Mechanical implications of high current densities in flip-chip solder joints

We studied the electromigration damage to flip-chip solder joints of eutectic Sn/Pb under current stressing at room temperature with a current density of 1.3 × 10⁴ A/cm². The height of the solder joints was 100 μm. The mass accumulation near the anode side and the void nucleation near the cathode were observed during current stressing. In the preliminary experiment, the surface marker movement technique was used to measure the atomic flux driven by electromigration and to calculate the product of effective charge number and diffusivity (D × Z*) of the solder. Subsequent experiments revealed that the presence of thermomigration due to joule heating makes the extraction of the product of effective charge number and diffusivity erroneous when using marker movement technique.