Abstract:
According to one embodiment of the invention, a testing apparatus for executing highly accelerated life testing on at least one test subject includes at least one structure operable to thermally stress the test subject via conduction and at least one pneumatic hammer operable to input imparting vibrations to the test subject. According to another embodiment of the invention, a method for executing highly accelerated life testing of at least one test subject includes applying a thermal stress to the test subject via conduction at a rate of change of at least 8° C. per minute and imparting vibrations to the test subject at a rate of at least 3 Gs rms.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of application Ser. No. 11/278,765 filed Apr. 5, 2006, entitled Conduction-Cooled Accelerated Test Fixture. 
     
    
     GOVERNMENT FUNDING 
       [0002]    This invention was made with Government support under contract N00019-02-C-3002 awarded by the Department of the Navy. The Government has certain rights in this invention. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0003]    This invention relates generally to the field of highly-accelerated life testing (HALT) fixtures and, more particularly, to a conduction-cooled accelerated test fixture. 
       BACKGROUND OF THE INVENTION 
       [0004]    It is important for a manufacturer to test its products before releasing them to the public to ensure that the products function reliably when released. Faulty or dysfunctional products can often cause consumer confidence in the manufacturer to decrease, and in addition, can have costly repercussions for the manufacturer consisting of, among other things, product recalls, product liability suits, and the like. However, thorough testing of consumer products can be realized through the use of HALT fixtures. 
         [0005]    HALT fixtures are designed to test products to uncover design defects and weaknesses in electronic and electro-mechanical assemblies by applying extreme vibrational and thermal stresses to the product. The thermal stresses can consist of rapid and extreme temperature changes. Through the application of such stresses to a product during HALT testing, the HALT fixture can emulate in a brief time frame (i.e., a few days or hours) the entire lifetime of stresses that a product will typically undergo during conventional use. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one embodiment of the invention, a testing apparatus for executing highly accelerated life testing on at least one test subject includes at least one structure operable to thermally stress the test subject via conduction and at least one pneumatic hammer operable to input imparting vibrations to the test subject. According to another embodiment of the invention, a method for executing highly accelerated life testing of at least one test subject includes applying a thermal stress to the test subject via conduction at a rate of change of at least 8° C. per minute and imparting vibrations to the test subject at a rate of at least 3 Gs rms. 
         [0007]    Certain embodiments of the invention may provide numerous technical advantages. For example, a technical advantage of one embodiment may include the reduction of overlooked design flaws or weaknesses, which reduction results from more accurate emulation of the test subject&#39;s thermal environment during HALT testing. An additional technical advantage of this embodiment and/or of an alternate embodiment may include chamber-free HALT testing. 
         [0008]    Although specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a more complete understanding of example embodiments of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a schematic diagram of an example embodiment of a testing apparatus housed inside of a chamber; 
           [0011]      FIG. 2  is an illustration of the testing apparatus of  FIG. 1 ; 
           [0012]      FIG. 3A  is an illustration of the inner face of a rail of the testing apparatus of  FIG. 1 ; 
           [0013]      FIG. 3B  is an illustration of an alternate view of the inner face of the rail of  FIG. 3A ; 
           [0014]      FIG. 3C  is a schematic diagram of a vertical cross-section of the short side of the rail of  FIG. 3A ; and 
           [0015]      FIG. 3D  is a schematic diagram of a vertical cross-section of the long side of the rail of  FIG. 3A . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    It should be understood at the outset that although example embodiments of the present invention are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or in existence. The present invention should in no way be limited to the example embodiments, drawings, and techniques illustrated below, including the embodiments and implementation illustrated and described herein. Additionally, the drawings are not necessarily drawn to scale. 
         [0017]      FIG. 1  is a schematic diagram of an example embodiment of a testing apparatus  100  housed inside of a chamber  184 . The testing apparatus  100  is operable to stress a test subject  120  by applying either or both of a thermal stress and vibrational stress to the test subject  120 . The test subject  120  can include one or more electrical circuit cards or other electrical components. In one example implementation, the test subject  120  is a circuit card that contains a protective cover; however, test configuration apparatus  100  may be used with a variety of types of test subjects. 
