Thermal analysis of multichip LED packages

Abstract

Thermal transient measurements of high power GaN-based LEDs with multi-chip designs are presented and discussed. Once transient cooling curve was obtained, the structure function theory was applied to determine the thermal resistance of packages. The measured total thermal resistances from junction to ambient were 19.87 K/W, 10.78 K/W, 6.77 K/W for the one-chip, two-chip and four-chip package, respectively. The contribution of each component to the total thermal resistance of the package can be calculated from the cumulative structure function and differential structure function. The total thermal resistance of multi-chip package is found to decrease with the number of chips due to parallel heat dissipation. Very useful thermal design rule for high power multi-chip LED package is analogized from the experiments. It was found that the effect of the number of chips in a package on the thermal resistance depends on the ratio of partial thermal resistance of chip and that of slug. Thermal resistance for full color multi chip LEDs, where each chip is driven independently, was measured as well and the implication was discussed.

Research on LED Performance of Glass Substrate with COB Packaging

“…发光二极管(LED)照明具有高光效、 响应快、 寿命长、 节能环保等优点， 已经在汽车、 装饰、 道路、 办公、 手 机、 显示屏等多个领域得到广泛应用。LED 产业链中的 LED 封装技术， 是影响 LED 特性的关键因素之一 [1][2][3][4][5] 。 随着 LED 封装技术的不断创新， LED 管芯的封装从单芯到 N 颗管芯的集合封装， 如板上芯片(COB)、 覆晶薄 膜(COF)等， 由少串多并的低电压模块转向多串少并、 多芯封装的高压 LED(HVLED)模块。HVLED 在小电 流 下 工 作 ， 本 身 发 热 就 低 多 了 ， 因 而 将 N 颗 小 功 率 管 芯 串 联 封 装 在 玻 璃 基 板 上 成 为 了 不 同 于 以 往 的 新 封 装 理念， 并迅速发展了起来。 本 文 针 对 行 业 内 目 前 研 究 较 热 的 玻 璃 基 板 材 质 进 行 了 研 究 ， 与 陶 瓷 等 基 板 材 料 进 行 对 比 ， 发 现 透 明 的 玻璃也适合作为 COB 封装的基板。采用玻璃基板背面刷银层和设置铝材卡口的机械连接结构， 较好地降低 了整灯中玻璃基板 COB 的胶面温度， 并通过实验得知了银层厚度与胶面温度的关系。 2 LED 玻璃基板热性能及散热 大功率 LED 电光转换效率为 30%， 而 70%的电转换为热 [6] 。这一方面导致 LED 芯片结温升高， 导致发光 能量下降和芯片光谱红移， 光谱红移偏离荧光粉吸收峰， 致使荧光粉发光效率降低 [7] ； 另一方面使 LED 产生 热应力， 导致寿命降低甚至芯片失效 [8] [9] 。由于芯片衬底已与芯片装成一个整体， 芯片衬底与基板为点焊接技能， 环境热沉常用 [11] ， 但 导 热 界面材料易固化、 老化， 使得导热性能下降； 导热垫片则增加了热界面层数和厚度 [12][13]…”

Analysis of Thermal Resistence for High-Power Light-Emitting Diodes

“…4) Compare result of the two tests, and calculates the difference of electric power's and luminous power's, P E= P E1 -P E2 , P OPT= P OPT1 -P OPT2 . From equation (2) (3) (4)can derive R θ J-A = (V f1 -V f2 ) / K(P E -P OPT ) (6) The transient rise of junction temperature was recorded every microsecond by a thermal transient tester (T3Ster), and that will significantly raise the measurement accuracy [5]. The transient temperature data collected by the T3Ster and then was processed by software to give a plot the thermal capacitance versus cumulative thermal resistance.…”

Thermal analysis of multi-chip module high power LED packaging

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