Copper Paste Solvent Blend for Oxidation-Resistant Die Bonding
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Solution Overview
Problem
Copper paste used in die bonding for power modules often suffers from oxidation during storage and sintering, leading to reduced die shear strength and thermal conductivity due to particle agglomeration and surface oxidation.
Innovation Solution
A copper paste formulation comprising copper powder and an alcohol solvent blend, where the solvent includes a combination of monohydric and dihydric alcohols with specific viscosity ranges, enhancing oxidation resistance and die shear strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper particles are made finer to promote sintering, then sinterability is improved, but particle agglomeration occurs leading to holes, protrusions, and cracks that reduce die shear strength
Solution Approach 1:
The patent uses a composite particle system consisting of copper core particles coated with a copper alloy layer containing 5-20 mass% tin. This composite structure prevents agglomeration of fine copper particles while maintaining sinterability, as the alloy coating creates repulsive forces between particles and prevents direct copper-copper contact that would lead to clumping.
Solution Approach 2:
The patent modifies the physical and chemical parameters of copper particles by controlling particle size distribution (D10: 0.5-2.0 μm, D50: 3.0-6.0 μm, D90: 8.0-15.0 μm) and applying a copper alloy coating with specific composition (5-20 mass% tin). These parameter changes enable fine particles to sinter properly without agglomerating, resolving the contradiction between sinterability and surface uniformity.
2Reliability
If copper particles are finely divided to increase surface area for sintering, then sintering is promoted, but oxidation resistance deteriorates due to increased specific surface area
Solution Approach 1:
The patent creates a composite particle structure with a copper core and a copper-tin alloy coating layer. This composite structure protects the fine copper particles from oxidation while maintaining their high surface area for sintering. The alloy coating acts as a protective barrier against oxidative environments.
Solution Approach 2:
The copper-tin alloy coating serves as an intermediary protective layer between the fine copper particles and the oxidizing environment. This intermediate layer prevents direct contact between oxygen and the copper surface, thereby maintaining oxidation resistance while preserving the high surface area needed for effective sintering.
3Productivity
If copper paste is press-sintered under low temperature and short time conditions, then processing efficiency is improved, but sintering is incomplete resulting in insufficient die shear strength
Solution Approach 1:
The patent optimizes sintering parameters by controlling particle size distribution (D10: 0.5-2.0 μm, D50: 3.0-6.0 μm, D90: 8.0-15.0 μm) and applying a copper alloy coating with 5-20 mass% tin. These parameter changes enable complete sintering to be achieved under reduced conditions (200-300°C for 1-30 minutes), simultaneously improving productivity while maintaining or enhancing die shear strength.
Solution Approach 2:
The copper-tin alloy coated particles create a composite structure that facilitates rapid and complete sintering under low temperature and short time conditions. The alloy coating promotes sintering kinetics, allowing the process to be completed efficiently while achieving the required mechanical strength.
4Strength
If traditional high-lead-content solder paste is used, then bonding strength is achieved, but thermal conductivity is insufficient for high power dissipation applications
Solution Approach 1:
The patent replaces traditional high-lead solder paste with copper-based paste featuring controlled particle size distribution (D10: 0.5-2.0 μm, D50: 3.0-6.0 μm, D90: 8.0-15.0 μm) and copper-tin alloy coating (5-20 mass% tin). This parameter change transitions the material system from solder-based to copper-based, simultaneously achieving bonding strength comparable to or exceeding traditional methods while providing superior thermal conductivity for high power dissipation applications.
Solution Approach 2:
The patent uses copper-tin alloy coated copper particles as a composite material system that combines the bonding capabilities of traditional solder paste with the superior thermal conductivity of copper. This composite approach eliminates the need for lead-based solder while achieving both mechanical bonding and thermal management requirements.
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 copper paste exhibits excellent oxidation resistance and superior die shear strength in the sintered body, ensuring effective heat dissipation and bonding performance.
Implementation Method 1
The copper paste exhibits excellent oxidation resistance and superior die shear strength in the sintered body
Implementation Method 2
a press sintering process for heating the conductive paste while applying a pressure of approximately 20 MPa
Implementation Method 3
The sintered body formed from the conductive paste exhibits excellent thermal conductivity, allowing heat generated during the operation of the semiconductor element to be efficiently transferred to the insulating heat-dissipation substrate
Data Source
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AI summary
A copper paste according to the present invention contains copper powder and an alcohol solvent, where the alcohol solvent contains a first alcohol composed of at least one type of alcohol selected from the group comprising monohydric alcohols and dihydric alcohols, which has a viscosity of 3 mPa·s or more and 70 mPa·s or less at 25°C; and a second alcohol composed of at least one type of dihydric alcohols and trihydric alcohols, which has a viscosity of 300 mPa·s or more and 1000 mPa·s or less at 25°C, and the viscosity of η10 at a shear rate of 10 s-1at 25°C is 1 Pa·s or more and 50 Pa·s or less, and the square root of √σ0 of the Casson yield stress of σ0 is 10 Pa1/2 or less.