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26 The PCB Magazine • January 2016 accomplish this combination, I reached out to Mike Vinson, with Averatek Corp., which manu- factures using a patented innovative and addi- tive metal "print and plate" process. This addi- tive technology enables the creation of trace and space widths below 10 microns and enables the direct deposition of copper and other metals on a variety of substrates. One of the first questions I wanted to answer was this: What would drive the need for gold traces rather than the traditional copper traces? What I have learned is that neural probes are be- ing used in many clinical settings for diagnosis of brain diseases such as seizures, epilepsy, mi- graines, Alzheimer's and dementia. Microelec- tronic technologies are opening new and excit- ing avenues in neural sciences and brain machine interfaces. With this area of science and research, biocompatibility of the neural probes to mini- mize the immune response is critical. Copper, nickel and chromium can all adversely impact cells in the area of the electrodes. Flexible mate- rials, such as polyimide, are commonly used in implanted devices to match the geometric and flexibility requirements of implants. Metallizing with gold provides further compatibility versus less noble conductors such as copper or nickel. With a better understanding of the reasons behind the request for gold traces, the burning question was, how does the additive print and plate process enable both the fine lines and the gold metallization? Fine Lines and Gold Metallization The traditional PCB manufacturing process is accomplished by a subtractive etch process. The PCB manufacturer will start with a panel of copper-clad material. In other words, the full panel, often 18" x 24", is covered in copper. The traces and spaces are created with a develop- etch-strip process that essentially removes the unwanted copper from the panel leaving the de - sired trace patterns. Often over-simplified, this process is quite complex. After vias are drilled, electroless copper is deposited and resist is lami- nated prior to the photolithography process. Following the imaging process, panels are devel- oped to remove resist that was not exposed, the copper is electroplated, and then tin is plated as a temporary etch resist. The remainder of the resist is stripped, the etch process removes the unwanted copper and the temporary tin plating is then stripped. Additive technology is a reversal of this pro - cess. The manufacturer begins with the bare sub- strate. In the case of a neural probe, this is likely a polyimide material. The desired circuit pattern is then created by adding the metal layer to the substrate. Averatek has developed a proprietary nano-catalytic ink that enables a simplified five step process. The bare substrate is prepared. Vias are drilled. The ink is coated and cured. The ink is then patterned with photolithographic imag - ing. Finally, metal is plated to this pattern. In this neural probe application, the metal is gold but metallization could also be copper or other metals. The key to this technology lies with the MEDICAL RESEARCH IS GOLDEN Flex talk Figure 1: cross-section of low-force, high-performance probe solution. Figure 2: Fine lines on polyimide flex material.

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