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The miniaturization of electronic systems and the explosive increase in their usage has increased the climatic reliability issues of electronics devices and components, especially when metal/alloy parts are exposed on the PCB assembly surface or embedded within the multilayer laminate. Problems are compounded by the fact that these systems are built by multi-material combinations and additional accelerating factors such as corrosion causing process related residues, bias voltage, and unpredictable user environment. Demand for miniaturised devices has resulted in higher-density packing, with reduction in component size and closer spacing thereby increasing the electric field, while thinner metallic parts need only nanogram levels of metal loss for causing corrosion failures.
During the past couple of decades, the use of electronic devices has increased in gigantic proportions. Mobile phones are obvious examples of how devices integrate more and more complex functions, such as camera, GPS and several wireless communication technologies. The integrated device is expected to be cheap, while the applications necessitate it to be robust, durable, and reliable at all environmental conditions, including severe conditions. Industrial electronics is another sector where the electronic controls and other devices are used irrespective of the type of industries and environmental conditions. The vast majority of these electronic systems are not produced with serious consideration of the climatic reliability aspects. Climatic reliability issues that led to corrosion can introduce intermittent malfunctions and permanent failures, which cause severe economic loss.
Miniaturization and high-density packing are other reasons for increased corrosion reliability problems for the electronic devices. In order to provide additional functionalities and increase the number of components per unit area on a PCBA, PCBs today are made with multilayers, commonly 8 to 12 layers. The line width, distances, and sizes of the components on the PCBAs are then reduced considerably. Over the last 10 years, the size of electronics has been reduced by over 70%. For flip-chip ICs, miniaturization amounts to ~ 90%. Even material loss on the order of nanograms can cause reliability problems.
The average size of dew droplet formation on a surface at different temperatures varies from 20 to 50 mm at about 50% RH. Hence, the smaller size of a PCB makes it easy for a local electrochemical cell to form, due to the formation of a water layer connecting two electrical points, the thickness of which is determined by the humidity levels, conditions on the PCBA surface including cleanliness, roughness, and the relative temperature to the atmosphere. Read the full article here.Editor's Note: This article originally appeared in the April 2014 issue of SMT Magazine.