Mechanism of electromigration-induced failure in flip-chip solder joints with a 10-μm-thick Cu under-bump metallization

Abstract

The electromigration-induced failure in flip-chip eutectic SnPb solder joints with a 10-μm-thick Cu under-bump metallization (UBM) was studied without the effect of current crowding in the solder region. The current crowding occurred inside the UBM instead of in the solder joint at the current density of 3.0 × 104 A/cm2 because of the spreading of current in the very thick Cu UBM. In these joints, the failure occurred through a two-stage consumption of the thick Cu UBM in the joint where electrons flowed from the chip to the substrate. In the first stage, the Cu UBM dissolved layer by layer rather uniformly across the entire Cu UBM–solder interface. In the second stage, after half of the Cu UBM was dissolved, an asymmetrical dissolution of Cu UBM took place at the corner where electrons entered from the Al interconnect to the Cu UBM. Experimental observation of dissolution steps of the 10-μm-thick Cu UBM is presented. The transition from the first stage to the second stage has been found to depend on the location of current crowding in the flip-chip joints as the UBM thickness changes during the electromigration test. The current distribution in the flip-chip solder joints as a function of UBM thickness was simulated by three-dimensional finite element analysis. The dissolution rate of Cu UBM in the second stage was faster than that in the first stage. The mechanism of electromigration-induced failure in the flip-chip solder joints with a 10-μm-thick Cu UBM is discussed.

Optima design of contact opening for relieving current crowding effect in flip-chip solder joints

“…Since the different thickness of the UBM was adopted in the flip-chip solder joints [7,8], the effect of the UBM thickness on the optima diameter of the contact opening will also be discussed in this study. In Figure 3(a), the optima diameter of the contact opening is 100 J.lffi for the solder joints with I-J.lffi-thick eu UBM.…”

Failure mechanism of flip-chip circuit interconnects induced by electromigration

“…The significance of electromigration in Al interconnects has been established early in the development of integrated circuits [1][2][3][4]. The high density flip-chip solder bump is also sensitive to high current density except for Al interconnects [5][6][7]. Electromigration should be considered in the design process of an integrated circuit to ensure reliable operation over the target lifetime.…”

Failure of Flip-Chip Circuit Interconnects under High Current Density

“…The significance of electromigration in Al interconnects has been established early in the development of integrated circuits [1][2][3][4]. The high density flip-chip solder bump is also sensitive to high current density except for Al interconnects [5][6][7]. Electromigration should be considered in the design process of an integrated circuit to ensure reliable operation over the target lifetime.…”