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.
Trace Migration
Copper Movement
Metal ion diffusion through a dielectric substrate creates a conductive path between adjacent circuit traces. Trace migration refers to the electrochemical process where metal atoms move under the influence of an electrical potential and humidity. This phenomenon degrades insulation resistance and induces unintended electrical connections in high density printed circuit boards.
It stops applying when moisture levels fall below the threshold required to facilitate ion transport through the resin matrix.
Dielectric Breakdown
Surface moisture on the insulating material provides a medium for ions to transition from the cathode to the anode. Dendritic growth develops along these paths as a reaction product of the anodic dissolution of copper. High voltage gradients across small gaps speed up the arrival of metal ions at the interface between the conductor and the substrate.
These growths reduce the dielectric integrity of the board and lead to short circuits between isolated features. Standard industrial testing uses accelerated humidity chambers to verify that internal materials resist this electrochemical activity.
Manufacturing Controls
Laminate selection influences the resistance to ion mobility within the polymer structure of the board. Manufacturers specify low moisture absorption materials to minimize the availability of water molecules. Surface cleaning steps remove ionic contaminants that provide the chemical catalyst for electrochemical transport.
Application of a conformal coating creates a physical barrier that restricts moisture access to the copper surfaces. Solder mask chemistry must also demonstrate high chemical stability to prevent the release of conductive ions during the reflow heating cycle. Effective designs incorporate sufficient spacing to ensure that electrochemical growths do not bridge the physical gap between adjacent conductors during the expected lifespan of the hardware.