Oxidation Prevention
Inert gas shielding replaces ambient air during the thermal interconnection stage of printed circuit assembly to limit the growth of metallic oxides on exposed solder joints. A nitrogen reflow atmosphere maintains low oxygen concentrations inside the heating zones of the conveyor furnace to prevent surface degradation during the molten phase of soldering. Higher oxygen levels cause poor wetting across copper pads and terminations, which increases the likelihood of voids and cold solder joints appearing after cooling.
Pure nitrogen gas displaces oxygen molecules from the localized processing area. This gas displacement effectively keeps surface tensions low enough for molten solder to spread across metallic surfaces. Reduced oxide film formation improves the structural integrity of every solder joint.
Thermal Conductivity
Gases with high molecular purity move heat through forced convection systems with specific thermodynamic efficiency. A nitrogen reflow atmosphere changes the heat transfer coefficient compared to standard shop air because nitrogen density behaves differently under the fluctuating temperatures found in infrared or convection heating chambers. Operators adjust conveyor belt speeds to compensate for these variances in heat delivery.
Precise flow regulation avoids cooling down components too rapidly, while high purity prevents contamination from particulate debris or moisture that air currents carry into the tunnel. Sensors mounted inside the cabinet monitor oxygen parts per million to trigger automated alarms when levels rise above thresholds. Consistent monitoring keeps the solder melt profile uniform across entire panels of boards.
This chemical consistency ensures reliability during reflow.
Operational Cost
Economic factors influence the decision to implement gas injection systems because the recurring expense of liquid nitrogen storage and distribution impacts the total cost per board assembly. High volume production facilities justify the installation of membrane generators or cryogenic tanks when the reduction in rework or scrap rates offsets gas supply charges. Maintenance requirements include checking seals around the furnace entry and exit points to stop atmospheric infiltration.
Even minor leaks create turbulence and draw oxygen into the heating zone, which negates the benefits gained from inert environments. Tight furnace seals minimize consumption rates. Proper sealing produces the highest return on investment.
