Tin-Plated Pin Terminal for Solderability and Low Insertion Force
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Solution Overview
Problem
Pin terminals face challenges in solder wettability and insertability due to the formation of enlarged plating layers, which increase friction and require high insertion forces, and the post-plating method necessitates a Pd plating layer, complicating manufacturability and leading to potential short circuits from whisker formation.
Innovation Solution
A multistage plating method combining pre-plating and post-plating with specific heat treatment is used to form a tin-based layer with controlled thickness variations, preventing the formation of enlarged plating layers and whiskers, thereby enhancing solder wettability and insertability while eliminating the need for Pd plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tin-based plating layer is formed to improve solder wettability, then solder wettability is improved, but enlarged plating layers form increasing friction and insertion force
Solution Approach 1:
The patent applies different plating thicknesses to different regions of the pin terminal. The tip covering portion has a thickness of 0.01 μm or more and 0.5 μm or less, while other portions have different thickness ranges. This local differentiation ensures sufficient solder wettability at the tip while preventing excessive plating buildup that would increase insertion force.
Solution Approach 2:
The patent controls the plating thickness parameter within specific ranges to resolve the contradiction. By setting the tip covering portion thickness to 0.01-0.5 μm and controlling the difference between maximum and minimum thickness to 0.20 μm or more, the patent optimizes both solder wettability and insertability.
2Reliability
If post-plating method is used to ensure solder wettability, then solder wettability is improved, but Pd plating layer is required complicating manufacturability
Solution Approach 1:
The patent extracts and eliminates the Pd plating layer from the conventional post-plating structure. By using a tin-based plating layer with controlled thickness distribution instead of the traditional Cu/Ni/Pd structure, the patent simplifies the manufacturing process while maintaining solder wettability.
Solution Approach 2:
The patent uses a composite plating structure with a tin-based layer having specific thickness characteristics. This composite approach combines the benefits of solder wettability from tin with controlled thickness to prevent manufacturing complexity, replacing the multi-layer Cu/Ni/Pd structure.
3Area of stationary object
If conventional plating is applied to ensure coverage, then coverage is improved, but whisker formation occurs causing potential short circuits
Solution Approach 1:
The patent changes the plating parameters by controlling the thickness distribution of the tin-based layer. By setting specific thickness ranges and thickness differences, the patent prevents the conditions that lead to whisker formation while maintaining adequate coverage for solder wettability.
4Reliability
If plating layer thickness is increased to improve solder wettability, then solder wettability is improved, but insertability deteriorates due to enlarged plating layers
Solution Approach 1:
The patent applies local quality by differentiating plating thickness between the tip covering portion and other portions. The tip covering portion has controlled thickness (0.01-0.5 μm) sufficient for solder wettability, while avoiding excessive thickness that would cause enlargement and poor insertability.
Solution Approach 2:
The patent optimizes the thickness parameter within the range of 0.01 μm or more and 0.5 μm or less for the tip covering portion, and controls the thickness difference to 0.20 μm or more. This parameter optimization balances solder wettability enhancement with maintainment of good insertability.
Data Source
AI summary
A pin terminal includes a bar-like base material and a plating layer covering a predetermined region of the base material. A constituent material of the base material is pure copper or a copper alloy. The plating layer includes a tin-based layer made of metal containing tin. One end side of the base material includes a tip covering portion. The tin-based layer includes the tip covering portion. The tip covering portion covers an entire region in a circumferential direction on the one end side of the base material. A difference (t1−t2) between a maximum value t1 and a minimum value t2 of a thickness of the tip covering portion measured at a measurement location set at a spot of 1 mm from one end of the pin terminal along a longitudinal direction of the pin terminal is 0.20 μm or more.