Capacitor With Conductive Pad For Fluxless Soldering
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Solution Overview
Problem
The manufacture and installation of feedthrough filter capacitor assemblies for implantable medical devices, such as pacemakers, are costly and complex, with limited capacitance due to small capacitor size and vulnerability to temperature-induced cracking, and current methods require chemical etching to remove solder oxide layers for reliable connections.
Innovation Solution
A capacitor assembly with a conductive pad applied to the top portion around apertures, allowing feedthrough pins to be extended through and soldered with fluxless solder preforms, ensuring reliable electrical connections without chemical etching, using silver-palladium or gold-beryllium conductive material for enhanced solder flow and oxidation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small discoidal capacitor is installed in the annular space between terminal pin and ferrule, then the feedthrough assembly can be compact, but the capacitance is limited and the capacitor is vulnerable to temperature-induced cracking
Solution Approach 1:
The capacitor construction transitions from a two-dimensional discoidal shape to a three-dimensional structure that utilizes the vertical space within the ferrule. The capacitor plates are stacked vertically with insulating spacers, creating a multi-layer configuration that increases capacitance while fitting within the same footprint space, thereby avoiding the limitations of small discoidal capacitors.
Solution Approach 2:
The capacitor assembly uses composite materials including ceramic or plastic capacitor plates, insulating spacers, and conductive materials. This composite construction provides both the necessary electrical capacitance and mechanical strength to withstand temperature variations without cracking, improving reliability while maintaining compact dimensions.
2Reliability
If chemical etching is used to remove solder oxide layers, then reliable electrical connections can be achieved, but the manufacturing process becomes complex and costly
Solution Approach 1:
The solder preforms are pre-alloyed with specific compositions during manufacturing that inherently prevent oxide formation or facilitate oxide removal during soldering. This preliminary preparation of the solder material with optimized metallurgical properties eliminates the need for subsequent chemical etching steps, simplifying the manufacturing process while ensuring reliable electrical connections.
Solution Approach 2:
The soldering process parameters are optimized by using preforms with specific alloy compositions and controlled melting characteristics. The metallurgical parameters of the solder preform are engineered to achieve proper wetting and bonding without requiring aggressive chemical etching, thereby reducing process complexity while maintaining connection reliability.
3Reliability
If the capacitor is directly connected to the terminal pin and ferrule, then EMI filtering is effective, but the installation process is costly and complex
Solution Approach 1:
The capacitor assembly is segmented into modular components including capacitor plates, insulating spacers, and terminal connections. This segmentation allows for simplified assembly where each component can be independently positioned and connected, reducing installation complexity and cost while maintaining the electrical connectivity needed for effective EMI filtering between the terminal pin and ferrule.
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
This approach simplifies and economizes the installation process, providing reliable and high-quality electrical connections while preventing capacitor cracking and oxidation issues, enhancing the reliability and capacitance of the feedthrough assembly.
Implementation Method 1
silver-palladium or gold-beryllium conductive material for enhanced solder flow and oxidation resistance
Implementation Method 2
soldering the feedthrough pin to the inner diameter portion of the capacitor with the solder preform
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A filtered feedthrough assembly (10) includes a capacitor (14) comprising a top portion (144), a bottom portion (145), an outer diameter portion (141) and an inner diameter portion (143). The inner diameter portion defines at least one aperture extending from the top portion to the bottom portion. A conductive pad (149) of conductive material is applied to the top portion around the at least one aperture. A feedthrough pin (13) extends through each of the apertures and is soldered to the inner diameter portion of the capacitor by application of a solder preform (18) upon the conductive pad of conductive material.