What is a desiccant Dry Cabinet?
A desiccant dry cabinet is an enclosure with a supply of desiccant which maintains an internal environment of 1-50% RH. Desiccant dry cabinets are also called: Desiccators, Dry Boxes, Dehumidifying Cabinets, and Ultra Low Humidity Storage Cabinets. Click here to view the CleanPro Desiccant Cabinets we offer, or keep reading to learn more about them.
How do CleanPro Cabinets desiccant dryers function?
Depending on the size and type of model in question, up to three High Performance Dehumidifying Units may be installed. These units are simple and reliable and are the result of many years of research. The diagram to the right shows the basic operation of the dryer. These dryer units contain a specially chosen desiccant that is exposed to the cabinet interior for a period of time, during which moisture is trapped within the desiccant.
Depending on the set points selected by the user, the dryers will seal themselves off from the cabinet interior regularly during operation for recycling and refreshing. The desiccant is refreshed by heating it and allowing the trapped moisture to escape as vapor (H2O) through vents located at the back of the cabinet.
Once refreshed, the unit is ready to seal off he exterior venting, and re-open itself to the interior to continue dehumidification. An electronically controlled cycle ensures that the dryer units are operating in tandem, providing drying power at all times.
What is the recovery time on a CleanPro Cabinet?
This may be the single most important issue, after Min RH level. Recovery time refers to the time required for the cabinet to reduce the RH level back to <5% RH after the door has been opened and closed. All CleanPro Cabinets are equipped with an ‘Auto-On’ feature which activates a fan inside the dehumidification units, causing air movement within the cabinet and allowing the newly introduced moisture to be captured before it can begin to degrade the parts already in storage. The graph to the left illustrates how a CleanPro Cabinet recovers after 1, 2, and then 3 doors are open.
This approach provides excellent recovery time, certainly better than the ‘static’ approach used by some of our competitors. In situations where the opening of doors is exceedingly frequent, and plumbing permits, an optional Nitrogen purge may be installed. This purge would be activated upon the door closing and would continue for a 10-15 minute period (depending on set parameters) allowing the quick voiding of any ambient moisture introduced into the cabinet. This method of recovery will utilize approximately 1/20 - 1/100 the consumption of a standard nitrogen storage cabinet of the same size.
Why be concerned with moisture?
…And what to do to protect your valuable MSD inventory.
Components will begin to absorb moisture from the air as soon as they are removed from protective storage (Moisture Barrier Bags, N2 Cabinets, Desiccating Cabinets) and condensation will form on its surfaces. Within a fairly short time moisture will permeate the inside of the package. If reflow soldering is performed under these conditions, the moisture will form into a vapor creating pressure inside the package that almost always results in internal damage to the part (cracks or ‘popcorning’). Initally, no irregularities may be visible, defects can be difficult to detect, even if tested electrically. However, corrosive ions may eventually find their way through the cracks, corroding and eventually destroying the circuitry inside the chips.
IPC/JEDEC J-STD-033a (July 2002) lays out very specific guidelines for MSD’s once they have been removed from the MBB quality storage, regarding exposure times to various moisture levels in the production facility, and the approved methods for voiding the parts of that moisture. Some of these methods and procedures can become very confusing, and difficult to implement.
CleanPro Desiccant Cabinets are well equipped to deliver the constant < 5% RH that IPC/JEDEC J-STD-033a (July 2002) demands in order to be “considered equivalent to storage in a MBB with unlimited shelf life”. This allows for the return of parts NOT sealed in a MBB for safe storage. In fact dependent on the trype of parts, the total exposure, and the total storage time in the CleanPro Cabinet, floor life can be reset to zero. This is something that cannot be achieved with an N2 cabinet.
What should be stored in a Dry Desiccant Cabinet?
- Any component classified as an MSD (Moisture Sensitive Device), particularly deices classified as level 4-5a. These devices are most susceptible to moisture related defects.
- Partially populated double sided boards. While waiting to re-enter production to have second side assembly done, components begin to absorb moisture that could do harm once the PCB is introduced back to the reflow oven.
Will storing my components in a CleanPro Dry Cabinet satisfy IPC JEDEC-J-STD-033?
