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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.

In this research we investigated the contact angle of commercial SnAgCu solder paste mixing with some carbon allotropes such as graphite, graphene quantum dots, and fullerene of varying concentrations with melting temperature, wettability, interfacial microstructure. The wettability was assessed in terms of the contact angle. The in-line digital holography was used for determining the contact angle and morphological of samples at each temperature which the samples have been heating from room temperature until the melting temperature. In the experiment, only one beam was used as the object and reference beams which recorded by a CMOS camera. The recorded image was reconstructed by the angular spectrum digital holography numerical programing. Using the reconstructed images of our results, the shape and contact angle of solder pastes can be investigated.

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.

The feasibility of transient liquid phase (TLP) bonding technology for high-temperature endurable power electronics packaging has been evaluated in this study. An Ag-Sn3.0Ag0.5Cu hybrid solder paste was fabricated and used as a bonding material. The bonding reactions between chip/substrate and hybrid solder paste and die shear strengths of the TLP-bonded joints were evaluated during conventional soldering and vacuum soldering processes. Compared to the conventional soldering, the vacuum-soldered joints had fewer voids and relatively good metallurgical microstructures. After TLP bonding, (Cu,Ni)6Sn5, Ag3Sn, and Cu6Sn5 intermetallic compounds formed at the chip interface, in the middle of the joint, and at the bottom interface, respectively. It was confirmed that the vacuum soldering process could create good interfacial uniformity with minimal voids in the Si chip/ceramic substrate joints. The formation of voids during TLP bonding significantly affected the mechanical shear strength of the TLP-bonded joints. The vacuum-soldered joints had high shear strength values of approximately 40 MPa. To ensure the high joint strength and long-term reliability of Sn-based TLP-bonded joints, critical void control in the joints is needed.

In this study, thermo-compression(TC) and vacuum reflow(VR) bonding processes of fine pitch interconnection were optimized using Type 7 Sn-3.0Ag-0.5Cu solder paste. A chip with Cu pillar Sn-2.5Ag bumps and BT substrate with ENEPIG surface finish were used, and the thickness and the aperture ratio of the metal mask were 30 ㎛/50 ㎛ and 70%/100%, respectively. As a result of optimizing the printing process, a metal mask with a thickness of 30 ㎛ and an aperture ratio of 100% was selected. As a result of the TC and VR bonding processes optimization, Cu6Sn5 and (Cu,Ni)6Sn5 IMC layers were formed on the top and bottom of the solder joint, respectively. In the conventional TC process sample, the thickness of the solder was measured to be 4.1 ㎛, and the IMC thickness ratio was calculated to be 40%. Also, in the TC and VR process samples with solder paste, the thickness of the solder was measured to be 6.5 ㎛ and 10.3 ㎛, respectively, and the ratio of the IMC thickness was calculated to be about 32% and 43%. It was expected that it would be beneficial to reliability by reducing the occurrence and propagation of cracks in the solder joint due to the effect of lowering the IMC thickness ratio as the volume of the solder becomes larger than that of the conventional TC process.

This article focuses on the study of voids in the solder joint interface of flip-chip LEDs. Additional flux is added to the solder paste to reduce the frequency of voids, and the mechanical properties of the solder joints are compared and analyzed. Two kinds of fluxes (NC559-TPF, TSF-6516) are selected. They are used in two kinds of solder pastes (lead and lead-free solder paste). The amount of flux added is 0 mL, 0.4 mL, and 0.8 mL. The other preparation conditions for all combinations are the same and are within the recommended scope of the manufacturer's documentation. X-rays are used to detect and analyze the distribution and quantity of voids in the solder layer. A push–pull tester is used to analyze and evaluate the mechanical strength of the solder joints. A scanning electron microscope was used to observe the microscopic morphology of the cross-section of the solder joint and the fracture morphology of the interface after the shear test. It was found that adding a proper amount of high-activity flux to the solder paste can reduce the frequency of voids and improve the mechanical reliability of the solder joints. Finally, we tested the thermal performance of the flip-chip LED filament for verification.

Purpose In the production processes of electronic devices, production activities are interrupted due to the problems caused by soldering defects during the assembly of surface-mounted elements on printed circuit boards (PCBs), and this leads to an increase in production costs. In solder paste applications, defects that may occur in electronic cards are usually noticed at the last stage of the production process. This situation reduces the efficiency of production and causes delays in the delivery schedule of critical systems. This study aims to overcome these problems, optimization based deep learning model has been proposed by using 2D signal processing methods. Design/methodology/approach An optimization-based deep learning model is proposed by using image-processing techniques to detect solder paste defects on PCBs with high performance at an early stage. Convolutional neural network, one of the deep learning methods, is trained using the data set obtained for this study, and pad regions on PCB are classified. Findings A total of six types of classes used in the study consist of uncorrectable soldering, missing soldering, excess soldering, short circuit, undefined object and correct soldering, which are frequently used in the literature. The validity of the model has been tested on the data set consisting of 648 test data. Originality/value The effect of image processing and optimization methods on model performance is examined. With the help of the proposed model, defective solder paste areas on PCBs are detected, and these regions are visualized by taking them into a frame.

