UNDERFILL PROCESS FOR FLIP-CHIP LEDS

• US 20090230409A1
• Filed: 03/17/2008
• Published: 09/17/2009
• Est. Priority Date: 03/17/2008
• Status: Abandoned Application

• Current Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.), Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Inventors: Martin, Paul S., Basin, Grigoriy, Diana, Frederic, Simonian, Dima
• Application Number:
  US12/050,082
• Publication Number:
  US 20090230409A1
• Time in Patent Office: Days
• US Class Current: 257/88
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/73204 the bump connector being embedded into the layer connector
• CPC Class Codes: H01L 24/97 the devices being connected to a common substrate, e.g. interposer, said common substrate being separable into individual assemblies after connecting
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/54 having a particular shape
• CPC Class Codes: H01L 33/56 Materials, e.g. epoxy or silicone resin

Abstract

An underfill technique for LEDs uses compression molding to simultaneously encapsulate an array of flip-chip LED dies mounted on a submount wafer. The molding process causes liquid underfill material (or a softened underfill material) to fill the gap between the LED dies and the submount wafer. The underfill material is then hardened, such as by curing. The cured underfill material over the top and sides of the LED dies is removed using microbead blasting. The exposed growth substrate is then removed from all the LED dies by laser lift-off, and the underfill supports the brittle epitaxial layers of each LED die during the lift-off process. The submount wafer is then singulated. This wafer-level processing of many LEDs simultaneously greatly reduces fabrication time, and a wide variety of materials may be used for the underfill since a wide range of viscosities is tolerable.

Claims

1. A method for fabricating a light emitting device comprising:

providing a flip-chip light emitting diode (LED) die on a submount, there being a gap between the LED die and the submount, the LED die having a bottom surface facing the submount and a top surface opposite the bottom surface;

molding an underfill material over the LED die so that the underfill material encapsulates the LED die and substantially completely fills the gap between the LED die and the submount; and

removing the underfill material at least over a top surface of the LED die.

2. The method of claim 1 wherein the LED die comprises epitaxial layers grown on a growth substrate, wherein a surface of the growth substrate is the top surface of the LED die, the method further comprising removing the growth substrate from the epitaxial layers after molding the underfill material over the LED die.

3. The method of claim 2 wherein the substrate is removed from the epitaxial layers by a laser lift-off technique after the step of removing the underfill material.

4. The method of claim 1 wherein removing the underfill material comprises removing the underfill material using microbead blasting.

5. The method of claim 1 wherein removing the underfill material comprises removing the underfill material by etching.

6. The method of claim 1 wherein molding the underfill material over the LED die comprises:

providing a solid underfill material in a mold;

heating the mold to melt or soften the underfill material;

positioning the LED die on the submount with respect to the mold to compress the melted or softened underfill material and encapsulate the LED die; and

cooling the underfill material.

7. The method of claim 1 wherein molding the underfill material over the LED die comprises:

positioning the LED die on the submount with respect to a mold;

creating a substantial vacuum between the submount and a mold cavity;

filling the mold cavity under pressure with a liquid underfill material to encapsulate the LED die; and

curing the underfill material.

8. The method of claim 1 wherein molding the underfill material over the LED die comprises:

filling a mold cavity with a softened underfill material;

immersing the LED die into the softened underfill material; and

curing the underfill material.

9. The method of claim 1 wherein providing a flip-chip LED die on a submount comprises providing a plurality of LED dies on a submount wafer, the submount wafer having electrodes bonded to corresponding electrodes of the plurality of LED dies, each LED die having a gap between the LED die and the submount wafer, and wherein the step of molding the underfill material is performed simultaneously on all the LED dies.

10. The method of claim 9 further comprising singulating the submount wafer to separate LED dies mounted on their respective submount portions, after the step of removing the underfill material.

11. The method of claim 1 wherein the underfill material is a polymer.

12. The method of claim 1 wherein the underfill material is an epoxy molding compound.

13. The method of claim 1 wherein the LED die comprises epitaxial layers grown on a growth substrate, wherein a surface of the growth substrate is the top surface of the LED die, wherein removing the underfill material comprises removing the underfill material to fully expose all side surfaces of the growth substrate.

14. The method of claim 1 wherein molding the underfill material over the LED die comprises providing a solid underfill material in a mold cavity, heating the mold to melt or soften the underfill material, compressing the underfill material, then cooling the underfill material to harden it and encapsulate the LED die.

15. An intermediary light emitting device prior to singulation comprising:

an array of LED dies mounted on a submount wafer, the submount wafer having electrodes bonded to corresponding electrodes of the LED dies, each LED die having a gap between the LED die and the submount wafer; and

an underfill material molded over all the LED dies simultaneously and completely encapsulating all the LED dies, the underfill material substantially completely filling the gap between each LED die and the submount wafer.

16. A light emitting device comprising:

a flip-chip light emitting diode (LED) die;

a submount on which the LED die is mounted, there being a gap between the LED die and the submount; and

a molded underfill between the LED die and the submount.