Oxide-Resistant Feedthrough Capacitor for AIMD Grounding
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Solution Overview
Problem
Existing feedthrough capacitors in active implantable medical devices face challenges with high-frequency performance due to titanium oxide formation, which increases equivalent series resistance and degrades capacitor performance, and the use of gold braze for attachment is expensive and inefficient.
Innovation Solution
A hermetically sealed filtered feedthrough assembly with an oxide-resistant metal addition, comprising a conductive core and cladding, provides a reliable low-impedance ground path by using a conductive core and cladding materials like stainless steel and gold, palladium, or platinum, with a braze or solder connection to the ferrule, avoiding direct contact with titanium to prevent oxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the capacitor ground plates are directly connected to the titanium ferrule, then the grounding is simple and direct, but titanium oxide formation increases the equivalent series resistance and degrades high-frequency performance
Solution Approach 1:
An oxide-resistant metal addition (such as gold, palladium, or platinum) is introduced as an intermediary between the capacitor ground plates and the titanium ferrule. This intermediate layer prevents direct contact between the capacitor and titanium, thereby preventing oxide formation that would increase equivalent series resistance. The metal addition serves as a mediator that maintains low impedance grounding while protecting against oxidation, thus preserving high-frequency performance without significantly increasing structural complexity.
2Reliability
If gold braze material is used to form the hermetic seal, then the hermetic sealing is reliable and oxide-resistant, but the manufacturing cost increases significantly
Solution Approach 1:
The oxide-resistant metal addition is applied locally only at the specific grounding interface where the capacitor connects to the ferrule, rather than using gold braze material throughout the entire hermetic seal structure. This localized application provides oxide resistance and reliable electrical connection precisely where needed (at the grounding point) while minimizing the consumption of expensive precious metals in other areas of the device.
3Quantity of substance
If titanium ferrule is used for the hermetic seal, then the material is cost-effective and provides good hermetic sealing, but titanium oxide formation creates high impedance ground paths
Solution Approach 1:
The oxide-resistant metal addition serves as a protective intermediary layer between the titanium ferrule and the capacitor ground plates. This intermediate layer prevents direct oxidation of the titanium surface at the grounding interface, eliminating the high impedance path caused by titanium oxide formation. The titanium ferrule maintains its cost-effective and hermetic sealing properties, while the metal addition protects against the harmful oxidation effect at the critical electrical connection point.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces the equivalent series resistance and maintains high-frequency performance while minimizing the use of expensive materials, ensuring reliable and efficient electromagnetic interference filtering in medical devices.
Implementation Method 1
titanium tends to form oxides which act as either insulators or semi-conductors. Accordingly, grounding the feedthrough capacitor electrode plates directly to the titanium ferrule is contra-indicated
Implementation Method 2
an insulator of an electrically non-conductive material, the insulator comprising an insulator outer surface extending from an insulator first end to an insulator second end
Implementation Method 3
mount one or more feedthrough or MLCC-type capacitors right at the point of leadwire entrance so that the capacitor can be coupled to high frequency EMI signals from the lead conductors directly to the AIMD housing, which acts as an energy dissipating surface
Data Source
AI summary
A hermetically sealed filtered feedthrough assembly for an active implantable medical device includes an electrically conductive ferrule hermetically sealed by a first braze to an insulator. A conductor is hermetically sealed to and disposed through the insulator. A filter capacitor has an active electrode plate and a ground electrode plate which are disposed within and supported by a capacitor dielectric in an interleaved, partially overlapping relationship. A first passageway is disposed through the capacitor dielectric having a capacitor internal metallization which is connected to the active electrode plate. A capacitor external metallization electrically connects to the ground electrode plate. An oxide-resistant metal addition includes a conductive core with a conductive cladding of a different material. A first electrical connection is between the oxide-resistant metal addition and the capacitor external metallization. A second electrical connection is between the oxide-resistant metal addition and the ferrule.