onformal Coatings and Area Array Components

摘要

High performance electronic products must continue to operate in life critical/operational critical situations, even in a harsh environment. These products often include conformal coating materials to protect printed circuit assemblies from dirt, moisture and other detrimental environmental hazards. The Restriction of Hazardous Substances (RoHS) legislation has led to a growing use of conformal coating materials as a tin whisker risk mitigation strategy. In these applications, conformal coating material must be consistent in terms of thickness and coverage on the printed circuit assembly. Since the absence of conformal coating on adjacent leads of a leaded surface mount component can increase the risk of shorting due to corrosion or tin whiskers, coating processes generally strive for uniform coverage over all surfaces. However, the desire to ensure that all surfaces be adequately coated can potentially lead to excessive coating that can adversely affect solder joints in area array components such as ball grid arrays (BGAs), chip scale packages (CSPs) and flip chips (FCs). Studies have shown that the presence of conformal coatings underneath area array components generate stresses that can lead to solder damage, such as that shown in Figure 1.