Reflow Duration
Solder molten state duration measures the elapsed time surface mount solder alloys remain above their melting temperature inside a reflow oven. Surface mount assembly reflow monitoring tracks liquidus time to ensure proper wetting and reliable intermetallic layer formation. The boundary of this thermal metric extends strictly from the melting point transition during heating to the solidification point during cooling.
Intermetallic Formation
Maintaining molten solder for an adequate duration allows liquid metal to wet component leads and printed circuit board pads completely. Insufficient time above liquidus causes incomplete solder wetting and high voiding rates within surface mount connections. Extended duration above liquidus promotes excessive intermetallic compound growth, which weakens joint mechanical strength and accelerates embrittlement failure.
SAC305 lead-free alloy profiles target liquidus duration between sixty and ninety seconds to balance complete wetting against thermal degradation of sensitive active components. Reflow oven zone temperatures and conveyor speeds are adjusted continuously to maintain target liquidus duration across light and heavy thermal mass boards.
Process Window
Thermal profiling tools equipped with thermocouple data loggers verify that every board location satisfies specified liquidus duration limits. Departures from the established thermal window require oven conveyor speed adjustments prior to production batch processing.
