Effect of ultrasonic capillary dynamics on the mechanics of thermosonic ball bonding (original) (raw)
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Ultrasonic wedge/wedge-wire bonding is used to connect electrical terminals of semiconductor modules in power electronics. The wire is clamped with a tool by a normal force and ultrasonic vibration is transmitted through the wire into the interface between wire and substrate. Due to frictional processes contaminations like oxide layers are removed from the contact zone and the surface roughness is reduced, thus the real contact area is increased. In the next step of bond formation, thermomechanical forces create micro-junctions between the wire and substrate and the bond strength increases. The bond parameters like the bond normal force, the ultrasonic vibration amplitude and the geometry of the clamping tool show a high influence on the strength and reliability of the wire bond and need to be investigated in detail. Therefore, in this contribution the dynamical behaviour of the ultrasonic system, the wire and the substrate are modeled in form of substructures, which are connected b...
In situ ultrasonic force signals during low-temperature thermosonic copper wire bonding
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IEEE Transactions on Components, Packaging and Manufacturing Technology, 2013
ABSTRACT A ball bonding process in wire bonding generally involves impact followed by ultrasonic (US) bonding prior to wedge bonding. During the ball bonding process, the impact force flattening the free-air ball introduces significant localized out-of-plane compressive stress on the pad and the low-k structure beneath. The subsequent process of US bonding induces in-plane and shear stresses to the structure. High induced stress during bonding is not desirable, as it may lead to pad damage or cratering of the silicon structure. In this paper, we report on studies conducted on using four piezoresistive sensors embedded underneath the center of the bond pad for the evaluation of in-plane and out-of-plane stresses, which covers both the impact and US stages during the ball bonding process. Different levels of impact force, bond force, bonding duration, and US power are investigated using gold wire bonding for feasibility and sensitivity studies of the stress sensors. Fast Fourier transform (FFT) and inverse FFT are used for noise filtering and to isolate the US signal yielding a continuous output signal from the in situ measurement of contact and US stages during the ball bonding process. It is found that the stress sensors are sensible to capture different impact force, bond force, bonding duration, and US power.