Power Semiconductor Press-Fit Terminal Constriction Design
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Solution Overview
Problem
Power semiconductor devices with high current densities face challenges in assembly due to increased terminal rigidity, leading to potential connection failures and reduced reliability, especially with temperature changes causing stress and increased contact resistance.
Innovation Solution
The design incorporates a constriction portion with lower rigidity than the terminal, allowing it to deform and absorb positional deviations and thermal stresses, ensuring easy mounting and reliable electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cross-section area of the terminal is made large to handle high current density, then the current carrying capacity is improved, but the rigidity of the terminal increases making it difficult to accommodate placement errors and inclination
Solution Approach 1:
The terminal structure is designed with non-uniform cross-sectional area along its length. The root portion has a larger cross-section for high current carrying capacity, while the intermediate portion has a reduced cross-section providing flexibility. This local variation in geometry allows each part of the terminal to have optimized properties for its specific function.
Solution Approach 2:
The terminal is divided into distinct portions with different structural characteristics: a root portion for mechanical support and current conduction, an intermediate portion with reduced rigidity for stress absorption and alignment tolerance, and a distal portion for electrical connection. This segmentation allows the terminal to simultaneously achieve rigidity where needed and flexibility where beneficial for assembly.
2Reliability
If there is a difference in linear expansion coefficient between the power semiconductor device and the connected apparatus, then temperature changes cause repeated stress in the terminal, but increasing terminal rigidity would prevent deformation
Solution Approach 1:
The terminal's rigidity parameter is varied along its length by changing the cross-sectional area. The intermediate portion has reduced rigidity to allow controlled deformation that absorbs thermal expansion stress, preventing stress concentration that would compromise contact reliability under temperature cycling conditions.
3Adaptability or versatility
If a bent portion is formed at the leg portion to follow placement error, then the adaptability to positional deviation is improved, but the insertion process becomes complex requiring precise face pressing
Solution Approach 1:
Instead of a fixed bent portion that requires precise insertion alignment, the terminal incorporates a flexible intermediate portion that can dynamically deform during insertion to accommodate positional deviations. This dynamic adaptation simplifies the insertion process by eliminating the need for precise face pressing while maintaining adaptability to misalignment.
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 configuration enhances the reliability and ease of assembly of power semiconductor devices by reducing stress on contacts and preventing excessive deformation, even under conditions of temperature change and positional errors.
Implementation Method 1
the constriction portion with a lower rigidity can deform preferentially to the outer terminal portion to thereby reduce the stress
Implementation Method 2
if there is a difference in linear expansion coefficient between the power semiconductor device and the connected apparatus, because of a temperature change during their use or at the time of starting/stopping operation thereof, there is also a possibility that a stress is repeatedly produced in the terminal
Data Source
Figure 1A
Figure 1B~2
Figure 3
AI summary
This invention is provided with: a circuit board(5) which is placed in a package (2) and in which an electric circuit including a power semiconductor element (6) is formed; and a plurality of press-fit terminals (3) each having a wire-bond portion(35) electrically connected in the package (2) to the electric circuit, a press-fit portion (32) for making electrical connection with an apparatus to be connected, and a body portion (33) whose one end portion continuous to the wire bond portion (35) is internally fastened to the package (2) and whose other end portion supports the press-fit portion (32) so as to place the press-fit portion away from the package (2); wherein in each of the plurality of press-fit terminals (3), at a portion in the body portion (33) exposed from the package (2), there is formed a constriction portion (36) that is constricted from both sides in a direction perpendicular to the center line, so as to leave a portion around the center line.