Abstract:
An enclosure for storing of moisture sensitive devices (MSD&#39;s). The enclosure includes a plurality of compartments, each continuously purged with dry air supplied by a commercially available de-humidifier. MSD&#39;s housed in said compartments are thus protected from absorbing moisture which could cause cracking of the devices after being mounted on printed circuit boards and subjected to the high temperatures associated with wave solder and solder reflow processes.

Description:
CROSS-REFERENCE TO RELATED INVENTIONS 
     This application claims the priority benefit of U.S. Provisional Patent Application No. 61/101,210, filed Sep. 30, 2008 and U.S. Provisional Patent Application No. 61/099,964, filed Sep. 25, 2008, each of which is hereby incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the storage of electronic moisture sensitive devices (MSDs) prior to mounting onto a printed circuit board. More particularly, this invention relates to humidity-free enclosures for storing electronic moisture sensitive devices (MSDs) in a dry atmosphere thereby minimizing moisture damage to the MSDs prior to and while soldering them onto a printed board. 
     2. Description of the Background Art 
     The process for fabricating printed circuit board (PCB) assemblies for electronic equipment involves mounting electronic components onto the PCB and then heating the PCB in a solder re-flow oven, as in the case of surface mount devices, or in a wave solder machine, in the case of pin-through-hole devices. Unfortunately, electronic components are sensitive to moisture absorption during storage prior to being mounted onto the PCB. Such moisture absorption can frequently later result in damage to the components in the form of cracks due to thermal expansion, or moisture overpressure, of the residue moisture once the components are mounted onto the PCB and exposed to the high oven temperatures associated with the solder re-flow or wave-solder process. Once cracking occurs, air and moisture may contact the circuitry inside the package causing it to corrode and ultimately fail. It is therefore desirable that the electronic components be stored in a dry atmosphere before being mounted onto the PCB such that they will be as free of moisture as possible before they are mounted and soldered in place. 
     Presently there exist many ways to minimize the moisture damage to electronic components. One method involves subjecting the components to a slow bake process to drive out moisture prior to their mounting and soldering onto the PCB. However, the baking of the electronic components requires an extra step in the PCB fabrication process thereby increasing manufacturing time and cost. 
     Another method for minimizing moisture damage to electronic components comprises storing them in an enclosure providing a dry condition until just prior to mounting and soldering them onto the PCB. U.S. Pat. No. 6,622,399 entitled “Apparatus and Method for Maintaining a Dry Atmosphere to Prevent Moisture Absorption and Allow Demoisturization of Electronic Components” and U.S. Pat. No. 7,137,194 entitled “Apparatus and Method for Maintaining a Dry Atmosphere in Surface Mount Device Placement Machine”, the disclosure of each of which is hereby incorporated by reference herein, disclose known methods for minimizing moisture damage. Unfortunately, however, these storage enclosures involve exposing all the components in the enclosure to the ambient humid atmosphere when only one component is being withdrawn from the enclosure. 
     Therefore, one object of this invention is that it may provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the electronic component storage art. 
     Another object of this invention is that it may provide a storage enclosure employing single component packages stored in single storage compartments allowing a component to be removed from its storage compartment without interfering with any other component in another storage compartment of the enclosure assembly. 
     Another object of this invention is that it may provide a storage enclosure assembly employing single component packages stored in single storage compartments allowing a component to be loaded into its storage compartment without interfering with any other component in any other compartment of the storage enclosure. 
     The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Various embodiments of the invention may have none, some, or all of these mentioned objects. Accordingly, these objects or other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     For the purpose of summarizing the invention, this disclosure provides an apparatus and method for inventory control and storage of moisture sensitive printed circuit board components, such as surface mount components, in a dry atmosphere. Conventionally, electronic components are packaged and supplied on reels or in trays, known as waffle trays. The apparatus of the disclosure comprises a storage enclosure assembly, which may be stationary or on wheels, comprising a plurality of storage compartments for housing of the reels and waffle trays, and a dry air delivery system. 
     A sealed compartment door provides access to each of the compartments. The storage compartments are preferably configured to hold up to four waffle trays or from one to four reels depending on the sizes of the reels. Dry air supply and manifolds in the form of secondary chambers are operatively interconnected in parallel to a dry air delivery system for providing a supply of dry air to the plurality of storage compartments. The dry air delivery system preferably provides a supply of dry air, but other appropriate gases may be utilized. 
