Layer thickness control for stereolithography utilizing variable liquid elevation and laser focal length

• US 20020195748A1
• Filed: 08/22/2002
• Published: 12/26/2002
• Est. Priority Date: 08/29/2000
• Status: Active Grant

• Current Assignee: Warren M. Farnworth
• Original Assignee: Warren M. Farnworth
• Inventors: Farnworth, Warren M.
• Granted Patent: US 6,896,837 B2
• Time in Patent Office: Days
• US Class Current: 264/401
• CPC Class Codes: B29C 2035/0838 using laser
• CPC Class Codes: B29C 2037/903 by means of a computer
• CPC Class Codes: B29C 64/135 the energy source being concentrated, e.g. scanning lasers or focused light sources
• CPC Class Codes: B29K 2995/0073 smooth
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: B33Y 40/00 Auxiliary operations or equipment, e.g. for material handling
• CPC Class Codes: B33Y 40/20 Post-treatment, e.g. curing, coating or polishing

Abstract

An apparatus and method for controlling the surface level of a liquid residing within a relatively vertically stationary workpiece support platform disposed within a reservoir for use in stereolithographic processes wherein a layered object or structure is formed by selectively curing portions of the liquid to at least a semisolid state in multiple, at least partially superimposed layers. Providing precise control of liquid depth over the vertically stationary platform as well as focusing of a laser beam for curing the liquid at the varying surface levels thereof relative to the vertically stationary platform is effected using a laser range finder system controlled by a computer used to control the stereolithographic process in a closed loop fashion.

Claims

1. A method for providing at least an underfilled encapsulant structure for a flip-chip configured semiconductor device having a plurality of external conductive elements projecting from an active surface thereof, the method comprising:

placing at least one flip-chip configured semiconductor die facing active surface down and above an upper surface of a platform while resting on a plurality of external conductive elements projecting from the active surface;

tilting the platform at an acute angle to the horizontal while raising a surface level of a curable liquid at least above an uppermost edge of the active surface with the at least one semiconductor die in a tilted orientation; and

returning the platform to a horizontal orientation without causing any portion of the active surface to extend above the surface level of the curable liquid.

2. The method of claim 1, further including, after returning the platform to a horizontal orientation, traversing a substantially vertical beam of electromagnetic radiation about a periphery of the at least one semiconductor die to at least partially cure a portion of the curable liquid adjacent the at least one semiconductor die.

3. The method of claim 2, further comprising traversing the substantially vertical beam of electromagnetic radiation about an entire lateral periphery of the at least one semiconductor die and trapping uncured curable liquid under the active surface thereof.

4. The method of claim 1, further including reducing an elevation of the surface level of the curable liquid while returning the platform to the horizontal orientation whereby, when the platform reaches the horizontal orientation, the surface level of the curable liquid is at an elevation less than a height of the at least one semiconductor die.

5. The method of claim 1, further including tilting the platform prior to raising the surface level of the curable liquid.

6. The method of claim 1, further including tilting the platform substantially concurrently with raising the surface level of the curable liquid.

7. An apparatus for providing at least an underfilled encapsulant structure for a flip-chip configured semiconductor device having a plurality of external conductive elements projecting from an active surface thereof, the apparatus comprising:

a reservoir;

a platform disposed in the reservoir and having an upper surface for supporting at least one semiconductor die thereon;

a drive assembly operably configured for tilting the platform to a selected acute angle to the horizontal within the reservoir;

a liquid displacement structure for selectively varying a surface level of a curable liquid material contained in the reservoir; and

a source of electromagnetic radiation configured to generate, focus and traverse a substantially vertical beam of electromagnetic radiation over the platform.

8. The apparatus of claim 7, further comprising at least one sensor for providing data to make a determination as to a distance between a location on or above the platform and a reference location above the platform.

9. The apparatus of claim 8, wherein the at least one sensor comprises a plurality of sensors.

10. The apparatus of claim 9, wherein the plurality of sensors comprises a plurality of laser range finders disposed above the platform.

11. The apparatus of claim 8, wherein the source of electromagnetic radiation is adapted to vary a focal length of the beam of electromagnetic radiation responsive at least in part to the provided data.

12. The apparatus of claim 11, wherein the source of electromagnetic radiation is adapted to vary a focal point of the beam of electromagnetic radiation to coincide with the surface level of the curable liquid within the reservoir.

13. The apparatus of claim 12, further comprising a computer for controlling tilting of the platform by the drive assembly, varying the surface level of the curable liquid with the liquid displacement structure, generating and traversing the beam of electromagnetic radiation with the source of electromagnetic radiation, and focusing the beam of electromagnetic radiation to a selected focal length using the data provided by the at least one sensor.

14. The apparatus of claim 13, wherein the computer is further adapted to control the liquid displacement structure to provide a selected depth of curable liquid above the platform upper surface.

15. The apparatus of claim 14, wherein the computer is further adapted to verify accuracy of the selected depth of curable liquid responsive to data provided by the at least one sensor.

16. The apparatus of claim 15, wherein the computer is adapted to control and terminate variance of the surface level of the curable liquid with the liquid displacement structure responsive to multiple samples of data provided by the at least one sensor during the variance process.