PCB Fabrication

PCB gold finger design and processing

by:A-TECH      2021-03-10
1. The definition of gold finger (Gold Finger or Edge Connector) Insert one end of the PCB board into the connector card slot, and use the connector pin as the outlet of the pcb board to connect to the outside, so that the pad or copper skin is inserted in the corresponding position. The pins are contacted to achieve the purpose of conduction, and the pad or copper of the pcb board is immersed in gold or nickel-plated. Because it is in the shape of a finger, it is called a gold finger. 2. The surface treatment method of gold finger PCB is nickel-plated gold: the thickness can reach 3-50u'. Because of its superior electrical conductivity, oxidation resistance and wear resistance, it is widely used in gold finger PCBs that need to be frequently plugged or unplugged. The PCB board that is often mechanically rubbed, but because the cost of gold plating is extremely high, it is only used for partial gold plating such as gold fingers. The PCB calls it: selective electrogold process, the color of electrogold process is silvery white, and there is no sinking gold The disadvantage is that the solderability is slightly worse. Picture: Selective electric gold finger PCB (spray tin + gold finger area electric gold) 2. Immersion gold: the thickness is conventional 1uFlatness and solderability, it is widely used in high-precision PCB boards with button positions, binding IC, BGA and other designs. For gold finger PCBs that do not require high wear resistance, you can also choose the whole board immersion gold process. The cost of the gold process is much lower than that of the electro-gold process. The color of the immersion gold process is golden yellow. Picture: Full-board immersion gold PCB 3. Points to note when designing the gold finger. When designing the PCB, you can see the appearance and package similar to the picture below. The first reaction is that there is a gold finger on the board. A simple way to judge the gold finger: the TOP and BOTTOM surfaces of the device have PIN devices; there will be a fool-proof U-shaped groove as shown in the figure below. There are gold fingers on the board. In order to increase the wear resistance of the gold finger, the gold finger usually needs to be electroplated with hard gold. The detailed processing of the gold finger on the PCB board: 1) For the PCB board that often needs to be plugged and unplugged, in order to increase the wear resistance of the gold finger, the gold finger usually needs to be plated with hard gold. 2) Gold finger Need chamfering, usually 45°, other angles such as 20°, 30°, etc. If there is no chamfer in the design, there is a problem; as shown in the figure below, the arrow shows a 45° chamfer: 3) The golden finger needs to be made in one piece Solder mask window treatment, PIN does not need to open steel mesh; 4) Immersion tin and silver solder pads need to be at a minimum distance of 14 mils from the top of the finger; it is recommended that the pads be designed to be at least 1mm away from the finger position, including via pads; 5) Gold Do not cover the surface of the finger with copper; the picture below shows the design of a gold finger, for reference: 6) All layers of the inner layer of the gold finger need to be copper-cut, usually the width of the copper is 3mm larger; it can be used for half-finger copper and the whole finger Copper cutting. In the PCIE design, it is also specified that all the copper in the gold finger area should be cut off; the impedance of the gold finger will be lower, and copper cutting (knock out under the finger) can reduce the impedance difference between the gold finger and the impedance line At the same time, it is also good for ESD; it is recommended: all copper is cut under the gold finger pad. Fourth, the precautions for PCB gold finger processing 1. The thickness of the board that can be beveled is 1.2-2.4m can be beveled. Not This board thickness range cannot be beveled. 2. The depth and angle of the beveled edge are generally between 20-45 degrees by default. There must be enough beveled edge spacing between the gold finger and the board edge, according to different gold finger PCB board thickness or For design requirements, we recommend that the distance between the gold finger and the edge of the board be 0.6-1.5mm during design to avoid hurting the gold finger when beveling. If the distance between the gold finger and the board edge is less than 0.6mm, the bevel treatment will cause damage to the gold. Finger wind risk. The following is a schematic diagram of several common bevel angles and depths for your reference. Plate thickness 1.6mm, hypotenuse depth 1.4mm, hypotenuse angle 25 degrees, plate thickness 1.6mm, hypotenuse depth 1.3mm, hypotenuse angle 25 degrees, plate thickness 1.8mm, hypotenuse depth 1.8mm, hypotenuse angle 20-25 degrees, Thickness of 1.2mm, bevel depth of 0.4mm, bevel angle of more than 45 degrees. The information is researched and organized by the professional PCB manufacturer, 'No matter how urgent, it can be on schedule' and trusted by 300,000 customers worldwide. Order address: www .
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