In–Bi low-temperature SLID bonding for piezoelectric materials

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Originality/value

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.

Citation

Aasmundtveit, K.E., Eggen, T., Manh, T. and Nguyen, H.-V. (2020), "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-10-2017-0034