Optical microsystems, which can be fabricated using replication technology and assembled using optical surface mounting techniques, can offer compact, cost-effective solutions for applications in optical communication, metrology, sensors, illumination and displays. Especially adapted to the needs of mid-size volume production of a few hundred to thousands modules is wafer-scale replication.
The fabrication of single micro lenses or lenslet arrays on wafer substrates and the wafer-scale replication of such lens arrays for optical microsystems in sol-gel materials is under development as a cost-effective alternative to lens fabrication in glass. For an optical microsystem with a compact module for laser beam forming, wafer-scale, singlesided and double-sided replication has been developed to fabricate refractive or diffractive optical elements onto glass substrates. Combined opto-mechanical modules have been UV-cast-replicated from a sol-gel master in a single step. In addition, step & repeat replication can be employed for the fabrication of large arrays of custom specific lenses. Replication accuracy of better than a wavelength has already been achieved for refractive lenses with 50 μm SAG. Finally, diced optical components from the replicated wafers will be used for the manufacturing of micro-optic systems. A six-axis robot motion, automated optical alignment and laser-reflow soldering method is used to assemble the photonics modules. This method, called TRIMO-SMD (three-dimensional miniaturized optical surface-mounted device), is currently being made commercially available by Leica Geosystems AG.
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.