Mechanical Behaviors of Flip-Chip Packaging

Investigators: Toshio Nakamura and Yu Gu. Dept of Mechanical Engineering, SUNY at Stony Brook. 

Sponsor & Collaborator: Institute of Materials Research and Engineering, Singapore.

Project aimed at enhancing the understanding of mechanical behaviors as well as properties of materials used in solder bump, under bump metallurgy (UBM), and interconnect/metallization of IC's. The research project evaluates the reliability of these electronic components under various loading conditions and determining optimized configurations to minimize potential failures. The project mainly focuses on the investigation of internal stresses in the UBM and the interconnect regions, and systematic analyzes of the strength and fracture of these microstructures.

Outline

  • Models of flip-chip packages

  • Multi-scale finite element analysis

  • 2D fracture analysis

  • 3D stress analysis

  • Fatigue life estimation

Models of Flip-Chip Packages

       Flip-chip packages: 

  • high I/O capability

  • small profiles

  • good electrical performance

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  • extreme size differences among various components

  • considerable material mismatch

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       Material properties (only solder bump are treated as elastic-plastic material): 

Multi-Scale Finite Element Analysis

       The global model: 

       The cell model/region (Al bond pad, passivation, and UBM layers are added in): 

       FE mesh for the global model: 

       FE mesh for the cell model: 

       Global analysis (Mises stress)--- critical regions: 

       Cell analysis --- possible failure interface: 

  

2D Fracture Analysis 

       Short delamination analysis: same crack length but different (position) solder bumps. 

       Short delamination analysis: effect of crack length. 

       Behaviors of long delamination:  

   

3D Stress Analysis

       3 dimensional flip-chip packages (one quarter of the entire model): 

       FE mesh for the 3D global model: 

       FE mesh for the 3D cell model (1/2 of the 3D cell region): 

       Boundary displacement transmission from the global to the cell model: 

       3D global analysis: 

   

       Average shear strains of solder bumps in the 3D package and its comparison to the 2D model: 

       3D cell analysis --- Mises stress of small components and related interfaces: 

Fatigue Life Estimation

       Equivalent shear strains based on the 2D global model: 

       Changes of the equivalent shear strains: 

       Based on the Coffin-Manson law, when the fatigue ductility exponent is chosen as -0.5, the mean cycle of failure are 2318 from the change of averaged shear strains and 3024 from the change of maximum shear strains.