSP is an acronym that refers to Organic Solderability Preservatives. It's a thin layer of protective material that serves as a passivation layer, which is applied using a chemical reaction that coats the copper surface with an organic film. The purpose of the OSP is to protect the surface of the copper from tarnishing and oxidation, which can harm the performance of your circuit board.

So, what are the pros and cons of OSP?

OSP Pros:

• OSP protects copper from oxidation and tarnishing.
• The organic layer is thin and cost-effective.
• The entire PCB assembly process is environmentally friendly.
• The OSP process is precisely controlled and reliable.

OSP Cons:

• It's not suitable for lead-free soldering applications.
• The surface can get easily damaged during handling.
• The shelf life of OSP PCBs is relatively short.
• The protective layer can dissolve in water.

Immersion Tin - What It Is and Whether It's Right for You

Immersion tin is the PCB substrate that provides a layer of tin coating through immersion in a chemical bath. The plating process is selective, meaning only the copper surface is coated with tin. The primary purpose of the immersion tin coating is to protect the copper contacts from corrosion and oxidation, hence ensuring reliable soldering.

What are the pros and cons of immersion tin?

Immersion Tin Pros:

• The tin layer is relatively thick and offers excellent heat resistance.
• It's an excellent choice for lead-free soldering processes.
• The coating's uniformity is consistent and reliable.
• Immersion tin offers a superior shelf life.

Immersion Tin Cons:

• Immersion tin requires more expensive equipment and hard to manage during the PCB assembly process.
• It requires a more controlled process to ensure a reliable layer of coating.
• Some people have reported compatibility issues with the coating and specific components.

Conclusion

While both finishes protect copper from corrosion and oxidation, immersion tin is a superior choice when dealing with lead-free soldering applications. This is because it's relatively more robust and offers excellent heat resistance.

On the other hand, if you're focused on cost-effectiveness, environmentally-friendly PCB assembly, and you don't anticipate a high degree of thermal cycling, OSP provides a reliable option.

Ultimately, the choice between OSP and immersion tin depends on various factors, including the PCB components and intended application. By considering the pros and cons of both finishes, you'll be in a position to make an informed decision that suits your needs.

References

1. H. Thongpanich, C. H?ger, M. C. Lemmens, A. De Keersmaecker, and G. Van der Plas, "OSP coatings for printed circuit boards," Proceedings of the 18th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, Arcachon, 2008, pp. 949-956, doi: 10.1109/REDFA.2008.4801891.
2. R. Sharma, C. Lal, and M. Baghini, "Effect of bath chemistry on immersion tin plating," 2017 International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS), Chennai, 2017, pp. 459-462, doi: 10.1109/ICECDS.2017.8389250.
3. "PCB Surface Finishes Comparison," November 2021, Custom Circuit Boards, Accessed on January 25, 2022, [https://www.customcircuitboards.com/pcb-surface-finishes-comparison]