Why is the thickness of FPC gold finger reinforcement always inaccurate?

嘉立创FPC

Why is the thickness of FPC gold finger reinforcement always inaccurate? [Copy link]

The professional term for gold finger is board edge connector, which is generally composed of one or two rows of golden conductive contacts. Because the surface of the pad is immersion gold or gold plating process, and the conductive contacts are arranged like fingers, it is commonly known as "gold finger".
Many engineers think that the total thickness of gold finger = FPC board thickness + PI reinforcement thickness, but the board sent back is too thin to be used. The feedback is as follows:

So how to calculate the PI reinforcement thickness according to the total thickness requirement?
In fact, the total thickness of the gold finger is related to the thickness of the solder mask (cover film) and the copper thickness. The FPC board thickness we are talking about includes the thickness of all solder masks and all copper foils on the front and back. The gold finger conductive contacts are open windows and have no solder mask, so the actual thickness of the board should be reduced by the thickness of this layer of solder mask. In the same way, some gold fingers do not have copper on the back, and the thickness of the board needs to be reduced by the thickness of this layer of copper foil. Therefore, if you want to meet the total thickness requirements, you need to increase the thickness of the reinforcement material to meet the total thickness requirements.
1. Take Jialijie FPC as an example: the corresponding relationship between board thickness, copper thickness and cover film thickness is as follows:

The above board thickness includes the film thickness and copper thickness.
2. Calculation rules:
(1) There is copper on the back of the gold finger: a layer of film thickness needs to be removed (there is no film on the gold finger, so this thickness needs to be subtracted)
(2) There is no copper on the back of the gold finger: a layer of film thickness needs to be removed, and then a layer of copper thickness needs to be removed (there is no copper on the back of the gold finger, so in addition to subtracting the film thickness, this layer of copper thickness needs to be subtracted)
For example: if the total thickness of the gold finger area is 0.3mm, the board thickness is 0.11mm, and there is no copper on the back of the gold finger, the theoretical thickness of PI reinforcement = 0.3-(0.11-0.0275-0.012) = 0.2295mm, and PI needs to be 0.25mm.



Now you understand! FPC has many board thicknesses and many colors of solder mask. In this case, is it still a bit difficult to calculate the PI thickness? Don't worry, Jialichuang has developed a calculation tool for everyone. You can contact me to get it. Just enter the total thickness requirement, select the board thickness, whether the back of the gold finger is copper-covered, and the color of the solder mask, and then you can calculate the thickness required for PI reinforcement.