Mixed flowing gas (MFG) is a type of laboratory environmental testing for products, particularly electronics, to evaluate resistance to corrosion due to gases in the atmosphere. Mixed Flowing Gas (MFG) test is a laboratory test in which the temperature (°C), relative humidity (%RH), concentration of gaseous pollutants (in parts per billion, ppb or parts per million ppm level), and other critical variables (such as volume exchange rate and airflow rate) are carefully defined, monitored and controlled. The purpose of this test is to simulate corrosion phenomenon due to atmospheric exposure. The electronic product is exposed to gases such as chlorine, hydrogen sulfide, sulfide, nitrogen dioxide and sulfur dioxide at levels in the ppb range, in a controlled environmental chamber. Test samples that have been exposed to MFG testing have ranged from bare metal surfaces, to electrical connectors, and to complete assemblies. In regards to noble metal plated connector applications, MFG testing has been widely accepted as a qualification test method to evaluate the performance of these connectors.With regard to electrical and electronic applications, MFG testing has been widely accepted as a qualification test method to evaluate performance in the presence of environmental pollutants. The MFG exposures are generally used in conjunction with procedures which evaluate contact or connector electrical performance, such as measurement of electrical contact resistance before and after MFG exposure.
With regard to noble metal plated connector applications, MFG testing has been widely accepted as a qualification test method for evaluating the performance of connectors.
Exova MFG testing chamber attributes:
- Multiple-gas atmospheres controllable at the parts per billion (ppb) level
- No time limit on exposure
- Temperature and humidity control
- Chamber size: 24 inches wide by 28 inches long by 15 inches high
In addition to make-up air and water vapor, three or four corrosive gases are typically used. These pre-diluted gases are fed through mass flow meters into a mixing chamber prior to introduction into the MFG exposure chamber. The concentration of each gas can be controlled to the part per billion levels using these mass flow meters. The gases used in the test are chlorine (Cl), hydrogen sulfide (H2S), sulfur dioxide (SO2), and nitrogen dioxide (NO2).
All of the gases have natural and man-made sources. Different gaseous pollutants dominate in different field environments. The concentrations of the corrosive gas species can range up to 2 parts per million (ppm) each, or 2000 parts per billion. The relative humidity of the gas mixture is usually maintained between 70 – 75%, sometimes as high as 95%, and the temperature between 25 – 40° C (77 – 104° F). The duration of the test is variable, but is usually a maximum of 504 hours or 21 days.
Several general and industry-specific standards are available for mixed flowing gas testing methods. General standards include the following:
- ASTM B 827-97 – Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests.
- ASTM B 845-97 – Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
- ANSI/EIA-364-65A- Mixed Flowing Gas
- IEC 60068-2-60 – Flowing Mixed Gas Corrosion Test
- ISO 21207 — Corrosion tests in artificial atmospheres – Accelerated corrosion tests involving alternate exposure to corrosion-promoting gases, neutral salt-spray and drying.
- DC-10611 Rev-A
Some industry-specific standards we commonly test to include:
- General Motors GMW3431. Section 4.4.7.
- Daimler Chrysler DC-10611 Rev-A.
- Comcast Drop Passive Evaluation – Splitters, Section 4.4.
Since the MFG is an accelerated testing method, the determination of acceleration factor would be helpful to understand the durability or reliability of the device under test. In other words, if samples can survive a certain number of days in the testing chamber, it would be very useful to approximately estimate how many years it can last without corrosion problems in the field.
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