Tell you the detailed specifications and standards of PCB gold fingers

PCB Gold Fingers are narrow gold-plated connectors on the edge of a PCB that can be used to connect multiple boards. Gold fingers are chosen because they have the highest corrosion resistance and electrical conductivity, second only to copper and silver. Sometimes gold is combined with cobalt and nickel to increase the wear resistance of the fingers. the PCB is connected/disconnected multiple times. Therefore, these connection points (fingers) must be able to handle some wear and tear.

Plating Process for PCB Gold Fingers The plating process begins after the deposition of the solder resist and before the surface is polished. It consists of the following steps:

Nickel plating: Initially, 2 to 6 microns of nickel are plated on the edges of the finger connector.

Gold plating: In this step, 1 to 2 microns of hard gold are plated over the nickel layer. Generally, cobalt is also added to the gold to increase the surface resistance.

Beveling: The edges are then beveled/tapered at a specific angle (30 to 45 degrees) to make it easier to insert into the respective slots.

PCB Gold Finger Design Specifications:

1. The internal PCB layer facing the PCB edge must be free of copper to prevent exposure during chamfering.

2. It is not recommended to include PTH within 1mm of the gold finger.

4. Maintain a minimum distance of 0.5mm between the gold finger and the board contour.

5. Any compromise of the standard spacing values may result in PCB weaknesses and failures.

6. Do not use soldermask or screen printing near gold fingers.

7. Gold fingers should be placed with the center of the PCB facing outward.

IPC has set some standards for the production of PCB gold fingers. the IPC standards are summarized below:

Chemical composition: In order to maximize the rigidity of the PCB gold finger edge, the gold plating layer should contain 5% to 10% cobalt.

Thickness: The coating thickness should be in the range of 2 to 50 micro inches.

Appearance Test: Appearance inspection through a magnifying glass. Contact edges should be smooth and surfaces should be clean and free of excessive coatings such as nickel.

Tape Test: This test is performed to check the adhesion of the gold plating on the contacts. In this test, the tape is fixed on the contact edge and removed. In the next step, the tape is checked for traces of plating. If there is any gold on the tape, the coating is considered insufficient for continuous injection and ejection.