Abstract:
An apparatus and a method for testing semiconductor devices such as integrated circuits having a handler for picking up an integrated circuit to be tested and placing the picked up integrated circuit into an automatic circuit test apparatus. When the circuit to be tested is inserted into the test apparatus an extraneous signal shield is automatically engaged to enclose the device being tested and protect the circuit, being tested, from stray extraneous electromagnetic signals during the test thereby preventing said stray electromagnetic interference from inducing errors in the tested circuit.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to an apparatus and a method for testing semiconductor devices such as integrated circuits. More particularly, the present invention is directed to a handler for placing an integrated circuit to be tested into an automatic circuit test apparatus while simultaneously protecting the circuit, being tested, from stray extraneous electromagnetic signals during the test thus preventing cross talk and other electromagnetic interference from inducing errors in the tested circuit.  
           [0003]    2. Background of the Invention  
           [0004]    The present invention generally relates to an automatic integrated circuit test apparatus provided with a means for protecting a circuit or device during test from being affected by extraneous electromagnetic signals such as alternating current (AC) interferences. This is achieved, in the present invention, by sealing all the avenues by which such signals can reach the circuit under test. This is especially achieved, in the present invention, by providing the tester with a unique handler that will, during the test, automatically encase the semiconductor circuit or device under test with a shield that attenuates or prevents extraneous electromagnetic signals that may cause test errors, from reaching the device being tested.  
           [0005]    As is well known to the art, integrated circuits have a number of signal interface points or pins, herein after referred to as input/output pins, that are used to transfer data, in the form of electrical signals, into or out of the integrated circuits. During operation a select number of these pins are used to introduce the necessary control functions such as the circuit clocks, test modes, test control data, and etc. to the integrated circuit while the remaining signal interface pins are used to transfer data into and out of the data storage circuits contained in the integrated circuit.  
           [0006]    At the present time, such AC defect testing requires the use of high frequency automated test equipment (ATE) that provides a tester contact for each signal interface pin on the integrated circuit, i.e., for both functional circuit pins and data storage pins. Often, under test conditions, the device being tested will function correctly in a direct current (DC) mode, that is, it will carry the proper current but, under AC test conditions, will exhibit false alternating current (AC) characteristics, e.g., the rise and fall times of signals will be altered such that the circuit appears to no longer meet its output specification. These false readings come about because extraneous electromagnetic signals from outside sources, such as adjacent testers, fluorescence lights, cell phones, nearby cell phone towers, radio security systems, and other modern electronic devices, can produce capacitively or inductively induce extraneous signals in the input/output pins of the device under test and thus create erroneous device outputs. These false readings result in either the scrapping of good devices or additional, more rigorous and/or extensive testing of the integrated circuit. In either case such false readings greatly increases the cost of such devices.  
           [0007]    Furthermore as semiconductor chips or modules continue to increase in pin count and become faster they also become more sensitive to such extraneous electromagnetic signals. With every such an increase in sensitivity to stray electromagnetic signals testing of such devices has found to result in even more false test readings.  
           [0008]    Even though the present high frequency, high pin count testers used in the industry are well designed, increasing sensitivity of the semiconductor devices or circuits to extraneous electromagnetic signals makes it increasingly difficult to provide automated test equipment that can speedily test the newer more complex integrated circuits without encountering the problems created by such extraneous electromagnetic signals.  
           [0009]    With newer, higher storage capacity, and more sensitive integrated circuits the need of protecting them from such stray electromagnetic signals is even greater. None of the presently available automatic loading testers provide such protection.  
           [0010]    Therefore, there are compelling economic reasons to provide a tester in which the integrated circuit being tested is protected from such extraneous electromagnetic signals during testing.  
         SUMMARY OF INVENTION  
         [0011]    The present invention is thus directed to an apparatus and a method of testing semiconductor devices or modules in which extraneous electromagnetic radiation is either attenuated or prevented from reaching and affecting the device under test.  
           [0012]    The present invention is further directed to an automated semiconductor test apparatus that cannot only automatically load and test an integrated circuit but one that will also automatically shield the device under test from being exposed to extraneous electromagnetic sources that can cause erroneous output signals in the tested device.  
           [0013]    The present invention accomplishes this desirable result by providing, on the device handler, a shield that will automatically enclose and protect the device under test from stray electromagnetic signals when the device under test is inserted into the test socket.  
           [0014]    In this way, the present invention achieves accurate testing of such integrated circuits while using commercially available testers.  
