Variable Porosity Bond Layer for Power Semiconductor Thermal Management
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Solution Overview
Problem
Conventional high temperature bonding methods for power semiconductor devices, such as TLP sintering, result in bond layers with uneven porosity distribution, leading to increased susceptibility to cracking due to thermal expansion mismatches between substrates, particularly at the edges where less voids form, making them more dense and prone to cracking.
Innovation Solution
A method involving the application of varying forces to different areas of a substrate assembly during high temperature bonding, using a low melting point material and high melting point materials, to create a bond layer with a variable porosity distribution, where more dense areas are formed under applied force and less dense areas are formed without force, enhancing thermal conductivity and compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional high temperature bonding methods (TLP sintering) are used to bond substrates, then a bond layer is formed with high temperature stability, but the porosity distribution becomes uneven with less voids at edges, making the edge areas more dense and susceptible to cracking
Solution Approach 1:
The patent applies different forces to different areas of the substrate assembly during bonding - a first force to a first area and no force or a second force to a second area. This creates a bond layer with spatially varying porosity: areas under force have less porosity and higher density, while areas without force have more porosity and lower density. This local differentiation of properties allows the bond layer to have both high temperature stability and improved crack resistance at edges through controlled porosity distribution.
2Strength
If force is applied over the entire bonding assembly during high temperature bonding, then a strengthened bond layer is formed, but voids are suppressed near edges resulting in a more dense edge area that is more susceptible to cracking
Solution Approach 1:
The patent deliberately creates local quality differences in the bond layer by applying force only to specific areas rather than uniformly across the entire assembly. The first area under force develops a dense, strong structure, while the second area without force develops a more porous, compliant structure. This local differentiation allows the bond layer to exhibit both strength where needed and compliance at edges to prevent cracking.
Solution Approach 2:
The patent utilizes controlled porosity as a functional material property. By preventing void formation in areas under force while allowing or encouraging void formation in areas without force, the patent creates a bond layer where porosity distribution is used to achieve different mechanical properties - dense regions for strength and porous regions for compliance and crack resistance.
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 results in a bond layer with improved thermal and mechanical properties, reducing the likelihood of cracking by creating more compliant edges and maintaining high thermal conductivity, thus extending the operational life of the bond layer.
Implementation Method 1
a low melting temperature material, such as tin, diffuses into high melting temperature materials, such as copper, silver, or nickel
Implementation Method 2
an initial melting phase wherein a low melting temperature material, such as tin, diffuses into high melting temperature materials
Implementation Method 3
applying heat to the substrate assembly to form a bond layer between the first and second substrates
Data Source
AI summary
Methods and systems of bonding substrates include disposing a low melting point material and one or more high melting point materials having a higher melting temperature than a melting temperature of the low melting point material between a first substrate and a second substrate to form a substrate assembly including a contacting surface comprising first and second areas; applying a first force at the first area; and applying heat to form a bond layer between the first and second substrates. A first formed porosity of the bond layer is aligned with the first area of the contacting surface. A second formed porosity of the bond layer is aligned with the second area of the contacting surface to which the first force was not applied, and the first formed porosity is different from the second formed porosity.