Conductive anodic filament failure

The density of IC packaging technologies such as ball grid array (BGA) and chip scale packages continues to increase. In turn, this requires greater intercoimection density in the printed circuits onto which they are assembled. The need for increased density in the PCB impacts each of the components of the base material as well as the way in which they are manufactured. To achieve high levels of interconnection, component pitch densities result in smaller and more closely spaced plated through holes and circuit features. As the space between these holes and features decreases, the potential for conductive anodic filament (CAE) failures increases substantially. 

It is significantly accelerated by the presence of hydrolyzable ionic contaminants (for example, hahdes and acids from flux residues or extracted from polymers). Delaminations or voids that promote the accumulation of moisture or contaminants can promote dendritic growth. Conductive anodic filament growth (discussed later) is a special case of dendritic growth. Time to failure is inversely proportional to spacing squared and voltage. The failure mechanisms in accelerated tests have been reviewed. ... 

Identify probable failure modes (e.g., solder joint fatigue, conductive anodic filament growth). Accelerated rehabihty tests are based on the premise that the frequency and/or severity of the environmental exposure can be increased to accelerate the incidence of the failure that... 

Temperature, Humidity, Bias. These tests are designed to promote corrosion on the PCB surface and conductive anodic filament growth, either of which can cause insulation resistance failures. 

While this degradation process was discovered by accelerated-life-testing and discussed in the literature almost 20 years ago (Lahti et al., 1979 Lando et al., 1979), the authors have never observed or been told of a field failure due to conductive anodic filaments. This testing served to alert designers to the need to ... 

In electrochemical migration, failure can occur due to dendrite growth, open circuit short, or conductive anodic filament (CAP) formation. Dendrites can form on the surface due to con-taminahon left by the solder flux (paste) or other residues. Under a bias voltage, the metal at the anode goes into solution, migrates toward, and plates-out at the cathode. The nature of the dendrite will depend upon the surface metallization. The following oxidation reactions can occur at the anode ... 

S. R. Stock, Analysis of Catastrophic Failures Due to Conductive Anodic Filament (CAF) Formation, Electronic Packaging Materials Science X, Vol 515, D.J. Belton, M. Gaynes, E.G. Jacobs, R. Pearson, and... 

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