Mixed Flow Gas (MFG) Chamber

Multiple-gas atmospheres controllable at the ppm level	No time limit on exposure
Temperature and humidity control	Large chamber
Two entire systems operating in parallel	ASTM B827, ASTM B845, EIA-364-65A, IEC 60068-2-60, DC-10611 Rev-A

These are used to simulate or amplify exposure to environmental conditions which electrical contacts or connectors can be expected to experience in various application environments. 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.

Short  in a microelectronic circuit due to corrosion attack and dendritic growth

The mixed flowing gas (MFG) test is a laboratory test in which the temperature, relative humidity, concentration of gaseous pollutants, 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.  Test samples that have been exposed to MFG testing have ranged from bare metal surfaces, to electrical connectors, and to complete assemblies. 

These are used to simulate or amplify exposure to environmental conditions which electrical contacts or connectors can be expected to experience in various application environments. 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 to evaluate the performance of these connectors.

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 (Cl₂), 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 200 parts per million (ppm) each. 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 in the range of 500 hours.

Several general and industry-specific standards are available for mixed flowing gas testing methods.  General standards include the following.

ASTM B 827 – Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests.

ASTM B 845 – 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.

Some industry-specific standards for which Matco Associates, Inc. has experience with include the following.

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.   Correlations need to be drawn between accelerated test exposed and long-term field exposed samples and components.Test samples which have been exposed to MFG tests have ranged from bare metal surfaces, to electrical connectors, and to complete assemblies. In addition to make-up air and water vapor, typical corrosive gas species used in MFG testing include chlorine, nitrogen dioxide, hydrogen sulfide, and sulfur dioxide. The concentrations of the corrosive gas species can range up to 200 parts per million (ppm) each. The relative humidity of the gas mixture is usually maintained between 70 – 75% and the temperature between 30 - 40° C (86 - 104° F). The duration of the test is variable, but is usually in the range of 500 hours.