High-energy X-ray Tomography for 3D Void Characterization in Au–Sn Solid-Liquid Interdiffusion (SLID) Bonds

Abstract

Au-Sn SLID bonding is a technique originally developed for harsh environment applications. The technology has recently shown promising results for ultrasound transducer fabrication. Characterizing the spatial and size distributions of voids is crucial for developing a fabrication process that satisfies acoustic requirements. This measurement is traditionally done by optical or electron cross-section microscopy that gives the void distribution in a randomly selected physically cut plane. X-ray micro computed tomography is a powerful tool for non-destructive three-dimensional imaging of void distributions, but is challenging to use in high-density materials like the ones used in ultrasound transducers. We demonstrate that monochromatic, high-energy synchrotron X-ray tomography can give 3D images of such a challenging sample, resolving µm-sized voids in the bondline. The void distribution is highly non-uniform, implying that traditional cross-section microscopy would give different results depending on the plane of sectioning. Computed tomography allows the voids to be parametrized and treated statistically, revealing a wide distribution of void sizes, a tendency to form oblate voids with size-dependent orientation, as well as porous networks.

Laboratory X-ray Microscopy of 3D Nanostructures in the Hard X-ray Regime Enabled by a Combination of Multilayer X-ray Optics

“…For the reliability of the resulting products, the control of the formation and growth of intermetallic compounds (IMCs) and the detection of voids is crucial. In addition to the conventional use of optical or electron microscopy after the destructive cross-section preparation of the 3D IC stack, micro X-ray computed tomography Nanomaterials 2024, 14, 233 2 of 8 (XCT) has been proven to be a powerful tool for the nondestructive three-dimensional imaging of voids [5]. However, increasingly smaller feature sizes in advanced packaging and the need to detect smaller defects require X-ray imaging solutions with higher spatial resolution, i.e., nano XCT in a lens-based X-ray microscope.…”

Localized Induction Heating of Cu-Sn Layers for Rapid Solid-Liquid Interdiffusion Bonding Based on Miniaturized Coils

“…In 1966, Bernstein presented for the first time the SLID mechanism of the binary systems Ag-In, Au-In, and Cu-In [16]. Today, Au-Sn [14,17,18] and Cu-Sn [14,19,20] are the most studied SLID systems with process temperatures above 278 • C and 232 • C, and IMC melting temperatures at about 500 • C and 700 • C, respectively. Therefore, SLID bonding is one of the most interesting low-temperature packaging technique, especially for wafer-level and 3D integration.…”