IMPLANTABLE CERAMIC DEVICE ENCLOSURE

Abstract: An implantable medical device (200) has a novel ceramic enclosure (202) with joinable multi-layered clamshells (204, 206). In the preferred embodiment one half (206) of the enclosure (202) carries the hybrid circuitry and feedthroughs of, for example, a pacemaker, while, the other half (204) carries a battery. The advantages over the prior art include higher transparency to radio frequency waves (for telemetry purposes), and reduced costs and constructions time. In a preferred embodiment, the device (200) with a ceramic enclosure (202) has a novel multi-layered ceramic feedthrough substrate in place of a prior art glass-to-metal feedthrough substrate, leading to lower costs and a higher feedthrough density.

Description: IMPLANTABLE CERAMIC DEVICE ENCLOSURE FIELD OF THE INVENTION The present invention relates to the packaging of implantable medical devices such as artificial cardiac pacemakers and the like. BACKGROUND OF THE INVENTION Generally speaking, a cardiac pacemaker or implantable pulse generator (IPG) is an electrical device used to supplant some or all of an abnormal heart's natural pacing function, by delivering appropriately timed electrical stimulation signals designed to cause the myocardium of the heart to contract or "beat". Using telemetry, modern pacemakers are often programmable with regard to data and functionality prior to, and even after implant. Typical pacemakers are enclosed by metal casings such as titanium, which has good body compatibility. However, metal enclosures often cause interference during telemetry. To create pacemakers and other implantable medical devices with enclosures which are transparent to radio frequency (RF) waves during telemetry, the enclosure can be constructed of ceramic material, for example. Such is the approach of U.S. Patent No. 4,785,827 issued to Fischer, and U.S. Patent No. 4,991,582 issued to Byers et al. Implantable medical devices of the above-mentioned type have a hybrid circuit with feedthroughs attached thereto and leading through a glass-to-metal feedthrough substrate to the connector block for electrical coupling to a lead (for stimulating, sensing, or both functions) . As a result of the construction of prior art substrates, fewer feedthroughs can be handled than is desirable, and costs of producing such substrates is expensive. SUMMARY OF THE INVENTION In view of the foregoing, it is a first object of the present invention to provide an implantable medical device which is nearly transparent to radio frequency waves for telemetering purposes, especially in the 400 kilohertz to 40 megahertz frequency range. It is a second object of the present invention to provide an implantable medical device wherein its feedthrough substrate provides for a higher density of feedthroughs. It is a third object of the present invention to provide an implantable medical device wherein its feedthrough substrate is less expensive than prior art feedthrough substrates. It is a fourth object of the present invention to provide an implantable medical device satisfying the above objects wherein its enclosure is ceramic. It is a fifth object of the present invention to provide an implantable medical device wherein the enclosure walls are electrically conducting. In order to satisfy the above objects and others, the present invention provides a packaging arrangement for the outer packaging of an implantable medical device at least including: a ceramic enclosure having an opening for receiving circuitry of the implantable medical device; and a multi-layered feedthrough substrate for coupling to the ceramic enclosure at edges around the opening, the substrate having multiple feedthroughs for electrically coupling the circuitry inside the enclosure to the outside of the enclosure. The present invention also provides a packaging arrangement for the outer packaging of an implantable medical device at least including: a first multi-layered enclosure shell; and a second multi-layered enclosure shell; wherein the enclosure shells are joinable to sealably enclose components of the implantable medical device, and layers of the enclosure shells are adapted to conduct signals between implantable medical device components mounted on the shells. The details of the present invention will be revealed in the following description, with reference to the drawing. BRIEF DESCRIPTION OF THE DRAWINGS The various figures of the drawing are briefly described as follows: Figure 1 is an exploded isometric view of a prior art pacemaker with a ceramic enclosure; Figure 2 is an exploded isometric view of a pacemaker employing the present-inventive features; and Figure 3 is an exploded isometric view of the pacemaker in Figure 2, additionally showing a connector block and a pacemaker lead. Figure 4 is a isometric view of a pacemaker employing the present-inventive ceramic enclosure; Figure 5 is an isometric view of the battery-carrying half of the ceramic enclosure of the present invention. Figure 6 is an isometric view of the hybrid circuit and feedthrough-carrying half of the ceramic enclosure of the present invention; and Figure 7 is an exploded isometric view of the pacemaker in Figure 4, without a connector block. