Rolled Annealed (RA) Copper, has been used extensively in the flex circuits manufacturing and rigid-flex PCB fabrication for decades. The grain structure and smooth surface is ideal for dynamic, flexible circuitry applications. Another area of interest with rolled copper types exists in the high-frequency signals and applications. It has been proven that copper surface roughness can impact high-frequency insertion loss and a smoother copper surface is advantageous. Also check another type Electro Deposited (ED) Copper.
How to Make RA Copper Foil? RA copper foil is made by running a copper strip through successive smaller and smaller gaps in a rolling mill until it reaches the desired thickness. Rolled copper is smoother and can be made very flexible by annealing. Because it is smooth, its bond to laminates is totally dependent on the quality of the treatment it receives and the adhesive properties of the resin system employed. RA copper also has a different grain structure than ED copper and will etch at a different rate. Much of the RA copper in the laminate industry is used in flexible circuits, typically boned to a polyimide film with an acrylic adhesive.