Method for providing hermetic electrical feedthrough
This invention provides methods for the processing of platinum metallized high temperature co-fired ceramic (HTCC) components with minimum deleterious reactions between platinum and the glass constituents of the ceramic-glass body. The process comprises co-firing a multilayer laminate green ceramic-glass body with via structures filled with a platinum powder-based material in a reducing atmosphere with a specified level of oxygen partial pressure. The oxygen partial pressure should be maintained above a minimum threshold value for a given temperature level.
1. A method of fabricating a hermetic electrical feedthrough, the method comprising:
providing a ceramic sheet, and having an upper surface and a lower surface, wherein said sheet includes silicon dioxide;
forming at least one via hole in said sheet extending from said upper surface to said lower surface;
inserting a conductive thickfilm paste, including platinum, into said via hole;
laminating said sheet with said conductive thick film paste in said via hole between an upper ceramic sheet, and a lower ceramic sheet, to form a laminated substrate wherein said via hole is encased in ceramic;
selecting an oxygen controlled environment, between 10 −38 and 10 −3 atmospheres of oxygen partial pressure, by introduction of other gasses selected from the group consisting of C0 2 /CO, C0 2 /NH 3 , C0 2 /H 2 , H 2 0/H 2 , H 2 0/NH 3 , H 2 0/CO, Nitrogen, or Argon, to balance platinum oxidation and silicon dioxide decomposition of said laminated substrate;
firing said laminated substrate in said oxygen controlled environment to a temperature to sinter said laminated substrate to form a single sintered structure and cause said conductive thick film paste in said via hole to form a metallized via, including platinum in contact with ceramic, and cause said laminated substrate to form a fired laminated substrate and a hermetic seal around said metallized via; and
removing said upper sheet material and said lower sheet material by lapping or grinding, to expose an upper and a lower surface of said metallized via.
2. The method according to claim 1 , wherein said sheet is formed of material comprised of at least 90% aluminum oxide.
3. The method according to claim 1 , wherein said fired laminated substrate after said firing and material removal steps is less than or equal to 40 mils thick.
4. The method according to claim 1 , wherein said fired laminated substrate after said firing and material removal steps is less than 15 mils thick.
5. The method according to claim 1 , wherein forming at least one via hole in said sheet comprises punching said via hole using a punch tool, etching said via hole using a solvent etching, using laser ablation or drilling said via hole.
6. The method according to claim 1 , wherein inserting a conductive material into said via hole comprises:
disposing said sheet with said via hole between a stencil layer and a vacuum base, wherein said stencil layer includes at least one through hole that is aligned above said via hole;
rolling said conductive material across said stencil layer; and
pulling said conductive material into said via hole through said hole in said stencil layer with a vacuum created by said vacuum base.
7. The method according to claim 1 , further comprising laminating said sheet with paste filled via holes between said upper sheet and said lower sheet to form said laminated substrate;
placing said sheet with paste filled via holes together with said upper ceramic sheet and said lower ceramic sheet in a heatpress; and
applying heat and pressure by said heatpress until said laminated substrate is formed.
8. The method according to claim 1 , wherein said ceramic material comprises aluminum oxide, zirconium oxide or a mixture thereof.
9. The method according to claim 1 , wherein said fired laminated substrate has a thickness of less than 20 mils after removing said upper ceramic sheet and said lower ceramic sheet material.
10. The method according to claim 1 , wherein said fired laminated substrate has a thickness of 15-20 mils after removing said upper ceramic sheet and said lower ceramic sheet material.