Terminal Fitting Plating Structure for Low Insertion Force
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Solution Overview
Problem
Terminal fittings with Sn plating layers experience high friction coefficients and surface oxidation when exposed to hot and humid environments, leading to increased contact resistance and corrosion, particularly in connectors with multiple terminal fittings.
Innovation Solution
A terminal fitting with a plating film structure that includes a Ni foundation layer, a Ni3Sn4 layer, and an outermost layer containing a Sn parent phase and an intermetallic compound (Ni0.4Pd0.6)Sn4, which reduces friction coefficient and suppresses surface oxidation, even in harsh environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Sn plating layer is used on the terminal fitting surface, then the terminal fitting has good electrical conductivity and solderability, but the friction coefficient increases and terminal insertion force becomes large
Solution Approach 1:
The patent applies composite plating structure with multiple layers (Ni foundation layer, Ni3Sn4 intermediate layer, and outermost layer with Sn parent phase and intermetallic compounds). This composite structure combines the electrical conductivity benefits of Sn with the low friction properties of Pd-containing intermetallic compounds, resolving the contradiction between good electrical contact and low insertion force.
Solution Approach 2:
The outermost layer is designed with specific local composition containing Sn parent phase and dispersed intermetallic compounds ((Ni,Pd)Sn4, NiSn, etc.). This local quality variation within the plating layer provides both electrical conductivity (from Sn) and low friction coefficient (from intermetallic compounds at the surface), addressing the contradiction between conductivity and insertion force.
2Force
If a Sn—Pd alloy-containing layer is formed on the base material to reduce terminal insertion force, then the friction coefficient decreases, but surface oxidation resistance in hot and humid environments deteriorates
Solution Approach 1:
The patent uses a composite outermost layer containing Sn parent phase, Pd-containing intermetallic compounds, and other intermetallic compounds in specific proportions. This composite structure balances the low friction properties of Pd-Sn intermetallics with the oxidation resistance provided by the multi-layer configuration and controlled composition, resolving the contradiction between insertion force and environmental resistance.
Solution Approach 2:
The patent specifies precise compositional parameters for the outermost layer (Sn parent phase with dispersed intermetallic compounds including (Ni0.4Pd0.6)Sn4, NiSn, and Ni3Sn4 in controlled amounts). By optimizing these parameters, the patent achieves both low friction coefficient (reduced insertion force) and sufficient oxidation resistance in hot and humid environments.
Data Source
AI summary
A terminal fitting that can reduce the terminal insertion force and can suppress surface oxidation of a plating film, even if the terminal fitting is exposed to a hot and humid environment, and a connector that uses the terminal fitting. The terminal fitting includes a metal base material, and the plating film. The plating film includes a Ni foundation layer, an outermost layer exposed at the outermost surface, and a Ni3Sn4 layer formed between the Ni foundation layer and the outermost layer. The outermost layer includes a Sn parent phase, and intermetallic compound that is dispersed in the Sn parent phase, and is made of (Ni0.4Pd0.6)Sn4. The intermetallic compound protrudes from the lower side of the outermost layer to the Ni3Sn4 layer side, and is partially buried in the Ni3Sn4 layer. A connector includes the terminal fitting, and a housing that holds the terminal fitting.