| Summary: | 碩士 === 義守大學 === 機械與自動化工程學系碩士班 === 97 === Wirebonding assembly has been widely used in the semiconductor package for the past two decades. The welding wire bonding technology is based on electricity as a link and as the transmission of signals. Material strength of copper wire is higher than gold wire. Higher strength copper brings about Al pad shovel (excessive plastic deformation) around the ball bond when wirebonding process is conducted. Reliability in Copper wire bonding process includes ball lifted, peeling and cracking beneath bond pad. Manufacturing process also required special attention to prevent oxidation.
This research involves in four parts: In the first, Young’s modulus on ultra thin surface is experimentally determined by nano indentation instrument. Secondary, Atomic Force Microscopy (AFM) is applied to measure interfacial frictional coefficient and the surface roughness. In the third, corrosion experiments for gold wire and copper wire are performed and observed for metallographic. The last is that numerical prediction for wirebonding process is conducted based on commercial finite element software of ANSYS/LS-DYNA.
The surface tensile mechanical properties for ultra thin gold wire, copper wire and Al pad are obtained through nonointentation technology. Atomic Force Microscopy (AFM) is applied to measure the micro surface coefficient of frictional force. The measured interfacial coefficient of frictional force between silicon-based cantilever beam and specimen material need to be correlated on thrust force and normal force. Surface roughness on Al pad is specially focused because uneven surface will affect the wire bonding process. Therefore, the interfacial frictional mechanism on Al pad needed to be carefully analyzed.
The accurate experimental material data should be reflected as input for the precise finite element analysis. Numerical model based on explicit time integration scheme software ANSYS/LS-DYNA is developed to predict the first bond (ball bond) of wirebonding process. The impact effects on structure stressed area during wire bonding process are investigated and the shovel (large plastic deformation) of Al pad was observed during transient ultrasonic vibration stage. It is noted that the material of bond pad should be Al-Cu pad instead of pure Al pad. Special emphasizes are focused on the underlay via layouts and the optimal design of microstructure beneath the bond pad. A series of comprehensive parametric studies were conducted in this research.
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