Medical electronic devices which contain feedthrough components of this type have long been used on a mass scale, in particular as cardiac pacemakers, implantable cardioverters (especially defibrillators) or cochlear implants. The device could also be less complex, however, and for example could be constituted by an electrode lead or sensor lead.
Most implantable medical electronic devices of practical significance are intended to deliver electrical pulses to excitable body tissue via suitably placed electrodes. Many devices can also selectively measure signals of the nerve tissue in the patient's body and can record or evaluate said signals over a relatively long period of time in order to select individually tailored therapy and in order to monitor the success of the treatment in vivo. In order to perform this function, electronic/electrical function units for generating and regulating the pulses and for measuring stimuli are housed in the housing of the device. Electrodes or connections are provided externally on the device for at least one electrode lead, in the distal end portion of which the electrodes are attached to the tissue for pulse transmission.
For this purpose, an electrical connection must be established between the electrical and/or electronic components arranged in the housing interior and the respective electrode leads. This electrical connection is generally provided by means of a feedthrough and/or what is known as a header.
Here, a feedthrough of this type ensures at least one electrical connection between the interior of the housing and the exterior, and at the same time hermetically seals off the housing of the implant. The header fastened via the feedthrough guides the electrical connection of the feedthrough further to a contact point and serves for plugging the at least one electrode lead into a corresponding, usually standardized, socket. An electrical contact is thus produced between the implant and the connection piece of the electrode lead at the contact points of the socket. A feedthrough and a header can also be provided in a single component. In this case as well, a combined component of this type will be referred to hereinafter generally as a feedthrough.
The flange, which is required in order to hermetically seal the housing or implant with the feedthrough, usually consists of a metal (for example, titanium) or an alloy (for example, Ti-6Al-4V). It is advantageous to produce flange material and housing or implant material from materials of the same type so as to be able to join these to one another more easily in subsequent processes. The insulation body of the feedthrough consists substantially of a poorly conductive material (for example, insulation ceramic).
The contact elements penetrate through the insulation body and are electrically insulated from one another and with respect to the flange by means of the insulation body. The elements usually consist of highly conductive metals (for example, tantalum, niobium, titanium, platinum) or alloys (for example, PtIr, FeNi, 316L). Wire portions, or what are known as pins, are frequently used for the production of contact elements.
A great challenge is that of coordinating the different physical properties of the components and materials, in particular the coefficients of thermal expansion, with one another so that a sufficient seal can be ensured for the feedthrough over the intended service life.
When producing ceramic feedthroughs, the component parts (for example, insulation ceramics, flange, pins) are joined by means of a brazing process. In order to ensure the quality of the brazed connections in the case of feedthroughs of the aforementioned type, the respective insulation bodies are provided in part with a metal coating, which is intended to guarantee the brazing capability of the insulation body. The coating is an elemental metal (for example, tungsten, niobium, titanium) or an alloy. The coating is usually deposited on the insulation ceramic by means of a Physical Vapor Deposition (PVD) process and has a typical layer thickness of 1-20 μm.
It goes without saying that this metal coating can be provided merely in regions and must have a predefined structure, because the insulation ceramic of the feedthrough electrically separates two potentials from one another in a confined space (on the one hand the ground potential at the flange or housing, and on the other hand the signal potential at the pin). The separation of the potentials can be achieved by removing the coating again in part, or by applying no coating in part.
During the coating process, a sufficiently thick layer that is as homogeneous as possible must be ensured. However, in the case of the finished feedthrough component, the anticipated potentials must be prevented from being short-circuited, or the insulation resistance must be prevented from decreasing inadmissibly.
If a coating applied to the insulation ceramic is divided into areas by means of mechanical removal (for example, grinding, lapping), appropriate contours and dimensions must be provided already by the manufacturer of the insulation ceramic. During the decoating, the insulation ceramic is exposed to mechanical pressure and/or tensile loading, which stresses the product.
Alternatively, the coating can be structured by means of masks already during the application process. The masking process places high demands on the dimensional accuracy of the insulation ceramic and processing capability of the coating process. In order to obtain constant process results, the maskings and the insulation ceramics must match one another exactly in terms of dimension and tolerance, even with different batch sizes and over a number of processes. As a result of the coating, the masks lose their dimensional accuracy and must be reworked or replaced.
The masks must rest very closely around the insulation ceramics, since otherwise coating is also applied behind the mask. If the masks rest on the insulation ceramics in an irregular manner, this leads to an irregular coating edge and thus inevitably also to deviations in the electrical properties (for example, capacitance, inductance) of the insulation ceramics and, thus, also to batch deviations of the feedthrough and the medical device. The masks used during the process themselves cast shadows and thus reduce the deposition rate on the insulation ceramics to be coated. Furthermore, irregular transitions between the coating and masked region lead to visual anomalies on the product or lead to problems in subsequent processes, and therefore are undesirable.
The mechanical fitting and removal of the masks is subject to very high demands on the repeatability of handling systems (robots, linear axes, camera systems). In the event of improper handling, the insulation ceramic or coating thereof can be destroyed (for example, scratched, abraded).
Very small structures over a number of layers can be produced only by means of a multi-stage process or by means of photolithography. For photolithography, the insulation ceramic is coated partially or wholly with a photoresist. This is exposed, and developed as appropriate. The remaining photoresist layer is removed and serves as a masking, which can be stripped again from the component after the coating process.
The present invention is directed toward overcoming one or more of the above-identified problems.