Damian Nowak

Analysis of steady-state and transient thermal properties of cermet, polymer and LTCC thick-film resistors

Purpose – The purpose of this paper is to present the results of thermal analysis of cermet resistors made on alumina or LTCC substrate and polymer thick-film resistors embedded in FR-4 substrate. Design/methodology/approach – The study was performed using a thermal imaging method. The research was carried out with an additional consideration of such factors as sheet resistance (which depended on the type of resistive paste), the size and topology of element and the kind of contact material (Cu, Ag or Ni/Au). A few key points on the element were specified for which a more thorough analysis was carried out. The results were approximated by physically acceptable function which allowed to determine the influence of different mechanisms of heat transfer and determine their time and thermal constants. Findings – The effectiveness of heat dissipation from resistor is determined by the type of substrate material, width of conductive paths, and contact material. The best results were observed for elements with wi...

Miniaturization of thick–film resistors by laser–shaping

This paper presents manufacturing process of laser-shaped thick-film resistors as well as their chosen electrical, geometrical, microstructural and stability properties. Test structures were based on commercially available conductive and resistive pastes deposited on Al2O3 substrates. Resistors made in standard screen printing process after firing were patterned using laser beam in order to minimize their planar dimensions to tenths of millimeter and below. Prepared samples were subjected to number of electrical tests and some characteristic parameters like temperature coefficient of resistance (TCR) were calculated based on these measurements. Test samples were also exposed to long-term thermal ageing. Moreover the laser profilometer was used for three-dimensional characterization of components. Scanning electron microscope (SEM) was used for the microstructural analysis and the EDS (Energy Dispersive X-ray Spectroscopy) of samples is given.

Analysis of electromigration phenomenon in thick-film and LTCC structures at elevated temperature

Studies on electromigration phenomenon in thick-film structures on alumina and LTCC substrates are presented in this paper. The effects of storage of Au and Ag electrode patterns in temperature range up to 300 °C under voltage bias were examined. The leakage characteristics of electrodes with 100 μm spacing at 50 V dc bias as a function of time and temperature are presented and analyzed. Scanning electron microscope (SEM) equipped with the energy-dispersive X-ray spectroscopy (EDX) detector was applied for determination of metal ions transport. Test structures with Au-based conductive material are much more resistant to electromigration than Ag-based layers.

High temperature LTCC package for gas sensor

Ceramic technologies, especially LTCC (Low Temperature Co-fired Ceramics), offer a reliable platform to build highly stable and reliable sensors and packages, possible for application in harsh environment such as high temperature, high pressure, aggressive media and space. LTCC allows also to fabricate resistors, capacitors, inductors, heaters and many other passive components buried within ceramic substrate. In this paper package for SiC-based hydrogen sensor is presented. Heater located inside package heats the gas sensor whereas temperature sensor allows to control current temperature. Moreover package enables electric connection between SiC-based sensor and outside contacts. It also protects wire connection against mechanical destruction. The temperature field distribution was simulated. Moreover, the effect of pulse temperature changes and long-term ageing on electrical parameters of heater were investigated. Basic electrical parameters of integrated heater as well as temperature field distribution on sensor surface were presented, too.

Mechanical properties of SMD interconnections on flexible and rigid substrates

Purpose – The paper aims to investigate on the mechanical properties of surface-mount device (SMD) interconnections made on flexible and rigid substrates. Design/methodology/approach – The durability of joints to shear strength was measured with tensile machine. Investigations were carried out for 0402- and 0603-sized ceramic passives and integrated circuits in SOIC-8, TSSOP-8, XSON3 and XSON6 packages. Three types of flexible substrates (Kapton, Mylar and Pyralux) and two types of rigid substrates (LTCC and alumina) were used. SMD components were mounted with SAC solder or electrically conductive adhesive. Contact pads were made of Ag-based polymer paste on flexible substrates and PdAg-based cermet paste on ceramics. The shear strength was measured for as-made and long-term thermally aged test structures. The average durability and standard deviation were compared for different combination of materials. Moreover, mechanical properties of interconnections made of polymer thick-film pastes or electrically/...

