Nano-Silver Paste Fabrication for High-Strength Copper Bonding
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Solution Overview
Problem
Commercially available silver pastes lack sufficient bonding strength for joining copper to copper, requiring additional resin or lower conductivity, which is inadequate for high-intensity applications in micro-junctions and micro-electromechanical systems (MEMS).
Innovation Solution
A method of fabricating a nano-silver paste by reducing silver nanoparticles using silver nitrate and employing a silver precursor, such as 2-ethylhexanoic acid, to enhance bonding strength, involving chemical reduction and hot-pressing at 250°C under 10 MPa pressure to achieve a copper/silver/copper structure with improved interface intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If commercially available silver paste is used for joining copper to copper, then conductivity is maintained, but bonding strength is insufficient
Solution Approach 1:
The patent changes the chemical composition parameters of the silver paste by incorporating silver nanoparticles (0.1-10 μm) and silver precursor particles (1-10 μm) in specific ratios. The silver precursor particles convert during firing to additional silver, creating a dual-component system that enhances both bonding strength and electrical conductivity simultaneously, resolving the contradiction between strength and reliability
Solution Approach 2:
The patent creates a composite material system combining silver nanoparticles and silver precursor particles (such as silver acetate, silver formate, or silver oxalate) with organic vehicle. This composite structure provides synergistic effects where nanoparticles contribute to conductivity and precursor particles enhance bonding strength through controlled conversion during firing, achieving both high strength and reliability
2Strength
If additional resin is added to increase bonding strength, then intensity improves, but conductivity decreases
Solution Approach 1:
The patent extracts the harmful effect of excessive resin by limiting organic vehicle content to 1-20 wt% and replacing functional resin with silver precursor particles. The precursor particles provide bonding enhancement without the insulating properties of resin, maintaining electrical conductivity while achieving required bonding strength
Solution Approach 2:
The patent changes the composition parameters by using silver precursor particles (1-10 μm) as the primary bonding-enhancing component instead of resin. The precursor particles convert to metallic silver during firing, providing both mechanical strength and electrical conductivity, thus resolving the trade-off between strength and conductivity
3Temperature
If silver nanoparticles are used to reduce melting point for low-temperature sintering, then sintering temperature decreases, but bonding strength is insufficient
Solution Approach 1:
The patent merges silver nanoparticles (for low-temperature sintering capability) with silver precursor particles (for bonding strength enhancement) in a dual-component system. The nanoparticles enable sintering at 700-900°C while the precursor particles contribute to bonding strength through their conversion process and particle-size-dependent mechanical properties, achieving both low-temperature processing and high bonding strength
Solution Approach 2:
The patent changes the particle size distribution parameters by combining two distinct size ranges: nanoparticles (0.1-10 μm) for melting point reduction and precursor particles (1-10 μm) for strength enhancement. This bimodal size distribution optimizes both sintering temperature and bonding strength, resolving the contradiction between processing temperature and mechanical 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 nano-silver paste achieves a resistance of (3.09±0.61)×10−5 Ω·cm and a copper/silver/copper junction intensity of 36 MPa, significantly surpassing commercial pastes, ensuring reliable bonding and reduced signal delay and heat dissipation.
Implementation Method 1
silver nitrate is used as a silver ion source to reduce the silver nanoparticles through a chemical reduction
Implementation Method 2
hot-press the nano-silver paste at 250 celsius degrees (° C.) for cracking organic components contained inside with pure silver left
Implementation Method 3
the silver nanoparticles can be sintered at a low temperature to form a dense sintered bulk for reducing the surface energy
Implementation Method 4
an organic acid is used as a protective agent to protect a surface of the silver nanoparticles
Data Source
AI summary
A method is provided to make a nano-silver paste. An organic acid is used as a protective agent. Silver nitrate is used as a source of silver ions to reduce silver nanoparticles on a surface protected by the organic acid. The particle size of the silver nanoparticle is 45 nanometers. In the other hand, a silver precursor of organic metal is synthesized. The organic metal is cracked at 200 celsius degrees (° C.) to fill pores left during sintering. After mixing the silver nanoparticle, the silver precursor and the solvent, the nano-silver paste is obtained. After being heated at 250° C. for 30 minutes, the nano-silver paste has a resistance of (3.09±0.61)×10−5 Ω·cm. By being heated at 250° C. and applied with a pressure of 10 MPa to be hot-pressed for 30 minutes for joining copper to copper, the nano-silver paste obtains a bonding strength reaching 36 MPa.