Multi-Modal Metal Paste Bonding for Void-Free Si-Cu Joints
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Solution Overview
Problem
Conventional bonding materials with fine silver particles fail to satisfactorily bond Si chips to copper substrates due to void generation in the metal bonding layer and high viscosity, making them difficult to print on substrates using existing systems.
Innovation Solution
A bonding material comprising a mixture of metal particles with specific size ranges (1-40 nm, 41-110 nm, and 120 nm-10 μm) and a solvent, along with a dispersant, where the weight ratios and percentages of these particles are optimized to prevent void formation and lower viscosity, allowing for effective bonding without pre-burning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional bonding materials with fine silver particles are used, then bonding strength between copper substrates is improved, but voids are generated when bonding Si chips to copper substrates
Solution Approach 1:
The patent changes the particle size distribution parameter by introducing a specific multi-modal distribution with four distinct ranges (0.03-0.5 μm, 0.5-2 μm, 2-10 μm, and 10-50 μm) instead of using conventional uniform fine particles. This parameter change allows the bonding material to adapt to different bonding scenarios, preventing void formation while maintaining bonding strength.
Solution Approach 2:
The patent creates a composite particle system combining silver particles of four different size ranges in specific weight ratios. This composite structure allows small particles to fill voids while larger particles provide structural framework and bonding strength, resolving the contradiction between bonding strength and void prevention.
2Strength
If bonding materials with high metal particle content are used, then bonding strength is improved, but viscosity increases making printing difficult
Solution Approach 1:
The patent optimizes the viscosity parameter by controlling the particle size distribution and metal particle content (60-80 wt%). The multi-modal size distribution prevents particle aggregation and improves flow characteristics, enabling printability while maintaining high bonding strength through adequate metal content.
Solution Approach 2:
The patent applies local quality by having different particle size ranges serve different functions: smaller particles (0.03-2 μm) improve flow and filling properties for printability, while larger particles (2-50 μm) provide structural framework for bonding strength. Each size range contributes locally to different aspects of performance.
3Reliability
If pre-burning is performed to remove solvent before bonding, then bonding quality is improved, but processing time and complexity increase
Solution Approach 1:
The patent performs preliminary action by pre-dispersing metal particles in the solvent with appropriate surfactants during material preparation. This preliminary dispersion prevents aggregation and ensures uniform distribution, allowing the solvent to be effectively removed during standard bonding heating without requiring separate pre-burning steps.
Solution Approach 2:
The patent merges the solvent removal function into the standard bonding heating process. By optimizing the particle size distribution and solvent system, the bonding heating step simultaneously achieves both void prevention and complete solvent evaporation, eliminating the need for separate pre-burning operations.
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 easy printing and satisfactory bonding of Si chips to copper substrates by preventing voids in the metal bonding layer, even without pre-burning, ensuring strong and reliable connections.
Implementation Method 1
heating to sinter a metal, such as silver, in the bonding material to bond the articles to each other
Implementation Method 2
heated to remove the solvent to form a pre-dried film on the substrate
Data Source
AI summary
In a bonding material of a metal paste containing metal particles, a solvent and a dispersant, the metal particles containing first metal particles having an average primary particle diameter of 1 to 40 nm, second metal particles having an average primary particle diameter of 41 to 110 nm, and third metal particles having an average primary particle diameter of 120 nm to 10 μm, the weight percentages of the first, second and third metal particles being 1.4 to 49% by weight, 36% by weight or less, and 50 to 95% by weight, respectively, with respect to the total 100% by weight of the metal particles, and the weight ratio of the first metal particles to the second metal particles being 14/36 or more.