This paper aims to demonstrate low-temperature bonding for piezoelectric materials at temperatures well below the relevant Curie temperatures so as to avoid depolarization of the piezoelectric material during bonding.
Au-coated test samples of lead zirconate titanate (PZT) are bonded to a WC-based resonant backing layer with In–Bi eutectic material in which the In–Bi metal system is a preform or thin, evaporated layers. The bonded samples are characterized using electrical impedance spectroscopy and cross-section microscopy. The first technique verifies the integrity of polarization and reveals the quality of the bondline in a non-destructive manner, particularly looking for voids and delaminations. The latter technique is destructive but gives more precise information and an overview of the structure.
Successful low-temperature (115°C) bonding with intact PZT polarization was demonstrated. The bondlines show a layered structure of Au/Au–In intermetallic compounds (with Bi inclusions)/Au, capable of withstanding temperatures as high as 271°C before remelting occurs. For bonded samples using In–Bi preform, repeatable bonds of high quality (very little voiding) were obtained, but the bonding time is long (1 h or more). For bonded samples using evaporated thin films of In–Bi, bonding can be performed in 30 min, but the process needs further optimization to be repeatable.
Low-temperature solid-liquid interdiffusion (SLID) bonding is a novel technique, merging the fields of low-temperature solder bonding with the SLID/transient liquid phase (TLP) approach, which is normally used for much higher temperatures.
The present work was funded by the Research Council of Norway through the NANO2021 program (project number 235302/O70; B-EAM – Advanced Assembly Technologies for Electro Acoustic Module used in Ultrasound Cardiovascular Applications). The Research Council of Norway is also acknowledged for the support to the Norwegian Micro- and Nano-Fabrication Facility, NorFab, project number 245963/F50. The authors thank Zekija Ramic and Anh-Tuan Thai Nguyen, both HSN, for Au electroplating of samples.
Aasmundtveit, K., Eggen, T., Manh, T. and Nguyen, H. (2018), "In–Bi low-temperature SLID bonding for piezoelectric materials", Soldering & Surface Mount Technology, Vol. 30 No. 2, pp. 100-105. https://doi.org/10.1108/SSMT-10-2017-0034Download as .RIS
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