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Thermo-mechanical FEM analysis of lead free and lead containing solder for flip chip applications

: Gonzalez, M.; Vandevelde, B.; Vanfleteren, J.; Manessis, D.

International Microelectronics and Packaging Society -IMAPS-:
15th European Microelectronics and Packaging Conference & Exhibition 2005. Conference programme & proceedings : June 12 - 15, 2005, Brugge, Belgium, IMAPS
Reston, Va.: IMAPS, 2005
European Microelectronics and Packaging Conference and Exhibition (EMPC) <15, 2005, Brugge>
Fraunhofer IZM ()

A variety of lead free alloys have been developed to replace the commonly used tin lead solder. At present, the leading candidates are SnAgCu, SnAg and SnCu solder alloys. Nevertheless, the major concern regarding the rather new alloys is the fatigue reliability. The lack of reliability data of these solder materials makes every step towards the replacement of lead containing solder very difficult. A 3D Finite Element Model (FEM) was used to simulate the visco-plastic constitutive behavior of the solder when submitted to a thermal cycle test. When the solder is subjected to cyclic stresses generated during the thermal cycling, the reliability of the solder joint depends on its resistance to fatigue. The goal of the thermo-mechanical analysis in the electronic industry is to be able to predict, before extensive testing, the reliability of the solder joints. This paper focuses on predicting the thermomechanical behavior of fine pitch flip-chip packages using SnAgCu and SnPb solder alloys. Flip Chip attachment has been chosen in this study because is a cost-efficient interconnection technology with small size and superior electrical and thermal performance. Three different sizes and 2 different pitches were analyzed. The number of cycles to failure was correlated to the accumulated creep strain using an empirical relationship found in literature. Moreover, the results also indicate that this lead free alloys may be used as alternative solder to improve the resistance to fatigue when compared with standard lead containing solder.