Ceramic Laminate Body Multilayer Bonding Stress Management

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Solution Overview

Problem

Ceramic laminate bodies for gas sensor elements face issues of cracking and flaking due to differences in degreasing contraction factors and thermal expansion coefficients between ceramic sheets and bonding layers during the firing and cooling processes.

Innovation Solution

A ceramic laminate body with a multilayer intermediate bonding layer structure, where the innermost end portions of the unit intermediate layers are displaced from each other, dispersing stresses and preventing cracking or flaking by matching degreasing contraction rates and thermal expansion coefficients between ceramic sheets.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a single-layer intermediate bonding layer is used to bond ceramic sheets, then the bonding process is simple, but stress concentration occurs during firing and cooling causing cracking or flaking

Engineering Contradiction:

Improvebonding process simplicityVSAvoidcracking resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The intermediate bonding layer is divided into multiple sub-layers (first intermediate bonding layer and second intermediate bonding layer) with different compositions and contraction rates. This segmentation allows each sub-layer to handle different stress conditions during firing and cooling, preventing stress concentration and cracking while maintaining manufacturing feasibility.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If ceramic sheets with different material compositions are used, then functional requirements are met, but difference in thermal expansion coefficients causes stress during cooling

Engineering Contradiction:

Improvematerial composition varietyVSAvoidthermal stress

Core Design Contradiction:

Adaptability or versatilityVSStress or pressure

Solution Approach 1:

Different intermediate bonding layers are assigned different material compositions and contraction rates matched to adjacent ceramic sheets. The first intermediate bonding layer has contraction rate close to the first ceramic sheet, while the second intermediate bonding layer has contraction rate close to the second ceramic sheet. This local quality matching reduces thermal stress at each interface during cooling.

Inventive Principle:

Principle #3Local quality

3Strength

If bonding layer paste contains large amount of binder or solvent, then bonding strength is improved, but difference in degreasing contraction factor causes stress during temperature rising

Engineering Contradiction:

Improvebonding strengthVSAvoiddegreasing stress

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

The bonding layer is segmented into multiple sub-layers with progressively adjusted binder/solvent content. This allows the degreasing process to occur in stages with reduced stress at each stage, while still achieving strong bonding. The first intermediate bonding layer has lower binder/solvent content to match the first ceramic sheet, reducing degreasing contraction stress.

Inventive Principle:

Principle #1Segmentation

4Device complexity

If innermost end portions of intermediate layers are aligned, then structure is simple, but stress concentrates at the boundary causing cracking

Engineering Contradiction:

Improvelayer structure complexityVSAvoidcracking resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The innermost end portions of the first and second intermediate bonding layers are deliberately positioned asymmetrically relative to each other, creating a staggered configuration. This asymmetry prevents stress concentration at any single boundary point during thermal processing, while the overall structure remains relatively simple with only two additional layers.

Inventive Principle:

Principle #4Asymmetry

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 multilayer structure effectively alleviates stresses, preventing cracking and flaking, thereby enhancing the reliability and longevity of the ceramic laminate body and gas sensor elements.

Implementation Method 1

a stress occurs due to a difference in linear coefficients of expansion of the two ceramic green sheets 112A, 114A

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the unburned laminate body is degreased during temperature rising step. When this takes place, since the bonding layer paste 116 contains a larger amount of binder or solvent than those contained in the ceramic green sheet 114 in normal practice. Therefore, during temperature rising step, a stress occurs in an area between the ceramic green sheet 114 and the bonding layer paste 116 due to a difference in degreasing contraction

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentUS7607339B2Ceramic laminate body, gas sensor element and related manufacturing method

Publication Date: 2009.10.27 DENSO CORP

AI summary

A ceramic laminate body, a gas sensor element employing such a ceramic laminate body and related manufacturing method are disclosed as including first and second ceramic sheets, made of material compositions different from each other, and an intermediate bonding layer, bonding the first and second ceramic sheets to each other so as to form a closed hollow space between the first and second ceramic sheets. The intermediate bonding layer has a multilayer structure including first and second unit intermediate layers laminated on each other such that innermost end portions of the first and second unit intermediate layers are displaced from each other to adapt a difference in degreasing contraction rates of associated component parts.