Bonded Body Chill Layer Prevents Kirkendall Voids

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Solution Overview

Problem

In power module substrates with heat sinks, the use of aluminum alloy members with low solidus temperatures and copper or silver metal members leads to the formation of Kirkendall voids due to diffusion imbalances, resulting in increased heat resistance and deteriorated heat dissipation characteristics.

Innovation Solution

A bonded body is formed by solid-phase diffusion bonding an aluminum alloy member with a chill layer having a specific crystal grain aspect ratio and diameter dispersed on the bonding interface, and a metal member from copper, nickel, or silver, with the chill layer thickness set to 50 μm or greater to obstruct diffusion migration and prevent Kirkendall voids.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If aluminum alloy member with low solidus temperature is used for heat sink, then heat dissipation efficiency is improved, but Kirkendall voids form due to diffusion imbalance, worsening bonding reliability

Engineering Contradiction:

Improveheat dissipation efficiencyVSAvoidbonding reliability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

A chill layer is formed on the bonding surface of the aluminum alloy member before bonding with the copper member. This preliminary action prevents diffusion imbalance and Kirkendall void formation during the bonding process, ensuring both heat dissipation efficiency and bonding reliability are achieved simultaneously

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The chill layer acts as an intermediary between the aluminum alloy member and the copper member. It mediates the diffusion process during bonding, preventing the formation of Kirkendall voids while maintaining the low solidus temperature advantage of the aluminum alloy for heat dissipation

Inventive Principle:

Principle #24Intermediary (Mediator)

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 configuration reduces heat resistance in the laminating direction and enhances heat dissipation characteristics by suppressing the formation of Kirkendall voids, ensuring reliable bonding and efficient heat transfer.

Implementation Method 1

solid-phase diffusion bonding an aluminum alloy member with a chill layer having a specific crystal grain aspect ratio and diameter dispersed on the bonding interface, and a metal member from copper, nickel, or silver, with the chill layer thickness set to 50 μm or greater to obstruct diffusion migration and prevent Kirkendall voids

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS10497585B2Bonded body, substrate for power module with heat sink, heat sink, method for producing bonded body, method for producing substrate for power module with heat sink, and method for producing heat sink

Publication Date: 2019.12.03 MITSUBISHI MATERIALS CORP

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.