MIL-HDBK-2164A Military Handbook: Environmental Stress Screening Process for Electronic Equipment

The “MIL-HDBK-2164A Military Manual: Environmental Stress Screening Process for Electronic Equipment” developed by the United States Department of Defense describes guidelines for environmental stress screening (ESS) of electronic equipment, including environmental operation, measures taken upon detection of defects, and screening documentation. These guidelines provide a uniform ESS process that can be used to effectively detect manufacturing defects in electronic equipment due to poor workmanship and defective or marginal parts. It also identifies design problems when the design is inherently fragile or when qualification and reliability growth tests are too innocuous or have not been performed.

The most common stimuli used in environmental stress screening are temperature cycling and random vibration. A viable ESS program must be dynamic. The screening program must be actively managed and tailored to the specific characteristics of the equipment being screened. It should be noted that there are no universal screenings that are applicable to all equipment.

ESS is part of an applicable engineering development, manufacturing corrective action and revision process rather than a test in the normal accept/reject sense. ESS is designed to encourage defects, not to simulate the operating environment, and therefore factory failures are encouraged. Root causes of ESS failures must be found and corrected before a full process can occur.

The process described here can be applied to electronic assemblies, equipment, and systems in six broad categories distinguished by field service applications:

1. Fixed land equipment

2. Mobile ground vehicle equipment

3. Ship equipment

3A Sheltered

3b Open

4. Jet aircraft equipment

5. Turboprop and rotary wing aircraft equipment

6. Air-launched weapons and mounted external stores

ESS scans are typically performed according to MIL-WDBK-781 guidelines to ensure that the hardware is free from manufacturing defects. Design and manufacturing practice require that environmental stress scanning be applied to:

• All material purchases containing electrical, electronic, electro-optical, electro-mechanical or electro-chemical components in the program definition and risk reduction, engineering and manufacturing development, production, fielding/distribution and operational phases.
• Re-supplies and supply of spare and repair parts where the cost of ESS implementation can be economically amortized.
• Warehouse revision programs with opportunities for significant cost savings.
• Non-developmental products, such as commercial off-the-shelf and domestic or foreign military products, only to the extent that ESS has been implemented and documented during previous production.
• Systems, equipment and spare parts specifically designed to receive ESS.

For all ESSs, the following conditions must be met:

• ESS can be applied at any level of production, from part to finished product. It is intended to screen for defects in a way that will not damage the properly manufactured material. Hardware that proves to be very fragile may be excluded because the scanning environments can be very damaging, but the exclusion rate should be included in appropriate documentation (such as a stress screening plan).
• All scans must be performed in accordance with applicable guidelines set forth herein.
• There should be evidence of quality control acceptance of all required inspection or testing activities prior to commencement of any contractual environmental stress screening and whenever maintenance is performed.
• All testing must be completed prior to packaging the equipment.
• The specified conditions must be applied in the order specified in the figure.
• The equipment should first be placed in the environmental chamber and then operated to ensure satisfactory performance of both the equipment to be scanned and the screening facility. The time taken to verify the facility's compatibility with the equipment should not be counted as screening time.
• When a fault occurs and the defect is isolated and corrected, the equipment should be operated and its performance monitored to ensure proper diagnosis and correction.
• Unless otherwise specified, the performance of the equipment shall be verified before and after each environmental scan. Continuous functional monitoring shall be performed in accordance with the form given in the standard.
• During all equipment operation, functional parameters such as voltage and current must be maintained at the specified nominal values.
• The equipment’s built-in testing capabilities must be maximized to aid in performance monitoring. Built-in testing is the only way to monitor performance.
• Anticipation of failure should not be grounds for maintenance, for example if an output is observed to be degraded but is still within specification, no replacement or adjustment should be permitted unless such adjustments are normally made manually.
• Faults detected during scanning should be counted as occurring during the perfect period if the equipment used to monitor performance characteristics during scanning would not have detected the fault.

Unless otherwise stated, measurements and scans must be performed under the following conditions:

• Standard environment: Measurements and controls are carried out under room environmental conditions as follows: temperature 25 degrees plus/minus 10 degrees, relative humidity, uncontrolled room environment, atmospheric pressure, uncontrolled field pressure.
• Controlled environment: When the environmental conditions need to be strictly controlled, the following should be noted: temperature 23 degrees plus/minus 2 degrees, relative humidity 50 percent plus/minus 5 percent, atmospheric pressure 96.45kPa.
• Thermal scanning tolerances: The scanned product must be completely surrounded by an air envelope, except at required support points. The temperature gradient across this envelope, measured close to the scanned product, must be within plus/minus 2 degrees of the scanning temperature and must not exceed 1 degree per meter or a maximum of 2,2 degrees total when the equipment is not operating.
• Vibration test tolerances: The acceleration force spectral density of the sweep control signal shall not deviate from the specified guidelines by more than plus/minus 20 dB over the entire test frequency range from 1.000 Hz to 3 Hz and by no more than i1.000 dB over the sweep frequency range from 2.000 to 6 Hz. However, drifts of minus 500 dB in the sweep control signal for frequencies greater than 6 Hz due to fixture resonance, sweep element resonance, or facility limitations may be tolerated.
• Time: Elapsed time should be measured to an accuracy of plus/minus 1.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "MIL-HDBK-2164A Military Handbook: Environmental Stress Screening Process for Electronic Equipment" standard are also provided to businesses.