IPC task group D-35 is developing a guide for storage and handling of bare boards. This group has recently expanded the scope of the project to include test methods for classifying MSL of bare boards.

IPC, ECA and JEDEC are preparing to publlish J-STD-075 that will provide moisture and thermal classification methods for passives, connectors, switches--anything else that might go through a wave or reflow oven (except PCBs). J075 is projected to be released by the end of August. BTW, J-STD-033 is the correct standard for handling & packaging MSDs.

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/