Meaning
Critical thermal duration tracks the period during which the solder alloy remains above its melting temperature during PCB assembly. Accurate reflow dwell time ensures that the solder completely wets the component leads and board pads without damaging the sensitive electronic parts. If this period is too short, the connection lacks structural strength and electrical reliability.
Thermal Profile
Oven sensors monitor the rise and fall of temperatures to create a reliable chart of the transition into the liquid phase. Balancing the reflow dwell time requires accounting for the thermal mass of the largest parts on the board compared to the smallest resistors. Typical intervals last between sixty and ninety seconds for standard lead-free alloys.
Wetting Action
Chemical flux activates during the heat process to strip away oxides and allow the metal atoms to fuse permanently. Sufficient reflow dwell time allows the molten metal to flow smoothly into all gaps through capillary action. Insufficient time results in grainy solder joints that break easily under mechanical shock.
Defect Prevention
Excessive duration in the molten state leads to heat damage in the component plastic and creates brittle intermetallic layers. Controlling the reflow dwell time minimizes the risk of component warping and prevents the creation of voids that reduce the cross-sectional area of the joint. Consistent results require precise speed control of the conveyor.
