Ceramic Frame Stress Mitigation in Semiconductor Devices
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Solution Overview
Problem
The semiconductor device's ceramic frame is prone to cracking due to differences in linear expansion coefficients between the copper base and ceramic frame, particularly at the boundary between the top and lower stage portions, leading to potential leaks during thermal cycling.
Innovation Solution
Incorporating a molybdenum buffer member between the copper base and alumina ceramic frame, and adding a reinforcing metal pattern on the lower stage portion, along with an upper stage connection portion to alleviate the stress concentration caused by the height difference, ensures the frame's integrity and prevents cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a copper base and alumina ceramic frame are directly mounted together, then the device structure is simple, but cracks occur in the frame due to different linear expansion coefficients during thermal cycling
Solution Approach 1:
A molybdenum buffer member is introduced between the copper base and alumina ceramic frame to serve as an intermediary layer. This buffer member has a linear expansion coefficient that bridges the gap between copper and alumina, reducing thermal stress concentration and preventing frame cracks during thermal cycling while maintaining structural integrity
Solution Approach 2:
The device employs a composite structure combining copper base, molybdenum buffer member, and alumina ceramic frame. Each material is selected for its specific properties: copper for electrical conductivity and heat dissipation, molybdenum for intermediate thermal expansion characteristics, and alumina for mechanical strength and insulation, creating a multi-material composite system that resolves the thermal expansion mismatch
2Reliability
If the frame has a large height difference between top and lower stage portions, then the sealing and electrode functions are improved, but stress concentration occurs at the boundary leading to cracks
Solution Approach 1:
An upper stage portion is added in the vertical dimension between the top and lower stage portions of the frame. This creates a stepped structure with three levels (top, upper stage, lower stage) that gradually transitions the height difference, distributing stress across multiple boundaries rather than concentrating it at a single sharp transition point
Solution Approach 2:
The frame is segmented into multiple stages (top portion, upper stage portion, lower stage portion) rather than a single continuous structure. This segmentation creates intermediate transition zones that reduce stress concentration at each boundary, preventing cracks while maintaining the necessary height differences for sealing and electrode functions
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 solution effectively prevents cracks in the lower stage portion of the frame, maintaining the semiconductor device's air-tightness and reliability during thermal stress, such as in a 50-cycle heat test from -65°C to 175°C.
Implementation Method 1
Since the copper base and the ceramic frame have different linear expansion coefficients, a crack can be generated in the frame due to a difference in linear expansion coefficient
Data Source
AI summary
A semiconductor device including a base, a buffer member, a frame, a lid, and a semiconductor element, is disclosed. The ceramic frame is mounted on the copper base with the molybdenum buffer member interposed therebetween. The semiconductor element is sealed in a space within the frame defined by the lid. The frame includes a top portion, a lower stage portion that is disposed below the top portion and is provided with an input electrode and an output electrode, and an upper stage portion. The upper stage portion is formed in an arrangement direction of the input electrode and the output electrode, and is formed below the top portion and above the lower stage portion. The upper stage portion includes an upper stage connection portion formed on the periphery of the lower stage portion in a direction intersecting the arrangement direction of the input electrode and the output electrode.