Checking Whether CAF Test Evidence Represents Your PCB

A material described as CAF resistant is not an unconditional guarantee for every PCB geometry and environment. Conductive-anodic-filament evaluation involves a defined specimen and test procedure. Review how closely that evidence represents the board and process you intend to release.

Read the scope of the test

IPC-TM-650 method 2.6.25 describes assessment of CAF and other internal electrochemical-migration behavior and identifies applications including laminate, design, and process evaluation. Its scope and specimen definitions matter when interpreting a supplier report. Use the current applicable method and the customer’s agreed criteria rather than treating a test name as a complete qualification. IPC: CAF resistance test method.

Request the report’s material identity, resin and reinforcement construction, board fabrication details, test-structure dimensions, conditioning, environmental exposure, applied bias, and monitored resistance criteria. Establish whether it evaluates the material supplier’s specimen, the fabricator’s process, or a structure representative of your product.

Compare the important differences

• Check conductor and hole relationships, including spacing and orientation.
• Compare the relevant layer construction and material combination.
• Review drilling, hole preparation, lamination, and other process differences identified by the supplier.
• Confirm preconditioning and thermal history.
• Identify differences between test exposure and the intended service environment.

For example, a report based on one hole-to-hole spacing does not automatically establish the behavior of a denser array using a different construction. The report remains useful evidence, but the difference should be evaluated rather than hidden behind the same laminate trade name.

Define the decision before requesting more testing

State whether the objective is initial qualification, a second-source comparison, a process-change assessment, or failure analysis. That purpose determines the appropriate specimens and comparisons. Ask the responsible reliability team and supplier to agree on the plan before samples are built.

If a test shows a resistance change, preserve the data and investigate the actual failure location and mechanism. Do not assume that every low-resistance result demonstrates the same internal filament mechanism; fixture, surface, and connection effects may need to be excluded through the procedure and analysis.

Keep the claim bounded

The release record should identify which material, construction, process, and test conditions are supported by the evidence. It should also state which changes require review. Avoid converting a passing accelerated test into an unsupported field-life prediction. The practical value of CAF evidence is in demonstrating a controlled, relevant comparison and maintaining the conditions that were evaluated.

Archive the complete test report rather than only its passing cover page, so future changes can be compared with the original specimen and conditions.