Mid‐Film Interconnects for Multilayer Microcircuit Packages

The mid-filmR process has been developed to combine the photolithographic capability of thin film technology and the low cost, non-vacuum processing of thick film technology. In this paper, we present results on the characterization of mid-film gold for multilayer applications. The effects of various processing parameters on the properties of the conductor were investigated to establish optimum processing conditions on alumina and dielectric-coated alumina substrates. The use of a resin thickness in the range from 5 μm to 15 μm and firing temperatures from 750℃ to 1000℃ produced conductor lines with sheet resistances less than 4 mΩ/□, and with adhesion strengths capable of with-standing a pull force of 2.3 Kg exerted on a 2.03 mm × 1.03 mm area. The conductor lines exhibited stable resistances upon several firings at 920℃. The ultrasonic bondability of 25 μm (1 mil) aluminum wire to the mid-film gold was observed to withstand pull forces of 7.3 ± 1.5 g before breaking the bond. In addition, it was confirmed that the resolution limit of the mid-film conductor is 50 μm for line widths and spaces. Furthermore, the prototype fabrication of a multilayer memory package has been successfully demonstrated using a combination of both mid-film and thick film processes. The finished packages were free of electrical shorts and conductor discontinuities and the resistance of the mid-film conductor lines was well within the required design specifications.