The conventional chip-on-board light-emitting diodes (COB-LEDs) with flat encapsulant layer present low light efficiency due to the total internal reflection (TIR) happens at the encapsulant-air interface. In this study, microlens array was realized on the flat encapsulant layer of COB-LEDs to diminish the TIR at the encapsulant-air interface. The microlens array was fabricated by selectively exposing the UV glue film in UV-light through a pre-designed photomask. Micro-pillars form after the UV-light exposure and microlens array forms spontaneously due to the wetting process of uncured UV glue on the micro-pillars. The geometry of the microlens array was experimentally optimized, and the light efficiency enhancement of COB-LEDs by the microlens array was analyzed. The results show that optimal geometry of microlens array with curvature of ~41° and base diameter of $\sim 87~\mu \text{m}$ can be realized by adjusting the UV-light exposure time as >40 s and UV glue film thickness as $> 80~\mu \text{m}$ . Compared to the traditional flat encapsulant layer, the microlens array with optimal geometry increases the light efficiency of blue and ~5000 K white COB-LEDs by 50.9% and 9.31%.

中文翻译：

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在平面封装层上实现微透镜阵列以提高 COB-LED 的光效

由于全内反射 (TIR) 发生在密封剂 - 空气界面，因此具有平坦密封剂层的传统板上芯片发光二极管 (COB-LED) 的光效率较低。在这项研究中，在 COB-LED 的平坦封装层上实现了微透镜阵列，以减少封装 - 空气界面处的 TIR。微透镜阵列是通过预先设计的光掩模在紫外光下选择性地曝光紫外胶膜来制造的。由于未固化的紫外线胶在微柱上的润湿过程，在紫外线照射后形成微柱，微透镜阵列自发形成。实验优化了微透镜阵列的几何形状，并分析了微透镜阵列对 COB-LED 光效的增强。 $\sim 87~\mu \text{m}$ 可以通过调整UV光曝光时间>40s和UV胶膜厚度为 $> 80~\mu \text{m}$ . 与传统的平面封装层相比，具有最佳几何形状的微透镜阵列将蓝色和~5000 K 白色 COB-LED 的光效率提高了 50.9% 和 9.31%。