1. FPC cover film
The FPC (flex pcb ) cover film is called CVL, and the ingredients are curing agent, methyl ethyl ketone, thinner, rubber, etc., and the dosages of different formulations are different.
The outermost layer shown by the arrow in the figure below is the cover film.
2. FPC film function
Generally, the main function is protect circuits.
Dustproof, anti-fouling, anti-static, protection circuit is not exposed to the air, to avoid oxidation and corrosion of copper foil. Cover the area with CVL in areas where gold plating is not required. And it can solder mask in SMT.
3. FPC (flexible PCB board) test board design:
50ohm 7.5mil microstrip line, length 8 inch.
4. Contrast test with cover film or not
(1) 50 ohm 7.5 mil, surface coating
(2)S21 (Insertion Loss)
Similarly, the S21 of the line-width surface-coated microstrip line is better than the case where the film is not covered, so the film is necessary. The same problem, the material of the film is not the same, and the signal loss is also different.