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Dissertação de mestrado integrado em Engenharia de Polímeros, In the automotive sector, the progressive evolution of technology leads to cars with more and complex electronics. Therefore, it is required to develop electronic systems reliable and safe for the customer. For these reasons, electronic circuits may be protected from the environment, specifically from humidity, to avoid failure. A common solution used to increase printed circuit board assemblies (PCBAs) reliability to humidity is the application of a surface protection polymer known as conformal coating. This dissertation main goal is to assess the materials interactions between a conformal coating, two different solder pastes and underfill, under humidity conditions. By the analysis of the results, it was possible to assess if the tested materials are compatibles and can be used together in a product. Considering the materials used, the influence of two thermal profiles (Low and Mid) was studied regarding both solder pastes, concluding that both provided equal behaviour to the PCBAs. Furthermore, the selected coating was thermally characterized by thermal analysis methods. It was possible to acknowledge that the solvent evaporation process occurs bellow room temperature and it continues until 120-150ºC where all organic solvents present volatilized experiencing a weight loss of approximately 70%. The remaining weight corresponds to the polyacrylate that starts to decompose above 260°C until 420°C and a weight loss of 100% is reached. Furthermore, all materials in study were thermally analysed under process conditions to characterize their main heat transitions and weight losses. The material interactions were evaluated by simultaneous thermal analysis (STA) by replicating production conditions. To have an in-deep overview of the interface, sectional cuts were performed on the crucibles that contained the material combinations studied in STA. It was possible to conclude that the materials are compatible since no adverse reactions were observed. In addition, material interactions and reliability against humidity were evaluated by characterization of the modified IPC-B-52 test vehicle concerning electrochemical migration (ECM) as the main failure mode related to humidity. It was possible to conclude that the material systems under study were compatible and robust against humidity since surface insulations resistance (SIR) failure was only caused by FODs (foreign object debris). Ion chromatography (IC) test results shown that all PCBAs were up to standard Bosch limits, however the reference samples showed high values of weak organic acids (WOA). Resistivity of solvent extraction (ROSE) test was used as a tool for process control only defining the qualitative value of ionic contamination for a specific system and conditions., No setor automóvel, tem-se verificado uma evolução progressiva da tecnologia levando à produção de automóveis com maior complexidade eletrónica. Sendo assim, é necessário desenvolver sistemas eletrónicos confiáveis e seguros para o cliente. Por esta razão os dispositivos eletrónicos precisam de ser protegidos das condições ambientais em especial de ambientes húmidos de modo a evitar a falha. Uma solução atualmente utilizada para aumentar a fiabilidade das montagens de placas de circuito impresso (PCBA) e a sua robustez à humidade é a aplicação de um polímero protetor da superfície conhecido como Conformal Coating. O principal objetivo desta dissertação é avaliar as interações entre o Conformal Coating, duas pastas de solda diferentes e Underfill, perante condições de humidade. Através dos resultados obtidos foi possível avaliar se os materiais testados eram compatíveis e se podiam ser usados em conjunto em produtos. Considerando os materiais utilizados, foi estudada a influência de dois perfis de reflow (Low e Mid) para duas pastas de solda, concluindo que ambos os perfis proporcionaram comportamento semelhantes aos PCBAs. Além disso, o revestimento selecionado foi caracterizado termicamente através de métodos de análise térmica. Foi possível constatar que o processo de evaporação de solvente ocorre abaixo da temperatura ambiente e continua até 120-150ºC onde todo o solvente orgânico volatiza havendo uma perda de massa de 70%. Os restantes 30% correspondem ao poliacrilato que começa a degradar acima de 260°C até 420°C onde atinge uma perda de massa de 100%. Além disso, os materiais em estudo foram analisados termicamente em condições de processo para caracterizar as suas principais transições de calor e perdas de massa. As interações entre materiais foram estudadas através da análise térmica simultânea (STA) replicando as condições de processamento. De modo a verificar as interações na interface foram realizados cortes seccionais nos cadinhos que continham as combinações de materiais estudados no STA. Foi possível concluir que os materiais são compatíveis, uma vez que não foram observadas reações adversas. Além disso, as interações e a fiabilidade dos materiais foram avaliadas pela caracterização do veículo de teste IPC-B-52 considerando a migração eletroquímica (ECM) como o principal modo de falha em condições de humidade. Foi possível concluir que os sistemas de materiais em estudo eram compatíveis e robustos à humidade, uma vez que a falha da resistência do isolamento da superfície (SIR) foi causada apenas por FODs (detritos de objetos estranhos). Os resultados do teste de cromatografia iónica (IC) mostraram que todos os PCBAs estavam dentro dos limites da Bosch, no entanto, as amostras de referência tinham valores elevados de ácidos orgânicos fracos (WOA). O teste de resistividade de extração do solvente (ROSE) foi usado como uma ferramenta para controlo do processo, definindo apenas o valor qualitativo da contaminação iónica para um sistema em condições específicas.

