Design tips for electronic devices operating in harsh environments

By Linda Liu, MKTPCB

With decades of experience in the PCB industry, MKTPCB is the leading PCBA solutions provider from Shenzhen, China (photo: MKTPCB)
With decades of experience in the PCB industry, MKTPCB is the leading PCBA solutions provider from Shenzhen, China (photo: MKTPCB)

Electronics devices designed for military, space, oil, and gas mining are exposed to some of the toughest working conditions. In this regard, they are required to function optimally under intense vibration, mechanical shock, high-temperature swings, and more. This article discusses the design tips for electronics designed to operate in space.

Electronics designed for space function reliably under strong vibrations, mechanical shocks, high-temperature fluctuations, a vacuum environment, and contact with ionising agents. We will look at some of the design tips that you need to consider when designing electronic devices for space.

Radiation
Radiation is among the most challenging space requirements for which to design. This is because electronics in space are exposed to various high-energy particles and electromagnetic waves from the sun, stars, and other planets. These ionising radiations lead to short-term turbulence to electronics and long-term problems to semiconductors. Therefore, long-term space missions should employ radiation-hardened components, which are rarely available. Besides, these components are relatively more expensive than their standard counterparts.

You can use regular commercial-off-the-shelf (COTS) components for short-term missions after evaluating their radiation tolerance. This significantly minimises the cost of designing for space electronics and increases the design alternatives. Below are more electronic design tips to mitigate radiation effects:

  • The printed circuit board design should contain the grounding of every stray metal island.
  • The memory technology should withstand ionising agents.
  • The write-enable strobes for the technology memory should be disconnected during flight to prevent damages caused by radiations.
  • For the software, essential records should be made redundant at three different points. Then, the software frequently scans these points to establish and rectify any fault. This technique is known as data triplication and comparison.
  • Multiple software and hardware regulators are used to enable the system to pull through any processor malfunction.
  • The application of these design techniques and radiation-hard components significantly reduces the potential risks of radiation compounds.

Shock and Vibration
Electronic devices for space are exposed to solid g-forces and vibrations during flights and experience intense shocks during the separation period. Here are some PCB design techniques you can apply to encounter the above issues:

  • The PCB should be enclosed in an aluminium housing with multiple screw-down locations. Each screw is tightened up to the required spin and strengthened with high-quality epoxy material.
  • The shock and vibration tolerance of all the PCB parts should be considered. For instance, because Class-2 ceramic capacitors are vulnerable to piezoelectric impacts (they create electric charges under mechanical force), you should reduce their application in essential analogue circuits.
  • Any large part soldered to the board should be bonded with epoxy.

Hard vacuum
Another extra consideration when designing for space is the requirement to function in a hard vacuum. Though most COTS devices are not designed for vacuum, they still perform well since adequate attention has been given to their thermal dissipation factors. Nevertheless, since convective thermal conduction happens outside the vacuum, parts are cooled through conductive or radiative heat transfer.

You can design your PCB to conductively transfer heat from parts into the aluminium heat sink by applying these techniques:

  • Both PCB sides should contain adequate copper to facilitate smooth heat transfer.
  • High heat emitting components are mounted near the heat sink tie-down joints.
  • Heat epoxy is selectively used in some components to boost their transmission capacity to the circuit board.

Vacuums often cause stuck gases to leak from parts – outgassing. Because these gases hinder other devices on spacecraft, every circuit board component used should have a low outgassing capacity. Besides, the PCB should be coated with minimal outgassing conformal sealant. The sealant offers the extra benefits of protecting the board from contamination during ground activities.

Rigorous product inspection via BGA reworking, conformal coating, IC programming, X-ray inspection, in-circuit testing (ICT), and automated optical inspection ensures the highest quality PCB assembly (photo: MKTPCB)
Rigorous product inspection via BGA reworking, conformal coating, IC programming, X-ray inspection, in-circuit testing (ICT), and automated optical inspection ensures the highest quality PCB assembly (photo: MKTPCB)

Harsh ground conditions
While space contains harsh conditions, some of the most challenging conditions exist on Earth. For instance, electronics working in deserts can experience daytime temperatures of more than 40° C and night temperatures of below freezing points. The devices experience intense vibrations from the rugged terrains, and desert dust storms can coat them thoroughly. These devices must be designed to tolerate high vibration and temperature swings. Continuous functioning of the machines is essential considering the remote location and hostile conditions. Therefore, PCB designers must pay close attention to design details, like integrating dust-proof connectors.

It is good to acknowledge that the users of your electronic products may be using them in less-than-standard conditions. For example, the radiated electrical disturbance from a power conversion system can lead to a malfunctioning laptop battery system located in the same room.

Setting design requirements
One of the primary steps in electronic design is outlining the product requirements. PCB manufacturers should collaborate with their clients to describe these requirements in a Product Requirements Document (PRD). Technicians will use the PRD as reference material throughout the PCB manufacturing process to make important decisions and execute validations.

Setting the product requirements from the onset of the manufacturing process prevents significant changes later on. Acknowledging product requirements and restrictions allows the technicians to offer the best architectural and design performance options. Setting the design requirements early facilitates a more effective and low-cost project implementation. Ensure that your PRD lays down the environmental conditions of the product. Some of the primary questions that you should include in your PRD include:

  • To what temperature, humidity, or pressure range will your product encounter?
  • To what vibration degree will the product experience?
  • To what level of electrical noise and dust will the product be exposed?

Critical requirements
When designing an electronic device for space, you must integrate some level of tolerance to harsh conditions into your design. At one point in your life, you might have dropped your television remote on the floor, used your smartphone in the rain, and maybe struck your smartwatch on a hard surface.

These products continued functioning because the designers foresaw those instances. In severe, harsh conditions like the outer space vacuum, or the high-temperature swings and dust storms of deserts, design requirements emerge even more critical to a device’s feasibility.

Linda Liu – overseas marketing manager for MKTPCBLinda Liu is the overseas marketing manager for MKTPCB, a PCB manufacturer that offers high-quality PCB products and services. Since 2012, she has established “first-of-its-kind” industry-changing and transformational businesses initiatives that increased revenue growth, brand exposure and market expansion for MKTPCB. Liu graduated from Western University with a bachelor’s degree in marketing.