Heavily phosphor loaded LED packages having higher stability

Abstract

Heavily phosphor loaded LED packages having higher stability and a method for increasing the stability of heavily phosphor loaded LED packages. A silicone overlayer is provided on the phosphor silicone blend layer.

Claims

1. A phosphor-loaded LED package comprising: an LED; a first layer comprising a gravitationally settled blend of phosphor and silicone overlaying the LED, wherein the blend comprises a phosphor to silicone weight ratio of at least 20%, and wherein the blend comprises at least K.sub.2SiF.sub.6:Mn.sup.4+ (PFS) phosphor; and an overlayer comprising silicone, said overlayer which overlays the first layer, wherein the silicone overlayer has a thickness of about 0.1 mm or greater, and wherein the silicone overlayer is made of the same silicone as in the phosphor silicone blend.

2. The LED package of claim 1, wherein the PFS phosphor in the phosphor silicone blend exhibits sensitivity to ambient moisture.

3. The LED package of claim 1, wherein the phosphor silicone blend further includes BSY phosphor.

4. The LED package of claim 1, wherein the LED consumes low to mid power and the blend comprises a BSY-PFS phosphor.

5. The LED package of claim 1, wherein the phosphor silicone blend layer has a thickness of about 0.2 mm.

6. The LED package of claim 1, wherein the silicone overlayer has a thickness between about 0.1 mm and 0.5 mm.

7. A phosphor-loaded LED package comprising: an LED; a first layer comprising a blend of phosphor and silicone overlaying the LED, wherein the blend comprises a phosphor to silicone weight ratio of at least 20%, and wherein the blend comprises at least yttrium aluminum garnet (YAG) and K.sub.2SiF.sub.6:Mn.sup.4+ (PFS) phosphor; and an overlayer comprising silicone, said overlayer which overlays the first layer.

8. The phosphor-loaded LED package of claim 7, wherein the silicone overlayer has a thickness of about 0.1 mm or greater.

9. The phosphor-loaded LED package of claim 7, wherein the phosphor silicone blend layer has a thickness of about 0.2 mm.

10. The phosphor-loaded LED package of claim 7, wherein the silicone overlayer has a thickness between about 0.1 mm and 0.5 mm.

11. The phosphor-loaded LED package of claim 7, wherein the silicone overlayer is made of the same silicone as in the phosphor silicone blend.

12. A phosphor-loaded LED package comprising: an LED; a first layer comprising a blend of phosphor and silicone overlaying the LED, wherein the blend comprises a phosphor to silicone weight ratio of at least 20%, and wherein the blend comprises at least K.sub.2SiF.sub.6:Mn.sup.4+ (PFS) phosphor; and an overlayer comprising silicone, said overlayer which overlays the first layer, wherein the silicone overlayer has a thickness of about 0.1 mm or greater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic view of an LED of the prior art.

(2) FIG. 2 illustrates an LED package with a silicone over layer.

(3) The present disclosure may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The present disclosure is illustrated in the accompanying drawings, throughout which like reference numerals may indicate corresponding or similar parts in the various figures. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the disclosure. Given the following enabling description of the drawings, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the art.

DETAILED DESCRIPTION

(4) The following detailed description is merely exemplary in nature and is not intended to limit the applications and uses disclosed herein. Further, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. While embodiments of the present technology are described herein primarily in connection with PFS LED packages, and especially the Nichia 757 BSY-PFS LED package, the concepts are also applicable to other types of phosphor loaded LEDs and especially with other types of heavily phosphor loaded LEDs. Specifically, the concepts are most applicable in LED packages where the phosphor to silicone weight ratio is high (20% and higher) and at least one of the phosphors exhibits sensitivity to ambient atmospheric constituents such as moisture.

(5) FIG. 1 shows an exemplary prior art LED package 10. The package 10 comprises a light emitting diode (LED) chip 12. A phosphor and silicone blend layer 22 overlays the chip 12. The LED chip 12 and phosphor silicone blend layer 22 are encapsulated with a lens 18. The LED package 10 includes an outside enclosure 30.

(6) The phosphor silicone blend layer 22 is radiationally coupled to the LED chip 12 in the direction indicated by arrow 24. Radiationally coupled means that the elements are associated with each other so that at least part of the radiation emitted from one is transmitted to the other.

(7) One embodiment of a heavily phosphor loaded LED package 50 having greater stability is shown in FIG. 2. The package 50 comprises a semiconductor UV or visible radiation source, such as a light emitting diode (LED) chip 52. A phosphor and silicone blend layer 54 overlays the chip 52.

