This study evaluated mechanical behavior of the intermetallic compounds (IMCs) formed at the interfaces between potential Pb-free solders (Sn-Ag-Cu and Sn-Zn) and the wires of Cu and Ag under different loading rates. Compared to Ag based IMCs, Cu based IMCs were harder and stiffer, but less strain rate sensitive. The morphology of the indent impression was found depending on the ratio of the modulus to hardness, and the crystal structure of the IMCs.

The effect of minor transition metal (TM) additives of Ni, Co, or Zn on the interfacial reactions of the solder joints between Sn–Ag–Cu (SAC) solder and the Cu/Ni(P)/Au substrate was investigated, especially subsequent to multi-reflowing. (Cu,Ni)6Sn5 formed at the interface of all the joints except that of SAC–Ni, of which the interfacial compound was (Ni,Cu)6Sn5. The interfacial compounds of the SAC–Co and SAC–Zn contained a small amount of alloying elements of less than 3 at.%. Two P-rich layers, Ni3P and Ni–Sn–P emerged at the interface of the SAC joints. Nanoindentation analysis indicates that the hardness and Young’s modulus of these two phases were slightly higher than those of the Ni(P) substrate, which were in turn much greater than those of the Cu–Ni–Sn compounds. Worthy of notice is that with TM additions, the Ni–Sn–P phase between Ni3P and interfacial compounds was absent even after 10 reflows. For the SAC–Co joints, the growth of Ni-containing intermetallic compounds within the solder gave rise to the excess Ni dissolution, which caused a discrete Ni3P layer and over-consumed Ni(P) substrate underneath the grooves in-between (Cu, Ni)6Sn5 scallop grains at the interface. This phenomenon is presented for the first time, and the mechanism is proposed in this study.

Using nanoindentation, this study develops the criteria to evaluate the creep performance of the intermetallic compounds (IMCs) formed at the interface of microelectronic solder joints. Regardless of crystal structure and melting point, the creep stress exponent (X), one of the parameters determining creep resistance, is in good agreement with tendencies of the work-hardening exponent (n) and also the ratio of yield stress (Y) to Young's modulus (E), which reveals the ability against plastic deformation.

To extend the application of lightweight Mg alloys in the automotive industry, this study suggests a b-based Mg-Li alloy (LAZ1110) with superior vibration fracture resistance by means of material design. In the coldrolled state, a strengthened b matrix by the additions of Al and Zn, as well as intergranular platelike a precipitates, which are able to stunt the crack growth, contributes to a comparable vibration life with commercial Mg-Al-Zn alloys under a similar strain condition.Due to the ultralow density and cold working ability, Mg-Li alloys, known as superlight alloys, have great potential for use as a structural material for transportation systems and portable electronic devices. An increase in the Li addition brings about the transformation of a (hcp) fi a + b (bcc) fi b and also an improvement of ductility along with the reduction in both the strength and strain hardening exponent. [1] To obtain a good combination of excellent formability and fair strength, Al, Zn, and Ag have been added for alloying modification. The literature indicates that the alloys containing Al and Zn are amenable to solution hardening and also aging hardening. [2] In the application of transportation systems, fracturing may occur in the structure under vibrating conditions, particularly when the vibration frequency meets local or general resonance even though magnesium is regarded as an excellent damping alloy. It has been reported that Mg alloys with high Li content possess great damping capacity but inferior strength, resulting in a poor vibration fracture resistance compared to Mg-AlZn when suffering the same vibration deformation. [3] The objective of this study is to develop a vibrationresistant superlight b-based Mg-Li alloy by way of alloying and process control. Nanoindentation was employed to examine the mechanical properties of each constitutional phase.The test materials include two Mg-Li alloys with the Li content, respectively, close to the left side and right side within the a + b two-phase region in which the Li content was from 5 to 11.5 wt pct. Those are Mg-11.2 wt pct Li-0.95 wt pct Al-0.43 wt pct Zn (LAZ1110) and Mg-5.71 wt pct Li-0.11Al wt pct-0.01 wt pct Zn (LA60) prepared for comparison. The compositions were analyzed by a glow discharge spectrometer. The as-received Mg-Li plates fabricated by extrusion were cold rolled to 3.3-mm sheets (rolling reduction: 35 pct) and then sectioned along the transverse direction. Parts of the cold-rolled LAZ1110 sheets were annealed at 250°C for 1.5 hours and referred to as the O samples. Phase identification of the samples was performed by an X-ray diffractometer operated at 30 kV and Cu K a radiation was used, with a scanning speed of 1 deg/min.In order to collect mechanical data for reference, tensile tests were performed. Rectangular specimens (gage length section: 20 mm 9 5 mm 9 3 mm) were prepared for tensile testing. The initial tensile strain rate was kept at 8 9 10 À4 s À1 . The mechanical performance of individual phase was evaluated by nanoindentation testing usin...