2021 International Conference on Electronics Packaging (ICEP), 2021
An allotropic phase transformation of CU<inf>6</inf>Sn<inf>5</inf> from a... more An allotropic phase transformation of CU<inf>6</inf>Sn<inf>5</inf> from a hexagonal <tex>$(\eta)$</tex> to monoclinic <tex>$(\eta^{\prime})$</tex> at 186–189 °C is scientifically interesting and technologically important to the microelectronic industry. As <tex>$\eta^{\prime}$</tex> lattice is crystallographically pseudosymmetrical with <tex>$\eta^{\prime}$</tex> the identifications of <tex>$\eta$</tex> and <tex>$\eta^{\prime}$</tex> and <tex>$\eta$</tex>-to-<tex>$\eta^{\prime}$</tex> transformation are extremely difficult via traditional analysis techniques. Herein, we conducted a study to characterize the allotropic phase transformation by Laue diffraction via synchrotron white X-ray nanodiffraction. The results showed that Laue diffraction analysis can well distinguish the two allotropic species <tex>$(\eta$</tex> and <tex>$\eta^{\prime})$</tex> in spite of the existence of pseudosymmetry in the η-Cu<inf>6</inf>Sn<inf>5</inf> lattice.
We investigated the influence of current stressing on a crystallographic microstructure of interm... more We investigated the influence of current stressing on a crystallographic microstructure of intermetallics in Cu/ Sn/Cu solder joints using electron backscatter diffraction (EBSD). After direct current (DC) stressing at 150°C for 10 d, the total Sn of the Cu/Sn/Cu was converted into a tri-layer structure of Cu 3 Sn/Cu 6 Sn 5 /Cu 3 Sn. The Cu 3 Sn layers that grew on the cathode and anode are asymmetrical during DC stressing. A preferred direction b 010N Cu 3 Sn along the current direction on the anode was found after current stressing.
We investigated the influence of current stressing on a crystallographic microstructure of interm... more We investigated the influence of current stressing on a crystallographic microstructure of intermetallics in Cu/ Sn/Cu solder joints using electron backscatter diffraction (EBSD). After direct current (DC) stressing at 150°C for 10 d, the total Sn of the Cu/Sn/Cu was converted into a tri-layer structure of Cu 3 Sn/Cu 6 Sn 5 /Cu 3 Sn. The Cu 3 Sn layers that grew on the cathode and anode are asymmetrical during DC stressing. A preferred direction b 010N Cu 3 Sn along the current direction on the anode was found after current stressing.
ABSTRACT Recently, Pd surface finishes over Cu substrates have been widely used in microelectroni... more ABSTRACT Recently, Pd surface finishes over Cu substrates have been widely used in microelectronic packaging to prevent pad oxidation before soldering and to improve the bondability with Cu wires. The interfacial reactions between these newly developed Pd-based substrates and Pb-free solders, particularly Sn-based solders, are of practical importance. To completely understand interfacial reactions and phase transformation phenomena, phase equilibrium information on solders, intermetallics, and substrate materials are required. In this study, the phase equilibria of the Cu-Pd-Sn ternary system at 200°C was investigated by scanning electron microscopy, electron probe microanalysis, and electron backscatter diffraction. Particular emphasis was placed on the Sn-rich corner of the isothermal section. To analyze the experimental results, a thermodynamic assessment was performed using the computer coupling of phase diagrams and thermochemistry method.
Spalling of intermetallic compounds in a massive scale has been reported in the literature for se... more Spalling of intermetallic compounds in a massive scale has been reported in the literature for several solder/substrate systems, including SnAgCu soldered on Ni substrate, SnZn on Cu, high-Pb PbSn on Cu, and high-Pb PbSn on Ni. In this work, a common mechanism based on thermodynamic arguments is proposed to explain this rather peculiar phenomenon that occurs across several systems. According
Journal of Materials Science: Materials in Electronics, 2006
The interfacial reactions between Sn-based solders and two common substrate materials, Cu and Ni,... more The interfacial reactions between Sn-based solders and two common substrate materials, Cu and Ni, are the focuses of this paper. The reactions between Sn-based solders and Cu have been studied for several decades, and currently there are still many un-resolved issues. The reactions between Sn-based solders and Ni are equally challenging. Recent studies further pointed out that Cu and Ni interacted strongly when they were both present in the same solder joint. While this crossinteraction introduces complications, it offers opportunities for designing better solder joints. In this study, the Ni effect on the reactions between solders and Cu is discussed first. The presence of Ni can in fact reduce the growth rate of Cu 3 Sn. Excessive Cu 3 Sn growth can lead to the formation of Kirkendall voids, which is a leading factor responsible for poor drop test performance. The Cu effect on the reactions between solders and Ni is then covered in detail. The knowledge gained from the Cu and Ni effects is applied to explain the recently discovered intermetallic massive spalling, a process that can severely weaken a solder joint. It is pointed out that the massive spalling was caused by the shifting of the equilibrium phase as more and more Cu was extracted out of the solder by the growing intermetallic. Lastly, the problems and opportunities brought on by the cross-interaction of Cu and Ni across a solder joint is presented.
