Bonding strength analysis for curing-in-the-loop precision bonding (Conference Presentation)

In micro-assembly of optical systems, active alignment can help to relax tolerances and guarantee optimal results for individual units by evaluating the actual system performance or suitable key-performance-indicators. Combined with capable micromanipulator technology bonding becomes the limiting factor in the overall assembly process. Due to unpredictable properties of the individual adhesive gap, volumetric shrinkage during curing is not sufficiently predictable for a robust compensation. In the past, Fraunhofer IPT presented curing-in-the-loop as a solution for increased precision in the bonding process. The measurement information from a preceding active alignment control loop can also serve as input during the bonding process. The observed and quantified shrinkage in the first moments of the curing process allows predicting the entire displacement due to volumetric shrinkage. A last correction step before the final curing dose leads the remaining shrinkage to approach the target pose. This curing-in-the-loop-strategy provides several parameters for tuning, which directly affect the achievable bonding strength. The segmentation in initial and final curing phase, the UV-doses, the time window to measure and evaluate and the amount of correction are just some examples. In this paper, we will present the bonding strategy and its parameters in detail and investigate the effects on the bonding strength of UV-cured adhesives. Especially the amount of correction during the curing process is an unknown process parameter.