Multilayer Varistor Sintering With Staged Oxygen Control
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Solution Overview
Problem
Multilayer varistors manufactured using the sintered compact formed by baking under a nitrogen atmosphere exhibit significant dispersion in varistor characteristics and insufficient voltage nonlinearity.
Innovation Solution
A method for manufacturing multilayer varistors involving the steps of forming a multilayer stack with green sheet layers and internal electrode paste layers, and then baking the stack in an atmosphere with controlled oxygen concentrations: initially at 1000 ppm or less from 500°C to 800°C, and subsequently at 1000 ppm or more to the maximum allowable temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If baking is performed under a nitrogen atmosphere, then the manufacturing process is simplified, but the varistor characteristics show significant dispersion and voltage nonlinearity is insufficient
Solution Approach 1:
The patent applies parameter changes by controlling the oxygen concentration in the baking atmosphere at specific levels (1000 ppm or less during initial heating, then 1000 ppm or more during final sintering) rather than using a simple nitrogen atmosphere. This precise control of atmospheric composition parameters resolves the contradiction by achieving both manufacturing feasibility and high precision in varistor characteristics.
2Ease of manufacture
If baking is performed under a nitrogen atmosphere, then the manufacturing process is simplified, but voltage nonlinearity is insufficient
Solution Approach 1:
The patent changes the atmospheric parameter from a reducing nitrogen atmosphere to an oxidizing atmosphere with controlled oxygen concentration (1000 ppm or more during final sintering). This parameter change enables the formation of proper grain boundary phases that provide excellent voltage nonlinearity while maintaining manufacturing feasibility through a controlled baking process.
3Manufacturing precision
If oxygen concentration is controlled during baking, then varistor characteristics precision is improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent segments the baking process into distinct stages with different oxygen concentration requirements: initial heating stage (1000 ppm or less) and final sintering stage (1000 ppm or more). This segmentation allows precise control of varistor characteristics while managing process complexity through clear, staged procedures rather than continuous complex control.
Solution Approach 2:
The patent employs parameter changes by adjusting oxygen concentration at different stages of the baking process. This systematic parameter control achieves high manufacturing precision in varistor characteristics while keeping the process complexity manageable through defined parameter transitions rather than continuous complex adjustments.
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 method significantly reduces the dispersion in varistor characteristics and achieves excellent voltage nonlinearity by controlling the oxygen concentration during the baking process.
Implementation Method 1
forming a sintered compact including an internal electrode inside by baking the multilayer stack
Implementation Method 2
baking the multilayer stack by setting an oxygen concentration in an atmosphere at 1000 ppm by volume or less while increasing a temperature from 500° C. to 800° C.
Data Source
AI summary
A method for manufacturing a multilayer varistor includes: a first step including providing a multilayer stack in which a plurality of green sheet layers, each containing a Zn oxide powder as a main component and a Pr oxide powder as a sub-component, and a plurality of internal electrode paste layers, each containing a Pd powder, are alternately stacked; and a second step including forming a sintered compact, including an internal electrode inside, by baking the multilayer stack. The second step includes: a first sub-step including baking the multilayer stack by setting an oxygen concentration in an atmosphere at 1000 ppm by volume or less while increasing a temperature from 500° C. to 800° C.; and a second sub-step including baking, after the first sub-step, the multilayer stack by setting the oxygen concentration in the atmosphere at 1000 ppm by volume or more while increasing the temperature to a maximum allowable temperature.