This paper investigates the effect of grain size on the evolution and shear behavior of lead-free solder joints. The grain size of the solder is 2-11 μm, 5-15 μm, 15-25 μm, respectively. The interface structure of the solder joint and the microstructure of the inferred surface are analyzed. The void ratio of the flip-chip solder layer is tested. In order to study the change of shear strength and fracture surface, the solder/copper joint was subjected to isothermal aging treatment (1000 h) under the environment of relative humidity of 85 °C/85%. The results show that the smaller the solder crystal grains, the larger the surface area of the crystal grains per unit mass. Because of the action of the liquid bridge force, tin powder agglomeration is prone to occur, which leads to a high void rate of the solder layer. At this time, a higher activity flux is required to remove oxides. Highly active flux (NC559-TPF) was added and verified. When the grain size is 5-15 μm, the solder paste has the best soldering performance. After the filament is aged for 1000 h, the junction temperature is the lowest. Secondly, the blue light flux is the highest.

Motivation: As passive components’ size gets smaller, quality rejects due to overhang and misalignment after the reflow appear more frequently. This situation is partly because the pass-fail criterion is set based on the offset concerning the component dimensions. Therefore, understanding the self-alignment characteristics of electronic components becomes very critical for surface-mount assembly yield. This research investigates the dissimilarity of self-alignment in the length and width directions. Approach: To avoid the argument of sample to sample variations, data are collected from 81 printed circuit boards (PCB) and 182,250 assembled components. Within a PCB, 25 different solder paste printing offset locations and 81 component placement offset settings are implemented. Component-placement positions before and after the reflow are monitored. The results are compared to identify different component sizes’ self-alignment characteristics in the length and width directions. Key findings: The misalignment of smaller passive components, e.g., R0402M(0.40 mm × 0.20 mm), is worse than the larger component under the identical solder paste printing and component placement conditions. Furthermore, the self-alignment characteristic in the length direction of these passive components, e.g., R0402M, to R1005M (1.00 mm × 0.50 mm) is superior to that of width direction. The observations are not consistent with the results found in earlier research that reported on larger components, e.g., C0402M(0.40 mm × 0.20 mm), to C3216M(3.20 mm × 1.50 mm).

For system manufacturers, packaging of the ball grid array (BGA) of wireless communication modules can be performed via solder paste printing. As reballing can be conducted via the pretinning process, it can be compatible with its existing surface mount technology (SMT). This study referred to the Taguchi experimental design to plan its experiment. Three quality characteristics related to the consistency of the solder volume are applied for printing, that is, the standard deviation of the deposition volume of solder paste on all bonding pads of a single component, the coplanarity of the solder balls of the component, and the height range of the solder ball of a single component, which were regarded as the response values. Important design and process parameters related to the pretinning process and the relative location of the bonding pads of components on a connecting board are considered as the controlling factors. Then, this study applied and integrated the results of two multivariate analysis methods, i.e., gray correlation of the principal components and a technique for order preference by similarity to ideal solution (TOPSIS), in order to determine the ideal solution and propose the optimal parameter combination: general squeegee: pressure 40 N and speed 30 mm/s; steel: separation distance 3 mm, speed 2 mm/s, and aspect ratio 0.17; and cleaning frequency: cleaning of stencils after the printing of every two boards. This method effectively improves the control of the solder volume in the pretinning process and meets the acceptance criteria of manufacturers.

Cr/Al/Ti/Au stacks with two thicknesses of Al layers were employed as reflective n-type electrodes for 274 nm AlGaN-based flip-chip deep ultraviolet light-emitting diodes (DUV LEDs). Large bulges arose in the annealed n-type electrode with 120-nm-thick Al layer, resulting in cracks within the upper rugged SiO2 passivation layer after burn-in test. Sn atoms from solder paste migrated along the cracks and served as leakage current channels, which accelerated device degradation. In contrast, the annealed n-type electrode with 60-nm-thick Al layer retained uniform morphology. And the DUV LEDs with such n-type electrode exhibited good reliability and normalized optical power of 86.8% after burn-in test of 1000 h. This study provides insight into electrode defects related degradation behavior and helps to improve the reliability of AlGaN-based flip-chip DUV LEDs with reflective electrode.

