Thermophysical Properties of Ni Films for LIGA Microsystems
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A6.2.1
Thermophysical Properties of Ni Films for LIGA Microsystems Diana-Andra Borca-Tasciuc1, Rajesh Nimbalkar2, Gang Chen3,1, Samuel Graham4, and Theodorian Borca-Tasciuc2, * 1
Mechanical and Aerospace Engineering Department, University of California at Los Angeles Los Angeles, CA 90095, U.S.A. 2 Mechanical, Aerospace, and Nuclear Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 3 Mechanical Engineering Department, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. 4 Mechanical Engineering Department, Georgia Institute of Technology, Atlanta, GA 30332, U.S.A.
ABSTRACT
This work reports temperature dependent thermophysical properties characterization of electrodeposited Ni and NiMn alloys intended for LIGA Microsystems applications. A steadystate method is used to determine the in-plane thermal conductivity. Anisotropic thermal diffusivity characterization is performed using a photothermoelectric technique. The measured thermal properties are dependent on the deposition method and also on subsequent temperature annealing steps. The thermal transport measurement results are correlated with scanning electron microscopy studies of the grain structure and measurements of the electrical transport properties.
INTRODUCTION
LIGA Microsystems requires use of electroplated components with good mechanical properties as molding tools for replication of polymeric parts. Ni and Ni alloys can be easily electrodeposited and exhibit enhanced mechanical properties when deposited with a nanocrystalline grain structure [1]. However, materials with refined grain structure are usually thermally unstable. Small grains have high surface to volume ratios and store more free energy in their boundaries. Addition of thermal energy to stored energy often results in grain growth [1]. Typically, grain growth is temperature dependent. Molding is done at higher temperatures, which poses a concern on the mechanical stability of nanocrystalline Ni and Ni alloy parts. Therefore it is important to understand how heating affects the structure of those materials. In addition, it is useful to develop methods to monitor the grain size during operation. One idea is to employ transport measurements to detect changes in microstructure. This work reports thermal transport measurements of as-grown and temperature annealed specimens of Ni electrodeposited from sulfamate and Watts baths, and electrodeposited NiMn alloys. The annealing temperatures are in the range of 300° C- 600° C. Results include *
Corresponding author. Email address: [email protected].
A6.2.2
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Figure 1. Experimental setup for in-plane thermal conductivity measurements. temperature dependent thermal conductivity in the plane parallel to the film and anisotropic thermal diffusivity at room temperature. Simple kinetic theory arguments are used to explain the experimental trends. The measured thermal diffusivities correlate well with predictions based on the Wiedmann-Franz
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