Patent attributes
In one embodiment, a flip chip LED is formed with a high density of gold posts extending from a bottom surface of its n-layer and p-layer. The gold posts are bonded to submount electrodes. An underfill material is then molded to fill the voids between the bottom of the LED and the submount. The underfill comprises a silicone molding compound base and about 70-80%, by weight, alumina (or other suitable material). Alumina has a thermal conductance that is about 25 times better than that of the typical silicone underfill, which is mostly silica. The alumina is a white powder. The underfill may also contain about 5-10%, by weight, TiO2 to increase the reflectivity. LED light is reflected upward by the reflective underfill, and the underfill efficiently conducts heat to the submount. The underfill also randomizes the light scattering, improving light extraction. The distributed gold posts and underfill support the LED layers during a growth substrate lift-off process.
