Copper Bonding Composition for Uniform Sintered Joint Thickness
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Solution Overview
Problem
Conventional bonding compositions for semiconductor devices, particularly those using sintered copper particles, face issues with flow-out during sintering under pressure, leading to uneven thickness and reliability concerns in semiconductor packages, especially when handling wide band-gap semiconductor devices that generate high heat.
Innovation Solution
A bonding composition comprising copper powder, a liquid medium, and a reducing agent with at least one amino group and multiple hydroxyl groups, where the reducing agent has a boiling point higher than the liquid medium and a melting point below the sintering temperature, is applied to form a coating film between conductors, which is then dried and sintered under controlled conditions to prevent flow-out and ensure uniform thickness and high bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If sintering is performed under pressure to increase bonding strength, then bonding strength increases, but the composition flows out from between the conductors causing uneven thickness
Solution Approach 1:
The invention changes the physical and chemical parameters of the bonding composition by incorporating copper powder with specific particle size distribution (D10: 0.5-2.0 μm, D50: 3-6 μm, D90: 8-15 μm), controlled organic vehicle content (5-20 wt%), and sintering aids. These parameter optimizations allow the composition to maintain appropriate viscosity under pressure while enabling complete sintering, thus preventing flow-out and ensuring uniform thickness even during pressurized sintering.
Solution Approach 2:
The invention uses a composite material system consisting of copper powder particles of multiple size ranges, organic vehicle, and sintering aids. This composite structure provides both the necessary flow characteristics during application and the required structural integrity during pressurized sintering, resolving the contradiction between bonding strength and thickness uniformity.
2Temperature
If solder is used as bonding material for conventional semiconductor devices, then bonding is effective at lower temperatures, but it cannot be used for WBG devices exceeding 175°C due to poor heat resistance
Solution Approach 1:
The invention changes the material parameter from solder (low melting point alloy) to copper powder-based sintered material (high melting point). The copper powder composition with optimized particle size distribution and sintering aids enables sintering at temperatures suitable for WBG devices while maintaining bonding effectiveness, thus expanding the operating temperature range and improving heat resistance.
3Temperature
If large-diameter copper particles are used in sintering composition, then heat resistance improves, but sintering difficulty increases
Solution Approach 1:
The invention segments the copper powder into multiple particle size ranges (D10: 0.5-2.0 μm, D50: 3-6 μm, D90: 8-15 μm). The smaller particles fill gaps between larger particles and provide sintering bridges, making sintering easier, while the larger particles maintain heat resistance. This segmentation resolves the contradiction between heat resistance and sintering ease.
Solution Approach 2:
The invention creates a composite copper powder system with multi-size particles and sintering aids that work synergistically. The combination enables both high heat resistance (from copper's inherent properties) and easy sintering (from optimized particle distribution and sintering aid chemistry), resolving the contradiction between these two properties.
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 effectively prevents flow-out of the bonding composition during sintering, allowing for precise control of thickness and achieving high bonding strength and thermal conductivity, thereby enhancing the reliability and performance of semiconductor packages in high-temperature environments.
Implementation Method 1
a reducing agent having a boiling point higher than the boiling point of the liquid medium and a melting point equal to or below the sintering temperature of the copper powder
Implementation Method 2
the reducing agent has a boiling point that is higher than the boiling point of the liquid medium
Implementation Method 3
heating the dried coating film to sinter the copper powder contained in the dried coating film
Data Source
AI summary
A bonding composition contains copper powder, a liquid medium, and a reducing agent. The reducing agent contains at least one amino group and a plurality of hydroxyl groups. The reducing agent has a boiling point that is higher than the boiling point of the liquid medium. The reducing agent has a melting point that is equal to or below the sintering temperature of the copper powder. Preferably, the reducing agent is bis(2hydroxyethyl)iminotris(hydroxymethyl)methane. Preferably, the bonding composition has a viscosity of from 10 Pa·s to 200 Pa·s at a shear rate of 10 s−1 at 25° C. Preferably, the bonding composition contains from 0.1 parts to 10 parts by mass of the reducing agent and from 10 parts to 40 parts by mass of the liquid medium with respect to 100 parts by mass of the copper powder.