Gold Fingers are the gold plated narrow connectors found on the edge of printed circuit boards to enable connections between multiple boards. They are made from flesh gold, the hardest form of gold available and work for a long time with superior conductivity. The thickness of gold fingers usually ranges from 3 to 50 microns.
Gold is chosen for these fingers as it has the highest corrosion resistance and electrical conductivity after Copper and Silver. Sometimes, Gold is combined with Cobalt and Nickel to increase the resistance of the fingers for wear and tear. PCBs are connected/disconnected from each other multiple times. So these connection points (fingers) need to be able to handle some wear and tear.
What is PCB Gold Finger Beveling?
The PCB Gold Fingers plating process starts after the solder mask deposition and before the surface finish. It includes the following steps:
- Nickel Plating: Initially, between 2 to 6 microns of Nickel is plated to the connector edges of the fingers.
- Gold Plating: In this step, between 1 to 2 microns of hard Gold is plated over the Nickel layer. In general practice, Cobalt is also added to Gold to boost the surface resistance.
- Beveling: The edges are then beveled/ tapered at a particular angle (30 to 45 degree) to make easier insertion to the corresponding slot
Design Specifications for PCB Gold Fingers:
- The inner PCB layers towards the PCB edges must be Copper-free, to prevent exposure at the time of Beveling.
- It is not advisable to include the plated through holes (PTH) within 1 mm of Gold Fingers.
- Maintain at least 0.5 mm of distance between the gold fingers and the board outline.
- Any compromise with the standard spacing values can lead to weak and malfunctioned PCB board.
- No soldermask or screen printing should be performed near the Gold Fingers.
- The Gold Fingers should be placed facing outwards from the PCB’s center.