BGA LIFETIME PREDICTIONS: INTERFACE STUDIES, NUMERICAL ANALYSIS AND EXPERIMENTAL COMPARISON
Author: Wolfgang H. Muller Company: Universitat-GH-Paderbom Date Published: 4/28/1997
Surface Mount International
Abstract: The successful and safe development as well as implementation of new types of ball grid array (BGA) assemblies crucially relies on the coupling of the demands of in-field conditions with results from advanced miniature experiments in combination with state-of-the-art finite element (FE-) computer simulations. The analyzing power of computers becomes even more important if the intention is to quickly develop highly miniaturized structures on the basis of an objective lifetime assessment and reliable damage characterization. Of particular interest and importance is the fatigue behavior of the solder ball joints in the aforementioned BGAs. The objective of this paper is, first, to numerically analyze the influence of changes in height of a BGA-assembly on the resulting thermal stresses and strains in the solder balls, the size of which is kept constant. Second, an attempt will be made to incorporate a developing intermetallic phase in the FE-model which is extremely thin and located at the junctions between the solder balls and the substrate and PC-board, respectively. It will be investigated how this influences the generation of irreversible strains in the eutectic solder material and, consequently, if and how the lifetime of the solder balls is affected. Specifically, the following configurations will be considered and modeled by means FE-analysis: . A super or S-BGA obtained by a reduction of the height of the previous model. . S-BGAS attached to a thinner size PC-board. . A y-BGA or chip-scale-package (CSP). As it is well known from the experimental as well as from the FE-point-of-view, the stresses and strains in a S-BGA (in combination with a suitable PC-board) are smaller than those in a standard P-BGA. However, the beneficial influence of a further reduction in size as well as change in geometry and load transfer when switching to CSPS still needs to be demonstrated.