Effects of solder paste on thermal and optical performance of high-power ThinGaN white LED

Abstract

Purpose Thermal management of high-power (HP) light-emitting diodes (LEDs) is an essential issue. Junction temperature (TJ) and thermal resistance (Rth) are critical parameters in evaluating LEDs thermal management and reliability. The purpose of this paper is to study thermal and optical characteristics of ThinGaN (UX:3) white LED mounted on SinkPAD by three types of solder paste (SP): No-Clean SAC305 (SP1), Water-Washable SAC305 (SP2) and No-Clean Sn42/Bi57.6/Ag0.4 (SP3). Design/methodology/approach Thermal transient tester (T3Ster) machine is used to determine TJ and total thermal resistance (Rth–JA). In addition, the LED’s optical properties are measured via thermal and radiometric characterization of power LEDs (TeraLED) system. The LED is mounted on SinkPAD using SP1, SP2 and SP3 by stencil printing to control a thickness of SP and reflow soldering oven to minimize the number of voids. The LED with SP1, SP2 and SP3 is tested at various input currents and ambient temperatures. Findings The results indicate that at high input current, which equals to 1,200 mA, Rth–JA and TJ, respectively, are reduced by 30 and 17 per cent between SP1 and SP2. At same current value, Rth–JA and TJ are minimized by 42 and 25 per cent between SP1 and SP3, respectively. In addition, at an ambient temperature of 85°C, Rth–JA and TJ are decreased by 34 and 7 per cent between SP1 and SP2, respectively. Similarly, the reduction in Rth–JA and TJ between SP1 and SP3 is 44 and 10 per cent, respectively. Luminous flux, luminous efficacy and color shift of the LED with the three types of SPs are compared and discussed. It is found that the SP1 improves the chromatic properties of the LED by increasing the overall light efficiency and decreasing the color shift. Originality/value Thermal and optical performance of ThinGaN LEDs mounted on SinkPAD via three types of SPs is compared. This investigation can assist the research on thermal management of HP ThinGaN-based LEDs.