         [0018]    The testing apparatus  100  includes, in this embodiment, a pair of structures  110  for thermally stressing the test subject  120  via conduction heating and/or conduction cooling. In this embodiment, structures  110  are referred to as rails  110  and are illustrated in greater detail in  FIGS. 2 through 3D . Conduction heating and/or conduction cooling of the test subject  120  occurs by first heating and/or cooling the rails  110 , which then conduction heat and/or conduction cool the test subject  120 . In one embodiment, the rails  110  abut the edges of test subject  120 , which allows the heating and/or cooling by conduction to take place. 
         [0019]    Conduction cooling may take place, in one embodiment, by first introducing liquid nitrogen (LN 2 ) into a pipe  130 ; however, other cooling fluids may be utilized. 
         [0020]    Previous HALT systems cooled and/or heated a test subject by convection, blowing cold and/or hot air over the test subject. Convection cooling, however, is not effective when testing a high-powered rail-cooled test subject because convection cooling does not accurately simulate the environment that the test subject is exposed to in the field. In particular, certain temperature gradients that the test subject is exposed to in the field cannot be recreated in a test setting by blowing cold and/or hot air over the test subject. In contrast, thermal stress testing of the test subject by conduction cooling and/or conduction heating more accurately simulates the environment that the test subject is exposed to in the field. Additionally, cooling and/or heating by conduction, as opposed to convection, in one embodiment, maintains a dry nitrogen atmosphere around the test subject, thereby eliminating potential electrical shorts due to moisture condensation. 
         [0021]    Referring back to  FIG. 1 , the LN 2  flows through the pipe  130  and enters the rails  110  through openings at the bottom of the rails  110 . After entering the rails  110 , the LN 2  flows throughout channels inside of the rails  110 , as is illustrated in, and described in greater detail in conjunction with,  FIGS. 3C and 3D . As the LN 2  flows through the internal channels of the rails  110 , the LN 2  evaporates, thereby causing the rails  110  to lose heat. Because the edges of test subject  120  abut the rails  110 , the heat loss experienced by the test subject  120  is transferred to the rails  110 , thereby conduction cooling the test subject  120 . After the LN 2  evaporates, the nitrogen gas exits the rails and vents across the test subject  120 . This process will be further described in connection with  FIG. 3A . It is noted that, in one embodiment, neither the LN 2  nor the nitrogen gas comes into contact with the electrical components of the card. 
         [0022]    Conduction cooling the test subject  120  provides a benefit of more accurately emulating the thermal environment of the test subject  120 . 
         [0023]    Conduction heating of the test subject  120  can take place by introducing one or more heated rods  172  into respective openings  112  in the rails  110 , as illustrated in  FIG. 2 . The rods  172  may include cartridge heaters, or other types of heaters. Referring back to  FIG. 1 , power is provided to the heated rods through a line  140 . When powered, the heated rods heat by conduction the rails  110 . Because the edges of the test subject  120  abut the rails  110 , heat is transferred to the test subject  120  through conduction. 
         [0024]    Additionally, the testing apparatus  100  vibrationally stresses the test subject  120 . Vibrational stress is generated, in one embodiment, by one or more pneumatic hammers  150  that are attached at one end  152  to the bottom of a base plate  180  upon which the rails  110  are fitted. The other end of each pneumatic hammer  150  is left unattached so that it can impart vibrations to the testing apparatus  100  when air is supplied to the pneumatic hammers  150 . The air that drives the pneumatic hammers  150  may be supplied to the testing apparatus  100  via pipe  170 . The testing apparatus  100  is fitted with shock mounts  160  between the base plate  180  and the base  182  of the testing apparatus  100  for dampening the vibrations generated by the pneumatic hammers  150 , in one embodiment. 
         [0025]    In one embodiment of the invention, the testing apparatus  100  is housed inside of a chamber  184 . Chamber  184  includes walls  186  that act as sound proofing, dampening the sound generated by the testing apparatus  100 . Although one embodiment of the testing apparatus  100  utilizes a chamber  184  as a housing, the testing apparatus  100  can be operated without such a chamber  184 , as can be seen in  FIG. 2 . 
