You are going to establish this by the kind of material your flex PCB needs. As well as resources, flexible PCBs are available in several production grades. PCB surface area treatment should be to protect the PCB surface with a protecting layer to prevent copper oxidation, corrosion and to boost https://metalpcbcopperbasedboard17155.blog-gold.com/38386422/a-review-of-arduino-high-speed-pcb-arduino