Light emitting diodes (“LEDs”) typically emit light in a wavelength band related to a semiconductor bandgap voltage; therefore the light often appears to humans to be of one color. “White” LEDs can be produced by fabricating an LED chip that emits visible light towards the blue end of the visible spectrum, and associating a phosphor with the LED chip. The phosphor fluoresces in the presence of the light emitted by the chip, re-emitting some of the light energy at longer wavelengths so that a human sees a light spectrum that approximates white light.
A phosphor is typically applied to an LED by mixing it with a liquid or gel binder, such as epoxy or silicone, which is then applied as a layer to the LED chip, or to a plastic or glass surface of the LED package. This approach poses certain difficulties. One is that phosphor fluorescence efficiency favors use of large phosphor particles, because smaller particles produce higher non-radiative effects (e.g., heat generation instead of fluorescence). However, maintaining a homogeneous mixture of phosphor particles in a liquid or gel favors use of small phosphor particles. For the latter reason, significant effort and expense is sometimes incurred to control phosphor particle size. For example, phosphor particle size may be controlled such that 90% of phosphor particles are within a tolerance of +−30% of some nominal target particle size within the range of approximately 5 to 50 microns.
The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods that are meant to be exemplary and illustrative, not limiting in scope. In certain embodiments, one or more issues and/or limitations associated with the above-described systems and methods have been addressed, while other embodiments are directed to other improvements.
In an embodiment, a method for depositing a phosphor layer on a light-emitting diode (“LED”) chip is provided. The method includes coating at least a light-emitting side of the LED chip with a phosphor-adhesive material, and exposing an exposed surface of the phosphor-adhesive material to phosphor particles such that the phosphor layer forms of phosphor particles that adhere to the exposed surface.
In an embodiment, a method for depositing phosphor layers on each of a plurality of LED chips includes mounting the LED chips to a common substrate, coating at least a light-emitting side of each of the LED chips with a phosphor-adhesive material, and exposing exposed surfaces of the phosphor-adhesive material to phosphor particles such that the phosphor layers form of phosphor particles that adhere to the exposed surfaces.
In an embodiment, a processed LED chip includes an unpackaged LED chip, a phosphor-adhesive material applied to a light-emitting side of the LED chip; and a phosphor layer formed of phosphor particles adhered to the phosphor-adhesive material.
In an embodiment, an LED chip assembly includes a plurality of unpackaged LED chips mounted to a common substrate, a phosphor-adhesive material applied to a light-emitting side of each of the LED chips, and phosphor layers on each of the LED chips, formed of phosphor particles adhered to the phosphor-adhesive material on each of the LED chips.
Exemplary embodiments are illustrated in the drawings. It is intended that the embodiments and drawings disclosed herein are illustrative rather than limiting.
Various modifications to the described embodiments will be readily apparent to those skilled in the art, and the principles herein may be applied to other embodiments. Thus, the present disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.
Step 104 coats at least a light-emitting side of the LED chip with a phosphor-adhesive material. In the context of this disclosure, the term “phosphor-adhesive material” means a material capable at least of adhering to a surface to which it is applied, and that presents a surface that the phosphor particles will adhere to. The phosphor-adhesive material may be, for example, a gel, a silicone, or an epoxy. The phosphor-adhesive material may be applied, for example, utilizing conventional techniques such as by emitting it from a nozzle (including utilizing ink jet technology), painting or brushing, or screen printing. Optionally, step 104 may configure thickness and/or refractive index of the phosphor-adhesive material for desired optical properties, such as for example to function as an antireflective coating atop the LED chip. Step 104 may also, in certain embodiments, apply the phosphor-adhesive material to a substrate upon which the LED chip and/or other LED chips are mounted. Examples of step 104 are coating LED chips 20 with phosphor-adhesive materials 30, 30′ or 30″ as shown in
Step 106 applies phosphor particles to an exposed surface of the phosphor-adhesive material such that a layer of the phosphor particles adheres to the exposed surface to form a phosphor layer. For example, in step 106 the phosphor particles may be poured or dispensed from multiple points (e.g., like orifices of a salt shaker) over the phosphor-adhesive material. The phosphor particles and/or the LED chip with the phosphor-adhesive material may be agitated (e.g., by shaking a fixture or assembly holding the LED chip, or a substrate on which the LED chip and/or other LED chips are mounted, or by movement of air to agitate the particles) so that the phosphor particles have opportunities to stick to the exposed surface. Examples of step 106 performed in this manner include dispensing phosphors over phosphor-adhesive materials as shown in
The density of phosphor particles that stick to the phosphor-adhesive material may be very uniform when applied according to embodiments herein, because such particles may stick to the adhesive but not stick to each other. That is, when step 106 is performed such that the phosphor particles have substantial opportunity to move about on the exposed surface, a phosphor particle will stick to the surface wherever there is an opening large enough to accommodate the particle, but once all such openings have phosphor particles stuck in them, no more phosphor particles will stick. In such a case, the phosphor particles will substantially form a uniform layer one particle thick (e.g., a “particle monolayer”) on the phosphor-adhesive material.
If desired, an optional step 108 may remove phosphor particles that have not adhered to the exposed surface, from the LED chip. For example, step 108 may consist of turning over the LED (and/or a substrate on which the LED chip and/or other LED chips are mounted) such that phosphor particles that did not adhere, simply fall away. Other examples of step 108 include utilizing mechanical agitation, blowing air or another suitable gas, or rinsing with a liquid, to remove phosphor particles that did not adhere to the exposed surface. A further optional step 110 cures the phosphor-adhesive material; examples of step 110 are baking or exposing a phosphor-adhesive material that includes an epoxy to ultraviolet (“UV”) light so that the exposed surface is no longer capable of adhering particles that are not already adhered to the surface.
The sequence of at least steps 104 and 106, (with or without associated steps 102, 108 and 110) may be repeated. This may be desirable to increase a density of the phosphor particles in a path of light emitted from the LED chip, and/or to facilitate deposition of different kinds of phosphors. Further optional steps 112 and 114 provide a layer of protective material, optionally cured in step 114, that chemically passivates or mechanically protects the phosphor layer(s), the underlying phosphor-adhesive materials, the LED chips and/or substrates. Steps 104 and 106 may also be repeated in order to form a multi-layer structure that minimizes internal reflections and maximizes absorption and fluorescence. This is done by controlling thickness and/or refractive index of the phosphor-adhesive layers.
While the examples described in this disclosure relate to coating LED chips and/or assemblies with phosphor layers, it will be appreciated by those skilled in the art that the methods described and claimed herein may be useful in other phosphor applications. For example, the methods may be utilized to apply phosphors or other particles to diverse surfaces, and the objects formed thereby may be used for any purpose; in particular, these methods could be utilized to apply phosphors to LED chips in standard LED packaging. Application of the methods described herein to such other objects or surfaces may thus be considered to fall within the scope of the disclosed embodiments.
The changes described above, and others, may be made in the phosphor deposition methods described herein without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not a limiting sense. The following claims are intended to cover generic and specific features described herein, and should be construed to encompass any statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between.
This application claims priority to U.S. Provisional Patent Application No. 61/495,226, filed 9 Jun. 2011, which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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61495226 | Jun 2011 | US |