Asymmetrical External Terminal Structure for Solder Stress Relief
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Solution Overview
Problem
High-power semiconductor modules face issues with thermal stress leading to solder peeling and cracking due to uneven thermal expansion, as existing terminal designs fail to effectively absorb stress changes, particularly when the terminal is soldered in the longer direction of a rectangular substrate.
Innovation Solution
The semiconductor-module external terminal features asymmetrical grooves on its bending portions to alter bending and shear strengths, allowing the terminal body to deform and absorb stress, thereby preventing solder fractures and cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional terminal with symmetrical structure is used, then the manufacturing is simple, but the terminal body cannot effectively absorb thermal stress causing solder cracks
Solution Approach 1:
The patent applies asymmetry by providing grooves of different depths at different positions on the terminal body. Specifically, a first groove is provided at a first position and a second groove is provided at a second position, where the depths of the grooves are different. This asymmetric groove structure creates non-uniform stress distribution that allows the terminal body to deform and absorb thermal stress effectively, preventing solder cracks while maintaining manufacturing feasibility.
Solution Approach 2:
The patent applies local quality by creating varying groove depths at specific locations on the terminal body rather than using a uniform structure. The different groove depths at different positions create localized stress concentration and deformation zones that match the thermal stress distribution pattern, enabling the terminal to absorb stress where needed while maintaining overall structural integrity.
2Strength
If the terminal body is made rigid to maintain structural strength, then the bending and shear strength are high, but thermal stress cannot be absorbed leading to solder peeling and cracking
Solution Approach 1:
The patent applies parameter changes by modifying the groove depth parameter at different positions on the terminal body. By creating grooves with different depths, the local flexibility and stress absorption capacity are adjusted without compromising the overall structural strength of the terminal body. This parameter variation allows the terminal to maintain strength while acquiring stress absorption capability.
Solution Approach 2:
The patent applies segmentation by dividing the terminal body into different regions with different groove characteristics. The first groove at the first position and the second groove at the second position create segmented zones with different mechanical properties, allowing each zone to handle stress differently while working together to protect the solder joints.
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 asymmetrical grooves enable the terminal body to effectively absorb thermal stress, reducing the likelihood of solder cracks and fractures, even under significant thermal stress conditions.
Implementation Method 1
thermal stress (bending stress and shear stress) causes a problem such as solder peeling and cracking when stress is applied to a substrate due to the temperature rise of the substrate
Implementation Method 2
a soldered portion located at the bottom portion of the external terminal is subjected to uneven stress due to a difference in thermal expansion of the sealing material
Data Source
AI summary
A semiconductor-module external terminal includes a bottom portion to be soldered and a terminal body vertically bent from the bottom portion, and the terminal body includes a first groove on a left end side and a second groove on a right end side of a bending portion which is bent immediately above the bottom portion, and the first groove and the second groove are asymmetrical with respect to a center line passing the terminal body in a vertical direction.