Thermosonic bonding of gold wire onto silver bonding layer on the bond pads of chips with copper interconnects |
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Authors: | Cheng-Li Chuang Jong-Ning Aoh |
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Affiliation: | (1) Department of Occupational Safety and Health, Chung Shan Medical University, 402 Taichung, Taiwan, Republic of China;(2) Department of Mechanical Engineering, National Chung Cheng University, 621 Chiayi, Taiwan, Republic of China |
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Abstract: | A copper pad oxidizes easily at elevated temperatures during thermosonic wire bonding for chips with copper interconnects.
The bondability and bonding strength of a gold wire onto a bare copper pad are seriously degraded by the formation of a copper
oxide film. A new bonding approach is proposed to overcome this intrinsic drawback of the copper pad. A silver layer is deposited
as a bonding layer on the surface of copper pads. Both the ball-shear force and the wire-pull force of a gold wire bonded
onto copper pads with silver bonding layers far exceed the minimum values stated in the JEDEC standard and MIL specifications.
The silver bonding layer improves bonding between the gold ball and copper pads. The reliability of gold ball bonds on a bond
pad is verified in a high-temperature storage (HTS) test. The bonding strength increases with the storage time and far exceeds
that required by the relevant industrial codes. The superior bondability and high strength after the HTS test were interpreted
with reference to the results of electron probe x-ray microanalyzer (EPMA) analysis. This use of a silver bonding layer may
make the fabrication of copper chips simpler than by other protective schemes. |
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Keywords: | Silver bonding layer thermosonic wire bonding chips with copper interconnects high-temperature storage (HTS) test |
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