Effects Of Laser Parameters On The Mechanical Response Of Laser Irradiated Micro-Joints
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Effects Of Laser Parameters On The Mechanical Response Of Laser Irradiated MicroJoints Ahsan Mian1, Tonfiz Mahmood2, Greg Auner3, Reiner Witte4, Hans Herfurth4, and Golam Newaz2 1 Mechanical and Industrial Eng., Montana State University, 220 Roberts Hall, Bozeman, MT, 59717 2 Mechanical Engineering, Wayne State University, Detroit, MI, 48202 3 Electrical and Computer Engineering, Wayne State University, Detroit, MI, 48202 4 Center for Laser Technology, Fraunhofer USA, Plymouth, MI, 48170 ABSTRACT This paper is devoted to the laser irradiated joints between glass and polyimide. To facilitate bonding between them, a thin titanium film with a thickness of approximately 0.2 µm was deposited on glass wafers using the physical vapor deposition (PVD) process. Two sets of samples were fabricated where the bonds were created using diode and fiber lasers. The samples were subjected to tension using a microtester for bond strength measurements. The failure strengths of the bonds generated using fiber laser are quite consistent, while a wide variation of failure strengths are observed for the bonds generated with diode laser. Few untested samples were sectioned and the microstructures near the bond areas were studied using an optical microscope. The images revealed the presence of a sharp crack in the glass substrate near the bond generated with the diode laser. However, no such crack was observed in the samples made using fiber laser. To investigate further the reasons behind such discrepancy in bond quality, three-dimensional uncoupled finite element analysis (FEA) was conducted for both types of samples. The transient heat diffusion-based FEA model utilizes the laser power intensity distribution as a time dependent heat source to calculate the temperature distribution within the substrates as a function of time. INTRODUCTION Novel biomedical products, implantable microsystems in particular such as devices that electrically stimulate and / or record neural activity [1, 2], are designed with a high level of device integration and miniaturization that pose new challenges to their assembly and packaging. Such devices may include various biocompatible materials such as glass, ceramic and polymers that must be reliably joined in similar and dissimilar combinations. Conventional joining techniques such as the use of adhesives have several drawbacks such as they often lack longterm stability, shrink during curing, and sometimes do not meet biocompatibility requirements. High heat input during soldering or brazing may potentially damage the implant electronics that are being packaged. The common disadvantage of all of the conventional joining processes is that they do not perform well for localized bonding at the sub-millimeter scale. These limitations can be overcome by laser joining techniques that intrinsically provide excellent focusing to spot sizes in the micrometer range. In addition, the precise control of the laser power in the focal spot enables highly localized processing with minimum heat effect outside the
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