Molded Semiconductor Module Stepped Creepage Design
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Solution Overview
Problem
Current molded semiconductor module designs fail to meet the required creepage distance standards due to the limited gap between the module and the cooler, leading to increased complexity and cost in cooler design, and suboptimal material properties.
Innovation Solution
A dual-gauge leadframe with a thicker and thinner part, where the semiconductor die is attached to the thicker part, and a molding compound with a stepped region is used to increase the creepage distance, allowing for additional isolation material in the gap between the module and the cooler without violating the sub 1 mm distance requirement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a flat molded semiconductor module is pressed onto a cooler with only TIM separating them, then the module achieves good thermal contact, but the creepage distance is significantly reduced because the gap is less than 1 mm and must be handled as non-existent according to safety standards
Solution Approach 1:
The patent introduces a stepped region on the bottom surface of the molding compound that creates additional vertical and horizontal dimensions for the creepage path. Instead of relying solely on the lateral distance along the module bottom, the stepped region adds vertical segments (first and second generally vertical parts) and a horizontal segment (generally horizontal part) that collectively increase the creepage distance in three-dimensional space, allowing the creepage path to exceed 1 mm even when the module is pressed directly onto the cooler with minimal TIM thickness.
2Reliability
If the cooler is specially designed with a plateau in the region of attachment to increase creepage distance, then the creepage distance is improved, but the cost and complexity of the cooler design increase
Solution Approach 1:
Instead of modifying the cooler design to provide a plateau or larger footprint (which would increase cooler complexity and cost), the patent inverts the approach by modifying the module itself - specifically, by creating a stepped region on the bottom surface of the molding compound. This shifts the complexity from the cooler side to the module side, allowing the cooler to remain simple while still achieving the required creepage distance through the module's three-dimensional stepped structure.
3Reliability
If the cooler is designed with a smaller footprint than the molded semiconductor module, then the creepage distance may be increased, but the cost and complexity of the cooler design increase
Solution Approach 1:
Rather than requiring the cooler to have a smaller footprint or specially designed plateau (which increases cooler complexity), the patent inverts the solution by creating the creepage-enhancing structure on the module side through the stepped region. This allows the cooler to maintain its simple, cost-effective design while the module's stepped bottom surface provides the necessary three-dimensional creepage path.
4Ease of manufacture
If tolerances and material properties (stiffness, minimum wall thickness) are considered in cooler design, then manufacturing feasibility is improved, but both plateau and smaller footprint options become suboptimal
Solution Approach 1:
The patent segments the bottom surface of the molding compound into a stepped region with distinct vertical and horizontal parts, allowing each segment to be optimized independently. The first generally vertical part, generally horizontal part, and second generally vertical part can each be designed with appropriate dimensions and thicknesses that satisfy manufacturing tolerances and material property requirements, while collectively providing the necessary creepage distance. This segmented approach avoids the suboptimality of both plateau and smaller footprint designs.
Data Source
AI summary
A semiconductor module includes: a dual-gauge leadframe having thicker and thinner parts, part of the thinner part forming a high voltage lead; a semiconductor die attached to the thicker part; and a molding compound (MC) encapsulating the die. The thicker leadframe part is disposed at a bottom side of the MC. A side face of the MC has a stepped region between the high voltage lead and thicker leadframe part. A first generally vertical part of the stepped region extends from the high voltage lead to the generally horizontal part, a generally horizontal part of the stepped region extends to the second generally vertical part, and a second generally vertical part of the stepped region extends to the bottom side of the MC. A linear dimension of the generally horizontal part as measured from the first generally vertical part to the second generally vertical part is at least 4.5 mm.