(8) The package 50 may include any semiconductor visible or UV light source that is capable of producing white light when its emitted radiation is directed onto the phosphor. The preferred peak emission of the LED chip 52 will depend on the identity of the phosphors used and may range from, e.g., 250-550 nm. In one preferred embodiment, however, the emission of the LED will be in the violet to blue-green region and have a peak wavelength in the range from about 420 to about 500 nm. Typically then, the semiconductor light source comprises an LED doped with various impurities. Thus, the LED may comprise a semiconductor diode based on any suitable III-V, II-VI or IV-IV semiconductor layers and having a peak emission wavelength of about 250 to 550 nm.

(9) Although the general discussion of the exemplary structures of the invention discussed herein are directed toward inorganic LED based light sources, it should be understood that the LED chip may be replaced by an organic light emissive structure or other radiation source unless otherwise noted and that any reference to LED chip or semiconductor is merely representative of any appropriate radiation source.

(10) The phosphor silicone blend layer 54 is desirably heavily loaded with phosphor, especially 20% or greater by weight phosphor. The phosphor silicone blend layer 54 is generally about 0.2 mm in thickness. In preferred embodiments, the phosphor is a blend of PFS phosphor and BSY phosphor or a spectrally similar phosphor. Particularly preferred are the Nichia Mint phosphor (BSY) and GE PFS phosphor, desirably in a low to mid power LED package. An example is the Nichia 757 package.

(11) A silicone overlayer 56 is provided on top of the phosphor silicone blend layer 54. The overlayer has a thickness of about 0.1 mm, desirably between about 0.1 and 0.5 mm. The silicone used is desirably the same type as than in the phosphor silicone blend layer 54.

(12) The silicone over layer 56 is desirably applied or synthetically created from the blend immediately following dispensing of the silicone/phosphor slurry and subsequent simultaneous curing to avoid separation. In a preferred embodiment, prior to curing the silicone phosphor blend in the LED package, the silicone protective over layer 56 can be formed by gravitational settling of the phosphor in the silicone blend. The settling process can be aided by artificially creating additional gravitational force via a centrifuge or like device. This gravitational action physically settles a phosphor silicone blend layer 54 down on the LED chip 52 and allows silicone seepage to the top to form a silicone only protective overlayer 56.

(13) The LED chip 52 and phosphor silicone blend layer 54 may be encapsulated with a lens 58. The lens 58 may be, for example, an epoxy, plastic, low temperature glass, polymer, thermoplastic, thermoset material, resin, or other type of LED encapsulating material as is known in the art. Optionally, the lens 58 is a spin-on glass or some other material having a high index of refraction. In one preferred embodiment, the lens 58 is a polymer material, such as epoxy, silicone, or silicone epoxy, although other organic or inorganic encapsulants may be used.

(14) The lens 58 is preferably transparent or substantially optically transmissive with respect to the wavelength of light produced by the LED chip 52 and phosphor silicone blend material 54. In an alternate embodiment, the package 50 may only comprise an encapsulant material without an outer lens.

(15) The outside enclosure 60 of the LED package is typically made of polymeric composite material EMC (Epoxy Moldable Compound). The LED chip 52 may be supported, for example, by a lead frame (not shown), by the self-supporting electrodes, the bottom of the enclosure 60, or by a pedestal (not shown) mounted to the shell or to the lead frame. The LED chip 52 is electrically attached to electrical contacts at the bottom surface of the outside enclosure 60. It is known to those skilled in the art that there could be multiple chips present in LED packages that have similar functional attributes.

(16) The silicone overlayer 56 has been quantified to provide about a 25% improvement in package color shift as compared to the same LED package without the silicone overlayer due to its protection of the phosphor and isolation from ambient constituents such as water.

Example

(17) Nichia 757 LEDs with high BSY-PFS phosphor loading (weight proportion Silicone:PFS:BSY of 49:40:11) were made with and without a silicone overlayer and compared under controlled operating conditions. In both cases the amount of phosphor used was the same and the LED drive and ambient conditions were kept the same. The LED operating conditions were 30 mA in a 47 C constant temperature chamber.

(18) Table 1 below shows the relative improvement in color shift.

(19) TABLE-US-00001 TABLE 1 Color Shift in MPCD After Hours of Operation Hours of operation 500 1000 2000 3000 4000 With silicone overlayer 0.51 0.64 0.7 0.8 0.9 Without silicone 0.77 0.81 0.8 0.94 1.26 overlayer

(20) The improvement in color shift after 500 hours of operation was 34% and after 4000 hours of operation was 29%.

(21) Alternative embodiments, examples, and modifications which would still be encompassed by the disclosure may be made by those skilled in the art, particularly in light of the foregoing teachings. Further, it should be understood that the terminology used to describe the disclosure is intended to be in the nature of words of description rather than of limitation.

(22) Those skilled in the art will also appreciate that various adaptations and modifications of the preferred and alternative embodiments described above can be configured without departing from the scope and spirit of the disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the disclosure may be practiced other than as specifically described herein.