材料科学
光电子学
光伏系统
光电流
发光二极管
电致发光
故障检测与隔离
炸薯条
欧姆接触
二极管
光电二极管
电气工程
计算机科学
纳米技术
电信
工程类
执行机构
图层(电子)
作者
Ping Li,Yumei Wen,Youhai Cai,Lian Li
摘要
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.
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