One thing that Captains Kirk, Picard, Sisko, Janeway and Archer all had in common was the ability to travel through hyperspace. For travel into deep space, this was a tremendous advantage as it allowed them and their respective crews to cross great distances while aging at a comparably almost negligible rate. The phenomenon where time apparently slows down at very high speeds is one of the reasons why long voyages into space are possible. Although going fast enough to approach the speed of light is not an easy achievement, the concept of accelerating time is a well-founded technique to peer into the future.
It is becoming routine for repairs to be done on the International Space Station and there was another historical fix-it job by NASA recently. Unfortunately, most space platforms, such as satellites and rockets, are not likely to be repairable once they leave earth. Therefore, it is necessary for aerospace electronics and systems to be thoroughly tested prior to launch. This includes testing that simulates the challenges likely to be encountered over a lifetime to ensure the board, device or system will not fail. This type of examination and analysis is known as a highly accelerated life test and is an essential tool to improve the reliability of critical systems. Let’s explore this type of testing and see how it is used to ensure aerospace electronics will stand the test of time.
Traveling through hyperspace
What is a Highly Accelerated Life Test?
It is not atypical for PCBAs to undergo testing to ensure the boards will perform as designed once installed in their intended environment. In fact, virtually all boards go through some degree of functional testing during development. Additionally, there are testing methods for PCB manufacturing that evaluate a board’s construction or analyze its structural integrity. These tests are good to employ; however, they are all test-to-pass examinations, which do not directly address reliability.
By contrast, highly accelerated life testing or HALT is specifically designed to test for reliability under stress by pushing the boards to failure. Knowing the limits before board breakdown is critical for boards that cannot be repaired once deployed; such as the many sensors for aerospace applications. A HALT test regimen usually consists of the following five individual tests:
Highly Accelerated Life Tests
- High-temperature stress
- Low-temperature stress
- Vibrational stress
- Thermal cycling
- Combined environment
Each of the tests above is designed to discover where or when a board or system reaches its maximum stress level. Let’s take a look at how this testing can be applied to aerospace electronics.
Applying HALT to Aerospace Electronics
All aerospace vehicles are comprised of and rely on circuit boards. The role of electronics in aerospace systems spans to virtually all functions; including operation, control, and communications. It is probably most informative to examine how HALT testing is applied by looking at an example. Therefore, let’s take a look at how an aerospace power electronics board, which is commonly used in all types of space vehicles can be tested.
HALT Tests for High Power Aerospace PCBAs
- High-temperature testing
Here the board is subjected to incremental increases in heat until some type of deformation, delamination, bending (for flex boards bending beyond the rated strength) or cracking, is detected.
- Low-temperature testing
This is the opposite of the high-temperature test where the temperature is incrementally lowered until the board fails from cracking or breaking.
- Thermal cycling
Thermal cycling is performed to determine how many extreme swings the board can withstand instead of absolute temperature for failure. Extremes need to be well above the board CTE rating.
- Vibration testing
Vibration testing can be used to analyze structural integrity, as with thermal testing, and solder joint quality.
- Vibration with heat and/or thermal cycling with vibration
The above tests can be performed in combinations as well as singularly, as this is more likely to occur in the actual environment.
The above list of tests is not exhaustive and the effect of other environmental hazards may also be tested. For example, humidity and radiation. Please, refer to IPC-9592A for more information on halt test types and procedures.
HALT testing is indeed a type of destructive physical testing, not to be confused with destructive physical analysis (DPA), although both are used to evaluate aerospace systems flight readiness. Yet, it is necessary to sacrifice a few boards to continually improve the board’s design and manufacturing until an acceptable reliability level can be reached, prior to deployment in a system intended for deployment in space.
|Tempo's Custom Avionics for PCB Manufacturing Service
Although this type of testing is sometimes required, it can be a more efficient process if you work with a contract manufacturer experienced in building boards to the quality level demanded for aerospace electronics; such as Tempo Automation, the leading PCBA manufacturer for fast, high-quality prototyping and low-volume board builds.
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.