Fabrication of microlens array encapsulation layer based on porous film by breath figure method for chip-on-board light-emitting diodes

High light extraction efficiency is strongly required in many illumination applications. In this study, a new method to fabricate microstructure array based on porous film and silicone gel (OE-6550, Dow Corning, USA) molding process for the blue chip-on-board (COB) packaging light emitting diodes (LEDs) is proposed and demonstrated. In this method, the porous film on the polymer surface is a polystyrene(PS) film. Use the chloroform to dissolve the PS, and after the volatilization of the chloroform solution the PS film has a porous structure with controlled size. Stable and ordered microstructure array is obtained after the solidification of the polymer on the porous film, and thus convex microstructure array is achieved. Experiments are conducted for performance verification. The results show that the radius of the micro-craters in this method were easily controlled in the range of 3μm to 12μm simply by changing the solution height of chloroform evaporating process. The microstructure array is using a molding process and transferred to surface silicone gel layer. The fabricated silicone gel with convex micro lens array is applied as the top encapsulation layer for COB packaging LEDs. Due to the suppression of the total internal reflection (TIR) between the encapsulant and air, the light extraction efficiency (LEE) is enhanced. The optical measurement results show that the LEE of the COB packaging LED with microlens array increased by 15.58% compared with that with flat encapsulation layer.