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22 The PCB Magazine • May 2014 telecommunications), graphite-based metalli- zation has found a significant growth avenue. With sequential lamination for HDI a critical aspect of the manufacturing processes, each sub-lam must be metalized. Direct metalliza- tion offers a much faster process compared with conventional electroless copper. In addi- tion, flexible circuitry is often manufactured in continuous roll-to-roll configuration (Fig- ure 9). Graphite-based metallization is partic- ularly useful for the higher productivity needs and the excellent adhesion to polyimide ma- terials. Figure 10 shows the any-layer circuit designs fabricated with a graphite-based metallization process followed directly with copper via fill plating. Figure 11 depicts a rigid-flex design fabricat- ed with graphite system. Summary Graphite-based direct metallization has p roven to be particularly useful for flexible and HDI circuit market segments. Combining the process's high productivity, the ability to coat a wide variety of resin systems and sub- strates as well as providing significant environ- mental advantages over conventional electro- less copper, has allowed for rapid growth of graphite-based direct metallization during the last five years. With improvements in colloid stability and conditioning of difficult to metalize substrate materials such as flex polyimide, PTFE, ceramic filled and other higher performance materials, graphite-based direct metallization systems are an enabler for the direct electroplating of com- plex interconnect technologies. PCB References 1. U.S. Patent #5,476,580. 2. "Printed Wiring Board Cleaner Technolo- gies Substitute Assessment: Making Holes Con- ductive," U.S. EPA, Washington, D.C. 3. Burger, L., Carano, M., et al, "Enhanc- ing the Performance of a Graphite-based Di- rect Metallization Process," IPC APEX EXPO, 2007. GRAPHITE-BASED DIRECT METALLIzATION continues Figure 10: any-layer circuit design for a smart phone, fabricated with graphite direct metalliza- tion followed by electroplating copper via fill. Figure 11: rigid-flex with blind via. michael carano is with omG electronic chemicals, a de- veloper and provider of pro- cesses and materials for the electronics industry supply chain and regular columnist for the PcB magazine. to contact carano, click here.