Thick-film System Research Articles

Evaluation of a Lead-Free Ultra Low Temperature Co-Fire Ceramic (ULTCC) Tape Designed for Lamination on Aluminum Substrates and a Compatible Co-Fireable Silver Conductor

Abstract Light-emitting diodes (LEDs) are the product of choice for many commercial and industrial lighting applications. Due to increasing power densities, alternative mounting solutions are being evaluated in order to achieve the lowest junction temperatures and lowest thermal resistances. Previous papers have explored the benefits of using a thick film system as opposed to a traditional Metal Core Printed Circuit Board (MCPCB). The advantage of being able to directly insulate a heat sink eliminates additional MCPCB layers and mechanical attachment that can decrease the thermal conductivity of the module and increase cost. Lower thermal resistance results in higher performing LED modules at a lower cost and a longer lifetime. A process has been developed and evaluated where an ultra-low temperature co-fired ceramic (ULTCC) tape will be laminsated directly on to an aluminum heat sink in order to electrically isolate the substrate. The green tape will then have a silver conductor applied to it and fired in one step. Using a tape system as opposed to an ink system creates many advantages. The tape system allows for processing in cavities, which is beneficial for recessed lighting and three-dimensional substrates. The co-firing silver conductor reduces the number of firing steps, leading to less dimensional variation of the heat sink and lower processing costs. This paper will discuss the material solutions, processing requirements, and reliability data for a completely co-fired ULTCC system on aluminum.

Microwave Characterization of a Thick Film System for Hybrid Packaging Applications

Abstract Thick film material systems for hybrid applications have existed for many years and have provided the ability to create high density interconnects in industries such as consumer, military, telecommunications and automotive electronic devices. Despite their breadth of applications, thick film hybrid circuits are rarely utilized for microwave/millimeter-wave packaging applications. In this work, the DuPont™ QM44 thick film dielectric is characterized up to 40 GHz. Test samples to characterize this thick film system consisted of the screen-printed QM44 multilayer dielectric and QG150 gold thick film conductor and vias on top of a 96% alumina substrate. Three different fabrication methods were used in the fabrication of the test samples to illustrate the effect of processing techniques on material loss properties, with the conductor lines formed through standard screen printing, chemical etching, and laser ablation. Laser ablation is a technique recently utilized to form transmission line features in low temperature cofired ceramic (LTCC) circuits [1] to increase dimensional precision when compared to standard screen printing. S-parameter measurements of microstrip transmission lines demonstrate a system loss at 30 GHz of approximately 0.8 dB/cm for chemical etching, 0.9 dB/cm for laser ablation, and 1.0 dB/cm for screen printing. Through careful design and good processing, acceptable microwave performance of the QM44 thick film system can be achieved up to 40 GHz.

Residual Stress Analysis of Thick Film Systems by the Incremental Hole-Drilling Method*

Abstract Residual stresses play an important role in coating systems as they determine their properties as well as their life-time behavior. In many industrial applications multi-layer systems are used. This work examines the applicability of the incremental hole drilling method to determine residual stress states in multi-layer coating systems, i.e. in the top-layer, in the interlayer and in the substrate. For this purpose systematic finite element (FE) simulations are carried out. Initially, the interfaces were assumed to be planar and subsequently rough interfaces were considered. The results indicate that thin interlayers with layer thicknesses smaller than 30 μm can be neglected in the evaluation of the measured strain relaxations, since they lead only to a minor stress deviation. In case of larger interlayer thicknesses a case-specific calibration, taking into account the exact build-up of the multilayer system, results in reliable determinations of the residual stress states, in the top-layer, the interlayer and the substrate. Finally the simulation results are applied to a model thick film system consisting of a thermally sprayed Al2O3-coating on a fine-grained construction steel (S690QL). Its residual stress state is determined experimentally by the incremental hole-drilling method.

