Composite Nanometal Paste for Low-Temperature Electronic Bonding
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Solution Overview
Problem
Conventional nanometal pastes with silver nanoparticles of 200 nm diameter exhibit lower electrical and thermal conductivities compared to lead high content solders, due to particle aggregation and large gaps in the bonding metal layer, necessitating the development of composite metal nanoparticles with improved dispersion and lower metalization temperatures.
Innovation Solution
A composite nanometal paste comprising composite metal nanoparticles with an organic coating layer and metal filler particles, where the particle diameters are optimized to fill gaps and sinter compactly, achieving high electrical and thermal conductivities, and a metalization temperature of less than 200°C, using alcohol-originating organic coating layers that decompose at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nanometal paste with 200 nm silver nanoparticles is used, then the paste can be applied for bonding, but the electrical and thermal conductivities are lower compared to lead high content solders due to particle aggregation and large gaps
Solution Approach 1:
The patent segments the bonding metal layer into two distinct particle size components: composite metal nanoparticles (1-100 nm) that fill gaps between larger metal filler particles (1-10 μm). This segmentation allows small particles to occupy interstices and large particles to provide structural framework, eliminating aggregation issues and maximizing packing density for superior electrical and thermal conductivities.
Solution Approach 2:
The patent applies local quality by assigning different functions to different particle sizes: ultrafine composite metal nanoparticles (1-100 nm) with organic coating layers are used specifically for gap-filling and forming continuous conductive networks in regions where complete metal contact is critical, while larger metal filler particles (1-10 μm) provide mechanical strength and overall structural integrity to the bonding layer.
2Length of moving object
If silver nanoparticles are used to achieve fine particle size, then the particle diameter is reduced, but the particles aggregate easily and form large lump-like particles
Solution Approach 1:
The patent introduces organic coating layers as intermediary substances on the surface of composite metal nanoparticles (1-100 nm). These organic coatings act as steric barriers that prevent direct metal-to-metal contact between nanoparticles, eliminating van der Waals attraction and preventing aggregation. The organic layers provide repulsive forces that maintain monodispersity and stable distribution of ultrafine particles in the paste formulation.
Solution Approach 2:
The patent creates composite metal nanoparticles consisting of a metal core (1-100 nm) surrounded by an organic coating layer. This composite structure combines the beneficial electrical and thermal conductivity of metal nanoparticles with the dispersion stability and anti-aggregation properties of organic materials, achieving both fine particle size and long-term monodispersity in the paste.
3Temperature
If conventional substitute solder (Sn/Ag/Cu) is used to replace Pb-free solder, then the melting point increases to 219°C, but this causes damage to the resin substrate due to low heat resistance
Solution Approach 1:
The patent fundamentally changes the metalization temperature parameter from conventional soldering temperatures (219°C for Sn/Ag/Cu) to ultra-low temperature processing (below 200°C, preferably 150-180°C) enabled by the organic coating layer decomposition. This parameter change allows bonding without exceeding the heat resistance limit of resin substrates, eliminating thermal damage while achieving reliable electrical and thermal conductivities.
Solution Approach 2:
The patent utilizes the phase transition (decomposition) of organic coating layers at controlled temperatures as the driving mechanism for metalization. The organic coatings decompose and volatilize at temperatures below 200°C, leaving behind sintered metal particle structures that form conductive pathways. This phase transition approach enables low-temperature bonding that is compatible with heat-sensitive resin substrates.
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 composite nanometal paste forms a compact metal layer with high electrical and thermal conductivities, surpassing conventional lead high content solders, and meets environmental standards with a low metalization temperature, suitable for electronic component bonding.
Implementation Method 1
a paste layer is formed between a lower body and an upper body by the composite nanometal paste, and the lower body and the upper body are bonded by sintering the paste layer into a metal layer by application of heat
Implementation Method 2
metalization temperature of less than 200°C, using alcohol-originating organic coating layers that decompose at low temperatures
Implementation Method 3
the lower body and the upper body are bonded by sintering the paste layer into a metal layer by application of heat
Implementation Method 4
using alcohol-originating organic coating layers that decompose at low temperatures
Data Source
AI summary
Provided is a composite nanometal paste, whose layer, when sintered in an inert gas under no load, gives a metal layer that is equal or superior in electrical conductivity and thermal conductivity to conventional lead-rich solders. The composite nanometal paste contains, as metal components, composite metal nanoparticles comprising metal cores with an average particle diameter of d (nm) and an organic coating layer formed around the circumference, and metal filler particles having an average particle diameter of D (nm), and satisfies the first relation d<D and the second relation d<100 (nm). When said organic coating layer volatilizes so that a metal layer is formed by sintering, the size relation between said average particle diameters d, D is designed so that said composite metal nanoparticle can be embedded in a hollow four pocket formed when it is assumed that four said metal filler particles are placed so that they come in contact with a tetrahedron, and it has a property in which said composite metal nanoparticles and said metal filler particles sinter compactly.