Measuring electronic resistance to monitor reliability
Conductive anodic filament (CAF) formation is a significant failure mode inside multilayer PCBs. It results from an internal electrochemical process forming corrosion products between two opposite, and usually adjacent, charged copper conductors. It leads to lower resistance pathways forming within the laminate.
There has been a significant increase in concerns about the effect of CAF on board reliability due to:
- the reduction of the inter-feature spacing caused by increased circuit density with finer PCB features and increased layer counts
- electronic circuits being subjected to increasingly harsh environments, especially in high reliability and safety critical applications
- higher soldering temperatures associated with lead-free solders which have the potential to affect laminate stability
During CAF testing, the electrical resistance is measured between vias, also known as vertical interconnect access, which are electrical connections between layers of an electronic assembly. A substrate is monitored when a voltage is applied, giving an indication of the propensity of the system to form these corrosion products. The equipment at NPL can detect leakage currents approaching pA, and can log resistance values every 10-20 minutes over test periods ranging from a few hours to several months. NPL has CAF measurement facilities for up to 512 channels per run with bias and measurement voltages from 5 to 1000V.
Our services and capabilities include:
- Via spacing evaluations
- PCB fabricator assessments
- Laminate resin system evaluation
- Laminate fiber style and board stack up reviews
Learn more about our capabilities
SIR, CAF and condensation testing for electronic assemblies
Find out more about the advantages of using CAF and SIR testing to evaluate assembly processes and materials. It also covers vehicle design, how to conduct testing and analyse the results. Watch webinar View slides
How to avoid conductive anodic filaments (CAF)
Outline of how CAF failures form and details about NPL’s results on which PCB fabrication and assembly variables, including PCB materials, via spacing, drilling, and number of reflows, have the greatest effect on CAF propensity. Watch webinar View slides
Susceptibility of glass-reinforced epoxy laminate to conductive anodic filamentation.
A study of FR4 laminates, in the form of high plated-through-hole (PTH) density multi-layer test circuits, exposed to different manufacturing conditions and studied for resistance to CAF. Download the report
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