PCB gold finger is a narrow gold-plated connector on the edge of PCB, which can be used to connect multiple boards. Gold fingers are chosen because they have the highest corrosion resistance and conductivity, second only to copper and silver. Sometimes gold, in combination with cobalt and nickel, increases the wear resistance of the fingers. PCB connected / disconnected multiple times. Therefore, these connection points (fingers) must be able to handle some wear.
The electroplating process of PCB gold finger begins after solder resist deposition and before surface polishing. It includes the following steps:
Nickel plating: initially, nickel plating between 2 and 6 microns to the edge of the finger connector.
Gold plating: in this step, hard gold between 1 and 2 microns is plated on the nickel layer. In general, cobalt is also added to gold to improve the surface resistance.
Bevel: then bevel / taper the edge at a specific angle (30 to 45 degrees) to make it easier to insert into the corresponding slot.
Design specification of PCB gold finger:
1. The internal PCB layer towards the edge of PCB must be free of copper to prevent exposure during chamfering.
2. It is not recommended to include PTH within 1mm of gold finger.
4. Keep a distance of at least 0.5mm between the gold finger and the circuit board outline.
5. Any compromise of the standard spacing values can lead to PCB weakness and failure.
6. Do not use anti welding or screen printing near the golden finger.
7. The gold finger shall be placed at the position with the PCB center facing outward.
The IPC has set some standards for the production of PCB gold fingers. IPC standards are summarized as follows:
Chemical composition: in order to maximize the rigidity of the edge of PCB gold finger, the gold plating should contain 5% to 10% cobalt.
Thickness: coating thickness shall be in the range of 2 to 50 microinches.
Appearance test: the appearance inspection is carried out through a magnifying glass. The contact edge shall be smooth, the surface shall be clean and free of excessive coating such as nickel.
Tape test: carry out this test to check the adhesion of gold plating on the contact. In this test, a tape is fixed to the contact edge and removed. In the next step, check the tape for traces of plating. If any gold is visible on the tape, the coating is not considered adequate for continuous injection and ejection.