Reliability of fine-line thick-film and LTCC conductors at high-temperature operation

This paper presents systematic studies of thick-film or LTCC fine-line conductors made with the aid of laser-shaping and operating at temperature up to 400°C. The minimum dimensions i.e. conductive path width and spacings were 50 μm. Such small patterns have been created by laser cutting of fired Au- or PdAg-based conductive films. Laser system equipped with Nd:YAG-laser (beam wavelength of 1064 nm) was applied. Additionally, part of the structures was covered with protective overglaze layer. The geometrical as well as electrical and stability properties in temperature range between 25°C and 400°C were measured and analyzed.

HIGH TEMPERATURE PROPERTIES OF MINIATURIZED THICK-FILM COMPONENTS

This paper presents systematic studies of thick-film or LTCC microcomponents (capacitors, inductors) made with the aid of laser-shaping and operating at temperature up to 450 °C. The minimum dimensions i.e. conductive path width and spacings were about 30 μm. Such small patterns have been created by laser cutting of fired Au- or Ag-based conductive films. Laser system equipped with Nd:YAG-laser (beam wavelength of 1064 nm) was applied. The inductance, capacitance, as well as parasitic impedances were measured in the frequency range from 10 kHz to 110 MHz and temperature between 25 °C and 450 °C.

Simulations of passive components in LTCC technology

The particular group of passives are magnetic and capacitive devices, which electrical parameters are tightly correlated with their geometry. A great variety of inductors and capacitors manufactured in different technologies are commonly applied in electronic circuits. Special attention should be paid at planar components that can be easily fabricated for example by thick-film and LTCC technology and integrated in Multi-Chip Modules (MCM). This paper presents some theoretical studies of planar inductors and capacitors. Specialised software for high-frequency EM (Electromagnetic) analysis was used for investigation of correlations between geometry of planar components and its basic parameters. Influence of planar dimensions, width of conductor paths and spacing on inductance/capacitance, quality factor and resonance frequency was determined.

Long-term stability of resistors embedded in printed circuit board

This paper presents principle of manufacturing process of thin-film resistors embedded in printed circuit boards (PCB) as well as their chosen electrical and stability properties. Test structures were fabricated on FR-4 laminate with Ohmega-Ply® technique basing on nickel-phosphorus alloy (NiP). The thickness of resistive foil was 0.4 µm and 0.1 µm with sheet resistance 25 Ω/sq. and 100 Ω/sq., respectively. Moreover, part of the samples was covered with two different types of cladding - Resin Coated Copper (RCC) or Laser Drillable Prepreg (LDP). The long-term stability of components was determined basing on resistance changes during ageing tests. The resistance was measured in two cases: at room temperature after keeping of samples at elevated temperature and/or humidity or directly during heating of resistors on hot plate. The measurements were carried out for structures after fabrication process as well as for resistors trimmed with Nd-YAG laser or treated with voltage pulses.

Towards the limits of thick-film resistors' miniaturization

This paper presents results of investigations devoted to miniaturization of thick-film resistors with the aid of laser cutting. The investigations were aimed at miniaturization of two resistor dimensions, namely length and width. Test structures were based on various combination of conductive and resistive inks deposited on Al2O3, or LTCC substrates. Resistors made in standard screen printing process after being fired were patterned using laser beam in order to minimize their planar dimensions to tenths of millimeter and below. Prepared samples were subjected to number of electrical tests and some characteristic parameters, like temperature coefficient of resistance (TCR) or pulse durability were calculated based on these measurements. Test samples were also exposed to long-term thermal ageing. The received parameters were compared to those exhibited by resistors with standard dimensions in order to evaluate differences in characteristics and to determine the current miniaturization limits of such components.