Abstract: The diffusion character of metal atoms in the interconnects of metal strips/solder bump was observed by series solder bumps on flip chip which were stressed by high density electric current under high temperature. Assumed that the diffusion of atoms was controlled by electrical stress and chemical potential gradient，the diffusion behavior of all metal atoms in interconnects was investigated. The Ni atoms in the Ni(V) finishes directionally diffuse along the electron flow and accelerate the interface reaction of Ni and Sn by electromigration. Thus the Ni(V) finishes lose the action of the diffusion barrier layer in turn that resulted in the direct connection of Al and the solder. The Al atoms migrate in the electron flow by the electron wind force induced the Al atoms content in solder near the passivation via increases with the stressed time. The vacancies move in the opposite direction with the Al atom flux，and collect in the Al strips. Then the voids appear after the supersaturation of vacancies. The Sn and Pb atoms in the solder diffuse along the concentration gradient because of the non-leading action of electromigration. The atoms in the solder driven by the chemical potential gradient and compression stress form the upward fluxes. The upward diffusion of solder erodes the Al strips，which made the Al strips failure due to the voids and corrosion. The Al and Sn/Pb atoms were driven by their respective dominant force，and result in durative mutual diffusion until the interconnects take place the open circuit because of the difference of mass flux.

Keywords: 
• flip chip /
• bump /
• electromigration /
• diffusion