PCB Fabrication

The FPC used in the mobile phone folding in the mobile phone PCB design needs very good flexibility

by:A-TECH      2021-03-23
As we all know, in the entire mobile phone PCB design, the FPC used in the mobile phone’s folding position needs very good flexibility, because the Ministry of Information Industry requires 50,000 times for the flip-top life of a folding mobile phone, and the current domestic first-line mobile phone manufacturers require 8 -100,000 times. Therefore, FPC is a key factor affecting the quality of folding mobile phones. In fact, the life of the flip cover of a foldable mobile phone is not entirely determined by the FPC. To be precise, it should be the compatibility of the FPC and the hinge mechanism. Therefore, the root cause should be that PCB manufacturers participate in the design of mobile phones at the same time, but it is currently difficult to do so. Therefore, to make a good mobile phone PCB circuit board, let's discuss the FPC side first. 1) Material selection: In order to ensure the bending performance, it is recommended to choose 0.5mil/0.5oz single-sided substrate, rolled copper (RA); Cover layer (cover film) choose 0.5mil. 2) Layer selection: At present, color screen mobile phones generally use 40PIN connectors, and the actual wiring is between 34 and 40, and the shape width of FPC is 3.2-4mm; if the line width of 3mil and 40 lines are used, only With a width of 3.6mm, it can be designed as a two-layer circuit. The current strength of 0.5oz, 3mil line width is 70UA.   3) Circuit design in the bending area:    a) There should be no through holes in the bending part;    b) Add protective copper wire to the two sides of the circuit. If there is not enough space, choose to add protective copper wire to the inner R corner of the bending part.   c) The connecting part of the circuit needs to be designed as an arc.   4) Bending area design (air gap): The bending area needs to be designed in layers, and the glue is removed to facilitate the effect of stress dispersion. The larger the bending area, the better without affecting the assembly.   5) Shielding layer design: At present, the shielding layer of mobile phones generally uses silver paste and copper foil, and Japanese mobile phones have a silver foil design.   a) The silver paste shielding layer is adopted, which reduces the actual number of active layers, facilitates assembly, simple process and low cost. However, because the silver paste is a mixture, the resistance is relatively high, about 1 ohm. Therefore, it is not possible to directly design the silver paste layer as the ground wire. b) The copper foil shielding layer, the number of active layers is increased by two layers, the cost is increased, but the resistance is lower, and it can be directly designed as a ground wire.   c) Silver foil shielding layer, the cost is too high.   6) Electroplating selection: In order to ensure the bending performance, some copper electroplating processes must be selected. A full copper electroplating process cannot be used.
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