Substrate With Low Elastic Modulus Layer For Thermal Stress
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Solution Overview
Problem
The existing substrates for electronic devices face issues with thermal stress due to differing coefficients of thermal expansion between the metal sheet and the wiring substrate, leading to cracking or separation of the bonding material, especially as devices miniaturize and the bonded area decreases.
Innovation Solution
A substrate configuration where a second wiring substrate with a lower elastic modulus is sandwiched between the first wiring substrate and the metal sheet, absorbing thermal stress through deformation and reducing the risk of bonding material cracks or separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal sheet and wiring substrate are bonded together with different coefficients of thermal expansion, then electrical connection is achieved, but thermal stress causes cracking or separation of the bonding material
Solution Approach 1:
The substrate is divided into three separate layers: a first wiring substrate, a second wiring substrate, and a metal sheet. This segmentation allows each layer to independently handle thermal expansion, reducing stress concentration in the bonding material between the first wiring substrate and metal sheet.
Solution Approach 2:
The second wiring substrate acts as an intermediary layer between the first wiring substrate and the metal sheet. This intermediate layer absorbs and distributes thermal stress, preventing direct stress transmission that would cause bonding material failure.
2Volume of moving object
If the bonded area between wiring substrate and metal sheet is reduced for miniaturization, then device size is reduced, but the risk of bonding material separation increases
Solution Approach 1:
By segmenting the bonding structure into two bonding interfaces (first wiring substrate to second wiring substrate, and second wiring substrate to metal sheet), the stress burden on each bonding material layer is reduced, allowing for smaller overall device size without compromising bonding reliability.
Solution Approach 2:
The elastic modulus of the second wiring substrate is specifically controlled to be lower than both the first wiring substrate and the metal sheet. This parameter change allows the second wiring substrate to deform more easily under thermal stress, protecting the bonding materials even in miniaturized devices with reduced bonded areas.
3Strength
If the elastic modulus of the intermediate layer is increased, then structural strength is improved, but thermal stress absorption capability is reduced
Solution Approach 1:
The elastic modulus of the second wiring substrate is optimized to be lower than both the first wiring substrate and the metal sheet. This parameter setting enables the second wiring substrate to serve as a stress-absorbing compliant layer while maintaining sufficient structural integrity for device assembly and operation.
Solution Approach 2:
The substrate assembly functions as a composite structure with three different materials having different elastic moduli. This composite configuration allows each material to contribute its optimal properties: the first wiring substrate provides structural support, the second wiring substrate provides stress absorption, and the metal sheet provides thermal conduction and mechanical strength.
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
This configuration effectively mitigates thermal stress, preventing cracks and separation in the bonding material, while allowing for a thinner, more reliable electronic device with improved stress distribution and bonding strength.
Implementation Method 1
the wiring substrate which is made from an insulating layer and the metal sheet have different coefficients of thermal expansion, and the metal sheet has a larger coefficient of thermal expansion than the wiring substrate. Therefore, when electronic elements are mounted on the top surface of the metal sheet of the above-mentioned substrate, heat generated during operation of the electronic elements creates thermal stress between the wiring substrate and the metal sheet
Implementation Method 2
thermal stress due to differences in the coefficients of thermal expansion of the first wiring substrate and the metal sheet is absorbed by deformation of the second wiring substrate, which has a relatively low elastic modulus
Data Source
AI summary
There is provided a substrate for mounting electronic elements, including: a frame-shaped first wiring substrate with a first through hole formed in an interior portion thereof; a flat plate-shaped or frame-shaped second wiring substrate arranged to overlap with a bottom surface of the first wiring substrate and electrically connected thereto; and a sheet-shaped metal sheet arranged to overlap with a bottom surface of the second wiring substrate such that the second wiring substrate is sandwiched between the first wiring substrate and the metal sheet, an area inside the frame-shaped first wiring substrate or areas inside the frame-shaped first wiring substrate and second wiring substrate being electronic element mounting areas, and the second wiring substrate having an elastic modulus lower than those of the first wiring substrate and the metal sheet.