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PCB-Aug2017

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44 The PCB Magazine • August 2017 by Joel Schrauben, Cameron Tribe, Christopher Ryder and Jan Kleinert ELECTRO SCIENTIFIC INDUSTRIES Abstract Glass offers a number of advantages as a di- electric material, such as a low coefficient of thermal expansion (CTE), high dimensional stability, high thermal conductivity and suit- able dielectric constant. These properties make glass an ideal candidate for, among other things, package substrate and high-frequency PCB ap- plications. We report here a novel process for the production of printed circuit boards and in- tegrated circuit packaging using glass as both a dielectric medium and a platform for wiring si- multaneously. An ultrafast laser is used to etch away the de- sired pattern (pads, wires and vias) in the glass, and copper plating is "seeded" through the la- ser-based deposition of copper droplets. The seeded area is then plated using electroless plat- ing followed by electroplating. Demonstrations of fine pitch wires, variable diameter through holes and blind vias, and a multilayer stack are shown. The deposits have a resistivity less than a factor of 1.5x that of bulk copper for 5-10 mm wires. Plated lines in borosilicate glass of 7-10 μm width and 5-20 μm depth and line spacing down to ~10 μm are demonstrated, as well as vias with a top diameter approaching 100 μm for 150 μm glass and 40 μm for 50 μm glass. The process presents the potential for sig- nificant material savings in terms of base mate- rials, process chemicals, and waste disposal/re- cycling costs (glass is on the order of 100-fold less expensive than some current high-frequen- cy dielectrics, and wet processes account for a large part of standard PCB/substrate manufac- turing). Additionally, the processes are amena- ble toward other dielectric materials such as FR- 4, polyimide and PTFE-based materials. Introduction Increased demand for high data transmis- sion rates is driving the development of small- er PCB features. Electrical circuits are reaching the physical limitations of traditional PCB di- electric materials under which electromagnetic compatibility can be controlled. Additionally, FEATURE

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