Lead Frame Jog Design for Creepage Distance
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Solution Overview
Problem
Packaged semiconductor devices struggle to meet the required creepage distance for high voltage isolation under worst-case dimensional conditions, as existing lead frame and package designs fail to achieve the necessary distance between high and low voltage leads.
Innovation Solution
The implementation of lead frames with progressively increasing offsets or jogs in the intermediate segments of leads and reduction in the cross-section of metal features like retention bars exposed through the encapsulant, along with a Y-shaped retention bar configuration, to enhance the creepage distance around the package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard lead frame and package designs are used, then manufacturing simplicity is maintained, but creepage distance between high voltage and low voltage leads is insufficient under worst-case dimensional conditions
Solution Approach 1:
The lead frame structure is segmented into multiple functional zones: high voltage lead region, low voltage lead region, and intermediate region with retention bars. This segmentation allows independent optimization of each region to achieve required creepage distance while maintaining overall structural integrity and manufacturability
Solution Approach 2:
Different regions of the lead frame are assigned different functional qualities: the intermediate region contains retention bars with specific cross-sectional dimensions to provide electrical isolation, while the high voltage and low voltage regions are positioned to maximize creepage distance. This local differentiation resolves the contradiction by optimizing specific areas rather than uniformly increasing overall complexity
2Reliability
If lead width and plating thickness are increased to meet creepage requirements, then creepage distance is improved, but the overall package dimensions and lead spacing must be increased
Solution Approach 1:
Retention bars are introduced as intermediary elements between high voltage and low voltage leads. These retention bars provide the necessary electrical isolation and contribute to creepage distance without requiring increased spacing between the functional leads themselves, thus maintaining compact package dimensions while meeting isolation requirements
Solution Approach 2:
Instead of increasing creepage distance solely in the horizontal plane by increasing lead spacing, the solution utilizes the vertical dimension through the retention bar structure. The retention bars extend in the thickness direction and provide isolation path length, allowing creepage distance requirements to be met without increasing the footprint or lead spacing
3Reliability
If retention bar cross-section is reduced to increase creepage distance, then isolation performance is improved, but mechanical strength and retention capability are reduced
Solution Approach 1:
The retention bar cross-sectional dimensions are optimized to specific parameter ranges: width between 0.1-0.5mm and thickness between 0.05-0.2mm. These parameter changes balance the competing requirements of providing sufficient creepage distance contribution while maintaining adequate mechanical strength for die retention and resistance to molding stresses
Data Source
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AI summary
A packaged lead frame includes a encapsulant having a first minor side, a second minor side opposite the first minor side, a third minor side, and a fourth minor side opposite the third minor side, and a plurality of leads along the third minor side between the first minor side and a center plane between the first and second minor side. The plurality of leads extend outwardly from the encapsulant at a first plane. Each of the plurality of leads includes a corresponding jog external to the encapsulant which jogs away from the center plane, wherein the corresponding jog of each lead from a first lead of the plurality of leads closest to the center plane to a last lead of the first plurality of leads closest to the first minor side jogs incrementally further away the center plane.