Flexible Printed Circuit (FPC): Process Flow And Applications

Label:Flexible Printed Circuit, FPC

Sep 19, 20242880

Flexible Printed Circuit (FPC): Process Flow And Applications

What is flexible printed circuit (FPC)

 

Compared with rigid PCB, FPC has the features of high wiring density, light weight, bendability, and three-dimensional assembly.

 

The excellent heat resistance enables the mounting of electronic components using reflow soldering (heated soldering process). FPC can withstand repeated bending, so it has become indispensable as component for moving parts of electronic equipment.

 

Process flow

 

1. Shearing

 

Flexible materials are packaged in rolls, and cut into required sizes according to MI dimensions.

 

2. Drilling

 

Drill holes or positioning holes in the material by CNC machining, which facilitates the conduction of copper materials on both sides after subsequent copper plating.

 

3. Plating through hole

 

For boards that have just had holes drilled, the upper and lower copper layers are not conductive, so through-holes need to be plated to form a conductive layer. Then hole copper is electrochemically plated on the conductive layer to achieve conductivity between the upper and lower copper layers.

 

4. Photosensitive film / exposure

 

A photosensitive film is pressed onto the electroplated board surface, and the circuit pattern is transferred to the photosensitive film.

 

5. Development / etching / film stripping

 

Development: Develop away the dry film without photolithography to expose the copper foil outside the circuit.

 

Etching: Use chemical solution to etch away the copper foil exposed after development.

 

Film stripping: Remove the dry film of the circuit with sodium hydroxide to reveal the final circuit pattern.

 

6. Coverlay pre-lamination

 

To prevent short circuit and oxidation, an insulating layer must be made on the conductor. The layer is called a cover film.

 

The process involves opening windows on the cover film where the copper needs to be exposed at the pad position, and then sticking the cover film with the opened windows on the etched board. The cover film is available in yellow, black, and white.

 

7. Metal finish

 

Here is the surface treatment. First coat a layer of nickel on the exposed pad, and then coa a thin layer of gold to prevent the pad from oxidation and improve solderability.

 

8. Silkscreen printing

 

Print required text on the board. The text ink is then hardened to prevent it from falling off.

 

9. Flying probe test

 

Test the conductivity by flying probe tester. It tests whether there are open or short circuits.

 

10. Add auxiliary materials

 

Add auxiliary materials, such as PI, electromagnetic shielding film, FR4, steel sheet, back adhesive, on the board according to your requirements.

 

11. Laser forming

 

Cut out the shape of the board by laser. Separate the unnecessary waste, and get the final shape of the board.

 

12. Final test and packaging

 

Screen out products with poor appearance, and package good ones.


 

Applications

 

1. Consumer electronics

 

FPC has important applications in consumer electronics. For example, in electronic devices such as smartphones, tablets and laptops, as well as wearable devices such as watches and bracelets, FPC products are used as flexible connection parts to connect various components and transmit signals.

 

The flexibility and bendability of FPC products enable them to adapt to the design requirements of devices in different shapes and sizes, providing a better user experience.

 

2. Automotive electronics

 

With the rapid development of automotive electronics, FPC products are increasingly used. You can see them in dashboard, central control panel, seat adjuster, in-car entertainment system, new energy battery cable, etc.. FPC products have a small size and good temperature resistance, which can meet the special needs.

 

3. Industrial control

 

Flexible PCB has long service life. It is resistant to aging. It can provide high-performance industrial control systems, and is often used in industrial robots, sensors, controllers, etc..

 

4. Medical equipment

 

FPC is also widely used in medical equipment, such as endoscopes, facial analyzers, MRI scanning helmets, etc..

 

5. Smart home

 

In the field of smart home, FPC is used in temperature measurement, smart switches, infrared remote control and sensors. You can see it in induction faucets, smart toilets, constant temperature insulation cups, remote control modules, etc..


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