Can FPC be repaired? How to repair it

Can the soft circuit board be repaired

The soft circuit board can be repaired. We will give a detailed description of the maintenance of FPC flexible circuit board's open circuit.

1. Remove 21 screws and uncover the old background of the keyboard, revealing a piece of white flexible circuit board. There is also a small green main control circuit board in the upper left corner. It is said that the FPC (Flexible PCB) of the keyboard is made of polyester film (PET, a polymer plastic film). There are three layers in total. The upper and lower layers are printed with silver paste or silver foil, and the middle layer is used for insulation (to separate the upper and lower layers of boards to prevent short circuit. The upper hole can make the two layers of printed circuit boards short circuited instantly when you hit the keyboard, so as to input corresponding characters or commands.

2. Only a few keys fail, indicating that the keyboard main control board is normal. Take a look at the bottom of the flexible circuit board of the keyboard. The failed keys are distributed on the same line. Using the diode buzzer gear of the multimeter, walk through the FPC circuit to the connecting pin of the main control board (as shown in Figure 3), and the multimeter will not sound. After removing the main control board, it is found that this pin has been burnt black for several millimeters (other pins are also black, but not so serious), and it is open circuit.

3. If it is an ordinary PCB board, it is easy to open the circuit, just fly a wire with a soldering iron. But this is a flexible PCB, a plastic film, and welding is not feasible. Baidu once, it is said that you can use a pencil to draw a few strokes at the circuit breaker, but it is better to use conductive silver paint to repair the keyboard flexible circuit board soon. Baidu Encyclopedia said:

Conductive silver paint can make the current of non solderable points unblocked. It is widely used to repair open circuit (copper circuit broken) baseplates, automobile windshield film generators, TV remote controllers, capacity switches, audio and video tapes, discharge static ions, reduce the resistance of high-voltage contacts, seal and coat on plastic casings, and block high-frequency magnetic fields by closing screens. It can also be used to repair various flexible circuits of plastic circuit boards such as desktop computers and notebook keyboards.

What is a soft circuit board_ Can the soft circuit board be repaired

Conductive silver paint generally has strong adhesion, which can be attached to plastic, wood, interior walls, etc. It can dry quickly (about 3 to 24 hours), has low resistance and strong conductivity, and can adhere to any plastic fiber board and metal. It must be well mixed before use. After it is well mixed, it can be painted with a hard pointed brush or injected with a syringe. After it is dry, it can be sealed with Electrolube base plate film or contact protector. After it is used, the bottle cap must be tightly covered to prevent it from being dry.

Baidu knows that a friend said that it should pay attention to that the silver paint will spread slowly, so it should pay attention to the amount of coating (less is OK). The domestic conductive silver paint takes effect in about 12-24 hours (the time is determined according to the temperature and air humidity, and it also takes 3-12 hours for imported ones), or the hot air gun or hair dryer (the temperature is controlled at 40-50 degrees) can be used to accelerate the effective time of the conductive silver paint. Conductive silver paint has penetrating power, so it is better to pad a piece of paper on the back of the printing film in the keyboard, and the silver paint can be removed after it is dry. Another point is that conductive silver paint is non-conductive at ordinary times and can only conduct electricity after it is completely dry.

4. Conductive silver paint seems to be quite expensive, 0.3 ml (3 g) is about twenty or thirty yuan. I bought it specially to repair a broken keyboard. It's not worth it. I have to think of another way. I have tried to draw with a pencil, but the connection effect is not good. It is said that it is OK to stick a thin copper wire with transparent adhesive! I didn't have transparent adhesive tape, so I had to use double-sided adhesive tape for half a day. After it was glued (confirmed that there would be no short circuit), I used a meter to measure it. When it was connected to the computer, the eight keys worked normally. In the future, you can use Ctrl+Alt+A to screenshot, Ctrl+A to select all, and Alt+Tab to switch windows.

The above mainly introduces FPC maintenance methods