The role of a nonconductive film (NCF) on Cu/Ni/Sn-Ag microbump interconnect reliability
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The role of a nonconductive film (NCF) on Cu/Ni/Sn‑Ag microbump interconnect reliability Hyodong Ryu1 · Kirak Son1 · Jeong Sam Han2 · Young‑Bae Park1 · Tae‑Kyu Lee3 Received: 26 May 2020 / Accepted: 27 July 2020 / Published online: 11 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The use of a nonconductive film (NCF) to establish and enhance the stability of microbumps is crucial. Even though it is normal to apply NCF to microbump interconnection layers, understanding the behavior of microbump stability without the protection from a NCF is important. A free standing structure without a NCF can be used to determine the mechanical response of a single microbump. This information can be used to design robust interconnect structures. Electromigration (EM) tests were performed at 150 ℃ and 1.3 × 105 A/cm2 to investigate the effect of a NCF on the electrical reliability of Cu/Ni/Sn-Ag microbumps. The EM test results show different failure times and failure modes for Cu/Ni/Sn-Ag microbumps with the NCF and without the NCF. The microbump test samples with the NCF had a time to failure that was three times longer than that without the NCF. At a constant current density condition, the contribution of temperature-induced accelerated degradation and mechanical deformation factors were considered. A series of finite element and electron backscattered diffraction analyses revealed that the NCF restricted solder deformation and led to an increase in the back stress, which prolonged the EM lifetime.
1 Introduction Due to the rapid development of miniature, lightweight, high-performance, and multifunctional electronic devices, electronic device packages are adopting multipin and fine pitch structures to increase performance. Three-dimensional (3D) chip stack structures integrating various functional chips have been designed and developed [1–4]. Along with flip-chip packaging technology, multistacked structures with fine and complex designs have been increasingly used in the electronics industry in recent years [3–5]. Though challenges remain, solder bumps are limited * Young‑Bae Park [email protected] * Tae‑Kyu Lee [email protected] 1
School of Materials Science and Engineering, Andong National University, Andong‑si, Gyeongsangbuk‑do 36729, Republic of Korea
2
Department of Mechanical & Robotics Engineering, Andong National University, Andong‑si, Gyeongsangbuk‑do 36729, Republic of Korea
3
Mechanical and Materials Engineering, Portland State University, Portland, OR 97201, USA
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to a fine pitch below 100 μm because of the increased risk of bump bridging and misalignment. Even smaller bumps have been implemented and enabled, which increases in the current density, leading to an increased risk of electromigration (EM)-induced failure modes [6, 7]. Underfill has been commonly used in flip-chip joints and provides structural stabilization between the chip and substrate. It also relieves stress concentrations in the interconnections located at the perimeter o
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