Materials Science Forum Vol. 941

Abstract: Generally it is difficult to disperse nanosized particles uniformly in metal matrix. In this paper nanoSiC particles reinforced Al-5%Cu matrix composites were prepared by molten-metal process, combined with high energy ball-milling and ultrasonic vibration methods. Ultrasonic vibration treatment (UV) has been successfully used to disperse the particles distribution of nanoSiC_p particles in the matrix. Big aggregates of particles are eliminated by the effects of cavitation and the acoustic streaming of UV for 1 min. All the particles aggregates are eliminated and the particles are uniformly distributed in the melt after treated by UV for 5 min. The refinement of Al₂Cu phase in Al-Cu alloy is more obvious and more uniform distributed with the increase of UV time. The ultimate tensile strength (UTS), yield strength and elongation of the 1wt% nanosized SiC_p/Al-5Cu composites treated by UV for 5 min are increased by 37%, 9.5% and 270% respectively, compared with the untreated composites.

Abstract: To investigate the mechanism of crack initiation in the glass substrate, residual stress in the substrate was analyzed by the finite element method (FEM). A Si wafer that has the same mechanical properties of glass was prepared as the substrate. The thin Cu film layer was fabricated on the Si wafer by plating. The warpage of the wafer in the heat treatment process was investigated by laser displacement measurement. Residual stress was calculated by the obtained warpage value using the Stoney formula. It was found that the warpage becomes zero and the stress-free state occurs around at 150°C. On the basis of the FEM analysis result from 150°C to the room temperature in the cooling process, it was found that analyzed warpage values are almost analogous to measured ones. Also, it was confirmed that equivalent stress in the wafer in the vicinity of the Cu/Si interface increases and the stress-concentrated area expands there with increasing the thickness of the Cu film. The results indicates that crack initiation easily occurs in the glass substrate when the thickness of the Cu film increases. Moreover, from the results of the FEM analysis for the warpage of the wafer in the heating process, it was found that the analyzed warpage is good accordance with the measured one from room temperature to around 150°C.

Abstract: The effect of the cooling rate in bonding on IMCs formation and their morphology in the solder joint with Sn-3.0Ag-0.7Cu-5.0In (mass%) lead-free solder was investigated. As the substrate, the Cu plate and the Cu plate with electroplated Ni were prepared. Bonding was conducted in the vacuum atmosphere, and bonding temperature and time were 300°C and 10 minutes, respectively. The cooling rates in the bonding were changed from 0.02°C/s to 0.2°C/s. In both Cu/Cu and Cu/Ni joints, scallop-shaped IMCs form at the joint interfaces regardless of the cooling rate. In the Cu/Cu joint, Cu₆(Sn,In)₅ and Cu₃(Sn,In) layers form at the joint interface. In the Cu/Ni joint, (Cu,Ni)₆(Sn,In)₅ and (Cu,Ni)₃(Sn,In) layers form at the joint interface with Cu and the (Cu,Ni)₆(Sn,In)₅ layer forms at the joint interface with Ni. Die shear force of the Cu/Ni joints are a little larger than those of the Cu/Cu joints. Fracture occurs in the boundary between the scallop-shaped layer or the granular IMC layer and the layered IMC in both joints. The cooling rate from the peak temperature to solidification is an important factor to decide the shape of formed IMC. When the cooling rate is high and supercooling becomes large, formation of pillar-shaped IMCs occurs easily.

Abstract: Tensile and low cycle fatigue properties of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) lead-free solder were investigated using miniature size specimens and obtained data were compared to those of Sn-3.0Ag-0.5Cu (mass%). The microstructure of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge consists of dendritic β-Sn phases and ternary eutectic phases surrounding them which are composed of β-Sn, (Cu,Ni)₆Sn₅ and Ag₃Sn. Tensile strength and 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are superior to those of Sn-3.0Ag-0.5Cu at 25°C and 150°C. However, elongation of it is inferior to that of Sn-3.0Ag-0.5Cu at both temperatures. Fatigue lives of both alloys obey the Manson-Coffin equation and are analogous at 25°C. Although fatigue lives of both alloys decrease at 150°C, the fatigue life of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is inferior to that of Sn-3.0Ag-0.5Cu. At 150°C, the crack mainly progresses at grain boundaries of recrystallized grains. Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge has several grain boundaies which can be the origin of the crack so that fatigue lives degrade at 150°C.