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a prior art packaging arrangement/scheme 100 for a pacemaker. The arrangement 100 has a ceramic enclosure 102 with a metalized portion 103. A hybrid circuit 104 is attached to a feedthrough substrate 106 which is a glass-to-metal feedthrough assembly. Feedthroughs 108 (metal) electrically connect to components of the hybrid circuit 104 at one end, and are adapted to electrically connect a connector block (not shown) at the other (exposed) end. A weld ring 110 is welded on one side to the enclosure 102 (at the metalized portion 103) , and on its other side to the glass-to-metal feedthrough 106. The entire packaging provides an implantable medical device which is hermetically sealed. The present-inventive implantable medical device packaging arrangement/scheme 200 is illustrated in Figure 2. The ceramic enclosure 202 is composed of biocompatible 99.5 percent aluminum oxide in the preferred embodiment, which has been shown to have good tissue compatibility. A metalized portion 203 is formed by sputtering (as is known in the art) a thin film of niobium on the ceramic surface. A hybrid circuit 204 is connected to a novel multi-layered feedthrough substrate 206. The substrate 204 is composed of several layers of ceramic material with metal-plated input/output vias used to electrically connect the various layers. The plating metals may be gold and nickel, for example. As a result of the multi-layer and via configuration, a higher density of feedthroughs 208 are possible over the glass-to-metal feedthrough substrate (element 106 in Figure 1) approaches in the prior art. The substrate 206 can be constructed using techniques known in the art, such as is disclosed by Beth A. Hassler in "Fast Turnaround Multilayer Cofired Ceramic Motherboard Fabrication, " Proceedings of ASM' s 2nd Electronic Packaging: Materials and Processes Conference (October 1985) : 117-121. The above-mentioned article is hereby incorporated by reference- Two weld rings 210 and 212 are chosen to have thermal expansion characteristics sufficiently similar to the ceramic material used to maintain good bonding over a broad temperature range. Weld ring 210 is brazed to the metalized portion 203 of the ceramic enclosure 202, and welded to the weld ring 212. Weld ring 212 is also brazed to the multi-layered feedthrough 206. The welded and brazed surfaces complete a hermetic seal of the pacemaker. Figure 3 shows the pacemaker in Figure 2 with additional components. Namely, the pacemaker also has a connector block 314 which is fastened to the multi-layered feedthrough substrate 206. The connector block 314 electrically connects one or more pacemaker leads 316 to the feedthroughs 208 via lead clamps 318. The lead 316 is firmly held in place (in the lead clamps 318) by tightening set screws 320. Thus, electrical connection is made from the lead 316 to the connector block 314 to the feedthroughs 208 to the hybrid circuitry 204. Figure 4 shows an implantable medical device 200 employing the ceramic enclosure 202 of the present invention. In this case a pacemaker has two ceramic enclosure halves (or shells) 204 and 206 which are joined by weld rings 210 and 212 to form a hermetic seal. Each half 204 and 206 has a thin metalized layer for brazing the weld rings 210 and 212 thereto, respectively. A connector block 208 is attached to the enclosure 202. In the preferred embodiment, the enclosure half 204 carries a battery (not shown) mounted to its inside wall, while the enclosure half 206 carries both a hybrid electronic circuit and feedthroughs (see Figure 4) for connecting to the connector block 208. The feedthroughs provide an electrical connection between the hybrid circuitry and stimulation and sensing leads when attached to the connector block 208. The enclosure half 204 is shown in greater detail in Figure 5. The walls of the ceramic enclosure halves 204 and 206 are constructed of multiple ceramic layers (302 in Figure 3) , variously containing electrical conduction areas, vias for inter-layer communication, and electromagnetic interference (EMI) shielding areas. The layers may be constructed of biocompatible 99.5 percent aluminum oxide, for example, which has been shown to have good tissue compatibility. The ceramic enclosure shells 204 and 206 can be constructed using techniques known in the art, such as is disclosed in the previously mentioned article by Beth A. Hassler, in "Fast Turnaround Multilayer Cofired Ceramic Motherboard Fabrication. Thin ceramic layers are joined, and then form-molded at the corners (e.g., 306) . A metalized portion 304 is formed by sputtering (as is known in the art) a thin film of niobium on the ceramic surface. This provides good braze-bonding characteristics for attaching the ceramic wall to the weld ring 210. The weld ring 212 is attached to the enclosure half 206 in the same manner. The enclosure half 206 is detailed in Figure 6. The multi-layer nature of the wall 402 of the ceramic enclosure half 206 allows the hybrid circuitry 406 of the pacemaker to be mounted directly on the ceramic enclosure, thereby saving time, money and parts compared with prior art ceramic enclosures (which do not electrically connect the enclosed components) . In addition to the hybrid circuitry, the enclosure half 206 also has a feedthrough area 408. The several layers of the ceramic material have metal-plated input/output vias used to electrically connect the various layers. The plating metals may be gold and nickel, for example. As a result of the multi-layer and via configuration, a higher density of feedthroughs 410 are possible over the glass-to-metal substrate (element 106 Figure 1) approaches in the prior art. The feedthroughs 410 electrically connect the circuitry carried by the enclosure to the connector block 208. The weld ring 210 is chosen to have thermal expansion characteristics sufficiently similar to the ceramic material used to maintain good bonding over a broad temperature range. Figure 7 shows an exploded isometric view of the ceramic enclosure 202 for illustrative purposes. Variations and modifications to the present invention are possible given the above disclosure. However, such variations and modifications are intended to be within the scope of the invention claimed by this letters patent. For example, the packaging arrangement described supra, is optimal for bipolar pacing. The ceramic enclosure 202 may be coated with a thin metal layer (using sputtering techniques, for example) to enable unipolar pacing. Also bonding of the enclosure shells of the present invention need not be limited to the use of brazing and welding techniques.

