Connector Terminal with Localized Surface Roughness
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Solution Overview
Problem
Engaging type terminals for printed wiring boards face challenges in achieving a balance between low frictional properties for easy fitting and improved solder-bonding properties, as existing materials with high surface roughness for low friction often compromise on solder-bonding reliability, while thick Sn layers for better solder-bonding increase friction.
Innovation Solution
A terminal design featuring a punched Cu alloy strip with a coating of Cu—Sn alloy and Sn layers, where the Cu—Sn alloy is sandwiched between the base material and the Sn layer, and the Sn layer is smoothed by reflowing, resulting in a surface roughness that is higher for the engaging part than the solder-bonding part, ensuring low friction and enhanced solder-bonding properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the surface roughness is increased to achieve low frictional property, then the friction decreases and engagement becomes easier, but the solder-bonding property deteriorates
Solution Approach 1:
The patent applies different surface roughness characteristics to different regions of the terminal. The engaging part has a higher surface roughness (Ra ≥ 0.15 μm) to reduce friction and facilitate insertion, while the solder-bonding part has a lower surface roughness (Ra < 0.15 μm) to ensure good solder wettability and bonding reliability. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Reliability
If a thick Sn layer is applied to improve solder-bonding property, then the solder-bonding reliability improves, but the frictional property worsens
Solution Approach 1:
The patent controls the Sn layer thickness differently in different regions. In the solder-bonding part, a sufficient Sn layer thickness is maintained to ensure good solderability and bonding strength. In the engaging part, the Sn layer is made thinner or selectively removed to expose the Cu-Sn alloy layer, reducing friction and enabling smooth engagement. This spatial variation in layer thickness resolves the contradiction between solder-bonding reliability and low friction.
Solution Approach 2:
The patent selectively removes or reduces the Sn layer in the engaging part through etching or mechanical processing, extracting the excessive Sn that would otherwise increase friction. This leaves a thinner Sn layer or exposes the Cu-Sn alloy layer in the engaging region, while maintaining an adequate Sn layer in the solder-bonding region, thus resolving the friction-solderability contradiction.
3Ease of operation
If the Cu—Sn alloy layer is exposed to reduce friction, then the frictional property improves, but the solder-bonding property deteriorates
Solution Approach 1:
The patent exposes the Cu-Sn alloy layer selectively in the engaging part where low friction is required, while maintaining a complete Sn layer in the solder-bonding part where solderability is critical. This localized exposure strategy allows the Cu-Sn alloy to provide low-friction engagement surfaces without compromising the solder-bonding performance in other regions.
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 terminal achieves a low frictional property for easy engagement while maintaining excellent solder-bonding reliability, with the Cu—Sn alloy layer exposed on the engaging part and a thicker Sn layer on the solder-bonding part for improved wettability and bonding strength.
Implementation Method 1
the Sn layer is smoothed by a reflowing process
Implementation Method 2
forms a Cu—Sn alloy layer by the plated Cu layer and the plated Sn layer
Data Source
AI summary
A terminal for an engaging type connector includes a punched Cu alloy strip as a base material, a coating formed on the Cu alloy strip by postplating processes and including a Sn layer, and a Cu—Sn alloy layer sandwiched between the base material and the Sn layer. The Sn layer is smoothed by a reflowing process. The terminal has an engaging part and a solder-bonding part, and the surface of a part of the base material corresponding to the engaging part has a surface roughness higher than that of the surface of the base material corresponding to the solder-bonding part. The engaging part has a low frictional property and the solder-bonding part has improved solder wettability.