When designing circuit boards, operation and performance are preeminent considerations. And rightly so. After all, if the PCBA does not fulfill its objectives, all other considerations are moot. When developing boards for harsh environments, such as within automotive systems and space, successful operation and performance depend on the level of board protection instituted.
In many cases, PCBAs are deployed in enclosures that offer a measure of protection, at least against local environmental conditions. However, these do not provide sufficient resistance to the most significant threats to your board’s ability to perform its role aboard space vehicles. Therefore, you must prioritize aerospace corrosion protection to guard against premature board and mission failure.
How to Protect Your Boards From Corrosion
Many potential root causes can lead to corrosion on your aerospace PCBA, including moisture, which can occur at all stages of board construction. Therefore, your aerospace corrosion protection regimen should include preventive actions during fabrication and assembly.
Aerospace Corrosion Protection Methods
- During Fabrication
- Ensure that the PCB lamination process is performed in an environmentally controlled environment and proper PPEs are utilized.
- Make sure materials such as prepreg are stored to prevent moisture accumulation.
- Use meshed copper planes to help prevent moisture distribution between the layers of your stackup.
- Apply surface finishing to protect traces and pads before assembly.
- During Assembly
- Baking is an effective way to remove excess moisture from your PCBA.
- Although not mandated for all boards, cleaning is highly recommended for medical device PCBAs and should be performed for aerospace boards as well. Board cleaning can help remove loosely attached debris and other contaminants.
- Apply a protective coating.
- Thermoplastic covering is a method of enclosing the entire board to prevent external contamination.
- Microencapsulation is similar to thermoplastic enclosure; however, only select components or parts of the PCBA are covered.
- Conformal coating is the most common method of board protection and offers full coverage.
For the best protection against aerospace corrosion, a final layer of protective coating must be applied. Conformal coating offers the best options for both cost and ease of application.
The Best Aerospace Corrosion Protection for Your PCBAs
The aerospace industry is one of the most regulated industries in terms of PCBA manufacturing. However, there is not a specific regulation regarding aerospace corrosion protection. Instead, IPC-CC-830 Qualification and Performance of Electrical Insulating Compound for Printed Wiring Assemblies serves as the prevailing standard—independent of industry—for conformal coating application conformance. This standard includes chemical classifications, qualifying materials and chemicals and testing regimens intended to protect circuit boards against contamination, moisture and inadequate insulation, which can all lead to corrosion. Adherence to this standard is often mandated by aerospace industry organizations and should serve as a minimum requirement in meeting your aerospace corrosion protection strategy. Any aerospace corrosion protection plan should possess the following attributes:
PCBA Aerospace Corrosion Protection Attributes
Your conformal coating should be silicone, epoxy, urethane or parylene.
- Flame Resistance
Flame retardation is essential, as any burning will likely leave residue even if no component or trace is actually damaged.
- Thermal Shock
In space, abrupt and extreme temperature swings are distinct possibilities, especially if thermal control system (TCS) operations experience interruption or malfunction.
- Resistance to Moisture
Moisture, whether from condensation or other sources, can be introduced and cause damage during manufacturing or after board deployment. For the latter, conformal coating offers good protection.
- Hydrolytic Stability
PCBA Manufacturing for Extreme Environments - Part 1
Maintaining its solid state is also important for a good conformal coating application, as conversion to a gas—for example, due to high temperature—and mixture with moisture can lead to outgassing. This can present a serious problem in high-vacuum environments.
The list above is not exhaustive. Yet, it does highlight the most important attributes that you should incorporate into the protection against corrosion applied for your aerospace PCBAs.
|Tempo's Custom Avionics for PCB Manufacturing Service
Corrosion, or the conditions that could lead to corrosion, are constant threats throughout the development and deployment of your aerospace PCBAs. Therefore, it is essential to understand the sources of these threats and work with a CM that institutes processes to optimize your board protection. At Tempo Automation—the industry leader for fast, high-quality circuit board prototyping and low-volume manufacturing—we prioritize quality throughout our processes, and we will either outsource or apply in-house the best corrosion protection method for your board.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.