LED with high thermal conductivity particles in phosphor conversion layer
View Patent ↗In one embodiment, a solid cylindrical tablet is pre-formed for a reflective cup containing an LED die, such as a blue LED die. The tablet comprises uniformly-mixed phosphor particles and transparent/translucent particles of a high TC material, such as quartz, in a hardened silicone binder, where the index of refraction of the high TC material is matched to that of the silicone to minimize internal reflection. Tablets can be made virtually identical in composition and size. The bulk of the tablet will be the high TC material. After the tablet is placed in the cup, the LED module is heated, preferably in a vacuum, to melt the silicone so that the mixture flows around the LED die and fills the voids to encapsulate the LED die. The silicone is then cooled to harden.
1. A method of fabricating a light emitting diode (LED) module comprising:
providing a reflective cup containing at least one LED die;
positioning a solid piece in the reflective cup and over the LED die such that no portion of the solid piece extends laterally beyond the reflective cup, wherein the solid piece contacts inner walls of the reflective cup and creates a void around the LED die below the solid piece, the solid piece comprising:
a binder having a first index of refraction and a first thermal conductivity;
wavelength conversion particles uniformly mixed in the binder that convert first light emitted by the LED die to second light of a different wavelength; and
high thermal conductivity particles uniformly mixed in the binder, such that a bulk of the solid piece is the high thermal conductivity particles, the high thermal conductivity particles having a second index of refraction substantially equal to the first index of refraction and having a second thermal conductivity greater than the first thermal conductivity;
after the solid piece is positioned, softening the solid piece to flow the wavelength conversion particles, the high thermal conductivity particles, and the binder around the LED die to directly contact and encapsulate the LED die such that all materials in the softened piece are within the reflective cup, wherein the solid piece containing the uniformly mixed wavelength conversion particles and the uniformly mixed high thermal conductivity particles directly contact the LED die to draw heat away from the LED die; and
hardening the softened piece after encapsulation of the LED die.
2. The method of claim 1 wherein the step of softening the solid piece comprises heating the solid piece to melt the binder.
3. The method of claim 1 wherein the step of softening the solid piece is performed in a vacuum.
4. The method of claim 1 wherein the binder comprises silicone.
5. The method of claim 1 wherein the wavelength conversion particles comprise at least one phosphor.
6. The method of claim 1 wherein the high thermal conductivity particles comprise a quartz or crystalline silica.
7. The method of claim 1 wherein the high thermal conductivity particles comprise crystobalite.
8. The method of claim 1 wherein the high thermal conductivity particles comprise a glass.
9. The method of claim 1 wherein the high thermal conductivity particles comprise a majority of the solid piece.
10. The method of claim 1 wherein positioning the solid piece in the reflective cup comprises positioning the solid piece to be substantially centered in the reflective cup.
11. The method of claim 1 wherein the reflective cup is conical.
12. The method of claim 1 further comprising forming the solid piece by the method comprising:
mixing the wavelength conversion particles and the high thermal conductivity particles in the binder while the binder is softened to form a slurry;
forming a sheet of the slurry;
hardening the binder; and
separating the resulting hardened sheet into substantially identical solid pieces.
13. The method of claim 1 wherein the solid piece has a generally cylindrical shape.
14. The method of claim 1 wherein providing the reflective cup containing at least one LED die comprises providing a plurality of identical reflective cups on a substrate, each reflective cup containing at least one LED die.
15. The method of claim 1 wherein the hardened piece after encapsulation conducts heat from the LED die to the reflective cup and to a base of the reflective cup.
16. The method of claim 1 wherein the second thermal conductivity greater than three times the first thermal conductivity.
17. The method of claim 1 wherein the step of hardening the softened piece after encapsulation of the LED die causes the hardened piece to have a substantially flat top surface across the reflective cup.