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Effect of Voiding in Solder Joints on Thermal Performance of the LED
Keywords: LED, Solder Joint, Thermal management
Light-Emitting Diode (LED) lighting has potential to fundamentally alter lighting by replacing incandescent and fluorescent technologies because it offers significant energy saving, longer operational life, mercury-free materials, and many other advantages. Excellent thermal management and low-cost is vital for LED lighting to become the market standard for general lighting. The packaged LED is typically soldered to the metal-core printed circuit board (MCPCB). However, as the size of the packaged LED increases, voiding in solder joints becomes a major problem since voiding increases the thermal resistance. The research questions are: what is the effect of flux in solder paste and size of the package LED on the voiding? What is the relationship between the voiding and the thermal performance of the LED? In this study, a total of 72 packaged LEDs with three different sizes were assembled to MCPCBs using solder paste with two different types of fluxes. The voiding in solder joints was checked by X-Ray. The detailed void characteristics were analyzed. The LED’s junction temperature was measured based on the diode’s forward voltage junction temperature measurement method. The relationship between the junction temperature and the void characteristics was established. The results show that both flux in solder paste and the LED size have significant effect on the voiding. The results also indicate is that when the voiding percentage is less than 25%, the effect of voiding on the thermal performance is insignificance; when the voiding percentage is over 25%, there is weak positive correlation between the voiding and the thermal performance.
Jianbiao Pan , Professor
California Polytechnic State University
San Luis Obispo, CA

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