Parametric investigation of solder bumping for assembly of optical

Laser based solder bumping is a highly flexible and fast approach for flux-free soldering of micro-optical components in complex 3D geometries with localized and time restricted energy input. Solder joints provide superior mechanical strength, higher radiation stability, humidity resistance and a good thermal and electrical conductivity compared to adhesive bonding. Due to the good long term stability solder joints are feasible for the integration of optical, mechanical, electronic, and MEMS/MOEMS devices in multi functional hybrid optical assemblies. Comparative studies of solder bumping of optical components with sputtered thin film metallization on platforms made of Alumina (Al2O3) and Low Temperature Cofired Ceramics (LTCC) with both Au and AgPd thick film metallization were carried out using design of experiment methods (DoE). The influence of the system parameters, laser pulse energy and duration, distance, incidence angle and nitrogen pressure on targeting accuracy and bond strength were evaluated. The jetting of liquid solder spheres within a localized nitrogen atmosphere improves wetting on the respective wetting surfaces and simplifies the joining process due to integration of solder alloy preform handling and reflowing, thus showing great potential for a high degree of automation.