Lifetime Evaluation Technology Of White Power Led

Light-emitting diodes (light emitting diode, LED), as a new type of solid-statesemiconductor light sources, by virtue of long life, high luminous efficiency, energysaving and environmental protection, are gradually replacing the traditional lightsources, more and more widely used among the various lighting fields. Thedevelopment of GaN-based LED is rapid, the properties of LED is provingcontinually，there has been excellent performance of high-power LED devices such ashigh voltage LED, but these LED devices are lack of adequate reliability research. Inaddition, because the traditional accelerated lifetime test is too long, so the lifetime ofthe rapid replacement of white LED luminaires can’t get an accurate assessment, itrequires a new method of high confidence coefficient to evaluate the lifetime. In thispaper, the photoelectric properties of different types of GaN-based power LED weretested; the HV-LED chips was tested in reliability consideration; a new method ofaccelerated life test was used for testing the lifetime of white LED luminaire. Thispaper is support by national science and technology support program(No.2011BAE01B14), the main research results are as follows:（1）Selecting LED samples of color temperature2700K、3000K、4000K、5500K to carry out through25-900mA variable current experiments with testtemperature25℃. The blue shift of the peak wavelength is detected within the rangeof short wavelength which is due to the quantum restriction of stark effect; with theincrease of injection current, the climbing speed for LED luminous flux declinesgradually, the lighting effect first rises and then declines rapidly, which is because theelectron overflowing from the local state that caused non-radiation recombination; thecolor rendering index rises by30%-35%,the radiant quantity of blue chip is increasingand the transfer efficiency for fluorescent powder falls.（2）Carrying out variable temperature test for HV-LED sample(50V) from15℃to75℃. The result shows that the positive going input almost declines linearly withtemperature increment, the chip optical radiation efficiency decreases that is because the decrease of material`s forbidden bandwidth leads to the rise of augerrecombination rate in the chip quantum well; the spectrum of white light chip is moresmoother and the color rendering index rises slightly; the emission wavelength of bluechip and the excitation wavelength of fluorescent powder generates a certain degreeof mismatches giving rise to reduction of excitation efficiency so as to make thedecline of LED lighting effect.（3）Selecting LED sample with two kinds of SiC substrates to carry out variablecurrent test for which the results compares with sapphire substrate with the samepower. The results show that the LED lighting effect of SiC substrate falls slowly, theascensional range is bigger when at small current which is because of the good heatdissipation of vertical structure of SiC substrate and furthermore the defectconcentration of SiC is far below than sapphire; through measuring the I-Vcharacteristic of LED, it is found that the climbing speed for the LED voltage of SiCsubstrate is significantly lower than the sapphire substrate LED.（4）Taking24HV-LED(50V) chips as samples to carry out2000h currentaccelerated life tests, the three groups of current are20mA、30mA、40mA respectively.The falling range of luminous flux for HV-LED samples is from2.5%to9%, thelighting effect falls by2.7%to11.3%. Due to the combined action for lightattenuation mechanism and light output increase mechanism, the phenomenon ariseswhen the samples of luminous flux in the process of decline；the forward voltage ofsamples increase at large after aging owing to the rise of series resistanceand degeneration of ohmic contact; the weakening of radiant quantity of blue chipand the fall of stimulated phosphor efficiency leads to the decrease of total luminousintensity. The failure occurred during the sample aging conducted failure analysis, thestudy found a significant decrease in its flux is cracked by the phosphor layer, thephosphor degradation and decline epoxy transmittance. Combine the LED lightattenuation model and Bayesian estimation of the life, the life of the samples wereextrapolated to obtain a result is30833h. （5）Through the selection of indoor white light LED lamps from threeenterprises to carry out the aging test, which verified a new method for test thataccelerating the attenuation of LED lamp. The method that coming up with the aim toreduce the test time for lamp`s products, shorten the production cycle ofproducts. Carrying out the6000h accelerated life test to the samples below25℃and55℃obtained the data about the decline of light flux and the drift of colortemperature. The change of lumen maintenance carries through the verificationaccording to the samples under different temperature before and after aging thatproved that the method has a higher confidence coefficient. Finally the failureanalysis was made to the two LED lamps`samples through the electrical test of drivecircuit and chip which respectively obtained the conclusion for rectifier bridge failureand solder joint failure over the failure mode.