Reinhard Bauer

New design of an SnO2 gas sensor on low temperature cofiring ceramics

Abstract A new design for thick film gas sensors was investigated. The sensors were made by the low temperature cofiring ceramics (LTCC) technique with a platinum heater buried inside the multilayer structure. SnO2 or SnO2 with Pd as catalyst thick films were used as gas sensitive materials. The properties of the gas sensors were measured with methane and carbon monoxide. The results of our study show that LTCC can be successfully applied in sensor technology as well as confirming the correctness of the sensor design.

Electrical and stability properties and ultrasonic microscope characterisation of low temperature co-fired ceramics resistors

Abstract This paper presents systematic investigations of electrical and stability properties of various low temperature co-fired ceramics (LTCC) resistors. One of the goals of this work was to check the compatibility of LTCC materials (tapes, resistive and conductive inks) from various manufacturers. Three commercially available green tapes and three LTCC resistor/conductor systems were examined. The resistive inks with 1 k Ω/ sq . nominal sheet resistance were used. Buried (inside) and surface resistors were laminated and fired according to the tape manufacturers’ recommendations. The influence of dimensional effect on sheet resistance and hot temperature coefficient of resistance, the temperature dependence of resistance in a wide temperature range (from −180°C to +130°C), long-term stability of thermally aged as-fired resistors (150°C, 500 h) and durability to high-voltage micro- or nanosecond pulses (50 ns pulses with 4000 V/mm maximum electric field or 10 μs ones with 700–1000 V/mm electrical field) were carried out for electrical and stability characterisation of LTCC resistors. Non-destructive scanning acoustic microscope diagnostics was applied for structure investigation and estimation of lamination and cofiring process quality of buried LTCC resistors.

Optimization of thermal distribution in ceramics and LTCC structures applied to sensor elements

Thermal properties of Pt or RuO2 thick‐film heaters made on alumina, aluminum nitride or low temperature co‐fired ceramics (LTCC) were compared in the first step of our work. Special holes to improve the heat distribution were included. Several heater layouts were analysed. The heat distribution was measured by an infrared camera, at different heating power. Second, the optimization of LTCC constructions was carried out. The simple structure of LTCC permitted the achievement of a high package density. It was possible to integrate a heating element made from special thick‐film ink as a buried film, inside a substrate. An important step in our technology was the making of the holes. A pattern of holes (achieved by punching or laser cutting) around the heating area permitted a changeable heat gradient. The quality of lamination and the structure of the buried elements were investigated with an ultrasonic microscope.

Effect of incorporation of different additives in sustainable polymers on selected electrical and mechanical properties

We present here our findings on the influences of different additives on the electric and mechanical properties of a sustainable polymer. For our experiments, two different flame retardants, two fillers and one bio based fiber material were incorporated in the sustainable base polymer by melt compounding. Samples were produced and investigated. Main focus of the investigation was the influence of additive content on selected electrical and mechanical properties, like the breakdown voltage, the dielectric constant, the surface and bulk resistivity as well as the E-modulus. The E-modulus was determined by bending test. Our results show that influence depends on the type as well as the fraction of additive in the polymer. It was found that in general the incorporation of additives leads to a decrease in electric properties, however the magnitude depends on the actual additive. While every additive does influence the mechanical, the bio based fibers lead to an increase in the E-modulus and the flame retardants to a decrease in elasticity.

Investigation on an integrated liquid cooling system in LTCC-multilayer

Thermal management is one of the most important problems of electronic packaging design. Different concepts are discussed for material selection and design for LTCC modules. This paper gives an overview of the experimental and simulation results of a special concept with an integrated liquid cooling system in the LTCC multilayer. This concept, based on the integration of a channel system direct into the ceramic multilayer wiring board, allows large heat transfer from chip bond area to a heat sink. Some aspects of design and technology of such a channel pattern are discussed, along with results of experimental investigations on test multilayers. The main topics include the measurement and simulation results of some aspects in order to analyze the behavior and obtain optimization of such a set-up. The influences of the channel pattern and shape, liquid flow and multilayer design are demonstrated. Experiments with test modules have shown the real possibilities of such a concept. Optimized test modules allow applications with power dissipation of about 50 W/cm/sup 2/.

Investigation of wiring boards based on biopolymer substrates

The paper at hand engages the topic of the use of biopolymers in electrical engineering. While different articles on the functionalization of bio-based substrates by polymer thick film technique were published, only few dealt with the functionalization by metal foil lamination and subsequently etching. The latter is the research topic of the paper presented here. Bio-based substrates were functionalized by polymer thick film technique and foil lamination and subsequently etching. The surface roughness was assessed before and after the functionalization using 3D-light microscopy. Furthermore SMD-chips were mounted on the functionalized substrates using different techniques. The techniques were soldering and adhesive bonding. The joint between the substrate and the SMD-chips was evaluated with destructive shear force measurements. It could be shown, that metal foil laminated substrates get not as strong bonds as polymer thick film functionalized substrates, if adhesive bonding is used. However, the strongest bonds can be achieved by soldering. Additionally, the failure form was analysed and six failure types could be distinguished. The data seems to point to a connection between failure type and substrate/mounting technique combination.

Electron beam curing of pastes for the polymer thick film (PTF) technology

The PTF-technology is an additive process. The polymer pastes are structuring applied on a substrate by a screen printing process. Afterwards the structured polymer paste cures by a UV or thermal radiation. Thermal processes require temperatures of 60 to 200°C and curing times of 3 to 60 minutes. UV curing takes only 2 minutes but they have a great disadvantage. UV curing pastes required photoinitiators to start the polymerisation but these initiators have a negative influence of the long-term stability.

Properties and utilization of 3D bent-multilayer hybrid structures

The specific properties and advantages of the LTCC can be profitably included into the MCM (multi chip module) production technology, sensorial and three-dimensional application using multilayer structures. This paper deals with special treatment of LTCC, which is aimed at construction of 3D bent-multilayer hybrid structures for sensorial applications. The paper refers to general trends and gives an overview of hybrid technology progress and results of reached experiments: experimental analysis of 3D bent multilayer structures and their production technology, inside conductive inspection at bending vertex location represented by the non-destructive measurement of the transitional resistance between two conductive layers, measurement principle of the values of interconnection resistance and principle of the law value interconnection resistance based on computer aided semiautomatic measurements. The 3D bent-multilayer hybrid structures find utilization in sensorial application.

Materials made of renewable resources in electrical engineering

Technical requirements for materials in manufacturing of electronics are complex and in constant change. Especially demands have been raised in the area of environmental issues. Polymers based on renewable resources provide some interesting approaches to meet these demands. A general overview of polymers based on renewable resources is given highlighting the fascinating properties of these polymers. The relation between material properties and technological usability will be shown exemplary on PLA. Results showcasing the technological usability and the material properties will be discussed.

The design concept of system integration based on heterostructure

This study shows technological realization of heterostructure LTCC structure - HTCC substrate. Heterostructure realization results are analyzed regarding the application of LTCC ceramics and HTCC substrates where possible solution is local heat dissipation from power elements. Technological solution has been applied during the 3D integrations of mobile mini-machine control electronics in a System on Module (SoM) assembly.