| High power LEDs can be applied in headlamps, street lights, interior lighting, landscape lights, and et al. The LED is a promising lighting source due to its advantages, such as low working voltage, small size, long lifetime, high energy efficiency, and so on. However, on the current research level, as much as 70%-85% electricity input into LEDs will be transported into useless heat, and it is difficult for LEDs to dissipate the heat by themselves, which results in the raise of LEDs'junction temperature, the shortening of LEDs'lifetime and the decrease of LEDs'reliability. In this case, it is necessary to improve LEDs'heat dissipation speed substantially and achieve quickly decrease of LEDs'temperature for the widely application of LEDs.The flat micro heat pipe and the vapor chamber are passive heat conduction devices, which have been used in the temperature control of LED, based on their working fluid's two phase change. But the mini-type of these devices brings difficulties to their manufacture. Also, because of the scale effect, surface properties may have greater influences on their thermal conductivity. This paper utilized silicon, which could integrate the LED and the micro heat pipe together, as the substrate, and used Pyrex7740 glass as the cover to fabricate LED-micro-heat-pipes. In order to promote the heat conduction of the micro heat pipes, two optimization methods, shell-shaped covers and graphene modification, were used. The former one could shorten the time between the condensation of the working fluid and its fall-back to the grooves, and the later one could accelerate the cycle of the fluid due to the graphene's hydrophobicity. Substrates with LED electrodes and four different kinds of grooves were designed and fabricated for 3 W integrated vapor chambers. Vapor chambers were accomplished, after LED chips, micro fins and the substrates were integrated together.This paper built a testing platform to test the thermal capability of the fabricated devices. For the micro heat pipes, thermostatic waterbath was used to cool the heat pipe, and the test environment was vacuumed. The results showed that when the input power varied from 1 W to 5 W, the evaporator section temperature of the shell-shaped heat pipe was always lower than that of the normal heat pipe. When the input power was 5 W, the evaporator section temperature of the shell-shaped heat pipe was 7.8 ? lower than that of the normal heat pipe, and that of the graphene modified heat pipe was 7.3 ? lower than that of the heat pipe without graphene.The 3 W vapor chambers, which were 28.0 mm×14.6 mmx7.3 mm and lighter than 5 g, were also tested on the testing platform in the temperature of 20 ?, no force cooling was applied, and the heat was dissipated into the environment only through the micro fins. The testing results showed that the designed integrated vapor chambers could dissipate the heat generated by 3 W LED modules effectively. The vertical resistance could achieve 1 ?/W, and the highest temperature could be controlled lower than 65 ? at the load of 3 W.Above all, this paper designed and fabricated LED-micro-heat-pipes and integrated vapor chambers for the heat dissipation of high power LEDs. Testing results demonstrated that the shell-shaped covers and graphene modified grooves could both improve the heat conduction efficiency of the micro heat pipes. Meanwhile, the designed small-sized vapor chamber could also achieve good heat conduction effect for 3 W LEDs. This paper researched the heat conduction of micro heat pipes and vapor chambers, and made an attempt on new structures. The results of this paper have certain reference significance for thermal management of high power LEDs. |
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