           [0015]    Further the present invention reduces erroneous AC signals in tested circuits.  
           [0016]    These objects, features and advantages of the present invention will be become further apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings wherein: 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0017]    [0017]FIG. 1 is a schematic view of a prior art automatic tester;  
         [0018]    [0018]FIG. 2 is a detailed cross-sectional view of the pick up head of FIG. 1 holding a device in the test socket for testing taken along the line  2 - 2  of FIG. 8;  
         [0019]    [0019]FIG. 3 is a cross-sectional view of the pick up head of the tester of FIG. 2, provided with the present invention installed thereto, as it holds a device in the test socket for testing;  
         [0020]    [0020]FIG. 4 is an exploded, partially sectioned view of the automatic enclosing shield of the present invention;  
         [0021]    [0021]FIG. 5 is a top view of the bottom section of the automatic enclosing shield of the present invention;  
         [0022]    [0022]FIG. 6 is a bottom view of the bottom section of the automatic enclosing shield of the present invention;  
         [0023]    [0023]FIG. 7 is a top view of the floating block of the pickup head shown in FIG. 3;  
         [0024]    [0024]FIG. 8 is a side view of the floating block of the pickup head shown in FIG. 3;  
         [0025]    [0025]FIG. 9 is a top view of an improved floating block of the present invention;  
         [0026]    [0026]FIG. 10 is a top view of the mounting adapter plate of the present invention; and  
         [0027]    [0027]FIG. 11 is a bottom view of the mounting adapter plate of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0028]    Referring now to FIGS. 1 through 6 the present invention will be described in detail. FIG. 1 is a schematic view of a prior art automatic tester; FIG. 2 is a detailed cross-sectional view of the pick up head of FIG. 1 holding a device in the test socket for testing taken along the line  2 - 2  of FIG. 7; FIG. 3 is a cross-sectional view of the pick up head of the tester of FIG. 2, provided with the present invention installed thereon, as it holds a device in the test socket for testing; FIG. 4 is an exploded, partially sectioned view of the automatic enclosing shield of the present invention; FIG. 5 is a top view of the bottom section of the automatic enclosing shield of the present invention; FIG. 6 is a bottom view of the bottom section of the automatic enclosing shield of the present invention; FIG. 7 is a top view of the floating block of the pickup head shown in FIG. 3; FIG. 8 is a side view of the floating block of the pickup head of FIG. 7 taken along the line  8 - 8 ; FIG. 9 is a top view of an improved floating block of the present invention; FIG. 10 is a top view of the mounting adapter plate of the present invention; and FIG. 11 is a bottom view of the mounting adapter plate of the present invention.  
         [0029]    With reference now to the drawings and especially to FIG. 1, a typical automatic tester  20  of the prior art will be generally described. The tester  20  is basically a cabinet containing electrical circuitry (not shown) for applying selected electrical test signals to a semiconductor device in a test socket  29  mounted on the top surface  25  of the tester. The tester is also provided with an X-Y-Z drive mechanism  21  carrying a cantilevered elongated arm  22  which, in turn, carries on its cantilevered end  23  a circuit pick up head  24 . The drive mechanism  21  is designed to drive the arm  22  and pickup head  24  across the upper surface  25  of the tester  20  to a tray  26  containing a plurality of devices  27  to be tested. Once the pickup head  24  is properly positioned over the tray  26 , the head  24  is lowered until it contacts the surface of a selected device  27   a  in tray  26  at which time a vacuum system  28  is activated to hold the selected device  27   a  against the pick up head  24 . With the selected device  27   a  securely held against the head  24 , the mechanism  21  lifts the arm  22  and moves the selected device  27   a  over a test socket  29  provided on the upper surface  25  of the tester  20 . The head  24  lowers the selected device  27   a  into the test socket  29  and holds the selected device  27   a  in the socket  29  and the test is initiated. When the test is complete, the device  27   a  is lifted from the test socket  29  and the head  24  then carries the tested device  27   a  to either output tray  30   a  or  30   b  depending on the result of the test. Output tray  30   a  could, for example, be designated for those devices that tested good and tray  30   b  for those devices that failed the test.  
