Search results

This study investigates the impact of three parameters such as: number of LED chips, pitch and LED power on the junction temperature of LEDs using a best heat sink configuration selected according to a lower temperature. This study provides valuable insights into how to design LED arrays with lower junction temperatures.

To determine the best configuration of a heat sink, a numerical study was conducted in Comsol Multiphysics on 10 different configurations. The configuration with the lowest junction temperature was selected for further analysis. The number of LED chips, pitch and LED power were then varied to determine the optimal configuration for this heat sink. A general equation for the average LED temperature as a function of these three factors was derived using Minitab software.

Among 10 configurations of the rectangular heat sink, we deduce that the best configuration corresponds to the first design having 1 mm of width, 0.5 mm of height and 45 mm of length. The average temperature for this design is 50.5 C. For the power of LED equal to 50 W–200 W, the average temperature of this LED drops when the number of LED chips reduces and the pitch size decreases. Indeed, the best array-LED corresponds to 64 LED chips and a pitch size of 0.5 mm. In addition, a generalization equation for average temperature is determined as a function of the number of LED chips, pitch and power of LED which are key factors for reducing the Junction temperature.

The study is original in its focus on three factors that have not been studied together in previous research. A numerical simulation method is used to investigate the impact of the three factors, which is more accurate and reliable than experimental methods. The study considers a wide range of values for the three factors, which allows for a more comprehensive understanding of their impact. It derives a general equation for the average temperature of the LED, which can be used to design LED arrays with desired junction temperatures.

Proposes a new qualifying procedure for handling sales leads to replace traditional inquiry/lead management methods. Offers ways of turning an inquiry into a lead, and qualifying and grading leads. Demonstrates the benefits of qualifying approach. Compares booth‐qualified leads with telephone qualified leads, and concludes that advertising pays off when they are followed by effective inquiry qualification and lead management techniques.

The purpose of this paper is to discuss the possibility of using soldering process for the bonding of chip-on-flexible (COF) light-emitting diode (LED) packages to heat sinks. The common bonding materials are thermal conductive adhesives. For thermal performance and reliability concerns, Tin-Bismuth (SnBi) lead-free solder paste was used for the connection of the COF packages and the Cu heat sinks by a soldering process in this study. Meanwhile, the geometrical effect of the SnBi solder layer on the thermal performance was also investigated.

The effects of the bonding materials and the area of the solder layers on the thermal performance of the LED modules were investigated by finite element simulation and experimental tests.

The SnBi soldered modules show much lower thermal resistance at the bonding layers than the adhesive-bonded LED module. Vertical heat transfer from the LED chips to the heat sinks is the primary heat dissipation mode for the SnBi soldered modules. Thus, the LED module with local solder layer shows similar LED thermal performance with the full-area soldered module. Meanwhile, the local soldering process decreases the possibility to form randomly distributed defects such as the large area voids and residue flux in the solder layers.

The research is still in progress. Further studies mainly focus on the reliability of the samples with different bonding materials.

COF package is a new structure for LED packages. This study provides a comparison between SnBi solder and adhesive material on the thermal performance of the LED. Meanwhile, the authors optimized the geometrical design for the solder layer. The study provides a feasible bonding process for COF packages onto heat sinks.

This study provides a soldering process for the COF LED packages. The thermal performance of the LED light source was improved significantly by the new process.

Corrosion, the destructive attack upon metals and alloys (and other materials) by their environment, is a common and widespread phenomenon. Although corrosion in domestic life may be restricted to seizure of nuts and bolts or unsightly rust stains, its occurrence in industry, and especially the chemical industry, may have serious economic effects. Corrosion may cause any of the following:

Excellent resistance to a wide variety of corrosive media is one of the most valuable of lead's unique properties which include softness, malleability, high density and low melting point. Consumption of lead in Europe is rising despite the attractions of other alternative materials which have made considerable progress, though not on so wide a front since they lack the versatility of lead. This three‐part review covers the many facets of lead as it is employed in preventing corrosion.

The electronics industry will implement lead‐free soldering in the near future. Lead‐free implementation steps are divided into lead‐free process and lead‐free product. The eutectic Sn/Ag/Cu alloy seems to have become the most widely used alloy in the implementation of lead‐free processes. In this study, the requirements for component placement are discussed from the lead‐free process point of view. Experiments concerning the self‐alignment capability and tack strength of both tin‐lead and lead‐free solder pastes are presented. According to the results, a bigger variation in self‐alignment capabilities can be expected when using a lead‐free paste. The paste properties affecting the self‐alignment mechanism and tack strength are also discussed.

The contamination of potable water due to the corrosion of lead pipes has been described in an earlier paper. The problem has been considerably reduced by the substitution of lead by copper pipes in new buildings. These copper plumbing systems, however, are often joined by lead‐tin solders which can corrode. The resulting concentrations of lead are often above the maximum admissable level of 0.05 mg 1— for drinking water. This paper reviews the use of solder and the various investigations into the corrosion of soldered joints.

AN OVERLAY bearing is a bearing with a precision electroplated overlay of lead‐tin or lead‐indium alloy, 20 to 40µ thick. This lead‐alloy overlay is generally applied to a copper‐lead or lead‐bronze substrate, which is itself bonded to a steel backing. Bearings of this construction are probably the most extensively used type of engine bearings; many millions are manufactured annually. The main functions of the overlay are to provide a seizure‐resistant surface, to increase the tolerance of the bearing for dirt and wear‐debris, and to protect the lead in the underlying copper‐lead or lead‐bronze alloy from corrosion by oxidized oil. When mineral oils are exposed to air oxidation for prolonged periods at elevated temperatures, weak organic acids are formed which can dissolve pure lead. The lead in copper‐lead or lead‐bronze is present as a separate, unalloyed phase, very susceptible to corrosion by weak organic acids. However, it has been known for some time that if lead is alloyed with indium or tin it is not corroded in this way. Most bearing manufacturers incorporate at least 4%w indium or 8%w tin in overlays to make them resistant to corrosion, but precise information on the amounts of alloying element required is not available.

This paper will describe tests of the interconnect reliability of BGA components with tin‐lead bumps soldered with lead‐free solder paste during temperature cycling. Tin‐lead BGA components soldered with tin‐lead solder paste and lead‐free BGA components soldered with lead‐free solder paste were used as a reference. The lead‐free solder used was eutectic tin‐silver‐copper. Two kinds of surface finishes were used on the printed circuit boards (PCB), an immersion gold over electroless nickel and an organic solderability preservative. The test PCBs were temperature‐cycled for 2500 cycles in the range of −40°C to +125°C and they were continuously electrically monitored during the cycling. The results of the temperature cycling test showed that lead‐ containing BGA components soldered with lead‐free solder paste don't show any serious reliability risks and can actually withstand temperature cycling stresses better than entirely lead‐free BGA assemblies.

There have been some recent and definitive developments in the selection of lead counsel and plaintiffs in class actions under the Private Securities Litigation Reform Act. The authors track the trends and report the developments.