FlexiblePrinted Circuit, FPC is favored for its light weight, thin thickness, free bending and folding and other excellent characteristics, but the domestic quality inspection of FPC is still mainly rely on manual visual inspection, high cost and low efficiency. With the rapid development of the electronics industry, circuit board design is becoming more and more high-precision and high-density. Traditional manual inspection methods can no longer meet the production needs. FPC defect automatic detection has become an inevitable trend of industrial development.

In consumer electronic products with movable structures (such as side-sliding mobile phones), in order to ensure that the product slides more than 150,000 times in the bent state, a single-layer FPC (flexible circuit board) is usually used to electrically connect two different modules . With the development of smart phones, their operating frequencies and transmission rates are getting higher and higher. When using MIPI or MDDI and other interface protocols, the impedance of the differential pair wiring needs to be controlled to a certain range, which requires that the differential pair signal corresponds to a layer Reference plane. In the existing technology, FPC design usually uses an additional layer or two layers of copper foil as the reference plane, which will double the cost. At the same time, increasing the number of copper foil layers will increase the thickness of the FPC and cause slippage. The performance is greatly reduced, and reducing the number of times the FPC slides affects the life of the product. If impedance control is not performed in the sliding area, product performance will be reduced.

Basic structureedit

Copper Film

Copper foil: basically divided into electrolytic copper and rolled copper. The common thickness is 1oz 1/2oz and 1/3 oz

Substrate film: There are two common thicknesses: 1mil and 1/2mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Cover Film

Cover film protection film: for surface insulation. Common thicknesses are 1mil and 1/2mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Release paper: avoid the adhesive sticking to foreign matter before pressing; easy to work.

Stiffener Film (PI Stiffener Film)

Reinforcement board: Reinforce the mechanical strength of FPC, which is convenient for surface mounting operations. The common thickness is 3mil to 9mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Release paper: avoid the adhesive sticking to foreign matter before pressing.

EMI: Electromagnetic shielding film to protect the circuit inside the circuit board from outside interference (strong electromagnetic area or susceptible to interference area).