Lead Frame Layout for Creepage, Clearance, and Die Pad Stability
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Solution Overview
Problem
High voltage semiconductor packages face challenges in maintaining adequate creepage and clearance while minimizing package size, especially with additional terminals that require more leads, which can compromise the separation distance between voltage-blocking leads.
Innovation Solution
A lead frame design with a row of leads featuring a first outermost lead continuously connected to the die pad and a second outermost lead with a central span width greater than interior and outer spans, along with angled edges and tapered configurations, enhances creepage and clearance by stabilizing the die pad and reducing lead vibration during wire bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additional terminals are added to high voltage semiconductor devices, then device functionality and performance are improved, but creepage and clearance between voltage-blocking leads are reduced
Solution Approach 1:
The lead frame utilizes a multi-dimensional layout where leads are arranged in multiple rows and columns rather than a single linear arrangement. This spatial distribution across different dimensions allows additional terminals to be added while maintaining adequate creepage and clearance distances between voltage-blocking leads through optimized positioning in the lead frame structure.
Solution Approach 2:
Different regions of the lead frame are designed with different lead configurations. Voltage-blocking leads have optimized spacing and positioning in critical areas, while other leads accommodate additional terminals. The lead frame structure provides localized optimization where creepage and clearance are maintained between high-voltage leads while allowing dense packing in non-critical areas.
2Volume of moving object
If package size is reduced, then miniaturization goals are achieved, but creepage and clearance between leads are compromised
Solution Approach 1:
The lead frame transitions from a two-dimensional planar arrangement to a three-dimensional structure with leads extending at different heights and angles. This vertical dimensionality allows creepage and clearance to be maintained through z-axis separation while reducing the overall footprint area, enabling miniaturization without compromising electrical isolation.
Solution Approach 2:
The lead frame structure nests multiple leads within a compact configuration where inner leads are positioned closer to the center and outer leads are arranged around them. This nested arrangement maximizes space utilization while maintaining minimum creepage and clearance distances between adjacent leads, achieving miniaturization with preserved electrical isolation.
3Productivity
If leads are positioned closer together, then package density is improved, but lead vibration during wire bonding increases
Solution Approach 1:
The lead frame provides localized mechanical support structures at specific positions where leads are most susceptible to vibration. Reinforcement ribs and support elements are strategically placed beneath critical leads to provide local stiffness without increasing overall package size, thereby reducing lead vibration during wire bonding while maintaining high package density.
Solution Approach 2:
The lead frame utilizes composite material construction combining different metal alloys with varying mechanical properties. Softer materials provide flexibility to absorb vibration, while harder materials provide structural rigidity. This composite approach allows leads to be positioned closely together while the material composition dampens vibration during wire bonding operations.
Data Source
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AI summary
A lead frame includes a die pad, a row of two or more leads that extend away from a first side of the die pad, and a peripheral structure disposed opposite the die pad and connected to each lead. A first outermost lead is continuously connected to the die pad. A second outermost lead has an interior end that faces and is spaced apart from the die pad. A width of the second lead in a central span of the second lead is greater than the width of the second lead in interior and outer spans of the second lead, the interior span of the second lead separating the central span of the second lead from the interior end of the second lead, the outer span of the second lead separating the central span of the second lead from the peripheral structure.