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July 2016 • SMT Magazine 41 ing results are not shown here as they also per- formed similarly to before. However, now the two acrylic results are different, with the single coated acrylic showing a large drop in SIR, in- dicating that the corners of the tracks are not covered. Supporting this conclusion, the image in Figure 13 shows corrosion at the track edge, and with corrosion products forming across the top of the coating between the anode and cathode. The acrylic-1 results show the SIR dropping to 106Ω from the first condensation event, with the behavior remaining broadly consistent through the following condensation cycles. With the double coated acrylic, the SIR results are not as bad, but SIR values are drop- ping below 108Ω, and with a trend of decreas- ing SIR with each condensation cycle. The 1oz copper SIR pattern boards the results in Figure 9 do not show any difference between the sin- gle and double coated boards, but with the 3oz copper SIR pattern boards the results do show a clear difference, and furthermore the acrylic coating can be seen to failing in either single or double coated condition. Hence the geom- etry challenge of the 3oz copper tracks for the acrylic-1 coating has been shown by it failing the condensation test. From above this coating passed the humidity test at 40°C/93%RH, and the same coating with the 1oz copper tracks also passed. Thus the incremental geometry challenge and the fine control of the condens- ing condition in this experimental arrangement allows detailed and robust characterization of coating performance. As can be seen, the dewpoint is within a few degrees of the ambient conditions at all of these conditions. At 30°C and 90% RH, a com- mon enough condition in South East Asia, and North East America for example, the dewpoint is only 28°C (i.e., if the substrate is just 2°C cooler than the ambient air, condensation can begin to form). As condensation proceeds from the forma- tion of droplets and then coalescence to the formation of a continuous water layer, with the surface then saturated, it is essentially the same as if it were submerged in water, although there will not be the same dilution effect of ionic con- tamination. Conformal coatings are known to protect poorly in such immersion conditions. The reasons for this are easy enough to un- derstand. Conformal coatings are typically ap- plied in the liquid state and dry by a variety of mechanisms. During the drying process, the materials are subject to gravity and capillary forces, making it difficult to ensure uniform and even thickness of the applied coating. When the surface is covered by a continuous water layer, any uncoated, partially coated or defectively coated areas will immediately be exposed to liquid water. Whilst liquid water is not a very good conductor of electricity (5.5 x 10-8 S/m), the presence of ionic species greatly increases the conductivity of water. In today's no-clean chemistry dominated production process, the presence of ionic species is impos - sible to avoid. The combination of lack of coating coverage (or sufficient thickness), the presence of ionic species and the presence of even nano-layers of moisture can have a devastating effect on elec- tronics, resulting in short-circuits or even per- manent corrosion. Given the proximity of the dew point to am- bient conditions in a variety of common work- ing environments, the impact of condensation on the reliable operation of conformal coated PCBs requires more thorough examination. There are existing methods for generating condensing conditions within humidity cham- bers, utilizing differing approaches. The biggest challenge to creating condensation in humidity chambers is related to the chamber hardware itself. It is designed to produce a stable, con- densation free environment. The most simplis- tic method, and one that will struggle to gener- ate condensation, is to ramp the temperature and humidity condition as quickly as possible causing a condensation event. However, cham- ber design is continually improving, and striv- ing to avoid any such condensation event. A second approach is to introduce moisture by a secondary moisture source. This can be either by an independent heated water tray (as in test K15 from GS 95024-3-1) [1] or direct jetting of at- omized water droplets. A third approach uses a multi-chamber approach where the working area climatic environment is rapidly changed by injecting an alternative environment from a reservoir chamber. CONDENSATION TESTING—A NEW APPROACH