Hermetic Feedthrough Titanium Hydride Coating
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Solution Overview
Problem
Conventional metallizations in feedthrough assemblies for implantable medical devices, such as cardiac pacemakers, face issues with titanium reacting with gold to form brittle intermetallic alloys, leading to hermeticity failures and corrosion, especially when exposed to body fluids, and require thick barrier layers that can cause residual stresses and processing challenges.
Innovation Solution
A titanium hydride coating is applied to the ceramic surfaces, which partially decomposes during brazing to form pure titanium, enhancing gold adhesion without detrimental reactions and improving wetting, using a thin layer that can be applied via dip/spray/paint coating with a binder to reduce residual stress and maintain a hermetic seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a barrier layer comprising molybdenum or niobium is applied to prevent intermetallic alloys, then the formation of titanium-gold intermetallic is prevented, but corrosion and hermeticity failures occur during implant applications
Solution Approach 1:
The patent changes the material parameter from conventional barrier metals (molybdenum, niobium) to a titanium-based barrier alloy containing tungsten. This parameter change maintains the barrier function against intermetallic formation while improving corrosion resistance in body fluids, thereby resolving the contradiction between preventing intermetallic reactions and avoiding corrosion.
Solution Approach 2:
The patent employs a composite barrier layer comprising titanium and tungsten (Ti-W alloy) instead of pure metals. This composite material combines the beneficial properties of titanium (adhesion to insulator, low reactivity with gold) and tungsten (high corrosion resistance, low diffusion coefficient), simultaneously addressing both the intermetallic prevention and corrosion resistance requirements.
2Reliability
If the niobium or molybdenum layers are maintained at relatively high thicknesses to retain the barrier effect, then intermetallic reaction is prevented, but residual stresses increase and can be detrimental to the integrity of the metallization layer
Solution Approach 1:
The patent changes the material composition parameter to Ti-W alloy, which has different physical and mechanical properties compared to pure niobium or molybdenum. The Ti-W barrier layer achieves the required barrier effect with reduced thickness, thereby minimizing residual stresses while maintaining hermeticity and preventing intermetallic formation.
3Strength
If conventional metallization with titanium and molybdenum or titanium and niobium is used, then bonding of gold to insulator is achieved, but titanium reacts with gold to form brittle intermetallic alloys
Solution Approach 1:
The patent introduces a Ti-W barrier layer as an intermediary between the titanium adhesion layer and the gold braze material. This intermediate barrier layer prevents direct contact and reaction between titanium and gold, eliminating the formation of brittle intermetallic alloys while maintaining the bonding strength through the titanium- insulator interface.
Solution Approach 2:
The use of Ti-W composite barrier material provides both the adhesion properties of titanium and the low reactivity/corrosion resistance of tungsten, creating a metallization structure that achieves strong bonding without detrimental intermetallic reactions.
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 titanium hydride coating ensures a strong, hermetic bond between gold and alumina ceramic, preventing intermetallic reactions and corrosion, while maintaining a thin, uniform layer that reduces processing time and equipment maintenance, achieving a reliable seal with improved wetting and reduced residual stress.
Implementation Method 1
the deposited titanium hydride is first partially decomposed to form pure titanium intermixed with titanium hydride
Implementation Method 2
The combination of pure titanium and titanium hydride contributes toward adhesion of gold with the alumina ceramic without any detrimental reaction between pure titanium and gold
Data Source
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AI summary
The application of a titanium hydride coating on a ceramic, preferably an alumina ceramic, as a facile and inexpensive approach to bond gold to the ceramic during brazing is described. During the brazing process, the deposited titanium hydride is first partially decomposed to form pure titanium intermixed with titanium hydride. The combination of pure titanium and titanium hydride contributes to improved adhesion of gold with the alumina ceramic without any detrimental reaction between pure titanium and gold. The titanium hydride coating can be applied by dip/spray/paint coating.