Ohmic Silver Paste Composition for High-Temperature Varistor Welding
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Solution Overview
Problem
Existing strontium titanate ring varistors face challenges in achieving high-temperature resistance welding while maintaining good ohmic contact and resistivity, leading to issues like electrode burning and poor welding performance, which are not adequately addressed by prior art methods.
Innovation Solution
A bottom ohmic silver paste containing doped tin dioxide SnO2 micro powder, glass powder, organic solvent, and organic binder is used, sintered at 800-860°C, forming a stable ohmic contact and enabling efficient laser and high-frequency welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reductive metal powder (zinc, aluminum, nickel) is added to silver paste to form ohmic contact, then ohmic contact characteristics are improved, but sintering temperature must be limited to 550-620°C to prevent oxidation of reductive metals
Solution Approach 1:
The invention changes the chemical composition parameters of the silver paste by replacing reductive metals (Zn, Al, Ni) with tin powder and specific glass powder formulations. This parameter change allows the sintering temperature to be increased from 550-620°C to 800-860°C while maintaining ohmic contact characteristics, as tin and the specialized glass powder remain stable at higher temperatures without oxidizing like the previous reductive metals
Solution Approach 2:
The invention creates a composite silver paste material consisting of silver powder, tin powder, and specifically formulated glass powder (containing SiO2, B2O3, Al2O3, and other oxides). This composite material combines the electrical conductivity of silver with the high-temperature stability of tin and the protective/melting properties of the glass matrix, enabling both ohmic contact and high-temperature sintering capability simultaneously
2Ease of manufacture
If sintering temperature is increased to form dense silver layer for welding, then welding performance is improved, but reductive metal in ohmic silver paste oxidizes and loses ohmic characteristics
Solution Approach 1:
The invention changes the chemical composition parameters by substituting oxidation-prone reductive metals with oxidation-resistant tin powder and stable glass powder. This allows the sintering temperature to be raised to 800-860°C to form a dense, weldable silver layer while the tin and glass components remain stable and prevent degradation of ohmic characteristics during high-temperature processing
Solution Approach 2:
The glass powder acts as an intermediary material that melts during sintering to facilitate the formation of a dense silver layer and strong adhesion to the substrate, while tin powder serves as an intermediary that enables high-temperature processing without oxidation. These intermediary materials mediate between the requirement for high-temperature sintering and the need to preserve ohmic characteristics
3Ease of manufacture
If multi-layer silver paste is printed to increase silver layer thickness for welding, then welding performance is improved, but production cost and material cost increase
Solution Approach 1:
The invention changes the compositional parameters of the silver paste to include tin powder and specialized glass powder that enable single-layer printing to achieve both ohmic contact and sufficient thickness for welding. This eliminates the need for multi-layer printing processes, reducing production steps, material consumption, and overall cost while maintaining welding performance
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 ensures stable ohmic contact, improves welding performance, reduces production costs, and enhances the non-linear volt-ampere characteristics of strontium titanate ring varistors, meeting modern welding requirements.
Implementation Method 1
the sintering temperature of the strontium titanate ring varistor electrode can only be controlled in the range of 550° C.-620° C.
Implementation Method 2
After high temperature oxidation treatment, the surface of strontium titanate ceramics has an oxygen adsorption layer
Implementation Method 3
the sintering temperature of the strontium titanate ring varistor electrode can only be controlled in the range of 550° C.-620° C.
Implementation Method 4
After screen printing and electrode sintering, a semiconductor ceramic sensor with both nonlinear volt-ampere characteristics and capacitive characteristics is finally fabricated
Implementation Method 5
glass powder, organic binder, and grinding
Data Source
AI summary
The present invention provides a bottom ohmic silver paste for strontium titanate ring varistor including silver powder, doped SnO2 micro powder, glass powder, organic solvent and organic binder, and the mass ratio of the silver powder, the doped SnO2 micro powder, the glass powder, the organic solvent and the organic binder is 65-85:0.9-4.3:0.5-5:10-20:10-15. The present invention also provides a preparation method and use of the bottom ohmic silver paste for strontium titanate ring varistor of the present invention.