The available experimental data for the density and viscosity of liquid cadmium, cobalt, gallium, indium, mercury, silicon, thallium, and zinc have been critically examined with the intention of establishing both a density and a viscosity standard. All experimental data have been categorized into primary and secondary data according to the quality of measurement, the technique employed and the presentation of the data, as specified by a series of criteria. The proposed standard reference correlations for the density of liquid cadmium, cobalt, gallium, indium, silicon, thallium, and zinc are characterized by percent deviations at the 95% confidence level of 0.6, 2.1, 0.4, 0.5, 2.2, 0.9, and 0.7, respectively. In the case of mercury, since density reference values already exist, no further work was carried out. The standard reference correlations for the viscosity of liquid cadmium, cobalt, gallium, indium, mercury, silicon, thallium, and zinc are characterized by percent deviations at the 95% confidence level of 9.4, 14.0, 13.5, 2.1, 7.3, 15.7, 5.1, and 9.3, respectively.

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Reference Data for the Density and Viscosity of Liquid Cadmium, Cobalt, Gallium, Indium, Mercury, Silicon, Thallium, and Zinc

With more consumer products moving towards environmentally friendly packaging, making solder Pb-free has become an urgent task for electronics assemblies. Solder joints are responsible for both electrical and mechanical connections. Solder joint does not have adequate ductility to ensure the repeated relative displacements due to the mismatch between expansion coefficients of the chip carrier and the circuit board. Materials behavior of solder joints involves a creep–fatigue interaction, making it a poor material for mechanical connections. The reliability of solder joints of electronics components has been found playing a more important role in service for microelectronics components and micro-electro-mechanical systems. So many researchers in the world investigated reliability of solder joints based on finite element simulation and experiments about the electronics devices, such as CR, QFP, QFN, PLCC, BGA, CSP, FCBGA and CCGA, which were reviewed systematically and extensively. Synchronously the investigation on reliability of solder joints was improved further with the high-speed development of lead-free electronic packaging, especially the constitutive equations and the fatigue life prediction equations. In this paper, the application and research status of constitutive equations and fatigue life prediction equations were reviewed, which provide theoretic guide for the reliability of lead-free solder joints.

Reliability behavior of lead-free solder joints in electronic components

The Cu–Fe-based coating was produced on copper alloy substrate by laser induction hybrid rapid cladding (LIHRC). The results showed that the maximum laser scanning speed and the maximum powder feeding rate can be increased to 3200 mm/min and 110 g/min, respectively. The coating was mainly composed of α-Fe and e-Cu phases. At the bottom of coating, Cu-rich matrix took on planar growth and columnar dendritic morphology. In the center of coating, Fe-rich spherical particles containing a supersaturated Cu were embedded in Cu-rich matrix and many fine Cu-rich grains were precipitated inside the Fe-rich spherical particles. However, at the top of coating, the smaller Fe-rich spherical particles were embedded inside the larger Cu-rich spherical particles which were embedded in the dendritic Fe-rich matrix. The microhardness of coating was much three times higher than that of substrate.

Investigation of Cu-Fe-based coating produced on copper alloy substrate by laser induction hybrid rapid cladding

The Chinese medicine herb pair Flos Lonicerae japonicae (FLJ) and Forsythiae fructus (FF), is a representative heat-clearing (qing re) and detoxifying (jie du) combination that exhibits many pharmacological activities, including antibacterial, antiviral, antitumor, anti-inflammatory, and antioxidant effects. Extensive phytochemical studies have identified a series of bioactive compounds, such as chlorogenic acid from FLJ and forsythoside A from FF. This article provides a comprehensive review on the chemical and pharmacological principles of the traditional functions of FLJ-FF, and sheds light on further developments of this herb pair.

https://link.springer.com/content/pdf/10.1186%2Fs13020-015-0044-y.pdf

Chemistry and pharmacology of the herb pair Flos Lonicerae japonicae-Forsythiae fructus

http://www.ysxbcn.com/down/upfile/soft/20111118/32-p389.pdf

Microstructure and properties of CuCr contact materials with different Cr content

The recent development of Cu Cr contact materials for high power vacuum interrupters is concluded. It includes the origination of Cu Cr alloy and technical advantages; the characteristic of Cu Cr binary diagram and the difficulties in convenient casting process; the main preparation processes of Cu Cr alloy, such as powder sinter, sinter and vacuum infiltrate and arc melting process; the influence of impurities, such as residual gases, residual carbon and the third element in Cu Cr alloy, on the properties of Cu Cr alloy etc. Also, it summarizes the effect of Cu Cr alloy and its microstructure on the basic electrical properties of the vacuum contactor (such as circuit interruption ability, resistance to erosion by arc, current chop etc.). Finally, the developing direction of the Cu Cr contact materials in the future (Cr particle dispersion, alloy recycle and qui fast solidification process, and spray forming etc.) are also discussed.