     In certain embodiments, the dry air supply and manifolds are operatively interconnected to each storage compartment in parallel to a dry air delivery system in such a manner that the dry air flow is allowed only when the storage compartment contains one or more reels or trays and the door is closed, thereby assuring that dry air is supplied to the storage compartment only after the reels or trays are loaded therein. 
     More particularly, when the compartment door is opened for inserting the reels or trays, a valve assembly located at the back of the storage compartment closes off airflow to the storage compartment to prevent the intrusion of a high concentration of ambient moist air into the secondary chambers. Once the reels or trays are loaded into the storage compartment and the door is closed, the valve assembly re-opens to allow the flow of dry air into the storage compartment. 
     Conversely, upon opening the compartment door to remove the reels and trays, the valve assembly closes to stop the flow of dry air into the storage compartment and to preclude the humid moist air from entering the dry air delivery manifold. Preferably, if no other reels or trays have been loaded into the storage compartment once the door is re-closed, the valve assembly remains closed, thereby precluding any residual moisture in the compartment from entering into the dry air delivery system. 
     In other embodiments, the dry air supply and manifolds formed from secondary chambers are operatively interconnected to each storage compartment in parallel to a dry air delivery system in such a manner that the dry air flow is accessible to the storage compartments on a continuous basis, thereby assuring continuous purging of the compartment with moisture-free air without regard to whether the compartment door is opened or closed or whether any reels or trays have been inserted or removed. 
     More particularly, when the compartment door is opened for insertion or removal of the reels or trays, any moisture entering the compartment due to exposure to ambient air is quickly purged from the storage compartment as soon as the compartment door is closed. 
     Purging takes place as dry air from the secondary chambers enters the compartment through a small hole, while contaminated air exits via another small hole connected to the return duct. From here it is directed by forced convection back to the dry air delivery unit where it is exposed to desiccants and dried before being circulated back into the supply duct. When any compartment door is opened, the forced convection mechanism will stop which in turn isolates all other compartments from any moisture present in the opened chamber. The flow of dry air resumes as soon as the compartment door is closed and latched. 
     Accordingly, the apparatus and method of the invention may therefore allow for single compartment, single location control with total flexibility, allowing for opening and closing of only one small compartment at a time to reduce the effects of ambient moist air contamination of the dry air supply. 
     The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood so that the present contribution to the art can, be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and possible objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which: 
         FIG. 1A  illustrates an example enclosure in accordance with one embodiment of the present disclosure comprising a plurality of individual component compartments and a dry air delivery system; 
         FIG. 1B  illustrates the example enclosure of  FIG. 1A  having additional main front doors in a closed position; 
         FIGS. 2A-B  illustrate the details of the interior mechanism within one embodiment of a component compartment of the enclosure in  FIG. 1A ; 
         FIG. 3  illustrates one example of a large component storage reel placed in position within a vertical component compartment in accordance with the enclosure in  FIG. 1A ; 
         FIG. 4  illustrates one example of small component storage reels placed in position within a vertical component compartment in accordance with the enclosure in  FIG. 1A ; 
         FIG. 5  illustrates one example of component storage waffle trays placed in position within a horizontal component compartment in accordance with the enclosure in  FIG. 1A ; 
         FIG. 6A  illustrates an example enclosure in accordance with another embodiment of the present disclosure comprising a plurality of individual component compartments, a dry air delivery system and additional shelving space; 
         FIG. 6B  illustrates the example enclosure of  FIG. 6A  having additional main front doors in a closed position; 
         FIG. 7  illustrates the details of an embodiment of a component compartment of the enclosure in  FIG. 6A ; 
     
    
    
     Similar reference characters refer to similar parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1A , a large enclosure assembly  1  is shown containing a plurality of component storage compartments and a dry air delivery system  2 . Although the dry air delivery system  2  utilized in the embodiment depicted in  FIG. 1A  is comprised of a commercially available dehumidifier integrated into the enclosure assembly itself and capable of delivering dry air to all of the storage compartments, other forms of dehumidifiers or equipment capable of providing a continuous flow of dry air would suffice. Such as, for example, the source providing a continuous flow of dry air could be located external to the enclosure assembly  1  and then operatively coupled to the enclosure assembly  1  by way of hoses and the like to provide a continuous flow of dry air to the storage compartments  3  and  4 . In the configuration depicted, twenty-one horizontal storage compartments  3  and twelve vertical compartments  4  are provided. It should be understood, however, that other combinations and arrangements of horizontal and vertical storage compartments  3  and  4  may be provided depending on the quantities required for a particular application. The storage compartments  3  and  4  are generally accessed by individual doors hinged or pivotally coupled at the right  5  in the case of the horizontal compartments  3 , or at the bottom  6  in the case of the vertical compartments  4 . The storage compartment doors, which preferably embody soft, elastomeric seals, are held tightly closed by means of spring latches (not shown in  FIG. 1A  but see  FIG. 2A  and discussion) so the storage compartment interiors are isolated from ambient air. Although the enclosure assembly  1  illustrated in  FIG. 1A  employs the use of hinges and spring latches to forcibly hold the storage compartment doors in place, other various fastening means and soft pliable materials commonly used in industry for accomplishing container or compartment sealing tasks may be applied to the storage compartment doors so to accomplish the same sealing effect of the storage compartments  3  and  4 . 
