MLCC External Electrode Structure for Moisture-Resistant Soldering
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Solution Overview
Problem
Conventional multilayer ceramic capacitors face issues with moisture infiltration during the formation of plating layers on external electrodes, leading to degraded insulation resistance.
Innovation Solution
The proposed multilayer ceramic capacitors feature external electrodes with a C-shape structure, where Sn is concentrated in a second region, occupying at least 90% of the area, to prevent moisture infiltration and enhance solder wettability, allowing for the use of the capacitors without additional plating layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plating layer is formed on the external electrode, then solder wettability is improved, but moisture infiltrates into the capacitive body through the external electrode, degrading insulation resistance
Solution Approach 1:
The external electrode is designed with a non-uniform Sn concentration distribution: a first region with low Sn concentration (area ratio < 90%) and a second region with high Sn concentration (area ratio ≥ 90%). This local quality variation allows the electrode to exhibit different properties in different regions, preventing moisture infiltration while maintaining solder wettability.
Solution Approach 2:
The external electrode is constructed as a composite material system containing both Ni and Sn particles with specific weight ratios (Ni: 85-99 wt%, Sn: 1-15 wt%). This composite structure combines the corrosion resistance of Ni with the solder wettability of Sn, while the specific composition prevents moisture infiltration.
2Ease of operation
If additional plating layers are applied to enhance solder wettability, then bonding capability is improved, but manufacturing complexity and process time increase
Solution Approach 1:
The external electrode with optimized Ni-Sn composition and C-shape structure serves multiple functions simultaneously: it provides solder wettability, prevents moisture infiltration, and eliminates the need for additional plating layers. This multi-functionality simplifies the manufacturing process and improves productivity.
Solution Approach 2:
The desired Sn concentration distribution and protective characteristics are built into the external electrode during the initial firing process, rather than requiring subsequent plating operations. This preliminary action eliminates additional manufacturing steps and reduces process time.
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 design effectively prevents moisture from entering the capacitive body, maintains high insulation resistance, and allows for direct bonding to mounting electrodes using reflow solder, improving manufacturing productivity.
Implementation Method 1
Sn is concentrated in the second region, and when a square measurement region of about 10 μm× about 10 μm is selected from the second region in the section, an area of Sn is greater than or equal to about 90% with respect to a total of an area of Ni and the area of Sn in the measurement region
Implementation Method 2
the infiltration of the moisture into ceramic element body 103 (capacitive body) is prevented
Data Source
AI summary
A multilayer ceramic capacitor includes ceramic layers, internal electrodes, opposed principal surfaces, opposed end surfaces, and opposed side surfaces, and external electrodes on a surface of the capacitive body. The external electrodes include Ni and Sn, and have a C-shape on the end surface of the capacitive body and the principal surfaces when a section parallel to the side surfaces is viewed, the C-shape external electrodes include a first region and a second region completely surrounding the first region, an area of Sn is greater than or equal to about 90% with respect to a total of an area of Ni and the area of Sn, and in the first region, the area of Sn is less than about 90% with respect to the total of the area of Ni and the area of Sn appearing in a measurement region.