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Printed Circuit Board (PCB) Gold Finger Introduce and Board Chamfer Design

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, gold fingers are used in various devices like smartphones and smartwatches.

PCB Gold Finger Surface Treatment

Nickel-plated gold: thickness up to 3-50u", due to its excellent electrical conductivity, oxidation resistance and wear resistance, it is widely used in gold finger PCBs that require frequent insertion and removal or PCB boards that require frequent mechanical friction. The cost plating is extremely high, and it is only suitable for local gold plating such as gold fingers.

Immersion gold: The conventional thickness is 1u", up to 3u". Due to its excellent electrical conductivity, flatness and solderability, it is widely used in high-precision PCB boards with button positions, bonding ICs, BGAs, etc. Gold finger PCBs with low wear resistance requirements can also be selected for the entire plate immersion gold process. The cost of the gold immersion process is much lower than the cost of the gold gold process. The color of the immersion gold process is golden yellow.

PCB Gold Finger And Board Chamfer Design

When you see a shape and package similar to the one shown below in the PCB design, the first reaction is to have gold fingers on the board. A simpler method for judging the golden finger: the TOP and BOTTOM sides of the device have PIN devices, there will be a U-shaped groove as shown below.

PCB gold finger

When there are gold fingers on the board, you need to do the details of the gold finger.

Gold finger detail processing in PCB:

1) In order to increase the wear resistance of gold fingers, gold fingers usually need to be plated with hard gold.

2) The gold finger needs to be chamfered, usually 45°, and other angles such as 20°, 30°, etc. If there is no chamfer in the design, there is a problem; as shown below, the arrow shows a 45° chamfer:

board chamfer design

3) The gold finger needs to do a whole piece of solder mask to open the window, and the PIN does not need to open the steel mesh;

4) The sinking and sinking silver pads need a minimum distance of 14 mil from the tip of the finger, recommended design. When the pad is more than 1mm from the finger position, including the via pad.

5) Do not lay copper on the surface of the gold finger.

6) All layers of the inner layer of the gold finger need to be cut by copper. Usually, the width of the copper is 3mm; the half finger copper and the whole finger can be cut. In the PCIE design, there is also a copper indicating that the gold finger area is completely cut off.

The impedance of the gold finger will be lower, and the copper cut (under the finger) can reduce the impedance difference between the gold finger and the impedance line, and it is also good for ESD.
Incorrect chamfering often leads to the loss of the function of the board part, so there is a gold finger board, so be sure to label the correct chamfer specification, including the angle and depth. The circuit board factory has collected the gold finger chamfer specifications of the current common board types. For those not mentioned, it must be confirmed to the customer.

1. PCI board card chamfer standard

2. PCIE 1.0 board chamfer specification

3. PCIE 2.0 board chamfer specification

 

4. AMC board chamfer specification

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