Split Lead Frame Stacked Capacitor Thermal Stress
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Solution Overview
Problem
Stacked multilayer ceramic capacitors face inefficiencies in heat dissipation, thermal stress, and mechanical shock resistance due to their design, leading to potential cracking, shorting defects, and performance issues under vibration and extreme conditions.
Innovation Solution
A split lead frame configuration that enhances heat transfer and mechanical stability by providing larger electrical contact areas with the substrate, allowing for improved thermal stress tolerance and reduced inductance, and can be attached using fasteners for enhanced vibration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If stacked multilayer ceramic capacitors are mounted on aluminum substrate, then heat dissipation is improved, but thermal stress causes cracking and shorting defects
Solution Approach 1:
The patent introduces an intermediate layer between the aluminum substrate and the stacked capacitor. This intermediate layer acts as a thermal stress buffer that accommodates the differential thermal expansion between the aluminum substrate and the capacitor, preventing cracking and shorting defects while still allowing effective heat dissipation from the capacitor to the substrate.
Solution Approach 2:
The patent modifies the thermal and mechanical parameters of the mounting structure by selecting materials with appropriate thermal expansion coefficients and thermal conductivities. The intermediate layer is specifically chosen to have thermal expansion properties that bridge the gap between aluminum substrate and ceramic capacitor, reducing thermal stress while maintaining heat dissipation efficiency.
2Strength
If epoxy is used to adhere capacitor to board, then vibration resistance is improved, but thermal stress problems occur due to expansion or contraction of epoxy
Solution Approach 1:
The patent replaces the epoxy intermediary with a metal intermediate layer that has superior thermal stability and matched thermal expansion properties. This metal layer maintains strong mechanical adhesion between the capacitor and substrate while being thermally stable across operating temperature ranges, eliminating the thermal stress problems associated with epoxy materials.
3Power
If heat conduction path is extended through stacked capacitor height, then voltage rating is improved, but heat conduction efficiency decreases
Solution Approach 1:
The patent enhances heat conduction by adding lateral thermal pathways through extended lead frames that spread heat laterally across the substrate in addition to the vertical conduction path through the capacitor stack. This multi-dimensional heat dissipation approach maintains effective heat removal while preserving the vertical stacking configuration needed for high voltage rating.
Solution Approach 2:
The patent segments the heat conduction path into multiple parallel pathways: vertical conduction through the capacitor stack and lateral conduction through the lead frames and substrate. This segmentation creates redundant thermal routes that improve overall heat conduction efficiency without compromising the voltage rating determined by the capacitor stack geometry.
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 split lead frame design improves heat transfer, reduces thermal stress, and enhances mechanical stability, resulting in better performance and reliability of stacked multilayer capacitors under varying conditions.
Implementation Method 1
Heat conduction occurs through an internal electrode to the silver end terminations through the solder to the lead frames and then into a circuit board or other substrate
Implementation Method 2
since the temperature in the vicinity of the source changes greatly when the source is turned on and off, a significant amount of thermal stress occurs at a ceramic capacitor mounted on the aluminum substrate, which has a high coefficient of thermal expansion
Data Source
AI summary
A capacitor device, which is mountable on a substrate, has an electrically conductive bottom lead frame with a bottom plate mountable substantially parallel to, and in contact with, the substrate and an electrically conductive top lead frame having a top plate spaced apart from the bottom plate and a first transition portion having a first end connected to the top plate and a second end, opposite the first end, electrically connectable to the substrate. Multilayer capacitors are mounted between the top plate and the bottom plate. The capacitors have opposed end terminations electrically connected to the top and bottom plates, such that internal electrode plates are substantially nonparallel to the substrate.