CMX released optoelectronic nitride for high density optical quantum white LED

Abstract: white LED is toward higher efficiency, better light quality, higher package density and higher reliability of the direction of development. The properties of nitride red phosphor which directly affects the efficiency of light, color temperature, color rendering index of white light LED and service life, especially its resistance to high temperature and high humidity performance for light effect in high power devices to maintain the rate of color and anti drift performance plays a vital role. CMX released a new series of pink photoelectric products, resisting high temperature and high humidity environment erosion showed good stability, has important role on the reliability of the high power white LED devices to improve the.

1, high power devices within the working environment changes caused by the fluorescent powder trust challenge

Throughout the course of development of white LED technology, packaging structure from the line, plastic half package type to the surface mount type (SMD, PCT and EMC subdivided into PPA, etc.) to integrated type (COB) and high power ceramic package, at the same time in order to meet the general requirements of lighting, color index rising. White LED is toward higher efficiency, better light quality, higher package density and higher reliability of the direction of development.

The fluorescent powder and the chip is a core part of white LED devices, especially with the power density of white LED devices continue to improve, the reliability of the nitride is extremely critical, the performance will maintain rate for white LED light effect and anti color drift performance significantly affected, thereby affecting the service life of the product. With the continuous development of EMC, WLP and CSP model, also accompanied by a sharp rise in package density and input power, blue photon emitted by the chip density increased dramatically, fluorescent powder during excitation phosphor particles of the body temperature rises rapidly due to non radiative heat release. According to our previous study, only this one factor may cause the phosphor particles temperature rose to 200 degrees Celsius, far higher than the chip junction temperature (120 DEG C), taking into account the fluorescent powder also has high density blue light irradiation and chip heat conduction effect, further pushing up the phosphor particles itself (temperature at about 220 degrees Celsius), that is to say, since the internal phosphor particles and colloid colloid interface to form a very steep temperature gradient. As a result of the existence of the quenching of the phosphor itself will lead to a significant reduction in the thermal equilibrium state of the light effect, up to 15%. With the continuous improvement of chip technology, chip size will continue to decrease, further improve the efficiency and power density will further exacerbate the problem.

Fig. 1 Schematic diagram of temperature field around phosphor particles

At the same time, it is more noteworthy is that the high temperature and high humidity environment formed by the high temperature and high temperature of the water vapor and the high temperature of the phosphor itself is a more severe test. The fluorescent powder scheme at present high color white, yellow and green aluminate powder (including LuAG and Ga-YAG) has good chemical stability, the LuAG because of its excellent characteristics in thermal quenching characteristics, so in the production of high power devices or place on the reliability of the requirements are particularly high, LuAG is the preferred green powder. And to improve the color rendering index plays a crucial nitride (including SCASN and CASN two series) in high temperature and high humidity under the action of facing extremely severe challenges. Japan's NIMS Jie Zhu J. in 2015 Mater. Chem. published a paper in the proposed reaction mechanism in water under the action of CASN and its degradation mechanism is red, in the presence of H2O (Sr, Ca) N element in the AlSiN3:Eu oxidation by H2O immersion, in the form of (Sr, Ca) Al2Si2O8 and Ca (OH) 2 at the same time, also released ammonia, the specific reaction is as follows [1], namely (Sr, Ca) AlSiN3:Eu powder in water vapor under the action of change at the same time activator ion Eu2+ was oxidized into Eu3+ phase occurs in the matrix, which leads to the luminescent properties of the serious deterioration. 2 (Sr, Ca) AlSiN3 (s) + 10H2O (g), (Sr, Ca) Al2Si2O8 (s) + 6NH3 (g) + Ca (OH) 2 (s)

Fig. 2 Schematic diagram of AlSiN3:Eu (SrCa) failure mechanism caused by water vapor effect [1]

2, high temperature and humidity performance evaluation

For the performance of the pink reliability for accurate evaluation, this study on the experimental conditions of high humidity and high temperature cooking were adjusted, the heating temperature is controlled at about 125 DEG C, so that the fluorescent powder slow deterioration in cooking under relatively mild conditions, by prolonging the cooking time, degradation behavior can be more to study the delicate pink. The cooking conditions for 0.18MPa, 100%RH and 125 DEG C, the evaluation consists of two parts: one is the direct fluorescent powder cooking, every time to remove some of the fluorescent powder sample, micro morphology and color drift test; the second part is to be measured by several kinds of phosphor packaging forms in the same package. Made of beads, and beads placed in the environment of aging, and the test lamp through different treatment time after index. Finally, through the above two aspects of the test data on the reliability of the nitride quality rapid evaluation. The table below lists out the study collected at home and abroad several major enterprise products red fluorescent powder.

Three, analysis and results

1) microscopic morphology

Figure 2a, 2b and 3b respectively, figure 3A shows sample1 and sample2 powder samples initial shape and morphology of 48h after cooking after treatment. By comparing the morphology, it can be very intuitive to judge the changes in the morphology of phosphors. The sample1 samples after 48h after cooking, fluorescent powder body