         [0030]    As shown in greater detail in FIGS. 2, 8, and  9 , the test head  24  is comprised of a base  14  to which is affixed a floating block  15  carried by an alignment base  18 . The alignment base  18  is provided with a pair of alignment pins  19  that pass through respective alignment holes  16  in the floating block  15 . As shown more fully in FIGS. 7, 8, and  9 , the floating block  15  is also provided with alignment pins  17  which align and position the head  24  with respect to the socket adapter plate  39  which is nested in a docking plate  35 . The test socket  29  contains a recess  31  designed to couple the device under test to the internal circuitry of the tester  20  via a printed circuit card  32 . Both the test socket  29  and the underlying printed circuit card  32  are correctly positioned on the upper surface of the tester  20  by vertical locating pins  33  and  34  positioned in and jutting out of the upper surface  25  of tester  20 . It should be understood that each different type of circuit to be tested requires a unique test socket  29  and printed circuit card  32 .  
         [0031]    Over the top of the test socket  29  there is positioned the docking plate  35  which is held over and aligned to the socket  29  via pins  37  and  38 . The socket adapter plate  39  is designed to nest in recess  36  in the docking plate  35 . The socket adapter plate  39  is designed to accept and align the pickup head  24  such that the circuit  27   a  carried by the head  24  will be precisely aligned with and properly placed in the recess  31  in the test socket.  
         [0032]    Since such testers are currently available in the marketplace and their use and construction is well known, further description of the construction or operation of such testers is not deemed necessary.  
         [0033]    In these prior art testers, interfering signals, from various outside signals such as adjacent testers, fluorescence lights, cell phones, nearby cell phone towers, radio security systems, and other modern electronic devices were found to capacitively or inductively induce extraneous signals in the device under test. To eliminate these problems various solutions to control or prevent such signals from reaching the device being tested were attempted. For example, the use of a single Faraday cage built around the tester room was not satisfactory because it was found that adjacent testers in the room will often cause significant interference especially when testing similar product lines. Enclosing each individual tester in its own separate Faraday cage was then considered but the cost was found to be prohibitive. Additionally the use of such individual cages was found to be a significant hindrance to productivity because of the difficulties encountered during loading and unloading of the circuits as well as during tester setup, maintenance or repair.  
         [0034]    It was thus necessary to find a simple, inexpensive way of screening the device while it was being tested from such extraneous interfering signals while avoiding the difficulties noted above. The present inventors undertook an extensive study of the problem and found that the primary avenues by which interfering signals reached the device under test were, as shown in FIG. 2, via a gap  41  around and between the pickup head  24  and the socket adapter  39  and docking plate  35  and via the space  42  between the lower surface  35   a  of the docking plate  35  and the upper surface  25  of the test socket  29  as shown in FIG. 2. The inventors first quantified the signal levels in the environment that caused interference and then after further study and experimentation determined that if the levels of the interfering signals were attenuated by between 40 dB(decibels) and 80 dB they would not interfere with the test. This level of attenuation was found sufficient to effectively eliminate interference not only from adjacent testers but also from other sources such as those above described.  
         [0035]    The present invention, as shown in FIGS. 3, 4,  5 ,  6 ,  7 ,  8 ,  9  and  10  was then devised and was found to achieve this level of signal attenuation. More specifically, the present invention comprises a first attenuating or signal blocking shield in the form of a mounting adapter plate  45  fixedly positioned between the upper surface  25  of the tester  20  and the bottom of the docking plate  34  around the test socket  29  and a second signal blocking or attenuating automatically enclosing ring shield or screen  50  affixed to the pickup head  24 . The first attenuating or signal blocking shield, i.e., the mounting adapter plate  45 , once installed, remains fixedly in position all during the operation of the tester. The ring shield  50 , however, is designed to automatically enclose or seal off the test socket  29 , from extraneous electromagnetic signals, only when the pickup head  24  is holding a device  27   a  in the recess  31  of test socket  29 . In this way the present invention blocks or attenuates any potentially interfering outside signals from affecting the device  27   a  being tested.  
         [0036]    The present invention is thus simple, inexpensive and automatically shields the device under test without interfering with the test or hindering access to the product under test or to maintenance or repair of the tester.  
