Li Ping, Wen Yumei, Cai Youhai, Li Lian
College of Opto-electronic Engineering, The Key Laboratory for Opto-electronic Technology and Systems of Ministry of Education, Chongqing University, Chongqing 400044, People's Republic of China.
Rev Sci Instrum. 2009 May;80(5):055108. doi: 10.1063/1.3137055.
This paper proposes an online noncontact fault detection method during light emitting diode (LED) chip packaging, which is based on the photovoltaic effect in p-n junctions. Once a LED chip bonded on a lead frame is illuminated, the photocurrent will flow through the loop circuits formed by the lead frame. Through characterization of the weak photovoltaic response in the lead frame with the 20 LED chips, five LED faults, including chip defects (chip quality and chip contamination) and bonding deficiencies (disconnection, debonding, and rebonding), can be detected before packaging. A high-sensitivity photocurrent detection instrument has been developed to detect different color (red, yellow, green, and blue) and different size LED chips (9-15 mil) on LED assembly line. A key feature of the new instrument is the capability to tune and implement the maximum output power (photocurrent) in the loop lead frame by designing the high-efficiency magnetic core, the magnetic coil and the detecting system. Experiments demonstrate that the photovoltaic behaviors for LED p-n junctions are directly related to the LED electroluminescent characteristics, and the internal optoelectronic characteristics and the external Ohmic contact performances can be derived by detecting the photocurrent of LED chips. The LED online noncontact fault detection instrument based on the photovoltaic effect can be used to substitute for the ordinary electroluminescence online contact fault detection instrument.
本文提出了一种在发光二极管（LED）芯片封装过程中的在线非接触式故障检测方法，该方法基于p-n结中的光伏效应。一旦粘贴在引线框架上的LED芯片受到光照，光电流将流经由引线框架形成的回路。通过对带有20个LED芯片的引线框架中微弱光伏响应的表征，可以在封装前检测出五种LED故障，包括芯片缺陷（芯片质量和芯片污染）和键合缺陷（断开、脱键合和重新键合）。已开发出一种高灵敏度光电流检测仪器，用于在LED装配线上检测不同颜色（红色、黄色、绿色和蓝色）以及不同尺寸（9 - 15密耳）的LED芯片。新仪器的一个关键特性是能够通过设计高效磁芯、磁线圈和检测系统，在回路引线框架中调节并实现最大输出功率（光电流）。实验表明，LED p-n结的光伏行为与LED的电致发光特性直接相关，并且通过检测LED芯片的光电流可以推导出其内部光电特性和外部欧姆接触性能。基于光伏效应的LED在线非接触式故障检测仪器可用于替代普通的电致发光在线接触式故障检测仪器。
