Deposition of Thick Film Fine Line Patterns by Direct Writing

The process of the direct deposition of thick film materials (somewhere known as direct writing) on ceramic and silicon substrates was investigated. Some newly achieved findings and results are described in this paper. Such approach was chosen as a low cost and prompt alternative for deposition of thick film pastes, especially by low volume batches. The use is for hybrid IC´s, as well as for a wide range of non-conventional applications (for example for front side of solar cells, antennas, CSP interposers etc.). This relatively new technique offers significant cost and time benefits across a wide spectrum of applications because it eliminates expensive masks and tools. Developed at Brno University of Technology is reasonable and no expensive equipment for direct writing deposition with basic characteristics somewhere between the dispensing and the jetting technique. This equipment consists of a plotter drive unit with dispensing head (with z axis motion) which is situated beyond the x, y axis table, and a control unit with software capable to process CAD data. The substantial part of the head is the z axis holder with syringe and dispensing nozzle. The paste is extruded through a hollow needle, working as a non contact dispense nozzle. Z axis motion is required when the head moves down to the paste transfer position and after pattern completion moves up to the starting position. Paste viscosity including temperature conditions, pressure in the cartridge, speed of the nozzle and distance between the nozzle and substrate are the most important parameters for achieve the optimal setting and resulting paste transfer reproducibility. That is the reason why we investigate in more detail the paste transfer which depends essentially on paste viscosity.

Obviously constant pressure, optional heating of the cartridge and constant movement of either the needle or the substrate also have a significant impact on the uniform and homogeneous paste transfer. Various materials under various process conditions are applied to achieve favourable results with good quality and reproducibility.

Subsequently, the shape of the deposited layer has been observed, measured and evaluated. Also electrical properties of the deposited conductor materials were evaluated.