Jenn-Ming Song

Microstructure and tensile properties of Sn–9Zn–xAg lead-free solder alloys

Abstract Microstructural features and tensile properties of Sn–Zn eutectic alloys with varying Ag content were examined in this study. Results indicate that the main effects of Ag addition were reduced strength and greater ductility due to the differences in the morphology and distribution of second phase particles. Also, a modified structure caused by rapid solidification resulted in better tensile properties.

Interfacial reactions between Bi-Ag high-temperature solders and metallic substrates

This study investigated the interfacial morphology and tensile properties of the joints between Bi-Ag solders and two metallic substrates, Cu and Ni. Instead of forming intermetallic compounds, grooving occurred at the intersections of Cu grain boundaries with the Bi-Ag/Cu interface and thus provided mechanical bonding. As for the Ni substrate, cellular NiBi3 was observed at the interface and also, massive NiBi3 in the form of long blades emanating from the interface was located within the solder region. A thin NiBi layer formed through a solid-state reaction between NiBi3 and the solder. The formation of those Ni-Bi intermetallics had a strong influence on the tensile strength and fracture morphology of the Bi-Ag/Ni joints.

One-step synthesis of uniform silver nanoparticles capped by saturated decanoate: direct spray printing ink to form metallic silver films

The one-step synthesis and spectroscopic characterizations of size-controlled silver nanoparticles are described. The transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric-mass analysis (TGA-MS) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the decanoate-protected silver nanoparticles. TEM analysis showed that spherical nanoclusters of 7.52 +/- 0.57 nm were produced. Furthermore, the particle sizes are uniform with a narrow size distribution. For all samples, Ag 3d(5/2) and 3d(3/2) components appeared at 368.5 and 374.5 eV, respectively, in the XPS spectrum; these values compare very well with the typical values of carboxylate-protected Ag nanoparticles. A thermal analysis mass spectrometer was used to analyze the desorption behavior of decanoate-protected nanoparticles. From the desorption maximum temperatures of 181 and 263 degrees C, activation energies of 27.2 and 32.2 kcal mol(-1) for the desorption processes in the Ag MPCs were obtained, assuming a first-order reaction and using a pre-exponential factor of 1 x 10(13) s(-1). A specific resistivity of 6.097 microOmega cm for the silver metal film (0.7 microm) on a Si wafer can be produced simply by thermal annealing of an Ag monolayer-protected clusters film under an atmosphere of 90% N(2)-10% H(2) at 300 degrees C for 1 h.

Alloying modification of Sn–Ag–Cu solders by manganese and titanium

Abstract Effects of Mn and Ti additives on the microstructure and solidification behavior of Sn–1.0Ag–0.5Cu alloys (SAC105), as well as mechanical properties, were investigated in this study. Results show that alloying of Mn and Ti resulted in dramatically reduced undercooling, coarse eutectic structure and extended volume fraction of proeutectic Sn of which the dendritic size was refined. Those thermal and microstructural changes might be ascribed to the formation of MnSn 2 and Ti 2 Sn 3 intermetallic compounds (IMCs) which appeared respectively in the Mn-doped and Ti-doped samples. Nanoindentation tests demonstrated that the heterogeneous IMCs produced by alloying were harder and stiffer than the inherent IMCs, Ag 3 Sn and Cu 6 Sn 5 . Worthy of notice is that the elastic modulus of SAC105 alloys decreased with only a minor alloying addition due to the shrunken eutectic regions and coarsened eutectic microconstituents. With a larger quantity of additives, an ascending elastic modulus could be obtained because of the strengthening effect by hard heterogeneous compounds.

Behavior of intermetallics in liquid Sn-Zn-Ag solder alloys

This study investigated the characteristics of the intermetallics that appear in Sn-Zn-Ag solder alloys, particularly their behavior in molten solder during cooling and remelting. The results indicated that the intermetallics, which deplete the Zn-rich phase, were present in the form of inhomogeneous dendrites and consisted of two intermetallic phases, ∈-AgZn 3 and γ-Ag 5 Zn 8 . These Ag-Zn intermetallics formed as the primary dendrites upon cooling from temperatures slightly below 300 °C. These intermetallics transformed into coarse nodules with a stable, high Ag-content phase when isothermally heated at 250 °C. These massive intermetallic particles tended to settle at the bottom of the melt due to low buoyancy. Isothermal heating at slightly above 300 °C resulted in the rapid melting of these intermetallics. Subsequent quenching caused numerous fine dendritic intermetallics to form throughout the solder.

