What printed circuit board finishes are available in order to produce lead-free solder joints?

TWI Frequently asked questions

by Simon Mason

There are several established finishes available that do not contain lead, but offer acceptable solderability and shelf-life properties. These are:

1. Organic Solderability Protective (OSP). This is a very thin organic coating over the copper, giving a flat, clear finish.
2. Immersion Silver. The copper areas are plated with a thin layer of silver, leaving a flat, shiny, silver coloured finish.
3. Immersion Tin. The copper areas are plated with a thin layer of tin, giving a flat, matt, 'silver' coloured surface.
4. Immersion Gold/Nickel. The copper areas are plated with a nickel alloy which is subsequently plated with gold to leave a flat, gold coloured finish.
5. Lead-free solder levelled finish. The copper pads are covered with a thin coating of lead-free solder, giving a slightly uneven, silvery finish.

The choice of which of the above finishes to choose will be dependent on the individual circumstances of the assembler.