Search results

South Africa is the highest consumer of commercial energy per capita in Africa, ranking 16th in the world for primary energy consumption. It is also ranked among the bottom 50 of the 150 countries regarding energy efficiency. The cold chain is a large contributor through refrigerated transport vehicles. To comply with the changing climate regulations, cryogenic and eutectic systems are systems with great potential for small distance refrigerated transport. The purpose of this paper is to introduce eutectic system to medium distance refrigerated transport.

This study presents the potential use of Eutectic plates inside a medium refrigerated transport vehicle, by numerically investigating the characteristics of phase change material eutectic plates applied at low-temperature ranges. A physical model and a mathematical model for three-dimensional transient natural flow were developed as proposed by Xiaofeng and Zhang. Using the governing equation of mass, momentum and energy conservation, three Eutectic plate configurations were modeled and simulated in ANSYS Fluent for 5 h.

A uniform heat transfer and airflow condition inside a refrigerated compartment were predicted using the Reynolds stress model. The configuration with eutectic plates placed at the top and side showed great potential for the system functioning in the South African climate.

Medium refrigerated transport vehicle.

This configuration had a high-temperature distribution across the compartment and promoted high air circulations, showing that it could be ideal for medium refrigerated transport vehicles delivering perishable foodstuffs or non-food goods.

Sn‐Pb and Sn‐Ag bumps (130 μm diameter, 250 μm pitch) made using an electroplating process were studied. As a preliminary experiment, the effects of current density and plating time on the Sn‐Pb and Sn‐Ag deposits were investigated. The morphology and composition of the plated surface were examined using scanning electron microscopy. The shape and thickness of the solder bumps were also compared. Bump shear testing was performed to measure the adhesion strength between the solder bumps and the under bump metallurgy. In electroplating, the Sn‐Ag plating thickness was proportional to the current density, while plated Sn‐Pb thickness saturated above the limiting current density. The optimal conditions for solder bump fabrication were found at 6 A/dm² for 3 h in the case of Sn‐Pb bump plating and 6 A/dm² for 1 h for the Sn‐Ag bump plating. The bump shear strength for Sn‐Ag was found to be higher than that of Sn‐Pb.

This paper reviews the status of lead‐free solder development works. Some of the solder systems — Bi‐Sn, Bi‐Sn‐Fe, ln‐Sn, Sn, Sn‐Ag, Sn‐Ag‐Zn, Sn‐Ag‐Zn‐Cu, Sn‐Bi‐Ag, Sn‐Cu, Sn‐Cu‐Ag, Sn‐In‐Ag, Sn‐Sb, Sn‐Zn and Sn‐Zn‐ln — are discussed in more detail, while others are briefly commented on. In general, compared with eutectic Sn‐Pb solder, all the lead‐free solder alternatives investigated more or less exhibit some shortcomings, such as price, physical, metallurgical or mechanical properties. Relatively, Sn‐ln‐containing systems are more promising in terms of solder mechanical properties and soldering performance, although the price of ln may be a concern. Eutectic Sn‐Ag solder doped with Zn, Cu or Sb exhibits good mechanical strength and creep resistance, due to refined microstructure. The Bi‐Sn systems doped with other elements may have a niche in the low temperature soldering field. Eutectic Sn‐Cu has good potential due to its good fatigue resistance. The eutectic Sn‐Zn system modified with ln and/or Ag may be promising in terms of mechanical properties. Finding a lead‐free alternative for high temperature solders presents the biggest challenge to the industry.

The major objectives of this study are the engineering development and the structural analysis with finite element method (FEM) of a refrigerated container having a passive equipment and a remote control system to carry both fresh (+4°C÷±1°C) and frozen (−18°C÷−20°C) goods. The purpose of this paper is to offer some solutions to the many disadvantages of using phase change material (PCM) to refrigerate the insulated container for transporting both fresh and frozen goods.

In order to transport both fresh products (+4°C÷±1°C) and frozen products (−18°C÷−20°C), the PCM elements are filled with one eutectic liquid only, so as to avoid problems related to filling and emptying the eutectic plates, and to plate corrosion. Moreover, specially shaped air ducts and a cool flow control system are designed to maintain a uniform circulation of cool air and constant humidity values. All the structures of the container are correctly designed by means of FEM calculations to assure that all the structural, safety standards parameters are satisfied.

An innovative refrigerated container with PCM and a remote control system used to transport both fresh (+4°C÷±1°C) and frozen (−18°C÷−20°C) products, in which it is possible to maintain the temperature values for almost seven days, has been considered here. Many disadvantages due to the use of PCM have been eliminated. It is possible to maintain a uniform circulation cool air and humidity values within the design parameters by means of fans; moreover, this container is light and environmentally friendly. All structures of the container are designed using FEM.

