Sn-Pd Plated Board Terminal Friction and Solder Wettability
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Solution Overview
Problem
Conventional board terminals with Sn plating films have high friction coefficients due to the softness of Sn, leading to increased insertion force, especially in multi-pole connectors, and poor solder wettability, which reduces connection reliability.
Innovation Solution
A board terminal with a plating film featuring a Sn mother phase and Sn—Pd-based alloy phases on its surface, where the Pd content is not more than 7 atomic %, reducing friction coefficient and ensuring good solder wettability, comprising a base material like Cu alloy with a plating film structure that includes a Ni layer and a Sn—Pd alloy layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Sn plating film is used on the board terminal surface, then solder wettability is improved, but the friction coefficient increases leading to high insertion force
Solution Approach 1:
The plating film uses a composite structure with multiple layers (Ni layer, Cu layer, and Sn layer) where each layer contributes different properties. The Ni layer provides oxidation resistance and adhesion, the Cu layer provides ductility and solder wettability, and the Sn layer provides low friction coefficient. This composite structure resolves the contradiction by combining materials with complementary properties rather than using a single Sn layer alone.
Solution Approach 2:
Different layers of the plating film have different local properties optimized for specific functions. The Ni layer is positioned where oxidation resistance is needed, the Cu layer where ductility and solder wettability are needed, and the Sn layer where low friction is needed. This local differentiation of material properties allows the terminal to simultaneously achieve good solder wettability and low insertion force.
2Reliability
If the Sn plating layer is made thicker to improve solder wettability, then solder bonding reliability improves, but the softness of Sn increases the friction coefficient further
Solution Approach 1:
The invention uses a multi-layer composite plating film where the Sn layer is kept thin (0.5-2.0 μm) to maintain low friction, while the underlying Cu layer (1.0-3.0 μm) and Ni layer provide the necessary thickness and structural support for reliable solder bonding. This composite approach allows achieving good solder wettability without increasing the Sn layer thickness, thereby avoiding increased friction.
Solution Approach 2:
The Cu layer acts as an intermediary between the Ni layer and the Sn layer, providing a transition zone that contributes to both adhesion and solder wettability. The Cu layer's high ductility and affinity for solder allow good solder bonding even when the Sn layer is kept thin, thus mediating between the requirements for solder reliability and low friction.
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 low insertion force and improved solder bonding reliability, effectively reducing friction and maintaining excellent solder wettability, even with multiple terminals, by combining the softness of Sn with the hardness of Sn—Pd alloy phases.
Implementation Method 1
a friction coefficient on the outer surface of the outermost layer is reduced in the board terminal and an insertion force at the time of connection to a mating terminal can be suppressed to be low
Implementation Method 2
since the Pd content of the outermost layer is not more than 7 atomic %, good solder wettability can be ensured
Data Source
AI summary
A board terminal 1 includes a base material 11 made of a metal material and a plating film 12 covering a surface of the base material 11. The plating film 12 includes an outermost layer 120 having a Sn mother phase 120a and Sn—Pd-based alloy phases 120b dispersed in the Sn mother phase 120a, the Sn mother phase 120a and the Sn—Pd-based alloy phases 120b being present on an outer surface. A Pd content in the outermost layer 120 is not more than 7 atomic %. A board connector 2 includes the board terminal 1 and a housing 20 for holding the board terminal 1.