Analytical Models for Viscous Squeeze Flow Trace Swim in Multilayer Buildups
Analytical squeeze flow models predict trace swim by calculating hydrodynamic drag and side-wall pressure differentials across fine copper features during lamination.
Side Wall Pressure Differential
Plating Integrity
Electrodeposition thickness variations represent the localized difference in metal build up between the vertical surfaces of a printed circuit board through hole and the surrounding planar copper features. Side wall pressure differential occurs when electrolytic solution flow creates uneven agitation rates along the interior barrel walls during the copper plating cycle. Low fluid velocity zones often lead to thinner deposits compared to high flow regions.
Such variations constrain the mechanical reliability of the interconnection under thermal stress conditions.
Flow Distribution
Fluid dynamics inside an electroplating tank govern the uniformity of metal ion deposition across high aspect ratio holes. A side wall pressure differential arises from the geometry of the cathode assembly and the proximity of anodes. Nonuniform spray patterns or turbulent mixing zones create unequal convective mass transfer to the hole surfaces.
Engineers monitor pump pressure and solution chemistry to mitigate these gradients. Uniform ion concentration prevents excessive thinning at the center of the barrel compared to the hole entrances.
Reliability Impact
Microsection analysis confirms that significant discrepancies in deposit thickness reduce the fatigue life of plated holes. Side wall pressure differential causes uneven copper distribution that increases susceptibility to cracking during reflow soldering or temperature cycling. Thinner sections experience higher localized stress concentrations when the substrate expands at different rates than the metal.
Sturdy through hole performance demands consistent current density and optimal solution circulation to ensure mechanical stability.