Thermally Expandable Material Fail-Open Mechanism
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Solution Overview
Problem
Power semiconductor devices, such as MOSFETs, can fail in a short-circuit condition due to dielectric breakdown or metallization shorts, leading to localized resistive heating and potential thermal ignition, which poses a safety hazard, especially in automotive systems, as the thermal overload is difficult to detect and control.
Innovation Solution
Incorporating a thermally expandable material, like a bimetallic strip, that creates an open circuit between the semiconductor device and the circuit board when a high temperature is reached, preventing further heating by physically displacing the package and breaking the electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power semiconductor device operates in a short-circuit condition, then localized resistive heating occurs, but thermal ignition and safety hazards increase
Solution Approach 1:
The patent employs a thermally expandable material positioned between the semiconductor device and circuit board. When the device temperature exceeds a threshold, the material expands thermally, physically pushing the device away from the circuit board to create an air gap that interrupts the electrical connection and stops current flow, thereby preventing thermal ignition
Solution Approach 2:
The thermally expandable material acts as an intermediary element between the semiconductor device and the circuit board. It mediates the thermal protection function by expanding in response to heat and mechanically separating the device from the board, thus interrupting the electrical path without requiring external control systems
2Reliability
If reflowable thermal protection devices are coupled in series with the gate, then thermal protection is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the thermal protection function from the electrical circuit domain and implements it mechanically through a thermally expandable material. This eliminates the need for reflowable thermal protection devices coupled in series with the gate, simplifying the circuit configuration while maintaining thermal protection capability
Solution Approach 2:
The patent replaces the electrical/chemical protection mechanism (reflowable thermal protection devices) with a purely mechanical protection mechanism (thermally expandable material that physically separates the device). This substitution simplifies the overall system by eliminating complex circuit configurations
3Temperature
If local heating occurs in a small region of the semiconductor material, then high temperatures are achieved, but current detection becomes difficult
Solution Approach 1:
The thermally expandable material provides self-service thermal protection by automatically expanding when it reaches its thermal expansion temperature. This self-activating mechanism eliminates the need for external thermal detection and control systems, as the material directly responds to its own thermal state and interrupts the circuit autonomously
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 thermal ignition by ensuring an open circuit is formed at elevated temperatures, thereby safeguarding against device and system fires, without requiring additional components or series resistance, thus reducing costs and testing needs.
Implementation Method 1
a region of thermally expandable material configured to push the first surface of the semiconductor package away from the circuit board when a temperature of the thermally expandable material exceeds a first temperature
Data Source
AI summary
In accordance with an embodiment, a semiconductor package includes a first surface configured to be mounted on a circuit board, and a region of thermally expandable material configured to push the first surface of the semiconductor package away from the circuit board when a temperature of the thermally expandable material exceeds a first temperature.