Electroplating Interconnect Failure Modes in Advanced Packaging Lines
Enforce tight bath chemistry controls and continuous voltammetric screening to eliminate organic breakdown, microvoiding, and catastrophic copper interconnect scrap.
Microvoiding Kinetics
Meaning
Rate-controlling mechanisms of void formation and growth at the solder-substrate interface govern the long-term reliability and physical degradation of electronic connections. The study of microvoiding kinetics describes how atomic vacancies coalesce into microscopic gaps under the combined influence of solid-state thermal diffusion and intermetallic chemical reactions. This analysis applies to the intermetallic layers of tin-based solder joints on copper, nickel, or silver pad finishes.
It does not apply to macroscopic process voids caused by trapped flux volatiles or gases during the initial reflow soldering process.
Thermal Diffusion
The formation of Kirkendall voids is driven by the unequal diffusion rates of copper and tin atoms. As temperature rises, microvoiding kinetics accelerate, leading to a higher concentration of voids at the interface. This process is highly dependent on the storage temperature and the duration of thermal exposure.
Structural Impact
Continuous accumulation of these sub-micron gaps reduces the mechanical strength of the solder joint. When microvoiding kinetics are rapid, the interface becomes brittle and prone to fracture during drop testing. This deterioration is particularly critical for mobile electronic devices that suffer frequent mechanical shocks.
Inhibition Strategy
Introducing barrier layers such as nickel or palladium on the copper pad can suppress the atomic diffusion. This modification alters the microvoiding kinetics by lowering the activation energy for vacancy formation. This results in a more stable and reliable solder joint over the product’s lifespan.