Package Terminal C-Shape Bend Isotropic Stress Relief
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Solution Overview
Problem
The existing package terminals in power devices face reliability issues due to thermal stress from differing coefficients of thermal expansion and mechanical interference, leading to soldering layer fractures, especially when external forces align with the perpendicular direction of the Z-shape bend, which is not uniformly stress-relieved.
Innovation Solution
A package terminal design featuring a C-shape bend with a gradual change section, where the second section has a smaller area than the first section, providing isotropic stress relief and improved reliability by distributing stress evenly across the terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Z-shape bend is applied to the package terminal to release thermal stress, then the stress-releasing effect in the bending direction is improved, but the stress relief in the perpendicular direction is insufficient leading to directional selectivity
Solution Approach 1:
The patent applies a C-shaped curved bend instead of a Z-shape bend. The C-shaped structure with its smooth curvature provides more uniform stress distribution in all directions compared to the angular Z-shape. The curved geometry allows the terminal to flex and absorb thermal expansion stresses from multiple directions, reducing the directional selectivity problem while maintaining effective stress relief.
Solution Approach 2:
The patent employs a composite structure combining a bent portion with different cross-sectional areas (first section with larger area, second section with smaller area). This composite geometric design creates a gradient structure that optimizes both stress relief capability and isotropic performance. The varying cross-section allows the terminal to handle stresses from different directions more uniformly.
2Ease of manufacture
If the package terminal is designed with uniform cross-section, then the manufacturing process is simplified, but the stress concentration at the soldering points increases reducing reliability
Solution Approach 1:
The patent implements local quality variation by designing the bent portion with non-uniform cross-sectional area. The first section has a larger area to withstand higher stresses, while the second section has a smaller area to provide flexibility. This localized geometric optimization strengthens the soldering points without complicating the overall manufacturing process, as the gradient structure can be achieved through standard forming operations.
3Device complexity
If the package terminal uses a straight design without bends, then the structural simplicity is maintained, but the thermal stress from coefficient of thermal expansion causes soldering layer fractures
Solution Approach 1:
The patent introduces a C-shaped curved bend into the terminal structure to address thermal stress issues. This curvature provides the necessary flexibility to accommodate thermal expansion and contraction without fracturing the soldering layers. The smooth curved geometry effectively distributes thermal stresses along the bent portion, preventing stress concentration at the solder joints while maintaining relatively simple manufacturing.
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 C-shape bent portion effectively reduces stress concentration at the soldering points, enhancing the reliability and yield point of the package terminal, allowing it to withstand complex mechanical conditions without directional selectivity, thus improving the overall reliability of the power electronic module.
Implementation Method 1
the bent portion includes a first end and a second end, the first end is connected to the end portion, the second end is connected to the base, the bent portion includes a second section, and an area of the second section is smaller than an area of the first section
Data Source
AI summary
A package terminal is provided, which comprising: a base; an end portion with a first section; and a bent portion having a C-shape bend with a gradual change section, wherein the bent portion includes a first end and a second end, the first end is connected to the end portion, the second end is connected to the base, the bent portion includes a second section, and an area of the second section is smaller than an area of the first section.