Method for making a biocompatible hermetic housing including hermetic electrical feedthroughs
A method for fabricating a biocompatible hermetic housing including electrical feedthroughs, the method comprises providing a ceramic sheet having an upper surface and a lower surface, forming at least one via hole in said ceramic sheet extending from said upper surface to said lower surface, inserting a conductive thick film paste into said via hole, laminating the ceramic sheet with paste filled via hole between an upper ceramic sheet and a lower ceramic sheet to form a laminated ceramic substrate, firing the laminated ceramic substrate to a temperature to sinter the laminated ceramic substrate and cause the paste filled via hole to form metalized via and cause the laminated ceramic substrate to form a hermetic seal around said metalized via, and removing the upper ceramic sheet and the lower ceramic sheet material from the fired laminated ceramic substrate to expose an upper and a lower surface of the metalized via.
1. A method of fabricating a biocompatible hermetic housing, comprising the steps of:
providing a ceramic sheet having a sheet upper surface and a sheet lower surface;
forming a plurality of vias in the ceramic sheet extending from the sheet upper surface to the sheet lower surface;
inserting an electrically conductive thick film paste into the plurality of vias, the thick film paste comprising ceramic and metal wherein the metal is selected from the group consisting of platinum, titanium, palladium, tantalum, and niobium;
laminating the ceramic sheet between an upper ceramic sheet containing no aligned vias and a lower ceramic sheet containing no aligned vias using a heatpress, the heatpress forming a laminated ceramic substrate;
firing the laminated ceramic substrate to a temperature to compress the thick film paste, sinter the laminated ceramic substrate, forming a single sintered structure comprised of the ceramic sheet, the upper ceramic sheet and the lower ceramic sheet, and forming a metalized via and a hermetic seal between the metalized via and the laminated ceramic substrate;
grinding the upper ceramic sheet and the lower ceramic sheet from the single sintered structure exposing an upper and a lower surface of the metalized via and forming a ceramic substrate having a substrate upper surface and a substrate lower surface with hermetic vias extending from the substrate upper surface to the substrate lower surface; and
forming a housing enclosing electronics using the ceramic substrate as a wall.
2. The method of claim 1 , wherein drawing the thick film past is with a vacuum.
3. The method of claim 1 , further comprising polishing the substrate upper surface and substrate lower surface so the metalized vias are flush with the substrate upper surface and substrate lower surface.
4. The method of claim 1 , wherein the step of providing the ceramic sheet is providing a sheet comprised of at least 90% aluminum oxide.
5. The method of claim 1 , wherein the step of grinding the upper ceramic sheet and the lower ceramic sheet to form the fired laminated ceramic substrate is grinding the substrate to 0.040 inches thick or less.
6. The method of claim 1 , wherein the step of grinding the upper ceramic sheet and the lower ceramic sheet from the fired laminated ceramic substrate is grinding the substrate to less than 0.015 inches thick.
7. The method of claim 1 , wherein the step of inserting a conductive thick film paste further comprises inserting the thick film paste comprising of platinum.
8. The method of claim 1 , wherein the step of forming at least one via is forming a via having a diameter of 0.020 inches or less.
9. The method of claim 1 , wherein the step of forming at least one via is forming a via having a diameter of 0.010 inches or less.
10. The method of claim 1 , wherein the step of providing a ceramic sheet is providing an unfired ceramic sheet.
11. The method of claim 1 , wherein the step of forming at least one via in the ceramic sheet is punching the at least one via with a punch tool, etching the via with a solvent, or forming the via by laser ablation or drilling.
12. The method of claim 1 , wherein the step of inserting a conductive thick film paste into the at least one via comprises:
disposing the ceramic sheet with the via between a stencil layer and a vacuum base, wherein the stencil layer includes at least one through hole that is aligned above the via;
rolling the conductive thickfilm paste across the stencil layer; and
pulling the conductive thickfilm paste into the via though the hole in the stencil layer with a vacuum created by the vacuum base.
13. The method of claim 1 , wherein the step of firing the laminated ceramic substrate further comprises evaporation, binder burnout and sintering of the laminated ceramic substrate.
14. The method of claim 1 , further comprising the step of providing the ceramic sheet that is comprised of aluminum oxide, zirconium oxide or mixture thereof.
15. The method of claim 1 , further comprising the step of providing the ceramic sheet that is comprised of 99% aluminum oxide or more.
16. The method of claim 1 , wherein the step of grinding the upper ceramic sheet and the lower ceramic sheet from the fired laminated ceramic substrate is grinding the substrate to a thickness of less than 0.020 inches.
17. The method of claim 1 , wherein the step of grinding the upper ceramic sheet and the lower ceramic sheet from the fired laminated ceramic substrate is grinding the substrate to a thickness of 0.015-0.020 inches.