Jedrzej Banaszczyk

Van Der Pauw method for measuring resistivities of anisotropic layers printed on textile substrates

Electrically conducting layers have been screen printed on woven textile substrates. Using the Van Der Pauw method for electrical resistivity measurements in thin layers, it was observed that the screen-printed layers showed anisotropic behavior. In order to be able to interpret the measurements correctly, a mathematical analysis of the measuring method has been established. From the experimental results one is then able to find the relation between the electrical resistivity in the warp versus the weft direction.

Generation of reduced dynamic thermal models of electronic systems from time constant spectra of transient temperature responses

This paper concerns the problem of generating reduced dynamic thermal models whose elements have physical interpretation. The compact models of an electronic system are generated here based on the analysis of the time constant spectra of system transient thermal responses. The proposed method is illustrated on a practical example of an integrated power amplifier with a heat sink. The experiments demonstrate the influence of contact resistance and cooling conditions on the resulting values of thermal model elements.

Dynamic thermal modelling of a power integrated circuit with the application of structure functions

This paper presents dynamic thermal analyses of a power integrated circuit with a cooling assembly. The investigations are based on the examination of the cumulative and differential structure functions obtained from the circuit cooling curves recorded during transient circuit temperature measurements. The experiments carried out and the comprehensive study of the computed structure functions rendered possible determination of the interface contact resistance and the heat transfer coefficient values necessary for numerical thermal simulations illustrating the influence of these thermal model parameters on circuit temperature.

Chimney Effect on Natural Convection Cooling of a Transistor Mounted on a Cooling Fin

The thermal impedance Z(th)(j omega) has been measured for the junction of a transistor mounted on a cooling fin. The setup was put inside a chimney in order to enhance the natural convection cooling. From the thermal impedance Z(th)(j omega) the influence of the chimney on the reduction in thermal resistance R-th=Z(th)(j omega=0) is clearly visible. A maximum improvement of almost 20% has been observed experimentally. Measuring the thermal impedance as a function of the angular frequency omega provides specific information about the thermal path being influenced by the chimney.

Current Distribution Modelling in Electroconductive Textiles

In this paper the current distribution within woven electroconductive textile sheets was investigated using a computer program written for the purpose of the simulations. An iterative method of solving very large resistor networks used to model textile sheets is discussed. The factors taken into account are the conductivity of the fibres, the contact resistance between the fibres, the contact angle a between the fibres and the electrodes, the size and the aspect ratio of the textile sheets. Maps of the current distribution generated by the program are included.

Application of Advanced Thermal Analysis Method for Investigation of Internal Package Structure

This paper presents an application of thermal analysis methods for the investigation of the internal structure of electronic device packages. The problem is illustrated based on the example of two silicon carbide power diodes. These diodes provided by different manufacturers have the same ratings and package type but one of the diodes exhibits oscillatory behaviour when used in a power converter. The presented results of thermal tests and analyses confirmed that there exist important differences between the two devices in their internal structures, possibly indicating the presence of some imperfections in the die attach or the wire bonds. These faults, in turn, have negative impact on their electrical performance in the investigated circuit.

About the collinear four-point probe technique´s inability to measure the resistivity of anisotropic electroconductive fabrics:

The sheet resistance of electrically conducting screen-printed surfaces can be measured with different techniques such as Van Der Pauw or four-point probe. As electroconductive textile materials show anisotropic behaviour we investigate the possibility of using the four-point probe method to measure the anisotropic properties of the electric conductivity. It was proved both theoretically and experimentally that no anisotropy can be detected with the collinear contacts of the four-point probe.

Determining Thermal Simulation Data from Transient Measurements

This paper illustrates how the information obtained from dynamic thermal measurements can be used directly for the determination of certain unknown thermal data necessary for simulation purposes. Experimental heating curves of a hybrid power amplifier are processed further to compute the time constant spectra of the thermal responses and to construct their corresponding structure functions. From these functions, the values of selected thermal model parameters, such as the heat transfer coefficient or the contact resistance are determined. Owing to this approach, it is possible to eliminate certain time consuming parameter optimization procedures.

Application of structure functions for the investigation of forced air cooling

This paper presents thermal analyses of a power amplifier placed in a wind tunnel. All the investigations are based on the transient temperature measurements performed during the circuit cooling process. The measured cooling curves were used to compute the cumulative and differential structure functions for the circuit with a heat sink. These functions helped to determine the optimal values of circuit model parameters necessary for numerical thermal simulations. The experiments demonstrated the influence of the wind speed on the value of the heat transfer coefficient and consequently on the temperature of the entire structure.

Thermal modelling of electronic systems based on spectral analysis of circuit temperature response

This paper discusses the problem of determining a thermal model of an electronic system based on the spectral analysis of its step temperature response. The proposed method yields equivalent RC Cauer ladder thermal models, which consist of only a few RC stages, but produce very accurate estimates of circuit temperature. Moreover, the values of model elements have physical significance. Such a thermal model can be easily used in the SPICE simulator for joint electro-thermal simulations of an electronic system. The entire process of the reduced model creation is illustrated in the paper on the practical example of an ASIC packaged and soldered to a PCB.