Capacitor Termination Using Transient Liquid Phase Sintering
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Solution Overview
Problem
Current methods for attaching external leads or lead frames to multi-layered ceramic capacitors lack reliability and efficiency, especially at high temperatures, and are not economically viable for lead-free applications, with existing Pb-free solders requiring high reflow temperatures and having limitations in material compatibility and processing costs.
Innovation Solution
The use of transient liquid phase sintering (TLPS) adhesives or polymer solders to form metallic external terminals that can be reflowed at lower temperatures, allowing for attachment to lead frames without compromising the bond, accommodating different surface finishes and component lengths, and providing high-temperature integrity without the need for solder balls, enabling stacked components with improved mechanical and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pb-free solders (SAC) are used for attachment, then environmental compliance is improved, but processing temperature must be increased to 260°C which compromises reliability
Solution Approach 1:
The patent changes the material parameters by using Sn-Sb-based solders with specific compositions (10-30% Sb) that have liquidous temperatures below 270°C, allowing lower processing temperatures while maintaining Pb-free compliance. This parameter optimization resolves the contradiction between environmental compliance and processing temperature requirements.
Solution Approach 2:
The patent employs composite solder materials combining Sn and Sb in specific ratios, creating a eutectic or near-eutectic alloy system that melts at lower temperatures than pure Sn or SAC solders. This composite approach enables reliable attachment at reduced temperatures, solving the reliability-temperature contradiction.
2Temperature
If high melting point materials are used for terminations, then temperature sustainability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies termination materials to the external leads before the soldering process, allowing the terminations to be pre-formed and positioned. This preliminary action simplifies the overall manufacturing process while ensuring the terminations can sustain high temperatures, as they are integrated into the attachment process rather than requiring separate high-temperature formation steps.
3Strength
If conventional soldering methods are used, then attachment strength is improved, but applicability to different surface finishes is limited
Solution Approach 1:
The patent develops termination materials and processes that universally accommodate different surface finishes (such as various platings and coatings) on external leads and lead frames. The Sn-Sb-based solder composition is designed to wet and bond effectively to multiple surface types, making the attachment process versatile and adaptable without requiring surface finish-specific optimization, thus resolving the strength-versus-versatility contradiction.
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 TLPS or polymer solder technology forms robust, high-temperature bonds that sustain integrity above 260°C, reducing manufacturing costs and processing complexity, while allowing for efficient stacking of components without gaps, enhancing mechanical and electrical properties, and providing a reliable lead-free solution for high-temperature applications.
Implementation Method 1
Transient liquid phase sintering conductive adhesive formulations disclosed in US Patent No. 5,853,622 combine TLPS materials with cross linking polymers to create an thermally and electrical bond having intermetallic interfaces between the metal surfaces created by TLPS process
Implementation Method 2
forming a joint when heating to the melting point of the lower temperature material is discussed in US Patent No. 5,964,395
Implementation Method 3
Transient liquid phase sintering conductive adhesive formulations disclosed in US Patent No. 5,853,622 combine TLPS materials with cross linking polymers to create an thermally and electrical bond
Implementation Method 4
forming a joint when heating to the melting point of the lower temperature material
Data Source
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AI summary
A capacitor has first planer internal electrodes in electrical contact with a first external termination. Second planer internal electrodes are interleaved with the first planer internal electrodes wherein the second planer internal electrodes are in electrical contact with a second external termination. A dielectric is between the first planer internal electrodes and the second planer internal electrodes and at least one of the external terminations comprises a material selected from a polymer solder and a transient liquid phase sintering adhesive.