Determining the thermal effects on general purpose pc boards is tough, but it’s another story to control board reliability in mission critical applications where a device failure is not an option.
In a recent discussion, Andy Burkhardt, technical marketing specialist at Polar Instruments, acknowledged the reliability issues for pc boards, adding: "Certainly moisture ingression, humidity and temperature all have effects on PCBs. More generally on reliability as a catalyst contributing towards other failure mechanisms, but particularly on insertion loss of surface microstrip traces and slightly less so for strip-line transmission line structures.”
Superior reliability is the pivotal issue for mission critical applications. Devices have to continue to function correctly and reliably under harsh and, sometimes severe conditions, including high moisture and humidity, high heat, freezing cold, electromagnetic interference and destructive electromagnetic pulses.
Think about the Mars Science Laboratory rover, Curiosity, which landed at Gale Crater on Aug. 6, 2012. It integrates the highest-end technology sensors and measuring systems to conduct unprecedented experiments on the Red Planet.
Curiosity has a number of pc boards communicating, interfacing, regulating and controlling various sensors and other scientific gear Take, for instance, Curiosity’s Mars Hand Lens Imager (MAHLI), which uses a 2-megapixel color camera with a focusing macro lens to observe textural, mineralogical, structural and morphological details in geologic materials. The MAHLI camera head electronics are laid out as a single rigid-flex substrate with three rigid sections that are sandwiched between housings that provide mechanical support and radiation shielding.
Location of MAHLI hardware aboard the Mars Science Laboratory rover, Curiosity, in the Spacecraft Assembly Facility
The aerospace industry requires pc boards with high reliability in extreme conditions. The MAHLI camera head is usually operated at temperatures of -40°C to +40°C on Mars. For that, NASA said it has been verified through testing on a non-flight unit to be able to survive nearly three Mars years of diurnal temperature cycles (down to -130°C) without any heating.
The graph shows the rise and fall of air and ground temperatures on Mars obtained by NASA's Mars Curiosity rover. The data cover Aug. 16 to Aug. 17, 2012, and were obtained by the Rover Environmental Monitoring Station. Ground temperatures vary from as high as 37 degrees F (3 degrees C) to as low as minus 131.8 degrees F (minus 91 degrees C), showing large temperature oscillations from day to night.
The imperatives are different, though, when human lives are at stake. If Golden Spike, a private company whose board includes former NASA engineers and spaceflight experts, delivers on its promises, it will offer rides to the moon by 2020 –for the modest sum of $1.5 billion for two people.
Advancing to new frontiers is exhilarating but, as lives depend on the products we provide, it's fundamental to never compromise on safety. Therefore, the aerospace electronics industry must continue to design products that meet the absolute highest standards.
See related links:
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Mars Curiosity gets down to science
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