Capacitive filtered feedthrough array for an implantable medical device

• US 6,660,116 B2
• Filed: 04/18/2002
• Issued: 12/09/2003
• Est. Priority Date: 03/01/2000
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Wolf, William D., Wiklund, Craig L., Volmering, James E., Haq, Samuel F., Malone, Patrick F., Strom, James, Seifried, Lynn M., Fraley, Mary A.
• Primary Examiner(s): MAYES, MELVIN C
• Application Number:
  US10/124,134
• Publication Number:
  US 20020166618A1
• Time in Patent Office: 600 Days
• Field of Search: 156/89.12, 156/89.16, 156/89.15, 156/89.18, 156/89.19, 156/89.21, 361/302, 607/5
• US Class Current: 156/89.12
• CPC Class Codes: A61N 1/3754 Feedthroughs
• CPC Class Codes: H01G 4/35 Feed-through capacitors or anti-noise capacitors
• CPC Class Codes: H05K 1/0306 Inorganic insulating substrates, e.g. ceramic, glass
• CPC Class Codes: H05K 1/112 directly combined with via connections
• CPC Class Codes: H05K 1/162 incorporating printed capacitors
• CPC Class Codes: H05K 3/4611 by laminating two or more circuit boards H05K3/4652 takes precedence
• CPC Class Codes: H05K 3/4629 laminating inorganic sheets comprising printed circuits, e.g. green ceramic sheets

Abstract

A capacitive filtered feedthrough assembly is formed in a solid state manner to employ highly miniaturized conductive paths each filtered by a discoid capacitive filter embedded in a capacitive filter array. A non-conductive, co-fired metal-ceramic substrate is formed from multiple layers that supports one or a plurality of substrate conductive paths and it is brazed to a conductive ferrule, adapted to be welded to a case, using a conductive, corrosion resistant braze material. The metal-ceramic substrate is attached to an internally disposed capacitive filter array that encloses one or a plurality of capacitive filter capacitor active electrodes each coupled to a filter array conductive path and at least one capacitor ground electrode. Each capacitive filter array conductive path is joined with a metal-ceramic conductive path to form a feedthrough conductive path. Bonding pads are attached to the internally disposed ends of each feedthrough conductive path, and corrosion resistant, conductive buttons are attached to and seal the externally disposed ends of each feedthrough conductive path. A plurality of conductive, substrate ground paths are formed extending through the co-fired metal-ceramic substrate between internally and externally facing layer surfaces thereof and electrically isolated from the substrate conductive paths. The capacitor ground electrodes are coupled electrically to the plurality of conductive, substrate ground paths and to the ferrule.

Claims

1. A method of manufacturing a filtered feedthrough assembly adapted to be fitted into an opening of a case of a hermetically sealed electronic device, the feedthrough assembly having an internally disposed portion configured to be disposed inside the case and an externally disposed portion configured to be disposed outside the case, the method comprising:

providing an electrically conductive ferrule having a ferrule wall adapted to be fitted into the case opening with an inner wall surface defining a centrally disposed ferrule opening and extending between opposed internally and externally facing ferrule sides;

forming a multi-layer, co-fired metal-ceramic substrate having opposed internally facing and externally facing substrate surfaces joined by a common substrate edge, the step of forming the metal-ceramic substrate further comprising;

forming a plurality of metal-ceramic substrate layers having internally and externally facing layer surfaces;

forming a plurality of substrate conductive paths extending through the co-fired metal-ceramic substrate between the internally and externally facing substrate surfaces and electrically isolated from one another; and

forming a further plurality of substrate ground paths extending through the co-fired metal-ceramic substrate between the internally and externally facing substrate surfaces and electrically isolated from the substrate conductive paths;

hermetically sealing the common substrate edge to the ferrule inner wall within the centrally disposed ferrule opening and electrically coupling the plurality of substrate ground paths to the ferrule;

forming a discoidal capacitive filter array formed of a ceramic capacitive filter substrate having an internally facing filter substrate side and an externally facing filter substrate side joined by a common filter substrate edge, the step of forming capacitive filter army substrate further comprising the steps of;

