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10 The PCB Magazine • June 2015 Abstract Today's wide variety of laminate materials and specialized dielectric choices pose a chal- lenge for process engineering. In particular, smooth surfaces, such as polyimide, flex cir- cuit substrates and rigid-flex constructions with window cut-outs, can be a challenge for electro- less copper and plating processes. Conventional electroless copper systems often required pre- treatments with hazardous chemicals or have a small process window to achieve a uniform coverage without blistering. To overcome the challenge of metallizing smooth surfaces, a new stress-free electroless copper was developed to serve this important sector of the printed circuit industry. Introduction As the thermal, physical, chemical and electrical properties of PCBs have advanced, so by Jason Carver and Alvin Kucera OM GrOuP ElEcTrOnIc cHEMIcalS A High-Reliability, Stress-free Copper Deposit for FPC, Polyimide and Rigid-Flex too have the substrates of construction. With a wide variety of substrates available, it is be- coming increasingly difficult to accommodate these new substrates in current manufacturing processes [1] . Polyimide resins (PI), for example, provide exceptional thermal and chemical sta- bility but remain challenging with industry standard processes. In particular, electroless copper deposition, the most commonly used method of metallizing a nonconductive sub- strate, is susceptible to blistering or peeling due to the low adhesion of the copper film to the substrate. Typically, electroless copper films require mechanical anchoring to provide ad- hesion to a substrate to prevent blistering. A roughened surface is commonly created with a chemical or plasma etch process to help create anchoring sites. Conventional chemical etches, which were primarily designed for epoxy sub- strates, are generally ineffective at activating PI substrates [2] . Plasma etching, which is effective at etching PI, is still insufficient to prevent peel- ing and blistering [3] . Some manufacturing pro- cesses have resorted to using an alkaline solu- FeAtuRe