Characterization of Vapour Phase Soldering Process Zone with Pressure Measurements

Purpose: With the spreading of Vapour Phase Soldering (VPS) technology it is important to understand and optimize the process itself. The paper presents a novel approach on the process zone characterization for direct feedback on the state of vapour, for better monitoring, control and understanding of the process. Design/methodology/approach: The simple model of condensation heating shows the importance of vapour concentration during condensation soldering. Different pressure sensors were applied in an experimental VPS station, where the hardware setup is focused for the current experiments. Static and dynamic pressure values are analyzed and correlated with additional thermal measurements. Findings: The results reveal the dynamics of the vapour blanket generation. The correlated measurements show different stages of the process initialization, highlighting better accuracy than sole temperature measurements of saturated vapour identification. It is possible to trace the height of the available saturated vapour blanket with static pressure measurements. Originality/value: The methods provide a completely novel approach from the aspect of process zone state variables and parameter characterization, focusing on pressure measurements. Practical implications: The VPS process may benefit from the more precise saturation detection, giving better control on the heat transfer, enabling more efficient production with the reduction of idle time, and resulting in better soldering quality. Social implications: Reducing the idle time of the VPS stations may result in better efficiency and smaller power consumption, reducing the environmental impact of the method

SUSTAINABLE RESOURCE UTILIZATION IN MANUFACTURING OF PRINTED CIRCUIT BOARD ASSEMBLY: EXERGY ANALYSIS OF THE PROCESS

Engineering for sustainable development requires prudent utilization of resources under economic, environmental and societal constraints. Resource utilization must follow a holistic approach. This brings in a need for comprehensive metrics which are simple, standard and universal. Thermodynamics may offer a metric that focuses on both quality and quantity of energy resources which may carry information to be combined with other metrics. This metric may be a thermodynamic property called exergy or available energy, which provides a better insight into resource use in both energy and non-energy producing systems. This thesis is devoted to a study of the exergy concept in manufacturing. A high volume PCB assembly, manufactured in a state of the art soldering facility is chosen for the study. Various mass and energy resources flowing through the production line were quantified in terms of exergy. On the basis of exergy content and exergy utilization in the production process, the sustainability in terms of resources use is discussed. An early version of this approach was presented at the International Symposium on Sustainable Systems and Technologies, IEEE, Washington DC, in May 2010

Effect of Intermetallic Growth on Durability of High Temperature Solders (SnAg, SAC305, SAC+Mn, SnAg+Cu Nano) in Thermal and Vibration Environments

The RoHS ban of lead from electronics has pushed the industry to find lead free alternatives. In high temperature environments, high lead solders have typically been used. A suitable lead free replacement alloy is required. In this study quad flat packages (QFP) and 2512 chip resistors soldered with commercially available Sn3.5Ag and SAC305, and experimental SAC+Mn and SnAg+Cu Nano alloys on ENIG finished copper were subjected to three tests. Isothermal aging at 185°C for up to 1000 hours and at 200°C for up to 500 hours were performed to measure the interfacial intermetallic thickness, assess intermetallic compounds, and view the microstructure. A durability assessment was performed featuring thermal cycling ranges of -40 to 185°C and -40 to 200°C intermixed with 50G vibration cycling to determine the most durable solder alloy. Failure analysis was performed to understand the durability results. Finally, shear testing was performed to determine a correlation between shear strength and durability. The results show SAC305 is the most reliable solder under these conditions

