Material Removal
The precise elimination of conformal coating or hardened residues from high density printed circuit board surfaces involves a thermal shock process. This cryo-abrasive scraping utilizes high velocity carbon dioxide pellets directed through a narrow nozzle to impact targeted substrate areas. The mechanical energy of the frozen media combined with the thermal contraction differential between the contaminant and the board substrate causes the unwanted material to brittle and detach from the underlying laminate or copper pads.
This method works on cured epoxy or urethane resins while leaving the base material integrity undisturbed. Operators calibrate the pressure levels to prevent damage to delicate surface mount components during the selective stripping of protective coatings for rework or analysis.
Process Kinetic
The kinetic force generated by the sublimation of the solid medium provides a clean mechanism for deburring and site preparation without chemical solvents. When the pellets strike the surface, the rapid phase transition from solid to gas expands the volume of the media exponentially. This sudden expansion lifts the contaminants away from the circuit features without abrasive wear on the conductive traces.
The technique remains effective because the difference in the coefficient of thermal expansion between the coating and the substrate facilitates an immediate shear at the bond line. Because the system requires no aqueous wash steps, the board experiences no moisture ingress into the plated through holes or internal layers. Technicians maintain control over the angle of incidence to ensure the stream removes only the specified layer while avoiding the displacement of nearby low profile components or fragile wire bonds.
Operational Boundary
The application limits exist where the board geometry prevents a clear line of sight for the nozzle tip or where component density blocks the effective extraction of the spent gaseous byproduct. This procedure creates a risk of static discharge if the equipment lacks grounding for the nozzle assembly and the board carrier. Proper ventilation within the workstation prevents the accumulation of carbon dioxide gas in the work area.
A failure to calibrate the pellet size leads to excessive force that pits the solder mask or fractures the solder joints. The technique remains a specialized solution for removing stubborn materials that resist chemical stripping agents.
