Fraunhofer researchers optimise endoscope with microbonding

Assembly Automation

ISSN: 0144-5154

Article publication date: 18 April 2008



(2008), "Fraunhofer researchers optimise endoscope with microbonding", Assembly Automation, Vol. 28 No. 2.



Emerald Group Publishing Limited

Copyright © 2008, Emerald Group Publishing Limited

Fraunhofer researchers optimise endoscope with microbonding

Article Type: Mini features From: Assembly Automation, Volume 28, Issue 2.

New type of microbonding prevents damage to endoscope lenses

Endoscopes are exposed to extreme fluctuations in temperature during sterilisation. The extremely sensitive objective often suffers as a result. Erroneous images are the consequence, so that many appliances have to be replaced prematurely. Scientists at the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM) in Bremen have now developed a process that significantly improves the durability and efficiency of endoscope objectives. IFAM is the largest independent European institute of research, development, and further education in the field of adhesive bonding technology. It offers engineers and technicians from all over Europe a seminal qualification programme with internationally recognised diplomas in adhesive bonding technology.

Modern medicine would be unthinkable without endoscopy. The optical instruments not only aid doctors in the examination of the intestinal tract and other parts of the body, but also provide invaluable services during operations, since medication can, for example, be administered and tiny instruments inserted via the endoscope.

Harmful stress

The frequent and necessary sterilisation of endoscopes does, however, subject the highly sensitive objectives to a great deal of stress. The endoscope objective is less than 2mm in diameter and consists of several lenses bonded one behind the other. Rapid heating to 1348 and subsequent cooling cause the lenses to expand considerably and then contract again.

The problem is that, because the lenses are made of chemically different types of glass, they do not do this uniformly. This causes stress inside the objective that can affect the bonding layers. These are only 5-10mm thick five to ten times thinner than a human hair and therefore not thick enough to counterbalance such stresses. Possible results: such “assembly stress” causes the bonding layer to become detached at some points so that small bubbles or marks can form there, which may blur or distort the image. The resulting images can be confusing and, in the worst case, even misleading to the examining doctor. If stress within the objective is too great, the entire adhesive bonding can tear.

Microbonding, a high-performance technology Scientists at the Fraunhofer IFAM in Bremen have now developed a highly efficient adhesive bonding process that can withstand such temperature shocks without the layer thickness having to be increased. This ensures the efficiency of the endoscope and significantly extends the instrument's life.

“We have selected and tested 25 adhesives. Not all deliver what the manufacturers promise,” explains Dr Thomas Gesang, a Microbonding Specialist with the Fraunhofer IFAM. He and his colleagues discovered that adhesives first hardened with ultraviolet light and then with heat are particularly well suited to micro-optical applications such as endoscope objectives. “It is not, therefore, merely a question of using the appropriate adhesive, but rather of optimising the entire adhesive bonding technology.” These include the careful cleansing and preparation of adhesive surfaces so that firm bonding can be achieved in the first place. To this end, the IFAM researchers used solvents in their trials; plasma methods are ideal for industrial application. Bubble-free, smooth application of the adhesive is an equally important aspect. This prevents stress that would later damage the bonding layer.

A complete know-how package

In order to avoid residual stress, it is essential that the bonding layer cures uniformly. This is quite a challenge with lens adhesives, however, since the lenses focus or scatter the UV light to which they are exposed differently, so that an inhomogeneous UV curing results. If adhesives that cure with a combination of UV light and heat are used, the curing stages can be co-ordinated so that residual stress is kept to a minimum. “It is important to take the different factors into account so as to keep assembly stress to an absolute minimum. We have developed a complete know-how package that ensures the quality of such micro- optical adhesive bonds,” says Dr Gesang.

Another area to which the scientists at the Bremen Fraunhofer IFAM are devoting their research is electro- optics. Here, they have experimented with VCSEL light-emitting diodes that are used in communication technology in order to convert optical signals into electrical ones. Owing to the adhesive bonding process developed by the scientists in Bremen, the components are mounted so enduringly in their housing that they remain in the same position precise to the micrometre for as long as 20 years without the slightest displacement.

Qualification in adhesive bonding technology is crucial to success “What is true of all areas of adhesive bonding technology is particularly apparent In microbonding, which can only develop its great potential if it is backed up by sophisticated know-how that's precisely implemented by trained production staff. Against the background of practice-related research, the Fraunhofer IFAM offers further training programmes that meet such high standards,” says Professor Dr Andreas Groß Head of Center, Adhesive Bonding Technology, at the Fraunhofer IFAM.

In the IFAM qualification programmes, planners, decision makers and practitioners acquire state-of-the-art knowledge in line with industry needs and at the same time profit from the latest scientific findings. The range of topics spans the great array of adhesives and their material-specific application as well as the most important trends in adhesive bonding research. The international European-certificate courses additionally introduced at the IFAM in English are based on many years of experience. Since, 1994, well over 2,000 machine operators, technicians and engineers from all branches of industry have been trained in Bremen. From the outset, the IFAM and its experts have made an international contribution, training technicians from the USA, Great Britain, Turkey, South Africa and Norway.

Information on the training courses

EWF European Adhesive Bonder: one week with 40h, working language English EWF European Adhesive Specialist: three weeks with 120h, working language English EWF European Adhesive Engineer: eight weeks with 324h, distributed over 11 months, working language English.

Further information at:; mailto:

Related articles