Circuit Substrate Brazing Protrusion for Thermal Cycling
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Solution Overview
Problem
Conventional ceramic metal circuit substrates face limitations in thermal cycle test (TCT) durability at elevated temperatures, particularly when the operation guaranteed temperature exceeds 175°C, due to insufficient bonding strength and heat stress management between ceramic and metal components.
Innovation Solution
A circuit substrate design featuring a ceramic substrate with a three-point bending strength of 500 MPa or more, bonded with metal plates via brazing layers containing Ag, Cu, and Ti, with controlled protruding portions and Vickers hardness, to enhance bonding strength and alleviate heat stress, allowing for reduced thickness and improved TCT characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the operation guaranteed temperature of the semiconductor element is raised to 175°C or more, then the power density and performance of the power module can be improved, but the TCT characteristic and reliability of the ceramic metal circuit board deteriorate due to insufficient bonding strength and heat stress management
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Vickers hardness of the protruding portion within 700-900 HV and the ratio of its length to thickness within 0.5-3.0. These parameter optimizations enable the bonding structure to withstand thermal cycling at 175°C while maintaining reliable bonding, thus resolving the contradiction between high-temperature operation capability and TCT durability
Solution Approach 2:
The patent employs composite materials by using a brazing material layer containing Ag, Cu, and Ti that forms a protruding portion with specific hardness characteristics. This composite bonding structure combines the advantages of different materials to achieve both strong bonding strength for high-temperature operation and sufficient flexibility to manage heat stress during thermal cycling
2Reliability
If the gap of the protruding portion is reduced to improve TCT characteristic, then the bonding strength can be enhanced, but the ability to alleviate heat stress and maintain reliability at 175°C or more is limited
Solution Approach 1:
The patent resolves this contradiction by optimizing two key parameters simultaneously: the Vickers hardness of the protruding portion (700-900 HV) and its length-to-thickness ratio (0.5-3.0). This dual parameter control creates a bonding structure that maintains strong adhesion while possessing sufficient elasticity to accommodate thermal expansion and contraction at high temperatures, achieving both strong bonding and heat stress resistance
3Power
If multiple semiconductor elements are mounted on a ceramic metal circuit board to increase power density, then the performance of the power module can be improved, but the arrangement interval between metal plates must be narrowed which complicates the structure and reduces TCT characteristic
Solution Approach 1:
The patent enables narrower arrangement intervals between metal plates by optimizing the protruding portion's geometry (length-to-thickness ratio of 0.5-3.0) and hardness (700-900 HV). These parameter changes allow the bonding structure to maintain reliability even when metal plates are closely spaced, enabling higher power density while preserving TCT characteristics through enhanced heat stress management in the bonding joints
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 design achieves improved TCT durability and heat release performance, enabling the use of thinner ceramic substrates and thicker metal plates, which reduces the size of semiconductor devices while maintaining high power density and reliability.
Implementation Method 1
The metal plate is bonded to the ceramic substrate via a bonding layer formed by using a brazing material
Implementation Method 2
The bonding layer has a protruding portion which extends onto the ceramic substrate in a manner to protrude from between the ceramic substrate and the metal plate
Implementation Method 3
At least one of an average value of Vickers hardnesses of 10 places of the first portion or an average value of Vickers hardnesses of 10 places of the second portion is 883 MPa (90 kgf/mm2
Data Source
Figure 1~2
Figure 3~4
AI summary
To improve a TCT characteristic of a circuit substrate. The circuit substrate comprises a ceramic substrate including a first and second surfaces, and first and second metal plates respectively bonded to the first and second surfaces via first and second bonding layers. A three-point bending strength of the ceramic substrate is 500 MPa or more. At least one of L1/H1 of a first protruding portion of the first bonding layer and L2/H2 of a second protruding portion of the second bonding layer is 0.5 or more and 3.0 or less. At least one of an average value of first Vickers hardnesses of 10 places of the first protruding portion and an average value of second Vickers hardnesses of 10 places of the second protruding portion is 250 or less.