Lead-Free Thick Film Resistor Composition for Stable Resistance
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Solution Overview
Problem
Conventional thick film resistors struggle to achieve stable resistance values and low temperature coefficient of resistance (TCR) in high resistance ranges without using lead-based glass, which is toxic and environmentally undesirable, leading to issues with resistor shape and electrical characteristics.
Innovation Solution
A thick film resistor composed of ruthenium dioxide conductive particles and a lead-free glass frit, fired at 600° C. to 900° C., with a specific glass composition and particle size distribution to maintain resistance values between 100Ω/□ and 10 MΩ/□ and TCR within ±100 ppm/° C., forming a stable conductive network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lead oxide-containing glass is used to achieve low softening point and superior wettability, then fluidity and adhesiveness are improved, but toxicity and environmental harm increase
Solution Approach 1:
The patent changes the chemical composition parameters of the glass from lead oxide-containing to lead-free by incorporating specific ratios of bismuth oxide (0.1-5.0 wt%), barium oxide (1.0-10.0 wt%), and zinc oxide (1.0-10.0 wt%). This parameter change maintains the necessary softening point and wettability characteristics while eliminating the toxic lead component, thus resolving the contradiction between ease of manufacture and environmental harm.
Solution Approach 2:
The patent creates a composite glass material system combining multiple metal oxides (bismuth oxide, barium oxide, zinc oxide, silica, etc.) to achieve the desired properties. This composite approach allows the glass to exhibit both low softening point and good wettability without relying on toxic lead oxide, thereby resolving the contradiction between manufacturing ease and environmental safety.
2Ease of manufacture
If lead component is used to achieve good wettability to alumina, then adhesiveness is improved, but excessive spreading and shape distortion occur
Solution Approach 1:
The patent adjusts the glass composition parameters by replacing lead oxide with a controlled combination of bismuth oxide, barium oxide, and zinc oxide. This parameter change modifies the surface tension and wetting characteristics of the glass, providing adequate adhesiveness to alumina substrates while preventing excessive spreading, thus maintaining proper resistor shape.
Solution Approach 2:
The lead-free glass composition acts as an intermediary material that mediates between the alumina substrate and the conductive component. By carefully selecting the glass composition (with specific ratios of metal oxides), the patent achieves balanced wettability that ensures good adhesiveness without causing the glass to excessively spread and distort the resistor shape.
3Manufacturing precision
If ruthenium composite oxides are used in high resistance range to achieve higher resistivity, then resistance value stability is improved, but decomposition to ruthenium dioxide occurs during firing
Solution Approach 1:
The lead-free glass composition acts as a protective intermediary environment during firing. The specific glass matrix (containing bismuth oxide, barium oxide, zinc oxide, and silica) creates a chemical environment that suppresses the decomposition of ruthenium composite oxides to ruthenium dioxide, thereby maintaining resistance value stability while ensuring compositional stability during the firing process.
Solution Approach 2:
The patent uses a composite material system where the lead-free glass matrix (comprising multiple metal oxides) works synergistically with the ruthenium composite oxide conductive component. This composite structure provides both the high resistivity needed for stable resistance values and the chemical stability required to prevent decomposition during firing at temperatures of 600-900°C.
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 provides resistors with stable resistance values and low TCR in high resistance ranges, reducing dependency on firing conditions and improving current noise characteristics, while being environmentally friendly by eliminating lead.
Implementation Method 1
a glass component that is essentially free of a lead component... a fired product of a resistive composition
Implementation Method 2
fired at 600° C. to 900° C.
Data Source
AI summary
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 thick film resistor is formed of a fired product of a resistive composition, wherein the thick film resistor contains ruthenium-based conductive particles containing ruthenium dioxide and a glass component essentially free of a lead component and has a resistance value in the range of 100 Ω/□ to 10 MΩ/□ and a temperature coefficient of resistance within ±100 ppm/° C.