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.

With the development of technology, wireless and IoT devices are increasingly used from daily life to industry, placing demands on rapid and efficient manufacturing processes. This study demonstrates the fabrication of an IoT device using a roll-to-roll printing process, which could shorten the device fabrication time and reduce the cost of mass production. Here, the fabricated IoT device is designed to acquire data through the sensor, process the data, and communicate with end-user devices via Bluetooth communication. For fabrication, a four-layer circuit platform consisting of two conductive layers, an insulating layer including through holes, and a solder resist layer is directly printed using a roll-to-roll screen printing method. After the printing of the circuit platform, an additional layer of solder paste is printed to assemble the electrical components into the device, inspiring the fully roll-to-roll process for device fabrication. Successful IoT device deployment opens the chance to broaden the roll-to-roll fabrication process to other flexible and multilayer electronic applications.

Driven by the need to deliver new, lead-free, eco-friendly solder pastes for soldering electronic components to Printed Circuit Boards (PCB), electrically conductive adhesives (ECAs) based on epoxy, carbon nanotubes (CNT), and exfoliated graphite (EG) were designed. The rheology of the adhesives prepared is paramount for the success of the deposition process, which is based on stencil printing. Thus, a rheological analysis of the process was first performed. Then, an experimental protocol was defined to assess the relevant viscoelastic characteristics of the adhesives for stencil printing application. Different composite formulations of epoxy/CNT/EG were produced. Their rheological characteristics were established following the designed protocol and benchmarked with a commercial solder paste. The thermal and electrical properties of the composite formulations were also characterized. As a result, a new, electrically conductive adhesive was delivered with potential to be an eco-friendly alternative to the solder paste currently used in stencil printing of PCB., This work was supported by the European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project n degrees 39479; Funding Reference: POCI-01-0247-FEDER-39479]. Additional funding by the by Portuguese Foundation for Science and Technology is acknowledged (projects UIDB/05256/2020 and UIDP/05256/2020).

The morphological changes of SAC305 solder alloy with the addition of 0.07 wt% graphene was investigated using selective electrochemical etching. To evaluate the effect of graphene inclusion, selective electrochemical removal of the beta-Sn phase from SAC305 and SAC305/0.07GNP was performed using a standard three-electrode cell approach at specific potentials determined by cyclic voltammetry. The phase, chemical structure and microstructural changes were observed. The texture and the phases of SAC305 solder paste were retained, while the microstructure of beta-Sn and Ag3Sn was refined owning to graphene addition. Sufficient removal of beta-Sn without affecting other phases was obtained by using etching potential below -350 mV. Due to Van der Waals force attraction, two types of agglomeration of graphene were observed from cross-sectional observation. Large agglomerations seen at the vicinity of solder/substrate interface were found to help in forming diffusion barrier. This contributes to the refinement of microstructure with the presence of graphene. Accurate observation regarding the shape and texture of the intermetallic compound (IMC) phases affected by the addition of graphene provided by selective electrochemical removal helps better insight into understanding the electrochemical dissolution mechanism of SAC alloys. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.