Microlens Fabricated By Water Droplets Condensation And Its Applications In Silicon-based LED Packaging

Color mixed light-emitting diodes(cm-LEDs)have become a new trend in the lighting field due to their high quality and low power consumption.Light extraction efficiency(LEE)and angular color uniformity(ACU)are important performance parameters for evaluating their quality.The traditional packaging structure cannot meet the requirements of high LEE and high ACU of cm-LEDs at the same time,which limits their development in the field of high-quality lighting.In this paper,concave microlens arrays(MLAs)with different morphology were fabricated on the surface of UV polymer film based on the technology of water droplet condensation imprinting under the condition of initiative cooling.The application of the prepared UV polymer film with concave MLAs in the cm-LEDs package can effectively improve the LEE and the ACU of the cm-LEDs.Compared with the traditional MLAs manufacture process,this solution has the advantages of simple engineering,low cost,and flexibly controllable morphology.The contents in details are described as following:The regulation rules of different process parameters on the MLAs morphology were analyzed theoretically.The results shown that the condensation temperature,condensation time and surface tension of the sacrificial layer were the key factors to adjust the MLAs morphology.Based on the initiative cooling water droplets condensation technology,the surface MLAs fabrication experiments were carried out.By adjusting the condensation temperature,condensation time,types of sacrificial layer materials and the extra volume of the sacrificial layer,we finally adjusted the size,the spacing and the cross-sectional morphology of MLAs.Based on the initiative cooling water droplets condensation technology,the curvature of MLAs was adjusted by adjusting the cooling temperature process parameters.Further,by introducing two-step cooling method to change the surface tension of the sacrificial layer polymer,the water droplets moved towards to the sacrificial layer under the influence of the Marangoni effect,and the curvature of MLAs could be continuously adjusted.A transmission model of light in polymer film with MLAs on its surface was established,and the influence of the morphological parameters of MLAs on LEE and ACU of the LED package module was theoretically analyzed.The application experiments of MLAs in LED package were carried out.The cm-LEDs were fabricated by packaging several high efficiency silicon-based LED chips in COB package form.The polymer films with MLAs were applied in the LED package structure.The optical test shown that the MLAs could improve the LED LEE by 11.4%under the test current of 500mA,and the maximum color difference of the LED module with or without MLAs package was 273K and 853K respectively under the test current of 200mA,which shown that the MLAs could effectively improve the ACU of LED.And the MLAs realized 9.1%improvement in the light extraction efficiency of cm-LEDs.