Electrostatic phosphor coating systems and methods for light emitting structures and packaged light emitting diodes including phosphor coating

• US 9,589,852 B2
• Filed: 07/22/2013
• Issued: 03/07/2017
• Est. Priority Date: 07/22/2013
• Status: Active Grant

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Seibel, Harry A. II, Collins, Brian Thomas
• Primary Examiner(s): Feliciano, Eliseo Ramos
• Assistant Examiner(s): SINGAL, ANKUSH K
• Application Number:
  US13/947,623
• Publication Number:
  US 20150024516A1
• Time in Patent Office: 1,324 Days
• Field of Search: 438/7
• US Class Current: 1/1
• CPC Class Codes: H01L 21/6715 Apparatus for applying a liquid, a resin, an ink or the like H01L21/67126 takes precedence
• CPC Class Codes: H01L 22/10 Measuring as part of the manufacturing process burn-in G01R31/2855
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/0095 Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination

Abstract

Methods are disclosed including applying a layer of binder material onto an LED structure. A luminescent solution including an optical material suspended in a solution is atomized using a flow of pressurized gas, and the atomized luminescent solution is sprayed onto the LED structure including the layer of binder material using the flow of pressurized gas.

Claims

1. A method, comprising:

biasing a luminescent solution comprising an optical material suspended in a solution at a first bias voltage level;

mounting an LED structure on a stage;

biasing the stage at a different voltage level than the first bias voltage level;

atomizing the biased luminescent solution using a flow of pressurized gas; and

spraying the atomized biased luminescent solution onto the LED structure using the flow of pressurized gas.

2. The method of claim 1, further comprising applying a layer of binder material to the LED structure before spraying the atomized biased luminescent solution onto the LED structure.

3. The method of claim 1 wherein the luminescent solution comprises wavelength conversion particles suspended in a volatile solvent, the method further comprising evaporating a solvent from the luminescent solution to provide a layer of wavelength conversion particles on the LED structure.

4. The method of claim 1, wherein the luminescent solution comprises wavelength conversion particles suspended in a nonvolatile solvent, the method further comprising curing the nonvolatile solvent to provide a layer including the wavelength conversion particles on the LED structure.

5. The method of claim 1, wherein the LED structure comprises an LED chip having a top surface and a wirebond pad on the top surface, the method further comprising bonding a wire to the wirebond pad before spraying the atomized biased luminescent solution onto the LED chip.

6. The method of claim 1, wherein the LED structure comprises an LED wafer, the method further comprising singulating the LED wafer into a plurality of LED chips after evaporating the solvent from the luminescent solution.

7. The method of claim 1, further comprising:

energizing the LED structure to cause the LED structure to emit light;

testing the optical characteristics of the LED structure; and

if the optical characteristics of the LED structure are not within a predetermined binning threshold, spraying additional luminescent solution comprising a phosphor suspended in a solution onto the LED structure, evaporating the additional luminescent solution to provide an additional layer of phosphor on the LED structure, and applying an additional layer of binder material onto the LED structure.

8. The method of claim 1, wherein the LED structure comprises an LED chip having a top surface and a wirebond pad on the top surface, the method further comprising mounting the LED within an optical cavity of an LED package before spraying the atomized biased luminescent solution onto the LED chip.

9. The method of claim 8, further comprising:

dispensing an encapsulant material into the optical cavity over the LED chip, thereby covering the LED chip including the layer of phosphor with the encapsulant material.

10. The method of claim 2, wherein the LED structure comprises an LED wafer, the method further comprising:

forming a plurality of electrical contacts on a surface of the LED wafer; and

forming a plurality of sacrificial patterns on respective ones of the plurality of electrical contacts;

wherein applying the layer of binder material comprises applying the layer of binder material to the sacrificial patterns and onto exposed surfaces of the LED wafer between the sacrificial patterns.

11. The method of claim 10, wherein the sacrificial patterns do not completely cover top surfaces of the electrical contacts, so that the applied binder material is at least partially on portions of the top surfaces of the electrical contacts.

12. The method of claim 1, wherein the atomized biased luminescent solution is sprayed onto the LED structure using a spray nozzle, wherein the beam directing unit includes a first conductive member that is biased to a first voltage level that is on one side of the spray of the atomized biased luminescent solution and a second conductive member that is biased to a second voltage level that is on another side of the spray of the atomized biased luminescent solution, and wherein the beam directing unit further includes a third conductive member and a fourth conductive member that may be biased to provide two dimensional control over the direction of the spray of the atomized biased luminescent solution.

13. The method of claim 1, further comprising using a focusing unit to adjust a radius of the spray of the atomized biased luminescent solution.

14. The method of claim 13, wherein the focusing unit comprises a conductive ring, and wherein the radius of the spray of the atomized biased luminescent solution is controlled by controlling a voltage level of the conductive ring.

15. The method of claim 1, wherein the stage includes a plurality of LED structures, and wherein the first bias voltage is only applied to a subset of the LEDs on the stage.

16. The method of claim 15, wherein the first bias voltage is selectively applied to the stage through row and column selectors.

17. A deposition system, comprising:

a liquid supply line;

a reservoir coupled to the liquid supply line and configured to supply a liquid solvent containing particles of optical material to the liquid supply line;

a first voltage bias unit configured to charge the liquid solvent and the particles of optical material at a voltage that has a first polarity;

a spray nozzle coupled to the liquid supply line and configured to receive the charged liquid solvent and particles of optical material from the liquid supply line;

a gas line coupled to the spray nozzle and configured to provide a pressurized gas to the spray nozzle;

a controller configured to control a flow of the charged liquid solvent into the spray nozzle;

a conductive stage positioned to provide a target for atomized particles of the charged optical material emitted by the spray nozzle; and

a second voltage bias unit configured to charge the conductive stage at a voltage that has a second polarity that is opposite the first polarity.

18. A method, comprising:

electrically biasing a luminescent solution comprising an optical material suspended in a solution at a first bias voltage level that has a first polarity;

mounting an LED structure on a stage;

biasing the stage at a different voltage level that has a second polarity that is opposite the first polarity;

flowing the electrically biased luminescent solution to a spray nozzle; and

spraying the electrically biased luminescent solution through the spray nozzle onto the LED structure using a flow of pressurized gas.