Rigid-flex Pcb Holes Metallization

Using electroless plating copper or electroplate process on double-side PCBs or multi-layers rigid-flex PCBs, some metal can be deposited on the dielectric surface of PI or EP materials. The layer of metal can realize interconnection of double side circuit. The hole metallization of rigid-flex PCBs which including Drill, Desmear, electroless plating, Electrical plating, is a key process in the manufacturing of rigid-flex PCBs. The plate-through-hole (PTH) require superior mechanical&electrical, excellent uniformity and integrality of copper layer, no lifted pad, no plated-hole-wall pull-away, no resin voiding and air bubbles. Because of the demands of electronic products(smaller, lighter, thinner)and high density assembly,the design and manufacture of PCBs have got a rapid progress and the requires of hole metallization of PCBs also become more strict. As the diameter of the hole become smaller and smaller, the hole metallization process become difficult to deal with. Now it has become the bottleneck of the PCB manufacture (specially the manufacture of rigid-flex PCBs).The development and prospect of rigid-flex FPC, the principle of the hole metallization process, influence of various process factor on product quality is introduced in this paper. The desmear process and the electroless plating copper process, which are the key processes, are studied and introduced in details.Because the material of rigid-flex PCBs is different from the rigid printed circuit board(RPCB) and the flexible printed circuit board(FPCB). The base materials of RPCB are epoxy resin , glass cloth, PTFE (Polytetrafluoroethylene), etc. The base materials of FPCB are polyimide resin and crylic adhesive, etc. Because of the low Tg temperature of these dielectric materials and the high heat produced by high-speed driller, some smear can be generated on the surface of hole and can induce defeat of plated-throught-hole. In RPCB the smear that caused by these materials can be get rid of using potassium permanganate.while rigid-flex PCBs is mainly based on materials, such as PI(Polyimide), epoxy,polyacrylates, this process can make the layers breakaway, So the smear caused by this material can't be get rid of using potassium permanganate.