Can you guess what do these two pictures represent?
A few weeks ago we wrote about corrosion testing and especially about mixed flowing gas (MFG) testing. We stated that corrosive environment is one of the most demanding use conditions. Air pollution, salt and dust combined with high levels of humidity often exists in use environments especially for industrial electronics, causing corrosion. This week’s picture is taken from a device tested in a dust test, which is another type of corrosion testing. The picture on the left shows capacitors and a heat sink, and the picture on the right shows a fan with settled dust.
Why is dust harmful? Dust often contains many different substances. Some of these substances can be very harmful. They can be corrosive or conduct electricity. Especially, when combined with high levels of humidity dust can be very harmful. Moreover, dust can be abrasive and cause wear in moving parts. In electrical devices dust can for example accelerate corrosive reactions, cause leakage currents and increase the heat load for components. Since electronics is getting smaller, the problems caused by dust are becoming increasingly important.
In the case seen in the pictures above, the tested equipment had a fan which was running during the dust testing. This is a good way to study how dust accumulates inside a device. In this case, the dust test was also combined with high humidity testing to study the effect of dust in humid environment. If the dust is hygroscopic and used in humid environments, corrosion can occur. This is because water with the salts in dust may form an electrolyte, which can enable many forms of corrosion. Additionally, in such situation leakage currents may easily occur.
Several different dusts are available for testing. Commonly used test dust, Arizona road dust, is a little hygroscopic itself. However, to increase hygroscopicity of the dust, salts may be added to the dust mix. Additionally, other substances may be added to dust to vary its properties.