Platinum Ceramic Wiring Substrate Thermal Stress
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Solution Overview
Problem
Wiring boards used in high-temperature environments, such as those near internal combustion engines, face challenges with oxidation and mechanical fracture due to thermal stress from differences in thermal expansion coefficients between the insulating substrate and connection pads.
Innovation Solution
A wiring board design featuring a connection pad with a first portion composed of platinum containing a ceramic component and a second portion made of platinum, where the second portion is laminated with multiple flat metal layers, reducing oxidation and mechanical fracture by suppressing thermal stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a connection pad is made of metallic material such as tungsten, molybdenum, copper, or silver and is provided as a metallized layer by simultaneous firing of the insulating substrate, then electrical conductivity and connection reliability are improved, but oxidation resistance deteriorates in high-temperature environments
Solution Approach 1:
The connection pad is constructed as a composite structure with a first portion made of platinum-containing ceramic material and a second portion made of platinum. This composite material approach combines the advantages of ceramic materials (oxidation resistance, thermal stability) with precious metals (electrical conductivity, brazing performance), thereby resolving the contradiction between connection reliability and oxidation resistance in high-temperature environments.
Solution Approach 2:
The invention changes the material composition parameters of the connection pad by incorporating ceramic components into the platinum matrix. Specifically, the first portion contains platinum and ceramic material in specific proportions, which modifies the physical and chemical properties to achieve both good electrical conductivity and excellent oxidation resistance at high temperatures.
2Reliability
If the connection pad is made of metallic material with different thermal expansion coefficients than the insulating substrate, then electrical conductivity is improved, but mechanical fracture resistance deteriorates due to thermal stress
Solution Approach 1:
The platinum-containing ceramic composite material in the first portion of the connection pad has thermal expansion properties that better match the insulating substrate compared to pure metallic materials. This composite structure reduces thermal stress concentration at the interface, preventing mechanical fracture while maintaining electrical conductivity through the platinum component.
Solution Approach 2:
The connection pad is divided into two portions with different material compositions: the first portion (platinum-containing ceramic) provides thermal stress relief and oxidation resistance, while the second portion (pure platinum) provides excellent electrical conductivity and brazing performance. This local differentiation of material properties allows each portion to optimize for its specific function.
3Ease of manufacture
If the connection pad surface is made flat, then manufacturing simplicity is improved, but heat-resistant performance deteriorates due to thermal stress concentration
Solution Approach 1:
The connection pad surface is designed with local quality differentiation: the first portion has a convex curved surface that reduces thermal stress concentration and improves heat resistance, while the second portion has a flat surface that facilitates manufacturing and assembly. This localized surface design allows each portion to optimize for its specific requirements.
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 design enhances the heat-resistant properties of the wiring board, preventing oxidation and mechanical failure, thereby providing improved reliability in high-temperature applications.
Implementation Method 1
the first and the second portion are, both, less prone to be oxidized even at high temperatures and hence oxidation in the connection pad or the like can be suppressed
Implementation Method 2
mechanical fracture in the connection pad or the like caused by a thermal stress resulting from a difference between thermal expansion coefficients of the insulating substrate and the connection pad
Data Source
Figure 1(a)~1(b)
Figure 2(a)~3
Figure 4
AI summary
A wiring board includes an insulating substrate (1) composed of a ceramic sintered compact; and a connection pad (2) disposed on a surface part of the insulating substrate. The connection pad includes a first portion (2a) disposed on the surface part of the insulating substrate and a second portion (2b) disposed on the first portion and an outer periphery of the second portion being located on an inner side of an outer periphery of the first portion. The second portion (2b) of the connection pad is composed of platinum, and at least an exposed surface part of the first portion (2a) of the connection pad is composed of platinum containing a ceramic component. Since a brazing material used when a lead terminal is joined to the connection pad does not readily flow onto the second portion (2b), an outer periphery of the brazing material and the outer periphery of the connection pad are located at different positions, and fracture in the connection pad caused by thermal stress concentration on the outer periphery of the connection pad, or the like is suppressed. Further, an exposed surface of the connection pad is composed of platinum or platinum containing a ceramic component, and therefore does not readily oxidize. Thereby, an excellent heat-resistant wiring board or the like can be obtained.