Chill Layer Bonded Body for Power Module Heat Sink
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Solution Overview
Problem
In power module substrates with heat sinks, the use of aluminum alloys with low solidus temperatures and copper or silver metal members often results in the formation of Kirkendall voids due to diffusion imbalances, leading to increased heat resistance and deteriorated heat dissipation characteristics.
Innovation Solution
A bonded body is formed by solid-phase diffusion bonding a metal member from copper, nickel, or silver with an aluminum alloy, where a chill layer with a specific crystal grain aspect ratio and diameter is dispersed on the bonding interface, obstructing metal element diffusion and suppressing Kirkendall void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid-phase diffusion bonding is performed between aluminum alloy and copper/silver metal members, then bonding strength is improved, but Kirkendall voids form due to diffusion imbalance, leading to increased heat resistance
Solution Approach 1:
A chill layer is introduced as an intermediary between the aluminum alloy and copper/silver metal members. This chill layer, formed by controlling crystal grain growth during casting, acts as a diffusion barrier that prevents the formation of Kirkendall voids while maintaining bonding strength, thereby resolving the contradiction between bonding strength and heat dissipation characteristics
Solution Approach 2:
The solidus temperature of the aluminum alloy is controlled to be lower than the eutectic temperature of the aluminum-copper/silver system. By changing the thermal parameters of the aluminum alloy (composition and solidus temperature), the diffusion behavior during bonding is modified to suppress Kirkendall void formation while maintaining effective bonding
2Ease of manufacture
If aluminum alloy with low solidus temperature is used, then bonding processability is improved, but diffusion imbalance occurs, forming Kirkendall voids
Solution Approach 1:
The chill layer serves as a mediator that compensates for the diffusion imbalance caused by using aluminum alloy with low solidus temperature. It provides a controlled interface structure that maintains bonding processability while preventing void formation, thus resolving the contradiction between ease of manufacture and manufacturing precision
3Reliability
If Ni plating film is formed on the surface, then bonding reliability is improved, but oxidation during bonding deteriorates the Ni plating film, reducing bonding reliability
Solution Approach 1:
The invention replaces the Ni plating film (which is vulnerable to oxidation) with a chill layer formed directly in the aluminum alloy structure. This chill layer is inherently resistant to oxidation and serves the same function of improving bonding reliability without being susceptible to oxidation damage during the bonding 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
This approach reduces heat resistance in the laminating direction and enhances heat dissipation characteristics by preventing void formation and improving bonding reliability between the aluminum alloy and metal members.
Implementation Method 1
a chill layer, in which a Si phase of which an aspect ratio of a crystal grain is 2.5 or less and a crystal grain diameter is 15 μm or less is dispersed, is formed on a bonding interface side with the metal member in the aluminum alloy member... obstructing metal element diffusion and suppressing Kirkendall void formation
Implementation Method 2
The aluminum alloy member and the metal member are subjected to solid-phase diffusion bonding
Data Source
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AI summary
A bonded body is provided that is formed by bonding a metal member formed from copper, nickel, or silver, and an aluminum alloy member formed from an aluminum alloy of which a solidus temperature is lower than a eutectic temperature of aluminum and a metal element that constitutes the metal member. The aluminum alloy member and the metal member are subjected to solid-phase diffusion bonding. A chill layer, in which a Si phase of which an aspect ratio of a crystal grain is 2.5 or less and a crystal grain diameter is 15 µm or less is dispersed, is formed on a bonding interface side with the metal member in the aluminum alloy member. The thickness of the chill layer is set to 50 µm or greater.