Issue link: https://iconnect007.uberflip.com/i/1073397
JANUARY 2019 I FLEX007 MAGAZINE 69 Routing in Bend Areas In addition to the conductors being perpen- dicular to the bend axis, it is also critical that the conductors do not traverse in the bend area (Figure 3). Button Plating When dealing with multilayer flex applica- tions that require a lot of bending, it is impor- tant to specify that button plating or via-only plating is required. Typically, when plating copper in the plated through-holes, the fabri- cator will be plating the full panel. This plat- ing process uses ED copper, which is not as flexible as the RA copper foil. This can impact the flexibility of the circuit in applications with tight bend radius or dynamic flexing require- ments. When button plating is specified, the fabricator will plate only the copper pads and through-holes—not the full panel. Many crack- ing failures have been resolved once the pro- cess to manufacture the flex circuit has been changed from plating copper on the circuit lay- ers and vias to a via-only plating operation. Balanced Construction The construction should be balanced from its centerline including copper, dielectric, and adhesive thicknesses. An unbalanced construc- tion will cause stress to occur in one direction, decreasing flex life. Minimum Bend Radius Even though flex circuits are very pliable and flexible, there are limits to their flexibil- ity. If the bend radius is too tight, the result can be delamination and conductor fracture (Figure 4). Figure 3: A poor versus a robust flex area design. Poor design Flex area Conductors traverse in bend area Robust design No conductors traverse in bend area Figure 4: Bend radius illustration.