Effect of bump shapes on the electromigration reliability of copper pillar solder joints

As the distance between the copper pillars and the size of the solder continues to shrink, the solder joints are subjected to extremely high current density and thermal energy density. This paper is aiming to analyze the electromigration reliability of solder joint with different shapes. Both experiment and finite element method (FEM) analysis were performed to investigate the Mean-time-to-failure(MTTF) of solder joints. Firstly, finite element models of solder joints were established. And then, the current density, temperature, and stress distribution in the solder joints were analyzed according to the model. After that, the chip samples were made by thermal compression bonding. The electromigration experiments were carried out at 150°C, and the interface evolution of solder joints with different shapes was analyzed. Finally, the modified Black's formula was adopted to calculate the MTTF of three different solder joints. According to the calculation results, it can be obtained that cylinder-shaped solder joints have better electromigration reliability than hourglass-shaped bumps and barrel-shaped bumps.