Joining technologies in optical and micro assembly

Bonding and laser soldering for harsh operating conditions

Joining technologies in optical and micro assembly have a critical influence on the accuracy and stability of the systems to be integrated in long-term use. This is particularly critical for harsh operating conditions in applications such as automotive, medical technology and aerospace. Fraunhofer IOF has extensive know-how in the field of bonding technologies for optical, opto-mechanical and opto-mechatronic systems as well as in the alternative laser-based soldering.

Your partner for the assembly of stable optical systems

In addition to the analytical and FEM-based simulation and optimization of joints, Fraunhofer IOF also conducts fundamental research into bonding and laser beam soldering technologies and adapts them to customer-specific tasks. This includes the selection of adhesives that are particularly suitable for optics and their solidification mechanism, the necessary pre-treatment of surfaces to be bonded, the reproducible application of the required adhesive volumes for both high and low viscosity media, as well as the statistical determination of strength and accuracy parameters. The same applies to the alternative laser beam soldering, in which inorganic-metallic soft solders are used as joining media with improved stability properties. An essential feature of all joining technologies is the know-how regarding the attainable accuracy and its stability under different environmental conditions.

Laser beam soldering for optical and opto-mechatronical systems

For laser-based soldering of optical components, the processes of laser through-hole soldering through transparent materials as well as solderjet bumping as a proprietary and patented technology are available. Laser through-hole soldering uses a sputtered, eutectic AuSn thin-film metallization that is applied to flat and polished glass and silicon surfaces. This makes it possible to produce flat joints with high strength and very good parallelism, as the quality of the optical surface is directly transferred to the precision of the soldered assembly.

In laser-based solderjet bumping, the molten solder is applied to almost any metallized 3D joining geometry using a dispensing capillary. This process is similar to bonding but replaces the joining medium with an inorganic-metallic soft solder with improved properties. The advantage here is the temporally and locally limited energy input using a laser to remelt the solder material. The patented technology is suitable for both macroscopic assemblies and miniaturized components such as, e.g., glass fibers.

Bonding for optical and opto-mechatronical systems

Bonding technologies for optics are developed at Fraunhofer IOF for demanding application scenarios in the automotive, medical technology and aerospace industries. The know-how includes certified adhesives, dispensing technologies for high- and low-viscosity adhesives with the smallest volumes in the nano- and picoliter range, the pre-treatment of surfaces via cleaning and plasma treatment, the application of adhesives with suitable elasticity to compensate for thermomechanically induced stresses, and special adhesives for optics with special properties, such as low outgassing, stability against radiation, or high humidity.

Our research strength

Research reports

The research strength of our experts is reflected, among other things, in the contributions to the Fraunhofer IOF Annual Report. Every year, selected research results from the previous year are published in this report (archive annual reports) Here you can find the articles on developments relating to joining technologies from previous years:

• »Assembly and joyning techniques for the Exomars expedition«
  (Annual report 2017, page 40-41)
• »Entangled photon source for quantum communication«
  (Annual report 2017, page 68-69)
• »Novel wire deflection system for electron beam lithography«
  (Annual report 2016, page 60-61)
• »Low-stress soldered lenses for high performance objectives«
  (Annual report 2015, page 54-55)