Hermetic RF Connector CTE Mismatch via Transition Sleeve
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Solution Overview
Problem
Conventional coaxial feed-through RF connectors face challenges in forming reliable hermetic seals within high CTE materials like aluminum, with solder joints experiencing cyclic fatigue and requiring complex and costly explosion or laser welding techniques to join dissimilar metals.
Innovation Solution
A coaxial feed-through RF connector design utilizing a stainless steel sleeve with a Kovar ferrule, where the stainless steel sleeve is laser-welded to the Kovar ferrule and soldered to an aluminum housing, providing a reliable hermetic seal due to the close CTE match with aluminum, and a non-hermetic solder joint connects the Kovar ferrule to the housing for a secure ohmic RF signal ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder joints are used to connect Kovar shell to aluminum housing, then the connector can be assembled, but the solder joints experience cyclic fatigue and fail to provide reliable hermetic sealing
Solution Approach 1:
The patent introduces a dissimilar metal transition sleeve as an intermediary component between the Kovar ferrule and aluminum housing. This sleeve is laser-welded to both materials, serving as a mediator that bridges the CTE mismatch gap. The transition sleeve absorbs thermal stress through its intermediate CTE properties, preventing solder joint fatigue while maintaining hermetic sealing integrity.
Solution Approach 2:
The patent changes the material parameter (CTE) of the connector assembly by introducing a transition sleeve with intermediate CTE properties. This parameter change creates a gradual CTE transition from Kovar (low CTE) to aluminum (high CTE), reducing thermal stress concentration at the solder joint interface and preventing cyclic fatigue failure.
2Reliability
If dissimilar metals (Kovar and aluminum) are joined using hermetic sealing techniques, then reliable hermetic seal is achieved, but the process becomes complex and costly requiring explosion or laser welding
Solution Approach 1:
The patent segments the joining process into two distinct operations: (1) laser welding the transition sleeve to the Kovar ferrule and aluminum housing, and (2) conventional soldering the Kovar shell to the transition sleeve. This segmentation allows each operation to be optimized independently, with laser welding providing the hermetic seal for dissimilar metals and soldering providing the electrical connection, thereby reducing overall process complexity.
Solution Approach 2:
The patent replaces the complex mechanical/explosive welding process with a combination of laser welding and conventional soldering. Laser welding provides the hermetic seal for the dissimilar metal interface, while conventional soldering handles the electrical connection, substituting a simpler, more controllable thermal process for the complex mechanical joining of dissimilar metals.
3Reliability
If Kovar shell is used for RF ground connection, then good electrical conductivity is achieved, but the CTE mismatch with aluminum housing causes solder joint fatigue
Solution Approach 1:
The patent applies local quality by using different materials for different functions: the Kovar ferrule provides hermetic sealing and low CTE for the glass-to-metal seal, while the aluminum transition sleeve provides CTE compatibility with the housing and electrical ground connection. This local differentiation of material properties optimizes both hermetic sealing and thermal compatibility without compromise.
Solution Approach 2:
The patent creates a composite structure consisting of Kovar ferrule + transition sleeve + Kovar shell assembly. This composite construction combines materials with different CTE properties in a hierarchical arrangement, where each layer serves a specific function and the overall assembly achieves both hermetic sealing and thermal compatibility with the aluminum housing.
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 enables a reliable and cost-effective hermetic seal within a high CTE material like aluminum, avoiding the issues of cyclic fatigue in solder joints and the complexity of dissimilar metal welding, while maintaining a secure RF signal ground connection.
Implementation Method 1
the stainless steel sleeve is laser-welded to the Kovar ferrule
Implementation Method 2
soldered to an aluminum housing, providing a reliable hermetic seal due to the close CTE match with aluminum
Implementation Method 3
a non-hermetic solder joint connects the Kovar ferrule to the housing for a secure ohmic RF signal ground
Data Source
AI summary
An improved feed-through RF connector uses structural materials with coefficients of thermal expansion selected to enhance the reliability of a hermetic seal. The design of the connector and the selection of materials facilitate easy installation and help avoid cyclic fatigue and cracks that could result in a loss of hermetic seal.