Lead-Free Resistive Composition for Stable Thick Film Resistors
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Solution Overview
Problem
Existing resistive compositions struggle to form thick film resistors without lead components, particularly in high resistance ranges, due to decomposition of ruthenium composite oxides and difficulties in maintaining a stable conductive network, leading to inferior resistance and current noise characteristics.
Innovation Solution
A resistive composition comprising ruthenium dioxide conductive particles and a lead-free glass frit, with specific glass composition and additives, forms a stable conductive network, achieving resistance values and TCR characteristics comparable to lead-containing resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead oxide-containing glass is used to achieve favorable fluidity, wettability, and adhesiveness, then the forming characteristics of thick film resistor are improved, but toxicity and environmental pollution increase
Solution Approach 1:
The invention extracts and removes the harmful lead oxide component from the glass composition while retaining the essential functional characteristics. The lead-free glass composition uses alternative oxides (B2O3, SiO2, Al2O3, CaO, ZnO, MgO) to achieve the same fluidity, wettability, and adhesiveness properties without the toxic effects of lead oxide.
Solution Approach 2:
The invention employs a composite glass composition made from multiple oxide components that work synergistically to replace lead oxide. The specific combination of B2O3 (20-40 mol%), SiO2 (30-50 mol%), Al2O3 (5-15 mol%), CaO (5-15 mol%), ZnO (5-15 mol%), and MgO (5-15 mol%) creates a composite material that matches the functional properties of lead oxide-containing glass without the harmful effects.
2Reliability
If lead component is used to achieve good wettability to alumina substrate, then adhesiveness is improved, but excessive spreading and shape distortion occur
Solution Approach 1:
The invention removes the lead component responsible for excessive wettability while preserving adequate adhesiveness through the lead-free glass composition. The alternative oxide combination provides controlled wettability that prevents both poor adhesion and excessive spreading.
Solution Approach 2:
The invention changes the chemical composition parameters of the glass by replacing lead oxide with a multi-component oxide system. This parameter change modifies the wettability characteristics to achieve optimal balance between adhesiveness and shape control during the firing process.
3Reliability
If ruthenium composite oxides are used in high resistance range to achieve higher resistivity, then resistance value is improved, but decomposition to ruthenium dioxide occurs at high temperature
Solution Approach 1:
The invention uses a composite conductive system combining ruthenium dioxide with other metal oxides (IrO2, PtO2, RhO2, PdO2, OsO2, RuO3, Ru2O3, Ru3O4). This composite structure provides high resistivity while enhancing thermal stability and preventing decomposition during the firing process.
Solution Approach 2:
The lead-free glass composition acts as an intermediary medium that stabilizes the ruthenium-based conductive particles during high-temperature firing. The glass matrix protects the conductive oxides from decomposing into less stable forms while maintaining the desired high resistance characteristics.
4Object-affected harmful factors
If lead-free glass is used to eliminate toxicity, then environmental compatibility is improved, but decomposition of conductive component and instability of conductive network occur
Solution Approach 1:
The invention employs a composite glass composition with multiple stabilizing oxides that work together to maintain conductive network stability without lead. The combination of B2O3, SiO2, Al2O3, CaO, ZnO, and MgO creates a chemically stable matrix that prevents decomposition of ruthenium-based conductors during firing.
Solution Approach 2:
The invention optimizes the compositional parameters of the lead-free glass to achieve appropriate melting temperature, viscosity, and chemical stability. The specific oxide ratios are tuned to ensure the glass remains stable at firing temperatures while maintaining the conductive network integrity of the thick film resistor.
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 composition enables the formation of stable, high-resistance resistors with improved current noise and process stability, free from lead-related toxicity, and maintains uniformity across a wide resistance range.
Implementation Method 1
The resistive composition is printed on an alumina substrate and then fired at a high temperature of 600°C to 900°C
Implementation Method 2
having favorable fluidity, wettability with the conductive component, superior adhesiveness to a substrate
Implementation Method 3
fired at a high temperature of 600°C to 900°C
Data Source
Figure 1A~1B
Figure 1C
AI summary
An object of the present invention is to provide a resistive composition that can form a thick film resistor excluding a toxic lead component from a conductive component and glass and having characteristics equivalent to or superior to conventional resistors in terms of, in a wide resistance range, resistance values, TCR characteristics, current noise characteristics, withstand voltage characteristics and the like. The resistive composition of the present invention includes: ruthenium-based conductive particles including ruthenium dioxide; a glass frit that is essentially free of a lead component; and an organic vehicle, wherein the glass frit is a glass frit which is constituted such that in a case where a fired product of a mixture of the glass frit and the ruthenium dioxide has in a range of 1 kΩ/□ to 1 MΩ/□, the fired product exhibits a temperature coefficient of resistance in a plus range.