Adapted time-power-profile for laser beam soldering with solder paste

Today laser beam soldering (LBS) is a non-standard manufacturing process for electronic packaging and interconnection technology. However due to the onwardly going miniaturisation and the world-wide trend towards lead-free solders LBS gains more attention for certain applications in this field. In mass-production, e. g. in interconnection technology of electronic devices, it is state-of-the-art to use solder alloys in the form of paste. Today it is a well-known process to handle or to deposit solder paste. Furthermore the composition of solder systems, consisting of metal alloys and fluxes, can be optimised for individual products and production conditions. Yet this optimisation process is only in part performed for LBS with solder paste. Therefore the application of standard reflow solder pastes for LBS poses problems like gas eruptions, solder balling and overheating. In order to overcome these quality problems an adapted time-power-profile for LBS with solder paste has been developed, using synchronised high-speed photography and detection of secondary emissions from the joining area. The evaluation of the experiments allows the generation of high quality solder joints with standard diode laser systems and solder pastes. In addition it is possible to realise an online-process control via detecting the secondary emissions from the subsequent transformation stages of the solder paste. Conclusively it can be said LBS is a stable, reproducible process for applications requiring a controlled locally limited heat input and reduced thermal and mechanical stress compared to conventional techniques.