Thin-film multichip module packages for high-end IBM servers

A new generation of multilevel thin-film packages has been developed for IBM high-end S/390® and AS/400® systems. Thin-film structures in these packages are nonplanar and can be fabricated by either pattern electroplating or subtractive etching. Selection criteria for choice of fabrication methods are discussed in terms of electrical performance requirements, ground rules, manufacturability, and cost issues. Two problems encountered in the development phase of the nonplanar thin-film structures were 1) accelerated etching of plated Cu features during Cu seed etching, and 2) corrosion of the bottom-surface metallurgy during etching of Cr at the top surface. Effective solutions were developed on the basis of underlying electrochemical phenomena. Finally, reliability stress procedures used to qualify these packages and results of these procedures are presented.