Surface mount technology is a common way to assembly electrical components onto PrintedCircuit Boards (PCB). To assemble the components, solder paste is used. One way to apply solderpaste onto PCB is jet printing.The quality of the solder paste deposits on the PCB depends on the properties of the solder pasteand the ejection parameters settings of the jet printer. Every solder paste is unique with its owncharacteristics. Solder paste dots are of good quality if the positioning of the dot is good, the dotis circular, and the number of satellites is at a minimum. A satellite is a droplet that has fallenoutside the main droplet. The parameters that have the most effect on the solder paste are thewaveform parameters Rise time and Voltage level.This master thesis examined the possibility to design and implement a feedback-based machinelearning algorithm that can find the most suitable value for the Rise time and Voltage level, thatgives good quality of the solder paste deposits. The algorithm that was used was a ReinforcementLearning algorithm. Reinforcement Learning is a reward-based learning algorithm where an agentlearns to interact with an environment by using trial and error. The specific algorithm that wasused was a Deep-Q-Learning algorithm. In this master thesis, it was also examined how the cameraresolution affects the decision of the algorithm. To see the implication of the camera resolution,two machines were used, an older and a newer machine were used where one of the biggestdifferences is that the camera resolution.It was concluded that a Deep-Q-Learning algorithm can be used to find the most suitable value forthe waveform parameters Rise time and Voltage level, which results in specified quality of thesolder paste deposits. It was also concluded that the algorithm converges faster for a lower cameraresolution, but the results obtained are more optional with the higher camera resolution. / Ytmontering är en metod som används för att montera elektriska komponenter på kretskort. Föratt kunna montera komponenterna används lödpasta. En teknik för att applicera lödpasta påkretskort är jet printing.Kvaliteten på lödpastavolymen på ett kretskort beror dels på egenskaperna hos lödpastan, dels påutskjutningssparametrarna hos jetprintern. Varje lödpasta är unik med hänsyn till flödesegenskaper. En lödpastadeposition har god kvalitet om depositionen har en bra position, omdepositionen är cirkulär och om mängden satelliter är minimal. En satellit är en droppe lödpastasom fallit utanför huvuddepositionen. Parametrarna som har störst effekt på lödpasta ärvågformsparameterna stigtid och spänningsnivå.Detta examensarbete undersökte möjligheten att hitta en feedbackbaserad maskininlärningsalgoritm som kan hitta de mest lämpliga värdena för stigtiden och spänningsnivå som ger godkvalitet på lödpastadepositionen. Algoritmen som användes var en Förstärkande inlärningsalgoritm.Förstärkande inlärning är en belöningsbaserad inlärningsalgoritm där en agent lär sig attinteragera med en miljö genom att använda trial and error. Den specifika algoritmen som användesvar en Deep-Q-Learning-algoritm. I examensarbetet undersöktes även hur kameraupplösningenspåverkar algoritmen och dess beslut. För att undersöka detta användes två maskiner, en nyare ochäldre version där att kameraupplösningen är lägre.Slutsatsen som drogs var att en Deep-Q-Learning-algoritm kan användas för att hitta det mestlämpliga värdena för vågformsparametrarna stigtid och spänningsnivå. En annan slutsats somdrogs var att algoritmen konvergerade snabbare när kameraupplösningen är lägre. Parapeternasom är optimala för den kameran med lägre upplösning är inte optimala för den kameran medhögre upplösning.

Printed circuit boards (PCBs) are essential components in various electronic devices, playing a vital role in their functionality. Over time, PCBs have evolved significantly, becoming smaller, more complex, and multi-layered to meet the demands of advancing technology and consumer preferences. The quality of solder paste deposits is measured by circularity, volume, positioning, and the number of satellites. Mycronic is a supplier of jet printing machines for PCB manufacturers and needs to investigate and counteract an unwanted variation in volume and positioning within the first dot of the solder paste strip, and its so-called “sea saw” effect for the following three dots.  This master’s thesis has two aims. The first aim is to develop and evaluate an experimental method to reduce variation between the dots in the strip. The second aim is to reduce the variation between the 1st dot and the following three dots by finding a combination of pre-feed, first, second, and third waveforms to obtain improved precision, volume, circularity, and reduced volume variation. Using an experimental design a full factorial design was used, examining six experimental factors. The design was further augmented with a central composite design to describe the second-order model. The knowledge from the experiment was used to optimize and improve the quality factors of jet printing, which were verified with an additional experiment. The results of the study provided compelling evidence that only the selected experimental factors had a significant impact on improving the volume metric. It was observed that the presence or absence of satellites during the experiment did not have any effect on the results, and neither did the positioning and circularity factors contribute to any improvement or deterioration. Specifically, the most significant difference in volume between 1st and following three dots for the optimized solution is 0.5 nl, and the currently used settings have a difference of 2.65 nl. The experimental approach employed in this master's thesis holds excellent promise for Mycronic, as it paves the way for the future development of piezo-actuation profiles (i.e. specific settings for the jet printer). The potential contributions to the industry are significant, particularly in terms of advancing the methodology for investigating and enhancing the quality metrics of piezo-actuation profiles through experimental means. This research opens up new avenues for Mycronic to refine its printing processes and improve overall print quality, ultimately leading to better outcomes for their customers.

It was investigated the colour reproduction on prints made in ink-jet printer. Experimentally investigated gradation characteristics of CMYK colours. It was made a 26 step strip with raster dots from 0 to 100 %. Prints were made at different printing regimes on papers with different whiteness. Zone optical densities were measured, compared with theoretical density values and gradational distortions were determined. Also were measured 100% raster strips in CIE L*a*b* coordinate system and defined the maximum reproduction of colours in ink-jet printer.