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Voids formation and Cu3Sn growth mechanisms in Cu/Cu3Sn/Cu6Sn5 system under air in Cu/SnAg joints for microelectronic packaging

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Abstract

The technological advances reached today in semi-conductor devices and their applications increased the challenges in terms of power density. The introduction of new and high-temperature mission profiles made the integrated circuits packaging reach their limit and emerged new reliability issues that did not exist for previous generation devices. As a response to the increasing power density issues, the transient liquid phase bonding (TLPB) technique, which consists of transforming pure metals or alloys into intermetallic compounds (IMCs) with high-thermal stability, is one of the most studied techniques nowadays. The same principle is used also to increase the thermal stability of a system by the solid-state reaction (SSR) technique. The present work focus on the solid-state reactions occurring during transformation, under air atmosphere, of the initial Cu/Cu3Sn/Cu6Sn5/Cu3Sn/Cu system to the final Cu/Cu3Sn/Cu system with a much higher thermal stability. The experiments were performed on interconnections using Cu pillar and SnAg solder alloy technologies. Cu and Sn-2 wt%Ag bumps with a size of 90 × 90 µm2 were deposited using electro-chemical deposition process with a thickness of 20 µm and 15 µm, respectively. In a first step, the initial system was obtained using the TLPB process in the Cu/liquid Sn/Cu system performed under air at 250 °C. Afterwards, the isothermal SSR process in the Cu/Cu3Sn/Cu6Sn5/Cu3Sn/Cu system was studied at 250 °C under air for holding times from 1 to 124 h. After the experiments, cross-sections of the samples were characterized by optical and scanning electron microscopy. The growth kinetics of Cu3Sn compound was studied for samples with two initial thicknesses of Sn-Ag alloy: 15 and 30 µm. A critical thickness of Cu3Sn layer beyond which a drastic change in its growth kinetics was observed. This phenomenon was accompanied by a significant change in the microstructure of the joint. An island-shape microstructured Cu3Sn within Cu was observed accompanied by formation of Cu oxide layers. The growth mechanisms of Cu3Sn phase responsible for different observed microstructures are presented and discussed.

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The authors declare that no funds, Grants, or other support were received during the preparation of this manuscript.

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Authors and Affiliations

  1. CEA, LETI, MINATEC Campus Univ. Grenoble Alpes, Grenoble, France

    El Mostafa Barik & Charlotte Gillot

  2. Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMAP, 38000, Grenoble, France

    El Mostafa Barik & Fiqiri Hodaj

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  1. El Mostafa Barik
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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by all authors. The first draft of the manuscript was written by all authors and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Barik, E.M., Gillot, C. & Hodaj, F. Voids formation and Cu3Sn growth mechanisms in Cu/Cu3Sn/Cu6Sn5 system under air in Cu/SnAg joints for microelectronic packaging. J Mater Sci: Mater Electron 33, 26190–26204 (2022). https://doi.org/10.1007/s10854-022-09305-3

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