Relationship between edge drift and atomic migration during electromigration of eutectic SnPb lines

Abstract

The existence of an incubation stage before edge drift occurs was found by examining the electromigration characteristics of eutectic SnPb solder in an edge drift structure using in situ scanning electron microscopy and the interruptive test method. During this incubation stage, the depletion of Pb was observed at the cathode end. From the change in resistance, the activation energies for the incubation and edge movement stages were calculated to be 0.88 and 1.02eV, respectively. Based on a comparison of the activation energies for each stage with the previously reported values, it is believed that, during the incubation stage, Pb migrated before Sn and that the edge movement resulted from the migration of Sn. These results suggest that Pb depletion is a prerequisite for electromigration-induced void nucleation in eutectic SnPb solder.

Abnormal Failure Behavior of Sn-3.5Ag Solder Bumps Under Excessive Electric Current Stressing Conditions

“…Although there are significant resistance ratio variations from 5% to 100%, the activation energy maintains a constant value of 0.94 eV, with the exception of when the resistance ratio is 5%. Reported values for activation energy of IMC growth in Cu-Sn systems are 0.9 eV to 1 eV, 12,13,[19][20][21][22][23] which are comparable to the activation energy obtained in this study. Even if various reaction and diffusion mechanisms occur simultaneously during current stressing, the dominant mechanism is identified as interfacial void formation after excessive Cu-Sn IMC growth in the solder joint accelerated by severe Joule heating.…”

“…6b an additional error is included in the n value due to temperature variations between 177°C and 204°C by different Joule heating values for current density variations between 3 9 10 4 A/cm 2 and 4.6 9 10 4 A/cm 2 . This high n value compared with previously reported values 12,13,[19][20][21][22][23] implies that the electromigration test conducted in this study is highly accelerated and leads to changes in failure mode such as excessive local Joule heating inside the flip chip solder bump. Electromigration-induced electrical failure phenomena strongly depend on atomic diffusion kinetics, which is accelerated by both current density and temperature.…”

“…Some reports in the literature demonstrate a minor increase in resistance prior to the abrupt resistance increase at open failure for eutectic solder bump, which can be considered a dominant, void nucleation mechanism. 16,19,20 Figure 9 shows the change in activation energy as a function of the increasing resistance ratio. Although there are significant resistance ratio variations from 5% to 100%, the activation energy maintains a constant value of 0.94 eV, with the exception of when the resistance ratio is 5%.…”

“…The CuSn IMC thickness doubled at the substrate side. This asymmetric IMC growth seems to result from the well-known IMC polarity effect, 12,13,[19][20][21][22][23][24] which creates an electron pushing force that drives Cu atoms to migrate with the electron flow from the chip, as shown in Fig. 8a. Step 1 is related to the dissolution of the chip-side Cu UBM and Cu-Sn IMC and the thickening of the substrate-side Cu-Sn IMC due to a polarity effect.…”

Failure mechanisms of solder interconnects under current stressing in advanced electronic packages

“…Brandenburg and Yeh observed Pb migration with the electron flow above 100°C accompanied by phase separation in tin-lead solder [6]. This was also supported by later findings in EM experiments above 100°C [11,12]. In the case of EM at 100°C, Agarwal et al examined the EM behavior and identified that Pb is still the dominant diffusion species [13].…”