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Technical Briefs

Effects of the Thermocompression Bonding on the Microstructure and Contact Resistance for the Ultrafine Pitch Chip-on-Glass Packaging With Nonconductive Film

[+] Author and Article Information
Jianhua Zhang

Key Laboratory of Advanced Display and System Applications of Ministry of Education, Shanghai University, No. 149 Yanchang Road, Shanghai, P.R. China; School of Mechatronics Engineering and Automation, Shanghai University, No. 149 Yanchang Road, Shanghai, P.R. China

Jinsong Zhang

School of Mechatronics Engineering and Automation, Shanghai University, No. 149 Yanchang Road, Shanghai, P.R. China

Lianqiao Yang1

Key Laboratory of Advanced Display and System Applications of Ministry of Education, Shanghai University, No. 149 Yanchang Road, Shanghai, P.R. Chinayanglianqiao@shu.edu.cn

1

Corresponding author.

J. Electron. Packag 132(4), 044501 (Dec 03, 2010) (6 pages) doi:10.1115/1.4002898 History: Received February 24, 2010; Revised September 24, 2010; Published December 03, 2010; Online December 03, 2010

Nonconductive film (NCF) is a challenging potential material to substitute the application of anisotropic conductive film in the ultrafine pitch chip-on-glass (COG) packaging. The NCF interconnection requires a high bonding temperature and pressure to form joints, and this causes new reliability concerns. This study investigated effects of the thermocompression bonding parameters on the microstructure and geometric size in the joints to a COG module packaged with NCF. The results revealed that the high temperature and pressure compressed the joints to become wider and shorter. A dual layer of intermetallic compounds consisting of AuSn2 (ε phase) and AuSn4 (η phase) was found in each joint. They were the two kinds of interphases with different melting points (AuSn2:309°C and AuSn4:257°C) during the interfacial reaction between Au and Sn. At the low temperature (below the melting point), the high pressure induced the residual inner stress to generate the cracks in the joints, and this also increased the contact resistance of the joints. The contact resistance increased with the pressure elevating at the same temperature and with the temperature degrading at the same pressure. In the COG packaging with NCF, a proper elevating of the bonding temperature could produce a stable direct connection with the low contact resistance.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

A COG module with different interconnections using (a) ACF and (b) NCF

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Figure 2

A schematic diagram of the COG module

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Figure 3

The Au/Sn bumps and the ITO tracks fabrication

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Figure 4

The flow chart for the thermocompression bonding process

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Figure 5

The size changes of the cross section with different thermocompression bonding parameters: (a) the average width and (b) the average height

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Figure 6

SEM images of joints with different bonding parameters: (a) at 210°C/85 MPa, (b) at 210°C/115 MPa, (c) at 250°C/85 MPa, and (d) at 250°C/115 MPa

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Figure 7

Different compositions in the Au–Sn IMCs layer of a joint with 250°C/115 MPa: (a) two types of Au-Sn IMCs, (b) Au–Sn alloy phase diagram, (c) alloy compositions of AuSn2 phase, and (d) alloy compositions of AuSn4 phase

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Figure 8

A COG module for the four-point resistance measurement

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Figure 9

The contact resistance and IMC thickness versus the bonding parameters

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