Stainless Steel Lead Frames for Capacitors
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Solution Overview
Problem
The development of lead frames for tantalum and niobium capacitors faces challenges in finding materials that balance conductivity, thermal resistance, strength, ductility, and cost, with conventional copper-based alloys being expensive and compromising on these properties.
Innovation Solution
The use of Ferritic stainless steel, non-Ferritic stainless steel, or carbon steel as a base material for lead frames, plated with a nickel strike and outer layers, offering comparable performance to traditional lead frames at a lower cost, with stainless steel providing reliable conductivity, attachment, and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper-based alloys are used as base material for lead frames, then good electric conductivity is achieved, but cost increases significantly
Solution Approach 1:
The patent applies composite material structure by combining stainless steel base material with plated outer layers (such as tin, silver, or copper plating). The stainless steel provides mechanical strength and thermal resistance, while the plated layers provide the necessary electrical conductivity and solderability, creating a composite structure that balances multiple requirements at lower cost than solid copper alloys.
Solution Approach 2:
The patent changes the material parameters by selecting stainless steel grades (such as 304, 316, or 430) with specific compositional ranges and implementing controlled plating thicknesses (typically 0.5-5 micrometers). This parameter optimization allows the lead frame to achieve adequate conductivity through the plated layers while the stainless steel core provides structural integrity, resolving the cost-conductivity contradiction.
2Ease of manufacture
If stainless steel is used as base material for lead frames, then cost is reduced and thermal resistance is improved, but electric conductivity decreases compared to copper
Solution Approach 1:
The patent uses a composite structure where stainless steel serves as the base material providing mechanical properties and thermal resistance, while outer plated layers (tin, silver, or copper) provide the necessary electrical conductivity pathway. This composite approach allows the stainless steel to reduce cost and improve thermal resistance while the plated layers compensate for the conductivity deficiency.
Solution Approach 2:
The patent applies local quality by concentrating the conductive material (plated layers) only where electrical connection is needed at the contact surfaces, while the bulk of the lead frame structure uses cost-effective stainless steel. This localized application of expensive conductive material minimizes cost while maintaining necessary electrical performance.
3Reliability
If copper-based alloys are used as base material, then electric conductivity is maintained, but thermal conductivity is high which can damage the dielectric
Solution Approach 1:
The patent employs composite material structure where stainless steel base material provides low thermal conductivity to protect the dielectric from heat, while plated outer layers maintain adequate electrical conductivity. This composite structure physically separates the thermal and electrical conductivity requirements, allowing optimization of each property independently.
4Ease of manufacture
If lead frame thickness is reduced to lower cost, then material cost decreases, but strength and rigidity are compromised
Solution Approach 1:
The patent uses composite material where stainless steel provides high strength-to-weight ratio and rigidity, allowing thinner cross-sections compared to copper alloys. The plated layers add minimal thickness but provide necessary surface properties. This composite structure maintains mechanical strength at reduced overall thickness and cost.
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 solution provides lead frames with superior performance to traditional copper-based alloys at a significantly lower cost, ensuring reliable electrical connections, reduced heat transfer, and enhanced corrosion resistance for tantalum and niobium capacitors.
Implementation Method 1
The base metal is then preferably plated with a nickel strike or other conventional barrier layer and then with final outer plating layers
Implementation Method 2
good electric conductivity which is necessary to transmit electrical impulses to and from the integrated circuit
Implementation Method 3
minimal thermal conductivity to prevent heat from board mounting from transmitting to the Ta/Nb pellet and damaging the dielectric or cathode material
Data Source
AI summary
A Ferritic stainless steel, non Ferritic stainless steel or carbon steel based lead frame and method for producing same is provided. The lead frame is preferably used for TantalumNiobium capacitors but could possibly be applicable to other integrated circuits with the same operating parameters. Any reference to Tantalum capacitors in this application applies equally to Niobium capacitors unless otherwise noted. The lead frame is prepared by choosing one of Ferritic stainless steel, non Ferritic stainless steel or carbon steel as a base metal and rolling it to a final required thickness. The base metal is then preferably plated with a nickel strike or other conventional barrier layer and then with final outer plating layers(s). The exact thickness and choice of layering varies and can be tailored to meet the requirements of each lead attach process.