Cu-Cr contact materials for high power vacuum interrupters

The influence of Ti on hydrogen diffusion in low carbon steel was studied by Davanathan's electrochemical method. The experimental results show that the strong trapping of hydrogen is appeared in the steel in which the Ti precipitated as dispersed TiC during aging after solution treatment. The trapping energies of the precipitation of dispered TiC are evaluated as 27.88±0.18 and about 21 kJ/mol respectively before and after the α→γ phase transformation of the steel. However, these do not coincide with the value of 94.55 kJ/mol reported by Pressouyre. The lowest apparent diffusion coefficient of hydrogen in the steel Fe-0.2Ti-0.1C is found after solution-treated at 1200℃ and aged at 550℃. It seems to be caused by the low temperature precipitate TiC with non-cubic structure and by many lattice vacancies which distort the local periodical potential fields around it.

TRAPPING OF HYDROGEN BY PRECIPITATE TiC IN LOW CARBON STEEL

A new control casting technique was designed for making homogeneity immiscible alloy in earth gravity field by Marangoni migration of the secondary phase drops in the melting alloy under a temperature gradient. In the technique, the droplet of the secondary phase ahead the solid-liquid interface of the melt of the immiscible alloy will make Stokes movement in gravity field and Marangoni movement in the opposite direction of gravity field in temperature gradient field. As a result, the net velocity of the droplets in the melt will be dependent on the size of the droplets. When the size of the droplets is very small,Marangoni movement of the droplets will dominate, otherwise Stokes movement will dominate. When the net velocity is zero, there will be a critical size of the droplet. By controlling the stability of the solidification process, an ingot with uniform distribution of the dropletscan be obtained. The critical size of the secondary phase droplets was estimated by the following equation Solidification test on Al-Bi and Al-Pb alloy showed that the size of the Bi or Pb particles in Al matrix is roughly the same order of magnitude as that obtained by above equation.Finally, a new conception, precipitation incubation period, was suggested in the discussion.

Preparation of homogeneity immiscible alloy by marangoni convection

Microstructure and thermal fatigue behavior of Pb-free solder interconnects in ceramic ball grid array (CBGA) packages were examined by cross-sectional microscopy, thermal cycling experiments and finite element modeling. In the as-reflowed condition, Cu6Sn5 and Ag3Sn formed at the solder interfaces with Cu and Ag metallizations respectively. Following thermal cycling, the Cu6Sn5 layer grew thicker and Cu3Sn was found at the interface with Cu metallization. On the ceramic side, visible thickening of the Ag3Sn layer was also observed. The morphology of Ag3Sn in the solder near the interface changed from strip-like to spherical shape. As a result of repeatedly thermal cycling, the fatigue crack appeared first at the corner of the solder ball with the chip, where the maximum shear stress was found by the finite element analysis. The cracks preferred to propagate along the Cu6Sn5/solder interface on the side of the print circuit board and in the solder joint near the interfacial Ag3Sn layer on the ceramic side.

Microstructure and Fracture of Pb-free Solder Interconnects in Ceramic Ball Grid Array Packages under Thermal Cycling

The buffer layer material itself may be influential to the bond strength between active brazing filler and ceramics. For Ag_(57)Cu_(38)Ti_5 filler metal, Cu or Ta is excellent buffer layer material, but Kovar or Ni-15Cr-15Co is worse. It was important to design a layer of soft buffer, such as Cu, to relax interfacial stress rather than hard buffer layer, such as Mo, to avoid stress. There is an optimum thickness range of soft buffer layer, saying h/L=0.02-0.1. It was a good solution to the interfacial stress problem to use soft/bard buffer layer to increase metal/ceramics joint strength. Finally, an idea of designing gradual materials as buffer layer between metal and ceramics was suggested.

Xian Aiping

Papers

Cu-Cr contact materials for high power vacuum interrupters

TRAPPING OF HYDROGEN BY PRECIPITATE TiC IN LOW CARBON STEEL

Preparation of homogeneity immiscible alloy by marangoni convection

Microstructure and Fracture of Pb-free Solder Interconnects in Ceramic Ball Grid Array Packages under Thermal Cycling

BEHAVIOUR OF BUFFER LAYER IN JOINING OF SIALON CERAMICS TO 4OCr STEEL