Vacuum Substrate Cooling via Sealed Gas Pressure
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Solution Overview
Problem
Existing methods for cooling large area substrates in vacuum are ineffective for achieving rapid cooling without causing substrate deflection and stress, which can lead to breakage, and are not suitable for high throughput and low-cost manufacturing of CdS/CdTe photovoltaic modules.
Innovation Solution
The apparatus employs sealed gas volumes between cooling plates and the substrate, maintaining higher pressure than the ambient vacuum, with inert dry nitrogen as the heat transfer gas, to prevent deflection and stress, and allows for controlled cooling with linear motion of the plates, ensuring efficient heat transfer without direct contact that could damage thin films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radiation cooling alone is used in vacuum, then the substrate can be cooled without direct contact, but the cooling time is excessively long (hours instead of minutes)
Solution Approach 1:
The patent introduces a gas medium (such as nitrogen or helium) as an intermediary between the substrate and the cooling environment. This gas medium enables conductive and convective heat transfer, dramatically accelerating the cooling process from hours to minutes while still preventing direct contact between the substrate and cooling surfaces, thus maintaining substrate integrity.
Solution Approach 2:
The patent utilizes pneumatic principles by introducing a controlled gas flow into the vacuum chamber during the cooling process. The gas flow creates convection currents that enhance heat removal from the substrate, transforming the cooling mechanism from pure radiation to a combination of conduction, convection, and radiation, thereby reducing cooling time significantly.
2Productivity
If fast cooling methods are used to reduce cooling time, then productivity increases, but substrate deflection and stress occur leading to breakage
Solution Approach 1:
The gas medium serves as a cushioning intermediary that enables rapid heat transfer without requiring direct contact between the substrate and cold surfaces. This eliminates the mechanical stress and deflection that would occur with direct contact cooling methods, allowing fast cooling while maintaining substrate integrity.
Solution Approach 2:
The patent changes the physical parameters of the cooling environment by introducing a gas medium with specific thermal conductivity and heat capacity properties. By selecting appropriate gases and controlling their pressure and flow rate, the system achieves optimal heat transfer coefficients that enable rapid cooling without exceeding the substrate's thermal stress tolerance.
3Loss of time
If direct contact cooling is used, then cooling efficiency is high, but thin films on the substrate are damaged
Solution Approach 1:
The gas medium acts as a protective intermediary layer between the substrate and the cooling environment. This layer enables efficient thermal conduction and convection while physically preventing direct contact between the substrate (with its delicate thin films) and any cooling surfaces or mechanisms, thus protecting the thin films from damage.
Solution Approach 2:
The patent replaces mechanical direct-contact cooling systems with a gas-phase cooling system. Instead of using physical contact with cold plates or cooling surfaces that could damage thin films, the system uses gas molecules to transfer heat through conduction and convection, eliminating the mechanical damage risk while maintaining high cooling efficiency.
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 approach enables rapid cooling of substrates from 200°C to 25°C within 2-4 minutes, maintaining substrate integrity and allowing for high-volume processing, while using the same gas for both cooling and ambient conditions to prevent contamination and reduce costs.
Implementation Method 1
Gas flowing through these thin heat transfer regions is the transfer medium employed to either heat or cool the substrate in a vacuum
Implementation Method 2
The rate of radiation cooling is governed by the difference in temperature between the hot object and the colder surroundings. The thermal radiation cooling rate is proportional to the quantity Thot4−Tcold4.
Data Source
AI summary
The present invention is directed to an apparatus and method for rapid cooling of a large substrate in a vacuum environment. A first cooled plate is brought into close proximity with one surface of a flat substrate. The spatial volume between the first cooling plate and the substrate is sealed and brought to a higher pressure than the surrounding vacuum level to increase the cooling efficiency. A second cooled plate is brought into close proximity with the opposite surface of the flat substrate. A second spatial volume between the second cooling plate and the substrate is sealed and the gas pressure is equalized to the gas pressure in the first spatial volume. The equalization of the gas pressure on both sides of the flat substrate eliminates deflection of the substrate and bending stress in the substrate.