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68 FLEX007 MAGAZINE I JANUARY 2019 side against the drum provides the smoother finish (Figure 1). Rolled-Annealed (RA) Copper Foil RA copper foils are created by successively passing an ingot of solid copper through a roll- ing mill and then applying high temperature to anneal the copper (Figure 2). RA copper foil has higher ductility and elongation than ED copper, which is why it is best for bending applications. Grain Direction Matters RA copper is primarily used in flexing and bending applications. Circuit direction and ori- entation on a manufacturing panel are critical to maximizing the flex life in dynamic flex- ing applications. Grain direction is positioned perpendicular to the bend axis because bend- ing across the grain direction will inherently negate the advantage of the elongated grain structure. Figure 1: The ED copper process. Figure 2: The RA copper process.