Method and apparatus for accurate die-to-wafer bonding

1. A method, comprising:

providing a substrate having a plurality of conductive pads;

placing a plurality of semiconductor dies on the plurality of conductive pads in a manner such that an entire bottom surface of each of the semiconductor dies is placed on a respective conductive pad;

placing a mold device on the substrate, the mold device having a plurality of recesses, wherein the placing the mold device includes covering each of the semiconductor dies by a respective one of the recesses; and

thereafter bonding the semiconductor dies to the conductive pads.

2. The method of claim 1 , wherein the placing the mold device substantially restricts movement of the semiconductor dies that are covered by recesses in the mold device.

3. The method of claim 2 , wherein the placing the mold device includes restricting a movement range of each semiconductor die covered by the recess to be less than about 5 microns in any lateral direction.

4. The method of claim 1 , wherein the placing the mold device includes securing the mold device with respect to the substrate, so that the mold device is substantially free of lateral movement with respect to the substrate.

5. The method of claim 1 , wherein the placing the mold device includes applying pressure to the semiconductor dies through the mold device.

6. The method of claim 1 , wherein the recesses each have a sloped profile.

7. The method of claim 1 , wherein the bonding includes heating the substrate, the semiconductor dies, and the mold device in a reflow oven.

8. The method of claim 1 , further including:

applying a flux material on each of the conductive pads before the semiconductor dies are placed on the conductive pads; and

aligning each of the recesses of the mold device with a respective one of the semiconductor dies before the mold device is placed on the substrate.

9. The method of claim 1 , wherein the semiconductor dies include light-emitting diode (LED) devices.

10. A method of light-emitting diode (LED) packaging, comprising:

providing a sub-mount having a plurality of bonding pads disposed thereon;

coupling a plurality of LED dies to the plurality of bonding pads, wherein each LED die is coupled to a respective one of the bonding pads through direct surface contact;

providing a mold apparatus, the mold apparatus including a plurality of concave recesses;

placing the mold apparatus over the sub-mount, wherein each LED die is housed in a respective one of the recesses; and

thereafter heating the sub-mount, the LED dies, and the mold apparatus in a thermal reflow process, thereby causing the LED dies to be bonded to the bonding pads, respectively;

wherein each recess substantially restricts a positional shift of the LED die below with respect to the bonding pad coupled thereto during the heating.

11. The method of claim 10 , wherein the placing the mold apparatus includes positionally securing the mold apparatus relative to the sub-mount.

12. The method of claim 10 , wherein the placing the mold apparatus includes applying a predetermined amount of pressure to the LED dies through the mold apparatus.

13. The method of claim 10 , wherein the placing the mold apparatus includes aligning the recesses with the LED dies through an optical positioning process.

14. The method of claim 10 , wherein the recesses of the mold apparatus each have a non-uniform cross-sectional profile.

15. A method of light-emitting diode (LED) packaging, comprising:

providing a sub-mount having a plurality of conductive elements disposed thereon;

providing a mold having a plurality of concave recesses;

placing a plurality of LED dies to the plurality of conductive elements, wherein each LED die is placed to a different one of the conductive elements, and wherein a lateral dimension of each LED die is smaller than a lateral dimension of the conductive element to which the LED die is coupled;

thereafter covering the plurality of LED dies with the mold over the sub-mount, wherein the plurality of LED dies is aligned with the plurality of recesses, respectively, such that each recess restricts movements of the LED die underneath; and

performing a heating process to the sub-mount, the LED dies, and the mold, thereby causing the plurality of LED dies to be bonded to the plurality of conductive elements, respectively.

16. The method of claim 15 , further comprising: securing the mold to the sub-mount before the performing the heating process, such that the mold is free of lateral movement relative to the sub-mount.

17. The method of claim 15 , further comprising: applying a downward force to the mold after the covering the plurality of LED dies.

18. The method of claim 15 , wherein the covering the plurality of LED dies is performed at least in part through an optical positioning process.

19. The method of claim 15 , wherein the recesses of the mold each have a non-uniform cross-sectional profile.

20. The method of claim 19 , wherein at least some of the recesses each have a trapezoidal cross-sectional profile.