Lead Frame Design for Face-Down Capacitor Current Path Reduction
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Solution Overview
Problem
Face-down terminal solid electrolytic capacitors have a long current path distance between the anode and cathode, leading to high equivalent series resistance (ESR) and inductance (ESL) values, especially in high frequency bands, which limits their performance.
Innovation Solution
A lead frame design with a connecting portion that shortens the current path between the anode and cathode terminals, featuring a frame body with anode and cathode terminal forming portions spaced apart, and a connecting portion extending from the cathode terminal forming portion to a position near the anode terminal forming portion, allowing for a more direct connection and reduced ESR and ESL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitor element is disposed between anode and cathode portions with lower ends connected by a coupling portion, then the capacitor structure is stable and manufacturable, but the current path distance between anode and cathode becomes considerably long
Solution Approach 1:
The patent transitions from a vertical current path (through the coupling portion) to a horizontal current path (along the principal surface). The anode terminal forming portion and cathode terminal forming portion are disposed at different positions on the principal surface, allowing current to flow horizontally across the lead frame rather than vertically through the coupling portion, thereby shortening the current path distance while maintaining structural stability.
Solution Approach 2:
The lead frame is segmented into distinct functional portions: a frame body, an anode terminal forming portion, and a cathode terminal forming portion. This segmentation allows each portion to be optimized independently - the frame body provides structural support while the terminal forming portions are positioned to minimize current path distance, resolving the contradiction between structural stability and current path length.
2Ease of manufacture
If the current path distance is long, then the capacitor structure is easier to manufacture with standard processes, but the ESR and ESL values of the entire capacitor remarkably increase
Solution Approach 1:
The patent changes the geometric parameters of the lead frame, specifically the positions of the anode and cathode terminal forming portions on the principal surface. By optimizing these positional parameters, the current path distance is minimized, which directly reduces ESR and ESL values while maintaining ease of manufacture through standard lead frame fabrication processes.
3Strength
If the coupling portion connects anode and cathode lower ends, then the capacitor element is securely held, but the skin depth decreases in high frequency band leading to increased ESR and ESL
Solution Approach 1:
The patent changes the dimension of current flow from vertical (through the coupling portion connecting lower ends) to horizontal (across the principal surface). This dimensional change reduces the effective current path length that contributes to ESR and ESL in high frequency bands, while the terminal forming portions maintain secure electrical connection through their design on the principal surface.
Data Source
AI summary
In a lead frame for use in fabricating a face-down terminal solid electrolytic capacitor having a capacitor element an anode terminal, and a cathode terminal, a frame body has a connecting portion for being connected to the capacitor element. The connecting portion extends from a cathode terminal forming portion in a first direction to a position near an anode terminal forming portion. The anode terminal forming portion is connected to the frame body and used for forming the anode terminal. The cathode terminal forming portion is connected to the frame body and used for forming the cathode terminal. The anode terminal forming and the cathode terminal forming portions are spaced to each other in the first direction on a principal surface of the frame body.