Yu-Xun Wang

Growth of CuAl intermetallic compounds in Cu and Cu(Pd) wire bonding

In this study, Cu wire bonds are aged at 150, 175, 250, and 350 °C for time ranging from 5 min to 2000 h. The top temperature of 350 °C is chosen to have the fastest kinetics, while maintaining the same types of stable intermetallics (IMCs) according to the Al-Cu binary phase diagram. Two types of Cu wire are used, including bare Cu wire and Pd coated Cu wire. To avoid possible damages from conventional mechanical polishing processes, all cross-sections are carried out by using an Ar ion beam cross-section polisher. Observations are carried out using a field-emission scanning electron microscope. The compositions of IMCs are determined by using a state-of the-art field-emission electron microprobe. According to the results of this study, in the as-bonded condition, the IMC formed is CuAl2. Its morphology is island-type and covers only a small percentage of the interface. During aging, the growth directions of IMCs are both lateral and perpendicular to the interface. At the lowest temperature (150 °C), the growth of IMCs is very slow. Even after 2000 h of aging, a large portion of Al remains un-consumed, and the IMCs formed are CuAl2 and CuAl. The growth rate increases very rapidly with temperature. At the highest temperature (350 °C), most of the Al is consumed after only 30 min of aging, and a thick layer of Cu3Al2 form over CuAl and CuAl2. Detailed morphological evolutions of IMCs for all temperatures are described. The Pd atoms in Pd-coated Cu wire do not participate in the interfacial reaction, and have no marked effect on the growth rate of IMCs. There is no detectable Pd signal in the IMCs. With the formation of IMCs, the Pd atoms are rejected into Cu in front of the IMCs.

Benzenetricarboxamide-cored triphenylamine dendrimer: nanoparticle film formation by an electrochemical method

By dropwise addition of a solution of tricarboxamide-cored triphenylamine dendrimer G1 in THF into water (5 × 10−6 M), nanoparticles with average diameters of 80 ± 20 nm were formed and collected by centrifugation. The particles show aggregation induced emission and emit green light under photoluminescence conditions. The particles can be fused together by applying a concept of electrochemical curing; the G1 particles are coupled through electrochemical oxidation to form a film. This method provides a fast assembling process for constructing films in a few seconds. Fabrication of electrochromic and fluorescence switching devices was demonstrated.

Effects of Aspect Ratio on Microstructural Evolution of Ni/Sn/Ni Microjoints

Under the simultaneous influence of volume shrinkage and surface solder diffusion, the microstructural evolution in Ni/Sn/Ni microjoints exhibits a conformable tendency among different joint sizes. This conformable tendency is the necking of the Sn layer and the initiation of voids which occur only near the periphery of the Sn layer. The reasons for this joint-size dependency have been theoretically evaluated and proposed in this study. This dependency remains applicable until the Ni3Sn4 layers growing in opposite directions impinge on each other. Afterward, microvoids are able to form everywhere along the centerline of the joints. It is hypothesized that the electrical and mechanical performance of microjoints is significantly related to the microstructures in these joints. With the help of the joint-size dependency proposed in this study, it is expected that the dimensional design of microjoints is capable of being optimized to assure high reliability.