The First Thin Film Electronic Package: From Invention to Manufacturing

As late as the end of the 1970’s, electroplating was regarded as a mystical shop art that had no place in microelectronic fabrication. In 1979 IBM introduced a magnetic thin film head made possible by a newly invented process that was based on electroplating – an achievement that cast electroplating in a new light. Today, electroplating has spread into applications ranging from nanoscale patterning of copper BEOL wiring below 10 nanometers on silicon chips to the deposition of materials for synthesis into photovoltaic layers on 60 cm by 120 cm solar panels, and has also made possible the use of metal structures in MEMS devices. The successful production of the thin film head with its precisely patterned high aspect ratio copper coils and its permalloy elements with tightly controlled magnetic properties, which plating experts of the 1970’s deemed impossible to do by plating, made device fabricators receptive to the electrochemical technology they once shunned.

An important new application of electroplating technology was in the fabrication of the multichip module. In advanced computers, these modules were multilayer ceramic structures that provided the power connections to the circuit chips and had a top layer of copper strip lines for data transmission between chips. The strip lines consisted of copper conductors with a rectangular cross-section that might be 6 µm high and 10 to 20 µm wide embedded in polyimide between two ground planes. These structures, which were essentially low-loss transmission lines, had to have precisely controlled propagation characteristics to minimize pulse distortion. Plating through a lithographic mask was an effective way of insuring the tight control on the geometry of the lines necessary to meet this requirement. One aspect of this talk will be to highlight the technical aspects of integrating electrochemical technology into the fabrication process for the transmission lines. The other will address how the scientists and engineers from the IBM T.J. Watson Research Center who had created the thin film head, worked with the development and manufacturing engineers at IBM’s East Fishkill plant to bring electrochemistry into their production line.

 References:

S. Krongelb, J.O. Dukovic, M.L. Komsa, S. Mehdizadeh, L.T. Romankiw, P.C. Andricacos, A.T. Pfieffer, K. Wong, The Application of Electrodeposition to Advanced Package Fabrication, SPIE Vol. 1389, International Conference on Advances in Interconnection and Packaging, pp. 249-256 (1990).

S. Krongelb, L.T. Romankiw, J.A. Tornello, Electrochemical Process for Advanced Package Fabrication, IBM J. Res. Dev. 42 (5), pp. 575-585 (1998).

S. Krongelb, L.T. Romankiw, E.D. Perfecto, K.K.H. Wong, Electrochemical Processes in the Fabrication of Multichip Modules, Chapter 11, pp 337-372 in Microelectronic Packaging, edited by M. Datta, T.Osaka, J.W. Schultze, CRC Press, Boca Raton, FL (2005).