Reliability Assessment of BGA Interconnects With CADMP-II

Abstract

Recently the plastic ball grid array (PBGA) has been gaining industry-wide acceptance in high pin count applications as a low-cost alternative to fine-pitch leaded packages such as the plastic quad flat pack (PQFP). The main factors leading to its use include low cost, high I/O density, a small footprint, and the potential for superior electrical and thermal performance with respect to PQFPs [Houghton 1993; Freyman and Pennisi, 1991]. However, concerns about interconnect reliability remain, particularly for systems to be joined with novel solders or conductive adhesives, which are being used increasingly both for environmental reasons and because of the need for higher temperature operating systems. Thus there exists a need to accurately evaluate design trade-offs arising due to these failures in order to increase reliability and drive design improvements. A PC-based CAD tool for the assessment of the reliability of PBGA interconnects is presented. This tool facilitates the use of physics-of-failure methodology in design for reliability, virtual qualification and the selection of accelerated test conditions. The tool assesses candidate and existing package designs for reliability in many different environments using a database of fully validated physics-of-failure models. These models calculate times-to-failure for the fundamental mechanisms which cause failure of area array packages housing both bipolar and CMOS based systems. Particular focus is placed on the use of this tool for analyzing the reliability of area array solder joint interconnects, including those made with lead-free solders and conductive adhesives, and on conductive filament formation between the traces in a plastic ball grid array. The addition of the appropriate material properties for high temperature, fatigue resistant, lead-free solders to the materials database, the development of a package designer for PBGA designs, and the incorporation of failure mechanism models for flip chip solder fatigue, PBGA solder joint shear and tensile fatigue, and PBGA conductive filament formation will be discussed. The ability to use this tool to conduct assessments of the susceptibility of PBGAs to non-interconnect failure mechanisms is an added advantage as it permits a determination of the relative importance of interconnect failure as a failure mode.