Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
2000-04-24
2003-07-01
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C174S050560, C607S036000
Reexamination Certificate
active
06586675
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to feedthrough devices having grounded leads. In particular, the invention relates m to feedthrough devices with grounded leads that are suitable for use in medical implant devices or implantable pulse generators, such as pacemakers.
BACKGROUND OF THE INVENTION
It is desirable that feedthrough devices for such uses be of reduced size while maintaining a hermetic seal. There are numerous applications where it is desirable to carry electrical signals through a metal casing and to ground the electronic devices inside to the metal casing using ceramic-to-metal or glass-to-metal seals. For certain electrical devices, especially those for use in a living body, it is necessary to pass a wire into the housing of the device while maintaining a hermetic seal. For example, pacemakers designed for implantation in a living body require an opening in the housing of the device in order to pass conductive wires to the internal electric components. Because there is an absolute need to prevent body fluids from entering the interior of the device, the pass-through opening in the housing must be sealed in a gas-tight and liquid-tight manner.
In many instances, the size of the feed-through must be minimized due to constraints on the size of the completed device. This is particularly applicable, but not limited to the situations encountered in implantable devices such as cardiac pacemakers, cardiac defibrillators, cochlear implants, implantable hearing devices, and the like. Feed-through devices and the leads attached thereto must be robust enough to withstand manufacturing processes and the usage of the devices, and at the same time be made economically. The size of the feedthrough device limits how small an implantable device can be, because the width of a pacemaker or defibrillator case must be, at minimum, slightly larger than the width of the feedthrough.
Conventional feedthrough devices typically include a metallic ferrule, an insulating material, and at least one wire lead. If the feedthrough is used in a medical implant, the materials used should be biocompatible and resistant to corrosion, because the feedthrough becomes part of a case that protects the electronics inside the body.
More particularly, feedthrough devices have been employed in implantable devices, as disclosed and described in U.S. Pat. Nos. 5,905,627; 5,896,267; 5,825,608; 5,650,759; 4,940,858; and 5,866,851 as examples, which are hereby incorporated herein by reference. Typically, feedthrough devices include a metallic ferrule, which may have one or more flanges formed therein to facilitate mounting the device to the implantable medical device. The ferrule also has one or more openings through which a lead wire (or wires) may extend. Each lead wire is encapsulated and hermetically sealed within an insulating material that fills the remainder of the opening in the ferrule. The insulating material is bonded to both the lead wire and ferrule by glass sealing or brazing. The coupling of the above components must be done in such a way as to maintain a hermetic seal between each lead wire and the insulating material, and between the insulating material and the ferrule.
Some of the current practices employed for grounding electronic devices to a case in these feedthrough assemblies involve steps that use unnecessary space, are inefficient, and may cause yield problems. For example, one current practice includes attaching a lead directly to the case of the device, either by brazing or welding. However, in many instances, it is desirable for a lead to be grounded to the feedthrough upon delivery to an upper level assembly manufacturer. By having the ground wire in place prior to being delivered to an upper level assembly manufacturer, the upper level manufacturer is able to test the feedthrough device and any potentially attached electronics, rather than jeopardize the entire upper level assembly or case to which the device would be attached.
Current practice also involves welding a ground wire directly to a ferrule, away from the insulating material. Welding, however, is more labor intensive and expensive than brazing. A brazed joint is typically sturdier than a welded joint as well. Additionally, either brazing or welding the ground wire directly to the ferrule takes up a significant amount of space on the ferrule, because such a procedure requires an additional braze or weld joint. It also makes orienting the lead more difficult, because there is nothing supporting the sides of the ground wire. This additional braze joint must also be spatially separated from the original braze joints (those associated with the insulating material to metallic ferrule joints securing the wire lead) because the ground wire/ferrule braze joint can exert stress on the original braze joints, thus weakening both joints.
Additionally, brazing a ground wire into a separate opening on the ferrule also requires a separate braze load to be placed at the ground wire/ferrule interface. See, for to example, U.S. Pat. No. 5,905,627 issued to Brendel et al. Passing a ground wire through the ferrule in this manner, thus requiring an additional braze joint to be made, may adversely affect yields. As stated, a high integrity hermetic seal for medical implant devices is critical in order to prevent body fluids from penetrating the implanted device. Additionally, if the ground wire is to be placed in a thin area of the ferrule due to space constraints, assembly is more difficult because of the fixtures that would be required to hold the lead in position.
Furthermore, welding a ground wire to the ferrule after assembly of the feedthrough is also labor intensive and not as reliable. Welding a ground wire to the ferrule followed by brazing is more reliable but still labor intensive. This again requires a significant amount of space on the ferrule due to the additional braze joint that is necessary. In addition, this arrangement will not allow the ground wire to pass through the ferrule, which may be necessary for some implant devices.
In the special case in which a grounded lead must pass through the insulating material, present technology includes welding the ground wire to the ferrule or medical device case after assembly. For example, in the instance where a ground wire must pass through insulating material to ease attachment of a capacitor, it may be preferable to test the feedthrough/capacitor prior to welding the feedthrough assembly into the case that protects the electronics inside the body, as described above. This testing is impractical when the ground wire is welded to the case. If the ground wire is welded separately to the ferrule, the device requires more space.
There is also an industry practice of grounding a lead that is brazed to a ceramic. This involves laying a metallization layer or conductive member between the ferrule and the ground wire, across the surface of the ceramic, prior to brazing. The use of this procedure can cause yield problems due to braze flow between the ferrule and the ground wire, as capillary action may cause braze material to wick between the distinct braze joints, causing one or the other joint to have too much or too little braze.
Accordingly, there is a need in the art for a feedthrough device having a ground wire electrically coupled to the ferrule and located at an interface or opening of the ferrule and the insulating material. This has the advantages of minimizing the total space required for the device, providing efficient assembly, and minimizing the number of separate braze joints, thus improving the yield of the device while providing a reliable hermetic seal.
SUMMARY OF THE INVENTION
The present invention relates to a feedthrough device comprising a metallic ferrule, an insulating material, and a ground wire that is coupled to both the metallic ferrule and to the insulating material. The ground wire is preferably brazed to the metallic ferrule and to the insulating material, creating a single braze joint. The invention also relates to methods of coupling the ground
Bealka David Joseph
Da Costa Pedro Henrique
Harris Anton
Kilpatrick & Stockton LLP
Mallatt Kristin D.
Morgan Advanced Ceramics, Inc.
Reichard Dean A.
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