Pressure Removal
Process technology in reflow soldering utilizes a controlled atmosphere to extract entrapped gas pockets from molten solder joints. Implementing differential pressure evacuation ensures that the atmospheric pressure surrounding the assembly drops below the internal pressure of the gas bubbles trapped within the liquid alloy. This pressure imbalance forces the voids to expand and migrate toward the surface where they rupture and release.
The operation occurs while the alloy remains fully liquid to permit the metallic structure to flow back together and heal the pathway left by the departing gas.
Cycle Operation
Extraction of the gaseous inclusions requires a structured transition through several stages of pressure reduction. The chamber holding the board undergoes a rapid drop in pressure from atmospheric levels to a vacuum level between ten and one hundred millibar. Maintaining this vacuum for a specific duration allows the buoyancy forces to overcome the surface tension of the liquid solder.
If the vacuum remains active for too long, the alloy can experience excessive outgassing or solder balling. Reintroducing inert nitrogen gas restores the chamber pressure to atmospheric levels and completes the process before the cooling phase begins, ensuring that the total exposure time under vacuum does not exceed thirty seconds.
Defect Prevention
Verification of the solder joint integrity relies on automated transmission x-ray inspection to measure the remaining void area. Excessive voiding in critical thermal or electrical pathways reduces the cross-sectional area and decreases the fatigue life of the connection. Applying differential pressure evacuation regularly reduces the total voiding percentage from up to twenty percent down to less than two percent.
This reduction prevents localized overheating during subsequent operation of the electronic assembly.
