AuSn solder in photonics assembly

Soldering is used today in various applications and therefore has to fulfill different requirements. In photonics integration AuSn solder plays a special role. It is used as a fluxless process which is mandatory in order to avoid any contamination of optical surfaces. Post cleaning processes are often excluded as the results are often not satisfying and difficult to monitor. For optical alignment often a post bonding accuracy of 1 mum is required. This will need a precise bonder or self-alignment capability provided by the solder. To keep the position stability for long time AuSn is especially recommended due to the high creep resistance up to high temperatures.