Bonded Body with Mg-Concentrated Layer Suppresses Kirkendall Voids
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Solution Overview
Problem
The formation of Kirkendall voids at the bonding interface between aluminum alloy members and metal members, such as copper, nickel, or silver, leads to increased heat resistance and deteriorated heat dissipation characteristics in power module substrates with complex heat sinks.
Innovation Solution
A bonded body is created by solid-phase diffusion bonding an aluminum alloy member with a Si concentration of 1-25 mass% and a metal member, where a Mg-concentrated layer with a concentration of 3 mass% or greater is formed at the bonding interface, suppressing the occurrence of Kirkendall voids and reducing heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid-phase diffusion bonding is performed between aluminum alloy member and metal member (copper, nickel, or silver), then bonding strength is improved, but Kirkendall voids form at the bonding interface causing heat resistance to increase
Solution Approach 1:
An intermediate layer comprising a first region (Al-rich intermetallic compound layer with thickness of 1-10 μm) and a second region (transition layer with gradient composition) is formed between the aluminum alloy member and metal member. This intermediate layer mediates the diffusion process, preventing direct formation of Kirkendall voids while maintaining strong bonding, thereby resolving the contradiction between bonding strength and heat dissipation characteristics.
Solution Approach 2:
The invention controls the thickness and composition parameters of the intermediate layer formed during bonding. By adjusting the Al-rich intermetallic compound layer thickness to 1-10 μm and creating a gradient composition in the transition layer, the diffusion rate is optimized to prevent void formation while ensuring adequate bonding strength, thus improving both bonding quality and heat dissipation.
2Ease of manufacture
If aluminum alloy member with high Si concentration is used, then manufacturing cost is reduced, but bonding ability with metal member deteriorates due to oxide film formation
Solution Approach 1:
A protective film is formed on the surface of the aluminum alloy member before bonding to prevent oxide film formation. This preliminary protective action allows the use of high-Si aluminum alloys (which are cheaper) without suffering from poor bonding ability, as the protective film prevents oxidation that would otherwise hinder bonding.
Solution Approach 2:
The intermediate layer with controlled composition and structure acts as a mediator between the high-Si aluminum alloy and the metal member. It facilitates bonding by providing a diffusion pathway that bypasses the oxide film issue, enabling successful bonding of cost-effective high-Si alloys.
3Reliability
If Ni plating film is formed on the surface through electroless plating, then bonding reliability is improved, but manufacturing complexity increases due to masking process requirements
Solution Approach 1:
The invention extracts and eliminates the masking process from the manufacturing sequence by directly forming the necessary intermediate layer through controlled diffusion bonding without requiring Ni plating. This removes the complex masking step while maintaining bonding reliability through the engineered intermediate layer structure.
Solution Approach 2:
Instead of using Ni plating with its associated masking complexity, the invention changes the approach by controlling the diffusion bonding parameters to directly form an Al-rich intermetallic compound layer with specific thickness and composition. This parameter-controlled approach achieves bonding reliability without the complex masking process.
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 approach effectively lowers heat resistance in the laminating direction and enhances heat dissipation characteristics by obstructing metal element diffusion, resulting in improved bonding reliability and reduced manufacturing costs.
Implementation Method 1
The aluminum alloy member and the metal member are subjected to solid-phase diffusion bonding
Implementation Method 2
A compound layer, which is formed through diffusion of Al of the aluminum alloy member and a metal element of the metal member, is provided at a bonding interface
Data Source
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AI summary
A bonded body is provided in which an aluminum alloy member formed from an aluminum alloy, and a metal member formed from copper, nickel, or silver are bonded to each other. The aluminum alloy member is constituted by an aluminum alloy in which a concentration of Si is set in a range of 1 mass% to 25 mass%. The aluminum alloy member and the metal member are subjected to solid-phase diffusion bonding. A compound layer, which is formed through diffusion of Al of the aluminum alloy member and a metal element of the metal member, is provided at a bonding interface between the aluminum alloy member and the metal member. A Mg-concentrated layer, in which a concentration of Mg is set to 3 mass% or greater, is formed at the inside of the compound layer, and the thickness of the Mg-concentrated layer is set in a range of 1 µm to 30 µm.