This paper presents a refrigerated container with passive equipment and a remote control system to carry both fresh (+4°C÷±1°C) and frozen (−18°C÷−20°C) goods in which it is possible to maintain the temperature values necessary for almost seven days. The container is equipped with a remote control system powered by photovoltaic panels which works in real time, is capable of giving information about the environmental parameters set in it and monitors the state of products by means of a network of sensors. Furthermore, the remote control system can send information about the position of the container to a remote control centre. The relevant structural conditions are numerically (FEM) evaluated and reported.

The purpose of this paper is to examine the microstructure and evaluate the intermetallic compounds in the following lead‐free solder alloys: Sn_98.5Ag_1.0Cu_0.5 (SAC105) Sn_97.5Ag_2.0Cu_0.5 (SAC205) Sn_96.5Ag_3.0Cu_0.5 (SAC305) and Sn_95.5Ag_4.0Cu_0.5 (SAC405).

X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to identify the main intermetallics formed during solidification. Differential scanning calorimetry (DSC) was used to investigate the undercooling properties of each of the alloys.

By using XRD analysis in addition to energy dispersive spectroscopy (EDS) it was found that the main intermetallics were Cu₆Sn₅ and Ag₃Sn in a Sn matrix. Plate‐like ε‐Ag₃Sn intermetallics were observed for all four alloys. Solder alloys SAC105, SAC205 and SAC305 showed a similar microstructure, while SAC405 displayed a fine microstructure with intermetallic phases dense within the Sn matrix.

Currently, low‐silver content SAC alloys are being investigated due to their lower cost, however, the overall reliability of an alloy can be greatly affected by the microstructure and this should be taken into consideration when choosing an alloy. The size and number of Ag₃Sn plate‐like intermetallics can affect the reliability as they act as a site for crack propagation.

Composite ceramic has the excellent properties at normal and high temperatures, especially when the structure of the composite eutectic is triangular symmetrical. Obviously, mechanical behavior and fracture properties of composite ceramic closely relates to the micro-structure of symmetrical triangular eutectic. In order to reveal the mechanical properties of eutectic composite ceramic, it is necessary to determine the intrinsic strength of triangular composite eutectic. Since the fiber and matrix of triangular symmetrical composite eutectic sharing a same covalent bond, the theoretical cohesion strength of symmetrical triangular eutectic was obtained by the combination-separation displacement of intrinsic bond. Basing on micro-structure plastic deformation before fracture of composite eutectic matrix, the dislocation pile-up model of eutectic composite ceramics was established. And then intrinsic bond fracture shear stress of triangular symmetrical composite eutectic was given by using the theory of dislocation pile-up. According to the macroscopic structure properties of triangular symmetrical composite eutectic and the distribution of stress field of composite eutectic, intrinsic strength of eutectic was obtained. The results shows that intrinsic strength of triangular symmetrical composite eutectic possessed clear size-dependence and the stress decreases with the increases of the diameter of fiber inclusions.

Microwave modules and hybrid circuits have some unique requirements that demand extremely precise dispensing and placement, delicate handling and well controlled curing (or reflow). Assembly of these products can be challenging and defects may result in labor‐intensive manual assembly methods. A better way is to apply automated manufacturing techniques to the assembly of microwave modules and hybrid circuits and thereby eliminate many of the variables that may narrow the process window.

This report, presented as the keynote paper at Surface Mount International, is the culmination of joint efforts to assess the use of lead in electronics assembly. The study, which is presented in two parts, involved the collaboration of the following participants: B. R. Allenby and J. P. Ciccarelli, AT&T, Basking Ridge, New Jersey; I. Artaki, J. R. Fisher and D. Schoenthaler, AT&T Bell Laboratories, ERC, Princeton, New Jersey; T. A. Carroll, Hughes, El Segundo, California; D. W. Dahringer, Y. Degani, R. S. Freund, T. E. Graedel, A. M. Lyons and J. T. Plewes, AT&T Bell Laboratories, Murray Hill, New Jersey; C. Gherman and H. Solomon, GE Aerospace, Philadelphia, Pennsylvania; C. Melton, Motorola Inc., Schaumburg, Illinois; G. C. Munie, AT&T Bell Laboratories, Indian Hill, Naperville, Illinois; and N. Socolowski, Alpha Metals, Jersey City, New Jersey. Part 1 was published in the previous issue of Circuit World, Vol. 19, No. 2.