| dc.description.abstract | With the rapid development of high-power light emitting diodes (LEDs), the power applied on LED devices has increased much more than expected. If the heat generated in high-power LED cannot be dissipated efficiently, the lifetime of the device will rapidly decrease. Therefore, thermal management of packages is a critical issue for high-power LEDs. Among the thermal issues for LED packages, their die-attachment onto thermal substrates has attracted a great deal of attention.
In this thesis, Sn/Bi/Zn/Bi/Sn solder layers are deposited on the LED/Ni/Cu surface as a die-attached material. In discussion part I, the size of bottom Sn clusters will increase with the Sn deposition rate. The liquid surface layer formed by the high surface temperature will facilitate the coalescence of Sn clusters. Then, different size of Sn clusters could be deposited by controlling the deposition rate of Sn. In discussion part II, Bi was deposited on the surface of Sn clusters. The large Bi clusters would be formed on the large Sn clusters due to coalescence of eutectic droplets. After the deposition of Bi/Zn/Bi on Sn surface, the large Bi clusters would be formed on the surface of high Sn deposition rate. However, a smooth Sn-Bi-Zn eutectic layer was formed on the surface of high Sn deposition rate after the deposition of Sn capping layer due to the formation of large amount of liquid phase and better wettability. On the contrary, a rough surface would be formed by the coalescence of eutectic droplets in the low Sn deposition rate. In discussion part III, the smooth surface with smaller contact height between Cu metallization layer and Ag substrate surface would have higher wetting force on the two plates. Therefore, less of air would be trapped at the bonding interface after the die-bonding process. The die strength of smooth Sn/Bi/Zn/Bi/Sn surface would be higher due to the less formation of void at the bonding interface.
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