Influence of the Interfacial Roughness on Residual Stress Analysis of Thick Film Systems by Incremental Hole Drilling

Thick film systems with coating thicknesses between 50 and 1000 µm are often fabricated by thermal spray processes. During the deposition and due to the substrate pre-treatment residual stresses, which influence the coating properties, develop. Due to the substrate preconditioning thermal spray coatings exhibit a large interfacial roughness. This study investigates the application of the incremental hole-drilling method on thermal spray coatings. The focus is on the influence of the interfacial roughness on the residual stress evaluation. A systematic FE-study was carried out in order to minimize the final error for the residual stress evaluation. The simulation results are transferred to experimental hole-drilling results of a thermally sprayed model thick film system. Finally, the hole-drilling results are compared to the residual stress depth profile that was determined by X-ray diffraction in combination with successive electrochemical layer removal. The results clearly show that the effect of the interfacial roughness can be neglected for residual stress calculation if the mean coating thickness is properly considered for calculation of the calibration function / parameters.

Optimal materials and process conditions of functional layers for piezoelectric MEMS process at high temperature

Pb(Zr0.52Ti0.48)O3 (PZT) thick film-based micro-transducers demonstrate excellent piezoelectric performances. However, its powder-based film requires very high sintering temperature to obtain high density and good electromechanical properties of the active film. High processing temperature enables inter-diffusion or reaction between PZT active materials and Si-based substrate to result in device failure via volatilisation of PbO especially over 800°C. Therefore the preventive solution to this problem should be considered in fabricating silicon-based piezoelectric microdevices for the better performance. In this research, compatibility in the interface stability and adhesion between the layers of the overall integrated piezoelectric thick-film devices were thoroughly investigated for the successful application of the process at high temperature. The Pt (or PtOx)/TiO2/SiNx/Si substrate represented the best interfacial properties among various combinations of structural substrates, so this structure is highly recommended to integrated piezoelectric thick-film microelectromechanical system devices.

Synchrotron X-ray induced damage in polymer (PS) thin films

Thin polystyrene (PS) films ( M w = 234,000) are spin coated on silicon substrates with a Chromium (Cr) layer as a sandwiched metallic layer that produces photoelectrons (by synchrotron X-rays). Earlier studies on synchrotron radiation damage in PS films, without metallic layer, have shown a decrease in interfacial roughness and a slight increase in thickness, at temperatures below T g [A.G. Richter, R. Guico, K. Shull, J. Wang, Macromolecules 39 (2006) 1545]. Similar trend is observed in the presence of a thin layer of Cr film (∼2.5 nm). For the sample with a thick Cr layer the opposite effect was observed for X-ray radiation damage. For the 50 nm thick Cr film system thickness of the polystyrene film decreased by ≈4.4% which amount to a loss of about 0.021 nm 3 per incident photon in the fluence range studied (6.8 × 10 9 photons mm −2 to 1 × 10 14 photons mm −2). Interfacial roughness also increased from about 1.0 nm to 2.1 nm in the process. These effects are explained by invoking the presence of more number of X-ray induced photoelectrons and secondary electrons for 50 nm thick Cr film case compared to 2.5 nm thin film case.

Advanced thick film system for AlN substrates

Substrates with high thermal conductivity continue to be in great demand for their ability to enable smaller and denser high power circuits. BeO has been used for this purpose for many years with thick film materials. However, due to health and environmental concerns with BeO, many manufacturers feel compelled to switch to alternative substrates. This paper will discuss a thick film system consisting of conductors, dielectric, and resistors developed specifically for use with the most likely alternative, AlN substrates. This system will soon find broad use in applications such as power resistors for telecom, optoelectronic submounts, and high‐power automotive applications.

A robust low cost thick film system for the consumer market

This paper describes the fabrication and test of a new low cost thick film system using base metals. The resistor pastes were developed using non-precious metal oxides and contain molybdenum trioxide and other additives. The conductors are either silver or nickel. The dielectrics contain barium oxide, but, unlike ruthenium based resistors, on related dielectrics, there is very little difference in resistor behavior on alumina from that on the dielectrics investigated. Long term stability tests show that the new resistor family, while less stable than those based on ruthenium, is suitable for many low cost applications. Results suggest that high temperature ageing tends to minimize contact effects and that they are compatible with both silver and nickel terminations.

