Quantitative Evaluation of Strength Degradation at Interfaces in IC Packages and Formulation of a Fundamental Mechanical Device Reliability Strategy

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Interfaces in package assemblies where delaminations during processing and service are identified. A fundamental approach for designing and predicting the mechanical reliability of these interfaces is proposed, with a view to replace the current empirical and rather time-consuming approaches that utilize accelerated test protocols. Implementation of the proposed strategy requires (1) the development of a fundamental interface-strength-measuring tool capable of testing interfaces, in-situ, in actual device and package structures, (2) measurement of the tensile strength, in-situ, of the selected interface as a function of humidity, temperature, and time variables, and (3) quantification of the moisture content using FTIR and thermogravimetric analyses on each tested sample. These will result in "interface strength charts" for predicting degradation at the selected interface for varying humidity and temperature conditions. Well developed simulation codes can then predict stress concentrations, moisture accumulation, and temperature rise at any of the interfaces within the package assembly for determining (a) whether the interface will be able to survive processing and system integration cycles during the design phase itself, prior to any IC fabrication and packaging, and (b) the level of interface strength needed at the time of manufacturing for ensuring a prescribed service life. The above procedure will first be demonstrated by studying the underfill/Si3N4 passivation layer interface. Measurement of the interface tensile strength, in-situ, will be accomplished by modifying a laser spallation method, developed previously by the PI.