I have been given a new design which has an underfilled leaded BGA on an SnPb soldered assembly (however many passive components are PbF).

The underfill has a snap cure of 160C for 7 minutes after a 90C pre-heat and dispense.  The PCB is FR-4 with a 170Tg min and the assembly is double sided SMT with selective soldered thru hole connectors.  It's is a Class 3 assembly.

From my understanding, components are generally not harmed by a few well controlled SMT cycles consisting of a soak period in the 150-180C range, followed by a ramp-up to 210-235C for reflow.   But in total, they dwell about a third of the time of the snap cure.  Is the snap cure comparatively benign or harmful or are there too many depends?

Appreciate any comments.

Thanks Gregg

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