Segmented Lead Frame Clip for Semiconductor Thermal Stress
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Solution Overview
Problem
The connection between copper lead frames and semiconductor dies experiences stress due to differing thermal expansion coefficients, leading to cracks and failure, especially at high voltages and frequencies.
Innovation Solution
A lead frame design with spaced-apart contact elements, allowing lateral expansion and reduced stress, featuring multiple contact portions that can expand sideways, and a soldered connection with optional outgassing holes for enhanced durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the lead frame uses copper material with high electrical conductivity, then electrical propagation characteristics are improved, but thermal expansion stress increases due to different thermal expansion coefficients between copper and semiconductor materials
Solution Approach 1:
The second contact element is divided into multiple contact portions (at least two) that are spaced apart from each other. This segmentation allows the contact element to accommodate thermal expansion by distributing the stress across multiple separated contact areas, preventing concentrated stress that would lead to cracking in the semiconductor die.
2Ease of manufacture
If the contact element is designed as a single continuous structure, then manufacturing is simplified, but stress concentration occurs during thermal expansion leading to semiconductor die failure
Solution Approach 1:
The contact element is segmented into multiple contact portions with spaces between them, maintaining manufacturing simplicity while dramatically improving reliability by preventing stress concentration during thermal cycling.
3Area of stationary object
If the contact areas are closely spaced, then the electrical connection area is maximized, but thermal expansion stress concentrates and causes cracks in the semiconductor material
Solution Approach 1:
The contact element is divided into multiple contact portions spaced apart from each other. This segmentation distributes the thermal expansion stress across separated contact areas, preventing stress concentration and cracking while maintaining adequate total contact area for electrical connection.
Solution Approach 2:
The contact portions are positioned to contact specific local areas of the semiconductor die drain, with spacing between contact portions that allows for thermal expansion accommodation. Each contact portion maintains sufficient contact area for electrical connection while the spacing prevents stress concentration.
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
This design reduces stress by over 50% and ensures a durable connection, preventing semiconductor die failure under high voltage and frequency conditions.
Implementation Method 1
The connection comprises a mechanical and an electrical connection. Lead frames as such are known, and are an evolution of prior wire bond connections.
Implementation Method 2
Copper and semiconductor materials have different thermal expansion coefficients, which may lead to the connection between the lead frame and the semiconductor die being stressed when the lead frame heats.
Data Source
Figure 1~2
Figure 3
AI summary
A lead frame for connecting a semiconductor die to a base plate, the lead frame comprising: one or more lead portions, configured for connecting the lead frame to the base plate; a first contact element configured to be connected to a source of the semiconductor die; and a second contact element configured to be connected to a drain of the semiconductor die, wherein the second contact element comprises at least two contact portions that in an assembled state of the lead frame each contact the drain of the semiconductor die with a contact area thereof, the contact areas of the respective contact portions being spaced apart from each other.