Offset-Angle Busbar Structure for Thermal Stress Relief
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Solution Overview
Problem
The difference in coefficients of thermal expansion between semiconductor power module substrates and busbars leads to stress and potential disconnection at their interface due to varying thermal loads, reducing the reliability of the construction.
Innovation Solution
A busbar design with twisted sections that form an offset angle between the legs and feet, allowing for reduced stress at the interface by accommodating thermal expansion mismatch, and a method for manufacturing such busbars involving stamping, bending, and twisting of metal sheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional busbar structure with straight legs and feet is used, then the electrical connection is simple and direct, but the thermal expansion mismatch causes high stress and potential disconnection at the interface
Solution Approach 1:
The patent applies curvature by twisting the leg of the busbar along its longitudinal axis, forming a helical or spiral shape instead of a straight configuration. This curved geometry allows the busbar to accommodate thermal expansion differences between the copper busbar and ceramic substrate by flexing and deforming in a controlled manner, thereby reducing stress at the connection interface and preventing disconnection while maintaining electrical connectivity
Solution Approach 2:
The patent changes the geometric parameter of the busbar leg from a straight linear form to a twisted three-dimensional configuration. This parameter change introduces flexibility and stress distribution capabilities, allowing the connection to withstand thermal cycling without failure while maintaining reliable electrical contact
2Reliability
If the busbar is made from solid copper with high conductivity, then electrical performance is excellent, but the large coefficient of thermal expansion causes compatibility issues with the substrate
Solution Approach 1:
The twisted configuration of the busbar leg acts as a mechanical compliance element that absorbs thermal expansion differences. The helical geometry allows the copper busbar to expand and contract along its length without transmitting excessive stress to the ceramic substrate, effectively decoupling the thermal expansion behaviors of the two materials while maintaining electrical connectivity
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 offset angle design significantly reduces stresses at the interface, enhancing the reliability of the busbar-substrate connection by aligning thermal expansion mismatches, thereby preventing disconnection and improving the durability of semiconductor power modules.
Implementation Method 1
A problem occurs because the thermal expansion of the substrate and that of the busbar can be very different, due to the fact that their coefficients of thermal expansion (CTEs) are different.
Implementation Method 2
A typical power module comprises a baseplate on which is mounted a substrate such as a direct bonded copper substrate (DBC)... use a busbar structure to conduct a current in or out of the module
Data Source
AI summary
A conducting busbar (2, 4) suitable for use in a semiconductor power module (8) is provided. The busbar (2, 4) comprises a main plate (210, 410), one or more legs (220, 420) extending from the main plate (210, 410), and one or more feet (230, 430) formed at the free end of the legs (220, 420). According to the invention, the intersection line (L) between at least one of the legs (220, 420) and the associated foot (230, 430) forms an offset angle (α) with respect to the longitudinal direction (X) of the main plate (210, 410).