Silver-Free Active Metal Ceramic Substrate Bonding
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Solution Overview
Problem
Conventional direct-bonding-copper (DBC) ceramic substrates face issues with thermal stress and high manufacturing costs due to the use of silver-copper-titanium (Ag—Cu—Ti) metal composite materials, which lead to peeling and electro-migration, and are inadequate for high-temperature, high-power applications.
Innovation Solution
A method involving the use of silver-free solder pastes with active metals like titanium and copper to form sub-solder layers on ceramic substrates, followed by high-temperature vacuum sintering to create a strong bonding layer without silver, enhancing the bonding force between the ceramic and conductive metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional active metal brazing paste material containing silver-copper-titanium (Ag-Cu-Ti) metal composite material is used, then bonding strength between copper foil and ceramic substrate is improved, but manufacturing cost increases and electro-migration issues occur
Solution Approach 1:
The patent removes silver (Ag) from the traditional Ag-Cu-Ti brazing paste composition, extracting the problematic noble metal component that causes high cost and electro-migration issues. The resulting Cu-Ti-based paste maintains bonding functionality without silver, resolving the contradiction between bonding strength and manufacturing cost.
Solution Approach 2:
The patent replaces expensive silver-containing brazing material with a cheaper copper-titanium-based paste that does not rely on noble metals. This substitution uses more affordable materials (Cu and Ti) to achieve the same bonding function, directly addressing the high manufacturing cost issue while maintaining adequate bonding strength for power module applications.
2Strength
If conventional active metal brazing paste material containing silver is used, then bonding strength is improved, but electro-migration problems occur due to silver residue after etching
Solution Approach 1:
The patent extracts and removes silver (Ag) from the brazing paste composition entirely, eliminating the source of electro-migration problems. By using a silver-free Cu-Ti-based paste, the harmful electro-migration effect is prevented at its source while maintaining the necessary bonding strength through the active metal titanium component.
Solution Approach 2:
The patent converts the potential harm of using expensive silver-containing materials into a benefit by deliberately excluding silver and using a copper-titanium system. This approach transforms the high cost and electro-migration risks into advantages of lower cost and improved electrical stability, while the titanium component continues to provide effective bonding to the ceramic substrate.
3Device complexity
If direct-bonding-copper (DBC) ceramic substrates are used without bonding material, then manufacturing simplicity is improved, but thermal stress causes copper layer peeling at high temperatures
Solution Approach 1:
The patent introduces an active metal brazing paste containing titanium as an intermediary bonding layer between the copper foil and ceramic substrate. This intermediary layer absorbs thermal stress through its material properties and creates a gradient transition, preventing direct stress transfer that would cause peeling in DBC structures, thereby improving thermal stability while adding minimal process complexity.
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 method improves bonding strength and reduces manufacturing costs by eliminating electro-migration issues while maintaining high reliability for high-power applications.
Implementation Method 1
Active metal elements (e.g., Ti, Zr, Ta, Nb, V, or Hf) of the active metal brazing substrate materials can wet a side surface of a ceramic substrate, so as to braze an ultra-thick copper foil onto the ceramic substrate at a high temperature.
Implementation Method 2
coating a first solder paste prepared by mixing a first metal solder material and a first organic medium onto a side surface of a ceramic substrate, and drying the first solder paste to form a first sub-solder layer
Implementation Method 3
followed by high-temperature vacuum sintering to create a strong bonding layer without silver
Data Source
AI summary
A method for producing an active metal ceramic substrate includes: coating a first solder paste prepared by mixing a first metal solder material and a first organic medium onto a ceramic substrate, and drying the first solder paste to form a first sub-solder layer; coating a second solder paste prepared by mixing a second metal solder material and a second organic medium onto the first sub-solder layer, and drying the second solder paste to form a second sub-solder layer; and disposing a conductive metal layer onto the second sub-solder layer, so as to form the active metal ceramic substrate. The first metal solder material includes a first active metal. The second metal solder material includes a metal tin and a metal copper, and selectively includes a second active metal. The first metal solder material and the second metal solder material do not contain any metal silver.