Dry Packing

Dry packing  is the process of putting moisture-sensitive plastic surface-mount devices in moisture-resistant bags or moisture barrier bags (see Fig. 1) to prevent them from absorbing moisture from the atmosphere.  Moisture ingress into plastic packages can result in popcorn cracking during board mounting.  Popcorn cracking refers to package cracking caused by abrupt vaporization of internal package moisture.

Different packages have different levels of moisture sensitivity.  The amount of time that the units can spend outside the moisture barrier bag once it is opened is known as the floor life.  Thus, units must be board mounted before the specified floor life is reached.  Units can not stay indefinitely inside the moisture barrier bag too.  Shelf life is the amount of time that the units can be kept inside the bag from the date the bag was sealed.  The shelf and floor lives of a lot must be labeled on the dry pack of the lot.

Prior to dry packing, units must be baked to drive any internal moisture away. JEDEC J-STD-033 gives the recommended bake conditions and durations prior to dry packing.

The baked units, which should be in tubes, trays, or a reel, are then put inside the moisture barrier bag along with, if possible, a desiccant (see Fig. 2) for moisture absorption and a moisture indicator card (see Fig. 3) which can indicate the highest moisture level that the units have been exposed to inside the bag.  Dry packing is completed by vacuum-sealing the bag.