Samuel Hildebrandt

Thin film structuring on LTCC

With the increase of transmission frequencies in telecommunications, the requirements for structural resolution and accuracy of substrates for high frequency circuits rise as well. Through its material properties, low temperature cofired ceramics (LTCC) are well suited to these special applications. However, the classical thick film structuring methods reach their limits with these requirements. Thin film structuring is an alternative. In this work 15 mum lines and 25 mum spaces are demonstrated in a 120 nm thin Ti/Pt metallization by means of lift-off patterning. By adding copper galvanically to a sputtered seed layer a film thickness up to 6 mum can be reached. Using this semiadditive process, 60 mum lines and 25 mum spaces are realized. The reliability of SMT components soldered onto the film is analyzed after temperature cycling.

Influence of accelerated aging on the acoustic properties of a ceramic microsystem for structural health monitoring

Carbon fibre reinforced polymers (CFRP) are widely used wherever weight has to be reduced without compromising the mechanical properties of parts. One popular application is in aerospace. To reduce failure analysis (maintenance) time and eventually detect impacts even during flight it is necessary to durably mount an array of miniaturized sensors on CFRP elements. Especially the acoustic properties of the interface (adhesive) between ultrasound transducer and CFRP need to be constant over time (or at least show an predictable behaviour). LTCC-based transducers allow the integration of reliable electronics into the ultrasound sensor. For electrical circuits on ceramic substrates, lifetime predictions are basically known. In contrast, no investigations about the “acoustic lifetime” of an ultrasound sensor interface are known. The paper describes the fabrication and assembly of realistic test specimens as well as the accelerated aging by temperature cycling and temperature / humidity test. To evaluate the adhesive, lifelike ultrasound signals are sent and received with different types of solid mount LTCC-based sensors. Furthermore the electrical impedance of the piezoelectric transducers is analyzed.

Dimensioning of peltier cooling system for laser applications in an electric cabinet

The focus of this paper is the development of a suitable thermoelectric cooling solution (TECs) for fiber-coupled laser diodes of an optical power supply by thermal simulation via PSpice or LTSpice. As a first step it was necessary to create a working model of the thermal circuit of the TEC. As a consequence it was possible to simulate an existing cooling system and to evaluate the accuracy of the model with real measurement data. The obtained results as well as the gained knowledge of the thermal design lead to the development of a new construction of a double stage cooling system using TECs.

Temperature compensated field bus sensor interface for applications in process engineering

A robust, high precision sensor interface (SI) for in-situ temperature measurements in process engineering is presented. Wiring and interference are minimized by directly connecting thick film technology based sensing elements (SEs) to the interface PCB. Fully digital calibration, operating temperature compensation and noise canceling are demonstrated. A low-noise supply scheme for a wide range of operating voltages is examined. Parallel operation of up to 120 units on a self-managing CAN field bus is discussed. The protocol for the sensor interfaces user-friendly generic serial ACM USB connection is illustrated.