Alexandru Vasile

4 P soldering model for solder joints quality assessment

The reliability of microelectronics components and assemblies it should be considered as expression of solder joints functionality. The functions are in close connection with the microstructure of the solder joints, which are the result of the soldering Process temperature gradient action over the trinomial solder alloy/Paste, electronic components terminals/Pin and PCBs Pads finishes. Consequently the solder joints quality can be correctly evaluated taking into consideration not only the severally intrinsic parameters of the trinomial elements, Pad-Paste-Pin, but also interrelate the complex reaction at the interface between them and interdependence with the soldering Process parameters. Therefore the solder joints can be considered result of a complex function of 4P elements defined before. In the paper, a 4P Soldering Model will be proposed in order to characterize the solder joints quality, emphasizing dynamics of Pad-Paste-Pin-Process elements synergistically interactions. The different pad finishes (NiAu, ImmAg, ImmSn, HASL, OSP) realized on PCBs having different core material, (FR4, Glass, Al, Cu, Al2O3), the components terminals/pins/balls having different finishes, the different solder paste type and the reflow soldering process (infrared-convection/vapour phase/LASER) with their typically parameters are the 4P Soldering Model variables. Practical experiments were designed in order to study 4P Soldering Model elements, Pad-Paste-Pin-Process, interactions.

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.

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.

EDLC characterization platform

Technological improvements have led to the development of low resistivity materials with higher surface which are capable of storing more energy in the form of electrical charge. These developments as well as a better theoretical understanding of the process of charge transfer, a process that appears in double layer type materials, led to the development of capacitors with high capacitance, known as EDLC (Electrochemical Double-Layer Capacitor). It is important for the user to be able to predict the behaviour of the EDLC in different conditions. This paper introduces a platform which can be used to obtain the capacitance as a function of voltage, time or temperature.

Remote Control Module for Infusion Pump Medical Device

In current medical practice best treatment can be obtain only with permanent monitoring, but lack of human resources leads to many patients under observation of only one medical person. This can be possible only using remote control of medical devices in client-server architecture: one computer in guard room connected to many medical devices from different rooms. This paper describes hardware and software aspects of such a structure and then presents their implementation in a real system -an infusion pump device upgraded with remote access capabilities using communication software written in high level language and an electronic module based on modern system-on-chip microcontroller. This work is apart of a research project of Romanian Ministry of Education and Research regarding modern infusion pumps.

Wearable Vital Parameters Monitoring System

The system we propose monitors body temperature, heart rate and beside this, it tracks if the person who wears it suffers a faint. It uses a digital temperature sensor, a pulse sensor and a gravitational acceleration sensor to monitor the eventual faint or small heights free falls. The system continuously tracks the GPS position when available and stores the last valid data. So, when measuring abnormal vital parameters the module will send an SMS, using the GSM cellular network , with the persons social security number, the last valid GPS position for that person, the heart rate, the body temperature and, where applicable, a valid fall alert or non-valid fall alert. Even though such systems exist, they contain only faint detection or heart rate detection. Usually there is a strong correlation between low/high heart rate and an eventual faint. Combining both features into one system results in a more reliable detection device.

Aspects of serial communication in a network of medical devices

Patient treatment in any hospital may require perfusion devices. Modern technology in this area is related to electronic-controlled devices that can be remotely accessed from a central place (guarding room). Because electromagnetic radiation is a big issue in medical world, remote access solutions must be wire-based, and RS485 serial communication is an effective solution. As part of a research project of Romanian Ministry of Education and Research regarding modern infusion pumps, deep investigations in serial communication aspects are performed. Different software communication protocols are analyzed and the optimal one is chosen according to different criteria - hardware and software implementation effort, costs and resistance to perturbations.

Optical transmission techniques

An optical transmission system is a method of transferring information in the shape of bits or symbols for the case of digital systems, and of analogue waves for the case of analogue systems, between fixed points located on a fiber optics cable. Today and in the near future there are numerous such transmission techniques available. The increase of demands for data transfer from phone subscribers can be met only by means of digital techniques applied in the local network, in addition to the use of digital telephone exchange and of the digital transmission systems in the trees network. In order to increase the quantity of information transferred through one fiber, optical multiplexing techniques have been conceived and tested. The optical multiplexing is additional to the electrical signal multiplexing. The requests for the access network will become more and more complex, a larger flexibility and a wider band being needed. For the purpose of complying with these requests, the coherent simultaneous or alternative transmission towards the optical amplifiers represents a factor of technical progress. The multiplexing with wave length division allows for more channels to be transported through the same fiber with different wave lengths, in one or both directions.

Optic fiber access network through SDH systems

The communication networks, highly specialized, were developed according to the type of transmitted information (vocal signal, data bases, TV signals). Presently, the networks’ evolution is targeted towards high velocities and services integration, networks characterized by SONET/SDH standards. SDH (Synchronous Digital Hierarchy) is the first standard, which provides an integrated system of network management and maintenance, ensures a uniform and global hierarchy of multiplexing and has advantages concerning the configuration of external network types. In this paper is described an access network for voice and dates communications, on optic fiber, built up with LOGES 2M Alcatel access routes (2 Mbps access) and with SDH transmission systems type Alcatel 1641SM (155Mbps).

Accurate modeling of supercapacitors for DC operation regime

Supercapacitors or Electrochemical Double Layer Capacitors (EDLC) have been intensively studied in the last years for promising applications in vehicle traction used in parallel with batteries or fuel cells, but also for energy storage purposes. The investigations presented in this paper offer an electric model that can be used to model the charge/discharge behavior in DC regime or low frequency pulses. In this sense, the methods for characterization are according to standard IEC 62391. It should be mentioned here that the models include a nonlinear capacitance and all elements are temperature dependent. The values of the circuit elements are valid for the specific capacitor, but the procedure for testing can be used in general situations.