Sulfuration-Resistant Chip Resistor Nickel Plated Layer
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Solution Overview
Problem
Chip resistors made with silver-based cermets are susceptible to sulfuration, leading to open circuits due to poor adhesion of protective layers and ambient air penetration, which is problematic in automotive and industrial applications, and existing solutions either increase thickness or compromise conductivity.
Innovation Solution
A chip resistor design where a nickel plated layer is used to seal silver terminal electrodes by activating the edges of an external non-conductive protective coating for better adhesion and platability, eliminating the need for additional protective layers and maintaining conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver-based cermets are used for terminal electrodes, then high electrical conductivity and oxidation immunity are achieved, but susceptibility to sulfuration increases leading to open circuits
Solution Approach 1:
A nickel intermediate layer is introduced between the silver-based terminal electrode and the external protective coating. This nickel layer serves as a mediator that provides both sulfur proofing and good adhesion to the protective coating, while maintaining electrical conductivity. The nickel layer prevents direct contact between sulfur compounds and silver, eliminating sulfuration while preserving the electrical properties of the silver electrode.
Solution Approach 2:
The terminal electrode structure is transformed into a composite system consisting of multiple layers: silver-based cermet terminal electrode, nickel intermediate layer, and external protective coating. This composite structure combines the advantages of each material - silver provides high conductivity, nickel provides sulfur resistance and adhesion, and the protective coating provides environmental barrier.
2Reliability
If additional protective layers are added to seal terminal electrodes, then sulfuration resistance is improved, but resistor thickness increases
Solution Approach 1:
The nickel layer is positioned to serve multiple functions simultaneously: it acts as an adhesion promoter for the protective coating, provides sulfur proofing for the silver electrode, and maintains electrical conductivity. By merging these functions into a single layer rather than adding separate layers for each function, the overall thickness increase is minimized while achieving comprehensive protection.
3Reliability
If non-metal protective coating is applied over silver electrodes, then oxidation protection is achieved, but adhesion to plated metal layers deteriorates allowing air penetration
Solution Approach 1:
The nickel layer serves as an intermediate layer between the non-metal protective coating and the plated metal layers. This intermediate nickel layer provides excellent adhesion to both the organic protective coating and the metal plated layers, creating a strong bond that prevents air penetration while maintaining the oxidation protection benefits of the non-metal coating.
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 effectively prevents sulfuration without increasing the chip resistor's thickness, ensuring good platability and conductivity, and is applicable to all sizes, including small resistors, by using a nickel plated layer to seal silver electrodes from the ambient atmosphere.
Implementation Method 1
a plated layer of nickel 17 that covers face sides of the substrate, the top and bottom electrodes, and overlapping partially external protective coating 16
Implementation Method 2
metallizing edges of the external protective coating by sputtering
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A chip resistor includes an insulating substrate 11, top terminal electrodes 12 formed on top surface of the substrate using silver-based cermet, bottom electrodes 13, resistive element 14 that is situated between the top terminal electrodes 12 and overlaps them partially, an optional internal protective coating 15 that covers resistive element 14 completely or partially, an external protective coating 16 that covers completely the internal protection coating 15 and partially covers top terminal electrodes 12, a plated layer of nickel 17 that covers face sides of the substrate, top 12 and bottom 13 electrodes, and overlaps partially external protective coating 16, finishing plated layer 18 that covers nickel layer 17. The overlap of nickel layer 17 and external protective layer 16 possesses a sealing property because of metallization of the edges of external protective layer 16 prior to the nickel plating process.