Technical Library | 2023-03-16 18:57:32.0
Outline * Introduction & Background * Factors Affecting CAF Formation * CAF Formation ** Catastrophic Field Failure of Military Hardware ** Laboratory Experiments * Conclusion
Technical Library | 2021-07-27 14:49:16.0
Conductive anodic filament (CAF) formation, a failure mode in printed wiring boards (PWBs) that are exposed to high humidity and voltage gradients, has caused catastrophic field failures. CAF is an electrochemical migration failure mechanism in PWBs. In this article, we discuss CAF, the factors that enhance it, and the necessary conditions for its occurrence. Published studies are discussed, and the results of historical mean time to failure models are summarized. Potential reasons for CAF enhancement solutions are discussed, and possible directions in which to develop anti-CAF materials are proposed.
Technical Library | 2021-07-27 14:57:18.0
It should be noted that this is an overview paper that represents the early stages of an ongoing investigation into the causes and effects between conductive anodic filament (CAF) formation and printed wiring board (PWB) material damage. Our belief is that certain or specific types of material damage can increase the propensity for CAF formation. The preliminary data collected suggests is that there is no statistical correlation between the general definition of material damage (cohesive failure) and CAF. The resulting dichotomy is that we find no CAF failures in some coupons that have obvious material damage and we find CAF failures in coupons that don't exhibit material damage.
Technical Library | 2021-07-27 14:59:56.0
With increasing focus on reliability and miniaturized designs, Conductive Anodic Filament (CAF) as failure mechanism is gaining a lot of attention. Smaller geometries make the printed circuit board (PCB) susceptible to conductive anodic filament growth. Isola has carried out work to characterize the CAF susceptibility of various resin systems under different process and design conditions. Tests were carried out to determine the effect of various factors such as resin systems, glass finishes, voltage bias and hole and line spacings on the CAF resistance. This work was intended to provide information to the user on the suitability of various grades for specific end use applications. The focus of the work at Isola is to find the right combination of process and design conditions for improved CAF resistant products.
Technical Library | 2023-03-16 18:51:43.0
Conductive anodic filament (CAF) formation was first reported in 1976.1 This electrochemical failure mode of electronic substrates involves the growth of a copper containing filament subsurface along the epoxy-glass interface, from anode to cathode. Despite the projected lifetime reduction due to CAF, field failures were not identified in the 1980s. Recently, however, field failures of critical equipment have been reported.2 A thorough understanding of the nature of CAF is needed in order to prevent this catastrophic failure from affecting electronic assemblies in the future. Such an understanding requires a comprehensive evaluation of the factors that enhance CAF formation. These factors can be grouped into two types: (1) internal variables and (2) external influences. Internal variables include the composition of the circuit board material, and the conductor metallization and configuration (i.e. via to via, via to surface conductor or surface conductors to surface conductors). External influences can be due to (1) production and (2) storage and use. During production, the flux or hot air solder leveling (HASL) fluid choice, number and severity of temperature cycles, and the method of cleaning may influence CAF resistance. During storage and use, the principal concern is moisture uptake resulting from the ambient humidity. This paper will report on the relationship between these various factors and the formation of CAF. Specifically, we will explore the influences of printed wiring board (PWB) substrate choice as well as the influence of the soldering flux and HASL fluid choices. Due to the ever-increasing circuit density of electronic assemblies, CAF field failures are expected to increase unless careful attention is focused on material and processing choices.
Technical Library | 2023-03-16 19:07:51.0
HISTORY: * In the late 1970s an abrupt unpredictable loss of insulation resistance was observed in PCBs, which were subject to hostile climatic conditions of high relative humidity and temperature while having an applied voltage. * The loss of resistance, even leading to a short circuit was observed to be due to the growth of a subsurface filament from the anode to the cathode. * The term "Conductive Anodic Filamentation" (CAF) was coined.
| 1 |
.gif)
