Fraunhofer: Solder bumping to replace adhesives in optical devices

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The Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) in Jena, Germany, has developed optical components that employ Pac Tech GmbH’s specialist solder bumping technology instead of adhesives.

Conventional optical components in microscopes or cameras are kept in place by adhesives. When in vacuum or in high temperature environments, the optical properties of the lenses are altered. Gas molecules from adhesives under vacuum deposit on the lenses, where elevated heat renders the adhesives soft or brittle, causing them to slip out of place.

The IOF has replaced the use of adhesives using solder bumping (a technology normally used in electronics manufacture) to join optical components. Erik Beckert from the IOF says: “This has a definite advantage: the solder material is resistant to extreme temperatures and radiation, and also conducts heat and electricity.”

The technique consists in passing small balls of solder through a capillary where they are heated by a laser beam. The resulting liquid solder droplets are directed to the spot where they will fix the lens by a nitrogen pressure pulse. The droplets cool and solidify within a few milliseconds.

Beckert says: “This process can be automated and is very flexible. We can apply the solder downwards or from various other angles and in places that are difficult to access.”

Beckert estimates that this system will be optimised for use in production by 2009/2010. Researchers will present prototypes of optical components fixed in place by solder bumping at Optatec in Frankfurt from 17 to 20 June 2008.