Laminate Mount Structure for Thermal Stress Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing mount structures for heat-generating devices like LEDs face challenges in efficiently dissipating heat due to increased thermal stress and strain, leading to crack formation and reduced heat dissipation properties, especially when the joining area is large, and the use of Sn—Pb solder exacerbates these issues.
Innovation Solution
A mount structure is developed with a laminate configuration that includes a ceramic substrate electrode and a metal substrate electrode joined by a laminate with specific interface layers and solder joining portions, where the thickness of the laminate is between 30 μm and 100 μm, and the differences in solder joining portion thickness, elastic moduli, and linear expansion coefficients are minimized to reduce stress concentration and prevent crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the joining area is increased to dissipate heat more efficiently, then heat dissipation performance is improved, but thermal stress and thermal strain increase leading to crack formation
Solution Approach 1:
The joining portion is divided into multiple regions with different solder thicknesses. The first region has a first thickness and the second region has a second thickness different from the first. This segmentation allows different parts of the joining area to handle thermal stress differently, preventing crack propagation while maintaining large overall joining area for heat dissipation.
Solution Approach 2:
Different regions of the joining portion are given different local properties through varying solder thickness. The first region and second region have distinct thickness characteristics optimized for their specific locations, allowing the structure to better distribute and manage thermal stress across the large joining area.
2Reliability
If a thick first joining material is used to reduce stress, then crack resistance improves, but ceramic substrate inclination occurs due to wettability differences
Solution Approach 1:
The joining material is segmented into multiple regions with different thicknesses rather than using a uniformly thick layer. This segmentation allows stress management while controlling the overall profile to prevent substrate inclination during mounting.
Solution Approach 2:
Different local thicknesses are implemented in different regions of the joining material. The first region has a first thickness and the second region has a second thickness, creating local quality variations that balance stress distribution with substrate flatness maintenance.
3Ease of manufacture
If Sn-Pb based solder is used for joining, then ease of manufacture improves, but bearing strength is low making crack suppression difficult
Solution Approach 1:
The joining portion uses a composite structure with multiple materials including Sn-Pb based solder in the first region and a different solder material in the second region. This composite approach combines the ease of manufacture of Sn-Pb solder with the high strength of other solder materials, achieving both manufacturability and crack resistance.
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 proposed mount structure effectively withstands large thermal stress and prevents crack development, ensuring reliable heat dissipation and maintaining the ceramic substrate's orientation, thus enhancing the performance of heat-generating devices like LEDs.
Implementation Method 1
two members, which are a substrate and a heat dissipation section, are joined for transporting heat from the substrate on which elements are mounted to the heat dissipation section
Implementation Method 2
As the temperature is changed due to heat generation when the mount structure is operated, thermal stress and thermal strain are generated due to a difference in linear expansion coefficients between members
Data Source
AI summary
A mount structure having a joining capable of withstanding development of cracks generated by thermal stress due to repeated temperature changes in a mount structure having the joining of a large area is formed by joining a ceramic substrate electrode of a ceramic substrate and a metal substrate electrode of a metal substrate by a laminate, in which the laminate is formed by stacking a first interface layer, a first solder joining portion, a second interface layer, a first buffer material electrode, a buffer material, a second buffer material electrode, a third interface layer, a second solder joining portion and a fourth interface layer in this order from the ceramic substrate electrode toward the metal substrate electrode, a thickness of the laminate is 30 μm or more and 100 μm or less, a difference between a thickness of the first solder joining portion and a thickness of the second solder joining portion is within 25%, and differences in elastic moduli and in linear expansion coefficients between the first solder joining portion and the buffer material are respectively within 62%.