Power Semiconductor Device Stress Mitigation Thermal Fatigue

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Solution Overview

Problem

Conventional power semiconductor devices have insufficient thermal fatigue durability at high operating temperatures, leading to reliability issues due to thermal stress concentration at the bonding interfaces.

Innovation Solution

A power semiconductor device design featuring a power semiconductor element with a stress mitigation portion connected via a sintered metal layer as the primary bonding interface and a solder layer as the secondary bonding interface, where the sintered metal layer has higher hardness and strength than the solder layer, thereby distributing thermal stress more effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the operable temperature of the power semiconductor element is increased to reduce device size, then the current value per unit area increases and device size is reduced, but thermal stress concentration at the bonding interface increases leading to insufficient thermal fatigue durability

Engineering Contradiction:

Improvedevice sizeVSAvoidthermal fatigue durability

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

A stress mitigation portion is introduced as an intermediary component between the power semiconductor element and the wiring portion. This stress mitigation portion has a thermal expansion coefficient that is higher than that of the power semiconductor element, allowing it to absorb and mitigate thermal stress generated during temperature cycling, thereby preventing direct stress concentration at the bonding interface and improving thermal fatigue durability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The thermal expansion coefficient parameter is strategically selected for the stress mitigation portion to be higher than that of the power semiconductor element. This parameter change creates a gradient in thermal expansion properties that distributes thermal stress more effectively, preventing stress concentration at critical bonding interfaces while maintaining device functionality at elevated temperatures

Inventive Principle:

Principle #35Parameter changes

2Strength

If a silver-based bonding layer is used to bond the electrode and wiring portion, then bonding strength is improved, but the electrode is likely to be damaged when operable temperature is sufficiently increased

Engineering Contradiction:

Improvebonding strengthVSAvoidelectrode damage resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The stress mitigation portion serves as a mediator between the electrode and wiring portion, absorbing thermal stress before it reaches the bonding layer and electrode. This intermediary structure protects the silver-based bonding layer and electrode from thermal damage while maintaining the benefits of strong bonding at elevated operating temperatures

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If an intermetallic compound layer is used to bond the electrode portion to the stacked body, then bonding strength is improved, but the intermetallic compound layer is likely to be damaged when operable temperature is sufficiently increased

Engineering Contradiction:

Improvebonding strengthVSAvoidbonding layer damage resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The stress mitigation portion acts as a protective intermediary that reduces thermal stress transmission to the intermetallic compound layer. By positioning this stress-absorbing component between the power semiconductor element and wiring portion, the bonding layer maintains its strength benefits while being protected from thermal fatigue damage at high operating temperatures

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

The design enhances the thermal fatigue durability and reliability of the power semiconductor device by distributing thermal stress more effectively, reducing damage to the bonding interfaces and maintaining high performance at elevated temperatures.

Implementation Method 1

a first bonding portion (sintered metal layer) that bonds the electrode (2) to the stress mitigation portion (6)

Methodology Applied

Scientific EffectSintering: Sintering

Implementation Method 2

a thermal stress generated in the power semiconductor device due to a difference in thermal expansion coefficient between the power semiconductor element and a wiring portion increases

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10727186B2Power semiconductor device

Publication Date: 2020.07.28 MITSUBISHI ELECTRIC CORP

AI summary

A power semiconductor device having a high degree of reliability even when an operable temperature of a power semiconductor element is sufficiently increased. The power semiconductor device includes: a power semiconductor element including an electrode formed on a first surface; a first stress mitigation portion connected to the electrode with a first bonding portion being interposed; and a wiring portion electrically connected to the first stress mitigation portion with a second bonding portion being interposed. A bonding strength of the first bonding portion is higher than a bonding strength of the second bonding portion.