IMS PCB Steel Substrate Thermal Expansion Matching

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Solution Overview

Problem

Existing power electronic devices face challenges in thermal management and mechanical stress due to mismatched thermal expansion coefficients between lead frames and insulated metal substrates, leading to instability in solder joints and potential cracking.

Innovation Solution

A power electronic device comprising an Insulated Metal Substrate Printed Circuit Board (IMS PCB) with a lead frame and substrate materials having closely matched thermal expansion coefficients, ranging from 60% to 140% of each other, to stabilize solder joints and reduce mechanical stress caused by thermal expansions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If lead frame and substrate materials have mismatched thermal expansion coefficients, then manufacturing flexibility is improved, but solder joint reliability deteriorates due to mechanical stress and cracking

Engineering Contradiction:

Improvematerial selection flexibilityVSAvoidsolder joint stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies parameter changes by carefully selecting substrate materials with specific thermal expansion coefficients that match the lead frame materials. The substrate material is chosen to have a thermal expansion coefficient within a specific range (60%-140% of the lead frame's coefficient), transforming the material selection into a parameter-matching problem that resolves the contradiction between manufacturing flexibility and joint reliability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by differentiating material requirements for different components: the substrate material is specifically selected for thermal expansion matching with the lead frame, while other PCB components can vary. This localized material optimization ensures solder joint reliability without compromising overall manufacturing flexibility.

Inventive Principle:

Principle #3Local quality

2Strength

If rigid lead frame configuration is used, then mechanical strength is improved, but thermal stress resistance deteriorates due to thermal expansion mismatch

Engineering Contradiction:

Improvelead frame mechanical strengthVSAvoidthermal stress resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent resolves this contradiction by changing the thermal expansion parameter of the substrate material to match the rigid lead frame's properties. By selecting substrate materials with thermal expansion coefficients within 60%-140% of the lead frame's coefficient, the patent maintains the mechanical strength benefits of rigid lead frames while compensating for thermal stress through parameter matching.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If thermal expansion coefficients are closely matched, then solder joint reliability is improved, but material selection range is reduced

Engineering Contradiction:

Improvesolder joint stabilityVSAvoidmaterial selection range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies parameter changes by defining a specific range (60%-140%) for thermal expansion coefficient matching rather than requiring exact matches. This parameter range approach maintains solder joint reliability while preserving sufficient material selection flexibility for different applications.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by focusing material selection constraints specifically on the substrate-lead frame interface, while allowing other PCB components to use a broader range of materials. This localized constraint ensures joint reliability without unnecessarily limiting overall material selection versatility.

Inventive Principle:

Principle #3Local quality

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 solution effectively stabilizes solder joints and reduces thermal stress, enhancing the reliability and durability of power electronic devices by minimizing cracks and ensuring favorable Temperature Cycling on Board (TCoB) performance.

Implementation Method 1

the lead frame has a rigid configuration and is made of a lead frame material having a first thermal expansion coefficient; and wherein the IMS PCB includes an insulated metal substrate that is made of a substrate material having a second thermal expansion coefficient within the range of 60% to 140% of the first thermal expansion coefficient

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10426028B2Printed circuit board with insulated metal substrate made of steel

Publication Date: 2019.09.24 INFINEON TECH AUSTRIA AG

AI summary

A power electronic device includes an Insulated Metal Substrate Printed Circuit Board (IMS PCB) and a power semiconductor device package. The power semiconductor device package includes a lead frame configured to electrically and mechanically couple the power semiconductor device package to the IMS PCB. The lead frame has a rigid configuration and is made of a lead frame material having a first thermal expansion coefficient. The IMS PCB includes an insulated metal substrate made of a substrate material having a second thermal expansion coefficient within a range of 60% to 140% of the first thermal expansion coefficient.