Copper Joining Paste for Pressureless Low-Hydrogen Bonding
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Solution Overview
Problem
Conventional bonding materials, such as high-lead solder and sintered silver layers, face challenges in achieving sufficient bonding strength and thermal conductivity at high temperatures without applying pressure, and sintered copper layers require hydrogen-free or low-hydrogen atmospheres to prevent explosions, making them costly and inefficient.
Innovation Solution
A metal paste comprising copper particles, a dispersion medium, a reducing agent, and a reduction aid with a coordinating compound, specifically an organic phosphorus or sulfur compound, is used to form a sintered copper layer under no added pressure conditions in a low-hydrogen atmosphere, ensuring sufficient bonding strength and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sintered silver layer is used to achieve high thermal conductivity and connection reliability, then thermal conductivity is improved (>100 Wm−1K−1), but high pressure is required which causes damage to semiconductor element chips and decreases throughput
Solution Approach 1:
The patent changes the material parameter from silver to copper particles, which have different sintering characteristics. Copper particles can achieve sufficient bonding strength at lower pressures compared to silver, thereby resolving the contradiction between connection reliability and damage to semiconductor elements during the bonding process
Solution Approach 2:
The patent uses copper particles instead of expensive silver particles. Copper is more cost-effective and can be used as a disposable bonding material that achieves the required performance without the need for expensive precious metals, while still providing adequate connection reliability
2Ease of manufacture
If sintered copper layer is used to reduce material cost and improve mechanical strength, then material cost is reduced and mechanical strength is improved, but high pressure is required which decreases throughput
Solution Approach 1:
The patent modifies the sintering parameters by using copper particles with specific size distributions and surface treatments that enable sintering at lower pressures. This allows the process to maintain high productivity without sacrificing the cost-effectiveness and mechanical strength benefits of copper
Solution Approach 2:
The patent introduces a dynamic approach by using a two-stage sintering process or by controlling the bonding pressure dynamically, allowing the system to achieve adequate bonding strength with lower peak pressures, thereby maintaining high throughput while using cost-effective copper material
3Strength
If sintered copper layer is formed in hydrogen atmosphere to achieve sufficient bonding strength, then bonding strength is improved, but explosion risk increases requiring explosion-proof facilities
Solution Approach 1:
The patent replaces the hydrogen atmosphere with an inert or controlled atmosphere during the sintering process. This eliminates the explosion risk associated with hydrogen while maintaining the bonding strength requirements, as the copper particles can be effectively sintered in the modified atmosphere without combustion hazards
Solution Approach 2:
The patent converts the potential harm of hydrogen atmosphere (explosion risk) into a benefit by using the controlled atmosphere to achieve effective copper particle sintering without the need for expensive explosion-proof facilities, while still obtaining sufficient bonding strength
4Ease of manufacture
If conventional high-lead solder is used to achieve easy bonding process, then ease of manufacture is improved, but thermal conductivity is insufficient (30 Wm−1K−1) and connection reliability is poor at high temperatures
Solution Approach 1:
The patent changes the material composition from high-lead solder to copper particles with specific surface treatments and size distributions. This material substitution maintains the ease of manufacture through simple screen printing and sintering processes while dramatically improving both thermal conductivity and connection reliability at high temperatures
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 metal paste enables the formation of a bonded body with high bonding strength and thermal conductivity without the need for pressure, while maintaining safety by operating in a hydrogen-free or low-hydrogen environment, thus addressing the limitations of existing materials.
Implementation Method 1
the reduction aid includes a coordinating compound having electron back-donation properties
Implementation Method 2
the coordinating compound is at least one selected from the group consisting of an organic phosphorus compound and an organic sulfur compound
Implementation Method 3
a metal paste for bonding including metal particles, a dispersion medium, a reducing agent, and a reduction aid, in which the metal particles contain copper particles
Implementation Method 4
a sintered copper layer using copper has been proposed. Copper has excellent mechanical strength compared to silver, high-temperature reliability can be easily obtained
Implementation Method 5
the bonding layer is required to have connection reliability and high thermal conductivity characteristics
Data Source
AI summary
A metal paste for bonding includes metal particles, a dispersion medium, a reducing agent, and a reduction aid, in which the metal particles contain copper particles, the reduction aid includes a coordinating compound having electron back-donation properties, the coordinating compound is at least one selected from the group consisting of an organic phosphorus compound and an organic sulfur compound, and the metal paste for bonding contains, as a reducing agent, 1.6 parts by mass or more and 10 parts by mass or less of a polyol-based compound with respect to 100 parts by mass of the total mass of the copper particles.