Multilayer Ceramic Substrate Thermal Expansion Gradient
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Solution Overview
Problem
Existing multilayer ceramic substrates face issues with disconnection of surface layer electrodes due to pore generation during the reduction in thickness, which affects the reliability and insulating properties of electronic devices.
Innovation Solution
A multilayer ceramic substrate design with a surface layer having a lower thermal expansion coefficient than the internal layer, utilizing glass containing 40-65% MO (CaO, MgO, SrO, BaO) and alumina, along with metal oxides like CuO and Ag2O, to promote vitrification and densification, thereby suppressing pore formation and electrode disconnection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of multilayer ceramic substrates is reduced to promote miniaturization, then the size of electronic devices is reduced, but pores are generated in the surface layer portion and internal layer portion causing disconnection of surface layer electrodes
Solution Approach 1:
The patent applies local quality by creating a gradient in thermal expansion coefficients across different layers. The surface layer portion has a lower thermal expansion coefficient than the internal layer portion, with the difference controlled within 0.3-1.5 ppmK−1. This localized property variation suppresses pore formation and electrode disconnection during cooling after firing, while enabling thickness reduction for miniaturization.
Solution Approach 2:
The patent changes the thermal expansion coefficient parameter between layers to resolve the contradiction. By setting the thermal expansion coefficient of the surface layer portion lower than that of the internal layer portion (difference of 0.3-1.5 ppmK−1), the patent prevents pore generation during thermal processing while maintaining reduced thickness for compact electronic devices.
2Strength
If the thermal expansion coefficient of the surface layer portion is set lower than that of the internal layer portion to improve flexural strength, then compressive stress is applied to outermost layers during cooling, but pores are generated causing disconnection of surface layer electrodes
Solution Approach 1:
The patent optimizes the thermal expansion coefficient difference parameter between surface and internal layers to within 0.3-1.5 ppmK−1. This controlled parameter change generates sufficient compressive stress on outermost layers during cooling to improve flexural strength, while avoiding excessive stress that would cause pore formation and electrode disconnection.
Solution Approach 2:
The patent uses composite materials with specific compositions in the surface layer portion containing glass (40-65 wt% MO), alumina (35-60 wt%), and metal oxides (1-10 wt%). This composite material design achieves the desired thermal expansion coefficient while maintaining structural integrity and preventing pore formation during thermal processing.
3Strength
If the difference in thermal expansion coefficient between surface layer portion and internal layer portion is increased to improve flexural strength, then compressive stress on outermost layers is increased, but pores are generated in the surface layer portion and internal layer portion
Solution Approach 1:
The patent precisely controls the thermal expansion coefficient difference parameter between layers within 0.3-1.5 ppmK−1. This optimized parameter range generates adequate compressive stress to improve flexural strength while preventing pore formation, thereby eliminating the harmful effect of pores without sacrificing structural strength.
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 reduces the disconnection of surface layer electrodes, maintains the insulating properties of the internal layer, and enhances the flexural strength of the substrate by controlling thermal expansion coefficients and metal oxide content.
Implementation Method 1
the thermal expansion coefficient of the surface layer portions is lower than the thermal expansion coefficient of the internal layer portion, and the difference in thermal expansion coefficient is 1.0 ppmK−1 or more
Implementation Method 2
utilizing glass containing 40-65% MO (CaO, MgO, SrO, BaO) and alumina, along with metal oxides like CuO and Ag2O, to promote vitrification and densification
Data Source
AI summary
A multilayer ceramic substrate that includes a surface layer portion positioned on an internal layer portion, and a surface layer electrode on a surface of the surface layer portion. The surface layer portion includes a first layer next to the internal layer portion, and the internal layer portion includes a second layer next to the first layer. The thermal expansion coefficient of the first layer is lower than the thermal expansion coefficient of the second layer. The first layer and the second layer each contain glass containing 40 weight % to 65 weight % of MO, where MO is at least one selected from CaO, MgO, SrO, and/or BaO); 35 weight % to 60 weight % of alumina, and 1 weight % to 10 weight % of at least one metal oxide selected from CuO and/or Ag2O.