The potential of newly-designed Zn-xSn (x ¼ 40, 30, and 20 mass%) and Zn-30 mass%In alloys as high temperature lead-free solders was evaluated, with particular focus on the fundamental thermal properties and phase stability during thermal and humidity exposure. From DSC results, the melting temperature of Zn-Sn alloys increased with decreasing Sn content, and the final undercooling was about 3 C. The liquid fraction of the alloys calculated using Scheil's model is lower than that of the alloys calculated according to the phase diagram by approximately 10 mass% at the eutectic temperature and 250 C. The coefficients of thermal expansion (CTE) of Zn-Sn alloys increased with decreasing Sn content, i.e. 29:2 Â 10 À6 ÁK À1 to 33:2 Â 10 À6 ÁK À1 in the temperature range of À50 C to 200 C for Zn-Sn alloys and 31:3 Â 10 À6 ÁK À1 in the temperature range of À50 C to 140 C for Zn-30In alloy. With increasing temperature above eutectic temperature, all alloys began to deform, indicating the formation of a liquid phase. The thermal deformation of Zn-Sn alloys decreased with increasing Sn content. The ultimate tensile strength (UTS) and 0.2% proof stress of the as-cast Zn-Sn alloys were almost the same, but the elongation of the as-cast Zn-Sn alloys decreased with increasing Sn content. After thermal and humidity exposure for 1000 h (85 C/85% Relative Humidity), only the outer surface of Zn-Sn alloys oxidized. However, Zn-30In alloy rusted quite seriously resulting in Zn oxidation after 1000 h. The UTS and 0.2% proof stress of Zn-Sn alloy slightly decreased with increasing exposure time. The elongation of Zn-Sn alloys decreased with decreasing Sn content for 100 h exposure. However, the elongation of Zn-Sn alloys showed no further degradation beyond 100 h exposure.

The interfacial reaction of Si die attachment with a high temperature lead-free solder of Zn-xSn (x = 20 wt.%, 30 wt.% and 40 wt.%) was investigated, and the currently used high temperature lead-free solder of Au-20Sn was compared. A sound die attachment to a Cu substrate can be achieved with Zn-Sn solder. No intermetallic compound (IMC) phase was observed in the solder layer, and only primary a-Zn and Sn-Zn eutectic phases were observed. At the interface with the Si die, with a metallization of Au/Ag/Ni, an AgAuZn 2 , IMC layer was formed along the interface, and the Ni coating layer did not react with the solder. At the interface with the Cu substrate, CuZn 5 and Cu 5 Zn 8 IMC layers were confirmed, and their thicknesses can be controlled by soldering conditions. During multiple reflows, the growth of these IMC layers was observed, but no additional voids or cracks were observed. For more reliable die attachment, a titanium nitride (TiN) coating layer was applied to suppress the formation of Cu-Zn IMCs. The Si die attached joint on the TiN-coated Cu was quite stable during the multiple reflows, and no visible IMC phase was confirmed in the interfacial microstructure.

The thermal fatigue reliability of Si die-attached joints with Zn-30wt.%Sn, high-temperature, Pb-free solder was investigated, focusing on the interfacial microstructure and joining strength of a Cu/solder/Cu joint during thermal cycling. A sound die attachment on an aluminum nitride (AlN) direct-bonded copper (DBC) substrate was achieved by forming Cu-Zn intermetallic compound (IMC) layers at the interface with the Cu of the substrate. During the thermal cycling test performed between À40°C and 125°C, thermal fatigue cracks were induced by the growth of Cu-Zn IMCs at the interface with the Cu. A thin titanium nitride (TiN) film was applied to suppress the formation of Cu-Zn IMCs. Adequate joint formation was accomplished by using an Au/TiN-coated DBC substrate, and only the TiN layer was observed at both interfaces. In conjunction with the TiN diffusion barrier, the Si die-attached joint created with Zn-30wt.%Sn solder exhibited a stable interfacial microstructure during thermal cycling. No microstructural changes, such as IMC formation, grain growth or formation of fatigue cracks, were observed, and the joining strength was maintained even after 2000 cycles.

About Emerald www.emeraldinsight.comEmerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of online products and additional customer resources and services.Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on Publication Ethics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation. AbstractPurpose -The paper's purpose is to provide a solution to a problem on dissolution and disappearance of copper electrodes in solder bath in lead free soldering on printed circuit board (PCB). Design/methodology/approach -The influence of the copper concentration, temperature, and flowing velocity of molten solder on the copper dissolution have been estimated, and it has been found that the dissolution rate of copper electrodes in Sn-3.0Ag-xCu solder alloys is defined by temperature and copper concentration in solder. Findings -It was found that increasing the copper concentration to 1.5 mass% in Sn-3.0Ag-xCu solder could lower the rate of copper dissolution to the equivalent level as that of the conventional Sn-Pb eutectic alloy at the temperature of 560 K. Research implications/implications -In this paper, a dissolution phenomenon has been studied on Sn-Ag-Cu system alloys. It is interesting about the effect of other elements for controlling the dissolution. Practical implications -The method to control the copper electrode dissolution in wave soldering is clarified. The copper dissolution rate for Sn-3.0Ag-1.5Cu solder can be lowered to the equivalent level as that of conventional Sn-Pb eutectic solder, even at 560 K. Originality/value -In this paper, a dissolution phenomenon has been evaluated by flowing molten solder which is close to one in a practical soldering. It is the most different point from earlier study.

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