The purpose of this paper is to report on a mode of failure observed during the life testing of epoxy-glass printed-circuit boards (PCB). Upon exposure to elevated humidity, circuits maintained under a dc bias have been observed(I-3) to develop either permanent or intermittent loss of insulation resistance. Visual examination has shown that this characteristic electrical behavior is accompanied by the fonration of growths emanating from the positively biased conductors (anodes) and growing along the reinforcing glass fibers. We refer to these growths as conductive anodic filaments (CAF).In another paper presented at this meeting3, Lahti et al. have reported that this failure mode, which occurs at high humidity, is often nearly temperature independent. This failure mode is also of great concern since current trends in PCB applications, especially in the telecommunication field, involve operation in more humid environments, such as outdoor installations. Further, the trend toward lower power dissipation by components, which results in a low operating temperature, will also tend to make the operating humidity of the PCBs higher. In addition, the increased use of lightweight, water penneable housings is aggravating the situation. These trends have begun relatively recently and therefore, even though the number of field failures so far attributed to CAF is small, the situation is potentially serious. This paper addresses the following questions:1. What material characteristics of PCB substrates make them susceptible to this mode of failure? 2. What is the mechanism of failure?3. What are the practical solutions to the problem?The results of electrical testing of several material systems in high humidity are reported here. A theoretical model for the failure mechanism is proposed, and the implications of the model on the probability of failure are discussed. A solution, which is limited to a class of PCB designs and which is being implemented, is presented. Some alternative solutions are also discussed. MaterialsTypical PCB substrates are reinforced polymeric composites. For

The concept of antiaromaticity as applied to 4n-x electron monocyclic conjugated systems is examined and two subtypes distinguished. Relative antiaromaticity is the term which describes cyclic systems which are less stable than acyclic conjugated analogues. Absolute antiaromaticity refers to cyclic systems which are less stable than even nonconjugated models (e.g., ethylene). The extensive experimental evidence for absolute antiaromaticity (particularly for cyclobutadiene and cyclopropenide) is critically examined and judged inconclusive in view of the existence of alternate, plausible rationalizations. Theoretical analysis also challenges the reality of absolute antiaromaticity, at least in the monocyclic series. Relative antiaromaticity is affirmed, but only for the three smallest monocyclic systems (the two mentioned above plus cyclopentadienylium).Previous to 1965, nonaromatic cyclic conjugated systems had sometimes been termed "pseudoaromatic". Included in this category, of course, were molecules having monocyclic systems of 4n-x electrons. In 1965 Breslow concluded that certain 4n monocycles are actually "antiaromatic", these including at least cyclopropenide (C3-) and 1,3-cyclobutadiene (C4), as well as possibly cyclopentadienylium (C5+).1 The term "antiaromatic" denoted and emphasized destabilizing cyclic conjugation. Two reference systems were considered for more

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