Solder paste is mainly used for welding of resistance, capacitance, integrated circuit (IC) and other electronic components in surface mounted technology (SMT) industry, and the performance of solder paste has a significant impact on the reliability of electronic components. In this paper, processing defects, failure cases and mechanism of electronic components caused by solder paste are analyzed systematically. Improper application of solder paste during welding can lead to numerous processing defects including poor wetting, tombstoning, bridging, solder joint crack, solder ball spattering, corrosion and so on. Finally, an evaluation method of material compatibility is described in this paper, which provides a reference for ensuring the quality of electronic process material and improving the reliability of SMT products.

Purpose The purpose of this study is to propose a novel simulation framework and show that it captures the main effects of the deposition process, such as droplet shape, volume and speed. Design/methodology/approach In the framework, the time-dependent flow and the fluid-structure interaction between the suspension, the moving piston and the deflection of the jetting head is simulated. The system is modelled as a two-phase system with the surrounding air being one phase and the dense suspension the other. The non-Newtonian suspension is modelled as a mixed single phase with properties determined from material testing. The simulations were performed with two coupled in-house solvers developed at Fraunhofer-Chalmers Centre; IBOFlow, a multiphase flow solver; and LaStFEM, a large strain FEM solver. Experimental deposition was performed with a commercial jet printer and quantitative measurements were made with optical profilometry. Findings Jetting behaviour was shown to be affected by not only piston motion, fluid rheology and head deformation but also the viscous energy loss in the jetting head nozzle. The simulation results were compared to experimental data obtained from an industrial jetting head and found to match characteristic lengths, speed and volume within ca 10%. Research limitations/implications The simulations are based on a rheological description using the Carreau model that does not include a time-dependent relaxation of the fluid. This modelling approach limits the descriptive nature of the deposit after impact on the substrate. The simulation also adopts a continuum approach to the suspension, which will not accurately model the break-off of the droplet filament under the characteristic diameter of the particles in the suspension. Practical implications The ability to accurately simulate the deposition of functional materials will enable the efficient development of novel product designs with a minimum of used resources and minimised product development duration. Social implications The ability to accurately simulate the deposition of functional materials will enable the efficient development of novel product designs with a minimum of used resources and therefore an improvement from a sustainability perspective. The ability to plan deposition strategies virtually will also enable a decrease in consumables at manufacturers which will in turn decrease their carbon foot print. Originality/value While basic fluid dynamic simulations have been performed to simulate flow through nozzles, the ability to include both fluid-structure interaction and multiphase capability together with a more accurate rheological description of the suspension and with a substrate for surface mount applications has not been published to the knowledge of the authors.

Effects of Mn-doped TiO2 nanoparticles on the wettability, printability and thickness of intermetallic layer of SAC30 on a Cu substrate were studied in this paper. Concentration of Mn-doped TiO2 nanoparticles was varied from 0.05 wt.% to 1[Formula: see text]wt.%. The wettability was evaluated in terms of contact angle of solder on the copper substrate and the printability was measured from the volume ratio of printed solder on the copper substrate to volume of stencil opening. The experimental results showed that 0.10[Formula: see text]wt.% Mn-doped TiO2 led to the lowest contact angle while the printability was decreased with the increase of the added nanoparticles and the thinnest intermetallic layer was found at 0.50[Formula: see text]wt.% Mn-doped TiO2 nanoparticles. Mn-doped TiO2 concentration was then optimized using a desirability function to find optimal values for the three responses. It was found that 0.07[Formula: see text]wt.% was the optimal concentration for the three metrics — wettability, printability and thickness of the intermetallic layer.

This study aims to identify and maintain optimal stencil printer settings in dynamic surface mount technology (SMT) assembly lines to control the solder paste volume transfer efficiency (TE) and increase the yield rates of surface mount assembly (SMA) lines. Stencil printing process (SPP) is a crucial procedure that determines the first pass yields in SMA lines. Stencil printing speed (PS) and printing pressure (PP) are two critical SPP parameters in the manufacturing process; identifying the optimal printer settings in complex fabrication environment is cost efficient but challenging. To search for the global optimal PS and PP values in real time with minimal computational efforts, a dynamic optimization SPP optimization system is proposed based on a novel guided evolutionary search (GES) strategy. The GES algorithm is flexible to adjust the feasible solution region based on real-time optimization results to maximize the probability of finding optimal solutions and minimize the computational burden. As a major extension on the classical evolutionary search, the GES minimizes the possibility to fall in the local optimal due to insufficiencies in the prediction accuracy and guarantees global optimality within the dynamically varying printing environment.