Claims: CLAIMS We claim: 1. A packaging arrangement for the outer packaging of an implantable medical device comprising: a ceramic enclosure having an opening for receiving circuitry of said implantable medical device; and a multi-layered feedthrough substrate for coupling to said ceramic enclosure at edges around said opening, said substrate having multiple feedthroughs for electrically coupling said circuitry inside said enclosure to the outside of said enclosure. 2. The packaging arrangement in claims 1-14 further comprising a connector block for coupling to said substrate, and for coupling to at least one electrical lead, said connector block electrically connecting said lead to said feedthroughs. 3. The packaging arrangement in claim 2 further comprising: a first weld ring for coupling to said ceramic enclosure; a second weld ring for coupling to said first weld ring, and to said multi-layered feedthrough substrate. 4. The packaging arrangement in claims 1, 2 or 3 wherein said ceramic enclosure further comprises a metallic outer layer. 5. A packaging arrangement for the outer packaging of an implantable medical device comprising: at least a first multi-layered enclosure shell; and at least a second multi-layered enclosure shell; wherein said enclosure shells are joinable to sealably enclose components of said implantable medical device, and layers of said enclosure shells are adapted to conduct signals between implantable medical device components mounted directly on at least one of said shells. 6. The packaging arrangement of claim 1 wherein the layers of said enclosure shells are ceramic. 7. The packaging arrangement of claim 1 or 5 wherein at least one of said enclosure shells comprises a multi-layered feedthrough having multiple feedthroughs for electrically coupling circuitry mounted on said shell to the outside of said shell. 8. The packaging arrangement of claim 6 wherein at least one of said enclosure shells comprises a multi-layered feedthrough having multiple feedthroughs therein for electrically coupling circuitry mounted on said shell to the outside of said shell. 9. The packaging arrangement of claim 1 or 6 wherein said first enclosure shell is adapted to carry a hybrid circuit of a pacemaker, and said second enclosure shell is adapted to carry a battery circuit of said pacemaker. 10. The packaging arrangement of claim 7 wherein said first enclosure shell is adapted to carry a hybrid circuit of a pacemaker, and said second enclosure shell is adapted to- carry a battery circuit of said pacemaker. 11. The packaging arrangement of claims 5-8 wherein said first enclosure shell is adapted to carry a hybrid circuit of a pacemaker, and said second enclosure shell is adapted to carry a battery circuit of said pacemaker. 12 The packaging arrangement of claims 5-8 further comprising a connector block for coupling to said enclosure shells. 13. The packaging arrangement of claims 5-12 wherein said enclosure shells further comprise an outer metallic layer. 14. A package for hermetically enclosing an implantable medical device comprising multilayer materials and having a set of electrical feedthroughs integrally formed in a ceramic layer of said multi-layer to electrically couple outer electrical connectors to electrical circuits mounted directly to and inside said package.

Inventors: DONDERS ADRIANUS P, HASSLER BETH ANNE, DONDERS, ADRIANUS, P., HASSLER, BETH, ANNE
Applicants: MEDTRONIC INC, MEDTRONIC, INC.
Application year: 1995
Main classification: A61N1
IPC codes: A61N1