Characterization of Electrical Failure Modes in Chip-on-Board Assemblies for Extreme Temperature Environments

Future space missions to Mars and the outer planets will have to operate on the planet surface in temperatures that range from −200°C to 40°C. These missions will require sensors, instruments and motors to operate for extended periods that exceed the duration of any planetary surface mission to date. Currently the Mars Science Laboratory rovers planned for 2009 will be required to survive a mission life of about 500 Martian sols. The Martian solar day is called a sol and is equal to 24 hours and 39 minutes of an Earth day. This extended mission requirement is beyond the reliability threshold of present electronic materials and interfaces such as those used on the Mars Exploration Rovers. The combination of correct materials, electrical interconnection and packaging design are critical to ensuring long life when the range between minimum and maximum temperatures approach or exceed 200°C. The Jet Propulsion Laboratory as part of the Mars Technology program is performing a series of designed experiments to determine the best electronic packaging materials that would survive 500 Martian sols in the temperature range of −120°C to 85°C. This technology development is part of the preparation effort to design and build survivable electronics for the Mars Science Laboratory rovers and related future outer planet missions. This technology development program is called Temperature Cycle Resistant Electronics (TCRE) and is a 3 year design for electrical interface reliability activity. The experiment team assembled 27 different types of test vehicles which are the result of a full factorial designed experiment. There were 10 samples of each type assembled for statistical confidence to yield a total of 270 test vehicles. The basic test vehicle design consists of silicon die mounted to a substrate with gold wire bond electrical interconnects. Continuous electrical paths were designed into the substrate and the dice. The basic experiment consists of assembling three different types of substrates, three different types of die attach materials and three different types of over coat material. The test vehicles were subjected to 1500 thermal cycles (three times required mission life) from −120°C to 85°C over nine months. Open electrical circuits were observed over time due to material interactions over this temperature range that created electrical failures. This paper summarizes the failure results and identifies the material sets that survived this phase of the experiment for 1500 extreme temperature cycles.