D.Q. Yu

Improvement of wettability and tensile property in Sn–Ag–RE lead-free solder alloy

Abstract The influence of mixture (La, Ce) rare earth elements (RE) on wettability and tensile property in Sn–3.5Ag solder alloy was investigated. The wetting property was improved by 0.25–0.5% addition of (La, Ce) rare earth elements into the Sn–3.5Ag solder alloy, while over addition of the rare earth elements up to 1.0 wt.% reduced the beneficial influence. The ultimate strength and ductility were also enhanced by 0.25–0.5% addition of (La, Ce) rare earth elements, while the change of melting temperature was negligible.

The evaluation of the new composite lead free solders with the novel fabricating process

With the development of surface mount technology, especially for optical and optoelectronic devices, solders having improved mechanical properties are required for application that demand high reliability and dimensional stability. Using composite solders, by the addition of reinforcement particles to a conventional solder alloy, is an attractive potential method to enhance the mechanical properties. Recently, we developed a new process to fabricate composite lead free solders. 3%, 5%, and 10% weigh percentage of Y/sub 2/O/sub 3/ rare earth oxides were milled with RMA flux and then Sn-3Ag-0.5Cu powders were added, to form a new solder paste. The microstructures of the new composite solders are investigated and it is proved that with this new process, the reinforcement particles disperse in the solder quite finely and the addition of 3% and 5% rare earth oxides increases the shear strength of the solder joints dramatically, while 10% addition decreased the strength. At the same time, the addition does no harm to the wetting properties.

Microstructure and interface reaction between Sn-3.5Ag solder and electroplated Ni layer on Cu substrate during high temperature exposure

The microstructure and interface reaction between Sn-3.5Ag solder and electroplated Ni layer on a Cu substrate was studied. The results show that the electroplated Ni layer can effectively hinder the inter-diffusion between Sn-3.5Ag solder and Cu substrate after soldering and aging. The intermetallic compound (IMC) formed at the interface is quite thin after soldering and nano-size Ag/sub 3/Sn particles are also observed on the surface. Under low temperature (70/spl deg/C) exposure for 1000 h the IMC at the interface is Ni/sub 3/Sn/sub 4/. However, under high temperature (120/spl deg/C, 170/spl deg/C) exposure for 1000 h the IMC formed at the interface changes to (Cu/sub 1-x/Ni/sub x/)/sub 3/Sn/sub 4/ which implies that the Cu atoms from the Cu substrate diffuse into the Ni/sub 3/Sn/sub 4/ layer through the electroplated Ni layer. Coarse Ag/sub 3/Sn particles are also found on the surface of IMC after etching away the remaining solder at 170/spl deg/C aging for 1000 h. The growth kinetic of IMC layer during aging is x=(kt)/sup 1/2/ which implies that the growth of IMC is controlled by a diffusion mechanism. The activation energy of the IMCs is 132.404 KJ/mol which is larger than that of Cu/sub 6/Sn/sub 5/ (58.95 KJ/mol). It means that the growth rate of the IMCs is much slower than that of Cu/sub 6/Sn/sub 5/ under low temperature aging while a bit faster under high temperature aging.

Effects of Bi & Ni additives on the microstructures and wetting properties of Sn-Zn-Cu lead-free alloy

The microstructures and melting behaviors of (Sn-9Zn)-2Cu (SZC) lead-free solder with 3%Bi and various amount of Ni additions were studied in the experiment. The wetting properties and the interfacial reaction of these alloys soldering on a Cu substrate were also examined. The results indicated that the addition of 3% Bi could decrease the melting point and Ni would refine the microstructures and the rod-shape Cu/sub 5/Zn/sub 8/ phase changed into square-shape (Cu, Ni)/sub 5/Zn/sub 8/ phase. By using mildly active rosin (RMA) flux, the wetting angle of Sn-9Zn was 89/spl deg/ while that of SZC-3Bi-1Ni was 42/spl deg/. The improvement on wettability was due to the addition of the interface tension depressant Bi element and the formation of the (Cu, Ni)/sub 5/Zn/sub 8/ compound in the solder which refrained the oxidation of Zn atoms at the surface of the liquid solder. The lower surface tension lead to the better wettability. In addition, the interfacial phase of the solder/Cu joint was typically planar Cu/sub 5/Zn/sub 8/, which decreased from 4 /spl mu/m for SZC to 3 /spl mu/m in the SZC-3Bi-1Ni alloy.

High temperature synthesis of In-doped ZnO nano-structures on InP (001) substrate by pulsed laser deposition

ZnO nanostructures were grown on InP (001) substrate to achieve the In-doped ZnO nanostructure by pulsed laser deposition technique at high temperature. The FE-SEM images showed that the nanostructures grown at different temperatures have distinct dissimilar structures, and the morphology became better with increasing substrate temperature. The results of XRD showed that In element from InP substrates diffused into the ZnO layer to form In-doped ZnO nanostructures at the high temperature above 500°C. Energy dispersive chemical analysis (EDAX) is taken to ascertain the component of the nanostructure grown.