Designing Military-Grade PCBs: Key Rules and Considerations

PCBs used in military and defense purposes require a high degree of accuracy and reliability, along with the ability to function in extreme temperatures, abusive conditions, and highly demanding operational necessities. Unlike standard PCBs, the military-grade PCB design is subjected to stringent regulations regarding its construction, security, and performance maintenance in the latter stages of the product life cycle. 

For engineers and manufacturers focused on military application PCBs, having familiarity and understanding of the military PCB specifications and the best design approaches is fundamental. If you are in search of fast PCB assembly services or a custom PCB manufacturer, adherence to these rules will enable you to design military PCBs that are put through rigorous performance standards. 

What Makes Military PCBs Unique? 

Like any device with specialized purposes, military-grade PCBs have unique features for their design.

1. Military application PCBs need to have the following capabilities:

• Operate over a wide range of temperatures, humidity, and pressure. 
•  Endure vibration, shock, and other mechanical impacts. 
•  Tolerate corrosive substances, salt, and radiation. 
•  Provide high durability, security, and longevity. 

2. Must follow strict military PCB requirements such as IPC-6012, MIL-PRF-31032, and MIL-STD-810.

3. Failure of a military-grade PCB can pose a serious threat to crucial operations such as communication defense systems and unmanned aerial vehicles (UAVs). That is why utmost care must be taken in the design, materials, and manufacturing processes.  

Key Considerations When Designing Military Grade PCBs

1. Material Considerations

Using the proper material in military PCB fabrication directly enhances durability, thermal stability, and electrical performance efficiency.

Most Commonly Used PCB Materials in Military Settings:

• FR4-High TG: The most commonly used military PCB material, offering better thermal resistance due to its higher glass transition temperature.
• Polyimide: Excellent high mechanical strength coupled with high-temperature tolerance.
• Metal Core PCBs (MCPCBs): Perform excellently in power applications and heat dissipation.
• Teflon (PTFE): Used in high-frequency military RF and radar systems.
• Ceramic PCBs: Commonly used in missile guidance and aerospace electronics due to high thermal conductivity and electrical insulation.

Best Practice: Aim for lower dielectric loss and higher thermal and mechanical conductivity to maximize application reliability.

2. Standards for Military PCBs 

As with most military PCBs, these also need to comply with very strict IPC and MIL-SPEC requirements and standards in reliability and quality.

Primary Military Standards of PCBs:

• MIL-STD-810: Sets criteria for environmental testing under highly harsh conditions.
• IPC-A-610, Class 3 Parts B and D: Provides the minimum standards for assembling reliably used electronics with PCBs.
• IPC-6012 Class 3: Specifies high-performance PCBs that have no tolerance for failures.
• MIL-PRF-31032: Encompasses the design, fabrication, and functionality features pertaining to military PCBs.

Best Practice: Ensure that a contractor company takes custom PCB orders for military-grade, designed, and certified manufactured PCBs.

3. Thermoregulation of Military PCBs 

Dissipating heat prevents system failure. PCBs such as radars, avionics, and combat systems create and dissipate a considerable amount of heat.

Thermal Management Techniques

Improving the thermal management of PCBs involves:

• Utilizing thicker copper layers ranging from two to six ounces to optimize heat distribution.
• Incorporating thermal vias to create a passage from the components to the heat sinks.
• Using metal-backed PCBs due to their outstanding power dissipation features and mechanical support.
• Including heat sinks and cooling systems for high-power demanding applications.

Best Practice: Thermal simulation tools can effectively locate the PCB’s hotspots, improving its reliability.

4. High Reliability and Durability 

Military-grade PCBs are required to survive rough environments and a fair amount of mechanical abuse, such as shocks. 

How to Improve PCB Durability?

•  To prevent the breakdown of the traces, use heavy copper plating. 
•  Use conformal coatings such as acrylics or perylene for moisture and chemical shielding. 
• Use redundant circuits designed for mission-critical functions. 
• Use ruggedized enclosures to reinforce PCBs for impact protection. 

Best Practice: Conducting mechanical strength verifications such as shock and vibration testing is advisable. 

5. Signal Integrity and EMI Protection 

Military electronics are often expected to function in environments of high Electromagnetic Interference (EMI), so great care should be taken when ensuring the integrity of the signal being transmitted. This is the foremost principle for achieving reliable communications, radar, and avionics. 

How to Improve Signal Integrity in Military PCBs?

•  Controlled impedance design improves the transmission of signals and is thus recommended for stable signal transmission. 
•  Ground planes are great as they decrease noise and improve the effectiveness of shielding. 
• Sensitive circuits should be enclosed in metal boxes secured with EMI gaskets. 
• To prevent crosstalk, high-frequency components should be spaced out. 

Recommended: Carry out EMI analyses and shielding tests prior to commencing mass production. 

6. Layer Stack-Up and Multilayer PCBs 

For intricate, high-density circuits within the military, multilayer PCBs may be needed.

Multilayer PCB Considerations:

• Layer Count: 4-12 layers are typical for military radar systems and communication assemblies.
• Signal Integrity: Maintains signal and power for no-noise operations.
• Via Structures: Utilizes buried, blind, and microvias for compact designs.

Recommended: Consult a skilled custom PCB fabricator for the fabrication of multilayer PCBs with high functional capabilities.

7. Secure and Tamper-Proof Design 

Security is critical in tamper-proof military PCB designs to ensure there is no unauthorized access to the board. 

Key Security Measures:

• Embedded encryption chips for secured data transmission. 
• Anti-tamper circuits that turn off the board on breach. 
• Concealed routing of the traces to protect crucial connections. 
• RF shielding enclosures that leak data. 

Best Practice: To avoid counterfeiting, trusted verification partners for PCB manufacturing should be employed. 

8. Fast PCB Manufacturing for Military Applications 

When working on defense projects, fast PCB manufacturing is essential to meet deadlines. 

How to Speed Up Military PCB Production?

• Engage a certified turnkey PCB fabricator who does everything from design and fabrication to assembly. 
• Automated optical inspection (AOI) should be employed to identify defects as early as possible during the board’s manufacture. 
• Plan the arrangement for PCB cutouts to use resources efficiently and make assembling faster. 

Best Practice: Partner with an American military PCB contractor so that you can enjoy speedy service and meticulous quality assurance. 

Best Practices for Sustaining Quality and Dependability in Military PCBs 

The last phase of military-grade PCB design involves extensive verification and validation. 

Essential Testing Procedures for PCBs:

• Automated Optical Inspection (AOI): Finds surface anomalies, misalignments, and other defects. 
• X-ray Inspection:  Detects soldering errors, BGA malfunctions, and other faults within the equipment. 
• Thermal Stress Testing: Tests the device’s functionality during extreme temperatures. 
• Vibration and Shock Testing: Tests various military real-world scenarios. 

Best Practice: Always conduct a full inspection before deploying a system to critical mission assets. 

The Benefits of a Trustworthy Military PCB Fabricator 

Constructing advanced military PCBs involves a deep understanding of constituent materials, layout and EMI shielding, thermal control, and military PCB regulations. To obtain speed of production and flexibility on custom requests, a trusted manufacturer guarantees the design meets military standards for durability and reliability. 

Blind Buried Circuits is the go-to for custom high-performance military PCBs. We offer rapid prototyping, complete turnkey manufacturing, and expert guidance on PCBs for military applications. Contact us today to discuss your next military PCB project.