Sn-Cu Bonding Structure for High-Temperature Power Semiconductor Joints

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Solution Overview

Problem

Current bonding materials for power semiconductor devices lack high heat resistance and durability, particularly for temperatures above 175°C, and fail to maintain mechanical strength and bonding integrity under temperature fluctuations, limiting their application in advanced power electronics.

Innovation Solution

A bonding structure utilizing metal particles with a monoclinic, hexagonal, or other intermetallic compound crystals that form endotaxial junctions with a Sn alloy matrix, maintaining stability and preventing phase transitions, thereby enhancing heat resistance and mechanical strength across a wide temperature range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If conventional SnAgCu-based bonding material is used, then bonding is achievable at lower temperatures, but heat resistance and durability above 175°C are insufficient

Engineering Contradiction:

Improveheat resistanceVSAvoiddurability at elevated temperatures

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The invention uses a composite bonding material comprising metal particles with a core-shell structure. The core contains Sn or Sn alloy, while the shell contains intermetallic compound composed of Sn and Cu. This composite structure combines the low melting point advantage of Sn with the high heat resistance of Sn-Cu intermetallic compound, enabling reliable bonding at temperatures above 175°C without sacrificing durability.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention changes the chemical composition parameters of the bonding material by introducing intermetallic compound (specifically Sn-Cu system) into the shell layer. This compositional modification raises the operational temperature limit from 175°C to above 200°C while maintaining bonding functionality, effectively resolving the heat resistance contradiction.

Inventive Principle:

Principle #35Parameter changes

2Strength

If metal particle with intermetallic compound shell is used to suppress Kirkendall void, then bonding strength is improved, but uniform distribution of intermetallic compound over mating object during melting is difficult

Engineering Contradiction:

Improvebonding strengthVSAvoiduniformity of intermetallic compound distribution

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The invention applies local quality by concentrating the intermetallic compound specifically in the shell layer surrounding the Sn core, rather than attempting uniform distribution throughout the entire bonding material. This localized placement ensures that the intermetallic compound forms precisely at the bonding interface where it is needed to suppress Kirkendall void and enhance bonding strength, while avoiding the manufacturing difficulties of achieving uniform distribution.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The shell containing intermetallic compound acts as an intermediary layer between the Sn core and the mating object. During bonding, this shell layer facilitates controlled interaction at the interface, enabling the intermetallic compound to effectively suppress Kirkendall void formation and enhance bonding strength without requiring uniform distribution across the entire bonding material volume.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If bonding material must maintain mechanical strength under temperature fluctuations, then heat resistance is improved, but adaptability to different temperature conditions deteriorates

Engineering Contradiction:

Improvecompositional stabilityVSAvoidadaptability to temperature conditions

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The composite core-shell structure provides compositional stability through the heat-resistant Sn-Cu intermetallic compound shell while maintaining adaptability to different temperature conditions. The Sn core allows bonding at lower temperatures, while the intermetallic compound shell ensures stability at elevated temperatures up to 200°C and above, enabling the material to adapt to varying thermal environments without compromising mechanical strength.

Inventive Principle:

Principle #40Composite materials

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 bonding structure achieves superior heat resistance, mechanical strength, and reduced volumetric changes, enabling reliable bonding of power semiconductor devices even at elevated temperatures, surpassing the limitations of existing SnAgCu-based materials.

Implementation Method 1

the intermetallic compound crystal forming an endotaxial junction with the Sn alloy matrix

Methodology Applied

Scientific EffectEndotaxial junction:

Implementation Method 2

the Sn alloy matrix and/or the intermetallic compound crystal forming an epitaxial junction with the metal body or the alloy body

Methodology Applied

Scientific EffectEpitaxial junction: Epitaxy

Data Source

PatentUS11453089B2Bonding structure

Publication Date: 2022.09.27 NAPRA

AI summary

Disclosed is a bonding structure that includes an intermetallic compound crystal composed of Sn and Cu, and, an Sn alloy matrix composed of Sn and Cu, being intended for bonding a metal body or an alloy body, the intermetallic compound crystal forming an endotaxial junction with the Sn alloy matrix, and the Sn alloy matrix and/or the intermetallic compound crystal forming an epitaxial junction with the metal body or the alloy body.