Micro-bead blasting process for removing a silicone flash layer

• US 8,610,153 B1
• Filed: 08/21/2013
• Issued: 12/17/2013
• Est. Priority Date: 11/28/2011
• Status: Active Grant

• Current Assignee: Bridgelux Incorporated
• Original Assignee: Bridgelux Incorporated
• Inventors: West, R. Scott, Kwon, Mike, Tong, Tao
• Primary Examiner(s): MOORE, WHITNEY
• Application Number:
  US13/972,887
• Publication Number:
  US 20130337592A1
• Time in Patent Office: 118 Days
• Field of Search: 257/88, 257/98, 257/E33.06, 257/E21.001, 451/38, 438/27, 438/115
• US Class Current: 257/98
• CPC Class Codes: B24C 1/003 using material which dissolves or changes phase after the treatment, e.g. ice, CO2
• CPC Class Codes: B24C 1/04 for treating only selected parts of a surface, e.g. for carving stone or glass
• CPC Class Codes: B24C 3/322 for electrical components
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• 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 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2933/0033 relating to semiconductor body packages
• CPC Class Codes: H01L 2933/005 relating to encapsulations
• CPC Class Codes: H01L 33/54 having a particular shape
• CPC Class Codes: H01L 33/56 Materials, e.g. epoxy or silicone resin
• CPC Class Codes: H01L 33/58 Optical field-shaping elements

Abstract

Using compression molding to form lenses over LED arrays on a metal core printed circuit board leaves a flash layer of silicone covering the contact pads that are later required to connect the arrays to power. A method for removing the flash layer involves blasting particles of sodium bicarbonate at the flash layer. A nozzle is positioned within thirty millimeters of the top surface of the flash layer. The stream of air that exits from the nozzle is directed towards the top surface at an angle between five and thirty degrees away from normal to the top surface. The particles of sodium bicarbonate are added to the stream of air and then collide into the top surface of the silicone flash layer until the flash layer laterally above the contact pads is removed. The edge of silicone around the cleaned contact pad thereafter contains a trace amount of sodium bicarbonate.

Claims

1. A method, comprising:

directing a flow of air at a top surface of a flash layer, wherein the flash layer is disposed above a contact pad on a printed circuit board, and wherein the flash layer is made of silicone; and

colliding particles into the flash layer, wherein the particles are carried in the flow of air, and wherein the particles are collided into the flash layer until the flash layer laterally above the contact pad is removed.

2. The method of claim 1, further comprising:

forming the flash layer over the printed circuit board using compression molding.

3. The method of claim 1, wherein no holes pass from a top side of the printed circuit board to a bottom side of the printed circuit board.

4. The method of claim 1, wherein the contact pad is located on a top side of the printed circuit board, and wherein no electrical contacts are disposed on a bottom side of the printed circuit board.

5. The method of claim 1, wherein the flow of air is directed at the top surface of the flash layer at an angle that is within thirty degrees of a normal angle to the top surface.

6. The method of claim 1, wherein the flow of air is directed at the top surface of the flash layer at an angle that is within forty-five degrees of a normal angle to the top surface.

7. The method of claim 1, wherein the flow of air is generated by compressing the air to a pressure of more than fifty pounds per square inch and allowing the compressed air to escape from a nozzle that has a diameter of less than two millimeters.

8. The method of claim 1, wherein the flow of air is generated by compressing the air to a pressure between fifty and two hundred pounds per square inch.

9. The method of claim 1, wherein the flow of air emanates from a nozzle that is more than twenty millimeters from the top surface of the flash layer.

10. The method of claim 1, wherein the particles have a median diameter that is between forty and sixty microns.

11. The method of claim 1, wherein the particles are made of sodium bicarbonate.

12. The method of claim 1, wherein the flash layer has a top side, a bottom side, and four edges, wherein the contact pad disposed on the top side of the printed circuit board, and wherein the flash layer extends to each of the four edges of the printed circuit board.

13. The method of claim 1, wherein the silicone forms a lens above a light emitting diode, and wherein there are less than three millimeters between an edge of the printed circuit board and an edge of the lens.

14. A method, comprising:

positioning a nozzle within thirty millimeters of a top surface of a layer of silicone;

directing a stream of air that exits from the nozzle towards the top surface at an angle that is between five and thirty degrees away from a normal angle to the top surface;

adding particles to the stream of air such that the particles are carried by the stream of air and collide into the top surface of the layer of silicone, wherein the layer of silicone is disposed above a contact pad on a printed circuit board; and

colliding the particles into the layer of silicone until the layer of silicone laterally above the contact pad is removed.

15. The method of claim 14, further comprising:

forming the layer of silicone over the printed circuit board using compression molding.

16. The method of claim 14, wherein the layer of silicone covers a light emitting diode.

17. The method of claim 14, wherein the particles have a median diameter that is between forty and sixty microns.

18. The method of claim 14, wherein the particles are made of sodium bicarbonate.

19. The method of claim 14, wherein the layer of silicone forms a lens above a light emitting diode.

20. The method of claim 19, wherein the printed circuit board has an edge, and wherein there are less than three millimeters between the edge of the printed circuit board and an edge of the lens.