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Satellite PCB And Space-Grade PCBA Design Guidelines

This blog deals with the reliability of electronic systems within the context of aerospace engineering, where success is made possible through the reliable performance of electronic systems. In this regard, the reliability of printed circuit boards (PCBs) is of critical concern, as they offer the necessary support to electronic devices. In fact, space-grade PCBs are designed to exceed the reliability of commercial and industrial-grade PCBs, particularly the ability to perform within the extreme conditions of the space environment. Space-grade PCBs represent a comprehensive technological system that brings together materials science and validation processes.
space-grade pcb

What is a Space-grade PCB?

Space-grade PCBs are a type of electronic circuit board designed to perform within the extreme conditions of the space environment. In this regard, space-grade PCBs utilize special materials to ensure the desired performance within the space environment, which is characterized by high levels of radiation, extreme temperature fluctuations, and a vacuum environment.

What Makes Space-Grade PCBs Different?

In the context of conventional electronic circuit boards, space-grade PCBs are designed to perform within the extreme conditions of the space environment. In this regard, space-grade PCBs utilize materials that have low levels of outgassing. In addition, critical active devices are hermetically sealed within ceramic or metallic packages to minimize the effects of moisture absorption as well as space outgassing. Space-grade components are fully traceable to ensure that the components are sourced from a tested batch of components.
DimensionStandard PCBsAerospace-Grade PCBs
Core ObjectivesCost, Performance, Market CycleReliability, Long-Term Stability, Extreme Environment Adaptability
Typical Substrate MaterialsFR-4 (Glass Fiber Epoxy Resin)High-Frequency/High-Performance FR-4, Polyimide, Ceramics (Aluminum Oxide, Aluminum Nitride), Composite Dielectric Materials
Process and Certification StandardsIPC-A-600 and other general standardsMIL-PRF-31032 (US Military Standard), IPC-6012DS (Aerospace Addendum), ESA/NASA specific standards
Design Life and WarrantySeveral yearsDecades (e.g., geostationary satellites often require 15+ years)
Failure ToleranceAcceptable failure rateApproaching zero; single-point failure can lead to mission failure
Testing and ScreeningSampling testing100% screening, accelerated life testing, destructive physical analysis (DPA)

Standards Used in Space-Grade PCBA

In this context, some of the standards applicable to space-grade PCBs are as follows:

IPC-6012 (Class 3/3A)

Specifies the performance requirements of rigid PCBs, which must meet stringent defect criteria such as copper wicking (max 2.0 mils), inner layer separation, as well as plating voids.

IPC-A-610 (Class 3)

Specifies the criteria for continuous operation without faults within extreme conditions of the space environment, which includes exposure to extreme levels of stress as well as temperature fluctuations.

IPC-J-STD-001 (Class 3 + Space Addendum)

This standard outlines the requirements necessary to ensure continuous and high-performance operation, including very stringent requirements to prevent vacuum outgassing, ensuring Total Mass Loss (TML) ≤ 1.0%, and Collected Volatile Condensable Materials (CVCM) ≤ 0.1%.

ECSS (European Cooperation in Space Standardization)

This European Cooperation in Space Standardization provides a unified approach to minimize the total risk.

NASA Standards

NASA has very stringent standards for PCBs, including NASA-STD-8739, which outlines workmanship requirements for soldering and cabling.

Where is the Space-Grade PCBA Used?

Satellite System

In satellite systems, reliable PCBs are necessary to ensure signal integrity and power supply reliability, which are critical in satellite systems. Space-grade PCBs are used in satellite systems, specifically:
  • Communication systems
  • Power supply systems
  • Payload systems, including cameras, sensors, and antennas

Space Probes

Space probes also need space-grade PCBs to facilitate data collection, navigation, and reliable communication with Earth. Some examples include autopilots used in Mars rovers, cameras used in space probes, and detection systems used in the Deep Space Network, which need reliable PCBs to ensure the reliability of the system and handle extreme low temperatures, radiation, and communication delays.