forming a plurality of filter array conductive paths electrically isolated from one another and extending between the internally facing filter substrate side and the externally facing filter substrate side;

forming a plurality of discoidal capacitor filters each comprising at least one capacitor active electrode formed within the filter substrate and extending outward from a filter array conductive path and a common capacitor ground electrode;

mechanically joining the externally facing filter substrate side to the internally facing substrate side electrically connecting each filter array conductive path to a substrate conductive path; and

electrically connecting the common capacitor ground electrode of the discoidal capacitor filters to the plurality of substrate ground paths;

whereby the filtered feedthrough assembly provides a plurality of miniaturized, electrically isolated, and capacitively filtered, feedthrough conductive paths with low inductance each comprising a substrate conductive path joined to a filter array conductive path and extending between the internally disposed portion and the externally disposed portion when the feedthrough assembly is affixed into an opening in the case of the electronic device.

2. The method of claim 1, wherein the case of the electronic device and the ferrule is formed of metallic materials amenable to being welded together, the electrically conductive ferrule is further formed with a welding flange extending outwardly of the ferrule wall away from the ferrule opening for a predetermined distance defining a flange width, and the welding flange formed with a stress relieving thickness for absorbing stress caused by thermal welding energy applied to the ferrule and flange in the process of welding the flange to the case.

3. The method of claim 2, wherein the co-fired metal-ceramic substrate ceramic material is formed of one of the group consisting of alumina, aluminum nitride, beryllium oxide, and silicon dioxide that has a coefficient of thermal expansion compatible with the coefficient of thermal expansion of the material of the ferrule.

4. The method of claim 3, wherein the ferrule is formed of a conductive material selected from the group consisting of niobium, titanium, titanium alloys such as titanium-6Al-4V or titanium-vanadium, platinum, molybdenum, zirconium, tantalum, vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium, palladium, silver, and alloys, mixtures and combinations thereof.

5. The method of claim 1, wherein the metal-ceramic substrate is formed by the further method of:

forming a plurality of planar ceramic layers shaped in a green state to have a layer thickness;

forming a plurality of substrate conductive path via holes and ground path via holes extending therethrough between an internally facing layer surface and an externally facing layer surface;

filling conductive path and ground path via holes with conductive material;

forming conductive path traces and ground traces on selected ones of the internally and externally facing layer surfaces;

assembling and laminating the plurality of ceramic layers together;

punching the outer dimensions of the assembled and laminated plurality of ceramic layers;

co-firing the assembled and laminated ceramic layers from the green state to form the substrate having the opposed internally facing and externally facing substrate sides joined by a common substrate edge; and

machining and polishing the common substrate edge to enable to enable electrical connection of the ground vias in common and to the ferrule in the step of hermetically sealing the common substrate edge to the ferrule inner wall within the centrally disposed ferrule opening.

6. The method of claim 5, wherein the further method of hermetically sealing the common substrate edge to the ferrule inner wall within the centrally disposed ferrule or opening and electrically coupling the plurality of substrate ground paths to the ferrule comprises forming a substrate-ferrule braze joint of a conductive braze material.

7. The method of claim 5, wherein the plurality of substrate conductive paths extending through the co-fired metal-ceramic substrate between the internally and externally facing layer surfaces are formed by the further steps comprising:

placing a substrate conductor braze pad on the substrate internally facing side over an exposed conductive trace or via of each conductive path;

placing a bonding button over each exposed braze pad; and

applying heat to melt the braze pads and to thereby mechanically and electrically join the bonding button with the substrate conductive path.

8. The method of claim 7, wherein the externally disposed bonding buttons are formed of a conductive material selected from the group consisting of niobium, platinum or a platinum-iridium alloy, titanium, titanium alloys such as titanium-6Al-4V or titanium-vanadium, molybdenum, zirconium, tantalum, vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium, palladium, silver, and alloys, mixtures and combinations thereof.

