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Aug 2019

Mott Precision High Purity Flow Restrictors Save Millions on Wafer Fab Gas Vent Systems

With Mott Precision High Purity Flow Restrictors you can reduce the flow of a catastrophic gas leak in minutes, not hours, meet SEMI S2 and SEMI S6 Guidelines, and reduce air vent requirements to save millions on your vent system construction.  In addition, the Mott Precision Flow Restrictors do not cause a turbulent gas flow stream which can diminish the performance of critical gas control components like mass flow controllers, pressure switches and transducers.  In fact, Mott porous metal Flow Restrictors condition the gas into a laminar flow which improves the performance of these sensitive instruments.

Reduce Air Vent Requirements, Save in Hardware

Installing Precision Flow Restrictors inside the gas containment systems (i.e., valve manifold box, tool isolation box, and gas cabinet) to limit the gas flow in a catastrophic event will lower the needed air replacement flow rate in these vented containment systems. Lower required vent air flow means smaller vent piping sizes.  With smaller vent piping sizes, you can save substantially on cost across all connections from the sub fab to the air handling and abatement systems, all with the installation of a cost-effective Mott Precision Flow Restrictor.

Vent Catastrophic Leaks in Minutes, Not Hours

Mott Precision Flow Restrictors help create a safer environment in your fab by limiting gas flow in a catastrophic event. As you can see in the chart above, with a Mott Flow Restrictor installed, the time to vent a leak at 2,000 PSI is about 3 minutes, versus 1,000 minutes in a system without a Flow Restrictor.

As a general rule of thumb, Mott Precision Flow Restrictors are sized at 125% of the maximum flow of the mass flow controller, or the required process flow. They can be installed in the gas isolation box, VMB or in the cylinder cabinet. Limiting gas flow into the box will limit the maximum flow in a catastrophic gas leak.

If sized correctly, the Mott Precision Flow Restrictor can be installed into the gas system without detrimental impact on downstream instrumentation. In fact, Mott Precision Flow Restrictors condition the gas into a laminar flow, which improves the performance of thermal and pressure-based mass flow controllers.

Precision Flow Restrictors can also be used in soft venting; back filling chambers from vacuum to atmosphere, replacing needle valves, calibrated orifices and mass flow controllers.

Meeting SEMI S2 and SEMI S6 Guidelines

The SEMI S6 EHS Guideline for Exhaust Ventilation of Semiconductor Manufacturing Equipment1 states:

7.2.3.3.2 NOTE 24 Engineering controls, such as excess flow valves, flow switches and Flow Restrictors can be used to limit the available flow and, thereby, reduce the exhaust ventilation required.

7.6.2 As the exhaust ventilation flow requirements depend strongly on the potential release, the equipment supplier should consider limiting the available flow of substances of concern, such as with Flow Restrictors or excess flow valves, as a means of reducing the required exhaust ventilation flow.

The SEMI S2 Environmental, Health, and Safety Guideline for Manufacturing Equipment2 states:

22.2 Equipment exhaust ventilation should be designed and a ventilation assessment conducted in accordance with both § 23.5 and SEMI S6, to control, efficiently and safely, for potential worst-case, realistic employee exposures to chemicals during normal operation, maintenance, or failure of other equipment components (hardware or software). All design criteria and test protocols should be based on recognized methods.

1SEMI S2-1016b Edition 2017- Environmental, Health and Safety Guideline for Semiconductor Manufacturing Equipment

2SEMI S6-0707 Edition 2007 - EHS Guideline for Exhaust Ventilation of Semiconductor Manufacturing Equipment

The Benefits of Porous Metal Restrictors

Mott’s High Purity Flow Restrictors use unique porous metal media was developed specifically for semiconductor manufacturing and provide compact, long-lasting flow control coupled with:

  • Design to your spec

You provide Mott your required size, flow rate, gases used in your environment, and we design the Mott Flow Restrictor to your needs. Downstream flows range from 100 SLPM to <1x10-6 SCCM. Mott Restrictors withstand sustained temperatures to 450°C (inert gas), and pressures to 120 psig, standard; up to 1500 psig by request.

  • Cost-effective design

Mott’s simple Flow Restrictor design consists of a porous metal element inside a standard fitting, providing maximum strength and reliability at a minimum cost.

  • All-metal construction

Porous metal elements constructed of 100% stainless steel and permanently affixed into 1/4" face seal fittings. Other alloys and configurations are available. There are no elastomers or other non-metallic materials which could flex or shed particles.

  • Fixed, tamper-proof performance

Each Mott Flow Restrictor delivers the specified downstream flow for the life of the product. There are no moving parts or potential operator adjustments which can hamper performance.

  • Clog-free performance, with laminar flow

The porous metal element spans the full width of the inner channel, allowing gases to move through hundreds of microchannels without increasing flow velocity or creating irregular flow paths. Downstream flow is smooth and constant, and the media will not wear from friction, or clog when exposed to sporadic particles

 

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