Ceramic Circuit Substrate Brazing for Thermal Cycling Resistance
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Solution Overview
Problem
Ceramic circuit substrates in power modules face increased thermal stress due to harsher thermal cycling conditions, leading to bonding defects and cracks, despite previous methods controlling braze material length and structure, as greater stress concentrates in the braze material layer protruding portion under the outer edge of the copper circuit pattern.
Innovation Solution
The ceramic circuit substrate features a braze material layer with Ag-rich phases continuous for 300 μm or more towards the inside from the outer edge of the protruding portion, reducing interfaces between Ag-rich and Cu-rich phases, and a bonding void ratio of 1.0% or less, using a braze material composition of 85.0 to 95.0 parts by mass Ag, 5.0 to 13.0 parts by mass Cu, 0.4 to 2.0 parts by mass Sn or In, bonded in a vacuum or inert atmosphere at 770° C. to 900° C. for 10 to 60 minutes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the braze material layer protruding portion is used to relax thermal stress, then thermal cycling resistance is improved, but under harsher thermal cycling conditions, breaking occurs at the interface between Ag-rich phases and Cu-rich phases near the base of the braze material protruding portion
Solution Approach 1:
The invention changes the chemical composition parameters of the braze material, specifically setting Ag content to 85-95 mass% and Cu content to 5-15 mass%, creating a eutectic or near-eutectic composition that optimizes both stress relaxation and bonding strength under harsh thermal cycling conditions
Solution Approach 2:
The invention uses a composite braze material system combining Ag and Cu phases, where the Ag-rich continuous matrix provides stress relaxation while the Cu-rich dispersed phases enhance bonding strength, creating a synergistic composite structure that resolves the contradiction between softness and strength
2Strength
If Ag and Cu are used as braze material components, then bonding properties are improved, but interfaces between Ag-rich phases and Cu-rich phases become weak points under thermal stress
Solution Approach 1:
The invention applies local quality by creating a non-uniform microstructure where Ag-rich continuous phases are distributed throughout the braze material, providing localized stress relaxation zones at critical interfaces while maintaining overall bonding strength through the Cu-rich phases
Solution Approach 2:
The invention optimizes the Ag/Cu ratio parameter within specific ranges (Ag: 85-95 mass%, Cu: 5-15 mass%) to achieve a eutectic or near-eutectic composition that minimizes the formation of brittle intermetallic compounds and reduces the number of weak interfaces between Ag-rich and Cu-rich phases
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 enhances bonding properties and thermal cycling resistance, achieving a crack ratio of less than 2.0% after 2,500 cycles from −55° C. to 175° C., with a bonding void ratio of 1.0% or less and improved stress relaxation effects.
Implementation Method 1
there is a large difference between the thermal expansion coefficients of ceramic substrates and metal plates, and the load from repeated hot-cold cycles generates thermal stress caused by the differences in the thermal expansion coefficients at the bonding interfaces between the ceramic substrates and the metal plates... the braze material layer protruding portion... stress relaxation effects
Implementation Method 2
a braze material layer which comprises Ag, Cu, Ti, and Sn or In... bonding in a vacuum or inert atmosphere at 770° C. to 900° C. for 10 to 60 minutes... bonding void ratio of 1.0% or less
Data Source
AI summary
A ceramic circuit substrate having high bonding performance and excellent thermal cycling resistance properties, having a circuit pattern provided on a ceramic substrate with a braze material layer interposed therebetween, and a protruding portion formed by the braze material layer protruding from the outer edge of the circuit pattern, wherein: the braze material layer includes Ag, Cu, Ti, and Sn or In; and an Ag-rich phase is formed continuously for 300 μm or more, towards the inside, from an outer edge of the protruding portion, along a bonding interface between the ceramic substrate and the circuit pattern, and has a bonding void ratio of 1.0% or less.