Ceramic Copper Circuit Board Bonding for Low Warp Control
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Solution Overview
Problem
High bonding temperatures in ceramic copper circuit boards lead to thermal stress and distortion due to large copper crystal grains, which are difficult to control and result in increased load on bonding equipment.
Innovation Solution
A bonded body with a ceramic substrate and copper plate bonded via an active metal brazing layer, where the copper plate's surface has a controlled percentage of crystal grains with diameters greater than 400 μm, and the bonding temperature is maintained below 800°C to suppress grain growth and warp, using an active metal brazing material with specific compositions like Ag-Cu-Ti to enhance bonding strength and reduce thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high bonding temperature (780-850°C) is used to bond ceramic substrate and copper plate, then bonding strength is improved, but thermal stress increases causing distortion and large copper crystal grains form which are difficult to control
Solution Approach 1:
The patent changes the bonding temperature parameter from conventional high temperatures (780-850°C) to a lower range (720-800°C), and further optimizes it to 740-780°C. This parameter change reduces thermal stress and prevents excessive copper crystal grain growth while maintaining adequate bonding strength through optimized brazing material composition
Solution Approach 2:
The patent uses a composite brazing material containing Ag (30-70 wt%), Cu (5-40 wt%), and Ti (5-20 wt%). This composite material composition provides both strong bonding capability at lower temperatures and control over copper crystal grain growth, resolving the contradiction between bonding strength and distortion control
2Strength
If high bonding temperature is used, then bonding strength is improved, but load on bonding equipment increases
Solution Approach 1:
The patent reduces the bonding temperature parameter from 780-850°C to 720-800°C, which directly reduces the power consumption and load on bonding equipment while maintaining bonding strength through optimized material composition rather than relying solely on high temperature
3Manufacturing precision
If bonding temperature is reduced below 720°C, then thermal stress and distortion are reduced, but bonding strength decreases
Solution Approach 1:
The patent employs a composite brazing material with Ag (30-70 wt%), Cu (5-40 wt%), and Ti (5-20 wt%) that enables strong bonding at lower temperatures (740-780°C). The Ti component specifically controls copper crystal grain growth while Ag-Cu provides strong bonding, allowing both low warp and high bonding strength to be achieved simultaneously
Solution Approach 2:
The patent applies local quality by having the brazing material distribute differently at the bonding interface versus bulk. The Ti enriches at the interface to control grain growth locally, while Ag-Cu provides bulk bonding strength, enabling optimized performance at lower temperatures
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 approach effectively reduces warp and maintains high bonding strength, allowing for larger ceramic substrate sizes and enabling the production of multiple components with minimal distortion, while also suppressing Ag diffusion into the copper plate.
Implementation Method 1
a brazing material that includes Ag, Cu, Ti, or the like is used as a bonding layer
Implementation Method 2
a brazing material that includes Ag, Cu, Ti, or the like is used as a bonding layer
Implementation Method 3
the bonding is performed at a high bonding temperature of 780 to 850° C.
Implementation Method 4
a number percentage of copper crystal grains having major diameters greater than 400 μm
Data Source
AI summary
A bonded body includes a ceramic substrate and a copper plate, in which the copper plate is bonded to the ceramic substrate via a bonding layer, the copper plate includes a surface perpendicular to a direction in which the ceramic substrate and the copper plate are bonded, and a number percentage of copper crystal grains having major diameters greater than 400 μm in three 5 mm×5 mm regions included in the surface is not less than 0% and not more than 5%. The bonding temperature is favorably not more than 800° C. The number percentage of the copper crystal grains having major diameters greater than 400 μm is favorably not more than 1%.