In-vacuum bonding of X-ray optics by means of laser-based soldering
X-ray optics, such as e.g. for ESA's ATHENA (Advanced Telescope for High-ENergy Astrophysics) mission, often require that their alignment takes places under vacuum conditions, in particular when high precision and the compensation for vacuum-related distortion states is mandatory. In order to fixate the alignment state, standard bonding technologies for x-ray optics, such as clamping or adhesive bonding, only can be carried out at ambient conditions, causing a potential change of the alignment state when transiting from ambient condition to vacuum. In a study issued by ESA, the use of a specific laser-based soldering technology to be carried out under vacuum conditions was successfully conducted. The socalled "Solderjet Bumping"(SJB) technology combines solder alloy preform singulation and handling as well as laserbased reflow and placement at the desired, metallized bonding areas for x-ray optics. Achieving de-alignment less than a millirad during soldering under <1e-4 mbar vacuum condition is reported for complex and 3D x-ray optics geometries. Also, ca. twice the bonding strength was reached, compared to adhesive bonds carried out at ambient conditions.