Research on Online Detecting for LED Chips

Online test methods for LED chips during packaging process are not available at present.A non-contact technique based on the photovoltaic effect in p-n junctions and Faraday's law is presented,which is applied for detecting chips function and connection status between chips and lead frame during packaging process of LED chips.According to the closed circuit status of LED chips,induced circuit is composed of multi-circuit coil with high-permeability bar magnetic core.Different lapped ways of magnetic core are used to improve signal-to-noise ratio,optimal lapped way is determined according to the result of experiments.The experimental results show that the technique has a high detecting accuracy,and it can realize detecting for closed loop circuit photocurrent,which is just at micro-ampere magnitude.The calculation results are well consistent with the experimental results.