Research On Several Key Problems Of Online Test Of LED Chips' Optical Parameters

Light-emitting diodes(LEDs for short)have significant advantages of energy saving,environment friendliness and long lifetime.As a new kind of light source,LEDs are used in many industries.Limited to manufacturing techniques,the photoelectric parameters of LED chips in production lines have some discretization,bringing adverse effects to downstream yield.Hence,it's indispensable to test LED chips' photoelectric parameters online quickly in LED industry chain.Higher efficiency means more benefits.But with the improvement of test efficiency,more test error comes along.It's of great importance for the improvement of test efficiency to study on the mechanism of test error and propose corresponding compensation methods.This dissertation divided test errors into three types,error caused by very short test time,error caused by nonideality of test system and error occurring during the test process.Many influencing factors,including transient characteristics of test system,setup height,offset of integrating sphere,optical medium,neighbor die,temperature rise,ambient temperature fluctuation and so on,were studied in this dissertation.Main research content and results are listed below.A point-by-point correction method based on integration time is presented.Integration time is determined as the bottleneck of test efficiency after studying the transient response characteristics of the test system.Based on the working principle and response characteristics of a spectrometer,response characteristics of the test system in different integration time are calibrated by using standard chips,as well as transformation matrices between those in different integration time.Spectrum transforms between small integrating time and lager one are available with these matrices.The experiment shows that the presented method is helpful to reduce integration time without loss of accuracy.Compensation methods for test error resulting from the non-ideality of the test system are presented.Different influencing factors are studied respectively.Mathematical models are set up at first to study the relationship between the light entering the integrating sphere and test distance or installation offset of integrating sphere,and the experiment results shows good agreements with reference values.Then,experiments and Monte Carlo ray-tracing simulations are performed to study the influence of blue film and quartz glass on online test of flip chip light emitting diode(FCLED for short)chips.An attenuation ratio is defined to express the attenuation effect of blue film and quartz glass to radiation flux,and the experiment results shows good agreements with reference values.At last,Monte Carlo ray-tracing simulations are used to study the neighbor-die effect in online test of FCLED chips' optical parameters and current calibration method for online test of FCLED chips' optical parameters is amended and discussed.Compensation methods for heat-inducing error of online test of FCLED chips' optical parameters are presented in this dissertation.Heat-inducing error model of online test system is set up at first to study chips' temperature rise characteristics in testing process.Experiments are also performed to make a contrast,and the results show good agreements with reference values.Then temperature rise curves in different ambient temperature are studies based on the model.It turns out that these curves in different ambient temperature have similar trend.At last,the influence of ambient temperature fluctuation to radiant flux of chips is studied.A linear model is used to correct the test result.Experiments show the validity of presented method to correct heat-inducing error.Finally,uncertainty evaluation is performed based on the above study on each influencing factor.It turns out that uncertainty of online test of conventional LED chips' optical parameters is relatively small and little differences can be found between uncertainties resulting from different uncertainty items.Temperature fluctuation and neighbor-die effect are key sources of test uncertainty in online test of FCLED chips' optical parameters.Expanded related uncertainty reduces from 2.62% to 0.534% after compensation to two items.