Li-Yin Hsiao

Synthesis and Characterization of Lead-Free Solders with Sn-3.5Ag-xCu (x = 0.2 , 0.5, 1.0) Alloy Nanoparticles by the Chemical Reduction Method

Due to the concerns of human health and the natural environment, the investigation of an alternative Pb-free solder is necessary. Currently, near-eutectic SnAgCu alloys are being developed as a lead-free solder. In this study, lead-free solders with Sn-3.5 Ag-xCu x = 0.2, 0.5, 1.0 nanoparticles were synthesized by chemical precipitation with NaBH4. The X-ray diffraction XRD patterns revealed that the Ag3Sn was formed due to the alloying process. From the XRD patterns, only Cu6Sn5 was formed when Cu concentration was as high as 1.0 wt % in the derived nanopowders. The formation of Ag3Sn and Cu6Sn5 gave strong evidence that the nanoparticles were mixed homogeneously. From transmission electron microscopy observation, the isolated particles were close to spherical shape and the particle sizes of powders were about 5 nm. The field emission scanning electron microscopy morphology of SnAgCu nanoparticles indicates that the major particle size of SnAgCu nanoparticles is in the range of 40 nm. It was evidenced from the differential scanning calorimetry profile that the SnAgCu nanoparticles could be melted successfully. In the wettability test, good metallurgical bonding was revealed between solders and substrates after reflow. Thus, the nanoparticles derived by the chemical reduction method in this study can be used as appropriate solder powders in electronic packaging.

Electrochemical Properties of Nanosize Ni–Sn–P Coated on MCMB Anode for Lithium Secondary Batteries

Tin-based alloy/carbonaceous composite materials are attractions for Li-ion rechargeable batteries because of their high capacity. A novel Ni-Sn-P mesocarbon microbead (MCMB) composite material for lithium-ion batteries was prepared by an electroless plating method. On the basis of X-ray color mapping analysis by electron probe microanalyzer, the nanosize Ni-Sn-P was precipitated not only on the surface but in the interior of MCMB powders. The Ni-Sn-P/MCMB composite anode exhibited large capacity (418 mAh/g in the tenth cycle) and the coulombic efficiency of the Ni-Sn-P/MCMB anode is as high as 98% even after the twenty-fifth cycle. In addition, the Ni-Sn-P/MCMB composite anode showed a significant improvement in electrochemical performance. Therefore, the Ni-Sn-P/MCMB provides a new type of anode material for lithium-ion batteries with an enhanced capacity.

Intermetallic compound formation and diffusion path evolution in eutectic tin‐lead flip chip solder bumps after aging

Purpose – In the flip‐chip technology (FCT) used in current microelectronic packages, a Ni‐based under‐bump metallurgy (UBM) is widely used due to its slow reaction rate with Sn. In this study, solders joints of eutectic Pb‐Sn with a Ni UBM were employed to investigate the intermetallic compound (IMC) formation after aging at 150°C for various periods of time.Design/methodology/approach – The compositions and elemental re‐distribution in the IMC formed due to the interfacial reaction between the Ni/Cu UBM and eutectic Sn‐Pb solders were evaluated with an electron probe microanalyzer. The interfacial morphologies were revealed with the aid of a field‐emission scanning electron microscope through a special etching technique.Findings – At the centre of the chip side, two IMCs were found between the solder and Ni metallization. The scalloped‐like IMC was determined to be (Cu, Ni)6Sn5, while the nodule‐like IMC was (Ni,Cu)3Sn4. However, at the edge of the chip side, three IMCs were revealed. The scalloped‐like...

Synthesis and Application of Novel Lead-Free Solders Derived from Sn-based Nanopowders

Two kinds of lead-free solders derived from tin-based nanopowders were fabricated. One was the lead-free solders with Sn-Ag-Cu nanopowders, and the other was nano-sized Cu₆Sn₅ doped Sn-Ag-Cu solders. The lead-free solders with Sn-Ag-Cu nanopowders were synthesized by chemical precipitation with NaBH₄. The isolated particle exhibited a near spherical shape with particle sizes around 5 nm. The primary particle size of Sn-Ag-Cu nanopowders was in the range of 40 nm. Microstructural characteristics of particle growth were evaluated by TEM and FE-SEM. The primary particles after precipitation were (Ag,Cu)₄Sn with a size of 4.9 nm. It was also revealed that (Ag,Cu)₄Sn transformed into (Ag,Cu)₃Sn, when the total amount of Sn contributed from both (Ag,Cu)₄Sn and Sn covering the (Ag,Cu)₄Sn overtook that of (Ag,Cu)₃Sn. The nano-sized Cu₆Sn₅ doped Sn-Ag-Cu solder paste was produced by mixing Cu₆Sn₅ nanopowder into commercial SnAg solder paste. To realize the effect of Cu₆Sn₅ nanopowder doping, the ball shear strength of the joint was further investigated. The fracture behavior of Sn-Ag-Cu solder joints was probed with respect to the fracture surfaces, interfacial morphologies, and ball shear strength. It was demonstrated that the creep strain rate sensitivity of nano- Cu₆Sn₅ doped composite solder was higher than that of commercial Sn-Ag-Cu solder, although the creep hardness of both solders was nearly identical

Intermetallic Compound Formation and Diffusion Path Evolution in the Flip Chip Sn-37Pb Solder Bump after Aging

In the flip-chip technology of current microelectronic package, Ni-based under-bump metallurgy (UBM) is widely used due to its slower reaction rate with Sn. In this study, solders joints of eutectic Pb-Sn/Ni-UBM were employed to investigate the intermetallic compound (IMC) formation after aging at 150 degC for various periods of time. The compositions and elemental re-distribution in the IMC formed due to the interfacial reaction between the Ni/Cu UBM and eutectic Sn-Pb solders were deliberately evaluated with an electron probe microanalyzer. The interfacial morphologies were revealed with the aid of a field-emission scanning electron microscope through special etching technique. In the center of the chip side, two IMCs were found between solders and Ni metallization. The scalloped-type IMC was (Cu,Ni)₆Sn₅, while nodular-type IMC was (Ni,Cu)₃Sn ₄. However, in the edge of the chip side, three IMCs were revealed. The scalloped-type IMC was (Cu_1-y,Ni_y) ₆Sn₅, nodular-type IMC was (Ni_1-x,Cu _x)₃Sn₄, and layer-type IMC was (Cu_1-z,Ni_z)₃Sn. On the basis of elemental distribution in the quantitative analysis for the IMC and the related phase transition among the intermetallic compound formation, two distinct diffusion paths were proposed to illustrate the interfacial reaction and phase transformation between IMCs and solder in the Sn-Pb joints aged at 150 degC. These diffusion paths demonstrated two kinds of phase equilibrium, including (Cu_1-z,Ni_z)₃Sn/(Cu_{1 - y},Ni_y)₆Sn₅/solder and (Ni_1-x,Cu_x)₃Sn₄/(Cu_1-yNi _y)₆Sn₅/solder