Trimodal Metal Particle Aggregate for Low-Temperature Bonding
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Solution Overview
Problem
Conventional metal bonding compositions using nanoparticles and submicron particles face challenges in achieving sufficient low-temperature sintering and maintaining bonding strength due to particle aggregation and thermal decomposition of protective films, leading to void generation and reduced reliability.
Innovation Solution
A metal particle aggregate comprising silver and copper particles with specific diameter ratios (70% by mass or more of 100 nm to 500 nm, 55-65% by number of 50 nm to 100 nm, and 5-25% by number of less than 50 nm) covered with a uniform protective film, produced through a heat treatment process, is used to form a paste-like composition for bonding at relatively low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal particles of submicron size are used for bonding, then bonding material can be applied and sintered, but fine voids are easily generated in the bonding layer reducing bonding strength
Solution Approach 1:
The invention segments the metal particle size distribution into three distinct ranges (nanoparticles <50nm, submicron particles 50-500nm, and micro particles 500nm-2μm) with optimized ratios. This segmentation allows each particle size to fulfill specific functions: nanoparticles fill gaps and reduce voids, submicron particles provide bonding strength, and micro particles ensure structural integrity, thereby resolving the contradiction between manufacturability and bonding strength.
Solution Approach 2:
The invention applies local quality by assigning different particle sizes to different functional roles within the bonding layer. Smaller nanoparticles are concentrated in regions where void formation is problematic, while larger particles are positioned where structural support is needed. This localized functional assignment optimizes both void reduction and bonding strength simultaneously.
2Strength
If metal particles of nano size are used for bonding, then fine voids are suppressed, but bonding strength decreases with time due to protectant decomposition
Solution Approach 1:
The invention creates a composite particle system combining three different metal particle sizes with distinct properties. The multi-size composite structure allows nanoparticles to provide initial void suppression while larger particles contribute to long-term structural stability and bonding strength. The synergistic interaction among different particle sizes compensates for the weaknesses of individual particle types, achieving both high bonding strength and long-term reliability.
Solution Approach 2:
The invention changes the particle size distribution parameters by introducing a trimodal distribution instead of using a single particle size. This parameter change transforms the bonding material from a homogeneous particle system to a heterogeneous one, where the combined effect of different particle sizes addresses both void formation and long-term stability issues that plague single-size particle systems.
3Strength
If two or more kinds of metal particles with different average particle diameters are used, then high bonding strength can be achieved at low temperature, but particle aggregation occurs reducing dispersibility
Solution Approach 1:
The invention introduces an organic compound as an intermediary substance that mediates between metal particles of different sizes. This intermediary prevents direct aggregation between particles while maintaining their dispersed state during storage and application. The organic compound acts as a spacer and stabilizer, allowing the multi-size particle system to maintain stability without sacrificing the bonding strength benefits of particle size diversity.
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 enables the formation of a bonding layer with high bonding strength and long-term reliability at low temperatures, preventing void formation and enhancing the sintering process without the need for pressurization, while maintaining favorable paste viscosity and rheology.
Implementation Method 1
the metal particles are sintered to produce a bonding layer
Implementation Method 2
the protectant remains in a bonding layer, and is decomposed with time to generate voids in the bonding layer
Data Source
AI summary
A metal particle aggregate includes metal particles and an organic substance. The metal particles include first particles that contain one or both of silver and copper in an amount of 70% by mass or more relative to 100% by mass of all metals and have a particle diameter of 100 nm or more and less than 500 nm at a ratio of 20 to 30% by number, and include second particles that have a particle diameter of 50 nm or more and less than 100 nm, and third particles that have a particle diameter of less than 50 nm at a ratio of 80 to 70% by number in total. Surfaces of the first to third particles are covered with the same protective film.