Reiner Witte, Hans Herfurth, Stefan Heinemann

Fraunhofer Center for Laser Technology, 46025 Port Street, Plymouth, Michigan, USA

Abstract:  

New joining techniques are required for the variety of materials used in the manufacture of microsystems. Lasers are emerging as a useful tool for joining miniaturized devices. The beam can be focused to less than .001” allowing localized joining of very small geometries. There is minimal heat input into the part so distortion and change in material properties is minimal. The high quality of the laser welds and the precise process control enable hermetic sealing. Glass to silicon bonds are required in a vast array of opto-electronic components, including laser sources, sensors, switches and multiplexers. Typically, adhesives as well as direct and anodic bonding techniques are used to join the different materials. Adhesive residues, low bond strength, heating of entire parts during joining and poor long-term stability are disadvantages of these conventional techniques.

Laser bonding is a promising alternative due to the increased bond strength and high repeatability. Compact and efficient diode lasers equipped with fiber beam delivery in the power range of <50W are applied to the sandwiched glass-silicon structure. During bonding, the laser beam penetrates the upper part and is absorbed at the surface of the bottom part. A clean environment and good part fit-up is required to ensure proper bonding, high bond strength, and hermetic sealing. The process eliminates adhesives; therefore reducing costs due to shorter cycle times, lower maintenance and less inventory. The process requires no handling of toxic liquids and creates no fumes. Furthermore, the bonded parts are free of any residue or contamination, reducing scrap rates. This study investigates the process parameter window and determines the impact on the parts and the stability of the process. The results will lead to the development of several applications in the areas of telecommunications, biomedical devices and MEMS. This includes the encapsulation of MEMS, the covering of sensors and the packaging of biomedical products. The selectivity of the process will be demonstrated on flat coupons.