Rectangular Tantalum Wire Anode for Capacitor Reliability
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Solution Overview
Problem
Conventional tantalum capacitors face issues with low contact strength and excessive leakage current due to the use of circular anode leads, which fail to meet the stringent requirements for chemical purity, surface finish, and electronic properties, especially in miniaturized and high-capacity applications.
Innovation Solution
A manufacturing method for special-shaped tantalum wire involves heat treatment, high-temperature surface pretreatment in an oxygen atmosphere, rolling with lubrication to form a rectangular cross-section, and final annealing to enhance mechanical and electronic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional circular anode lead is used, then the manufacturing process is simple, but the contact area with tantalum anode pellet is small leading to low contact strength and excessive leakage current
Solution Approach 1:
The patent applies asymmetry by changing the wire cross-section from circular to rectangular with rounded corners. This asymmetric shape increases the contact area with the tantalum anode pellet while maintaining manufacturability through controlled rolling processes that create the specific geometric profile.
Solution Approach 2:
The patent transitions from a one-dimensional circular cross-section to a two-dimensional rectangular cross-section with rounded corners. This dimensional change significantly increases the surface area available for contact with the anode pellet, improving both contact strength and reducing leakage current.
2Reliability
If tantalum capacitors are miniaturized with higher specific capacity powder, then the electric capacity increases, but the sintering temperature must be reduced which further decreases the anode lead pullout strength
Solution Approach 1:
The rectangular cross-section with rounded corners provides increased surface area and improved geometric interlocking with the sintered anode pellet. This shape compensation allows for reliable mechanical bonding even at reduced sintering temperatures where the material bonding strength is inherently lower.
Solution Approach 2:
The rounded corners in the rectangular cross-section design provide curved surfaces that better conform to the porous structure of the sintered tantalum anode. This curvature improves contact area and mechanical interlocking, enhancing pullout strength without requiring higher sintering temperatures.
3Reliability
If the sintering temperature is reduced to maintain high specific capacity, then the porosity of tantalum powder is preserved, but the contact area between anode lead and anode pellet decreases leading to excessive leakage current
Solution Approach 1:
The rectangular cross-section with rounded corners inherently provides a larger contact area compared to a circular cross-section of equivalent area. This asymmetric geometry ensures sufficient contact area with the porous anode pellet structure even when sintering temperature is reduced to maintain high specific capacity.
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 method produces tantalum wire with improved pullout strength and reduced leakage current, meeting the strict requirements for anode leads in tantalum capacitors, thereby enhancing the reliability and performance of miniaturized capacitors.
Implementation Method 1
subjecting the heat treated tantalum wire to surface pretreatment at high temperature in oxygen atmosphere to form an oxide membrane on the surface-pretreated tantalum wire
Implementation Method 2
rolling the surface-pretreated tantalum wire with the oxide membrane formed thereon while lubricating with lubricant oil
Implementation Method 3
subjecting the feedstock tantalum wire to heat treatment
Implementation Method 4
subjecting the tantalum wire to final annealing
Data Source
Figure 1~2
AI summary
The present invention relates to a tantalum wire for anode lead of tantalum capacitors, characterized in that the cross section of the tantalum wire is approximate rectangular or regular rectangular. The present invention also relates to a process for manufacturing the tantalum wire, comprising the steps of: providing feedstock tantalum wire; subjecting the feedstock tantalum wire to heat treatment; subjecting the heat treated tantalum wire to surface pretreatment to form an oxide membrane on the surface-pretreated tantalum wire; rolling the surface-pretreated tantalum wire by lubricating with lubricant oil to make the cross section of the rolled tantalum wire being approximate rectangular or regular rectangular; subjecting the tantalum wire to final annealing.