Facilitating intermetallic formation in wire bonding by applying a pre-ultrasonic energy

It is conventionally believed that wire bonding initiates at the periphery of the contact area and no bonding occurs in the central area. However, this paper demonstrated that two bonding patterns exist, and are determined by bonding processes. If a selected pre-ultrasonic energy is applied, intermetallic compounds initiate in both peripheral and central area of bonds. However, if a pre-ultrasonic energy is absent, intermetallic compounds are only present at the peripheral area as conventionally reported. The application of the pre-ultrasonic energy significantly improves bonding strength, from 66.8 to 94.5MPa for 20@mm Au wire bonds, due to the intermetallic compounds of greater structured integrity. Two different mechanisms are respectively proposed to account for the intermetallic formation in the center and periphery of the bond interface.

[1]  Jae Pil Jung,et al.  Bonding mechanism in ultrasonic gold ball bonds on copper substrate , 2005 .

[2]  G. Harman,et al.  The Ultrasonic Welding Mechanism as Applied to Aluminum-and Gold-Wire Bonding in Microelectronics , 1977 .

[3]  Y. Zhou,et al.  A footprint study of bond initiation in gold wire crescent bonding , 2005, IEEE Transactions on Components and Packaging Technologies.

[4]  G. Harman,et al.  Wire bonding in microelectronics , 2010 .

[5]  V. L. Acoff,et al.  A micromechanism study of thermosonic gold wire bonding on aluminum pad , 2010 .

[6]  Baohua Chang,et al.  Effects of superimposed ultrasound on deformation of gold , 2009 .

[7]  Michael Mayer,et al.  Footprint study of ultrasonic wedge-bonding with aluminum wire on copper substrate , 2006 .

[8]  S. Timoshenko,et al.  Theory of elasticity , 1975 .

[9]  Mingyu Li,et al.  Evolution of the bond interface during ultrasonic Al–Si wire wedge bonding process , 2007 .

[10]  Junhui Li,et al.  Interface mechanism of ultrasonic flip chip bonding , 2007 .

[11]  Deming Liu,et al.  Effects of process parameters on bondability in ultrasonic ball bonding , 2006 .

[12]  Vadim V. Silberschmidt,et al.  A re-examination of the mechanism of thermosonic copper ball bonding on aluminium metallization pads , 2009 .

[13]  Narasimalu Srikanth,et al.  Effect of wire size on the formation of intermetallics and Kirkendall voids on thermal aging of thermosonic wire bonds , 2004 .

[14]  Vadim V. Silberschmidt,et al.  Initial bond formation in thermosonic gold ball bonding on aluminium metallization pads , 2010 .