     Referring further to  FIG. 1B , a smaller scale drawing of the enclosure assembly  1  is illustrated having first and second main doors  7  and  8  operatively coupled to the front of the enclosure assembly  1 . These first and second main doors  7  and  8  may be closed for added protection of the enclosure&#39;s contents and locked for added security. 
     Further, each of the horizontal and vertical storage compartments  3  and  4  in the enclosure assembly  1  is preferably provided with a bar code label to identify the components stored within. A bar code scanner connected to a microprocessor of the types commonly used in the industry for bar code reading can then be used to locate components in the enclosure assembly  1 , as well to provide inventory control by keeping track of which components are installed or removed from the enclosure assembly  1 . 
     Referring now to  FIG. 2A , the details of the interior mechanism within each vertical storage compartment  4  are illustrated. The details of the interior mechanism within the horizontal storage compartments  3  are identical to that of the vertical storage compartments  4 . The horizontal and vertical storage compartments  3  and  4  are preferably constructed of molded plastic containing an electro-static dissipative additive to prevent static electricity build-up which could cause damage to sensitive electronic components. The main housing  9  is preferably molded of black plastic, whereas the door  10  is preferably molded of clear, transparent plastic. The door  10  comprises a hinge  11 , an elastomeric seal  12  and a spring latch  13 . The door is opened manually by grasping and pulling on molded wing  14 . The main housing  9  is further sealed from ambient air by bottom wall  15 , top wall  16  and left side wall  17 . The right side wall of the main housing  9 , opposite the left side wall  17 , is formed by the left side wall  17  of another identical main housing  9  of an adjacent vertical storage compartment  4  which is bonded to the first vertical storage compartment  4  to form a sealed cavity. Additional vertical storage compartments  4  are bonded to each other in a likewise manner until the desired number of storage compartments  4  is achieved. The assembly of horizontal storage compartments  3  is performed in a similar manner and until the desired number of horizontal storage compartments  3  is achieved. A flat wall section (not shown) is bonded in place to seal the last of the vertical storage compartments  4  in the stack and likewise for the last of the horizontal storage compartments  3  in the stack. 
       FIG. 2A  depicts an empty vertical storage compartment  4  (no components installed). The rear wall  18  of the vertical storage compartment  4  is integrally molded to the bottom, top and left side walls  15 ,  16  and  17  respectively as well as the right side wall to form the main chamber  19  having a front opening  19   a  of the vertical storage compartment  4 . The rear wall  18  has an opening  20  that is sealed off by a means for regulating flow in the form of a valve assembly  21  comprised of a baffle  22 , an elastomeric seal  23 , an actuator  24 , extension posts  24   b  and springs  25 . The springs  25  keep the valve assembly  21  tightly closed to further seal the vertical storage compartment  4 . Adjacent to the rear wall  18  is a secondary chamber  26  which is supplied by air from the dry air delivery system  2  ( FIG. 1 ). All of the secondary chambers  26  containing the dry air are joined by connections formed by sealing gaskets  27  at both ends of the secondary chamber  26  such that dry air flows through and permeates all of the horizontally and vertically stacked storage compartments  3  and  4  as represented by the wavy arrows in  FIGS. 2A-B . 
       FIG. 2B  shows a partial view of the vertical storage compartment  4  which depicts what happens when a reel, waffle tray or other commonly used carrier, containing electronic components is installed in the storage compartment  4 . First the door  10  is opened. As soon as the reel or tray component carrier(s) is/are placed in the main chamber  19  through the front opening  19   a  and the door  10  is closed and latched, the reel or tray(s) containing the components contacts the actuator  24  of the valve assembly  21  and forcibly moves it and, by way of the extension posts  24   b , the attached baffle  22  in the direction  28  causing the springs  25  to compress, allowing air in the main chamber  19  to mix with dry air from the secondary chamber  26 , as depicted by the curved arrows. Moisture trapped in the main chamber  19  thus dissipates into the secondary chamber  26 . Since the secondary chamber  26  is being continuously supplied with de-humidified air, and the main chamber  19  is sealed from ambient air, it is only a matter of a short time before the dry air stabilizes in both chambers  19  and  26  and the electronic devices become protected in a dry atmosphere. 
