To find a reference value for the proper stocking and moisture protection of electronic
components, you can refer to IPC standards (IPC/JEDEC J-Std-033C).
This is unfortunately not the case if you are looking for guidance to handle printed circuit
boards.

Because there are no published standards yet for storage and moisture protection for
printed boards, they’re generally overlooked. But with the correct stocking control and
the help of professional drying methods, considerable advantages can be gained:
Coated printed boards will stay useable for a much longer time and damage during
reflow due to moisture can be completely eliminated.

Organic solderability preservative (OSP) coatings are among the leading surface finish
options in lead free soldering because they provide an attractive combination of
solderability, ease of processing and low cost. Compared to alternatives, however, they
tend to be the most prone to oxidation.
The cause for this lies in the pure copper surface protected only by the OSP coating
layer. Under normal climatic conditions in a manufacturing process, after only a few
minutes there will be a separation of a water film at the surface (3-5 atom layers). This
then starts a diffusion process which leads to a vapour pressure balance through the
OSP coat.

The electrolytic effect of the water molecules leads to rapid oxidation of the copper
surface which in turn allows the printed boards to fall under the minimum value of
wetability. This effect can also be found with non gas-proof coatings (e.g. nickel) but is
not as pronounced.

The packaging quality of PCBs as received from the manufacturers can also have a
significant effect. Often a simple foil bag or an ESD bag is used instead of a Moisture
Barrier Bag (MBB). With such packing, coated boards are likely to arrive having already
absorbed moisture, and stored like this they will be useless after a short time.
Desorption process desiccant drying cabinets, such as those pioneered by Totech can
be used for the careful drying of these and other moisture sensitive devices.

In addition to extending the safe and stable storage time, defects and damage such as
popcorning and delamination during the reflow process caused by moisture can be
avoided with the Totech desorption technology.

The Totech desorption process is cost-effective and easy. The previously absorbed
moisture is removed from the printed board without temperature stress and with a
controlled, revertive drying process in an atmosphere of less than 0,5 g/m³ vapour
content (in effect, a moisture vacuum). Further oxidation is stopped by the removal of the
electrolytic water molecules. Because Totech storage systems work at room
temperature, boards need not be removed until ready for processing. Dried and stored
in this way the OSP coated printed board is ideally protected and can be used over long
periods of time with steady wettability characteristics.

Dry storage is also necessary for a less critical coating; e.g. in the beginning the
wettability of the coating of a hot air tin-plated printed board is better than of OSP coated
printed boards. Here an oxide film forms on the surface under the influence of moisture
which can also limit good wetting and solderability. This problem can also be averted
with the help of a dry cabinet, enabling the retention of a constant wettability for a much
longer period of time.

With decades of professional experience in the field of ultra low humidity storage and
drying we are glad to advise and support you in the proper handling of your moisture

moisturesensitive electronic components and printed circuit boards.