Mass Flow Controller Back Pressure Adjustment for Low Flow Rates
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Solution Overview
Problem
Mass flow controllers face challenges in achieving low fluid flow rates in backpressure environments, particularly in semiconductor manufacturing, where rapid reduction of flow rates is required without compromising precision and efficiency.
Innovation Solution
A mass flow control apparatus featuring a control module, variable control valves, proportional control valves, pressure sensors, and a shutoff valve, which dynamically adjust fluid pressure and flow rates to maintain desired operating conditions, including a method for flow verification using pressure-volume-temperature measurements to ensure accurate flow control across varying pressures and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mass flow controller operates in a backpressure environment, then it can maintain stable upstream pressure, but it becomes difficult to achieve low fluid flow rates
Solution Approach 1:
A variable control valve is introduced as an intermediary component between the tool and the mass flow controller. This valve acts as a mediator to manage the backpressure environment, allowing the MFC to maintain stable upstream pressure while the variable valve handles the pressure differential needed to achieve low flow rates. The intermediary valve decouples the conflicting requirements of pressure stability and low flow capability.
2Speed
If the fluid flow rate is rapidly reduced to a low set point, then response time is improved, but flow control precision deteriorates
Solution Approach 1:
The system employs dynamic control by adjusting the variable valve's opening degree based on real-time flow rate requirements. During rapid flow reduction, the valve opens more to maintain pressure differential and flow control precision. At steady low flow rates, the valve maintains an optimal opening to preserve accuracy. This dynamic adjustment allows the system to achieve both fast response and high precision across different operating conditions.
3Productivity
If a variable control valve is added to manage backpressure, then low flow rate capability is improved, but device complexity increases
Solution Approach 1:
The variable control valve is designed to perform multiple functions: managing backpressure, enabling low flow rates, and assisting in flow verification through pressure differential measurement. By consolidating these functions into a single multi-functional component, the system avoids adding multiple separate devices, thereby limiting the increase in overall system complexity while achieving the desired low flow rate capability.
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
Enables rapid and precise adjustment of flow rates, extending the useful operating range of mass flow controllers and ensuring accurate delivery even at low flow rates, thereby improving manufacturing efficiency in semiconductor processes.
Implementation Method 1
A second pressure sensor located upstream from the variable control valve, the second pressure sensor configured to measure back pressure from the tool
Implementation Method 2
A thermal-based flow sensor includes fluid conduit with two spaced apart temperature responsive elements affixed to the exterior of the fluid conduit
Data Source
AI summary
A mass flow control apparatus comprising a proportional valve upstream of a flow measurement portion, a pressure sensing element fluidly connected to determine a fluid pressure downstream of the flow measurement portion, and a dynamically adjustable variable valve downstream of the flow measurement portion and adjacent to the pressure sensing element connection. Fluid conductance of the variable valve is adjusted according to a control scheme based upon limitations of the flow measurement portion. Integral flow verification may be enabled with additional fluid pathway elements upstream of the flow measurement portion.