When used in aerospace and military applications, printed circuit boards must be extremely reliable and rugged, with no room for error. An accurate grasp of how printed circuits must be designed and constructed to provide a very extended duration of operation in frequently quite harsh working circumstances is necessary for complex applications, such as space missions. Printed circuit boards used in aerospace applications are exposed to extreme conditions like radiation, chemicals, pollutants, and more, in contrast to the majority of typical PCBs.
As a result, these circuits must adhere to highly tight requirements, such as IPC-A-610E Class 3, which applies to high-performance types of electronic equipment whose uninterrupted operation is required even under the most demanding and challenging operating circumstances. The following are some of the principal uses covered by the IPC-A-610E Class 3 standard, which you can refer to from ipc-a-610 standard digital copy:
- Systems for satellite communication
- Applications for on-ground processing of data captured during flights or missions (ground stations), including navigation systems, control systems, and on-board avionic instruments
- Unmanned aerial vehicles (UAVs)
- Passive detection systems
Circuits used in aerospace applications must be able to tolerate and absorb significant shocks and vibrations as well as operate at extremely high temperatures. Considering that communicating via radio in the HF (or higher) band is a crucial component of these systems, they also share many aspects with PCBs for RF high-frequency applications. Operational at high altitudes increases the risk of radiation exposure, so PCBs and other electronic components must be built to survive high radiation levels for an extended period of time without suffering damage.
To help the designer in the challenging yet enjoyable task of developing a PCB for aerospace applications, common rules, and recommendations are offered.
Follow Reference Guidelines- Standards.
PCBs used in the aerospace sector must function with little maintenance and adhere to exacting safety and quality criteria. Because of this, PCB designers and manufacturers for aerospace applications are required to adhere to a certain set of reference standards. The IPC 6012DS, an amendment to the IPC-6012D standard that specifies accreditation and performance necessities for rigid printed circuit boards for aerospace and defense applications, is one of the reference standards. You could think of this standard as an improved version of IPC Class 3.
The aerospace standard AS/EN 9100, which includes a collection of guidelines created by the IAQG-International Aerospace Quality Group for excellence and risk mitigation in the aerospace industry, is also crucial. This international standard embodies the quality management system that is appropriate for the aerospace sector. The AS/EN 9100 standard adds further standards made especially for the aerospace environment in comparison to the ISO 9001 standard, with that it shares many components. PCBs created for this kind of application are required to adhere to the standard and come with a certification attesting to the manufacturing process's high quality.
Make Use Of Superior Materials.
Accuracy and durability are two specifications that must be met in the aerospace industry. Since maintenance interventions are either impractical or prohibitively expensive in many applications, the circuits must run continuously and faultlessly for extended periods of time. Utilizing high-quality materials and components that are readily available on the market for extended periods of time is the usual guideline.
Anodized aluminum is a frequently used substitute for copper that can address a number of heat dissipation issues. In actuality, anodized aluminum has ten times less thickness and a thermal conductivity that is 5 to 10 times higher than that of conventional materials like FR-4.
Utilize Technique For Heavy Copper.
With copper thicknesses between 2 and 6 oz/ft2 (or more), heavy copper technology enables heat dissipation naturally without the need for extra cooling systems, even when facing high-intensity currents. To further enhance heat dissipation, many manufacturers suggest integrating heavy copper solutions with the addition of multiple thermal vias.
Offers Exemplary Thermal Management.
As was already established, aerospace PCBs need to provide outstanding heat dissipation without the need for external heatsinks. Special solutions based on materials like Pyralux AP, FR408, and other metallic materials and components can be employed in conjunction with heavy copper technology and the widespread usage of thermal vias. In contrast to conventional PCBs, it is also recommended to widen the gap between the parts so that there is more room for heat dissipation.
Implement Conformal Coating
The PCB finishing materials should be selected to resist the most demanding working circumstances. The primary conformal coating methods include electrolytic nickel gold, chemical silver, hot air solder leveling, lead-free HASL, and ENIG- Electroless Nickel with Immersion Gold Coating. The conformal coating's application offers defense against the heat, humidity, wetness, and vibrations that can all be present in aerospace applications. In order to shield the finished printed circuit from contaminants or unintentional short circuits, the conformal coating should be applied after the acrylic-based spray.
Route Recommendations
In order to ensure excellent heat dissipation under all working situations, PCB traces should be selected for a size that can manage the highest current load. Angles on the traces must be smaller than 45°, as is the case with circuits with high-frequency signals, to ensure that the signal is sent uniformly and regularly across the circuit. Separating low-frequency from high-frequency electronic components will help prevent interference. The latter can produce waveforms and disturbances that can affect how low-frequency components function. The waveforms and noises reduce the signal's quality, jeopardizing the signal's integrity, which is essential for these applications.
Using Flexible And Flexible-Rigid PCBs
Flexible and rigid-flexible printed circuit boards are quite prevalent in satellite and avionics systems. However, unlike industrial or automotive uses, they are often made with polyamide rather than FR-4. This material has the ability to adapt to small places with ease, is extremely light, resistant to heat and chemical agents, and ensures a high level of durability.
Due to their strong durability against vibrations, shocks, temperature, and outside agents, superior mechanical and electric connection, and low weight, flex, and rigid-flex PCBs are widely utilized in the aerospace industry. A stiff-flex PCB is made up of printed circuit boards that are both rigid and flexible and are permanently attached to one another.
For challenging and constrained space applications, the proper application of rigid-flex and flexible PCBs offers an ideal solution. With fewer connectors and a tight connection between all of the circuit's components, this technique also ensures contact stability and polarity.
Conclusion
All electronic circuits that must adhere to the IPC-A-610 Class 3 and 3A standard, including printed circuits for the aerospace industry, must be created from beginning to end with the goal of achieving high electrical reliability, particularly in the most challenging and unusual operating conditions. Every electronic designer has an extremely difficult issue with PCB design, starting with choosing the best materials to survive harsh weather conditions with the ongoing failure-free operation.
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