Abstract:
The method and apparatus of the present invention provide for isolation of one or more modules during stress testing of an overall system. The isolated modules remain in direct contact with elements exposed to the test by placing the modules in an isolation box and electrically connecting these modules to the remaining modules in the isolation box. The isolation box protects the weaker modules from vibration stresses as well as temperature and pressure stresses.

Description:
CONTINUATION DATA CLAIMED BY APPLICANTS 
     This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/113,927 entitled “Method and Apparatus for Vibration and Temperature Isolation” and filed Dec. 24, 1998. 
    
    
     FIELD OF INVENTION 
     The present invention is directed to a method and apparatus for providing improved isolation for testing a subpart of a system. More specifically, the present invention is directed to a method and apparatus by which a modular component of a system can be at least partly isolated from stresses that are applied to the rest of the system as a part of a test. 
     BACKGROUND OF THE INVENTION 
     An important part of any attempt to deploy a newly designed system is the process of ascertaining whether the finally designed product will in fact operate at the required efficiencies and for a desired duration of time in the various physical environments in which it will be placed. 
     One technique by which devices are tested is to subject them to extreme temperature and vibration testing in a test chamber. The intent of the tests is to approximate what the expected life span of the device will be in its intended environment as well as to approximate the extreme environmental limits. Two commonly applied tests are the Highly Accelerated Life Test (HALT) and the Highly Accelerated Stress Screen (HASS). The HALT over stresses the device far beyond the intended end use environment looking for weaknesses and is commonly used during the design phase of a device. The HASS is similar to the HALT but is often used during the manufacturing phase as a screening test prior to installing the devices in the field. 
     One example of a system that would require such analysis is communications equipment, including wireless communications equipment, to be installed in the field. This type of equipment may include one or more circuit boards whose operation may be adversely affected by temperature and other environmental variables. In communications equipment, it is not uncommon for the system in question to include a plurality of modules or boards, some of which are more susceptible to damage in these tests than others. For example, one such “weaker” module might be a power supply board of a multi-circuit board system. The power supply might be a AC/DC converter that is known to be subject to failure if operated at a temperature outside he range of −10° to +80° C. or at a vibration of greater than 10 Grms (Gravity root mean square). However, the test conditions for the system using the power supply may be in the range of −70° to +90° C. and up to 29 Grms. For example, this can be desirable when testing more robust system components other than the module. Therefore, if the power supply is placed in the chamber with the rest of the system during such a test, it will likely fail and have a negative impact on the test of the rest of the system. 
     One solution to this problem is to place the weaker module outside the chamber in which the HALT or HASS tests are being applied. This has a drawback, however, as the electrical distance of separation between the module (outside the chamber) and the rest of the system (inside the chamber) may itself prevent the overall system from operating correctly. For example, in some systems, the electrical distance between components is important to timing (e.g., synchronization) between components. Also, this arrangement generally leads to unwieldy and complicated electrical interfaces between the module and the rest of the system, e.g., a separate wire must be run from each active pin on the module through the walls of the test chamber to the appropriate place in the rest of the system. It is therefore desirable to have a test chamber with the remainder of the system that is being subjected to testing. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for substantially isolating a module from the rest of the system of which the module is a part. In particular, the present invention provides an isolation container (“box”) it which a weaker module is disposed. One embodiment of the present invention comprises a box including damping elements so as to reduce the effect of vibration on the isolated module. In another embodiment, the box is equipped to receive compressed air that flows over the weaker module so as to maintain the module at an appropriate temperature. The box is designed to allow the module (e.g., a daughter board that plugs into a mother board) to be electrically connected to the rest of the system (e.g., the mother board with other modules) that is being subjected to the stress test. As used herein, the term “connect” is meant to encompass both direct and indirect connection. Thus A can be connected to B directly. Also A is “connected” to B if A is directly connected to C, and C is directly connected to B. A is “directly” connected to B if it sends signals through any medium from A to B. Thus, A can be directly connected to B via a wire, a soldered connection, an infrared link, an electromagnetic (e.g RF) link, etc. 
     One skilled in the art will understand that besides circuit boards for use in wireless communications, the invention can be used in other environments and should be understood to cover these other embodiments beyond those specifically described herein. For instance, certain system components include modules of varying strengths such that when the system is exposed to particular stress testing, one or more of the modules is at risk of failure or damage due to the stress testing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of an embodiment of the present invention. 
     FIG. 2 illustrates a top view of an embodiment of the present invention. 
     FIG. 3 illustrates an exploded view of an embodiment of the present invention. 
     FIG. 4 illustrates an exploded view of an embodiment of the present invention with a cavity. 
    
