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62 The PCB Magazine • March 2016 combination with reducing agent to modify the PI surface for a better attack of the initiator de- positing MnO 2 . Initiator The initiator is usually an aqueous solution of potassium or sodium permanganate that makes an oxidative reaction to selectively form manganese dioxide (MnO 2 ) on the conditioned dielectric area of the hole wall. MnO 2 is essen- tial in the polymerization of the conductive polymer on the wall surface. The conductivity of the subsequently deposited polymer layer is highly dependent on the right amount of MnO 2 presence on the surface. Catalyst The catalyst in DMS-E process is an aque- ous mixture of sulfonic acid and a micro emul- sion of EDT that reacts with MnO 2 as oxidizer. EDT radicals, created by the oxidation step, re- act spontaneously to form the polymer chain (Figure 7). The high Tg (T g 220–350 o C) polyimide flex- ible laminates require an extremely effective conditioning (i.e., an hydrophilicity step prior to chemical bonding of the conductive catalyst layer). The task of an effective conditioner sys- tem is the wetting of the resin and glass as well Figure 6: DMs-E process. Figure 7: Conductive polymer formation. direCt metallization system for flexible printed CirCuits