Recessed Power Module Base Plate Thermal Stress Management

Solution Overview

Problem

The use of AlSiC base plates in power modules for railway vehicles, when replaced with metals like copper or aluminum, leads to increased linear expansion coefficients, causing stress and deflection, which reduces reliability and heat dissipation due to the difference in expansion coefficients with sealing resin, and existing solutions like forming grooves in the base plate do not effectively address these issues.

Innovation Solution

A power module design featuring a recessed base plate with a hollow portion, where the insulating substrate is disposed, and sealed with a resin having a high linear expansion coefficient, allowing the base plate to deflect into a projecting shape, thereby reducing stress and improving reliability and heat dissipation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the base plate material is changed from AlSiC to metal materials such as copper and aluminium, then heat dissipation is improved, but the linear expansion coefficient increases causing increased stress and deflection

Engineering Contradiction:

Improveheat dissipationVSAvoidstress and deflection

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The invention changes the geometric parameters of the base plate by forming a recessed portion, which modifies the plate's stiffness distribution and deflection characteristics. This allows the use of high thermal conductivity materials while controlling the unwanted thermal expansion effects through structural design.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The recessed portion introduces a curved surface geometry into the base plate structure. This curvature modifies the stress distribution and deflection pattern of the base plate, reducing the harmful effects of thermal expansion while maintaining the beneficial heat dissipation properties of metal materials.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Temperature

If the base plate material is changed from AlSiC to metal materials such as copper and aluminium, then heat dissipation is improved, but the base plate deflects into a recessed shape with larger deflected amount

Engineering Contradiction:

Improveheat dissipationVSAvoidbase plate deflection

Core Design Contradiction:

TemperatureVSShape

Solution Approach 1:

The recessed portion introduces a curved surface geometry into the base plate structure. This curvature modifies the stress distribution and deflection pattern of the base plate, reducing the harmful effects of thermal expansion while maintaining the beneficial heat dissipation properties of metal materials.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The base plate is segmented into different regions with different thicknesses - a thinner central portion and a thicker peripheral portion forming the recessed structure. This segmentation allows different parts of the base plate to have different stiffness characteristics, controlling overall deflection while maintaining heat dissipation efficiency.

Inventive Principle:

Principle #1Segmentation

3Reliability

If a groove is formed in the base plate at an outer peripheral portion, then stress distribution at the end portion of the insulating substrate is improved, but the base plate still deflects into a recessed shape with larger deflected amount

Engineering Contradiction:

Improvestress distributionVSAvoidbase plate deflection

Core Design Contradiction:

ReliabilityVSShape

Solution Approach 1:

The recessed portion introduces a curved surface geometry into the base plate structure. This curvature modifies the stress distribution and deflection pattern of the base plate, reducing the harmful effects of thermal expansion while maintaining the beneficial heat dissipation properties of metal materials.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

Instead of only modifying the base plate in the planar dimension (as with a groove), the invention introduces a vertical dimension by forming a recessed portion with varying thickness. This three-dimensional structural modification more effectively controls both stress distribution and deflection characteristics.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 recessed base plate design reduces deflection and stress on the ceramic and solder portions, enhancing the reliability and heat dissipation of the power module while allowing for downsizing and improved bonding with the sealing resin.

Implementation Method 1

the hollow portion allows the base plate to deflect into a projecting shape, thereby reducing a stress on a ceramic portion and on a solder portion

Methodology Applied

Scientific EffectStress absorption:

Implementation Method 2

sealing resin for sealing a surface of the hollow portion side of the base plate, the insulating substrate and the semiconductor chip

Methodology Applied

Scientific EffectSealing:

Data Source

PatentUS10971424B2Power module and power convertor

Publication Date: 2021.04.06 MITSUBISHI ELECTRIC CORP

AI summary

A power module includes a recessed base plate having a hollow portion, at least one insulating substrate disposed in the hollow portion of the base plate, at least one semiconductor chip mounted on the at least one insulating substrate, and sealing resin for sealing a surface of the hollow portion side of the base plate, the at least one insulating substrate, and the at least one semiconductor chip.