Dissolution behavior of Cu and Ag substrates in molten solders

This study investigated the dissolution behavior of Cu and Ag substrates in molten Sn, Sn-3.5Ag, Sn-4.0Ag-0.5Cu, Sn-8.6Zn and Sn-8.55Zn-0.5Ag-0.1Al-0.5Ga lead-free solders as well as in Sn-37Pb solder for comparison at 300, 350, and 400°C. Results show that Sn-Zn alloys have a substantially lower dissolution rate of both Cu and Ag substrates than the other solders. Differences in interfacial intermetallic compounds formed during reaction and the morphology of these compounds strongly affected the substrate dissolution behavior. Soldering temperature and the corresponding solubility limit of the substrate elements in the liquid solder also played important roles in the interfacial morphology and dissolution rate of substrate.

Fabrication of single crystal CuGaS2 nanorods by X-ray irradiation

CuGaS(2) nanorods were synthesized by irradiating the precursor solution with intense X-rays. The products are single crystal nanorods with preferential [220] growth and a uniform size distribution. We also report on the photoresponse of drop-cast films of these nanorods.

Thermally assisted photoreduction of vertical silver nanowires

Vertically grown silver nanowires (Ag NWs) 100–150 nm in diameter and 5–10 µm in length have been successfully prepared by thermally assisted photoreduction (TAP) of aqueous silver nitrate (AgNO3) solution on anatase films without using surfactants, templates or seeds. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) show that the Ag NWs thus produced are single-crystalline with a preferred growth direction along [10]. Investigation of their electrical behavior, using a scanning electron microscope (SEM) equipped with a nano-manipulation device, showed that the resistivity of the Ag NWs is about 18.79 µΩ cm, indicating their excellent quality. The nucleation and yield (i.e. number of NWs per 100 µm2) are closely related to the crystallinity, surface morphology, and the photocatalytic ability of the anatase substrates. The length distribution of the Ag NWs is dominated by the temperature of the post-heat treatment, which affects the supply of thermal electrons for NW growth. It is also demonstrated that various face-centered cubic (FCC) metallic NWs, including gold and copper, can also be obtained by the TAP process. The yield of NWs is inversely proportional to the charge number of the metallic cations in aqueous solution.

Investigation of vibration fracture behavior of Sn-Ag-Cu solders under resonance

This study investigated the vibration fracture properties of Sn–Ag–Cu alloys with various Cu contents. Results show that the microstructure becomes finer with a higher Cu content. This leads to a lower damping capacity, higher deflection amplitude, and thus inferior vibration fracture resistance under a constant vibration force. It is of interest that when the Cu content reaches 1.5 wt%, the specimen possesses the highest damping capacity and greatest vibration life. The presence of massive primary Cu6Sn5 intermetallics probably accounts for this phenomenon.

Continuity and adhesion of Au deposits on electronic substrates by utilizing nanoparticle suspensions

Since nanosized metals exhibit a considerably lower melting point compared to bulk materials, nanometallic particle coated films can be deposited and cured to obtain electric conductors at a relatively low processing temperature. In this study, suspensions with Au nanoparticles of average size 3.9 ± 0. 7n m were prepared and spin-coated onto several commonly used electronic substrates (Cu, Ni and Al), and then thermally processed in a protective atmosphere. Experimental results show that the degree of continuity of the coated film on the Cu substrate was better than that on the Ni substrate, which was in turn better than the Al substrate. It was also found that isothermally heating the suspension at 300 ◦ C, a temperature greater than the melting point of the nanoparticles used, could produce fine Au deposits with acceptable adhesion. Worthy of notice is that, after a proper curing treatment, Au layers deposited with nanoparticle suspension exhibited superior adhesion to those produced by sputtering. (Some figures in this article are in colour only in the electronic version)