Optimising stencil printing process with 3D automatic solder paste inspection machine

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Supervisor:
Dr. Krammer Olivér
Department of Electronics Technology

The purpose of this thesis is to optimize the stencil printing used during the reflow soldering process in the electronic assembling industry. The applied gauge during the measurements is a 3D automatic solder paste inspection machine. In order to develop the process, I would like to design and implement experiments with proper parameters.

The first step towards optimization is a detailed research in literature of the reflow process and the design of experiments. During my design of experiment I applied the most commonly used methods (Taguchi).

Three experiments have been designed in which I would like to investigate the durability and impact of the nano coating to stencil printing. I would like to reduce the frequency of stencil cleaning as well. The third experiment analyses the impact of 4 factors (squeegee type, stencil frame type, printing speed, separating speed) to the transfer ratio of stencil printing.

The result of the first experiment is that with the applied printing setup the nano coating has no effect to the transfer ratio.

The second inspection proved that lack of stencil cleaning does not influence the transfer ratio but the standard deviation of the results. According to the absolute difference between the transfer ratios of two consecutive printing I recommend to implement a stencil cleaning after the 6th or 7th printing in order to ensure to stability of the process.

From the 4 factors chosen according to the literature of stencil printing my experiment showed that the two most significant are the frame type and the printing speed, but it depends on the type of components. Accordingly I recommend a compromise solution as an optimal. This solution guarantees the best average transfer ratio. My recommendation is enclosed head printing, 12 mm/s printing speed, 70 mm/s separating speed. For the frame type I recommend different variants depending on the component type. For 0,4 mm QFN and 0603 size component I recommend Hightension Vectorguard frame. For 0,4 mm QFP and 0402 size components I recommend normal Vectorguard frame. For 0,5 mm BGA and 0201 size discrete components I recommend mesh mounted stencil. For the issues occurring during production in connection with the amount of solder paste recommendation can be easily found by the last experiment.

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