Abstract:
Packaging for electronic components includes provisions to short selected electrodes of the components together. A plastic base portion with a plurality of component receiving cavities carries a flexible, carbonized shorting element which extends between cavities. The cavities include a recess which is adjacent to the shorting element. Components can be inserted into respective cavities, and some of the electrodes will contact the shorting element. Other electrodes will extend into the recess and not be shorted.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/945,448 filed Feb. 27, 2014, entitled, “Gas Sensor Packaging Including Means To Maintain Devices In A State Of Readiness”. The &#39;448 application is hereby incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The application pertains to structures which maintain gas sensors in a state of readiness for use. More particularly, the application pertains to packaging structures wherein gas sensor electrodes can be shorted together to minimize delays due to start-up or stabilization periods. 
       BACKGROUND 
       [0003]    In gas detection instruments employing an electrochemical gas sensor, a potentiostatic drive circuit is normally used to hold the sensor electrodes at the required potentials. These potentials may be equal or there may be a bias between them to drive the required electrochemical behaviour. 
         [0004]    The current generated by a sensor between the sensing and counter electrodes (or between one of these electrodes and an additional electrode) is amplified by additional circuitry. If the sensor is provided with a diffusion limiting gas access barrier and the electrode activity is adequate to consume all of the target gas entering the cell, then the current generated is proportional to the concentration of target gas in the environment. 
         [0005]    If, prior to installation in an instrument, the relevant electrodes of a gas sensor have not been maintained at the required relative potentials, for example (they have been allowed to drift to their open circuit potentials), there will be a significant delay in the sensor achieving its optimum operating condition. This could be due to chemical species forming on the electrode or in the electrolyte which would be consumed or reacted under normal operating conditions. For example, the sensor may exhibit an erroneous, high baseline reading indicating the presence of gas when in fact this output is merely a reflection of internal cell processes. 
         [0006]    Such effects gradually decline with continued operation, but there can be a significant delay before the sensor is capable of performing to specification. This is termed a start-up or stabilization period. Such periods can be many hours in extreme cases, depending on the design of the sensor, the performance requirements and the period for which the electrodes have been allowed to drift. 
         [0007]    For manufacturers who build and calibrate instruments (which may contain several different electrochemical sensors), such start-up delays can be a significant problem. They can lengthen the cycle time of the manufacturing process which in turn requires the instrument manufacturer to hold additional inventory and hence increase costs. 
         [0008]    Sensors which normally operate under bias are usually shipped on a pcb provided with a potentiostat and circuit capable of maintaining the required potentials for a limited period (compatible with the interval between sensor manufacture and instrument integration). The cost of such boards is not negligible and they are usually recycled back to the sensor manufacturer. This is time consuming and undesirable, but still preferable to dealing with long start-up times. For the majority of sensors which operate at zero bias, such complexity is not required, and creating a shorting connection between the relevant electrodes is adequate to maintain the sensor in a state of readiness. 
         [0009]    The prior art discloses attaching a spring (or similar) across sensor contact pins to create an electrical short. This is additional labor task which is detrimental to the productivity of sensor manufacture, and an equal labor task is necessary for the instrument manufacturer to remove the spring before installation. Many instrument manufacturers opt to not install a spring. The reduced labor cost is more valuable than a cycle time associated with waiting for the drive circuit to stabilize the electrodes. 
         [0010]    Preferably shorting links will only be applied between the required electrodes. Otherwise there is a risk of maintaining an electrode at an undesirable potential which can itself be a source of startup delay. For example, it may be undesirable to connect the counter electrode to the shorted sensing electrode-reference electrode pair, as in many cases it has a different Open Circuit Voltage and would therefore disturb the natural equilibrium of the reference. 
         [0011]    Thus, an approach which unselectively shorts all sensor pins is unlikely to be appropriate. This is one reason why simple foam pads of the type used to protect semiconductor components from electrostatic discharge are not an adequate solution to the problem, even for individually packaged sensors. Similarly, approaches where a metal foil-covered compliant pad is used to short all the pins has significant shortcomings for sensor users, even if the relatively small annular contact areas of the foils around the pins were felt to be adequate and reliable. An ESD bag would suffer from similar shortcomings. 
         [0012]    For containers holding multiple sensors, the above noted problems are greater. 
         [0013]    Other shortcomings are (a) that the contacts between the sensor pins are not robustly and continuously maintained and can depend on orientation; and (b) the resistivity of the materials used is not well matched to the requirements of the electrochemical processes. For example, many ESD foams exhibit resistances of the order of 100K ohms between sensor pins. ESD bags have too high a resistance and offer insufficient contact area with the pins. 
         [0014]    Electrochemical toxic gas sensors are packaged in a number of configurations which include (but are not limited to) multiple sensors packaged in trays, and individual sensors packaged in pots. Following the end of the manufacturing process, after exposing the sensors to a target gas to ensure sensor performance to a respective specification, the sensors are placed in storage locations or packaging trays. 
         [0015]    Using prior art methods, additional handling of the sensors is necessary to apply the shorting spring, or similar structure, with the possibility of double handling if sensors are stored in an un-shorted state, with springs added prior to shipping. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  illustrates a block diagram of a packaging system in accordance herewith; 
           [0017]      FIG. 2  is a plan view of the system of  FIG. 1 ; 
           [0018]      FIG. 3  is a sectional view taken along plane A-A of  FIG. 2 ; and 
           [0019]      FIG. 4  is an enlarged view of a portion of the sectional view of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    While disclosed embodiments can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles thereof as well as the best mode of practicing same, and is not intended to limit the application or claims to the specific embodiment illustrated. 
