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|Why Wedge Bond?|
|Keywords: Wire Bonding, Ultrasonic bonding, Wedge Bonding|
|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 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. Wedge bonding, because it directly deforms the wire without first forming a ball, is capable of producing a weld with minimum deformation. High quality welds can be produced with deformation of 20-25% larger than the wire diameter. Figure 1 shows the common bonding processes and compares their deformation as a function of initial wire diameter for an optimized process. New wedge bonders have many new capabilities. They are much faster than previous generation machines, now in excess of 6 wires/second. New constant loop height and constant loop length algorithms achieve optimum control of electrical properties (impedance, capacitance). Low loop capability is superior because there is no ball adding to the bond height. Bond placement accuracy has improved. New machines are capable of 1µm bond placement repeatability @3. This enables them to achieve the finest pitch available for any wire bonding process. Wedge bonding will be the leader in ultra fine-pitch interconnection.|
|Lee Levine, Consultant
Process Solutions Consulting, Inc.
New Tripoli, PA