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 cross-interaction 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 Cu3Sn. Excessive Cu3Sn 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.

Interfacial reaction issues for lead-free electronic solders

Composite lead-free solders, containing micro and nano particles, have been widely studied. Due to grain boundary drag or Zener drag, these particles can refrain the solder microstructure from coarsening in services, especially for Cu6Sn5, Ag3Sn intermetallic compounds and the β-Sn phases. Due to dispersion hardening or dislocation drag, the mechanical properties of the composite solder alloys were enhanced significantly. Moreover, these particles can influence the rate of interfacial reactions, and some particles can transform into a layer of intermetallic compound. Wettability, creep resistance, and hardness properties were affected by these particles. A systematic review of the development of these lead-free composite solders is given here, which hopefully may find applications in microbumps to be used in the future 3D IC technology.

Structure and properties of lead-free solders bearing micro and nano particles

Review Article: Effect of alloying elements on properties and microstructures of SnAgCu solders

The objective of this review is to study the interfacial intermatallic compounds (IMCs) between Sn–Ag–Cu based solders and common substrates, which play a crucial role in solder joints typically present in Pb-free electronics manufacturing. The microstructural evolution of IMCs at the solder/substrate interfaces is analyzed, while the models and theories describing the formation/growth mechanism of interfacial IMCs are also introduced. We focus on the influence of a variety of factors that have been reported recently, including substrates, minor alloying, mechanical stress, electromigration and thermomigration etc., as full understanding of the mechanisms that determine the formation and growth of interfacial IMCs is important to reach for developing high reliability solder joints. In the end of this review, the characteristics of the IMCs are compared and illustrated, which have marked effect on the mechanical properties and fracture behavior as well as reliability of solder joints.

A review on the interfacial intermetallic compounds between Sn–Ag–Cu based solders and substrates

Interfacial intermetallic growth and shear strength of lead-free composite solder joints

Effects of intermetallic compounds on properties of Sn–Ag–Cu lead-free soldered joints

Chemically inducing room temperature spin-crossover in double layered magnetic refrigerants Pr1.4+Sr1.6-Mn2O7 (0.0 ≤ x ≤ 0.5)

Iron-transition metal-based binary and ternary alloys have attracted great attention due to their relevant mechanical, electrical, and magnetic properties. In this paper, we systematically investigate the structural, magnetic, and magnetocaloric behavior of as-milled Fe65T35 (T = Ni and Mn) alloy. The polycrystalline alloys were produced by the planetary ball milling, using a powder-to-ball ratio of 1:3. A structural study reveals that both Fe65Ni35 and Fe65Mn35 compounds have stabilized in α and γ mixed phase within the cubic crystal structure. The alloyed compounds are further characterized by high-resolution field emission scanning electron microscopy (HR-FESEM), which confirms the mixing of both metals in the alloying process. Temperature-dependent magnetic studies do not show any blocking in zero-field-cooled and field-cooled results; however, the field-dependent magnetization study demonstrates the ferromagnetic nature with small hysteresis in both compounds. Both compounds show a significant magnetocaloric effect over a wide temperature range around room temperature. Fe65Ni35 exhibit a slightly higher value in comparison to Fe65Mn35. In both the alloys, magnetic entropy change follows the power law behavior against the external magnetic field, and the value of exponent ‘m’ explains the presence of magnetic correlation. Our investigation in this study communicates that the phase control or coexistence of both phases may be efficacious in obtaining the desirable characteristic of magnetic and magnetocaloric demeanors in such a binary Fe-T alloy.

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S.H. Huh

Papers

Effects of intermetallic compounds on properties of Sn–Ag–Cu lead-free soldered joints

Chemically inducing room temperature spin-crossover in double layered magnetic refrigerants Pr1.4+Sr1.6-Mn2O7 (0.0 ≤ x ≤ 0.5)

Structural, Magnetic, and Magnetocaloric Studies of Ball-Milled Fe100−xTx (T = Ni and Mn) Alloy

Maneuvering the magnetic anisotropy in single-phase nanocrystalline α-FeCo via external static magnetic field assisted one dimensional growth

Effect of PVP Assisted Growth of α-Mn2O3 Nanoparticles on the Structural, Microstructural, Magnetic and Optical Properties