SMTA International Conference Proceedings


Author: Tong Yan Tee et al.
Company: STMicroelectronics
Date Published: 9/21/2003   Conference: SMTA International

Abstract: Thermally enhanced BGAs are designed to have faster heat dissipation through features such as heat slug, heat spreader, and thermal solder joints. This paper studies the design comparison of five types of thermally enhanced BGAs, i.e. C2BGA (Conduction Cooled BGA), Metal-core BGA, Exposed Die LGA (Land Grid Array), Slug LGA and Spreader LGA. The solder joint reliability performance of thermally enhanced BGAs is benchmarked with conventional TFBGA.

Both global and local 3D FEA models are established to predict the fatigue life of solder joint during the thermal cycling test. Detailed pad design with realistic geometry of solder ball and non-linear material properties are considered in the model. The fatigue model applied is based on a modified Darveaux’s approach with non-linear viscoplastic analysis of solder joints.

For the test vehicles studied, the critical solder joints are located near the package corner. Design variations investigated include effects of key package dimensions and material properties. The choice of mold compound (MC) material is critical, and a material with higher CTE1 and lower modulus is preferred. Die size, die attach, and slug attach material have little effects on solder joint reliability.

It is observed that there is good correlation of fatigue life between modeling prediction and thermal cycling test for C2BGA. Reliability of C2BGA thermal solder joints is proven to be excellent, and heat can be conducted effectively away from the die to the PCB. This is crucial to the design of C2BGA. In addition, solder joint fatigue life is found related to package warpage induced during thermal cycling test. Design with smaller package warpage usually has a longer fatigue life.

Key words: BGA, thermal, fatigue, solder joint.

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