Power Semiconductor Device Phase-Change Thermal Interface
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Solution Overview
Problem
The existing power semiconductor devices experience a phenomenon known as 'grease pump-out' due to thermal expansion, leading to increased heat resistance and deteriorated heat dissipation characteristics under heat cycles, as the thermal conductivity paste is extruded from the radiating surface to the cooling fin.
Innovation Solution
A power semiconductor device design featuring a heat conduction layer on the radiating surface with a sealing material having a higher linear expansion coefficient than the insulating substrate, which remains solid at ambient temperature and liquid at higher temperatures, preventing extrusion by maintaining the heat conduction layer between the substrate and cooling unit during temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If thermal conductivity paste is applied to dissipate heat from power semiconductor elements, then heat dissipation is improved, but the paste is extruded from the portion between cooling surface and cooling fin under heat cycles
Solution Approach 1:
The patent changes the physical state parameter of the heat conduction material from solid paste to phase-change material that transitions from solid at ambient temperature to liquid at operating temperature. This parameter change allows the material to remain stationary when solid during assembly while becoming liquid to fill gaps and maintain thermal contact during operation, preventing extrusion under heat cycles
Solution Approach 2:
The patent applies phase transition phenomenon by using a heat conduction material that undergoes solid-liquid phase change at a specific temperature. The material is solid at ambient temperature for stable assembly, then transitions to liquid state at operating temperature to maintain thermal contact without being extruded, solving the reliability issue of paste retention under thermal cycling
2Loss of energy
If a cooling fin is attached to the radiating surface with thermal conductivity paste, then heat dissipation is improved, but the radiating surface warps with temperature changes causing paste extrusion
Solution Approach 1:
The patent changes the physical state parameter of the heat conduction material to accommodate the warping of the radiating surface. The phase-change material transitions from solid to liquid, allowing it to flow and fill the gaps created by thermal warping, thereby maintaining thermal contact without being extruded from the interface
3Loss of energy
If thermal conductivity paste is used for heat conduction, then heat dissipation is improved, but heat resistance increases due to pump-out phenomenon under heat cycles
Solution Approach 1:
The patent utilizes phase transition to maintain consistent thermal contact. The heat conduction material transitions from solid to liquid at operating temperature, allowing it to self-adjust and fill any gaps or voids that may form during thermal cycling, thereby preventing the increase in heat resistance that would otherwise occur due to paste pump-out
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 solution effectively prevents the extrusion of the heat conduction layer, maintaining efficient heat dissipation and reducing contact heat resistance, allowing for a compact cooling fin configuration and reliable cooling performance.
Implementation Method 1
The heat conduction layer is solid at ambient temperature and is liquid at a temperature higher than or equal to a phase-change temperature higher than ambient temperature
Implementation Method 2
The sealing material has a linear expansion coefficient greater than a linear expansion coefficient of the insulating substrate in an in-plane direction of the mounting surface of the insulating substrate
Implementation Method 3
The heat conduction layer is located on the radiating surface and is solid at ambient temperature and is liquid at a temperature higher than or equal to a phase-change temperature higher than ambient temperature
Data Source
AI summary
An insulating substrate includes a base portion that is made of metal and serves as a radiating surface, an insulating layer, and a circuit pattern. The insulating substrate has convex warpage in the radiating surface at ambient temperature. A power semiconductor element is mounted on the circuit pattern. A sealing material has a thickness greater than a thickness of the insulating substrate. The sealing material has a linear expansion coefficient greater than a linear expansion coefficient of the insulating substrate in an in-plane direction of a mounting surface of the insulating substrate. A heat conduction layer is located on the radiating surface of the base portion and is solid at ambient temperature and is liquid at a temperature higher than or equal to a phase-change temperature higher than ambient temperature.