Silicon bonding techniques for X-ray optics: A summary of R&D work carried out by the Experimental Facilities Division Optics Group (XFD-OP) through July 1995

Some of the most efficient heat-exchanger designs for direct-cooled optics consist of two or more pieces of silicon single crystal bonded to each other and attached to a coolant manifold. Therefore, achieving successful silicon-to-silicon and silicon-to-metal bonds has become one of the goals of the high heat load (HHL) optics program. A viable bond for a cooled silicon optic has to satisfy the following requirements: strain free; compatible with the coolant used; radiation resistant; coefficient of thermal expansion of the bonding agent must be close to that of silicon. The techniques that have been pursued by XFD-OP members are: Si-Si direct bonding; Si-Si die attach paste bonding; Si-Si and Si-metal epoxy bonding; Si-Si and Si-metal glass frit bonding; and Si-metal gold-based solder. A description of each of these techniques and their performance are described in this report.