Bonded Copper Plate Edge Profile for Thermal Cycling Durability
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Solution Overview
Problem
Conventional bonded substrates with copper plates bonded to silicon nitride ceramic substrates face challenges in improving thermal cycling durability due to stress concentration at the ends of the copper plates, which limits their reliability as insulating heat-dissipating substrates for power semiconductor devices.
Innovation Solution
A bonded substrate design featuring a copper plate with a flared end surface and a silver-containing brazing material layer, where the copper plate has distinct silver concentration regions and a bonding layer with a protruding portion to distribute stress, improving thermal cycling durability by reducing stress concentration at specific corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protruding portion is formed in the bonding layer to suppress stress concentration, then thermal cycling durability is improved, but manufacturing complexity increases
Solution Approach 1:
The end surface of the copper plate is designed with different regions having different properties: a first region with a first angle (45°-60°) and a second region with a second angle (10°-30°), creating local quality variations that distribute stress concentration to different areas, thereby improving thermal cycling durability without requiring complex protruding portions in the bonding layer
Solution Approach 2:
The copper plate end surface employs an asymmetric multi-region angle design rather than a uniform angle, with the first region having a steeper angle (45°-60°) and the second region having a gentler angle (10°-30°), which asymmetrically distributes stress and improves reliability while maintaining manufacturing feasibility
2Strength
If the bonding layer thickness is increased to improve bonding strength, then bonding strength is improved, but stress distribution capability deteriorates
Solution Approach 1:
The bonding layer thickness is optimized within a specific range (5-20 μm) to balance bonding strength and stress distribution capability. This parameter optimization ensures sufficient bonding strength while maintaining the layer's flexibility to distribute thermal stress effectively across the interface
3Reliability
If the copper plate angle is decreased to reduce stress concentration, then stress distribution is improved, but manufacturing precision requirements increase
Solution Approach 1:
The copper plate end surface is divided into multiple regions with different angle characteristics (first region: 45°-60°, second region: 10°-30°), allowing stress distribution to be achieved through localized angle variations rather than requiring extremely precise control of a single uniform angle across the entire end surface
Solution Approach 2:
The end surface is segmented into distinct regions with different angle ranges, which divides the stress distribution function across multiple zones. This segmentation makes the manufacturing process more feasible by allowing each region to be controlled within broader tolerance ranges rather than requiring precise control of a single angle
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 design effectively distributes stress across the copper plate's corners, enhancing the thermal cycling durability of the bonded substrate, particularly when the copper plate's angles and silver concentration gradients are optimized within specific ranges.
Implementation Method 1
a brazing material layer is formed on a silicon nitride ceramic substrate. The brazing material layer contains an active metal brazing material. The active metal brazing material includes metal powder containing silver and at least one metal hydride powder selected from the group consisting of titanium hydride powder and zirconium hydride powder
Implementation Method 2
Silver contained in the brazing material layer is diffused into the copper plate. A first thickness-direction region containing silver and having a first silver concentration and a second thickness-direction region having a second silver concentration lower than the first silver concentration are formed in the copper plate
Implementation Method 3
The first portion and the second portion form an angle of 135° or more and 165° or less on an outside of the copper plate. An extended plane of the first portion and the second main surface form an angle of 110° or more and 145° or less on a side where the second portion is located. When the bonded substrate is exposed to thermal cycling, stress is caused to be distributed to the vicinity of a corner between the first portion and the second portion and the vicinity of a corner between the second main surface and the end surface
Data Source
AI summary
A second main surface of the copper plate is opposite a first main surface of the copper plate, and is bonded to a silicon nitride ceramic substrate by the bonding layer. A first portion and a second portion of an end surface of the copper plate form an angle of 135° to 165° on an outside of the copper plate. An extended plane of the first portion and the second main surface form an angle of 110° to 145° a side where the second portion is located. A distance from the second main surface to an intersection of the first portion and the second portion in a direction of a thickness of the copper plate is 10 to 100 μm. The second main surface extends beyond the extended plane of the first portion by a distance of 10 μm or more.