     When door  10  is opened for removal of a component reel or waffle tray, springs  25  decompress and push the component reel or tray out slightly as the valve assembly  21  closes and once again seals the opening  20  of the rear wall  18  of the main chamber  19  preventing the flow of new moist ambient air from permeating into the secondary chamber  26 . This results in the dry air supply contained and flowing in the secondary chamber  26  having minimal exposure to moist ambient air, and, at the same time, does not interfere with the dry air atmosphere surrounding any other components stored in other horizontal or vertical storage compartments  3  and  4  in the enclosure assembly  1 . Through this process with enclosure assembly  1  and the valve assembly  21 , the single component, single location benefit is achieved. 
     The disclosed embodiment is further described in  FIG. 3  which shows a particular configuration where a large component reel  29  is installed in a vertical storage compartment  4 . The front view of a vertical storage compartment  4  is shown in  FIG. 3A , while the side view is shown  FIG. 3B . Door  10  is closed against elastomeric seal  12  and held in position via spring latch  13 . The valve assembly  21  is held open by action of the door  10  pushing on reel  29 , which in turn pushes on actuator  24  that is coupled to the baffle  22 , by way of the extension posts  24   b , to forcibly compress springs  25  and translate the baffle  22  away from the opening  20  in the rear wall  18  thereby opening the valve assembly  21 . This exposes the main chamber  19  of the vertical storage compartment  4  to the dry air supply flowing in the secondary chamber  26  from the dry air delivery system resulting in the reel components being stored in a dry atmosphere.  FIG. 3C  shows the door  10  opened in preparation for removal of the large component reel  29 . 
     It can be seen from  FIG. 3C  that the component reel  29  is pushed out slightly as springs  25  decompress upon the opening of door  10  which removed the translational force originally exerted by door  10  when it was closed. The decompressing of the springs  25  creates a translational movement of the actuator  24  and baffle  22  in the direction of the door  10  thereby closing the opening  20  in the rear wall  18  by way of the baffle  22  and its elastomeric seal  23  contacting the rear wall  18  thus preventing any contamination of the dry air flowing in the secondary chambers  26  by any new moist ambient air. Once the component reel  29  is removed and the door  10  is closed, the valve assembly  21  remains in its closed position until another package of components is installed. See  FIG. 2A . 
     The disclosed embodiment is further described in  FIG. 4  wherein another particular configuration is illustrated where two small component reels  30  are installed in a vertical storage compartment  4 . In this configuration a horizontal partition  31  has been installed in the storage compartment  4  to create two levels, thus allowing the accommodation of two small component reels  30 . The horizontal partition  31  is preferably molded of black plastic containing an electro-static dissipative additive to prevent static electricity buildup and is frictionally coupled to the left side wall  17  and the right side wall of the vertical storage compartment  4  (right side wall not shown but is formed from the left side wall  17  of the next adjacent vertical storage compartment  4 ). A spacer  32  is included to allow either one or both of the small component reels  30  to contact the actuator  24  and resultingly open the valve assembly  21  in a similar fashion as described previously herein. The spacer  32  is preferably molded of black plastic containing an electro-static dissipative additive to prevent static electricity buildup and can be removed when necessary to accommodate larger component reels in the vertical storage compartment  4 . The horizontal partition  31  may also be coupled to and made integral with the spacer  32 . Similarly, the addition of a vertical partition (not shown) can also be used to allow for the installation of four small component reels  30  of a narrower width. Similarly, the vertical partition can be frictionally coupled to the bottom and top walls  15  and  16  of the vertical storage compartment  4  or coupled to and made integral with the spacer  32 . The vertical partition is also preferably molded of black plastic containing an electro-static dissipative additive to prevent static electricity buildup. 
     Furthermore, it is possible to install only a vertical partition without the horizontal partition  31  to allow for two large but narrow component reels (not shown) to be installed in a single vertical storage compartment  4 . Configuration of the spacer  32  may vary freely from that shown in  FIG. 4  and could be nothing more than a block of foam. The spacer  32  need only be of such nature and/or configuration so as to facilitate sufficient translational movement of the actuator  19  when components are placed in the vertical storage compartment  4  and the door  10  is closed. 
