Norocel-Dragos Codreanu

Lead-free electronic system integrated in a Vapour Phase Soldering equipment prototype

The purpose of this paper is to present the applied research work, performed in POLITEHNICA University of Bucharest, Center for Technological Electronics and Interconnection Techniques (UPB-CETTI) in the frame of one European project and two diploma projects, oriented to the development of a VPS (Vapour Phase Soldering) equipment using ecological, lead-free, electronics and tailored to small and medium size electronics companies (SME) needs. The VPS technology seems to be today the most appropriate for many EMS companies, especially for SMEs. The lead-free electronic system developed in UPB-CETTI is in the stage of integration in a VPS equipment prototype, which is under construction in these months. The system can be embedded also in plotters, cutter plotters or milling/drilling equipment for PCB manufacturing.

PCB tracks thermal simulation, analysis and comparison to IPC-2152 for electrical current carrying capacity

Along with the introduction of the new IPC-2152 standard came several questions: What has changed? How does this new standard affect the PCB design? Are the simulation programs up to date with the standard? And the most important: In practice, how close are we to the standard? In this research, we developed a series of tests to analyze the real thermal behavior of tracks when charged with different constant currents. We used boards with different thicknesses (FR4 0.8mm, FR4 1.6mm, FR2 1.6mm, CEM 1.6mm) and 35um copper thickness and 1mm track width. We also performed simulations of the structures using Ansys. All the results were compared to IPC-2152 standard.

Investigations on current capabilities of PEDOT:PSS conductors

The organic electronics products becomes every day more and more present, especially known being organic light emitting diodes (OLED), organic photovoltaic cells (OPV) or organic thin film transistors (OFET). It is very important to have a reliable solution for interconnection of these devices in a manner similar to printed circuit boards. This paper will present results on electrical and thermal tests of organic conductors based on poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid (PEDOT:PSS) that can be used for data and power tracks. The samples are, and will be prepared by screen printing and ink-jetting, having silver paste and respectively ink based terminations. The results have shown that the current capabilities of PEDOT:PSS organic conductive tracks are limited by the dissipated power, due to relatively large resistance. As expected, the screen printed tracks having a higher thickness will have lower resistance. The temperature coefficient (TCR) has been found negative around -1000 ppm/°C.

Thermal investigations of solder joints used in power applications

A good way to characterize the quality of a solder joint is its thermal behavior at different currents and the current capabilities. The electrical current capabilities have been discussed in many other studies, but thermal investigations were not performed very often. The team developed a series of tests on boards with different configurations, and in all cases was proven that the solder joints heat up much less than the components or the tracks, and their temperature increases due to thermal conductivity from the surrounding elements.

Thermal investigations on high power LEDs

The present and near future lighting solutions will include surely power light-emitting diodes (LEDs). With increasingly power offered by the modern structures, thermal management issues can arise. In this paper we present thermal investigations on three type of power LED, of 1W, 3W and a 10W module. The investigations are oriented in direction of offering trusty suggestions and solutions regarding the thermal regime of discrete LED used as stand-alone or in assembly modules. The temperature will be determined through thermal simulation. The simulation based on finite-element models will bring valuable results, especially for multiple LED modules for which the model with thermal resistance offer only global results, without information of PCB temperature. For the measurements preparation the LEDs are attached to printed circuit boards (PCBs): classic FR4 and metal core PCB (MCPCB). The measurements will be done by combining thermocouples data acquisition system with IR thermovision camera.

Optimization of a heater geometry for flexible gas sensor applications

The need for low cost gas sensors has been required especially for home usage. Possible applications are, in buildings or basements where possible toxic gases can be accumulated, for example carbon monoxide, carbon dioxide, methane. This paper presents a first step in developing gas sensors based on impedance measurements. For optimal sensor operation a heater that should ensure uniform heating of the structure is required. We have proposed and realized a series of three geometries with different materials that will serve as heaters for future sensor development. The element of novelty consists in the use of flexible substrates. The heater will be supplied with appropriate voltage in order to obtain a working temperature between 80 and 100 °C. The temperature distribution was firstly simulated and subsequently measured by thermographical methods.

Modeling of heat dissipation in SMD chip components

The ever-rising pressure to reduce circuit board size to fit the ever-shrinking chassis challenges design engineers not just with size constraints, but power and thermal constraints concurrently. The power dissipation of a circuit is not necessarily reduced as technologies advance and circuits become smaller. It may not be an acceptable option to reduce the power dissipation and there may even be a drive to increase it. Reliability is a major concern of all electronic products manufacturers, and it is given by the reliabilities of the electronic components. One factor that determines the operation time of electronic components is temperature, and to be more precisely heat dissipation. There appears the problem of how heat is dissipated from SMD components, especially when no forced cooling is available.

Thermal investigation of a planar core power transformer

Power transformers integrating planar core technology are widely used in DC-DC systems that require high efficiency and low profile geometry, providing valuable manufacturing benefits as comparing to conventional wound wire technology. Planar transformers enhanced performance indicates the efficiency factor near unity. However, the presence of losses in transformers, although reduced, may conduct to a heat distribution analysis, which becomes more valuable in high density power systems. This article provides a thermal analysis over a planar transformer, of whom losses in the MHz region were the subject of a previous work. The thermal simulation has been performed considering the external top and bottom dual layer of the secondary winding turn. Furthermore, the transformer analysis may be of some concern in the heat distribution for both magnetic core and FR4 substrate in order to estimate the thermal stresses.

Microstructure comparative analysis of the solder joints based on SAC/SN100 soldering alloy type depending on the cooling rate

Microstructural analysis in the section of solder joints show a multilayer structure composed of IMC layers caused by the interface phenomena specific to soldering processes and a typical volume, unaffected by these phenomena, but depending of soldering process thermal profile, especially by the cooling zone parameters. In the paper were theoretically studied and experimentally evidenced genesis of the multilayer structure depending on the type of alloy and the specific cooling rate of the soldering process. Experiments were designed in order to obtain similar volumes of solder joints unaffected by the interface phenomena, taking into consideration Vapour Phase Soldering (VPS) processes characterized by different cooling rates and 6 types of Lead-Free solder pastes. The results highlight the microstructural differences in the unaffected by dissolution and diffusion volume of solder joints, between and for each type of solder pastes depending on the cooling rate. Based on these practical results could be improved the thermal profile of the soldering processes in VPS technology in order to increase the solder joints reliability.

SAC Alloys Implementation in Electronic Products Manufacturing

The paper intents to present the applied research performed by a few Romanian technological teams for an optimum implementation of SAC alloys in electronics industry, based on RoHS Directive, in order to investigate the behavior of SAC solder alloys in electronic products. Because manufacturers will need to ensure that their products comply with the requirements of European Regulations by July 2006 and designers are forced to change their strategy to accommodate lead-free soldering and not only, the paper shall emphasize the work on understanding and implementing SAC alloys, trying to underline advantages and disadvantages during the manufacturing flow. These new materials must be correctly modeled for their electrical characteristics when designers are involved in signal integrity analysis issues. Special component placement rules and new configurations of various structures/masks have to be designed for a good compliance between PCB layout design and manufacturing process. The main goal of the paper is to find and promote new methods for reducing to zero all unknown factors which can affect the assembling and manufacturing process of electronic products.