Toughness in the military cuts across the board. It's not just the tough personnel, but also the electronics and the computers used in the field. Of course, that means that the printed circuit boards (PCB) used in the defense sector need to be tough as nails.
While designing commercial PCBs is no walk in the park, designing and building military-grade PCBs requires special attention to durability and compliance. All the components have to withstand the demanding environment. Requirements of military-grade electronic PCBs include:
- Minimum tolerance (between 1 – 2%) compared to 5- 10% for commercial-grade electronic PCBs.
- Prolonged expected product lifetime of 5 – 15 years
- Ability to handle extreme conditions
- Stringent and specific design and layout techniques
- Better reliability, more robust, and more rugged
Achieving each one of these conditions requires ample preparation and considerations, which start at the design phase.
For a firm understanding of just how critical it is to get military-grade PCBs right, here are a few applications that rely on PCBs in the military:
- Base and camp protection and security systems
- Unmanned vehicles, military artillery and mortars
- Robotic systems
- Ruggedized computers
- Defense navigation and communication systems
- Satellite subsystems using embedded processors
OEM engineers undertaking military-grade electronics design need to be fully aware of the design considerations critical to the reliability and high-quality performance.
General Design Considerations for Military-Grade Electronics
All PCBs falling under this category should meet MIL-spec grade standards and pass the highest performance and functionality tests. General considerations for military PCBs include:
- Military-grade PCBs should handle the maximum current load.
- There should be a clear differentiation between low-frequency and high-frequency components. For example, some high-frequency components might produce waveforms that could affect the low-frequency components. These waveforms could add noise and reduce the quality of the signal. For the military, this is unacceptable.
- All clock signals should be clean and shielded.
- For smooth current transmissions, all the PCB routings should be maintained at a 45° angle or less.
- Finally, all military-grade PCBs should be manufactured in strict conformity to MIL-PRF-50884, MIL-PRF-55110, and MIL-PRF-31032 standards.
After familiarizing yourself with the design requirements, you should also factor in the best PCB substrate types for designing and manufacturing military-grade electronic PCBs.
Only the best quality and heat-resistant materials should be on the table. Military-grade electronics are often used in adverse conditions, including high temperatures. The PCBs should withstand and perform at a high level even in these conditions.
If heat dissipation is necessary, thermal compounds should be used. The finishing materials should also be carefully considered. They should support the PCB to perform in harsh environmental conditions.
High-quality materials that can withstand extreme weather and temperatures are a must. A firm understanding of the different composites, substrates, and elements to use in the PCBs is invaluable at this stage.
They must meet specific rigidity, flexibility, electrical, and thermal requirements to be considered military-grade. Some of the best materials to use for military PCB boards are:
- High-temperature laminates
In some cases, anodized aluminum is also used to minimize the effects of heat-induced oxidation.
Coating and Surface Treatment
The military has specific requirements for the surface treatment to protect the PCBs against hostile environmental conditions, including dust, water, vibration, and extreme temperatures. Therefore coating and surface treatments are important features for military-grade electronics. Copper coatings protect PCBs from easily rusting.
Depending on the functionality of the PCB, there are various surface treatment materials available:
- Hot air solder leveling (HASL)
- Electrolytic wire bondable gold
- Immersion silver
- Lead-free HASL
- Electrolytic nickel and gold
- Electroless nickel with immersion gold coating
Acrylic-based or acid-based sprays can also be used for conformal coating of the PCBs to further safeguard them from weather and other external factors.
Durability and reliability are primary concerns for the military. More so because the components are used in less-than-ideal situations and are subject to damage because of solder cracking, among other damages.
On average, military electronics have a lifespan of 5 – 15 years, guaranteeing durability, reliability, and longevity call for minimizing vibration of a mounted component.
For many military PCBs, through-hole mounting is the recommended method of mounting during PCB assembly. Boards manufactured using this technology are extremely durable. In addition, the method utilizes soldering from the top and bottom of the board, creating strong physical bonds between the components and the board.
PCB Testing Methods and Considerations
Thorough testing is vital to confirm the reliability and durability of the PCB in real-world applications. For military PCBs, the MIL-STD-202 standard is the basis of all testing methods for electronics.
After the PCB meets design for manufacturability considerations, it can be subjected to various tests, including:
- X-Ray inspection – Also referred to as AXI, the test checks for various defects like solder connections, barrels, and internal traces before the PCB can go into full manufacturing.
- Functional testing – The good-old functional test checks if the PCB will power up. How the functional test is carried out depends on the application.
Military PCBs can also be subjected to various other tests, including:
- Solderability tests
- PCB contamination test
- Time-domain reflectometer (in high-frequency boards)
- Solder float test
MIL-STD/ITAR/NADCAP: Understanding The Different Certifications and their applications
MIL-STD, ITAR, NADCAP … It’s easy to get lost in the alphabet soup of military, defense, and aerospace certifications.
Often confused with one another, many OEMs think just one certification will suffice versus all three.
To help you understand the differences and why all three are important, here’s a quick rundown of each standard:
MIL-STD standards cover the end characteristics of the product, as well as the processes, materials, and security standards to be followed in their production. MIL-STD includes five types of defense standards:
- Interface standards
- Design criteria standards
- Manufacturing process standards
- Standard practices
- Test method standards
These defense standards are meant to ensure the proper performance and logistical usefulness of military equipment.
ITAR standards focus on military equipment and sensitive information that might be involved with military equipment. The number of aspects of product development that are subject to ITAR regulations is substantial -- some obvious and not-so-obvious:
- Design info
- Development info
- Production processes
- Manufacturing steps
- Pictures of assemblies
- Repair processes of specific assemblies
- Testing protocols
A quality electronics contract manufacturer should verify that ITAR compliance is necessary upfront during the quoting process. That way it can ensure everyone involved in the process is adhering to an ITAR compliance checklist.
Nadcap is an accreditation program for companies in aerospace-related industries. Nadcap accreditation is issued at a company level for specific processes such as:
- Chemical processing
- Heat treating
- Conventional machining
- Nondestructive testing
These standards often work in tandem. Often, some of the technology being produced under MIL-STD compliance will be exported under ITAR regulations. Nadcap accreditation comes into play during construction with heat treatments, coatings, and more.
For MIL-STD grade electronics, ensuring your electronics contract manufacturer has up-to-date MIL-STD, ITAR, and Nadcap certifications will ensure that your PCB is suitable for all military-grade applications and sales.
More on Military-Grade Electronics:
It’s no secret -- there’s a tangled web of PCB design considerations when it comes to military-grade electronics. Ensure that your ECM is not only fully certified and accredited but also has proven experience producing military-grade components.
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