     The disclosed embodiment is further described in  FIGS. 5A-B  which show a horizontal storage compartment  3 . The front view of the horizontal storage compartment  3  with the hinge at right  5  and the molded wing  14  coupled to the door  10  is illustrated in  FIG. 5A .  FIG. 5B  is a top view of the horizontal storage compartment  3  showing two component containing waffle trays  33  positioned therein.  FIG. 5B  illustrates the inside of the main and secondary chambers  19  and  26  with waffle trays  33  being forcibly pushed by the door  10  which in turn is pushing on the actuator  24  causing it to have translationally moved toward the rear wall  18  resulting in an open valve assembly  21  in much the same manner as previously described with respect to  FIGS. 3A-C . The opening of the valve assembly  21  thereby exposes the stored components to the dry air supply flowing from the secondary chamber  26  creating a dry storage atmosphere. The waffle trays  33  are illustrated in a separated position by way of a first partition  34 . The first partition  34  is preferably frictionally coupled between the bottom and top walls  15  and  16  of the horizontal storage compartment  3 . Similarly, a second partition (not shown), mounted 90 degrees from the first partition  34 , may also be used to provide a second compartment layer, allowing for the positioning of four waffle trays  33  into the horizontal storage compartment  3 . 
     Referring now to  FIG. 6A , a disclosure of another embodiment of an enclosure assembly  40  is illustrated. The enclosure assembly  40  of  FIG. 6A  may be a stationary unit or mounted on wheels  41 . The enclosure assembly  40  is shown containing a plurality of horizontal storage compartments  42  and a commercially available de-humidifier  43  capable of delivering a dry air supply to all of the horizontal storage compartments  42 . In the configuration depicted, twenty-one horizontal compartments  42  are provided. It should be understood, however, that other horizontal combinations and arrangements of compartments  42  may be provided depending on the needs of a particular application. 
     The horizontal storage compartments  42  are accessed by doors  44  hinged at the right  45  which allow each door  44  to swing open in a horizontal plane. The doors  44  are held tightly closed against elastomeric seals (not shown in  FIG. 6A ) by means of latch knobs  46  pivotally coupled to the enclosure assembly  40  so to operatively contact a closed door  44  when rotated 90 degrees clockwise from the unlocked position to the locked position. When doors  44  are closed and forming a sealed contact, the horizontal storage compartments  42  is thus isolated from moist ambient air. Latch knobs  46  are preferably backlit by an LED which glows either red, signifying the unlocked position, or green, signifying the locked position thereby making it easy to quickly identify an unlocked storage compartment  42 . 
     Each door  44  embodies a secondary latch  48  in the form of a spring clip (shown in  FIG. 7 ) which helps to align the door  44  with its horizontal storage compartment  42  and hold the door  44  closed until the primary locking device, latch knob  46 , is actuated to the locking position. 
     The area adjacent to the horizontal storage compartments  42  may be configured in any manner for additional storage; for example, shelves  50  may be configured as shown in  FIG. 6A . 
       FIG. 6B  is a smaller scale drawing of the enclosure assembly  40  showing a first main door  51  and a second main door  52  incorporated into the enclosure assembly  40 . These first and second main doors  51  and  52  may be closed for added protection of the contents of the enclosure assembly  40  and locked for added security. 
     Each of the horizontal storage compartments  42  in enclosure assembly  40  is preferably provided with a bar code label to identify the components stored within. A standard bar code scanner connected to a microprocessor can then be used to locate components within the enclosure assembly  40 , as well to provide inventory control by keeping track of which components are held within or removed from the enclosure assembly  40 . 
     In referring now specifically to  FIG. 7 , the details of the interior and exterior construction of horizontal storage compartments  42  are illustrated by way of two adjacent horizontal storage compartments  42  shown for clarity.  FIG. 7  depicts a lower horizontal storage compartment  42   a  shown with its door  44   a  open and ready to accept components for storage, while the upper horizontal storage compartment  42   b  is shown with its door  44   b  closed and latched. Component reel  53  is shown being inserted into the lower horizontal storage compartment  42   a  as just one example of packaged moisture sensitive devices that can be stored in enclosure assembly  40 . The horizontal storage compartments  42   a  and  42   b  are preferably constructed of molded black plastic containing an electro-static dissipative additive to prevent static electricity build-up which could cause damage to sensitive electronic components. The doors  44   a  and  44   b  are preferably molded of clear, transparent plastic. 
