Dubravka Ročak

Low-frequency noise of thick-film resistors as quality and reliability indicator

Abstract The non-linearity and the noise of thick-film resistors are parameters that can be used to make a prediction of resistor reliability. The noise spectroscopy measurements of thick-film resistors are proposed as a diagnostic tool for the prediction of possible types of failure. The correlation between noise spectral density data and the results of accelerated aging of thick-film resistors at high temperature were made for HS80 and 2000 resistor pastes.

A reliability study of the lead-free solder connections of miniature chip components on hybrid circuits

The results of the influence of lead-free solder paste, design and process parameters on the attachment reliability of chip surface-mounted components (SMCs) on thick-film conductor pads are presented. The purpose of the investigation was to compare the quality of the soldered joints made with new solder pastes that do not contain lead with joints soldered with standard SnPb solders. The miniature zero-ohm chip resistors were soldered with selected lead-free solder pastes. The visual appearance of the solder joint according to the standards of lead-free soldered components was compared with components soldered with SnPb solders. On the test sample with soldered chip resistors connected in series, the solder-joint resistance was measured before and after temperature cycling. On the same test sample the solder-joint resistance changes were measured with impedance spectroscopy. After temperature cycling the damaged samples were analysed with SEM and EDS. The reliability test results after temperature cycling indicate two lead-free solder pastes that are the most convenient for chip-component soldering on thick-film conductor pads with the reliability of the joints being equal or better than solder joints with Pb-containing solder paste.

Comparison of new no-clean fluxes on PCBs and thick film hybrid circuits

Some new no-clean fluxes were investigated by measurement of ionic contamination of flux residues and influence of flux residues on surface insulation resistance (SIR) and electromigration (EM) between soldered conductors. Also copper corrosion test in the humidity chamber was performed on samples with fluxes investigated. The results of SIR, EM and copper corrosion tests were compared on test samples prepared as printed circuits and hybrid circuits.

Silicon pressure sensors with a thick film periphery

Silicon piezoresistive pressure sensor dies are mounted on a ceramic substrate where the signal conditioning electronics are implemented in thick film technology. In this paper some of these techniques, e.g. special attachment and bonding requirements, methods for temperature compensation, the principles of parameter adjustment, and encapsulation, are presented. For illustration two examples are described. The first is a multipoint monitoring system with 720 measuring points in a test mattress. The second example is a family of industrial pressure transducers.

Solder paste for fine line printing in hybrid microelectronics

A series of experiments was performed to evaluate the deposit consistency of solder paste from various producers, for fine line printing. Two main variables were chosen to determine the quality of the solder paste printing process. The results of a two-factorial experimental design are presented and the effect of these factors on solder paste thickness and visual appearance are discussed.

Low frequency noise in film resistors

The transport of charge carriers in conducting layers generate excess low frequency noise which is 1/fa type. The main problem is if 1/f fluctuation is caused by fluctuation of number of carriers acting in transport or by mobility fluctuation due to scattering process. The objective of our research consisted in finding a correlation between the noise spectral density and nonlinearity on one hand and device time stability and reliability on the other. The noise of thick film resistor pastes 2041 and 8039 (10 kΩ/sq.) was measured on resistors dimensions of 0.3×0.3 mm and 1×1 mm. The resistors were terminated by Ag/Pd and Ag conductors. Experimentally was observed, that noise spectral density is inversely proportional to the square of the sample length.

Thick Film Interconnections for Sensor Applications

Signal processing for some sensor applications demands circuits with specific characteristics, such as miniaturization, high functional density, high number of input ports, and high signal speed. For some sensors operating in industrial environments protection from electromagnetic interference (EMI) is also required. Thick film technology is convenient way to realize such circuits, but some special technological processes must be used. In this paper some of these will be presented through some examples of thick film multilayer hybrids. First is the multipoint pressure measuring system for medical applications. It is designed for measuring 720 pressure points in a test mattress for hospital patients. The second example is thick film multilayer interconnections for sensor array readout with high function density, high signal speed, and low interlayer capacitances. The third example is of thick film hybrid circuits for proximity switches.