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In Situ Measurement and Stress Evaluation for Wire Bonding Using Embedded Piezoresistive Stress Sensors

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6 Author(s)
Woon Yik Yong ; Institute of Microelectronics, Agency for Science, Technology and Research, Singapore ; Xiaowu Zhang ; Tai Chong Chai ; Alastair Trigg
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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.

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IEEE Transactions on Components, Packaging and Manufacturing Technology  (Volume:3 ,  Issue: 2 )