Bo Song, Michael H. Azarian and Michael G. Pecht
Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742, USA
Atmospheric dust consists of solids suspended in air. Dust is well known for its complex nature. It normally includes inorganic mineral materials, water soluble salts, organic materials, and a small amount of water. The impact of dust on the reliability of printed circuit board assemblies (PCBAs) is ever-growing, driven by the miniaturization of technology and the increasing exposure of telecom and information technology products to uncontrolled operating conditions.
A fundamental and systematic study on the impact of dust is needed, since little research has been performed in this area. We started by asking some basic questions about dust. Since dust is always present in the atmosphere, under what conditions is dust a reliability concern for electronics? What are the key characteristics of dust? Are some dust types worse than others; e.g., dust that is more hydrophilic? Should there be classifications of dust? How will different combinations of dust, voltage, relative humidity, temperature, and other factors affect electronic materials and circuits? This paper presents some of the results that are needed to answer these questions. A set of experiments was performed using real life dust collected from both indoor and outdoor areas. AC impedance spectroscopy (IS) was employed to measure the effect of dust exposure. We designed test coupons with adjustable spacing between electrodes and measured their electrical properties under different relative humidities. Measurements included pH and conductivity of aqueous solutions produced from dust samples as well as the composition of the dust samples. We found that dust had a significant impact on the reliability of PCBAs. Relating the test results to the analysis results, indoor dust is more sensitive to the change of relative humidity compared to outdoor dust due to the water soluble salts and particle sizes. At the same dust deposition density, indoor dust is more likely to induce moisture related failure, such as reduction of surface insulation resistance, electrochemical migration, and corrosion.
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