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Large Diameter Wedge Bonding of Round and Ribbon Wire for Automotive Applications
Keywords: Wire Bonding, Interconnect, Ribbon Bonding
Wedge bonding is widely used for interconnection of automotive Engine Control Modules (ECMs) and other under the hood devices. Large diameter aluminum or copper round or ribbon wire are commonly used because of the high current that many of these devices require. A 20 mil diameter, 100 mil length, 99.99% Al round wire can carry 120 Amps [A] safely (safe capacity is defined as less than 830C temperature rise) which is sufficient for a starter circuit. Figure 1 provides a graph of Safe Current Carrying Capacity [Amps] as a function of wire diameter and length for large diameter 99.99% Al wire. Bonding large diameter wire and ribbon requires a lot more energy than bonding fine wire. Ultrasonic generator output is in the 50 Watt range compared to .25 Watts for fine wire bonders. Bond parameters are higher and metallization thickness on leads or on substrates is higher. For cantilever leads the shape and size of the leads must accommodate the larger forces and provide a stable surface for bonding. A wire cutter is used to terminate the wire after second bond rather than the clamp tear used for a fine wire bonder. The dynamics of bonding heavy wire are very different from fine wire bonding. Relative stiffness (deflection under a load) for 20 mil wire is 160,000X that of 1 mil wire (stiffness is proportional to D4 ). During looping significant forces are applied to both the first bond and to the underlying metallization while bending the wire. Loop profile and trajectory have an important effect on minimizing those forces. Looping strategies that minimize bond stress have an important effect on bond quality. Wedge bonders can bond both ribbon and round wire on the same platform with only a minor changeover. Heavy wire wedge bonders can bond both round bonding wire of up to 20 mils diameter and ribbon up to 80 mils width x 12 mils thick. This presentation will focus on the use of heavy wedge bonding for automotive applications. Discussion of metallization requirements, wire properties, bonder parameters and bond strength testing will all be covered.
Lee Levine, Distinguished Member of the Technical Staff
Hesse & Knipps Inc
New Tripoli, PA

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