This paper on "Accelerated Method for Design and Durability of Electronic Interconnects Using the Unified Disturbance Constitutive Modeling" was presented at the NAFEMS World Congress on The Evolution of Product Simulation From Established Methods to Virtual Testing & Prototyping - 24-28 April 2001, The Grand Hotel, Lake Como, Italy.

Abstract

The development of a new accelerated procedure based on the unified constitutive modeling approach called the disturbed state concept (DSC) has led to a powerful engineering tool for the evaluation of fatigue life. The DSC allows, in an integrated framework, prediction of elastic, plastic, creep strains, microcracking, and fracture leading to fatigue failure. While the traditional finite-element method (FEM) based on continuum theory provides the stresses and strains at a point, without the influence of microcracking in the neighboring zones. The new accelerated DSC effectively eliminates the need to simulate thousands of thermomechanical cycles that can involve extensive computational effort and time. The procedures presented herein were developed under other previous and ongoing research [1-3] and involve full analysis for only a few cycles. Yet, they can allow evaluation of the cycles to failure and approximate distributions of disturbance for selected subsequent cycles.
This paper describes an application of this simplified analysis method to plastic ball grid arrays (PBGA), which are considered one of the most promising emerging technologies. Considering the complexity of geometry and possibility of using different sizes and topology, predicting and understanding factors affecting life cycles of the joints of these components are of major concern. Favorable comparisons were shown between test data and computer analysis.
Laboratory tests conducted at Boeing consisted of three groups of 144, 324, and 352 I/O PBGA devices that were exposed to thermal cycles between -40 to +125^oC. An example of a 144-pin PBGA is presented here. Computer simulation involves two basic steps. In the first step a nonlinear global model of the test board, including PBGA packages and using the Boeing-developed durability analysis procedure, is used to identify the critical solder ball. The critical solder ball is defined as the solder ball having the most severe differential displacements of all solder joints in the PBGA. In the second step a local two-dimensional plane stress structural model, including the reduced, accelerated disturbed state concept (RADSC), is used to analyze the critical solder ball. RADSC provides an accurate and economical prediction of fatigue life (number cycles to failure) under actual test conditions from only a few simulated cycles and is ideally suited for design and durability analysis.