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Description
The limitations of bond wire performance under pulsed conditions are of particular interest in the development of high current Photoconductive Semiconductor Switches (PCSS) for pulsed power applications. Literature regarding the limitations of bonded wires under DC (steady state) conditions are readily available. However, the current carrying capability of bond wires under pulsed conditions has not been studied extensively, especially for the case of the very small wires with less than 6.4x10-4 cm2 typically used for semiconductor development.
The current handling capabilities of gold cylindrical wires with radius 0.0254 mm (1 mil) and Aluminum ribbon wires with rectangular cross-section measuring 0.0254 mm x 0.2540 mm (1 mil x 10 mil) are investigated under pulsed conditions. Pulsed widths range from 8 µs to 24 µs with current peak densities covering 2.5 x 106 A/cm2 up to 6.2 x 106 A/cm2. The wires were bonded using a TPT HP05 manual wire bonder and two bonding techniques: ball bonding for cylindrical wire consisting of ultrasonic plus heat and wedge bonding for the ribbon wire consisting of only ultrasonic forces. Two failure modes are characterized: bulk failure and bond failure. Bond failure result in the wire disconnecting at the bond location. Alternatively, a bulk failure typically occurs along the wire itself.
Post mortem SEM imaging was used to determine if the wire was vaporized from excessive ohmic heating or if mechanical stresses played a role in the failure. High speed imaging was also used to capture the time progression of the failures. The integral of current action (ICA) is used to analytically predict the wire current limit for a specific excitation current. These theoretical predictions are compared with the experimental results.
This research was supported by the Air Force Research Laboratory (AFOSR) under contract number FA9550-14-1-0019.