Heaters for gas sensors from thick conductive or resistive films

The temperature of gas sensors influences their sensitivity, selectivity and response time. Most of them are operated at significantly elevated tempertures (e.g. electrochemical sensors based on semiconducting metal oxided require up to 900 °C). The possibility of using thick-film heaters in smart planar sensors if often reported. This paper, however, presents results of long-term high-temperature stability examinations of different resistor/conductor systems (in the temperature range 400–600 °C) and several conductive films with different metallurgy (for temperatures between 600 and 1000 °C). It is shown that the RuO 2/Au thick-film system based on commercially available resistive and conductive inks allows continuous, long-term operation up to 400 °C. Moreover, the allowable operating temperature is much higher for heaters made form conductive films; for example PtAu heaters can operate successfully up to 600 °C whereas fritless platinum heaters are satisfactory in the whole range demanded by electrochemical sensors.

AC measurements of thick-film conductor-insulator system near the percolation threshold†

AC measurements of a model two-phase thick-film system in the Frequency range l0mHz to 10 MHz have been performed. The influence of manufacturing conditions (glass-to-bismuth ruthenate ratio and peak firing temperature) as well as the topology of test samples on AC conductance and capacitance has been analysed.

Preparation and properties of a new thick film system : T. Inokuma, Yoshiaki Taketa and Miyoshi Haradome. Active Passive Electron. Compon.12, 119 (1986)

Preparation and properties of a new thick film system : T. Inokuma, Yoshiaki Taketa and Miyoshi Haradome. Active Passive Electron. Compon.12, 119 (1986)

Cathode ray tube bleed resistor reliability—a case study

AbstractThis paper describes, and gives a mathematical analysis of, the performance of two makes of CRT bleed resistors which exhibit markedly different characteristics under heat soak conditions. By examining the observed resistance changes with temperature, and relating these to the Arrhenius equation, the reaction activation energies can be determined.Further analysis of the power consumption characteristics of the resistors leads to the establishment of resistance‐time curves for both makes of resistor. These indicate very different conclusions than might otherwise have been drawn from initial test data. Finally the Monte Carlo' simulation technique is used to determine the most likely survival characteristics in a field situation, and a quantitative assessment of the reliability of CRTs using these bleed resistors is given.The construction of the resistor body is common to both makes and comprises a resistor substrate enclosed within an overcoat which is in turn encapsulated in epoxy. One make (type A) is a glass thick film structure, whereas the other is a polymer thick film system.

Preparation and Properties of a New Thick Film System

Work has been carried out to develop a new ruthenium oxide based thick film resistor whose resistance is independent of the contact area of the conductor to the resistor. Such a resistor can then be combined with a low cost silver conductor.It has been found that such a resistor can be made by doping a ruthenium oxide based thick film resistor with up to several percent of gold. With such a material it is possible to use silver or palladium silver (containing only very small amounts of palladium) as an electrode material and very few interactions have been found to occur between the resistor and electrode. Such a gold doped ruthenium oxide thick film resistor using silver electrodes has some major advantages as follows:-1. The resistor size can be made much smaller than normal.2. The design of a thick film hybrid circuit becomes easier.3. The resistor cost can be reduced.

A Thick Film Base Metal Resistor and Compatible Hybrid System

Non-noble metal thick film materials have been the topic of several recent papers.11,13,14,15This paper will focus on the first non-noble metal thick film system comprising conductors, dielectrics and most important, resistors for commercial use. Processing and performance data are presented in detail to illustrate the capabilities of these new materials. Circuit applications information is presented wherever possible. This new class of materials will enable the microelectronics industry to exploit new market opportunities previously unavailable due to the high costs of precious metal materials.

Structure and dc electrical properties of a Au–Rh-glass thick-film system

A study has been made of the structure and the dc electrical properties of a metal-glass thick-film system. The metal part is formed by thermal decomposition of an organometallic solution and consists of Au and Rh. The glass component is a lead boroaluminosilicate. The influence of the firing treatment, of the composition of the metal part, and of the metal-to-glass ratio on the structure and the electrical properties of the film has been investigated. Some glasses, derived from the original glass component, have been used. In this system it is possible to have very small temperature coefficients of resistance in a wide temperature range. Sheet resistances can vary by several orders of magnitude. Under certain conditions the conduction behaves anomalously below 186 K. The different types of conduction in this thick-film system are correlated with the different structures.