Electrical Intermittency
Brief and temporary increases in the electrical resistance of a conductive path during thermal transitions indicate a microscopic fracture in the copper plating. A transient resistance glitch usually appears when the board reaches a specific temperature and disappears once the board cools or heats further. This behavior makes the defect extremely difficult to find using static continuity tests at room temperature.
It often signifies a failure at the interface between a via barrel and an internal layer.
Resistance Spike
Thermal expansion pulls a cracked circuit apart just enough to break the connection. The resistance spike of the transient resistance glitch lasts for only a few seconds or milliseconds. Specialized test equipment with high sampling rates must monitor the circuit to capture these events.
Root Cause
Incomplete removal of resin smear or poor bond strength between copper layers creates the conditions for these failures. The root cause of the transient resistance glitch is frequently linked to the desmear or electroless copper deposition steps in the fabrication process. If the internal pad is not perfectly clean, the subsequent plating will not form a metallic bond.
This creates a mechanical contact that is sensitive to the physical movement of the board material. Identifying these glitches during the qualification phase prevents field failures in high reliability systems.
