Cu-Sn Alloy Plating for Low Insertion Force Connectors
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Solution Overview
Problem
Conductive materials for connecting parts in electrical wiring, such as connector terminals and bus bars, face challenges in maintaining low insertion force, low contact resistance, and reliability in harsh environments, including high temperatures and corrosive conditions, while also preventing peeling of Sn plating and ensuring solderability.
Innovation Solution
A conductive material comprising a Cu strip with a Ni covering layer, a Cu—Sn alloy covering layer, and an Sn covering layer, where the Cu—Sn alloy layer is between the base material and the Sn layer, and a bright or semi-bright Sn electroplating layer is formed on the outermost Sn layer, optimizing the thickness and structure to reduce friction, maintain contact resistance, and enhance solderability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Sn plating thickness is increased to maintain low contact resistance, then the contact resistance decreases, but the insertion force increases due to increased adhesion force between plating layers
Solution Approach 1:
The Sn plating is divided into multiple thin layers (first Sn plating layer, second Sn plating layer, and bright/semi-bright Sn electroplating layer) rather than using a single thick layer. This segmentation reduces the adhesion force between layers while maintaining sufficient Sn coverage for low contact resistance, thereby reducing insertion force without sacrificing electrical connection quality.
Solution Approach 2:
Different regions of the plating structure have different thicknesses and properties. The bright/semi-bright Sn electroplating layer provides a uniform thin coverage (0.01 μm or more) on the outermost surface for low contact resistance, while the underlying Cu-Sn alloy layer and base material provide structural support. This local quality differentiation allows optimization of both contact resistance and insertion force.
2Reliability
If the contact pressure is increased to maintain low contact resistance, then the contact resistance decreases, but the deformation resistance and shearing resistance increase
Solution Approach 1:
The plating structure is segmented into multiple layers with the Cu-Sn alloy layer providing mechanical strength and the Sn layers providing electrical conductivity. This segmentation allows the contact pressure to be distributed across layers with different mechanical properties, reducing deformation resistance while maintaining low contact resistance through adequate Sn coverage.
3Force
If the Sn plating thickness is reduced to decrease insertion force, then the insertion force decreases, but the Sn plating becomes susceptible to peeling and wear
Solution Approach 1:
The plating structure uses a composite of Cu-Sn alloy layer and Sn layers. The Cu-Sn alloy layer provides excellent adhesion to the Cu base material and resistance to wear and peeling, while the Sn layers provide low contact resistance and solderability. This composite structure achieves both low insertion force and high resistance to wear and peeling.
Solution Approach 2:
The Cu-Sn alloy layer acts as an intermediary between the Cu base material and the Sn plating layers. It provides a transition zone that enhances adhesion and prevents direct contact between the Sn layers and base material, thereby preventing peeling and wear while allowing the Sn layers to remain thin for low insertion force.
4Reliability
If a thick Sn plating layer is used to prevent peeling, then the resistance to peeling increases, but the friction coefficient increases and insertion force increases
Solution Approach 1:
The Sn plating is segmented into multiple thin layers instead of a single thick layer. This segmentation maintains resistance to peeling through the layered structure and adhesion promoters while reducing the overall friction coefficient and insertion force compared to a single thick Sn layer.
Solution Approach 2:
The plating structure changes the thickness parameter of Sn layers from thick to thin (with the bright/semi-bright electroplating layer being 0.01 μm or more but relatively thin). This parameter change reduces friction and insertion force while maintaining peeling resistance through the composite structure and adhesion promoters.
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 material achieves a low friction coefficient, reducing insertion force, maintaining low contact resistance in harsh environments, preventing Sn plating peeling, and ensuring reliable solderability, even in high-temperature and corrosive conditions.
Implementation Method 1
a bright or semi-bright tin electroplating layer having an approximately uniform thickness and an average thickness of 0.01 μm or more is formed on the outermost layer
Data Source
AI summary
Disclosed is a conductive material for a connecting part, including: a base material made up of a Cu strip; a Cu—Sn alloy covering layer having an average thickness of 0.2 to 3.0 μm; and an Sn covering layer, the Cu—Sn alloy covering layer being provided between the base material and the Sn covering layer, wherein in a cross section perpendicular to the surface of the conductive material, the diameter [D1] of the minimum inscribed circle of the Sn covering layer is 0.2 μm or less, the diameter [D2] of the maximum inscribed circle of the Sn covering layer is 1.2 to 20 μm, the difference in elevation [y] between the outermost point of the material and the outermost point of the Cu—Sn alloy covering layer is 0.2 μm or less, and a bright or semi-bright tin electroplating layer having an average thickness of 0.01 μm or more in an approximately uniform thickness is formed on the outermost layer as part of the Sn covering layer.