Gold Pocket Pad for Hermetic EMI Filter Grounding
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Solution Overview
Problem
Existing hermetic terminal subassemblies for active implantable medical devices face challenges in forming a reliable and oxide-resistant connection between the feedthrough capacitor ground metallization and the ferrule, particularly during high-temperature gold brazing operations, where the gold braze material fails to maintain its shape and form, leading to inadequate attachment and increased resistance due to titanium oxide formation.
Innovation Solution
A gold pocket pad is formed in the ferrule, which captures a gold preform that is reflowed at elevated temperatures, creating a thick, oxide-resistant metallurgical bond that prevents titanium oxide interference and ensures a stable electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional gold brazing is used to attach capacitor ground metallization to ferrule, then the connection can be formed, but the gold braze material fails to maintain its shape and form during high-temperature operations, leading to inadequate attachment and increased resistance
Solution Approach 1:
A pocket is formed in the ferrule surface before the brazing operation to pre-position and contain the gold preform. This preliminary structural preparation ensures that when gold is applied at high temperature, it remains confined to the pocket area and maintains the desired shape and thickness for reliable electrical connection.
Solution Approach 2:
The pocket structure creates a localized region with different geometric properties (depression/indentation) compared to the surrounding ferrule surface. This local modification allows the gold braze material to be concentrated and contained in a specific area, ensuring adequate thickness and shape control where it is most needed for electrical connection.
2Object-affected harmful factors
If thin gold layer is used to prevent oxide formation, then oxide resistance is improved, but the gold material is insufficient to prevent titanium oxide penetration at high temperatures
Solution Approach 1:
The pocket is formed in advance to define a containment volume that will hold an adequate amount of gold material. This preliminary preparation ensures that sufficient gold can be present during brazing to prevent oxide penetration, while the pocket walls constrain the gold to where it is most effective.
Solution Approach 2:
The pocket structure changes the geometric parameters of the gold layer by confining it to a depression in the ferrule surface. This allows the gold to achieve greater effective thickness in the vertical dimension (preventing oxide penetration) while maintaining controlled lateral dimensions, thus providing adequate oxide resistance without excessive material usage.
3Ease of manufacture
If gold preform is applied without containment structure, then the brazing process is simpler, but the gold flows away during high-temperature reflow, leading to inadequate attachment
Solution Approach 1:
The pocket is formed in the ferrule before applying the gold preform, creating a ready-made containment structure. This preliminary preparation allows the gold to be simply placed into the pocket without complex application equipment, while the pocket itself provides the containment needed to prevent gold flow during brazing.
Solution Approach 2:
The pocket acts as an intermediary structure between the gold preform and the ferrule body. It receives and holds the gold material in a controlled manner, mediating the interaction between the applied gold and the underlying ferrule surface, thereby ensuring proper gold distribution and preventing unwanted flow during high-temperature reflow.
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, oxide-resistant electrical connection that maintains high-frequency performance by preventing titanium oxide penetration and ensuring a consistent, low-impedance attachment, thus enhancing the filter performance and reducing the risk of electromagnetic interference interference in medical devices.
Implementation Method 1
A gold pocket pad is formed in the ferrule, which captures a gold preform that is reflowed at elevated temperatures, creating a thick, oxide-resistant metallurgical bond
Implementation Method 2
creating a thick, oxide-resistant metallurgical bond that prevents titanium oxide interference
Implementation Method 3
a gold preform that is reflowed at elevated temperatures (such as in a gold braze furnace)
Data Source
AI summary
A feedthrough subassembly for an active implantable medical device includes a metallic ferrule having a conductive ferrule body, at least one surface disposed on a device side, and a ferrule opening passing through the at least one surface. An insulator body hermetically seals the ferrule opening of the conductive ferrule body by at least one of a first gold braze ceramic seal, a glass seal or a glass-ceramic seal. At least one hermetically sealed conductive pathway is disposed through the insulator body. At least one pocket formed in the at least one surface has a gold pocket pad disposed within. When the first gold braze ceramic seal is present, the first gold braze ceramic seal and the gold pocket pad are not physically touching one another.