Regardless of the type of internet adapter that your computer uses (DSL, Wi-Fi or Ethernet), chances are that you routinely use optics for at least some of your Internet connectivity. Today, fiber optic cabling is available to some degree in most locations, including rural areas; for example, to provide last-mile connectivity to your business or residence. As most, if not all, of your location’s Internet connections flow through this bridge, it is the most critical part of the Internet from your perspective. And, when fiber optics are used this gives you the fastest broadband data transfer rates, up to 1Gbps.
An optical sensor on PCBA
The use of optical electronics is not limited to the Internet. In fact, a major thrust for NASA is to expand the current utilization of optical communication electronics in space. This goal is fueled by the many advantages that optical electronics or photonics promise to have over more conventional electronic devices. These include massive savings, lower overall costs, reduced power requirements, and extended mission life with up to a 100X data rate increase and lowered complexity. Thus, the role of electronics in aerospace systems is poised to continue to increase with an emphasis on integration with optical components and devices.
Let’s take a look at the best design practices for realizing well-manufactured optical electronics for aerospace. First, however, let’s orient ourselves with the most common usages of optical electronics in space today.
How Optical Electronics Are Used in Space
Not surprisingly, the most common usage of optics in space is for imaging. A good example is the Hubble Telescope, shown below.
Hubble Telescope instruments
As shown above, the Hubble telescope has a number of onboard instruments, including optical, that enables it to capture the fascinating astral images we marvel at. These instruments are the primary tools used to carry out the telescope’s mission; yet, they could not function without aerospace electronics playing their role to enable operations.
In addition to imaging, optical electronics play another important role in aerospace systems as sensors. These sensors may be used for positioning, targeting (for cameras), thermal detection, and other critical functions. In order to perform these types of functions, spacecraft (whether launch vehicles, satellites, or exploratory probes) leverage the faster transfer rates, greater signal density, and optical PCBA advantages for aerospace. However, doing so does present challenges.
Challenges of Using Optical Electronics in Space
The advantages of using optics for space missions extend to communications, including satellite-to-ground (downlinks), ground-to-satellite (uplinks), satellite-to-satellite (interlinks), and deep space links externally and free space optical (FSO) internal networks. These capabilities, similar to what is required for imaging and sensing systems, depend upon optical electronics components, such as optocouplers, amplifiers, detectors, attenuators, LEDs, lasers and modulators, and PCBAs for data and information processing and integration with other electronics devices and boards. However, the space environment does pose challenges, as listed below, that must be addressed.
Optical Electronics for Aerospace Challenges
- Thermal Cycling
One of the most significant challenges to optical electronics boards and systems in space is the constant cycling of temperature, which may range from extremely cold to severely hot within hours.
Another challenge is to determine the best materials to use. This includes board materials as well as component packaging materials. For example, ceramics are able to operate in environments with very high temperatures. As a consequence, ceramic-type dielectrics are frequently used in aerospace PCB design, especially for high-frequency as they are able to withstand extreme hot and cold temperatures. As an example, the dielectric Alumina, is ideal for high-quality applications and for reducing cost for mass production. It’s also excellent for anti-corrosion and thermal shock resistance. However, in space, relative long tin whiskers, which can create short circuits, have been observed when tin-plated ceramic packaging was used.
Another potential problem that can cause optic sensors to stop functioning is outgassing, which can form condensation on lenses and prevent absorption or diffraction.
As optical transmission and reception depend on refraction, the ability of light to cross material boundaries, small amounts of debris or contamination can significantly disrupt or even cease operation.
Fiber optic cables are not subject to EMI as they propagate light within a waveguide; yet, optical electronics are susceptible to radiation just as in other electronics circuitry.
Fortunately, there are design actions that can be taken to address these challenges.
How to Design Optical Electronics for Aerospace Systems
In the spirit of increased commercialization of aerospace applications, NASA and other space organizations have sought to increase the usage of COTS components whenever possible, without sacrificing established aerospace components manufacturing requirements. This includes an initiative by the Jet Propulsion Laboratory (JPL) to develop guidelines for the expanded use of photonic integrated circuits (PICs) in space. Whether for these planned utilizations or the current ones, you should institute design actions to ensure that your optical electronics for aerospace systems are well-built, as listed below.
Design Tips for Manufacturable Optical Electronics for Aerospace Systems
Design Tip #1: Perform thermal analysis
Analyzing and testing your board for the space environment in which it will be deployed is essential to ensure your components, boards, and devices can withstand the temperature swings that are common in space. This is in addition to electro-thermal simulation of the PCB layouts before fabrication, which should be done for all designs. Additionally, you need to consider thermal dissipation and distribution during manufacturing, especially during assembly, as vias can be sources for outgassing.
Design Tip #2: Apply parameter-based materials selection
Board materials and component packaging should be selected based upon their mechanical and thermal parameters to ensure they can withstand the pressure and temperature challenges of space deployment.
Design Tip #3: Ensure good soldering and PTH fill quality
Outgassing is caused by the release of trapped gas. Potential sources for trapped gas on circuit boards are solder connections and vias; therefore, you need to ensure your contract manufacturer (CM) applies good quality control to the assembly process.
Design Tip #4: Ensure boards are clean and properly packaged
The best ways to prevent contamination are through cleaning, coating, and following good package and storage guidelines. It is very important to assemble opto-electronics systems in certified clean-rooms and sealing the package hermetically will be very helpful. It also may be necessary to bake boards if they have been in storage for long periods before deployment.
Design Tip #5: Utilize radiation hardening techniques
Apply redundancy or shielding or other techniques depending upon the susceptibility of your optical electronic board or system.
Optical electronics provide several advantages over other electronic options for aerospace. And their utilization is only going to continue to grow. This, coupled with the expansion of space missions, presents many opportunities. However, good design tips must be applied to ensure that your optical PCBAs can survive the challenges of space.
|Tempo's Custom Avionics for PCB Manufacturing Service
At Tempo Automation, we are experienced in building boards for space, including deployment to other planets. We will work with you to ensure that your PCBAs are built to the highest quality standards, faster than anyone in the industry.
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.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on designing optical electronics for aerospace applications, contact us.