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Improvements of a PCB Technology for Micro Fluidic Devices
Keywords: Printed circuit board technology, micro fluidic system, PCB MEMS
When using PCBs for microfluidics there are a few problems to overcome. By applying the technology developed at the University of Rostock it is possible to build devices with the area of about 2 cm. However, the productivity of the technology used to be low. When creating monolithic fluidic systems, a bigger area and a very small failure rate are mandatory. A smaller failure rate of about 10% for building a 25cm fluidic system containing two pumps and some channels can be achieved by adding a new step in the production process. This step is heating up the PCBs over the glass transition temperature of the epoxy resin. As a result, the single PCBs are made to fit so that the 1...2 m thick glue layer is free of mechanical stress. In micro fluidic systems used for analysis, the cross contamination between two probes can be a problem. Cross contamination happens due to the wall roughness of the channel walls. When using areas as a channel wall where the copper is etched away, the mould from the adhesion treatment of the copper backside builds a wall with a roughness of about 20m. This is far too much. The roughness of the channel wall after the coverage with epoxy glue is investigated with the help of surface profiles and Raster Electron Microscope (REM) pictures. The contact to the copper lines of a PCB should be often avoided in micro fluidic systems. Some copper areas have functionality of sealing, e.g., valve seats. At these areas the copper has contact to the fluid. This fact can lead to two problems. One is that copper is toxic to organic samples and the other one is that the highly reactive copper oxidizes so that the valve seat is not able to seal. This is a major life time issue. The coverage with epoxy of these areas is required. The needed amount of epoxy for a full coverage is investigated and presented with the help of surface profiles, cross sections and REM pictures.
Stefan Gassmann,
University of Rostock
Rostock, M-V 18059,
Germany


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