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It is a well-known fact that printed circuit boards (PCBs) use copper surface finishes as a common practice. If left unattended and unprotected, copper will deteriorate and oxidize, leaving your circuit board unusable. 

A surface finish plays a vital role in creating an interface between a PCB and its components. Here are two of the main functions of a surface finish.

  • It helps protect the copper-based circuitry
  • It provides you surface that can facilitate soldering during the assembling process of soldering components to your PCB

What Is Immersion Silver?

Immersion silver surface finish is a type that you can apply directly over your printed circuit boards’ copper surface. This surface finish is most commonly used and ideal for metallic dome contacts, aluminum wire bonding, and EMI shielding. 

The thickness of this material is between 5 micro-inches and 12 micro-inches, respectively. Additionally, immersion silver has lasting capabilities for at least a year. 

Immersion silver surface finish does not react to copper the way Tin does. However, if you expose it to the air, it will tarnish; therefore, you must store the circuit boards with immersion silver finish in an anti-tarnishing packaging. 

If you do everything right and store it in proper packaging, the PCB will still be solderable for 6 to 12 months. However, once you have removed your printed circuit board from the packaging, you must make sure that it goes through soldering re-flow within the next 24 hours.

In case you wish to achieve a higher shelf life than gold, plating is the most viable solution. 

Benefits of Immersion Silver Surface Finish

PCBs always come with coated surface finishes. Adding a decent finish enables and ensures decent soldering capability, as well as it protects the copper circuitry of your circuit board from the outside air. There are several types of immersion finishes, such immersion tin, immersion gold, etc.; however, immersion silver is gaining popularity due to certain features it offers. 

It is attracting a lot of attention from the PCB manufacturers. Here are some of the key advantages that declare it to be the preferred material for surface finishing in the circuit board industry. 

  • It allows the proper spreading of solder on its surface, allowing better soldering of circuit board components. 
  • Immersion is one of the RoHS compliant PCB surface finishes, and it is also environmentally friendly. 
  • Compared to OSP “Organic Solderability Preservative” surface finish, the surface with immersion silver finish will demonstrate better resistance to several environmental aging factors. 
  • The immersion silver is a material surface finish that comes with the capabilities to survive multiple re-flows. 
  • Immersion silver has better and enhanced electrical properties. 
  • It produces a flat surface and facilitates strengthened solder joints than HASL surface finish. 
  • Immersion silver is immune to a phenomenon known as a black-pad interfacial fracture. 

All of the advantages mentioned above make immersion silver surface finish an ideal choice for PCB manufacturers. 

Choose Wisely

You must select an adequate surface finish for your PCBs. You can do so by considering several options while you factor material costs and performance requirements. 

For instance, you are looking for an option that is lower in cost than Tin-Lead. HASL may sound like a more obvious choice, but it is not the most suitable option, especially when it comes to RoHS compliant products. 

In case you are unsure of what type of surface finish you may need. You can always get help from third-party PCB fabrication services prior to making decisions you may regret later. A little bit of research will result in cost-effective and high-yielding design.  We are here to answer any questions you may have and help you make the best decision for you. Contact us today!

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Nova is a full-service printed circuit board assembler located in Denver, Colorado.