Study of mechanical response in embossing of ceramic green substrate by micro-indentation

📝 Abstract

Micro-indentation test with a micro flat-end cone indenter was employed to simulate micro embossing process and investigate the thermo-mechanical response of ceramic green substrates. The laminated low temperature co-fired ceramic green tapes were used as the testing material ; the correlations of indentation depth versus applied force and applied stress at the temperatures of 25 degrees C and 75degrees C were studied. The results showed that permanent indentation cavities could be formed at temperatures ranging from 25 degrees C to 75 degrees C, and the depth of cavities created was applied force, temperature and dwell time dependent. Creep occurred and made a larger contribution to the plastic deformation at elevated temperatures and high peak loads. There was instantaneous recovery during the unloading and retarded recovery in the first day after indentation. There was no significant pile-up due to material flow observed under compression at the temperature up to 75 degrees C. The plastic deformation was the main cause for formation of cavity on the ceramic green substrate under compression. The results can be used as a guideline for embossing ceramic green substrates.

💡 Analysis

Micro-indentation test with a micro flat-end cone indenter was employed to simulate micro embossing process and investigate the thermo-mechanical response of ceramic green substrates. The laminated low temperature co-fired ceramic green tapes were used as the testing material ; the correlations of indentation depth versus applied force and applied stress at the temperatures of 25 degrees C and 75degrees C were studied. The results showed that permanent indentation cavities could be formed at temperatures ranging from 25 degrees C to 75 degrees C, and the depth of cavities created was applied force, temperature and dwell time dependent. Creep occurred and made a larger contribution to the plastic deformation at elevated temperatures and high peak loads. There was instantaneous recovery during the unloading and retarded recovery in the first day after indentation. There was no significant pile-up due to material flow observed under compression at the temperature up to 75 degrees C. The plastic deformation was the main cause for formation of cavity on the ceramic green substrate under compression. The results can be used as a guideline for embossing ceramic green substrates.

📄 Content

9-11 April 2008 ©EDA Publishing/DTIP 2008

ISBN: 978-2-35500-006-5

Study of Mechanical Response in Embossing of Ceramic Green Substrate by Micro-Indentation

Y. C. Liu and Xuechuan Shan+

Singapore Institute of Manufacturing Technology (SIMTech),
71 Nanyang Drive, Singapore 638075

• Corresponding Email: xcshan@simtech.a-star.edu.sg (Xuechuan Shan)

Abstract- Micro-indentation test with a micro flat-end cone indenter was employed to simulate micro embossing process and investigate the thermo-mechanical response of ceramic green substrates. The laminated low temperature co-fired ceramic green tapes were used as the testing material; the correlations of indentation depth versus applied force and applied stress at the temperatures of 25 °C and 75°C were studied. The results showed that permanent indentation cavities could be formed at temperatures ranging from 25 °C to 75 °C, and the depth of cavities created was applied force, temperature and dwell time dependent. Creep occurred and made a larger contribution to the plastic deformation at elevated temperatures and high peak loads. There was instantaneous recovery during the unloading and retarded recovery in the first day after indentation. There was no significant pile-up due to material flow observed under compression at the temperature up to 75 °C. The plastic deformation was the main cause for formation of cavity on the ceramic green substrate under compression. The results can be used as a guideline for embossing ceramic green substrates.

I.
INTRODUCTION Low temperature co-fired ceramic (LTCC) has been used for many years in the microelectronics packaging industry. One of the important advantages of LTCC technology is that it can be used to generate 3D structures using multi-layers of tapes and it is a way to create multi-layer circuits with the help of single tapes and applying conductive, dielectric and resistive materials. It can be used for various applications such as telecommunication devices, microwave components, sensors, actuators, microfluidics, meso-system module, bio- medical devices, etc [1]. The green ceramic tapes are glass- ceramic composite materials. They include ceramic filler that is usually alumina, glass frit binder and organic vehicle for binding and viscosity control of the tape before sintering. Green ceramic tapes can be manipulated for fabricating 3D structures. The traditional techniques for structuring green ceramic tapes are micro punching, milling and laser machining, etc [2, 3].
Recently micro embossing technique has been applied to create 3D structures in ceramic multi-layers [1, 4, 5]. This opened a new possibility of patterning features with micrometer scales on green tapes. Micro embossing or imprinting is usually used for patterning microstructures on a polymeric substrate [6-8]. It uses a master mold to press onto a substrate material under a certain pressure and a temperature, which is usually above the glass transition temperature of the material, to transfer the mold patterns onto the substrate. After the temperature returns below its glass transition temperature, the mold is separated from the substrate, and the substrate material retains the shape of the mold patterns. In this process, temperature plays an important role to both the local-area fidelity and global uniformity of the structure formation. Higher embossing temperature could improve the fidelity of the structures but could cause serious thermal stress during demolding, which results in poor global flatness after demolding. With lower embossing temperature, the global flatness could be improved significantly [9]. Hence, a compromise between local fidelity of the embossed patterns and global flatness of the substrate has to be considered. Therefore, study of micro embossing at low temperature for green ceramic tapes is necessary. The recent development in micro-indentation instrument, i.e., depth-sensing indentation at elevated temperature, offers the capability to preciously control and monitor the load and penetration depth during the indentation process at the desired temperatures [10-12]. It is expected that the micro- indentation test can act as a convenient way to simulate micro embossing process and to study the mechanical response of the embossing materials at process temperature and applied pressure. In this paper, micro-indentation tests using a micro flat- end cone indenter at various temperatures have been performed on green ceramic tapes to simulate imprinting process and investigate the mechanical response during imprinting. The correlation of indentation depth versus applied force at different temperatures was studied. The temperature and load-dependent creep and creep strain rate during holding period were obtained and discussed. The instantaneous recovery and retarded recovery after indentation were investigated as well. 9-11 April

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