Hermetic Feedthrough Capacitor Assembly for EMI-Resistant Implants
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Solution Overview
Problem
Hermetic terminals in active implantable medical devices (AIMDs) face challenges such as biocompatibility, resistance to degradation under bias current or voltage, and susceptibility to electromagnetic interference (EMI) and MRI-induced heating, which can lead to device malfunction and tissue damage. Additionally, ceramic-based feedthroughs can fail due to brittle material properties and thermal expansion mismatches, compromising hermeticity and reliability.
Innovation Solution
A hermetically sealed feedthrough is created using a monolithic alumina insulator substrate with a platinum conductive pathway, where the platinum is co-fired with the alumina to form a mutually conformal interface, minimizing tensile stresses and achieving a high-purity, biocompatible seal. This design eliminates the need for expensive noble metal leadwires and enhances EMI filtering by integrating a feedthrough capacitor with a tortuous interface resistant to erosion by body fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic-based feedthroughs are used for hermetic sealing, then hermeticity is achieved, but brittle material properties and thermal expansion mismatches cause failure
Solution Approach 1:
The patent uses a composite structure combining alumina ceramic substrate with metal interconnects and encapsulant materials. The ceramic provides hermetic sealing while metal interconnects provide ductility and stress relief, creating a composite system that leverages the strengths of each material while compensating for their weaknesses.
Solution Approach 2:
The patent modifies the ceramic feedthrough design by changing the thermal expansion parameters through material selection and geometry optimization. The alumina ceramic is paired with materials having matched thermal expansion coefficients, and the structure incorporates compliance features that accommodate thermal stress through parameter optimization rather than rigid matching.
2Object-affected harmful factors
If noble metal leadwires are used for EMI shielding, then EMI filtering is improved, but cost increases significantly
Solution Approach 1:
The patent replaces expensive noble metal leadwires with less costly alternative materials such as platinum-free alloys or base metals with appropriate surface treatments. The design accepts that these alternative materials may have shorter service lives or require more frequent replacement, trading material cost for overall system economics while maintaining adequate EMI filtering performance through optimized geometry and shielding structures.
Solution Approach 2:
The patent changes the material parameters from noble metals to alternative conductive materials, and compensates for any performance deficiency by optimizing geometric parameters such as leadwire diameter, length, routing, and shielding configuration. The electrical and magnetic shielding effectiveness is achieved through parameter optimization rather than relying solely on expensive materials.
3Reliability
If platinum is co-fired with alumina to minimize stresses, then hermetic seal reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the platinum interconnect formation with the alumina ceramic sintering process into a single co-firing operation. Both materials are processed simultaneously at elevated temperatures, allowing the platinum to form hermetic seals with the ceramic while the ceramic sinteres, creating a integrated structure with minimized interfacial stresses from thermal mismatch.
Solution Approach 2:
The patent optimizes the co-firing process parameters including temperature profile, heating rate, holding time, and atmosphere composition to achieve simultaneous dense sintering of alumina and proper metallization of platinum. The process parameters are carefully controlled to ensure the platinum remains ductile during sintering and forms reliable hermetic seals without excessive complexity.
4Object-affected harmful factors
If feedthrough capacitor is integrated with hermetic terminal, then EMI filtering is enhanced, but device complexity increases
Solution Approach 1:
The patent merges the feedthrough capacitor structure with the hermetic terminal assembly, integrating the EMI filtering function directly into the feedthrough component. The capacitor is formed using the same ceramic substrate and metal interconnects, eliminating the need for separate discrete capacitor components and reducing overall device complexity through functional integration.
Solution Approach 2:
The patent designs the feedthrough component to serve multiple functions simultaneously: providing hermetic sealing, conducting electrical signals, offering EMI shielding, and incorporating capacitive filtering. This multi-functional design eliminates the need for separate components for each function, reducing overall device complexity while enhancing EMI protection capabilities.
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 provides a reliable, biocompatible, and cost-effective hermetic seal that minimizes stress-induced failures, reduces EMI interference, and maintains device functionality over the AIMD's service life, while also eliminating the need for expensive noble metal leadwires and enhancing EMI filtering capabilities.
Implementation Method 1
The substantially pure platinum and the alumina may be co-fired to form a hermetically sealed interface between the alumina and the platinum that is fundamentally matched or compressive
Implementation Method 2
A tortuous interface between the substantially pure platinum and the alumina may be formed that is resistant to erosion by body fluids
Data Source
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AI summary
A co-connected hermetic feedthrough, feedthrough capacitor, and leadwire assembly includes a dielectric substrate with a via hole disposed through the dielectric substrate from a body fluid side to a device side. A conductive fill is disposed within the via forming a hermetic seal and is electrically conductive between the body fluid side and the device side. A feedthrough capacitor is attached to the dielectric substrate and includes a capacitor dielectric substrate, an unfilled capacitor via hole including an inner metallization, a set of capacitor active electrode plates electrically coupled to the inner metallization, an outer metallization disposed and a set of capacitor ground electrode plates electrically coupled to the outer metallization. A conductive leadwire is disposed within the unfilled capacitor via hole. An electrical joint connects the conductive fill, the capacitor inner metallization along with the capacitor active electrode plates and the conductive leadwire.