         [0037]    Top and bottom views of the mounting adaptor plate  45  are shown respectively in FIGS. 10 and 11, In these FIGS. 10 and 11, the plate  45  has a central opening  97  there through that is large enough to surround the test socket  29  and is designed to enclose and seal off the region  42  existing between the lower surface of the docking plate  35  and the top surface  25  of tester  20  thus preventing undesirable signals from entering through the region  42 . This plate  45  can be comprised of any suitable conductive material such as steel, copper, brass, aluminum, and etc. The plate  45  is preferably provided with a first circumferential groove  98  in its top surface around the opening  97  and a second circumferential groove  99  in its lower surface around the opening  97 . Preferably the grooves  98  and  99  are offset from one another as shown in FIG. 3. These grooves are now filled with metallized coated elastomer rings  100  and  101  respectively. Such elastomers are currently commercially available and one such elastomer, suitable for use with the present invention, is sold as the 2400 General Metallized Fabric Coated Elastomer (part No. 2431-1011-0123) by the Tech-Etch Corporation located at 45 Aldrin Road, Plymouth Mass. These elastomer rings  100  and  101  are provided to assure that there is a tight conformal, attenuating seal between the docking plate  35  and the top surface  25  of the tester  20 . If the surfaces of the docking plate  35 , the tester  25 , and the plate  45  are perfectly flat the gaskets may be eliminated. However to achieve such a surface flatness can prove to be a long and expensive task. and thus such gaskets are recommended.  
         [0038]    The ring shield  50 , of the present invention, is affixed, via the floating head  15 , around the lower portion of the pickup head  24  such that when the device under test  27   a  is inserted into the test socket  29 , the gap  22  is matically sealed by the ring shield  50  and extraneous external signals either are completely prevented from passing through the gap  41  or attenuated to a level below which they cannot adversely affect the circuit  27   a  being tested.  
         [0039]    As shown in FIGS. 4, 5 and  6 , the ring shield  50  basically comprises two intermeshing rings  51  and  52  each of which have a respective central opening  53  and  54  shaped and sized to closely conform to the exterior shape of the pickup head  24 . In the present example the pickup head  24  is square and thus the central openings  53  and  54  in the rings are also square. It is to be understood that although here the pickup head  24  is shown, in the present example, as having a square exterior, its exterior could just as easily be round, elliptical, rectangular or polygonal. In such cases the central ring openings  53  and  54  would not be square as shown here but instead would be made to conform to the shape of the pickup head  24 .  
         [0040]    The present inventors further have found that the inner surface  55  of the upper ring section  51  should closely adhere to the exterior surface of the pickup head  24  and that any separation between the exterior surface of the pickup head  24  and the inner surface  55  of the upper ring section  51  should preferably be no more than 0.005 inches.  
         [0041]    The rings  51  and  52  are preferably formed of aluminum electroplated with either a coating of nickel having a thickness of between 0.0003 inches and 0.001 inches or a coating of nickel of the same thickness with a flash of gold thereon. It should also be understood that other metal or metal alloys of sufficient structural strength such as copper, brass, steel or etc. can be used in lieu of aluminum and other metallic plating materials can be used.  
         [0042]    The upper ring section  51  is also provided with a circumferential channel  56  on its lower face  57  and through horizontal holes  58  and  59  in opposing sides  51   a  and  51   b.  The through holes  58  and  59  are positioned so that they pass through the opposite sides  51   a  and  51   b  approximately halfway up the wall of the channel  34  and are adapted to accept pins  62  and  63  respectively. The other upper faces  51   c  and  51   d  of this upper ring section  51  are further respectively provided with through holes  60  and  61  that intersect the channel  44  and with tapped holes  64 ,  65 ,  66 , and  67 .  
         [0043]    The lower ring section  52  is provided with a raised circumferential wall  68  that is designed to fit into and intermesh with the channel  56  in the upper ring section  51 . Notches or slots  70  and  71  are provided on the top each opposite wall sections  68   c  and  68   d  such that the center of each respective notch is in line with the center of a respective one of the vertical through holes  60  and  61  in the upper ring section  51  when the wall  68 , carried on the lower ring section  52 , is inserted in the channel  56 . The top surface of the walls  68   a  and  68   b  of the lower ring section  52  are further each respectively provided with respective vertical recesses or blind holes  71 ,  72 ,  73  and  74  that can, but need not, be aligned with the tapped vertical holes  64 ,  65 ,  66 , and  67  when the lower and upper rings  51  and  52  are intermeshed. The lower surface of the lower ring section  52 , as shown in FIG. 6 is provided with a circumferential groove  95  and a metallized fabric coated elastomer ring  96  is positioned therein.  