    
     DETAILED DESCRIPTION 
     The illustrative embodiments disclosed below speak in terms of a box, but it should be understood that a box can be any shape container which is able to enclose a weaker module. 
     One embodiment of the present invention has been designed for use with the testing of circuit boards for deployment in the field in establishing wireless communication systems. 
     FIG. 1 shows a side view of an embodiment of the present invention. In FIG. 1, a circuit board  100 , also referred to as a mother board, has a plurality of electronic components  120  mounted thereon. The fact that the same reference numeral is applied to each of the components should not be considered an indication that all of those components are identical. This is simply used as a short-hand reference for the electrical components  120  themselves and can be meant to include any combination of memory chips, processors, capacitors, resistors, inductors or other electrical components which may be mounted on circuit board  100 . The isolation box  110  also can be mounted on the board  100  prior to its insertion into an environmental chamber  23 , such as a stress chamber. 
     The isolation box  110  comprises a first or top component  110 A and a second or bottom component  110 B, which are connected together in a manner which will also be described below. The isolation box encloses therein one or more modules, also referred to as daughter board(s), which are considered weaker and suspect with regard to the stress testing. Those modules can still be electrically connected to one or more elements on circuit board  100  via electrical connection port provided on the underside of isolation box  110 . Those electrical connection ports are not illustrated in FIG.  1 . 
     The box can have air ports  175   a  and  175   b  (only one of which is shown in FIG.  1 ). This permits a flow of compressed air across the surface of a board that is mounted inside the box  110  so as to maintain that board under the appropriate air temperature while the rest of the system is subjected to testing within the stress chamber. In order to control the air temperature, inlet air port  175   a  could be connected to a compressor with a low air volume at or below room temperature. 
     FIG. 2 illustrates a top view of an embodiment of the present invention on a circuit board. Again, circuit board  100  is shown with a plurality of electronic elements  120 . Furthermore, the isolation box  110  is shown with air ports  175   a  and  175   b  both visible. As can be seen, the ports are positioned to expose most of the inside of isolation box  110  to the flow of air, reducing the likelihood that the weaker module would be subjected to a substantial temperature gradient within the box. This entire assembly can be inserted within the environmental chamber, and the isolation box, based on its construction as described below, provides vibration damping for the weaker module as well as atmospheric/temperature protection so that this weaker nodule will continue to operate in an appropriate fashion even when disposed within the stress chamber. 
     FIG. 3 illustrates an exploded view of the system in accordance with an embodiment of the present invention. The isolation box is shown in two separate portions, top portion  303  and bottom portion  310 . These portions can be made of a material that will withstand the stress to be applied by the test, i.e., the testing temperature range and vibration maximum. Examples of such materials include DERLIN and ULTEM, both available from DuPont, or mumetal, which would also shield the weaker module from Electromagnetic Interference (“EMI”).The weaker module is shown as component  301 . This is a smaller circuit board which can have a plurality of electrical components mounted thereon, for example, components  371 ,  372  and  373 . Just as with electrical components  120  described above, these components mounted on the weaker module can include a myriad of electrical components and the reference numerology should not be taken as an attempt to divide the components into only three different types. Also shown on the weaker module  301  is a connector component  350  which allows for a pin or multi-pin connection between the electrical components on board  301  and one or more electrical components on board  100  in FIGS. 1 and 2. The connection can be by direct or indirect coupling and also could be achieved by infrared (“IR”) coupling, magnetic coupling, a header-multi-pin connector with ribbon cable, a wire or multi-conductor cable interconnection, a terminal strip with screws or similar coupling mechanisms. The module  301  has four apertures  325 ,  326 ,  327  and  328  which are used for mounting the board within the isolation box. The number of apertures is variable so long as the number of apertures provided for mounting enables a secure mounting of the module within the isolation box. 
     In this example, the module is mounted on fasteners  315 ,  316 ,  317  and  318 . These fasteners can include screws, posts, snap-in circuit board spacers, an any other type of fasteners which would act to stabilize the module  301  within the isolation chamber and prevent it shifting from side to side or twisting. A plurality af spacers,  305 ,  306 ,  307  and  308  are also mounted on these posts and positioned between the bottom portion  310  and the board  301 . These spacers act as a vibration damping mechanism and can include, for instance, rubber grommets, fiber washers, shoulder washers, or other rubber or elastomer material. The chosen spacers should provide appropriate levels of vibration damping. The bottom portion of the isolation box also includes one or more apertures, here shown collectively as  351 , for permitting access to the connector  350  from outside of the isolation box. Thus, as a plurality of pins may be disposed on the top surface of board  100  for connection with the module  301 , those pins can pass through the apertures  351  and come into contact with the connector  350  even while the module is in isolation in the isolation box. 
     A plurality of additional spacers,  335 ,  336 ,  337  and  338  are then mounted on the posts above the module  301  and between the module and the top portion of the box  303 . These spacers can be made of the same material as the spacers disposed below a module and also play a role in vibration damping. The posts  315 ,  316 ,  317  and  318  are secured into openings on the bottom side of the top portion of  303 , that is, the surface of top portion  303  that faces the module  301 . In addition, as seen in FIG. 4, one portion of the isolation box may include a cavity portion  360  so as to accommodate this electrical components of module  301 . This cavity also provides an open space for the compressed air flow entering through air port  175   a  and exiting via air port  175   b.  The compressed air which flows through the two ports and through the cavity disposed above module  301  permits a stable temperature of the components mounted on that module and the maintenance of an appropriate pressure on those elements even while the entire structure is submitted to environmental testing in the stress chamber. 
     Different size boxes can be used to accommodate different sized modules. Alternatively, an internal cavity could be adapted to hold different sized modules. Also, the box could be designed to accommodate multiple modules, such as in stacked configuration separated by spacers or other separators or in a side by side configuration. 
     The isolation box can be used in stress tests which vary such environmental parameters as temperature, temperature shock, vibration, EMI interference (used as a shield) and humidity. Example ranges for these parameters include: approximately −100° C. to 200° C. for temperature, approximately 60° C. or greater for temperature shock, approximately up to 50 Grms for vibration, and approximately 85° C. at 85% relative humidity for 165 hours for humidity. To isolate the weaker module in a himidity test, hermetic seals would have to be added to the isolation box. 
     The present invention thereby provides a method and apparatus by which one or more modules can be isolated from the negative effects of a stress test while still being electrically connected to other elements that are being subjected to the test as the overall configuration is placed in a testing chamber. This avoids the problem with prior art solutions which attempt to isolate weaker modules by keeping those modules out of the testing chamber all together. 
     While the present invention is described with respect to specific embodiments, these embodiments are not intended to limit the scope of the invention, which is defined by the appended claims.