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Investigations on Wire Bonding Capability of Selective Laser Melted Structures
Keywords: heavy wire bonding, additive manufacturing, selective laser melting
Digital manufacturing technologies can have a truly transformative influence on manufacturing flexibility and design freedom by cutting development time, enabling complex shapes and structures, and opening new fields of application. Various additive generated products are available for aerospace and healthcare sectors, but the potential of the additive manufacturing (AM) for electronic applications is yet to be explored. The selective laser melting (SLM) technology is a key driver for AM, as it allows the generation of threedimensional metal structures from powder based raw metallic materials. Now-a-days powder based metallic materials like titan, bronze, or aluminum are used as raw materials. In order to translate these prospects into functional electronic applications, the ability to apply standard as well as advanced packaging technologies on these SLM surfaces and substrates needs to be investigated. [1] Heavy wire bonding is the dominant top-level interconnect technology in power electronic assemblies [2]. Over 80 % of all top-level-interconnect techniques on power semiconductors are based on aluminum wires [3]. Not only cost-efficient and robust, but also being a flexible interconnection process, wire bonding bears the chance to be a valuable partner for additive manufacturing technologies in creating advanced layouts and packages [4]. In order to apply SLM into complex and highly integrated power devices, connections between AM-structures and active components such as bare dies, as well as to the peripheral package need to be established. Heavy wire bonding, as a versatile packaging technology, offers the possibility to go along with the additive manufacturing’s flexibility in order to facilitate individual power packages [5]. The paper will display the influencing factors, as well as the possibilities and challenges that come along with the process combination of SLM with heavy wire bonding. For the investigations, test samples were created from a bronze powder on a SLM-machine. Then, 300 μm aluminum and copper wires were bonded on the SLM generated structures. Wire bonding capability was analyzed on untreated as well as on post-processed surfaces. The influence and effectiveness of various steps of post-processing such as grinding, sandblasting, and cleaning were evaluated. Thus, interdependencies between both manufacturing process as well as the post-processing could be revealed. The effect of surface roughness and hardness of the assembly partner were investigated as well. To draw statistically backed conclusions, all tests were performed using DoE (Design of Experiment) studies. The primary characteristics besides the bond parameters that influence the wire bonding capability are focused in this paper. The process stability as well as the interconnection quality was evaluated by optical non-destructive laser microscopic analysis. Destructive pull and shear tests and metallographic cross sections were performed to evaluate the adhesion characteristics. The process stability and the yield obtained will be important factors to describe the process and to evaluate the industrialization potential. By a profound understanding of all interdependencies between the two processes, a flexible manufacturing technology for power devices can be established.
Christopher Kaestle,
Friedrich-Alexander University Erlangen-Nürnberg, Institute for Factory Automation and Production Systems
Nuremberg, Bavaria

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