No is the short answer, arbitrarily storing your MSDs in any desiccant cabinet, dry box, N2 (Nitrogen) cabinet, hot air box, or any other dehumidification device will not on its own satisfy IPC J-STD-033. It will not automatically ‘stop the clock’, however, the implementation and correct use (calculated storage duration based upon floor exposure, ect.) of a desiccant dry cabinet capable of maintaining less than 5% RH (such as a CleanPro Cabinet), is a crucial part of a strong MSD control program.
Do CleanPro Cabinets use heat to dissipate moisture?
Dehumidification of the cabinet is caried out by desiccant alone, with no cabinet heat involved. Optional cabinet heaters are available as an option. Please contact PAC for more information if you are interested in a cabinet heater.
Do CleanPro Cabinets require Nitrogen?
CleanPro desiccant dry storage products do not require nitrogen to maintain the RH levels indicated within the specifications. However for applications that require extreme frequency of door openings and where plumbing permits, an optional nitrogen purge may be installed.
What are the benefits of Desiccant Dry Cabinets over Nitrogen Cabinets?
Desiccant cabinets have lower running costs. N2 is void of all oxygen, it is unable to absorb O2, and as a result it is less effective than desiccant when used as a drying agent. It is typically used under positive pressure to continually displace the oxygen in the cabinet. CleanPro cabinets are portable with casters, and do not require plumbing, so they can be moved to a new location whenever required. CleanPro cabinets will maintain their internal environment for extended periods (10 to 24+ hours) during power down situations, continuing to protect your components. Nitrogen cabinets use a constant positive pressure flow to void the cabinets of all O2; this nitogen flows out into the prouction facility, reducing the oxygen density in the area, potentially causing discomfort to the staff.
What are the benefits of Desiccant Dry Cabinets over Moisture Vapor Barrier Bags (MBBs)?
Saves labor; Trays and reels can be placed directly into the cabinet without having to be placed in MBBs. Saves cost; Less desiccant abd MBBs required. More secure, no need to be concerned with calcualtions to determine the correct amount of desiccant, the quality and remaining absorbency of the desiccant, and potential mis-sealing, or the possibility of punctures to the bag itself.
What are the benefits of Desiccant Dry Cabinets over baking?
- Less costly than baking; with a monthly power consumption of only 40.4 kW it’s considerably less expensive than long duration bake cycles.
- More efficient; Components are being dehumidified while they sit in inventory, always ready for the next run.
- More convenient; Operators will be more inclined to place components into cabinets rahter than taking the time to re- bag, especially for short duration exposures.
- Space saving; smaller outside dimensions than that of comparable burn in cabinets as a result of insulation, wiring, ect.
- Better quality; Baking SMD packages may cause oxidation or intermetallic growths to form, which can reduce solderability. Component cariers may cause out gassing during baking, again, effecting the solderability.
- Less concern; Standards suggest when baking between 90-125°C. A max time of 48 hours be observed, then deviations should be requested. With desiccant cabinet storage there is no maximum to observe.
- Less handling; There is no need to transfer components from their standard packaging to high temp carriers in preparation for the bake, possibly introducing physical damage to the component itself.
Are CleanPro Cabinets cleanroom safe?
Not all cabinets are considered cleanroom approved, contact PAC to discuss cleanroom options and models.
Are CleanPro Cabinets ESD safe?
All CleanPro Cabinets are ESD safe. Standard features include stainless steel shelves, conductive glass, conductive paint on all cabinet surfaces, and earth lead.
What are the benefits of CleanPro Cabinet’s ‘Auto-On’ feature?
CleanPro cabinet auto-on feature provides an opportunity after each door opening to capture the newly introduced moisture before it has a chance to settle. The movement of the air (and its entrapped moisture) within the cabinet provides more opportunity for those moisture particles to pass within the desiccants reach.
Will RH levels remain constant within a CleanPro Cabinet?
Studies have shown that our technology, as designed into our dehumidification unit allows the cabinet to remain at the operator set RH without any difficulties.
What happens to my CleanPro Cabinet if the power goes out?
CleanPro Cabinets are designed and manufactured to be able to maintain an environment of <5% RH for a period of 10 days, and <10% RH for a period of approximately 20 days if the cabinets remain closed and no new moisture is introduced.
Can I monitor my CleanPro Cabinet(s) over a network?
Does the desiccant require replacing?
No, the desiccant is extremely well suited to the task and should perform under normal operating conditions for 10 years or more without replacement.
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