2021 International Conference on Electronics Packaging (ICEP), 2021
An allotropic phase transformation of CU<inf>6</inf>Sn<inf>5</inf> from a... more An allotropic phase transformation of CU<inf>6</inf>Sn<inf>5</inf> from a hexagonal <tex>$(\eta)$</tex> to monoclinic <tex>$(\eta^{\prime})$</tex> at 186–189 °C is scientifically interesting and technologically important to the microelectronic industry. As <tex>$\eta^{\prime}$</tex> lattice is crystallographically pseudosymmetrical with <tex>$\eta^{\prime}$</tex> the identifications of <tex>$\eta$</tex> and <tex>$\eta^{\prime}$</tex> and <tex>$\eta$</tex>-to-<tex>$\eta^{\prime}$</tex> transformation are extremely difficult via traditional analysis techniques. Herein, we conducted a study to characterize the allotropic phase transformation by Laue diffraction via synchrotron white X-ray nanodiffraction. The results showed that Laue diffraction analysis can well distinguish the two allotropic species <tex>$(\eta$</tex> and <tex>$\eta^{\prime})$</tex> in spite of the existence of pseudosymmetry in the η-Cu<inf>6</inf>Sn<inf>5</inf> lattice.
We investigated the influence of current stressing on a crystallographic microstructure of interm... more We investigated the influence of current stressing on a crystallographic microstructure of intermetallics in Cu/ Sn/Cu solder joints using electron backscatter diffraction (EBSD). After direct current (DC) stressing at 150°C for 10 d, the total Sn of the Cu/Sn/Cu was converted into a tri-layer structure of Cu 3 Sn/Cu 6 Sn 5 /Cu 3 Sn. The Cu 3 Sn layers that grew on the cathode and anode are asymmetrical during DC stressing. A preferred direction b 010N Cu 3 Sn along the current direction on the anode was found after current stressing.
We investigated the influence of current stressing on a crystallographic microstructure of interm... more We investigated the influence of current stressing on a crystallographic microstructure of intermetallics in Cu/ Sn/Cu solder joints using electron backscatter diffraction (EBSD). After direct current (DC) stressing at 150°C for 10 d, the total Sn of the Cu/Sn/Cu was converted into a tri-layer structure of Cu 3 Sn/Cu 6 Sn 5 /Cu 3 Sn. The Cu 3 Sn layers that grew on the cathode and anode are asymmetrical during DC stressing. A preferred direction b 010N Cu 3 Sn along the current direction on the anode was found after current stressing.
ABSTRACT Recently, Pd surface finishes over Cu substrates have been widely used in microelectroni... more ABSTRACT Recently, Pd surface finishes over Cu substrates have been widely used in microelectronic packaging to prevent pad oxidation before soldering and to improve the bondability with Cu wires. The interfacial reactions between these newly developed Pd-based substrates and Pb-free solders, particularly Sn-based solders, are of practical importance. To completely understand interfacial reactions and phase transformation phenomena, phase equilibrium information on solders, intermetallics, and substrate materials are required. In this study, the phase equilibria of the Cu-Pd-Sn ternary system at 200°C was investigated by scanning electron microscopy, electron probe microanalysis, and electron backscatter diffraction. Particular emphasis was placed on the Sn-rich corner of the isothermal section. To analyze the experimental results, a thermodynamic assessment was performed using the computer coupling of phase diagrams and thermochemistry method.
Spalling of intermetallic compounds in a massive scale has been reported in the literature for se... more Spalling of intermetallic compounds in a massive scale has been reported in the literature for several solder/substrate systems, including SnAgCu soldered on Ni substrate, SnZn on Cu, high-Pb PbSn on Cu, and high-Pb PbSn on Ni. In this work, a common mechanism based on thermodynamic arguments is proposed to explain this rather peculiar phenomenon that occurs across several systems. According
Journal of Materials Science: Materials in Electronics, 2006
The interfacial reactions between Sn-based solders and two common substrate materials, Cu and Ni,... more The interfacial reactions between Sn-based solders and two common substrate materials, Cu and Ni, are the focuses of this paper. The reactions between Sn-based solders and Cu have been studied for several decades, and currently there are still many un-resolved issues. The reactions between Sn-based solders and Ni are equally challenging. Recent studies further pointed out that Cu and Ni interacted strongly when they were both present in the same solder joint. While this crossinteraction introduces complications, it offers opportunities for designing better solder joints. In this study, the Ni effect on the reactions between solders and Cu is discussed first. The presence of Ni can in fact reduce the growth rate of Cu 3 Sn. Excessive Cu 3 Sn growth can lead to the formation of Kirkendall voids, which is a leading factor responsible for poor drop test performance. The Cu effect on the reactions between solders and Ni is then covered in detail. The knowledge gained from the Cu and Ni effects is applied to explain the recently discovered intermetallic massive spalling, a process that can severely weaken a solder joint. It is pointed out that the massive spalling was caused by the shifting of the equilibrium phase as more and more Cu was extracted out of the solder by the growing intermetallic. Lastly, the problems and opportunities brought on by the cross-interaction of Cu and Ni across a solder joint is presented.
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