In order to rapidly insert the latest technology and maintain our technological lead, commercial-off-the-shelf (COTS) components are increasingly incorporated into military applications. Not only does this significantly reduce the design cycle time to rapidly introduce equipment into the battlefield, it addresses the shrinking DoD market share and the declining supplier base for “Mil-Spec” components.

However, some COTS products may not hold up to harsh military environments and use. Many applications require COTS component modifications to meet the military environmental (MIL-STD-810), power (MIL-STD-704), and EMI (MIL-STD-461) standards.

Testing can determine a method in which COTS parts can be utilized in harsh conditions. The following example (Figures 4-1 through 4-3) shows a modification which meets MIL-STD-810F Method 509.4 for Salt Fog Testing. Sample specimens were shielded by the “device under test” and subjected to salt fog. The images show the corrosive effects due to electromechanical reaction and accelerated stress corrosion or formation of acidic/alkaline solution following salt ionization in water.

The following are some issues that a designer would have to consider when using COTS parts for the DoD, Navy, and Army.

• Pure tin plating should be avoided on COTS parts. It can cause the growth of tin whiskers. Refer to the Government Electronics and Information Association (GEIA)standards for guidelines on the use of lead free materials in military electronics modules.
  
  
• COTS connectors should be replaced with military qualified connectors to meet environmental and vibration requirements. In cases where COTS connectors can not be replaced due to special circumstances, a hard wire connection or a locking mechanism should be added to prevent loosening in a harsh environment. Applying shock absorbers or wire rope isolators to the design would also help with shock and vibration.
  
  
• Integrated circuits (ICs) that fall outside the temperature range for military operations should be replaced. Typically, commercial parts operate in a temperature range from 0-70°C while the military requires a -40°C to +85°C operational range. If the commercial ICs can not be replaced, a cooling or heating system must be used to ensure the ICs operate within the full military temperature range.
  
  
• Filters may be required to ensure COTS components pass radiated and susceptibility testing. A Pi filter or others such as a C filter, LC filter, ferrite beads, or inductor may be needed for power and signal lines. To save space, some manufacturers implement these filters within a custom connector, but these can be costly.
  
  
• Openings for all enclosures must be minimized to prevent radio frequency signals from entering the internal circuitry.
  
  
• Shielding on external cables is needed to reduce radio frequency coupling onto signal lines.

The benefits from using COTS components are worth the adaptations required. COTS parts allow applications to stay current through spiraling refinements, faster fielding, and accelerated implementation. By adapting to COTS insertion, we can reduce the typical defense system development cycle and provide numerous technology refresh and insertion points throughout the product lifecycle including sustainment.

The EMPF offers an array of testing and analytical services to be certain that your COTS parts can perform in harsh environments and extreme conditions. Please contact Ken Friedman at 610.362.1200, extension 279 or via email at kfriedman@aciusa.org.