Quantifying Microvia Plating Fatigue and Target Pad Separation Rates under Rapid Thermal Cycling
Continuous high-speed Kelvin monitoring during rapid thermal cycling isolates latent target pad separations that re-nest and pass static ambient tests.
Nanovoid Coalescence
Structural Failure
Structural failure occurs when microscopic gaps within the copper lattice or at the interface between the solder and the pad grow and merge under thermal or electrical stress. Nanovoid coalescence weakens the structural integrity of the interconnect and eventually leads to a complete open circuit. This phenomenon is often found in the intermetallic layer of a solder joint where impurities have been trapped during the plating process.
Small Gap
Small voids that are initially harmless begin to migrate and join together when the board is subjected to high temperatures or high current densities. Through nanovoid coalescence, these tiny spaces form a continuous crack that separates the copper pad from the solder or the via barrel. This is a common cause of failure in systems that operate at high power or in environments with frequent temperature swings.
Concentration Limit
Concentrations of organic brighteners or levelers in the plating bath that exceed the recommended limits are the primary source of the trapped gases that lead to this defect. When nanovoid coalescence occurs, it usually indicates that the chemistry in the electrolytic tank was not properly balanced or that the current density was too high during the deposition of the copper. Controlling the purity of the chemicals and the cleanliness of the copper surface before plating is the only way to prevent the formation of these voids.
Regular cross-sectional analysis and scanning electron microscopy are used to identify the presence of these defects before they cause field failures.