Lead-Free and PbSn Bump Electromigration Testing

Abstract

As the electronics industry continues to push for miniaturization, several reliability factors become vital issues. The demand for a high population of smaller and smaller solder bumps, while also increasing the current, have resulted in a significant increase in the current density. As outlined in the International Technology of Roadmap for Semiconductors (ITRS), this trend makes electromigration the limiting factor in high density packages. The heightened current density and correspondingly elevated operating temperatures are a critical issue in reliability since these factors facilitate the effects of electromigration. Therefore, as bump sizes continue to decrease, the study of electromigration reliability becomes crucial in order to understand and possibly prevent the causes of failure. A systematic study of electromigration in eutectic SnPb and Pb-free solder bumps was conducted in order to characterize the reliability of the Micro SMD package family. The testing includes both eutectic 63Sn-37Pb and 95.5Sn4.0Ag-0.5Cu solder bumps on an Al/Ni(V)/Cu under-bump-metallization. Mean-time-to-failure results are compared to Black’s Equation and cross-sections of the solder bumps are shown to analyze the mechanisms that led to failure.

Electro- and thermo-migration induced failure mechanisms in Package on Package

“…The EM and the TM induced mass flux values and mass flux divergences are clearly described with (1)- (5). For the temperature distribution used in (1)(2)(3)(4)(5) and the stress distribution, the dependencies are quite more complex. Hence a sensitivity analysis was performed by changing the material parameters of a few important parts of the package, and the heat transport coefficient (HTC) of the whole package.…”

“…In solder joints the material transport leads to void formation [2][3][4] and an accelerated intermetallic compound (IMC) growth [5,6]. While void formation directly leads to open contacts, the IMC (Cu 6 Sn 5 and Cu 3 Sn) growth influences the crack formation, and reduces the time to failure (TTF) during drop tests [7].…”

Finite element modeling on electromigration of solder joints in wafer level packages

“…The current density at the corner is approximately one order of the magnitude higher than the average current density in solder bumps. The third bump in Table 1 Electromigration basic parameters [3,[9][10][11][12][13][14].…”

“…The electromigration parameters for SnAgCu solder bump are listed in Table 1 [3,[9][10][11][12][13][14] where E A is activation energy, Z Ã is effective charge number, D 0 is self diffusion-coefficient, Q Ã is heat of transport, q 0 is initial electrical resistivity, a is temperature coefficient resistance, X is atomic volume, Boltzmann constant K B is 1.380662eÀ23, the electron charge e is 1.60219eÀ19, and the room temperature T 0 is 303.…”

Some remarks on finite element modeling of electromigration in solder joints

“…The epoxy, silicon chip and PCB in this model do not conduct electricity, thus very high resistance values are assigned to these materials. The electromigration parameters used in calculating the atomic fluxes by Equations 5-11 for SnAgCu solder bump are listed in Table 1 [10][11][12][13][14][15][16]. …”