Moisture Sensitive Devices (MSD) in the Electronic Assembly Process

ABSTRACT Controlling the assembly process and protecting against environmental factors starts immediately when raw materials arrive. Proper handling of electrostatic static discharge (ESD) is defined and well documented. For example, ESD is controlled by providing grounding points and heel straps, which are the norm in many facilities. Yet ESD is only one of the problems faced in the assembly process.

Another area of concern that is frequently underestimated is the impact of humidity on both components and bare boards (PBs). While most, if not all, manufacturing facilities are climate controlled, there are a number of instances when the floor-clock is accidentally started because moisture barrier bags (MBBs) are opened during inspection upon arrival.

Even when a MBB is resealed, the clock has not been paused and components remain at risk of absorbing moisture, which reduces the effective life of moisture sensitive devices (MSDs).

Bare boards are not currently subject to the same standards that MSDs face; however, the IPC D-35 subcommittee does have a working draft, IPC-1601, of Printed Board Handling and Storage Guidelines (1st working draft – April 9, 2009). Because there is no standard for monitoring and controlling the exposure of boards to moisture, prior to the assembly process, producers have been left on their own, to monitor and mediate any negative effects humidity may have on these raw materials.

This paper explores the effectiveness of handling and storing bare boards in a desiccant based, self-regenerating cabinet that can be used to pause and even reset the floor-clock for MSDs according to J-STD-033B01. Our findings suggest that these cabinets can also be used to prevent moisture related damage to bare boards during the assembly process.

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