         [0044]    Vertical slots  80  and  81  that pass horizontally through the respective walls  68   a  and  68   b  are provided such that they are aligned with the through horizontal holes  58  and  59  in the upper ring section  51  when the ring sections  51  and  52  are intermeshed or mated, i.e., when the wall  68  is positioned in the channel  56 . When the rings sections  50  and  51  are so mated and pins  62  and  63  are inserted respectively through the horizontal through holes  58  and  59  in the upper ring  51  and through the aligned slots  80  and  81  slots in the walls of the lower ring  32 , each spring  75 ,  76 ,  77 , and  78  inserted into a respective one of the blind holes  71 ,  72 ,  73 , and  74  must be of a length such that they will be compressed between the ring sections so as to maintain the ring sections apart a distance established by the length of the slots  80  and  81  and the diameter of the pins  62  and  63 .  
         [0045]    Once the sections  51  and  52  are assembled, the ring shield  50  is placed around the pickup head  24  and affixed to the floating head block  15  by screws  90 ,  91 ,  92 , and  93  passed through respective holes  110 ,  111 ,  112 , and  113  in the floating head block  15  and threaded into the tapped holes  64 ,  65 ,  66 , and  67  in the upper ring section  51  of the ring shield  50 . This secures the ring shield  50  around the pickup head  24 .  
         [0046]    The elastomer ring  96  located in the groove  95  in the lower face of the lower ring section  52  is once again formed of the 2400 General Metallized Fabric Coated Elastomer sold by the Tech-Etch Corporation and is provided to assure that there is a tight conformal, attenuating seal between the ring shield  50  and the upper surface of the socket adapter  39 .  
         [0047]    When a pickup head having such a ring shield  50 , fitted thereon, introduces a device to be tested into the recess  39  in the test socket  29 , the lower ring section is held tight against the upper surface of the socket adapter by the springs  75 ,  76 ,  77 , and  78  in the blind holes or recesses  71 ,  72 ,  73 , and  74  and the elastomer ring  95  is compressed to form a tight conductive seal between the ring shiled  50  and the socket adapter  39 . Further The wall  68  on the lower section being in the channel  56  in the upper ring section acts as a baffle and electromagnetic signals cannot pass there through. Thus the intermeshed rings  51  and  52  and the metallized fabric elastomer ring assuring that there is a tight attenuating seal across the gap  22  around the test head and the device under test such that extraneous electromagnetic signals can no longer reach the device under test via the gap  22 .  
         [0048]    [0048]FIG. 7 is a top view of the floating head block  15  provided with the tester by the manufacturer. This floating head block  15  has a central opening  107  through which the vacuum line is introduced into the head. This central opening  107  is bracketed by the through holes  16  through which the alignment base pins  19  extend, as shown in FIG. 2. This floating head block  15  has a central section  102  generally in the form of a square from which arms  103  and  104  extend. At the end of each arm  103  and  104  there is provided the vertical alignment pins  17  that descend into appropriate openings in the socket adapter plate when the pickup head inserts a device  27   a  into the recess  39  in the test socket  29  as shown in FIG. 2. With this manufacturers supplied floating head block  15  opposing sides  108  and  109  of the central region  102  align with the underlying edges of the pickup head. This provides a possibility that a gap can exist through which undesired signals can penetrate to the chip under test. To block or attenuate and such signals ribbons of metallized fabric coated elastomers  105  and  106  are placed along the sides  107  and  108  of the central square region  102  as shown in FIG. 7.  
         [0049]    An alternate solution is to redesign the floating head block  15  so the central section  102  has trapezoidal sides  114  and  115  rather than square sides as shown in FIG. 9. In this way the edges  108  and  109  of the pickup head are covered by the floating head block  15  and the unwanted electromagnet signals are attenuated or prevented from passing down beside the pickup head.  
         [0050]    Other alternate solutions will now become obvious to one skilled in the art after review of the present invention. For example a circumferential shield could be mounted directly on the floating block or on the fixture/socket adapter plate such that the pickup head would be received therein. It is also possible by careful machining of the pickup head, shield, floating block, the fixture/socket adapter plate and other associated parts that all metal mating surfaces between the associated elements of system could be made smooth enough that the compressive metallized polymers gaskets could be eliminated.  
         [0051]    Other adaptations such as mounting the compressive metallized polymer on the inside of the shield rings  51  or  52  or on the socket adapter plate instead of the shield assembly or even forming the floating block plate of a metallized polymer may also be possible.  
         [0052]    This completes the description of the preferred embodiment of the invention. Since changes may be made in the above construction without departing from the scope of the invention described herein, it is intended that all the matter contained in the above description or shown in the accompanying drawings shall be interpreted in as illustrative and not in a limiting sense. Thus other alternatives and modifications will now become apparent to those skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.