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Fineline circuits realization with liquid photoresist and DMD-based photolithographic technique for space electronics applications

Abstract Background: High-density interconnect (HDI) printed circuit board (PCB) packaging technology has gained greater significance in military and aerospace sectors. Manufacturing with fineline features and the impedance-controlled circuit pattern is a major technical challenge for which several methods have been reported. Aim: Herein, a novel process of HDI PCB fabrication has been presented using liquid photosensitive resist spray coating followed by digital micromirror device (DMD)-based micro-opto-electromechanical direct imaging photolithography to realize fineline circuit pattern. Approach: A fineline HDI circuit has been developed with minimum conductor trace width of <40  μm and spacing from the copper foil (18-μm thickness) cladded to dielectric substrate that comply the requirements of high reliability space electronics packaging. Such fineline conductor features have been exemplified with optical microscopy, SEM, and subjected to micro-sectioning. Results: The resulting undercut values and etched pattern have been found to be excellent. Leveraging the standard test method, the peel strength values of the realised fineline circuit patterns were measured to be more than 1.2  kg  /  cm2 required for high reliability space electronics packaging applications. Conclusions: The output paraments meet the space high-reliability requirements withstanding the stringent environmental conditions of ultra-high vacuum, vibration, and the extreme temperatures for longer durations.