Aerospace PCB Assembly for Mission-Critical Reliability

Fear of flying is a common phobia. The physics of the situation is one thing to wrap your head around, but the precision and reliability of the onboard electronics also give pause. Everyone has dealt with faulty electronics at some point in their life. Still, few encounter service disruptions in aerospace, and for a good reason: electronics manufacturers have invested considerable research and established standards that maintain the highest possible quality. The danger of even momentary loss of functionality in aerospace is too great to be acceptable.

For this reason, aerospace PCB assembly is demanding. We know it firsthand – the expectations and requirements of airborne electronic assemblies can be dizzying. Still, our ample experience in manufacturing NPIs for aerospace (and other industries) ensures devices meet design intent while soaring past operating criteria.

Aerospace PCB Assembly Considerations
	Obstacle	Countermeasures
Temperature	Large swings, harsh conditions, and aircraft must withstand various environments successfully.	Thermal modeling, matching components with board material CTEs to minimize stress/strain from cycling.
Pressure	Depressurization and pressurization can cause voiding via outgassing, reducing the long-term reliability of solder joints.	Improved inspection and processing to tamp down on material voids.
Corrosion	Boards and components can experience corrosion from liquids and gasses that disrupt continuity or result in an ESD event.	Hermetically sealed enclosures to prevent moisture and gas ingress.
Shock/Vibration	Depending on the severity, solder joints or the board can experience cracking and deformation around fasteners.	Smaller components (reduced weight) and higher pin count components (improved stress distribution).
Radiation	Solar radiation can bombard equipment in the upper atmosphere or spacefaring crafts, resulting in permanent device malfunction or failure.	Radiation-hardened components for better ionization resilience.

Some of the Challenges and Solutions of Aerospace PCB Assembly

Aerospace PCB assembly requires greater attention to detail than a standard fare board for obvious safety reasons. Aerospace electronics occupy the IPC Class 3 level of design and manufacturing specificity. It’s not only enough that electronics do not exhibit any downtime; the environmental swings during operation are extreme:

Temperature can differ by over 100℉ from the runway to cruising altitude. Components need to weather both ends of the spectrum flawlessly. In orbit, this temperature difference can more than double. Similarly, pressure can rapidly change from the surface to a vehicle’s maximum altitude.
Many of the most critical electronics have open-air exposure. At the bare minimum, a conformal coating prevents moisture ingress and particulate aggregation, whereas more robust enclosures can physically stabilize the board and improve strain relief for system interconnections.
Flight or launch is, mechanically, an inherently noisy process. Assemblies must have an improved emphasis on vibration damping. For example, press-fit components must solder down to aid in vibrational isolation.
For some applications where the atmosphere is either nonexistent or exceedingly thin, thermal management becomes more challenging due to the lack of convection cooling. PCBA design can increase the copper thickness to improve conduction/heat capacity, but this carries assembly challenges, too. Thicker copper can sink more heat during soldering processes while preventing the formation of acceptable solder joints. Increasing the temperature of the reflow oven/solder wave can damage components if settings exceed the maximum temperature rating. The board also encounters more thermal stresses, which can lead to defects like the delamination of copper traces from the substrate.

Aerospace PCB assembly has other factors to weigh. Class 3 electronics are exempt from RoHS compliance, unlike many in this day and age. While RoHS has helped reduce the amount of heavy metal pollution originating from electronics and manufacturing processes, two significant factors inhibit its adoption in aerospace:

Lead-free solders operate at relatively elevated temperatures. While compatible lead-free components are acceptable for higher temperatures, aerospace design wants to minimize thermal stress as much as possible. Keeping process temperatures (and overall heat flux) as low as possible minimizes strain development and resultant defects.

Eutectic tin-lead solder is excellent at preventing the formation of whiskers that spontaneously erupt from the surface of solder joints and can eventually grow long enough to short out nearby pins. Material research is ongoing into the phenomenon, but to this point, no replacement solder performs as strongly in this area as eutectic tin-lead.

Further Considerations for Aerospace Assembly

ESD prevention must also meet additional design requirements. While all of our assemblies contend with preventing shock and discharge that could render devices inoperable, the heightened reliability requirements of the industry mean a more rigorous approach is in order. Aerospace PCB manufacturing adheres to the ESD Class 0 rating, which employs the Human Body Model (HBM) and Charged Device Model (CDM) for components possessing withstand voltages below 250 V. Technicians handling devices will utilize protective equipment like wrist-strap monitors that constantly measure voltage and ESD footwear for improved grounding. Facility provisions include ESD installations and low-charging conductive flooring that pulls charge away from equipment and personnel to ground.

Weight can range from an impactful and growing cost driver to a mission criticality across the aerospace application spectrum. Electronic assemblies are, naturally, a substrate for conductive features and the components that most often provide the device’s functionality. Design reviews are critical to determining the perfect balance between system functionality and redundancy, and this begins with a BOM review that checks a litany of component aspects. Shaving weight in this manner may seem like overkill when some device packages range to the fractions of a milligram. Still, designers must remember the multiplicity of components across an entire system – hundreds, thousands, or more iterations may exist, and every ounce counts. Small individual weight reductions can result in performance gains, provided electrical parameters don’t suffer from component substitution or removal.

More significant weight savings are available with a flex or rigid-flex printed circuit, with the secondary benefit that a flex system is likely better suited for the heavy vibrations associated with takeoff and landing. Flex circuits are an entirely different animal than rigid boards and are more restrictive with design features. Still, the advantages of simplifying a board layout to a high-reliability flex connection are incalculable. As flex production does encounter additional processing challenges, a designer’s best bet is a PCB manufacturer with extensive experience. With more than four decades of creating NPIs in Silicon Valley and a recent high-volume expansion into Reno, we’re confident that our expertise fits the bill.

Your Contract Manufacturer Brings Assembly to New Heights

Aerospace PCB assembly is the pinnacle of DFM excellence, and we here at VSE are committed to supporting operations with top-of-the-line test fixtures and peripherals for the highest safety and reliability standards in electronics. Our engineers are wholly committed to building your designs while offering substantial industry experience to shorten lead times and improve performance. Alongside our valued manufacturing partners, we set our sights on exemplary quality for any production stage.

If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.