Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Intermetallic growth and thermal impedance at the In32.5Bi16.5Sn/Cu interface
    ( 2023)
    Chen, Chun-Hao
    ;
    Yang, Chunglin
    ;
    Chuang, Tung Han
    Present developing trends in the miniaturization and power escalation on electronic components have driven research interest in thermal interface materials (TIMs) to solve the fundamental issue of heat dissipation. Among the various TIMs, the In32.5Bi16.5Sn low melting alloy (LMA) has drawn much attention owing to its low melting point and great bondability, which could mitigate the warpage issue and provide very low thermal interface resistance. In this study, the Cu/In32.5Bi16.5Sn/Cu structure was used to simulate the practical conditions of the application of TIM in joining the substrate and heat sink. The thermal properties before and after an aging test at 80 °C were measured with a thermal tester, and the growth kinetics of the intermetallic compound (IMC) at the In32.5Bi16.5Sn/Cu interface were investigated. Without fast dissolution of Cu into the In32.5Bi16.5Sn alloy, the growth kinetics of the IMC at the interface were found to be diffusion-controlled at the temperature studied. It was found that the main change in the Cu/In32.5Bi16.5Sn/Cu system after the aging test was the thickening of the IMC, and the interface was free of cracks. As the aging time increased, the thermal impedance increased to twice that of the initial value, showing parabolic degradation, which is relevant to the growth kinetics of the IMC at the interface. Implications for the degradation of the thermal performance and further research are also discussed.
  • Publication
    Formation of Ag Dendrites During the Electrolytic Migration Between Ag-4Pd Wire Couple in Water Under Bias
    ( 2023)
    Chen, Chun-Hao
    ;
    Lin, Yancheng
    ;
    Wu, Poching
    ;
    Chuang, Tung Han
    The growth of Ag dendrites induced by the Ag ion migration between Ag-4Pd alloy wire couples immersed in pure water under bias was observed, and its failure mode leading to a short circuit was investigated. The experimental results indicated that the time of dendrite contact and short circuit decreased obviously with increases in voltage and wire pitch. In contrast, the formation time of hydrogen bubbles and Ag spikes in the initial stage of water drop tests decreased slightly with increases in applied voltage, leading to drastic increases in the Ag dendrite growth rate at higher voltages. During the electrolytic migration process, the outer surface of the anode wire oxidized into a continuous Ag2O layer with a porous grain structure. In addition, Ag+ ions were reduced to crystallographic Ag2O particles that formed a layer concealing the anode wire. Summarizing the observations of Ag dendrite growth and the Ag2O layer formed on cathode and anode wires, respectively, a reaction mechanism for the electrolytic migration of Ag-4Pd wire couple is proposed.
  • Publication
    The Effect of Oxalic Acid as the Pre-Activator for the Electropolishing of Additive Manufactured Titanium-Based Materials and Its Characterization
    ( 2022)
    Chen, Chun-Hao
    ;
    Lee, Chiayu
    ;
    Ger, Ming-Der Der
    ;
    Jian, Shunyi
    ;
    Hung, Jung Cherng
    ;
    Yang, Pojen
    ;
    Kao, Chunhsiang
    ;
    Ferng, Yi Cherng
    ;
    Huang, Yingsun
    ;
    Jen, Kuokuang
    The use of additive manufactured (AM) titanium-based materials has increased substantially for medical implants and aerospace components. However, the inferior surface roughness of additive manufactured products affects the outward appearance and reduces performance. This study determines whether activation treatment prior to electropolishing produces a better surface. Oxalic acid (OA) is used as a pre-activator using different experimental conditions and the surface roughness is reduced by electropolishing with an electrolyte of perchloric acid and glacial acetic acid. The SEM surface morphology, mechanical properties, phase transformation and electrochemical properties are measured to determine the effect of different degrees of roughness on the surface. The results show that the surface roughness of AM titanium-based samples decreases from 8.47 µm to 1.09 µm after activation using OA as a pre-treatment for electropolishing. After electropolishing using optimal parameters, the hardness and resistance to corrosion resistance are increased.
  • Publication
    Optimization of Ag-alloy ribbon bonding - An approach to reliable interconnection for high power IC packaging
    ( 2022)
    Chen, Chun-Hao
    ;
    Chuang, Tung-Han
    Ultrasonic ribbon bonding has drawn much attention in power electronic packaging as compared to conventional heavy wire bonding. This study evaluated the bondability of 100 × 1500 μm Ad-4Pd ribbon bonded on direct bonded copper (DBC) substrates metallized with Ni/Pd/Au layers through adjustment of the bonding parameters. The bonding patterns on the wedge bonds along with cross-sectional images of the polished interface were investigated, and the pull force and joint properties were examined by pull and shear tests. Failure codes indicated heel damage resulting from excessive ultrasonic energy, which was explained from the deformation point of view. Furthermore, footprint studies of the sheared surfaces indicated that increasing the bonding power could promote the bonding surface, as evidenced by the transition of the surface morphology from fretting to microwelds and finally fractured pieces of ribbons. This study may be of great importance in explaining the special features of ultrasonic ribbon bonding, as well as in providing a feasible solution for power electronic packaging with a better understanding of the importance of optimizing the bonding parameters.