Available Methods Of Dry Storage
There are a variety of options for ‘dry storage’ available that will satisfy current industry specifications. Methods commonly in use, but not limited to, are; MBB (Moisture Barrier Bags), N2 cabinets, dry air boxes and desiccant dry cabinets.
Many PCB manufacturing facilities are already utilizing one or more of the methods listed above. In some cases however the methods chosen are implemented without an evaluation of their actual effectiveness in the specific environment / application for which they were intended. Variables such as; how often will the inventory stored be accessed, are the packaging materials hygroscopic, have the parts been pre-conditioned, etc… are not always fully considered. Equally important is that these storage devices are rarely reviewed or audited for their effectiveness post installation, and commonly are in such disarray than they are known to be less effective than required.
It’s not uncommon to see moisture barrier bags remain unsealed for prolonged periods of time on a busy production floor, for silica gel sachets to be unknowingly used ‘past their prime’, or be stored in containers that are not air tight.
The calculation used to determine the volume of Silica Gel required to maintain the required relative humidity level (RH%) within a MBB is based upon an activity level of which the gel is expected to be capable. Improper handling or storage of Silica Gel sachets means that the activity level will be degraded.
Frequently N2 and dry air cabinets are in use with doors that no longer seal well when closed as a result of over use or abuse, causing them to be less effective than required, and driving running costs up. As a result of the passive nature of these ‘devices’ they are rarely monitored, maintained, or evaluated to determine if they are functioning in an adequate manner.
Desiccant dry cabinets although relatively new to North America have been popular in industrial and main stream Asia for decades, as a result of the humid climate. The wide variety of applications for humidity control products within that part of the world has led to a number of innovations and advances in desiccation technology that allows for the practical adaptation to the electronics manufacturing industry.
Whatever the method chosen, expectations will be the same; the assurance that the prescribed relative humidity level is maintained at all times, affording valuable moisture sensitive inventory the protection required.