Publications

In the present work the authors describe the adaptation of a standard SEM into a flexible microjoining tool. The system incorporates exceptional control of energy input and its location, environmental cleanliness, part manipulation and especially, part imaging. Beam energetics, modeling of thermal flow in a simple geometry, significant effects of surface energy on molten pools and beam size characterization are treated. Examples of small to micro fusion welds and molten zones produced in a variety of materials (Ni, tool steel, Tophet C, Si) and sizes are given. Future directions are also suggested.

A non-contaminating, non-contact method to open glass-cap type MEMS (Micro-electromechanical systems) packages by separating the silicon substrate from the glass cover using a CO2 laser is presented. Current methods for opening these packages are cumbersome, can lead to sample contamination and are not easily done under vacuum. The package is placed in an evacuated chamber connected to gas-sampling equipment and processed through a ZnSe (transparent to 10.6 μm laser radiation) window. Laser-induced heating promotes initiation and propagation of cracks in the cover glass or at the glass/Si interface resulting in separation of the cover from the substrate. Two techniques are discussed. First, local perimeter heating of the package creates a compressive stress zone, surrounded by a tensile stress zone. Tensile zone motion relative to natural or artificially induced flaws promotes selective crack growth and propagation leading to complete separation. Second, overall heating of the package creates a coefficient of thermal expansion (CTE) difference. In both techniques the sudden release of stored residual stresses may be sufficient to "flip" the lid off the substrate. Careful tuning of the process (temperature rise and energy density) is necessary to minimize or eliminate chip debris and avoid package degassing which confuses gas analysis.