Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-04-18
2003-12-09
Mayes, Curtis (Department: 2831)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S089150, C156S089160, C156S089180, C156S089190, C156S089210, C361S302000, C607S005000
Reexamination Certificate
active
06660116
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electrical feedthroughs of improved design and to their method of fabrication, particularly for use with implantable medical devices.
BACKGROUND OF THE INVENTION
Electrical feedthroughs serve the purpose of providing an electrical circuit path extending from the interior of a hermetically sealed case or housing to an external point outside the case. Implantable medical devices (IMDs) such as implantable pulse generators (IPGs) for cardiac pacemakers, implantable cardioverter/defibrillators (ICDs), nerve, brain, organ and muscle stimulators and implantable monitors, or the like, employ such electrical feedthroughs through their case to make electrical connections with leads, electrodes and sensors located outside the case.
Such feedthroughs typically include a ferrule adapted to fit within an opening in the case, one or more conductor and a non-conductive hermetic glass or ceramic seal which supports and electrically isolates each such conductor from the other conductors passing through it and from the ferrule. The IMD case is typically formed of a biocompatible metal, e.g., titanium, although non-conductive ceramics materials have been proposed for forming the case. The ferrule is typically of a metal that can be welded or otherwise adhered to the case in a hermetically sealed manner.
Typically, single pin feedthroughs supported by glass, sapphire and ceramic were used with the first hermetically sealed IMD cases for IPGs. As time has passed, the IPG case size has dramatically reduced and the number of external leads, electrodes and sensors that are to be coupled with the circuitry of the IPG has increased. Consequently, use of the relatively large single pin feedthroughs is no longer feasible, and numerous multiple conductor feedthroughs have been used or proposed for use that fit within the smaller sized case opening and provide two, three, four or more conductors.
Many different insulator structures and conductor structures are known in the art of multiple conductor feedthroughs wherein the insulator structure also provides a hermetic seal to prevent entry of body fluids through the feedthrough and into the housing of the medical device. The conductors typically comprise electrical wires or pins that extend through a glass and/or ceramic layer within a metal ferrule opening as shown, for example, in commonly assigned U.S. Pat. Nos. 4,991,582, 5,782,891, and 5,866,851 or through a ceramic case as shown in the commonly assigned '891 patent and in U.S. Pat. No. 5,470,345. It has also been proposed to use co-fired ceramic layer substrates that are provided with conductive paths formed of traces and vias as disclosed, for example, in U.S. Pat. Nos. 4,420,652, 5,434,358, 5,782,891, 5,620,476, 5,683,435, 5,750,926, and 5,973,906.
Such multi-conductor feedthroughs have an internally disposed portion configured to be disposed inside the case for connection with electrical circuitry and an externally disposed portion configured to be disposed outside the case that is typically coupled electrically with connector elements for making connection with the leads, electrodes or sensors. The elongated lead conductors extending from the connector elements effectively act as antennae that tend to collect stray electromagnetic interference (EMI) signals that may interfere with normal IMD operations. At certain frequencies, for example, EMI can be mistaken for telemetry signals and cause an IPG to change operating mode.
This problem has been addressed in certain of the above-referenced patents by incorporating a capacitor structure upon the internally facing portion of the feedthrough ferrule coupled between each feedthrough conductor and a common ground, the ferrule, to filter out any high frequency EMI transmitted from the external lead conductor through the feedthrough conductor. The feedthrough capacitors originally were discrete capacitors but presently can take the form of chip capacitors that are mounted as shown in the above-referenced '891, '435, '476, and '906 patents and in further U.S. Pat. Nos. 5,650,759, 5,896,267 and 5,959,829, for example. Or the feedthrough capacitors can take the form of discrete discoidal capacitive filters or discoidal capacitive filter arrays as shown in commonly assigned U.S. Pat. Nos. 5,735,884, 5,759,197, 5,836,992, 5,867,361, and 5,870,272 and further U.S. Pat. Nos. 5,287,076, 5,333,095, 5,905,627 and 5,999,398.
These patents disclose use of discoidal filters and filter arrays in association with conductive pins which are of relatively large scale and difficult to miniaturize without complicating manufacture. It is desirable to further miniaturize and simplify the fabrication of the multi-conductor feedthrough assembly
Although feedthrough filter capacitor assemblies of the type described above have performed in a generally satisfactory manner, the manufacture and installation of such filter capacitor assemblies has been relatively time consuming and therefore costly. For example, installation of the discoidal capacitor into the small annular space between the terminal pin and ferrule as shown in a number of these patents can be a difficult and complex multi-step procedure to ensure formation of reliable, high quality electrical connections.
Other problems have arisen when chip capacitors have been coupled to conductive trace and via pathways of co-fired multi-layer metal-ceramic substrates disclosed in the referenced '652, '358, '891, '476, '435, '926, and '906 patents. The conductive paths of the feedthrough arrays and attached capacitors suffer from high inductance which has the effect of failing to attenuate EMI and other unwanted signals, characterized as “poor insertion loss”.
A high integrity hermetic seal for medical implant applications is very critical to prevent the ingress of body fluids into the IMD. Even a small leak rate of such body fluid penetration can, over a period of many years, build up and damage sensitive internal electronic components. This can cause catastrophic failure of the implanted device. The hermetic seal for medical implant (as well as space and military) applications is typically constructed of highly stable alumina ceramic or glass materials with very low bulk permeability. The above-described feedthroughs formed using metal-ceramic co-fired substrates, however, have not been hermetic because the metal component of the substrate corrodes in body fluids, and the substrates have cracked from stresses that developed from brazing and welding processes.
Withstanding the high temperature and thermal stresses associated with the welding of a hermetically sealed terminal with a premounted ceramic feedthrough capacitor is very difficult to achieve with the '551, '095 and other prior art designs. The electrical/mechanical connection to the outside perimeter or outside diameter of the feedthrough capacitor has a very high thermal conductivity as compared to air. The welding operation typically employed in the medical implant industry to install the filtered hermetic terminal into the IMD case opening can involve a welding operation in very close proximity to this electrical/mechanical connection area. Accordingly, in the prior art, the ceramic feedthrough capacitors are subjected to a dramatic temperature rise. This temperature rise produces mechanical stress in the capacitor due to the mismatch in thermal coefficients of expansion of the surrounding materials.
In addition, in the prior art, the capacitor lead connections must be of very high temperature materials to withstand the high peak temperatures reached during the welding operation (as much as 500 C. °). A similar, but less severe, situation is applicable in military, space and commercial applications where similar prior art devices are soldered instead of welded by the user into a bulkhead or substrate. Many of these prior art devices employ a soldered connection to the outside perimeter or outside diameter of the feedthrough capacitor. Excessive and u
Fraley Mary A.
Haq Samuel F.
Malone Patrick F.
Seifried Lynn M.
Strom James
Chapik Daniel G.
Mayes Curtis
Medtronic Inc.
Wolde-Mihhael Girma
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