The Fraunhofer Institute for Laser Technology ILT has developed an innovative packaging process for micro-components and electronic parts based on laser glass soldering, which is suitable for use in mass production and, because it uses lead-free solders, fulfils the stringent environmental regulations of the EU’s RoHS Directive. Electronic and electrical products have to meet a diverse range of increasingly exacting demands, including high integration density, the combination of various materials with specific functionality, and rising requirements for thermal and mechanical stability. Hermetic packaging with high long-term stability poses particular challenges for the production technology, which can no longer be met by conventional methods such as gluing and soldering.
The relatively new joining technique subjects the total component to only minimal thermal loading. Research scientists at the Fraunhofer ILT are currently developing the technique with the aim of introducing it soon into series production. In this joining method the solder consisting of a glass particle paste is first applied precisely to the cover of the component using a print mask. The solder is then pre-vitrified in a kiln at a temperature of 350–500°C depending on the type of glass paste used, so that the binders in the paste evaporate. After the solder has cooled the electronic component is joined to the cover. A defined and locally limited temperature increase is achieved by scanning the solder seam with a laser beam. The rest of the component is not affected by this application of heat. Owing to the high scanning speed of up to 10,000mm per second, the joining process is quasi-simultaneously controlled. The entire solder contour is evenly heated, the cover can sink into the liquid solder bath and is thus hermetically connected to the component. Compared with gluing, Fraunhofer claims that the laser-based method achieves a considerable increase in the durability of the entire micro-component, and the permeability of liquids and gases is practically zero. What’s more, the solder seam is completely free of bubbles and cracks.
The technique is expected to have applications in the medical sector, OLEDs, and other miniaturised, high-precision components.