Tagungsbeiträge

The formation of the melt flow plays a key role in the production of glass due to the required homogeneity of the melt and the quality of the product. Recently, we have reported on the manipulation of the flow velocity of glass melts in crucibles realized by the generation of external Lorentz forces [1]. The electromagnetic effects can be applied to improve the mixing in the melt which results in an enhancement of the thermal and chemical homogenization. In this paper we want to summarize the results of in-situ measurements of temperature and compare these outcomes with the striae formation in solidified glasses in dependence on the used chemical composition of the glass melts (transparent, cobalt oxide doped glass). In the following we deduce the possibilities of acceleration, deceleration and even reversion of the flow from calculated values of the flow velocity resulting from the reversion of the external Lorentz force direction.

Low Temperature Cofired Ceramics, also referred to as LTCC, are interesting materials for the realisation of MEMS in the mesoscale, i.e. dimensions in the range of 100 [my]m up to millimetres. By laminating of several layers to one green part, complex three-dimensional structures are achievable. The typical pattern width of conventional used techniques like punching or laser cutting amounts to approx. 100 [my]m. These techniques usually cut the tape's thickness completely, therefore only structures with a depth of integral multiples of the tape's thickness can be produced and the precision depends on the tolerance of the doctor blade process. Microembossing adds to the variety of technologies for processing LTCC tapes. Structure dimensions of 50 [my]m can be realised easily. In addition to previous studies, focused on the aspect to produce conductor paths of high ampacity by embossing, the present work introduces an embossing technique to achieve fluidic channels with dimensions in the [my]m range under the use of conventional technologies. The embossing step, as a parallel procedure, can be easily integrated in the LTCC process chain. Embossing can be carried out either as the first step or after pre-processing like punching and via filling. The main process parameters are temperature, dwell time and the die's pressure. The embossing has been carried out at a temperature of 57˚C, using a die's pressure of 120 MPa and a dwell time of 5 minutes. Under this conditions, DuPont's 951 GreenTape AX has been moulded with an embossing die made of silicon. Figure 1 depicts profile scans of the mould and the embossed ceramic in the green stage. The lateral dimensions are impressed accurately. In z-dimension the embossed height is reduced to approx. 92 % of the mould's depth. The reason of this derivation might be the elastic deformation of the tape material. The embossed structures have been covered with one layer of DuPont's GreenTape 951 AT, which has a thickness of 114 [my]m in the green stage. No fugitive phases or any other additives have been used. The primary structures height has been reduced of approx. 10 [my]m by the lamination step. The samples have been sawn to examine the channels geometry after sintering. Figure 2 depicts a cross section and a longitudinal section of a channel. The channels have rectangular cross sections and dimensions of 35 [my]m × 35 [my]m. The dimensions of the mould are 50 [my]m in lateral direction and 65 [my]m in z-direction, respectively. In combination with electrical assembling, complex packages for pressure sensors, fluidic devices or BIO MEMS can be produced by this technique. A technique to produce micro fluidic channels in low temperature cofired ceramics (LTCC) is presented. The materials offer a high potential for chip integration and feature inert character as well as temperature resistance. To avoid contaminations, no fugitive phases or other additives have been used for the manufacturing of channels with rectangular cross sections. Fluidic interconnections for pressure sensors or chemical analysis devices can be produced with this method. In combination with other techniques, complex packaging for MEMS fluidic integrations or BIO MEMS can be realised.