Investigating solder wetting with Surface Evolver

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Supervisor:
Dr. Krammer Olivér
Department of Electronics Technology

Soldering is the most commonly used technology in electronics industry, which makes the electrical and mechanical contacting of electronic components possible in one step. The quality and lifetime of the solder joint formed during soldering is greatly influenced by the profile of the solder joint. The shape of the solderjoint is influenced by many factors, traditionally the impact of these factors is investigated through experiments, however this can require a great amount of time and resources. The profile of the solder joint can be described by mathematical models, thus making the investigation require less time and fewer resources. The subject of my thesis is the modelling of different soldering problems and optimizing the parameters based on the created models.

During my research I studied several topics, including the materials, methods and technologies used during reflow soldering, the theoritical background of surface tension and wetting of liquids, and methods for calculating the profile of liquid solder. I described the Surface Evolver software which was used to create the models, I presented some soldering problems found in literature and the models created to investigate them. During my work I created two models, and after validating their behavior with cross sections of real soldered samples I performed the investigations. In the first case the goal of the investigation was to determine the ideal solder paste volume for AOI, and in the second case the aim of the investigation was to determine the impact of geometric parameters on tombstoning.

The y-offset within the range of the investigation has no effect on AOI capability, but the effect of x-offset and rotation around x- and y-axis is a lot more significant. Based on the results the volume of solder paste used for stencil printig is ideal for the application, reducing the volume is not recommended. In the other case the geometry of the top side of the component has really low impact on tombstoning, but the effect of the width and height of the component and the impact of the geometry of the height spacer is notable. Based on the results the torque acting on the component can be somewhat reduced by reducing the height and changing the position of the spacer.

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