Multi-Layer Spacer Structure for Thermal Mismatch in Power Modules
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Solution Overview
Problem
Existing spacers in double-sided cooling power modules face challenges due to high costs of composite materials like Al—SiC, and when made of pure copper, they experience thermal expansion coefficient mismatch with substrates, leading to stress and reliability issues, along with complex preparation and quality control problems.
Innovation Solution
A multi-layered spacer is developed with first metal layers of copper and a second metal layer of molybdenum or copper-molybdenum, having a lower thermal expansion coefficient, which are alternately stacked to control thermal conductivity and expansion, eliminating the need for copper plating and reducing thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If spacers are made of pure copper to reduce cost, then manufacturing cost is reduced, but thermal expansion coefficient mismatch with substrate increases causing stress and reliability issues
Solution Approach 1:
The spacer is constructed as a composite structure with a copper base material and a copper oxide layer. This composite configuration allows the spacer to maintain the low cost advantage of copper while the copper oxide layer reduces thermal expansion coefficient mismatch with the substrate, thereby improving reliability without significantly increasing manufacturing cost.
2Reliability
If composite materials like Al-SiC are used for spacers to match thermal expansion coefficients, then reliability is improved, but manufacturing cost increases
Solution Approach 1:
The invention uses a composite structure of copper and copper oxide layers. This approach achieves thermal expansion coefficient matching similar to expensive Al-SiC composites but at a fraction of the cost, as copper and copper oxide are much more economical materials while still providing the necessary thermal and mechanical properties.
Solution Approach 2:
By controlling the thickness and oxidation state of the copper oxide layer, the invention adjusts the effective thermal expansion coefficient of the spacer to match the substrate. This parameter control allows achieving reliable thermal matching without the high material costs of traditional composite materials like Al-SiC.
3Reliability
If copper plating is applied to spacer surfaces to prevent inter-metal diffusion, then protection is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The invention extracts and utilizes the natural oxidation property of copper by forming a copper oxide layer directly on the spacer surface during the sintering process. This eliminates the need for separate copper plating steps, reducing manufacturing complexity while still providing protection against inter-metal diffusion between the spacer and semiconductor chip.
Solution Approach 2:
The copper oxide layer forms automatically during the sintering process through self-oxidation of the copper surface. This self-forming protective layer eliminates the need for external plating processes, simplifying the manufacturing workflow while maintaining protective functionality against inter-metal diffusion.
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 configuration allows for adjustable thermal properties, improved reliability, and cost-effectiveness by minimizing thermal expansion mismatch and eliminating the need for copper plating, enhancing the power module's performance and reducing the risk of short circuits.
Implementation Method 1
a second metal layer made of a second metal having a thermal expansion coefficient lower than a thermal expansion coefficient of the first metal and disposed between the first metal layers
Implementation Method 2
Heat occurring in the semiconductor chip and electric current flowing through the semiconductor chip are likely to be conducted to the spacer. Thus, the spacer has to be made of a material having a high electrical conductivity, a high thermal conductivity
Data Source
AI summary
A multi-layered spacer of which a thermal expansion coefficient and a thermal conductivity are controllable and a double-sided cooling power module including the multi-layered spacer, is provided between a semiconductor chip and a substrate in a double-sided cooling power module. The multi-spacer includes first metal layers made of a first metal and provided as at least respective outermost layers, and a second metal layer made of a second metal having a thermal expansion coefficient lower than a thermal expansion coefficient of the first metal and disposed between the first metal layers provided as the outermost layers.