Coil Component Terminal Electrode Tin Distribution
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Solution Overview
Problem
The existing coil components face issues with bonding strength between the metal wire and the terminal fitting or electrode, particularly due to the formation of Cu—Sn alloys during reflow processes, which can lead to the metal wire detaching from the wire connection portion, and this problem is exacerbated by the use of tin plating on nickel plating in terminal fittings.
Innovation Solution
A coil component design where the terminal electrode includes a wire connection area with a CuNi alloy and a mounting area with a higher tin content, where the wire connection area has a lower tin amount than the mounting area, ensuring minimal tin in the CuNi alloy formation during thermocompression bonding, and the mounting area has a thicker tin layer for solder wettability, with the tin layer thickness in the wire connection area being less than 1.2 μm to maintain bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a terminal fitting with tin plating on nickel plating is used, then solder wettability is improved, but bonding strength between metal wire and terminal fitting deteriorates due to Cu-Sn alloy formation during reflow
Solution Approach 1:
The terminal electrode is designed with different tin content in different regions: the wire connection portion has low tin content (0.1-5 mass%) to prevent Cu-Sn alloy formation and maintain bonding strength, while the mounting portion has high tin content (2-10 mass%) to ensure solder wettability. This local differentiation resolves the contradiction between bonding strength and solder wettability.
Solution Approach 2:
The terminal electrode is segmented into functionally distinct regions: a wire connection portion for thermocompression bonding with controlled low tin content, and a mounting portion for solder attachment with high tin content. This segmentation allows each region to optimize its properties for its specific function, resolving the contradiction.
2Ease of manufacture
If the wire connection portion contains a large amount of tin, then solder wettability is improved, but the metal wire may drop off during reflow due to alloy melting
Solution Approach 1:
The wire connection portion is designed with locally controlled low tin content (0.1-5 mass%) to prevent Cu-Sn alloy formation that would cause wire drop-off during reflow, while the mounting portion maintains high tin content for solder wettability. This local quality differentiation resolves the contradiction between solder wettability and wire connection reliability.
3Ease of manufacture
If uniform tin plating is applied across the entire terminal electrode, then solder wettability is ensured, but bonding strength at the wire connection portion deteriorates
Solution Approach 1:
Instead of uniform tin plating, the invention applies non-uniform tin distribution: the wire connection portion has minimal tin (0.1-5 mass%) to preserve bonding strength, while the mounting portion has abundant tin (2-10 mass%) for solder wettability. This local quality approach resolves the contradiction between uniform manufacturability and localized performance.
Solution Approach 2:
The terminal electrode surface is segmented into distinct plating regions with different tin concentrations. The wire connection portion and mounting portion are treated differently during the plating process, creating functionally optimized zones that resolve the contradiction between ease of manufacture and bonding strength.
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
This configuration enhances the bonding strength between the metal wire and the terminal electrode, preventing copper erosion and ensuring solder wettability while minimizing the formation of CuNiSn alloys, thus maintaining structural integrity during reflow processes and reducing production costs by eliminating the need for additional plating on the coil component base.
Implementation Method 1
a thermocompression bonding method is widely used. With the thermocompression bonding method, a CuNi alloy may be formed in the wire connection portion when the metal wire is made of copper.
Implementation Method 2
The tin plating ensures the wettability of solder at the time of mounting.
Implementation Method 3
Coil components of this kind include a metal wire that is wound around a base
Data Source
AI summary
Disclosed herein is a coil component that includes a base, a metal wire that is wound around the base and contains copper, and a terminal electrode that is provided on the base and contains nickel and tin. The terminal electrode includes a wire connection area to which an end portion of the metal wire is connected and which contains a CuNi alloy or a CuNiSn alloy, and a mounting area which is different from the wire connection area. The wire connection area includes a portion that contains a small amount of tin than the mounting area.