15 February 2018 Thermocompression bonding for high-power-UV LEDs
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UV LEDs are usually mounted in flip-chip technology by soldering or thermocompression bonding to allow the UV light to be emitted through the sapphire substrate. The thermal conductivity of solders is considerably smaller than that of the typical metals used for packaging such as Cu, Ag or Au. For thermosonic- or thermocompression bonding pure metals can be used, however, the contact area is reduced in comparison to soldered contacts. Thermal simulations with different ratios of the number and size of stud bumps to the total area illustrate the direct influence of these parameters on the thermal resistance. The deformation during the bonding process as a function of the processing temperature and the applied force is discussed together with the influence of preprocessing, e.g. coining. Approaches are presented to increase the bonding area to 70 % of the total pad area of the chip. The improvements in the thermal resistance are demonstrated by lock-in-thermography and SEM investigations.
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Indira Kaepplinger, Dominik Karolewski, Geert Brockmann, Thomas Ortlepp, Olaf Brodersen, Andreas Thies, Jens Rass, Sven Einfeldt, Neysha Lobo-Ploch, Christoph Stoelmacker, and Frank Schnieder "Thermocompression bonding for high-power-UV LEDs ", Proc. SPIE 10554, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXII, 105541B (15 February 2018); doi: 10.1117/12.2287720; https://doi.org/10.1117/12.2287720

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