9. The method of claim 5, further comprising:

in the green state and prior to assembling and laminating the ceramic layers, forming a plurality of spaced apart button cavities extending through the externally facing ceramic layer of the metal-ceramic substrate located to be aligned with the plurality of substrate conductor paths through the remaining ceramic layers; and

wherein the plurality of substrate conductive paths extending through the co-fired metal-ceramic substrate between the internally and externally facing layer surfaces are formed by the further method comprising;

placing a substrate conductor braze pad within each button cavity of the substrate internally facing side and over an exposed conductive trace or via of each conductive path;

placing a bonding button in each button cavity over each braze pad; and

applying heat to melt the braze pads and to thereby mechanically and electrically join the bonding button with the substrate conductive path.

10. The method of claim 5, wherein a conductive paste material selected from the group consisting of copper, tungsten, molybdenum and gold is used in the steps of filling conductive path and ground path via holes and forming conductive path traces and ground traces and is applied by screen printing to said ceramic layers in the green state.

11. The method of claim 5, wherein:

the capacitive filter array is formed through the further method of extending a filter array hole between the internally facing filter substrate side and the externally facing filter substrate side and through at least one capacitor active electrode; and

the method of mechanically joining the externally facing filter substrate side to the internally facing metal-ceramic substrate side and electrically joining each filter array conductive path to a substrate conductive path comprises the steps of;

placing a substrate conductor braze pad on the externally facing metal-ceramic substrate side over an exposed conductive trace or via of each conductive path;

placing the internally facing filter substrate side against the externally facing metal-ceramic substrate side with the filter array holes aligned with the substrate conductor braze pads on the externally facing metal-ceramic substrate side

placing solder material in the filter array holes to form a sub-assembly; and

heating the sub-assembly to reflow solder fill the filter array holes and mechanically bond with the substrate conductor braze pads on the substrate internally facing side, whereby the reflow solder within each filter array hole forms at least part of a filter array conductive path.

12. The method of claim 11, further comprising the method of placing an internally disposed bonding pad against the solder placed in each of the plurality filter array holes whereby the plurality of internally disposed bonding pads adhere to the reflow solder filling the plurality of filter array holes on the internally facing side of the capacitive filter array.

13. The method of claim 12, wherein the internally disposed bonding pads are formed of a conductive material selected from the group consisting of copper, nickel, gold and aluminum and alloys, mixtures and combinations thereof.

14. The method of claim 11, wherein the capacitive filter array is formed through the further method of:

forming a plurality of capacitor active electrodes the filter substrate and extending outward from a filter array conductive path,

applying a hole metallization layer within the hole electrically coupling the capacitor active electrodes together;

forming a further plurality of capacitor ground electrodes formed within the filter substrate and extending inward from the filter substrate edge,

applying an edge metallization layer overlying the filter substrate edge electrically coupling the capacitor ground electrodes together,

whereby each filter array hole is formed to extend between the internally facing filter substrate side and the externally facing filter substrate side and through the plurality of capacitor active electrodes.

15. The method of claim 1, wherein the method of mechanically joining the externally facing filter substrate side to the internally facing substrate side and electrically joining each filter array conductive path to a substrate conductive path comprises reflow soldering the filter array conductive path with the substrate conductive path.

16. The method of claim 1, further comprising a further method of:

providing a plurality of internally disposed bonding pads supported along the internally facing filter substrate side, each internally disposed bonding pad electrically conducted with a filter array conductive path of the capacitive filter array; and

providing a plurality of externally disposed bonding buttons supported along the externally facing metal-ceramic substrate side, each externally disposed bonding button electrically conducted with a substrate conductive path.

17. The method of claim 16, wherein the internally disposed bonding pads are formed of a conductive material selected from the group consisting of copper, nickel, gold and aluminum and alloys, mixtures and combinations thereof.

18. The method of claim 16, wherein the externally disposed bonding buttons are formed of a conductive material selected from the group consisting of niobium, platinum or a platinum-iridium alloy, titanium, titanium alloys such as titanium-6Al-4V or titanium-vanadium, molybdenum, zirconium, tantalum, vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium, palladium, silver, and alloys, mixtures and combinations thereof.