At the most basic level, a PCB surface finish is a plating or coating that is applied to the exposed copper of a circuit board. The surface finish not only protects the copper from oxidation, but also forms the foundation of connectivity between a PCB and a component.
Before choosing a service finish, you should have an answer to the following questions:
- How important is pad flatness for assembly?
- How solderable/ wettable does my circuit board need to be?
- Does my circuit board need to be lead free/ RoHS Compliant?
- Does my circuit board need gold or aluminum wire bonding?
- How many solder cycles will my circuit board be exposed to?
- Is the cost of surface finish a deal breaker?
- What's the minimum shelf life of my circuit board?
- What kind of storage conditions will my board be kept in?
Once you have a pretty solid idea of how you want your surface finish to perform, Amitron's PCB Surface Finish Comparison Chart below will come in handy:
In conclusion there is no "best" surface finish for all of your circuit board needs. PCB surface finishes should be selected based on the intended functionality of the end product. However, there are some emerging trends that we've noticed here at Amitron:
- The U.S Market tends to favor Immersion Silver for larger and thicker boards.
- The EU Market tends to favor Immersion Tin for smaller and thinner boards.
- Handheld electronics often use OSP or ENIG surface finishes.