Fabrication Of Screen Printed Doped Zinc Oxide Thick Film On Metal Substrate As Heat Sink For High Power Light Emitting Diodes
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Date
2018-05
Authors
Mah, Jian Wen
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Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
A large amount of heat trapped inside Light Emitting Diode (LED) package is the consequence of large thermal resistance between the heat source and the heat sink. These large thermal resistances created a huge amount of heat accumulated inside the LED package resulting in poorer luminous efficiency, shorter life time, shifting of emission wavelength and reliability issues. Typically, the junction temperature of the LED was found to be approximately 120°C on 250mA of applied forward current. In this project, pure and four different metal-doped ZnO thick films were deposited on Aluminium substrate by screen printing technique using nano-crystalline powder synthesized from co-precipitation method. The metal-doped powders were produced from 3wt%, 5wt%, 7wt%, and 9wt% of metal dopant during the co-precipitation process. The synthesized powders were thoroughly mixed with solvent to form a thixotropic paste and screen-printed before proceeding to the curing and firing process. TGA showed that the initial stage of thermal decomposition process of pure and metal-doped ZnO pastes was between 119°C and 134°C of heating temperature. 45wt% of pure ZnO paste was chosen due to the highest remaining weight after the heating process. Rheological behavior of pure and metal-doped ZnO paste showed thixotropic properties by having decreasing viscosity with increasing shear rate. Initial viscosity of the 45wt% pure ZnO paste was listed in the range from 200 Pa·s to 250 Pa·s, in accordance with the industrial requirement.
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Keywords
Screen printed doped zinc oxide thick film , heat sink for high power light emitting diodes