Classification and application of pcb gold fingers

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In modern high -tech equipment, many devices need to be connected to each other, which requires signal transmission. How to connect the two devices, the golden finger is an important hub in it. The golden finger is a connection contact between the motherboard and the graphics card or sound card.

The technology used to transmit these signals and commands is a huge leap for early electronic technology. Early electronic technology is usually composed of independent modules, which is difficult to communicate with each other. With the golden finger, the process of a circuit board was immediately read by the main processing board.

WHAT ARE GOLD FINGERS?

Gold fingers are the gold-plated columns that you see along the connecting edges of printed circuit boards (PCBs). The purpose of gold fingers is to connect a secondary PCB to the motherboard of a computer. PCB gold fingers are also used in various other devices that communicate via digital signals, such as consumer smartphones and smartwatches. Gold is used for the connecting points along a PCB because of the alloy’s superior conductivity.

There are two types of gold applicable to the PCB gold finger plating process:

       ➤Electroless Nickel Immersion Gold (ENIG): This gold is more cost-effective and easier to solder than electroplated gold, but its soft, thin (typically 2-5u” composition renders ENIG unsuitable for the abrasive effects of circuit board insertion and removal.

       ➤Electroplated Hard gold: This gold is solid (hard) and thick (typically 30u”), thus more ideal for the abrasive effects of constant PCB usage.

Gold fingers make it possible for different circuit boards to communicate with one another. From the power source to the device or equipment, signals must pass between several contacts for a given command to be enacted.

Once you press a command, the signal will pass between one or more circuit boards before it is read. For example, if you press a remote command on a mobile device, the signal will be sent from the PCB-enabled device in your hand to the near or distant machine, which in turn receives the signal with its own circuit board.

Golden finger classification

Generally speaking, the main role of gold finger is connection, so it must have good conductive performance, wear resistance, antioxidant performance, and corrosion resistance. According to its performance characteristics, the gold finger is divided into the following:

① Conventional gold finger: Qiping’s finger is characterized by the edge of the PCB board. The position is neatly arranged and the same length. The width of the pads is rectangular and widely used. It is often found in the type of network card and graphics card.

② long -term gold finger: that is, unsatisfactory gold fingers, characterized by rectangular pads with difficulty in the length of the PCB board, often found in memory, U disk, card reader, etc.

③ Segment gold fingers: In the new gold finger, unlike long and short gold fingers, segmented gold fingers are rectangular pads located at different lengths of the board, but the front end is broken.

What is the PCB gold finger plating process?

Here is a list of the process for hard gold plating to PCB gold fingers:

1) Covered with blue glue

In addition to the PCB gold finger pads that require hard gold plating, the rest of the PCB surface is covered with blue glue. And we make the conductive position and the direction of the board is consistent.

2) Remove the oxide layer on the copper surface of PCB pads

We use sulfuric acid to wash off the oxide layer on the surface of the PCB pads and then clean the copper surface with water. We then grind to further clean the PCB pad surface. Next, we use water and deionized water to clean the copper surface.

3) Electroplating nickel on the copper surface of PCB pads

We energize the cleaned gold finger pad surface to electroplate a nickel layer. Next, we use water and deionized water to clean the nickel plated pad surface.

4) Electroplating gold on nickel-plated PCB pads

We electrically plate a layer of gold on the surface of the nickel-plated PCB pads. We recover the remaining gold. Then we clean the gold finger surface with water and then deionized water.

5) Remove the blue glue

Now the hard gold plating of the PCB gold fingers is completed. We then remove the blue glue and continue with the PCB fabrication to the soldermask printing step.

How to use PCB Golden Finger

1. Edge Connectors
When an auxiliary PCB is connected to the main board, it does so through one of several female slots, such as PCI, ISA or AGP slots.
Through these slots, the gold fingers conduct signals between the peripherals or internal cards and the computer itself.

Edge connector sockets are surrounded by a plastic box that opens on one side and has pins at one or both ends of the longer edge. Typically, connectors contain tabs or notches for polarity to ensure that the correct type of device is inserted into the connector. The width of the socket is chosen based on the thickness of the connection plate. On the other side of the socket is usually an insulated piercing connector that connects to the ribbon cable. The motherboard or daughter card can also be connected to the other side.


2. Special adapters
Gold fingers Many performance enhancements can be added to a personal computer. By plugging vertically into the motherboard’s auxiliary PCB, the computer can provide enhanced graphics and high-fidelity sound. Because these cards are rarely connected and reconnected individually, the gold fingers are usually more durable than the cards themselves.


3. External Connections
Peripheral devices that have been added to the computer station are connected to the motherboard via PCB gold fingers. Devices such as speakers, subwoofers, scanners, printers, and monitors are plugged into specific slots on the back of the computer tower. In turn, these slots connect to the PCB that is attached to the motherboard.

Design Rules of PCB Gold Fingers

●Keep plated through holes away from the fingers by at least 1mm. Plated through holes require copper plating around the hole on all layers. This copper can flow onto the gold fingers during plating and cause contamination or plating thickness issues. Maintaining a 1mm keepout prevents this.

●Maintain spacing between the fingers and any solder mask or silkscreen printing. This prevents material from overflowing onto the fingers during application which can interfere with insertion.

●Orient the fingers on the side of the board opposite from the component center. This aids in insertion and alignment as it clears components on the bottom side.

●Do not place any SMD parts, plated through holes, or solder pads within 1mm of the fingers. This prevents interference with the interfacing connector.

●Remove all inner layer copper beneath the fingers, typically 3mm beyond the edge of the finger width. This prevents inner layer copper from being exposed during PCB beveling/chamfering which looks bad aesthetically.

●Limit the maximum finger length to around 40mm. Longer fingers are prone to damage during handling and insertion.

●Avoid soldermask or silkscreen printing in areas immediately adjacent to the fingers where material can overflow causing buildup issues.

●Design continuous openings in the solder mask around the fingers. This prevents the need for score lines or steel mesh.

PCB gold fingers play an important role in electronic products. They not only connect circuit boards and other electronic components, but also transmit signals and currents.The production process of PCB Gold Finger includes plating and anti-corrosion treatment to increase its electrical conductivity and corrosion resistance.PCB Gold Finger is widely used in cell phones, computers and automobiles. Through a deeper understanding of PCB gold fingers, we can better understand the principles of connection and transmission in electronic products.