Micro fabrication molding process

• US 4,381,963 A
• Filed: 07/30/1980
• Issued: 05/03/1983
• Est. Priority Date: 07/30/1980
• Status: Expired due to Term

• Current Assignee: University of Rochester
• Original Assignee: University of Rochester
• Inventors: Deckman, Harry W., Goldstein, Irving S., Kalk, Franklin D.
• Primary Examiner(s): Weston, Caleb
• Application Number:
  US06/173,533
• Time in Patent Office: 1,007 Days
• Field of Search: 156/58, 156/59, 156/242, 156/245, 156/304.1, 156/304.2, 29/463, 264/219, 264/220, 264/221, 264/225, 264/227
• US Class Current: 156/245
• CPC Class Codes: B29C 33/3878 used as masters for making successive impressions
• CPC Class Codes: G21B 1/19 Targets for producing thermonuclear fusion reactions, e.g. pellets for irradiation by laser or charged particle beams
• CPC Class Codes: Y02E 30/10 Nuclear fusion reactors
• CPC Class Codes: Y10T 29/49893 Peripheral joining of opposed mirror image parts to form a hollow body

Abstract

Identical half-section shells of microscopic size, such as hemispherical shells from which spherical laser fusion targets can be made are capable of mass production by micro fabrication molding techniques. A body (preferably a hollow glass microsphere which is called a glass microballoon) provides a pattern for the hemispherical shells, and is used to produce an original mold section. One or more master molds are formed from this original mold section by replication. Many identical replica molds are made by casting soluble material onto the master mold and removing them therefrom. The replica molds are coated with one or more layers which will form the hemispherical shell wall. The material coating the flat background around the hemispherical cavity is referred to as the flange and is removed to form free standing shells. In order to remove the flange material, the coated replica molds are overcoated with a soluble material which is etched away to the level of the flange. The remaining soluble material acts as a mask for the shell material when the flange material is etched away. The replica mold and overcoating body remain as a protective mask and are dissolved away to release the identical shell sections. These sections can be assembled to provide closed shells. Overlapping lips can be formed during flange removal so as to facilitate the assembly of the sections into the closed shells.

Claims

1. The process for fabricating conjugate shells which comprises the steps of making a first mold from a glass microballoon which has conjugate sections about a plane therethrough as a pattern which first mold has the shape of one of said sections, casting at least one master mold in said first mold, molding a plurality of replica molds of soluble material from said master mold, coating at least one layer in each of said replica molds to form shells therein, and dissolving said replica molds to produce a plurality of identical shells, each having the shape of a conjugate section of said microballoon.

2. The process as set forth in claim 1 further comprising mating pairs of said shells with each other to produce identical shells each having the same external size and shape as said pattern body.

3. The process as set forth in claim 1 wherein said process provides hemispherical shells, and said step of making said first mold with the shape of a hemispherical section comprises the use of a said microballoon as said pattern.

4. The process as set forth in claim 1 wherein said master mold casting step comprises the step of placing a material which is removable from said first mold upon hardening therein, and removing said material when it hardens to provide said master mold.

5. The process as set forth in claim 1 wherein said step of making said first mold comprises the steps of embedding said microballoon in an embedding medium, removing said medium to said plane, said plane being a plane through the equator of said microballoon.

6. The process as set forth in claim 5 wherein said removal step comprises etching of said medium to expose said microballoon to said plane.

7. The process as set forth in claim 6 wherein said embedding medium is of organic material, and etching with an oxygen plasma etch to remove said medium to said plane.

8. The invention as set forth in claim 5 further comprising the step of removing said microballoon to provide said section therein.

9. The process as set forth in claim 5 wherein said embedding medium is epoxy substantially free of particulates.

10. The process for fabricating conjugate shells which comprises the steps of making a first mold from a body which has conjugate sections at a plane therethrough as a pattern which first mold has the shape of one of said sections, casting at least one master mold in said first mold, molding a plurality of replica molds of soluble material from said master mold, coating at least one layer in each of said replica molds to form shells therein, dissolving said replica molds to produce a plurality of identical shells each having the shape of said section, said master mold casting step comprising the steps of placing a material which is removable from said first mold upon hardening therein, and removing said material when it hardens to provide said master mold, said first mold being made by casting epoxy having an absence of particulates around said body, removing said epoxy to said plane, and removing said body to provide the cavity having the same shape as said section therein, and said master mold casting step is carried out by placing liquid silicone rubber material on said first mold filing said cavity, causing said silicone rubber material to harden into said master mold, and removing said silicone rubber master mold.

11. The process as set forth in claim 10 wherein said master mold casting steps are repeated to as to provide a plurality of master molds.

12. The process for fabricating conjugate shells which comprises the steps of making a first mold from a body which has conjugate sections about a plane therethrough as a pattern which first mold has the shape of one of such sections, casting at least one master mold in said first mold, molding a plurality of replica molds of soluble material from said master mold, coating at least one layer in each of said replica molds to form shells therein, dissolving said replica molds to produce a plurality of identical shells each having the shape of said section, removing any flanges from said layers prior to dissolving said replica molds, said flange removing step comprising the steps of placing soluble material over said layers in said replica mold, filing the cavities therein over said layers to provide covering bodies on said layers, removing said covering bodies to expose the surface of said layers leaving a protective mask included in the cavity over said layers, removing said layers to the surface of said replica molds, and dissolving said mask in the cavities over said layers.

13. The process as set forth in claim 12 wherein said covering body and layer removal steps are carried out by selective etching.

14. The process as set forth in claim 12 wherein said replica mold and said covering body are formed from polymer material soluble in the same organic solvent, and said replica mold and protective mask dissolving steps are carried out together.

15. The process as set forth in claim 14 wherein said polymer is a positive photoresist.

16. The process as set forth in claim 12 wherein said layer coating step comprises coating a plurality of layers of different material in said replica molds upon the surface thereof having said cavity therein, and said flange removing step is carried out to provide complementary lips in different ones of said shells which overlap each other when said shell sections are assembled to form a closed shell.

17. The process as set forth in claim 16 wherein said body is a glass microballoon, said sections are hemispherical, said flange removal step is carried out by etching said covering bodies to the surface of a first of said layers therein, then on the first of a pair of said replica molds with the layer and protective mask in the cavity therein etching the inner one of said plurality of layers to the surface of an outer one of said plurality of layers, selectively etching away the outer one of said layer to the surface of said replica mold leaving a lip of said inner layer about equal to the thickness of said outer layer, on the second of said replica molds selectively etching the inner one of said plurality of layers to a level below the plane of the flange of an outer one of said plurality of layers about equal to the thickness of said outer layer, and then selectively etching said outer layer to the surface of said replica mold, thereby leaving a lip of said outer layer.

18. The process as set forth in claim 17 further comprising depositing witness films on the surface of said replica mold and on the layers therein.