Chip Resistor with Exposed Electrodes for Low TCR
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Solution Overview
Problem
Conventional chip resistors have a high temperature coefficient of resistance (TCR) due to the diffusion of CuNi in the resistive element into the upper-surface electrodes and protective layer, leading to increased resistance and reduced performance.
Innovation Solution
The design includes exposed upper surfaces and edge surfaces of the upper-surface electrodes, with a protective layer that does not cover the electrodes, allowing electric current to flow through the shortest path and reducing the TCR by minimizing the contact area with the resistive element, and additional plating layers for improved adhesiveness and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the protective layer covers the upper-surface electrodes, then the resistive element is fully protected, but the temperature coefficient of resistance increases due to diffusion
Solution Approach 1:
The protective layer is selectively applied only to portions of the resistive element that are not covered by electrodes, creating different protective states in different regions. This local differentiation allows the resistive element to be protected where needed while preventing diffusion at electrode interfaces, thereby resolving the contradiction between protection and TCR control.
Solution Approach 2:
The protective layer coverage is segmented into two distinct regions: covered portions (under electrodes) and uncovered portions (exposed resistive element). This segmentation prevents uniform diffusion across the entire resistive element, allowing the electrode interfaces to remain free from diffusion-induced resistance changes while other areas receive protective coverage.
2Reliability
If the upper-surface electrodes are fully covered by protective layer, then better protection is achieved, but electric current path is lengthened and TCR increases
Solution Approach 1:
The protective layer is extracted or removed from the regions where electrodes contact the resistive element, creating exposed areas that allow direct electrical contact. This extraction ensures that electric current can flow through the shortest possible path from electrode to resistive element without being obstructed by the protective layer, thereby maintaining high current flow efficiency while the protective layer still provides protection to other exposed areas.
3Strength
If plating layers are added to side surface electrodes, then adhesiveness and heat dissipation are improved, but device complexity increases
Solution Approach 1:
Plating layers are applied to the side surface electrodes to create a composite structure combining different materials with complementary properties. The plating layers provide enhanced adhesiveness to the substrate and improved heat dissipation capabilities, while the multi-layer composite structure manages the complexity through functional differentiation of each layer.
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 reduces the TCR, enhances the productivity of chip resistor manufacturing, and increases the rated electric power by optimizing the flow of electric current and heat dissipation.
Implementation Method 1
the diffusion of CuNi in the resistive element into the upper-surface electrodes and protective layer
Data Source
AI summary
A chip resistor includes an insulating substrate, a resistive element provided on an upper surface of the insulating substrate, a pair of upper-surface electrodes provided on respective ones of both end portions of an upper surface of the resistive element so as to expose a part of the upper surface of the resistive element from the upper-surface electrodes, and a protective layer that covers the part of the resistive element and that does not cover the pair of upper-surface electrodes. The pair of upper-surface electrodes have exposed upper surfaces and exposed edge surfaces, respectively. Each of the edge surfaces of the pair of upper-surface electrodes does not project outward from respective one of the edge surfaces of the insulating substrate. The chip resistor can reduce a temperature coefficient of resistance to improve the temperature coefficient of resistance.