Tin-Plated Connector Surface Morphology for Low Insertion Force
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Solution Overview
Problem
Tin-plated products used in insertable connecting terminals face issues with high insertion force and increased production costs due to surface roughening, which affects their solderability, whisker resistance, and heat-resisting reliability.
Innovation Solution
A tin-plated product with a substrate of copper or copper alloy, featuring an underlying nickel or copper-nickel alloy layer and an outermost copper-tin alloy layer with tin layers arranged in recessed portions, optimizing the area ratio and thickness to reduce insertion force while maintaining low production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the surface of the substrate is roughened to decrease insertion force, then the insertion force is reduced, but the production costs increase
Solution Approach 1:
The invention changes the surface morphology parameters by controlling crystal grain size (1.5-3 μm) and tin layer thickness (0.2-1.0 μm) to achieve low insertion force without requiring additional surface roughening processes, thereby avoiding increased production costs
Solution Approach 2:
The invention creates local tin-rich regions in recessed portions between crystal grains, where tin layers are concentrated (area ratio 20-80%), providing low insertion force at specific contact points without modifying the entire surface structure or requiring additional processing steps
2Reliability
If a complex multi-layer structure with intermediate layers is formed, then solderability and whisker resistance are improved, but the device complexity increases
Solution Approach 1:
The invention extracts and eliminates the intermediate nickel or copper-nickel alloy layer from the conventional multi-layer structure, relying instead on the optimized copper-tin alloy outermost layer with controlled crystal grains and tin layers to provide both low insertion force and reliable solderability without whisker formation
Solution Approach 2:
The invention creates a composite microstructure within the outermost layer, combining copper-tin alloy crystal grains with tin-rich phases in recessed portions, achieving multiple functions (low insertion force, solderability, whisker resistance) in a single integrated layer rather than through multiple separate layers
3Reliability
If the tin layer thickness is increased to improve corrosion resistance, then the corrosion resistance is enhanced, but the insertion force increases
Solution Approach 1:
The invention concentrates tin layers locally in recessed portions between crystal grains (area ratio 20-80%) with controlled thickness (0.2-1.0 μm), providing corrosion resistance at critical contact points while maintaining low insertion force through the overall surface morphology
Solution Approach 2:
The invention optimizes the ratio of tin layer thickness to crystal grain size (maximum thickness smaller than average particle diameter), creating a surface where tin provides corrosion protection without forming thick continuous layers that would increase insertion force
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 solution results in a tin-plated product with low insertion force and improved electrical performance, achieving reduced contact resistance and enhanced reliability at lower production costs.
Implementation Method 1
the copper-tin alloy layer being formed of a large number of crystal grains of a copper-tin alloy
Implementation Method 2
each of the tin layers being arranged in a corresponding one of recessed portions, each of which is formed between adjacent crystal grains
Data Source
AI summary
In a tin-plated product wherein a surface of a substrate 10 of copper or a copper alloy is plated with tin, an underlying layer 12 of at least one of nickel and a copper-nickel alloy is formed on the surface of the substrate 10, and an outermost layer formed on the surface of the underlying layer 12 is composed of a copper-tin alloy layer 14 and tin layers 16, the copper-tin alloy 14 being formed of a large number of crystal grains of a copper-tin alloy, each of the tin layers 16 being arranged in a corresponding one of recessed portions, each of which is formed between adjacent crystal grains of the large number of crystal grains of the copper-tin alloy, the adjacent crystal grains being adjacent to each other on the outermost surface of the outer most layer, the area ratio occupied by the tin layers 16 on the outermost surface being 20 to 80%, and the maximum thickness of the tin layers 16 being smaller than the average particle diameter of the crystal grains of the copper-tin alloy.