Space Stations

In space stations, reliability is of primary importance due to safety concerns. Hence, the PCBs used in space missions are designed with utmost accuracy, considering all the possible failure modes.

Launch Vehicles and Robots

Space-grade PCBs are commonly used in flight computers, ignition timing controllers, and separation sensor interfaces. These PCBs are designed to withstand the harsh environment and the high level of vibrations, shocks, and accelerations experienced during launch.

PCB Material Selection for Space Application

  1. Substrate materials: these should have low coefficients of thermal expansion, high glass transition temperatures, good dimensional stability, and radiation resistance. The materials are:
    • High Frequency/High Performance FR-4 for non-core components where higher performance characteristics are needed.
    • Flexible materials, such as polyimides, where Tg must be higher than 250°C.
    • Ceramics, such as alumina and aluminum nitride, where higher thermal conductivity and CTE matching of silicon are desired.
    • Teflon, which offers superior chemical resistance and outgassing characteristics, useful in vacuum applications.
  2. Copper, which is the primary conductor material, typically plated with electroless nickel immersion gold (ENIG) or hard gold to ensure solderability, corrosion resistance, and reliable contacts. In some cases, gold can replace copper in applications where it can be used.
  3. Conformal coatings are used to protect PCBs from moisture, salt spray, and mold, among other contaminants.

Design Guidelines for Space-Grade PCB

There are some guidelines to follow while designing the boards.

Thermal Management in a Vacuum

Thermal management in space-grade PCBs involves conduction and radiation, as opposed to convection. A copper weight of 2 oz or higher must be applied to the internal power and ground planes to enable horizontal heat distribution. Alternatively, thermal via arrays can be used to direct heat to internal planes or to an attached heatsink on the substrate.

Routing and Trace Reliability

Teardrops are incorporated at all pad-to-trace interfaces to ensure reliability. Traces are widened where possible. A perfectly symmetrical PCB layer stack-up is needed to ensure equal copper and dielectric thickness, thus reducing warpage during the reflow process.

Component Placement / Mechanical Support

Securement of components such as electrolytic capacitors, large inductors, and ball grid arrays must be provided. Epoxy stacking or underfill can be used, and clearance must be provided at the board edge to prevent chassis contact.

Failure Modes in Space-Grade PCB

A deep understanding of failure modes is vital for PCB reliability in aerospace applications. Such failure modes are used as a basis for pre-emptive protective measures. The failure modes mentioned below are considered the most critical and commonly occurring in space-grade PCBs used in space electronics such as satellites. Corresponding engineering measures are also mentioned for each failure mode:

  1. Thermomechanical fatigue failure:

    • Failure Mechanism: The PCB expands at a different rate compared to the ceramic components attached to it. The stress difference caused by thousands of orbital cycles causes the solder joint to crack, resulting in an open circuit.
      • Solder Joint Fatigue: Inconsistency in PCB substrate and ceramic component expansion causes shear stress between these materials due to thousands of thermal cycles. This causes crack development in solder joints.
      • Plated Through-Hole Cracking: The PCB substrate grows quicker in the Z-axis (thickness) in comparison to the copper barrel of the via. Extreme changes in temperature make the barrel of the substrate come apart and disconnect.
    • Strategies: Materials should be selected that have similar CTEs; optimize the structural design of pads and vias to disperse stress; extensive thermal cycling tests should be performed for verification.

  1. Outgassing (Gas Escape Pollution):

    • Failure Mechanism: Volatile organic compounds in PCB substrates, adhesives, coatings, or fluxes are slowly released in the space vacuum environment. These outgassed gases may condense on critical components such as optical sensor lenses, thermal control surfaces, or solar cell arrays, leading to permanent performance degradation.
    • Strategy: The materials used should be of aerospace grade with low outgassing characteristics; baking should be done at high temperatures before and after assembly; stringent quality control measures should be followed during the final assembly.

