What are gold finger pcb
In our current life, many signals are sent and received between multiple devices, and gold fingers are needed between circuit boards as the connection contacts between the sound card or graphics card and the motherboard and other devices to realize this connection command.
Put in simple term;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.
The pro and con of the gold finger and its application on the PCB.
Gold finger is the metal connector on the PCB, and gold finger is also known as Gold tips or Gold tabs.
Gold fingers are the gold plated connectors on the edge of PCB that arranged like fingers. During PCB manufacture process, gold finger will be coated with a layer of gold through a special process on the copper cad lamination. However, today, many PCB designer has replacing the surface finish of gold finger by tin plating.
For PCB designer, the aim of gold finger is to connect the PCB by compressing the corresponding slots with connector, which allows its to communicate with one device to another.
The advantages of using plating gold on gold fingers for the PCB: The gold finger can resist oxidation and it is durable with high conductivity.
The disadvantages of gold finger on the PCB: it has relatively uneven surface, the needs of connecting line and the price of gold finger is extremely expensive.
The difference between applying immersion gold and plating gold on the gold fingers is that immersion gold is easier to solder compare to plating gold and will not affect the signal, it is also hard to get oxidized. However the immersion gold is less durable.
Quality Measures for PCB Gold Fingers:
The Association Connecting Electronics Industries (IPC) has prescribed some standards for the production of PCB Gold Fingers. The IPC standards are summarized as follows:
Chemical composition: To achieve maximum rigidity along the edges of PCB Gold Fingers, the gold plating should consist of between 5 to 10% Cobalt.
Thickness: The plating thickness should be in the range of 2 to 50 microinches. The standard thicknesses by size are 0.031 inches, 0.062 inches, 0.093 inches, and 0.125 inches.
Visual test: The visual inspection is performed through a magnifying lens. The contact edges should be smooth, have a clean surface and also be free from excess plating like Nickel.
Tape test: It is conducted to check the adhesiveness of the gold plating along the contacts. In this test, a strip of tape is fastened over the contact edges followed by removing the same. In the next step, the tape is inspected for traces of plating. If any gold is visible on the tape, then the plating is considered as insufficient for continuous injection and ejection.
Production standards for gold fingers
Chemical composition: The gold plating should consist of 5-10% cobalt for maximum rigidity across the board edges.
Thickness: The plating thickness of gold fingers must fall between 0.002- 0.005 mils. The standard thickness dimensions are 3 mils, 62 mils, 93 mils, and 125 mils.
Visual test: A visual test is conducted with a magnifying lens to ensure edges are smooth, clean, and free of excess plating.
Tape test: It is done to check the adhesiveness of the gold plating. In this test, a strip of tape is placed along the contact edges. After removing it, the strip is inspected for traces of plating. If any gold plating is observed on the tape, then the plating lacks adequate adhesiveness.
Applications of PCB gold fingers
They have a wide range of applications in several industries including:
Telecommunication industry: Connection for network data transfer (communication adapter)
Computer application industry: Data transfer (laptop memory card, graphics card, etc.)
Industrial control system: Connection to different devices (factory robot arm, high-end consumer electronics, computerized industrial machines, etc.)
PCB GOLD FINGER BEVELING
On a circuit board, the PCB gold finger plating process is used after the solder mask and before the surface finish. The plating process generally consists of the following steps:
Nickel plating: Between three and six microns of nickel are plated first to the connector edges of the fingers.
Gold plating: Between one and two microns of hard gold are plated over the nickel. The gold is usually enhanced with cobalt for boosted surface resistance.
Beveling: The connector edges are beveled at specified angles for easier insertion on corresponding slots. Beveling is typically done at angles of 30 to 45 degrees.
On some circuit boards, certain gold fingers will be longer or shorter than others. For example, a circuit board may have longer fingers at one end. This way, the PCB is easier to insert into a slot, as the end with the longer fingers will snap into place more readily. From there, you simply push the other end of the PCB into place.
There are certain restrictions to the plating process. For example, certain distances are needed between the gold fingers and other parts of the circuit board. Key restrictions include the following:
Inner layers must be copper-free along the PCB edge to prevent copper exposure during the beveling stage.
Plated holes, SMD and pads should not be placed within 1.0 millimeters of the gold fingers.
Plated pads cannot exceed 40 millimeters in length.
A distance of 0.5 millimeters should exist between the gold fingers and the outline.
Any deviation from the standard spacing requirements around the gold fingers on a printed circuit board could result in a physically weak or dysfunctional card.
Where to find a Quality Gold Finger PCB Factory
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