Dynamic Four Wire Testing Essentials for Microvia Reliability Assessment
Dynamic four-wire testing isolates ambient and transient microvia resistance shifts during thermal stress to catch latent target pad defects before shipment.
Transient Open Circuit
Electrical Failure
Temporary loss of electrical continuity occurring for a duration of microseconds indicates a structural flaw in an interconnect. A transient open circuit is often the result of a crack that opens under thermal expansion and closes upon cooling. These events are difficult to capture because they leave no permanent evidence at room temperature.
Failure Mode
Stress from the surrounding epoxy pushes the fractured surfaces apart during the heating phase of a reflow cycle. A transient open circuit indicates that the mechanical bond within the via is failing. The electrical path is broken for a brief window before the material contracts and restores contact.
Vibration can also cause these momentary breaks if a solder joint or via barrel is compromised. Reliability decreases as these cycles repeat and the fracture grows.
Detection Protocol
Monitoring the net with a high-speed data logger is the only way to find these defects during stress testing. Test systems must log a transient open circuit that lasts only a few microseconds. Any spike in resistance that exceeds a defined limit for more than a set duration is recorded as a failure.
Traditional continuity testers are too slow to see these events and will report a false pass.