Electromigration Reliability of Advanced High-density Fan-out Packaging with Fine-pitch 2lm/2lm L/S Cu Redistribution Line

Chien Lung Liang, Yung Sheng Lin, Chin Li Kao, David Tarng, Shan Bo Wang, Yun Ching Hung, Gao Tian Lin, Kwang Lung Lin

研究成果: Article

摘要

The novel fan-out packaging incorporating fine-pitch small line width Cu redistribution line (RDL) technology was designed for achieving high-density packaging. However, the downsizing of Cu RDLs gives rise to increasing current densities and raises the electromigration reliability concerns. The failure mechanism involved under electromigration in the advanced fine-pitch package still remains unclear at the present stage. The present study investigated the electromigration reliability and the failure mechanism of an advanced fan-out packaging with fine-pitch 2μm/2μm line/spacing Cu RDLs, 3 μm in thickness and 20 μm or 600 μm in length, embedded in polyimide dielectric layers. The Cu RDLs were stressed with electric current at 8.8 × 105 A/cm2 under an ambient 180°C. The geometry effects of the Cu RDL on the electromigration performance were also elaborated, and the design rule was proposed for reliability optimization. The Cu RDL incorporating a bent-line (45°) structure was found to exhibit a better electromigration resistance, compared with the one incorporating a straight-line structure. The in situ resistance analysis revealed a steady resistance increase followed by a rapid resistance jump until open circuit failure for both 20-μm-long and 600-μm-long Cu RDLs. The fracture microstructures further revealed the failure occurrence in the middle region of the Cu RDL rather than on the cathode side, showing atypical failure mechanism under electromigration. The local heat accumulation in the middle region of the Cu RDL produced a large thermal gradient and further triggered Cu thermomigration, which were responsible for the electromigration-induced failure in the fine-pitch Cu RDLs.

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering

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