Through X-ray fluoroscopy inspection, internal structure analysis of LED lens module, SEM/EDS inspection and LED lens module luminous temperature analysis, the company's laboratory believes that the reasons for the light decay of LED lens modules are: different thermal expansion coefficients of packaging materials, LED The phosphor powder used in the lens module has poor heat dissipation performance, which generates a large amount of heat and accumulates inside the LED, which causes the internal temperature to be too high, and causes the LED lens module to break between different layers inside. At the same time, the existence of working voltage makes electromigration possible, resulting in the migration of K ions, the luminous efficiency of the fluorescent layer decreases with the continuous migration of K ions, and the intensity of yellow light decreases continuously, so the failed sample first appears light. fading phenomenon, and then the blue light phenomenon appears.

1. Use the naked eye analysis method

Visual inspection can be more obvious OKsample ratioNG-like fluorescent layer is brightly colored.

2. X-ray fluoroscopy

viaX< /span>Radioscopy,OKSamplingNGNo open circuit problem was found in the sample internal lines.

3 Microscopy

willOKand NGThe section is magnified under the metallographic microscope to observe the fluorescent layer and the chip layer.< /span>NGlike faults, while OKNothingYes.

4SEM/EDS analysis

viaSEM/ EDSAnalysis,OKNo gallium detected in the phosphor layer ( Ga) element, potassium was detected (K< span style="line-height:1.5;">) element, while NGLike fluorescencePowder layer detectedGa element, not detectedK element.

Visual inspection can be more obvious OKsample ratioNGThe fluorescent layer is brightly colored;LED SpectrogramIt can be seenOKSamplingNGSampleThe luminous intensity in the blue light area is basically the same, indicating that the chip is basically not damaged, and the phosphor luminous area appears Significant difference, NGlike blue light is relatively strongdegrees32%, significantly lower In OKlike70%;

OKSample andNGThe difference in the composition of the phosphor layer can basically determine that the failure phenomenon is caused by the denaturation of the phosphor during the working process; The failure mechanism is as follows:

In element analysis, we can see that there areLuelement and Kelement's presence, Phosphor efficiency increases with the addition of potassium ion concentration, The luminous intensity gradually increases. When the potassium ion increases to a certain value, the luminous intensity gradually decreases.Lu Ions are used to convert blue light to yellow lightUsed, then blue light and all Excited yellow light mixes to emit white light.

By temperature test we found the light decay of white light NGThe sample can reach a temperature higher than the blue light emittingNGSample, indicating that the phosphor is in good conditionIn contrast, the heat dissipation performance is relatively poor, and the internal temperature can reach a higher temperature in a short time. This product is used in the medical field and is used by dentiststhisLED As a light source, it takes a certain amount of time to diagnose a patient. After the diagnosis, it will be turned off. It will be turned on when the next patient comes over.Off for a certain period of time and then off, and so on, resulting in LEDThe lamp reaches a higher temperature every time it works, then drops to normal temperature, and then rises to The higher temperature cools down, The cycle causes thermal expansion and contraction of packaging materials, and due to the different thermal expansion coefficients of different packaging materials, the materials are constantly changing between high temperature and low temperature. Fractures or cracks occur. Both normal and failed samples were found to have faults, which may be due to the fact that the normal samples were already in the initial state of failure.

After the fault occurs, the phosphor layer contacts the light-emitting electrode to generate electromigration.NG< span style="line-height:1.5;">On the sample electrodeGa The ions are migrated into the phosphor layer, and the phosphor layer should haveKIons are migrated elsewhere. As K ions are migrated out of the phosphor layer, the luminous efficiency of phosphors keeps increasing. decrease, eventually resulting in a mismatch of the blue light emitted by the chip and the yellow light excited by the phosphor layer,resulting in normalLEDlamps experience light decay first,As the intensity of yellow light decreases,eventually emits blue light.

in conclusion

FailedLEDgenerated Possible causes of light decay and blue light: The thermal expansion coefficient of the packaging material is different, LEDThe heat dissipation performance of the phosphor used is not goodGood, and a large amount of heat is generated in the < /span>LEDinternal, causing the internal temperature to be too high, making LEDFractures or cracks appear between different layers inside, while The presence of working voltage makes electromigration possible, resulting inKIon migration, the luminous efficiency of the phosphor layer increases withK With the continuous migration of ions, the decreases, and the intensity of yellow light decreases continuously, so the failed sample first appears light decay, and then blue light.