     The horizontal storage compartments  42   a  and  42   b  are bonded together so that the bottom wall  54  of horizontal storage compartment  42   b  forms the top wall of horizontal storage compartment  42   a . Interlocking hinge features  55  are molded into the doors  44   a  and  44   b  and right side walls  56   a  and  56   b  of horizontal storage compartments  42   a  and  42   b  respectively and become connected by hinge pin  57 . Additional horizontal storage compartments (not shown) are likewise bonded to each other in a horizontal stack until the desired number is achieved. A flat cover (not shown) is bonded into place to seal the topmost horizontal storage compartment (not shown) in the stack. The door  44   a  is opened manually by grasping and pulling on molded wing  58 . A soft elastomeric seal  59  is operatively positioned around the front opening  49  of each of the horizontal storage compartment  42   a  and  42   b  so as to sealingly contact the doors  44   a  and  44   b  when they are in the closed position. A secondary latch  48  is attached to each door  44   a  and  44   b  to align such with its respective front opening  49  and to hold it closed. Latch knob  46   a  adjacent to the lower horizontal storage compartment  42   a  is shown in its counterclockwise or unlocked position, which allows the door  44   a  to be opened and closed. Once the door  44   a  is closed and secondary latch  48  is frictionally engaged, latch knob  46   a  is manually rotated 90 degrees clockwise to further tighten the door  44   a  against the elastomeric seal  59  providing an airtight fit. Door  44   b  of horizontal storage compartment  42   b  is shown in the closed position and held secure by latch knob  46   b  in its clockwise locked position. 
     At the rear of horizontal storage compartments  42   a  and  42   b  in  FIG. 7 , there are return air and supply secondary chambers  60  and  61  respectively which are both open at their respective tops and bottoms. With the horizontal storage compartments  42   a  and  42   b  stacked together these secondary chambers  60  and  61  connect to form passages or ducts through which respective return air and dry air is passed via forced convection provided by the dehumidifier  43 . More particularly, a first fan (not shown) in the dehumidifier  43  forces dry air, represented by arrows  62 , down through the supply secondary chamber  61 . A second fan (not shown) in the dehumidifier  43  draws return air, represented by arrows  63 , through the return air secondary chamber  60  up into a desiccant chamber (not shown) of the dehumidifier  43 . A small amount of bleed air  64  enters each horizontal storage compartment  42   b  through a bleed vent  65  where it circulates before expelled air  66  exits via a return vent  67  into the return air secondary chamber  60 . This provides each horizontal storage compartment  42   a  and  42   b  with a continuous purging with dry air to maintain a low humidity environment. Because the dry air  62  supplied in the supply secondary chamber  61  is under slight positive pressure, and the return air  63  in the return air secondary chamber  60  is under slightly negative pressure, the pressure in each horizontal storage compartment  42   a  and  42   b  remains close to neutral (atmospheric). 
     Thus, for example, when a door  44   b  is opened there is negligible transfer of air between the dry air  62  in the main chamber  47  and the potentially moist ambient outside air due to a lack of any meaningful pressure differentials. Any moist air that does enter the horizontal storage compartment  42   b  is quickly purged once its door  44   b  is again closed forming an air tight seal against the front opening  49  and the latch knob  46   b  is rotated to the locked position. Because the bleed vent  65  and the return vent  67 , generally providing for the circulation of dry air  62  through the main chamber  47 , are of relatively small diameters there is very little interaction between the various individual horizontal storage compartments  42 . As a result, when one door  44  is opened for component access, there is negligible effect on the stored components in other horizontal storage compartments  42 . The first and second fans (not shown) in the dehumidifier  43  are preferably operative to continuously operate as long as all the doors  44  to the horizontal storage compartments  42  are closed and their respective latch knobs  46  are in the locked position. Upon the rotation of any one latch knob  46  to a horizontal storage compartment  42  to an unlocked position, internal circuitry associated with the dehumidifier  43  activates to shut off power to the first and second fans. 
     The present disclosure includes that contained in the appended claims, as well as that of the foregoing description. Although this disclosure has been described in its preferred form in terms of certain embodiments with a certain degree of particularity, alterations and permutations of these embodiments will be apparent to those skilled in the art. Accordingly, it is understood that the above descriptions of exemplary embodiments does not define or constrain this disclosure, and that the present disclosure of the preferred form has been made only by way of example and that numerous changes, substitutions, and alterations in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.