Magnetic properties of ball-milled Fe–Mn alloys

BCC, FCC and HCP phases in Fe–13.7 wt% Mn alloys were studied by Mössbauer spectroscopy and X-ray diffraction, after ball milling. The relative amounts of the HCP and FCC phases increase with milling times up to 9 h and decline afterwards. Preliminary AC susceptibility measurements show that the blocking temperatures change for different milling times.     

The Dual Functionals for the Generalized Ball Basis of Wang-Said Type and Basis Transformation Formulas

The generalized Ball curves of Wang-Said type with a position parameter L not only unify the Wang-Ball curves and the Said-Ball curves, but also include several useful intermediate curves. This paper presents the dual functionals for the generalized Ball basis of Wang-Said type. The relevant basis transformation formulae are also worked out.     

Effects of load and thermal conditions on Pb-free solder joint reliability

Reliability of lead-free solder joints has been a hot topic widely debated in the electronic industry. Most published data indicate that a change to lead-free soldering has the potential benefit of more reliable solder joints than the current Sn-Pb eutectic solder joints. However, in reality many mechanical, metallurgical, thermal, and environmental factors affect the service reliability of solder joints. This paper tries to shed some light on the effects of mechanical loading and thermal conditions on solder joint reliability. These conditions are determined not only by external environments but also by the solder alloy itself and the joint geometry. Analyses with first principles are carried out on solder joints of both areal array and peripheral packages. Effects on fatigue life of solder joint geometry, thermal and mechanical characteristics of components and substrate materials, and application conditions are discussed. The analysis helps explain why lead-free solder joints may not be more reliable in certain application conditions than the current Sn-Pb eutectic solder joints.     

波峰焊接工艺技术的研究

作为一种传统焊接技术,目前波峰焊依然在电子制造领域发挥着积极作用。介绍了波峰焊 接技术的原理,并分别从焊接前的质量控制、生产工艺材料及工艺参数这三个方面探讨了提高波 峰焊质量的有效方法。     

焊膏印刷工艺的控制

在表面安装工艺中，焊膏印刷是一道关键的工序，膏印刷工艺的控制曩着组装板的质量。漏版、焊膏与印刷机是组成焊膏印刷工艺的三项基本内容，三方面相互联系，决定着整个工艺的品质，从焊膏的理化特性、漏版的设计制造以及焊膏印刷机工艺参数的优化设定等方面对焊膏印刷工艺的控制作了初步探讨。     

Effect of rapid solidification and small additions of Zn and Bi on the structure and properties of Sn-Cu eutectic alloy

The Sn-Cu eutectic alloy has been produced by rapid solidification using the melt-spinning technique, and both Zn and Bi have been added individually to it, in the ratio 0.5 wt.%. X-ray diffraction (XRD) analysis and differential thermal analysis (DTA) have been carried out. Resistivity, Vickers microhardness (HV), and yield stress (σ_y) have been measured. Also a new method for measuring creep has been described using a HV tester. The creep measured by this method is termed “microcreep.” It is a quick, nondestructive method and requires a small sample, about 1 cm², with thickness 1 mm or less. The results show that formation of Cu₃₉Sn₁₁ occurs due to the addition of both Zn and Bi. The addition of Zn increases HV and σ_y, but slightly lowers the creep resistance; however, the addition of Bi deteriorates the creep resistance. Also, it is found that the creep rate of as-quenched melt-spun alloys is high.     

Tensile, creep, and ABI tests on sn5%sb solder for mechanical property evaluation

Sn5%Sb is one of the materials considered for replacing lead containing alloys for soldering in electronic packaging. We evaluated the tensile properties of the bulk material at varied strain-rates and temperatures (to 473K) to determine the underlying deformation mechanisms. Stress exponents of about three and seven were observed at low and high stresses, respectively, and very low activation energies for creep (about 16.7 and 37.7 kJ/mole) were noted. A maximum ductility of about 350% was noted at ambient temperature. Creep tests performed in the same temperature regime also showed two distinct regions, albeit with slightly different exponents (three and five) and activation energy (about 54.4 kJ/mole). Ball indentation tests were performed on the shoulder portions of the creep samples (prior to creep tests) using a Stress-Strain Microprobe^@ (Advanced Technology Corporation) at varied indentation rates (strain-rates). The automated ball indentation (ABI) data were at relatively high strain-rates; however, they were in excellent agreement with creep data, while both these results deviated from the tensile test data. Work is planned to perform creep at high stresses at ambient and extend ABI tests to elevated temperatures.     

Microstructure characterization of Sn-Ag solder joints between stud bumps and metal pads

The microstructure of the flip-chip solder joints fabricated using stud bumps and Pb-free solder was characterized. The Au or Cu stud bumps formed on Al pads on Si die were aligned to corresponding metal pads in the substrate, which was printed with Sn-3.5Ag paste. Joints were fabricated by reflowing the solder paste. In the solder joints fabricated using Au stud bumps, Au-Sn intermetallics spread over the whole joints, and the solder remained randomly island-shaped. The δ-AuSn, ε-AuSn₂, and η-AuSn₄ intermetallic compounds formed sequentially from the Au stud bump. The microstructure of the solder joints did not change significantly even after multiple reflows. The AuSn₄ was the main phase after reflow because of the fast dissolution of Au. In the solder joints fabricated using Cu stud bumps, the scallop-type Cu₆Sn₅ intermetallic was formed only at the Cu interface, and the solder was the main phase. The difference in the microstructure of the solder joints with Au and Cu stud bumps resulted from the dissolution-rate difference of Au and Cu into the solder.     

Stress relaxation and creep in an impression test

A localized stress relaxation technique is described suitable for testing miniature structures and components. The actual size of the area that can be tested depends on the size of the indenter and the sensitivity of the load measurement device. However, the indenter should not be so small that macroscopic theory of deformation cannot be used. The technique described includes a quantitative treatment of the data which can be handled by a computer. Extensive data collection can be made so that many deformation parameters can be examined by using this simple test.