         [0021]    In one aspect, in embodiments hereof a shorting medium is integrated into the packaging or storage container. The respective sensor is immediately shorted once placed in the storage container. By using a purposefully shaped conductive material a short can be created only between the required sensor contacts. Those contacts which do not require shorting are isolated from the shorted contacts. 
         [0022]    By using a material which is conductive and has good elastic properties, contact resistance between the conductive material and the sensor contacts can be maintained prior to use by instrument manufacturers. The instrument manufacturer could then remove the sensor from the packaging without removing the shorting medium as it is retained in the packaging. This eliminates the labor associated with removing the spring from the sensor, or reduces the time required to match the electrodes with the instrument driver circuit or other shorting method for manufacturers who opt not to request a shorting spring. 
         [0023]    In another aspect, a common shorting method is provided for sensors packaged individually or bulk packed. For example, for sensor manufacturers who store all sensors in bulk trays prior to shipping and then configure packing to suit orders, the conductive material (whilst retained by the tray) could be detached via an intentional break point to allow sensors to be individually removed from the storage trays with the conductive material still attached to the sensor—allowing the sensor to be packaged individually without re-introducing a manual springing operation. 
         [0024]    An exemplary conductive material would preferably exhibit electrical characteristics of &lt;10 KOhms between the sensor contacts and have elastic properties sufficient to maintain contact resistance over shelf storage life. A conductive foam in accordance herewith can be shaped and incorporated into a carrier tray. The foam can be configured to provide a short between only the sensor contacts which require shorting to one another. Other contacts are isolated. 
         [0025]    In designing the properties of the shorting foam, or, link, it is useful to recognize how such sensors are shorted within unpowered instruments. This is useful to avoid the same type of start-up problems as can occur on first integration of a new sensor into the instrument. A recommended shorting resistor has a value on the order of 10K ohms. 
         [0026]    In yet another embodiment, a bulk packaging tray can be designed to retain the foam so that when a sensor is removed from a tray it is asynchronously unshorted. The foam can be designed to be used to pack sensors in bulk trays. Alternately, the foam can be interrupted to provide a shorting method for individual sensors. 
         [0027]    With respect to the figures, a packaging unit  10  includes a tray  12  which could be molded plastic or formed of a degradable, cardboard-like material. The tray  12  is substantially rigid and can be formed in a variety of shapes without limitation. The form factor of the tray  12  is not a limitation hereof. 
         [0028]    The tray  12  includes or defines a plurality  14  of cavities or pockets which receive and carry sensors, or other electronic components. The exact shape of the pockets  14  is not a limitation, except as described subsequently. 
         [0029]    As illustrated the pockets  14   a ,  14   b  can be formed or molded to any convenient shape for the component to be received in the packaging  10 . Where large numbers of components are to be packaged the members of the plurality  14  can be substantially identical. 
         [0030]    A plurality of conductive foam inserts  18  is carried by the tray  12 . Members of the plurality  18 , such as insert  18   a , as described above are loaded with carbon to form a shorting resistive element which interacts with selected electrodes, or pins, of sensors  20 ,  20   a  or other components to be carried by packaging  10 . 
         [0031]    In  FIG. 2 , the sensors  20 ,  20   a  are illustrated with their covers removed to illustrate how selected pins or electrodes can extend to and be in contact with the adjacent portion of insert, such as  18   a , to implement the shorting function between those pins. As shown in  FIG. 4 , the respective cavity  14   b  can include an open region, illustrated by recessed surface  14   c  into which a non-shorted pin is to extend, adjacent to but displaced from the respective portion of insert  18   a.    
         [0032]    As best seen in  FIG. 4 , with respect to representative cavity  14   b , tray  12  can be formed with a trough  12   a  which extends through a plurality of the cavities  14   b . The members of the plurality  18 , such as  18   a  are slidably received in the trough  12   a  with a press fit. It will be understood that other attachment mechanisms, such as adhesive, or overhanging moldings can be used to retain the inserts in respective ones of the troughs such as  12   a.    
         [0033]    To provide flexibility, break away regions  22  can be provided for the inserts  18  and/or the tray  12 . If desired, individual cavities, such as  14   b  can also be formed with bread away regions. 
         [0034]    In summary, the shorting foam and tray are designed to selectively short only selected pins or electrodes. Other pins are left isolated, see  FIG. 2 . 
         [0035]    The conductive foam is heavily carbon loaded to provide a resistance between pins of less than 10K ohms. When the sensor is inserted the pins slidably engage the adjacent conductive foam insert, see  FIG. 4 . 
         [0036]    As the foam is cut into strips and held in position in the tray, only the selected pins are shorted. This selective shorting of only 2 pins on a 3 pin sensor, for example, or two pins of a two pin component is achieved using low cost foam, integrated in to the package. This results in cost and labor savings for the manufacturer of cells and instruments. Neither the total number of pins nor the shorted number, per component, are limitations hereof. 
         [0037]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope hereof. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims. 
         [0038]    Further, logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be add to, or removed from the described embodiments.