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Comparative performance of gold wire bonding on rigid and flexible substrates

  • Yu Hin Chan
  • Jang-Kyo Kim
  • Deming Liu
  • Peter C. K. Liu
  • Yiu Ming Cheung
  • Ming Wai Ng
Article

Abstract

This paper reports comparative performance of wire bondability of electrolytically plated Au/Ni/Cu bond pads on rigid FR-4 and bismaleimide trazine (BT) PCBs, as well as flexible polyimide (PI) substrate. The metallization surfaces were treated with plasma to study the effect of bond pad surface cleanliness on wire bondability. Process windows were constructed as a function of bonding temperature and bond power for the individual substrate materials. Significant improvements of wire pull strength and process window were noted after plasma treatment with a substantial reduction in minimum bonding temperature from 120°C to 60°C for both the rigid and flexible substrates. The minimum bond power required to produce successful bonds decreased with increasing bonding temperature. At a bonding temperature of 120°C, the process window for the flexible substrate was wider than the rigid substrates. The wire bondability and wire pull strength of rigid substrates decreased with increasing bonding temperature above 120°C due to softening of the substrate which adversely affected the effective bond force and the transmission of ultrasonic energy. In contrast, the wirebonding performance of the flexible substrate remained stable at 120°C or above because the thermo-mechanical properties of flexible PI substrate were rather insensitive to temperature. The process windows of flexible substrates with and without stiffener showed similar bondability.

Keywords

Bonding Temperature Process Window Wire Bonding Flexible Substrate Plasma Cleaning 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The authors wish to thank the Innovation and Technology Commission (ITC), Hong Kong SAR Government for the continuous support of this project through the Innovation and Technology Fund (UIT/32). Assistant with experiments rendered by the Materials Characterization and Preparation Facilities (MCPF) and EPack Lab. at HKUST is also gratefully appreciated.

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Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  • Yu Hin Chan
    • 1
  • Jang-Kyo Kim
    • 1
  • Deming Liu
    • 2
  • Peter C. K. Liu
    • 2
  • Yiu Ming Cheung
    • 2
  • Ming Wai Ng
    • 2
  1. 1.Department of Mechanical EngineeringHong Kong University of Science & TechnologyClear Water BayHong Kong
  2. 2.ASM Assembly Automation Ltd.4/F., Watson CentreKwai ChungHong Kong

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