With the introduction of lead free, the risks associated with marginal or improper handling of MSDs has increased dramatically. Higher reflow temperatures drive up the saturated vapor pressure to double or even triple that present in tin lead reflow processes.
The higher temperature increases the water pressure inside the components, and as a result, the allowable moisture content and associated floor life have to be reduced. All moisture-sensitive components have to be requalified by their manufacturers for lead-free and they are typically downgraded by at least one and generally two levels of sensitivity.
This significantly affects how components must be are handled, processed and stored. Suddenly, manufacturers that are currently handling MSL 2 or MSL 3 components are now looking at processing MSL 5 or MSL 6.
The SMTA's MSD Council is among the those who have reported that even passive components (ceramic chip resistors and capacitors), normally classified as MSL 1 (unlimited floor life) have shown field failures after lead free reflow due to presence of moisture in the component.
Another major impact of lead free reflow for assemblers is the handling and storage of PWBs, as the incidence of delamination has increased with the change in thermal processing. PWBs need to be treated as MSL classification 4, in other words processed within 72 hours of open shop floor time. See http://www.superdry.info/