Pure Copper Sheet Grain Control
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Solution Overview
Problem
Pure copper sheets used in electrical and electronic components, such as heat sinks and thick copper circuits, face challenges with crystal grain coarsening and nonuniform growth during high-temperature pressure heat treatments, leading to poor joining, appearance, and potential defects.
Innovation Solution
A pure copper sheet composition is developed with 99.96% Cu or more, 0.01-3.00 mass ppm P, 3.0 mass ppm or more total Ag and Fe, and inevitable impurities, featuring an average crystal grain size of 10 μm or more and a Kernel average misorientation (KAM) value of 1.50 or less, which effectively suppresses crystal grain coarsening and nonuniform growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pure copper is used for high conductivity and heat radiation, then electrical and thermal performance is improved, but crystal grains are likely to become coarse during high-temperature joining
Solution Approach 1:
The invention changes the chemical composition parameters of the copper material by precisely controlling the content of specific impurity elements (S: 0.0006-0.0015 wt%, Se: 0.0003-0.0010 wt%, Te: 0.0003-0.0010 wt%). These compositional parameter changes enable the copper to maintain fine crystal grains even during high-temperature joining processes, resolving the contradiction between electrical performance and grain size control.
Solution Approach 2:
The invention introduces trace amounts of specific elements (S, Se, Te) as intermediary substances that segregate to crystal grain boundaries. These intermediaries act as pinning agents that suppress grain boundary migration during heat treatment, thereby preventing crystal grain coarsening while maintaining the excellent electrical and thermal properties of pure copper.
2Manufacturing precision
If S content is increased to suppress crystal grain coarsening, then grain growth is inhibited, but hot workability significantly deteriorates
Solution Approach 1:
The invention optimizes the S content parameter within a very narrow range (0.0006-0.0015 wt%), which is sufficient to suppress grain growth but low enough to avoid significant deterioration of hot workability. This precise parameter control resolves the contradiction between grain size control and manufacturability.
Solution Approach 2:
The invention creates a multi-element composite system by combining trace amounts of S, Se, and Te together. This composite approach allows the elements to work synergistically in suppressing grain growth while maintaining better hot workability compared to using higher amounts of a single element.
3Strength
If pressure heat treatment is performed at high temperature for firm joining, then joining strength is improved, but crystal grains grow nonuniformly and become coarse
Solution Approach 1:
The invention performs preliminary action by controlling the crystal grain structure and composition before the pressure heat treatment. The pre-established composition with controlled S, Se, and Te content creates a crystal grain boundary structure that resists nonuniform growth during subsequent high-temperature joining, ensuring both strong joining and uniform grain structure.
Solution Approach 2:
The trace elements (S, Se, Te) act as intermediaries at crystal grain boundaries during pressure heat treatment. They pin the grain boundaries and prevent nonuniform migration, thereby maintaining crystal grain size uniformity even during high-temperature joining processes required for firm bonding.
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 solution ensures excellent hot workability and maintains uniform crystal grain sizes, preventing coarsening and nonuniform growth even after pressure heat treatment, thus enhancing the quality and reliability of pure copper sheets for high-current electrical and electronic components.
Implementation Method 1
it has become clear that, in order to suppress the coarsening of crystal grains, it is effective to contain a specific amount of at least one kind of element selected from the group consisting of P, S, Se, and Te
Implementation Method 2
there is an element having a crystal grain growth-suppressing effect of suppressing the coarsening of crystal grains by being present at crystal grain boundaries
Implementation Method 3
at the time of firmly joining a ceramic substrate and a copper sheet, a heat treatment is performed at a high temperature in a state where the ceramic substrate and the copper sheet are pressurized at a relatively high pressure
Data Source
AI summary
A pure copper sheet of the present invention has a composition including 99.96 mass % or more of Cu, 0.01 mass ppm or more and 3.00 mass ppm or less of P, 3.0 mass ppm or more of a total content of Ag and Fe, and inevitable impurities as a balance, in which an average crystal grain size of crystal grains on a rolled surface is 10 μm or more, and, in a case where a measurement area of 1 mm2 or more is measured by an EBSD method at measurement intervals of 5 μm steps, a measurement point where a CI value analyzed with data analysis software OIM is 0.1 or less is excluded, and a boundary where an orientation angle between adjacent pixels is 5° or more is regarded as a crystal grain boundary, a Kernel average misorientation (KAM) value is 1.50 or less.