  1. Tin Whisker Growth Failure:

    • Mechanism: Under vacuum or stress, pure tin or lead-free tin electroplating can cause whisker growth, resulting in a short circuit between conductors.
    • Strategies: Avoid using pure tin plating and adopt tin-lead alloy; use a nickel barrier layer on copper conductors; control electroplating process parameters; apply conformal coating for physical separation; strictly follow aerospace standards for material screening and process control.

  1. Growth of conductive anodic filaments (CAF)

    • Mechanism: Copper ions from the anode move along the glass fibers in the presence of moisture and an electric field, resulting in shorts between conductors.
    • Strategies: Use CAF-resistant materials; ensure cleanliness of manufacturing environments and manufacturing process; CAF reliability testing.

  1. Radiation-induced failure:

    • Mechanism: Due to the presence of cosmic rays in space, failures are caused by single-event upsets in semiconductor devices or changes in parameters and functional failure due to accumulated doses.
    • Strategies: Radiation-hardened components; redundancy and error checking; physical shielding.

  1. Mechanical vibration and shock failure:

    • Mechanism: During launch, vibration and shock can cause components to separate from the structure, wires to break, solder joints to crack, and loose parts.
    • Strategies: Optimize layout and mechanical attachment by modal analysis and finite element analysis; use underfill for components with high weight; perform vibration, shock, and acceleration tests.

Study Case

Case 1: Failure of the Power Control Unit (PCU) of the Hubble Space Telescope (HST)

  • Incident: In 1999, failure of a PCU due to an open circuit in a critical resistor of the power regulator module caused a safe mode condition of the telescope. The root cause of failure was traced to a microcrack in the copper layer of a plated-through hole (PTH) of the PCB.
  • Analysis: The microcrack in the PTH caused an electrical open circuit after prolonged thermal cycling. This incident highlights the importance of plating holes, thermal cycling life, and destructive physical analysis (DPA) in space missions.
 

Case 2: PCB Reliability Balance of Commercial Satellite Constellations

  • Practice: Commercial space missions, such as SpaceX Starlink Satellite Constellation, involve balancing reliability in space with cost control.
  • Method: The use of flight-proven industrial off-the-shelf (IOTS) components in PCBs, along with PCB materials, simplification of the process of radiation hardening (system-level rather than device-level hardening), and process control/screening provide reliability in mass production. Although PCBs may not be qualified to top-level military or space standards, mission objectives are met due to system-level design and significant environmental stress screening.

Conclusion

Risk mitigation is of prime importance in designing space-grade and satellite-grade PCBs. It is not just enough to be proficient in PCB design software. One has to be proficient in materials science, be familiar with IPC standards, and understand the capabilities of PCB manufacturers. It is of prime importance to adopt risk mitigation in designing PCBs using rigorous design rules, Class 3/3A standards, and component selection. Although initial costs of genuine space-grade PCBs may be higher compared to commercial PCBs, they are far lower in comparison to the cost of mission failure.
 
Looking for a reliable partner for space-grade and satellite PCB assembly? FS PCBA provides high-reliability PCBs designed for IPC Class 3, ECSS, and aerospace requirements. Contact our engineering team for further discussion.

Appendix

  • Explanation of Key Terms:
    • Tg value: Glass transition temperature, above which the physical properties of the substrate decline sharply.
    • HDI: High Density Interconnect, which achieves higher wiring density through processes such as microvias and fine lines.
    • EMC: Electromagnetic Compatibility, the ability of a device to operate normally in its electromagnetic environment without causing interference to other devices.
    • CTE: Coefficient of Thermal Expansion, the expansion ratio of a material when its temperature increases by 1°C.
    • DPA: Destructive Physical Analysis, which involves dissecting components to verify the quality of internal structure, materials, and processes.
 
  • Recommended Extended Resources:
    • Book: <Spacecraft Electronic System Design and Reliability> (Professional Textbook).
    • Documentaries: “Cosmos: A Spacetime Odyssey” and “When We Left Earth: The NASA Missions” contain segments related to spacecraft manufacturing and testing, which provide an intuitive understanding of engineering challenges.

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