Ni-Barrier Silver Sintering Paste for Above-Melting Processing
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Solution Overview
Problem
Silver paste is not suitable for sintering operations requiring temperatures above its melting point (~968.1°C), limiting its application in processes like multi-layer varistor manufacturing where zinc oxide substrates need sintering at temperatures exceeding 1000°C.
Innovation Solution
A modified silver paste is developed by incorporating nickel particles or silver-coated nickel particles and/or glass frits/silver-coated silica additives to increase the melting point and form a protective barrier, allowing sintering at higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If pure silver paste is used for sintering, then excellent electrical conductivity and adhesion are achieved, but sintering temperature is limited to below the melting point of silver (~968.1°C)
Solution Approach 1:
The patent creates a composite paste system combining silver particles with nickel particles or nickel-coated silver particles, along with glass frit additives. This composite structure allows the paste to withstand sintering temperatures above 1000°C while maintaining adhesion and forming reliable conductive pathways, resolving the contradiction between temperature capability and material stability.
Solution Approach 2:
The patent modifies the paste composition by incorporating nickel particles (10-50% of total particles) with higher melting point, and adjusting silver particle content (50-90%). This parameter change in material composition enables the paste to maintain structural integrity at temperatures exceeding silver's melting point while preserving electrical conductivity.
2Temperature
If nickel particles are added to increase melting point, then sintering temperature capability is improved, but paste complexity increases
Solution Approach 1:
The patent applies local quality by coating nickel particles with silver (silver-coated nickel) rather than using pure nickel. This creates a localized structure where the nickel core provides high-temperature stability while the silver coating maintains electrical conductivity and surface properties, reducing the negative impact of composition complexity.
Solution Approach 2:
The nickel particles serve multiple functions: they raise the melting point for high-temperature sintering, act as a diffusion barrier to prevent substrate contamination, and when coated with silver, maintain electrical conductivity. This multi-functionality justifies the added compositional complexity.
3Object-affected harmful factors
If glass frits are used to create protective layer, then substrate diffusion is prevented, but manufacturing complexity increases
Solution Approach 1:
The patent introduces glass frit as an intermediary material that forms a protective barrier layer between the silver paste and the substrate during high-temperature sintering. This intermediary layer prevents direct diffusion and contamination while allowing the paste to be applied using standard screen printing techniques, minimizing manufacturing complexity.
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 modified silver paste enables sintering at temperatures above the melting point of silver, maintaining adhesion to substrates and preventing substrate diffusion, thus enabling reliable conductive pathways and contacts.
Implementation Method 1
metals, such as Nickel, that have a high melting temperature, can be used for alloying to the silver particles to increase the melting point of the silver paste
Implementation Method 2
In a second embodiment, additives such as glass frits or silver-coated fused silica may be used to create a protective layer disposed between the substrate and the silver paste to prevent diffusion of the silver onto the substrate
Implementation Method 3
a conductive paste according to the first illustrative example, wherein the conductive paste is disposed on the substrate forming electrically conductive pathways
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Disclosed herein is a novel enhanced silver-based paste using an alloying method to increase the melting temperature of the paste particles. In various embodiments, silver-coated Nickel particles, silver-coated silica particles or glass frits may be added to the silver paste in various concentrations to form an enhanced paste that performs when sintered at temperatures in excess of the melting temperature of the silver particles.