Abstract: A pillar shaped intermetallic compounds (IMCs) dispersed solder joint is a highly durable joint to achieve large area joining. The aim of this study is to investigate the ideal dispersion amount of pillar shaped IMCs. The dispersion rate of pillar shaped IMCs depend on the joining temperature. Pillar shaped IMCs dispersion rates are 3.5% and 5.5% when the joining temperature are 300 °C and 330 °C, respectively. Longitudinal elastic modulus are improved by forming pillar shaped IMCs. As a result of examination of the durability by the thermal cycle test, the durability of the joint with the dispersion rate of 3.5% was similar to that without pillar shaped IMCs, while that with the dispersion rate of 5.5% was remarkably improved. In the case of the dispersion rate of 3.5%, pillar shaped IMCs unevenly distributed and cracks tend to progress. On the other hand, in the case of the dispersion rate of 5.5%, pillar shaped IMCs were uniformly dispersed throughout the joint and suppressed crack propagation. Comparison of durability between pillar shaped IMCs solder and indium added solder to verify the effect of pillar shaped IMCs demonstrated that pillar shaped IMCs solder were more durable than indium added solder.

Abstract: We studied effects of sputtering pressure on growth of (ZnO)_x(InN)_1-x crystal films deposited at 450°C by rf magnetron sputtering. Epitaxial growth of (ZnO)_x(InN)_1-x films was realized on single-crystalline ZnO template. X-ray diffraction measurements show that full width at half maximum of the rocking curves from the (101) plane of the films reaches minimum value of 0.11º at 0.5 Pa. The sputtering gas pressure is a key tuning knob for controlling the crystal quality of ZION films.

Abstract: We have fabricated a new semiconducting material, (ZnO)_x(InN)_1-x (called ZION hereafter), which is a pseudo-binary alloy of wurtzite ZnO (band gap: 3.4 eV) and wurtzite InN (band gap: 0.7 eV). We have succeeded in fabricating epitaxial (ZnO)_0.82(InN)_0.18 films on ZnO templates by RF magnetron sputtering. XRD measurements show that the full width at half maximum of the rocking curves from (101) plane and (002) plane are significantly small of 0.11 ̊ and 0.16 ̊, respectively, indicating good in-plane and out-of-plane crystal alignment. High crystal quality of the films was also proved by deducing the defect density from XRD analysis showing that the edge type dislocation density is low of 8.2×10⁸ cm^-2. Furthermore, we observed room temperature photoluminescence from ZION films as a parameter of incident angle of He-Cd laser light. The results indicate that an emission peak of 2.79 eV is originated from ZION.

Abstract: We analyzed fluctuations of interactions between low pressure reactive plasmas and nanoparticles formed in the plasmas, to shed light on origins of fluctuations of interactions and to control fluctuations in plasma processes. Spatiotemporal fluctuations of nanoparticle density develop not only in a linear way but also in a nonlinear way. The results suggest nonlinear interactions potentially induce spatial and temporal process fluctuations.

Abstract: Gallium nitride (GaN)-based thin films consist of its nanocrystals are grown on some metal-foils and a multi-crystalline silicon (Si) substrates. Their morphologies are compared with each other and the differences are discussed. Pillar-shaped nanocrystals are observed in the film grown on the multi-crystalline Si substrate while such structures are not observed in the films grown on the metal-foils when they are grown at higher growth temperatures. On the other hand, the morphologies of the films grown on the metal-foils approach to pillar-like structures by reducing the growth temperature. Band-edge emission is clearly observed in a cathodoluminescence spectrum of the film grown on the metal-foil at the reduced growth temperature.

Abstract: Thin layers of intermetallic (IMC) were prepared using Solid-Liquid Inter-Diffusion (SLID) process. 3μm of Tin was deposited on SiC dice, then soldered on a copper substrate at different temperature: 250-300-330-370°C and different soldering times: 5sec-300 sec - 15 min - 1h. The composition of the IMC was identified using energy dispersive X-Ray spectroscopy (EDX). Two types of intermetallic layers were identified: Cu₃Sn and Cu₆Sn₅. The samples were tested using die shear test. Then the internal stress was measured by X-Ray Diffraction (XRD). XRD spectrum obtained spotted only pure copper present underneath the intermetallic layer. The results showed that the level of residual stress is related to the amount of voids in the solder.