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Bond Tool Life and Bond Process Improvement for Large Copper Wire
Keywords: Copper wire bonding, Large copper wire, Bond tool life
With the use of more efficient die attach technologies, the Al wire as the top side interconnect is becoming the bottle neck in power electronics. The Cu wire having higher electrical and thermal conductivities is a much more efficient and reliable interconnect. The Cu wire is a harder material and wears the bond tool much faster than the Al wire. Improving the bond tool life and maintaining the process stability are challenges for the Cu wire interconnect. The bond tool wear and failure mechanism are investigated. When a bond tool is worn, its groove volume gets larger and the Cu wire sinks more into the groove, so that the tips of bond tool get closer to the substrate. When the bond tool tip touches the substrate and leaves a mark, the ultrasonic energy is dispersed into the substrate and the bond strength is compromised. A bond tool made of a more durable material may have less wear and a longer life, but a new material would likely change the ultrasonic transmission and require a redesign of the entire ultrasonic system. This paper presents three realistic ways to extend bond tool life. By reducing bond tool groove depth, the tip of bond tool is further away from substrates and the bond tool can make more bonds before the tool is worn out and touches the substrate. By optimizing the bond process, a bond tool interacts differently with Cu wire and the bond tool life is doubled. A high coupling bond tool is developed to reduce the relative motion between the bond tool and Cu wire and decrease the bond tool wear. This bond tool has a longer lifetime and fewer Cu flakes generated during the bonding process. By combining bond tool geometry design and bond process optimization, the bond tool life is significantly extended and the process stability is improved.
Tao Xu,
Kulicke and Soffa
Santa Ana, California

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