Fabrication of Flexible Hybrid Circuits in Parylene

In recent years, with the increasing research interest in personalized medicine, new and disruptive technologies such as the Internet of Things (IoT) and flexible wearable electronics have emerged and have become trending topics in the scientific community. Despite consistent progress in the area of fully flexible electronics, these continue to reveal some restrictions, which can be overcome by traditional silicon integrated circuits (ICs). The combination between these technologies generated the new concept of flexible hybrid electronics (FHE) igniting a new generation of wearable health monitoring systems. This thesis reports a new way to the use parylene C as substrate, dielectric and encap- sulation layers to accommodate silicon ICs, surface mounted devices (SMDs) and thin metal layers, in order to create flexible and conformable double layered hybrid sensing membranes for body temperature monitoring, one of the most relevant physiological pa- rameters upon a medical diagnosis, since it’s among the main indicators for inflammation and infection. To achieve the thin metal and parylene C layers, thin-film microfabrica- tion techniques were employed and corroborated by superficial, electrical and structural characterization techniques. In addition the establishment of an electrical connection by the integration of silicon ICs and SMDs onto the thin metal layer was successfully tested using a low-temperature solder paste and a reflow oven, which reproduced a previously inputted time-temperature profile. Furthermore, this thesis analyses the repercussions of this integration procedure on the peel off process. Throughout this work, commercial body temperature measuring circuits were used as inspiration for the temperature sensing circuits developed. The interface between the produced membranes and their respective microcontrollers was also tested, although no temperature measurements were obtained due to parylene’s performance as a dielectric. The successful production of a fully functional flexible and conformable double layered hybrid sensing membrane could propel the adaptation of other rigid health monitoring electronics to FHE membranes, further engraving this technology into people’s daily lives.Com o crescente interesse na pesquisa em medicina personalizada, novas tecnologias como a Internet of Things (IoT) e a eletrónica flexível, surgiram e tornaram-se tópicos de tendência na comunidade científica. Apesar dos progressos na área da eletrónica totalmente flexível, continuam a existir algumas restrições, que podem ser superadas pelos circuitos integrados de silício (ICs) tradicionais. A junção entre estas tecnologias gerou um novo conceito de eletrónica híbrida flexível (FHE) dando início a uma nova geração de sistemas de monitorização de saúde. Esta tese aborda uma forma inovadora de usar parileno C como substrato, dielétrico e camada de encapsulamento para acomodar ICs de silício, surface mounted devices (SMDs) e camadas metálicas finas, a fim de criar circuitos em membranas híbridas de dupla camada flexíveis e conformáveis para monitorização da temperatura corporal, um dos parâmetros fisiológicos com maior relevância aquando do diagnóstico, uma vez que é um dos principais indicadores de infeções e inflamações. Para obter as camadas finas de metal e parileno C, foram empregues técnicas de microfabricação de filmes finos, corroboradas por caracterizações superficiais, elétricas e estruturais. Utilizando uma pasta de solda de baixa temperatura e um forno de refluxo, reproduzindo um perfil de tempo-temperatura, foi desenvolvido um protocolo para a conexão e integração de ICs na fina camada de metal. São ainda apresentados resultados relativos às implicações deste processo no método do peel off. Os circuitos desenvolvidos durante esta tese tiveram por base circuitos comerciais que medem a temperamtura corporal. Apesar da interface entre as membranas produzidas e os seus respetivos microcontroladores ter sido testada, não foi possível medir a temperatura com os circuitos desenvolvidos devido à performance do parileno como dielétrico. A produção bem-sucedida de uma membrana híbrida de dupla camada, flexível e conformável, totalmente funcional pode impulsionar a adaptação de outros equipamentos rígidos de monitorização de saúde para membranas híbridas flexíveis, inserindo ainda mais esta tecnologia na vida quotidiana

Modelling and simulation of paradigms for printed circuit board assembly to support the UK's competency in high reliability electronics

The fundamental requirement of the research reported within this thesis is the provision of physical models to enable model based simulation of mainstream printed circuit assembly (PCA) process discrete events for use within to-be-developed (or under development) software tools which codify cause & effects knowledge for use in product and process design optimisation. To support a national competitive advantage in high reliability electronics UK based producers of aircraft electronic subsystems require advanced simulation tools which offer model based guidance. In turn, maximization of manufacturability and minimization of uncontrolled rework must therefore enhance inservice sustainability for ‘power-by-the-hour’ commercial aircraft operation business models. [Continues.

Development of the core technology for the creation of electronically-active, smart yarn

The general use of textiles began twenty-seven thousand years ago. However, today, textiles are used, not only in the production of clothing but are also found in numerous applications in medicine, the military, transport, construction sectors and in many industrial applications. Normally textiles are passive, however active textiles have been developed that exhibit the capability of adapting their functionality according to changes in their surroundings, i.e. environment. Such textiles are known as Smart and Interactive Textiles (SMIT) and are capable of sensing and being active. The integration of semiconductor devices into textiles has enormous potential in the creation of SMIT. Such SMIT structures will pave the way for the creation of truly-wearable electronic systems in the near future. The aim of this research is the development of a core technology for embedding functional semiconductor devices within the fibres of a yarn, in order to create electronically-active yarns (e-yarn). Such electronically-active yarns will be the building blocks of the next generation of wearable electronics. Moreover, this will facilitate the creation of innovative solutions able to overcome current problems and difficulties which the manufacturers of wearable textiles are experiencing and open the doors for designers to develop the next generation of truly-wearable computers which are comfortable to wear, flexible and washable. The e-yarns could be used in medical applications such as monitoring of ECG, respiratory patterns, blood pressure and skin temperature. They could be adopted by industries such as automotive, retail, manufacturing, military, the internet of soft things, consumer products, sports, fashion and entertainment. The development of the core technology required raw materials analysis in terms of physical, mechanical and electrical properties; creation of interconnections of electronic semi-conductor chips with copper filaments; encapsulation of the interconnections to improve washability and provide extra mechanical strength to the core filaments prior to making the final yarn. The final step was the process of manufacturing yarns using the knit braiding technique. A number of prototypes of e-textiles were produced including illuminated yarns, thermistor yarns, RFID yarns, magnetic yarns, vibration sensor yarns, illuminated garment, illuminated car seat, RFID-intergraded garments, a temperature-monitoring fabric mat and temperature-monitoring socks in order to investigate the manufacturing viability, identify practical issues, and to promote the technology to attract further funds and potential commercial partners