         [0026]    A computer  190  controls the test settings of the testing apparatus  100 . Computer  190  controls the test settings of the testing apparatus  100  by transmitting signals through a line  191  to an environment controller  192 . Environment controller  192 , in turn, controls the heating, shaking, as well as cooling of the test subject  120  via control lines  194 ,  196 , and  198  respectively. Computer  190  may also receive test results from the testing apparatus  100  while thermal and vibrational stresses are applied to the test subject  120 . Additional details of test configuration apparatus  100  are described in conjunction with  FIGS. 2 through 3D . 
         [0027]      FIG. 2  is an illustration of selected portions of test configuration apparatus  100 . The frame of the configuration apparatus  100  includes structural support  183  and the base plate  180 . In this embodiment, the test subject  120  includes a plurality of circuit cards. The circuit cards are held in place by card guides  122 , which can be seen more clearly in  FIG. 3A . The card guides  122  are also the location where the rails  110  abut the test subject  120  and thus are the location where conduction heating and/or conduction cooling of the test subject  120  takes place. 
         [0028]    With respect to conduction cooling, the LN 2  is piped into the rails  110  through openings on the bottom of the rails  110 . This will be illustrated more clearly in  FIG. 3D . Once the LN 2  enters the rails  110 , it flows through various circular channels emptying into central channels, which extend the entire height of the rails  110 , in this embodiment. This will be illustrated more clearly in  FIG. 3C . Openings  102  of the central channels are illustrated in  FIG. 2  as the center openings in the top surface of the rails  110 , which openings  102  are flanked on two sides by three openings  112  for receiving the heated rods. From the central channels, the LN 2  flows into the cooling tubes, the openings  114  of which can be seen in  FIG. 2 . The cooling tubes extend the full length of the rails  110  and will be illustrated more clearly in  FIG. 3A . The cooling tubes are the location where the LN 2  evaporates, thus conduction cooling the rails  110  and the card guides  122  which conduction cool the test subject  120 . Variable-sized plugs can be inserted into the openings  114  of the cooling tubes, providing a means for adjusting the amount of cooling of the test subject  120 . In one embodiment, because each opening  114  is associated with a specific card guide  122 , the temperature of each circuit card can be controlled independently from the others. 
         [0029]      FIG. 3A  is an illustration of the inner face of the rail  110  of the test configuration apparatus. The rail  110  consists of the card guides  122  into which the test subject is inserted. As mentioned in  FIG. 2 , the card guides  122  are conduction cooled by evaporation of the LN 2  in the cooling tubes  113  within columns  115 . Variable-sized plugs can be inserted into the openings  114  of the cooling tubes  113  in order to control the amount of cooling of the test subject. Notches  124  in the rail  110  are openings from which the nitrogen gas vents after cooling the rail  110  and the card guides  122 . With respect to conduction heating, the heated rods mentioned in connection with  FIG. 1  can be inserted into the openings  112  to the heating tubes in the rail  110 . 
         [0030]      FIG. 3B  is an illustration of an alternate view of the inner face of the rail  110  of the test configuration apparatus. 
         [0031]    The conduction cooling of the rails will be described in more detail in  FIGS. 3C and 3D .  FIG. 3C  is a schematic diagram of a vertical cross-section of the short side of the rail  110 . 
         [0032]      FIG. 3D  is a schematic diagram of a vertical cross-section of the long side of the rail  110 . When thermally stressing the test subject by conduction cooling, LN 2  enters the rail  110  through slot  108 . The LN 2  is then circulated through the rail  110  via the circular channels  104  until it reaches the opening  106  to the central channel  103 . The LN 2  flows into the central channel  103 , which then distributes the LN 2  to each of the vertical cooling tubes  113 . As the LN 2  flows through the various channels, it evaporates, conduction cooling the rail  110  and card guides  122 , which conduction cools the test subject. 
         [0033]    The teachings of the invention described hereinabove are applicable to testing purposes other than HALT, such as Highly Accelerated Stress Screening (HASS). 
         [0034]    Numerous other changes, substitutions, variations, alterations and modifications may be ascertained by those skilled in the art and it is intended that the present invention encompass all such changes, substitutions, variations, alterations and modifications as falling within the spirit and scope of the appended claims.