Issue link: https://iconnect007.uberflip.com/i/1172746
OCTOBER 2019 I SMT007 MAGAZINE 77 tronics. This environment is much less controlled with higher maximum operating temperatures and far more opportunities for contamina- tion by fuels, oils, cleaning fluids, corrosive gases, metal particulates, and salt-water slush spray from treated road surfaces. Clearly, under- hood and other non-cabin electronic assemblies suffer much tougher environmental conditions and thus require the greater levels of protec- tion provided by a new type of conformal coating. Protective Coatings: The Next Generation Coatings for electronic assemblies destined for under-hood and other non- cabin applications are required to be extremely resistant to wet conditions, have excellent chemical resistance, be highly flexi- ble to survive thermal excur- sions and thermal shock, and be able to sur- vive the much higher operating temperatures. To counter these challenges, Electrolube has developed a new range of highly durable, sol- vent-free, modified polyurethane conformal coatings, which can be applied more thickly than regular conformal coatings and which cure within 10 minutes at 80°C, re-using exist- ing thermal curing ovens often used in sol- vent-based processes. Moisture Resistance Sharp-edge coverage—the ability of a coat- ing to completely and reliably cover device leads, solder joints and other metal surfaces to prevent susceptibility to corrosion—is a long- standing, well-known issue that has recently been highlighted within the IPC5-22ARR J-STD- 001/Conformal Coating Material and Applica- tion Industry Assessment. To demonstrate the importance of edge coverage and protection from liquid water in the form of condensation, the U.K.'s National Physical Laboratory (NPL) is currently working on the development of a controlled condensation test. NPL researchers have shown that at 40°C and 93% RH, a temperature differential of just 1.5°C can lead to the formation of moisture that is sufficient to reduce the surface insula- tion resistance (SIR) of a copper coupon from TΩ to 1MΩ (the limit of detection). Referring to Figure 2, the data from NPL clearly shows a significant drop in the SIR value of an uncoated assembly, limited protection by both the nano- coating and the single-coated acrylic, and improved protection from the double-coated acrylic. Both of the new urethane materials provide improved protection with UR3, in par- ticular, showing outstanding protective capa- bilities against condensing water. Figure 2: Comparison of condensation resistance of various coatings (data courtesy of NPL).