Measuring setup for compensation of shrinkage induced misalignments of adhesive bondings

Adhesive bonding is the major means of fixing mechanical and optical components and systems. However, the shrinkage of adhesives during curing changes their mutual alignment, depending on the thickness of the adhesive layer, the percentual volume shrinkage of the adhesives, the curing temperature, and the shape of the join patch. A concept for shrinkage compensation is the modification of the thickness of the adhesive layer by an offset during initial alignment, as a function of measured shrinkage properties. The developed measuring setup can characterize shrinkage properties with measuring uncertainties less than 1 μm and allows for discriminating between different reasons of misalignment during curing. It consists of two probes. One is fixed, and the other flexible in three degrees of freedom on an actuator system. Their positions are measured by two independent measuring systems which use customized mirror surfaces as reference planes and detect these by interferome ters and capacitive sensors. Materials with low coefficient of thermal expansion minimize potential thermally induced misalignment of the measurement device. The thermal distribution of the setup is stabilized by a cooling system and controlled by temperature sensors. The results show the measured absolute deviation of adhesive layers in a range of 1-5 µm and the change of the alignment status in three degrees of freedom (adhesive layer thickness, tip and tilt). The concept of offsetting the shrinkage induced misalignment was proven.