External Electrode Structure for Moisture-Resistant Electronic Components
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Solution Overview
Problem
The use of lead-free solder containing Zn in multilayer ceramic capacitors leads to the diffusion of Zn into Ni plating layers, causing the formation of voids that reduce moisture resistance and reliability due to water penetration, especially under high-temperature and high-humidity conditions.
Innovation Solution
A structure comprising an underlying electrode layer, a Ni alloy layer, a Ni plating layer, a Ni oxide layer with a thickness of 150 nm or less, and an upper plating layer, where the Ni plating layer has an average particle size of 2 μm or more, formed through heat treatment in a reducing atmosphere, inhibits Zn diffusion and maintains insulation resistance and solderability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder containing Zn is used for mounting, then environmental pollution is reduced and solderability is improved, but Zn diffuses into Ni plating layers causing void formation and moisture resistance degradation
Solution Approach 1:
A Cu-rich alloy layer is introduced as an intermediary barrier between the underlying electrode layer and the Ni plating layer. This alloy layer acts as a diffusion barrier that prevents Zn from the lead-free solder from penetrating into the Ni plating layer, thereby eliminating the harmful effect of Zn diffusion and void formation while maintaining the benefits of lead-free soldering
Solution Approach 2:
The external electrode is constructed as a composite multi-layer structure consisting of an underlying electrode layer, a Cu-rich alloy layer, a Ni plating layer, and a Ni oxide layer. This composite structure combines the advantages of each layer: the underlying electrode provides conductivity, the alloy layer prevents Zn diffusion, the Ni plating layer maintains solderability, and the Ni oxide layer provides protection
2Reliability
If Ni plating layer with fine particles is used, then solderability is improved, but Zn diffusion into Ni plating layer is facilitated causing reliability reduction
Solution Approach 1:
The Cu-rich alloy layer serves as a mediator that blocks Zn diffusion pathways to the Ni plating layer. By placing this intermediary layer between the solder joint and the Ni plating, the system achieves both goals: the Ni plating layer can maintain fine particle structure for good solderability while the alloy layer prevents Zn from reaching and degrading the Ni structure
Solution Approach 2:
Different layers are assigned different local qualities and functions: the alloy layer is designed with high Cu content to act as a Zn diffusion barrier, while the Ni plating layer maintains fine particle characteristics for optimal solderability. Each layer performs its specific function locally without compromising the other
3Reliability
If Ni oxide layer with larger thickness is used, then protection against Zn diffusion is improved, but solderability and circuit continuity are reduced
Solution Approach 1:
The thickness of the Ni oxide layer is precisely controlled within the range of 1 nm to 150 nm. This parameter optimization ensures that the layer is thick enough to provide protection against Zn diffusion and environmental corrosion, while remaining thin enough to maintain good solderability and electrical conductivity for circuit continuity
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 reliability and solderability of electronic components by preventing Zn diffusion and water penetration, maintaining insulation resistance even under high-temperature and high-humidity conditions, and ensuring continuous circuit function without cracking.
Implementation Method 1
the Ni plating layer having an average particle size of Ni particles of about 2 μm or more
Implementation Method 2
formed through heat treatment in a reducing atmosphere
Data Source
AI summary
A high-reliability electronic component without reduction in insulation resistance under high-temperature and high-humidity conditions has satisfactory solderability of external electrodes. The electronic component includes a main body and external electrodes disposed on surfaces of the main body, the external electrodes include underlying electrode layers each containing a metal, alloy layers each disposed on the corresponding underlying electrode layer, Ni plating layers each disposed on the corresponding alloy layer, Ni oxide layers each disposed on the corresponding Ni plating layers, and upper plating layers each disposed on the corresponding Ni oxide layer, each Ni oxide layer having a thickness of about 150 nm or less, and each Ni plating layer having an average particle size of Ni particles of about 2 μm or more. To form the Ni plating layers having reduced grain boundaries, heat treatment is performed at about 500° C. to about 900° C. inclusive in a reducing atmosphere having an oxygen concentration of about 100 ppm or less.