1. What is a PCB Gold Finger?
The gold finger of PCB is a gold-plated column seen at the edge of PCB connection. The purpose of Goldfinger is to connect the auxiliary PCB to the motherboard of the computer. PCB Goldfinger is also used in various other devices that communicate through digital signals, such as consumer smart phones and smart watches. Because the alloy has excellent electrical conductivity, gold is used for the connection points along the PCB.
PCB gold fingers can be divided into three types:
1.Ordinary PCB gold finger-the most common PCB gold finger, with horizontal or even array. The PCB pads have the same length, width and space.
PCB gold finger
2. Uneven PCB gold finger-PCB pads have the same width but different lengths, and sometimes the space is different.
For some PCBs, the gold finger is designed to be shorter than others. The most relevant example of such a PCB is a PCB for a memory card reader, in which a device connected with a long finger must first supply power to a device connected with a shorter finger.
3. Segmented PCB gold finger-PCB pads have different lengths, and the gold finger is segmented. The lengths of segmented gold fingers are different, and some of them are also out of line in the same finger of the same PCB. This PCB is suitable for waterproof and sturdy electronic products.
Segmented PCB gold finger
Second, PCB gold finger gold plating detailed tutorial
1. Electroless Nickel Plating and Gold Immersion (ENIG) This kind of gold is more cost-effective and easier to weld than electroplating gold, but its soft and thin composition (usually 2-5u ") makes ENIG unsuitable for the grinding effect of circuit board insertion and removal.
2. Electroplating hard gold This kind of gold is solid (hard) and thick (usually 30u "), so it is more suitable for the abrasive effect of PCB. Gold finger enables different circuit boards to communicate with each other. From power supply to equipment or equipment, signals must be transmitted between multiple contacts in order to execute a given command.
Electroplating hard gold After pressing the command, the signal will be transmitted between one or more circuit boards and then read. For example, if you press a remote command on a mobile device, the signal will be sent from your PCB-enabled device to a nearby or remote machine, which will receive the signal through its own circuit board.
3. What is the gold finger electroplating process of PCB?
Here's an example. The process of hard gold plating to PCB gold finger is as follows:
1) Cover with blue glue. Except for the PCB gold finger pad that needs hard gold plating, the other PCB surfaces are covered with blue glue. And we make the conductive position coincide with the direction of the board.
2) Removing the oxide layer on the copper surface of the PCB pad We washed the oxide layer on the PCB pad surface with sulfuric acid, and then washed the copper surface with water. Then, we grind to further clean the PCB pad surface. Next, we use water and deionized water to clean the copper surface.
3) Electroless nickel plating on the copper surface of 3)PCB pad We electrify the surface of the cleaned gold finger pad to electroplate the nickel layer. Next, we use water and deionized water to clean the surface of the nickel-plated pad.
4) electroplate gold on that nickel-plated PCB pad We electrify to electroplate a lay of gold on the surface of the nickel-plated PCB pad. We recycle the remaining gold. Then we still use water first and then deionized water to clean the surface of the golden finger.
5) Remove the blue glue. Now, the hard gold plating of PCB gold fingers is completed. Then we remove the blue glue and continue the steps of PCB manufacturing to solder mask printing.
PCB Gold Finger It can be seen from the above that the process of PCB Gold Finger is not complicated. However, only a few PCB factories can complete the gold finger process of PCB by themselves.
Third, the use of PCB gold finger
1. Edge connector When the auxiliary PCB is connected to the main motherboard, it is completed through one of several mother slots, such as PCI, ISA or AGP slots. Through these slots, Goldfinger conducts signals between peripheral devices or internal cards and the computer itself. The connector socket on the edge of PCI port slot on PCB is surrounded by a plastic box with one side open, and there are pins at one or both ends of the longer edge. Typically, connectors contain bumps or notches for polarity to ensure that the correct device type is plugged into the connector. The width of the socket is selected according to the thickness of the connecting plate. On the other side of the socket is usually an insulated piercing connector connected to a ribbon cable. The motherboard or daughter card can also be connected to the other side.
Card edge connector 2 and special adapter Golden Finger can add many performance enhancement functions to personal computers. By inserting the auxiliary PCB of the motherboard vertically, the computer can provide enhanced graphics and high-fidelity sound. Because these cards are rarely connected and reconnected separately, gold fingers are usually more durable than the cards themselves. Special adapter
3. External connection Peripheral devices that have been added to the computer station are connected to the motherboard through PCB gold fingers. Speakers, subwoofers, scanners, printers and monitors are all plugged into specific slots behind the computer tower. In turn, these slots are connected to the PCB connected to the motherboard.
Fourth, PCB gold finger design
1. The plated through hole should be far away from the gold finger PCB.
2. For PCB boards that need to be plugged and unplugged frequently, the gold finger generally needs hard gold plating to increase the wear resistance of the gold finger. Although electroless nickel plating can be used to precipitate gold and it is more cost-effective than hard gold, its wear resistance is poor.
3. The golden finger needs to be chamfered, generally 45, and other angles such as 20 and 30. If there is no chamfer in the design, there is a problem. As shown in the following figure, the arrow shows a 45 chamfer:
The chamfer angle of the golden finger is 45
4. The golden finger needs to be welded and windowed as a whole, and the PIN does not need to be opened with steel mesh.
5. The minimum distance between the solder pad and the silver pad is 14 mil. It is recommended that the pad be more than 1mm away from the gold finger position, including the via pad.
6. Don't apply copper on the surface of the golden finger.
7. All layers of the inner layer of the golden finger need to be cut with copper. Usually, the width of copper is 3mm, and half-finger copper and full-finger cutting can be done. In the PCIE design, there are signs that the copper of the golden finger needs to be completely removed. The impedance of the golden finger is low, and copper cutting (under the finger) can reduce the impedance difference between the golden finger and the impedance line, which is also beneficial to ESD.
