High-precision surface mount assembly of micro-optical components per laser reflow soldering: positioning accuracy and thermal stability

Abstract

A significant part of the work in developing micro-optics devices is solving the aspect of the packaging. The optical design requires very often an exact positioning of the optical components along the six degrees of freedom. Numerous techniques are now proposed for aligning (passively or actively) and fixing the optical components in the aligned position for a long-term stability. The Swiss Federal Institute of Technology in Lausanne and Leica Geosystems in Heerbrugg developed a novel automated assembly technique called TRIMO-SMD suited to assemble modules composed of small optical components (maximum diameter of 2mm). The attachment procedure is based on a highly stable laser reflow soldering process between standard metal holders housing the optical components and a metallized transparent mounting plate. The active alignment in all six degrees of freedom of the optical holder is performed with a high stiffness and high-resolution robot system. A test procedure has been developed for quantifying the positioning accuracy after soldering and the thermal stability of the TRIMO mounts. The displacements of the TRIMO holders during the soldering process and during a thermal load have been measured by means of standard laboratory vision sensors along with a 2D least square matching processing. One micron TRIMO assembly precision could be demonstrated.