Ceramic Substrate Exposure Region for Die-Capacitor Stress Relief
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In electronic modules, particularly those used in satellites, the difference in linear expansion coefficients between the metal base and the ceramic substrate induces strain and stress in the ceramic substrate, leading to potential cracking of die-capacitors mounted on the ceramic substrate during temperature cycle tests.
Innovation Solution
The electronic module design includes a ceramic substrate with an exposure region on its back surface where the back metal layer is not provided, allowing for stress alleviation by matching the substrate's edge shape to the die-capacitor's footprint and using eutectic solder with specific metal combinations like gold-tin, which reduces stress accumulation and prevents cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a back metal layer is provided on the entire back surface of the ceramic substrate for mounting, then the electrical connection and mechanical strength are improved, but the stress concentration increases leading to die-capacitor cracking
Solution Approach 1:
The back metal layer is segmented into multiple regions: a first region with full metal layer coverage for electrical connection, and a second region with reduced or no metal layer coverage for stress relief. This segmentation allows different areas to serve different functions - electrical connectivity and mechanical strength in the first region, and stress reduction in the second region.
Solution Approach 2:
Different regions of the back surface are given different metal layer configurations. The first region has a complete back metal layer for optimal electrical connection and strength, while the second region has a reduced or absent metal layer to minimize stress concentration. This local differentiation optimizes both electrical performance and stress distribution.
2Reliability
If the linear expansion coefficient mismatch between metal base and ceramic substrate is addressed by adding stress relief features, then the cracking resistance is improved, but the manufacturing complexity increases
Solution Approach 1:
The back metal layer pattern is designed in advance during the substrate fabrication process to include stress relief regions. This preliminary design of the metal layer distribution (with reduced coverage in certain areas) proactively addresses the thermal expansion mismatch issue before assembly, avoiding the need for additional stress relief features or complex post-processing.
3Stress or pressure
If the back metal layer coverage is reduced to alleviate stress, then the stress concentration is decreased, but the electrical connection area is reduced
Solution Approach 1:
The back surface is divided into functional zones: a first region with complete metal layer coverage that provides both electrical connection and mechanical strength, and a second region with reduced metal layer coverage that primarily provides stress relief. This segmentation ensures that electrical connection requirements are met in the first region while stress management is optimized in the second region.
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 effectively reduces the average stress on die-capacitors, preventing cracking and enhancing the reliability of electronic modules under extreme temperature conditions, as demonstrated by stress analysis and temperature cycle tests.
Implementation Method 1
The ceramic substrate is mounted on the metal base via eutectic solder
Data Source
AI summary
The electronic module including a metal base, a ceramic substrate, and a die-capacitor is disclosed. The ceramic substrate is mounted on the metal base via eutectic solder. The ceramic substrate includes a main substrate having a back surface facing the metal base and a front surface opposite to the back surface, and a back metal layer placed on the back surface of the main substrate and joined to the eutectic solder. The die-capacitor is mounted on the front surface of the ceramic substrate along one edge of the ceramic substrate. The back surface of the ceramic substrate is provided with an exposure region where the back metal layer is not provided. The exposure region includes a main region corresponding to an outer shape of the die-capacitor spreading along the front surface and an edge region extending from the main region to the one edge of the ceramic substrate.