Micross

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Why Wedge Bond?
Keywords: Wire Bonding, Wedge Bonding, Ultrasonic welding
In the past, ball bonding has dominated the interconnect market because of its high speed and capabilities. But now as interconnect density is becoming greater (the ITRS roadmap predicts that we are heading towards 20 µm pitch) ball bonding is reaching its limits. Wedge bonding, because it can produce a smaller full strength weld than ball bonding, has the potential to dominate the market in ultra fine-pitch devices. Wire bonding is a welding process and ultrasonic welding is accomplished by deforming the wire and the substrate together, forming them into an alloy of the two constituents. Ultrasonic energy enhances the process by lowering the flow stress and allowing easy slip mechanisms for dislocation movement (deformation occurs by the movement of dislocations). Wedge bonding, because it directly deforms the wire without first forming a ball, is capable of producing a weld with less deformation than ball bonding. High quality welds can be produced with bond width 20-25% larger than the wire diameter. This size is significantly smaller than the minimum size that a ball bonder can produce for the same wire diameter. Figure 1 shows the common bonding processes and compares their deformation as a function of initial wire diameter for an optimized process.
Lee Levine, Consultant
Hesse & Knipps Inc.
New Tripoli, PA
USA


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