To achieve a mechanically sound soldered joint, the glass must be coated all round with a layer of material capable of being soldered. This material must withstand high thermo mechanical loading and must be well wetted on the surface by the liquid metal solder. At the same time, however, no diffusion of the metal solder must be allowed to occur through the coating to the glass surface in order that the adhesive strength of the joint is not compromised. Coatings for the metalization and soldering of glass have been developed at Fraunhofer IWM. A system of multiple layers with a ceramic bonding agent and solder able intermediate and cover layers has proved itself particularly suitable. Thus the metal band can be joined to the glass by means of a metal coating of the glass and soft solder.
A promising approach to realizing high-performance, high-insulation window glazing is to create a long-lasting high vacuum between two sheets of glass. To enable this, the space for the vacuum between the flat glass panes must be sealed so as to be gas-tight and pressure-tight. A direct, rigid soldered join between the edges of the panes is only stable in the long term for small window dimensions. As the pane dimensions increase, the mechanical tensions acting at the rigid edge joint during use also increase. An edge joint concept has been devised at Fraunhofer IWM based on a soldering process that, featuring a flexible metal band between the panes, is also suitable for large glazing formats. The metal film used is specially adapted to the thermal expansion of the glass and can be soldered to glass using a metal solder.
To evaluate the mechanical strength of soldered glass-to-metal joints, a removal device is used to pull the metal film from the glass and thereby measure the adhesion strength.
We develop joint techniques that take into account the chemical, thermal and mechanical properties of glass as material. We functionalize glass surfaces by means of specially developed multi-layer coatings, evaluate soldering materials and adjust the process parameters as required. It is our aim to match the base material, solder material and process sufficiently closely that dimensionally stable and vacuum-tight joints are obtained.