Abstract:
A shielding apparatus was developed to eliminate electromagnetic waves interference (EMI) to an integrated circuit (IC) die while it is under test. The shielding apparatus comprises a conductive plate having a first and second surfaces and a central opening where the IC device is placed. The first surface includes a first EMI gasketted channel and a central cavity disposed inside of the gasketted channel. The second surface of the apparatus includes a second EMI gasketted channel and the central opening which extends through both the first and second surfaces. When the first surface mates with the surface of automatic test equipments (ATE) interface board, the first gasketted channel forms a tight seal. Similarly, when a plunger from a device handler mates with the second surface, the second EMI gasketted channel forms a seal that blocks out EMI. In this way, the IC device in the central opening of the apparatus is isolated from external EMI.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/688,391 filed Jun. 8, 2005, which is incorporated herein by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a shield developed to eliminate electromagnetic waves interference while testing radio frequency (RF) based products, specifically bit error rate (BER) failures on Bluetooth devices and gain measurement error on wireless local area network (WLAN) products caused by nearby WLAN access points and other transceivers. 
   2. Introduction 
   One of the last steps in the manufacturing process of a semiconductor device or an integrated circuit is the quality assurance (QA) process. In the QA process, automatic test equipment (ATE) is used to automatically test the device (device under test or DUT). During this QA process, the ATE applies test signals to the DUT and checks for appropriate responses. Based on the DUT&#39;s responses, the ATE marks the DUT as pass or fail by comparing the responses to predetermined signal response patterns. The appropriate response patterns are determined by the type of test employed and the type of product being tested. 
   DUTs that fail the initial QA process are typically fed through the ATE again to minimize false rejections. Once the DUT fails the second time, it is usually scrapped which will negatively affect production efficiency, cost, and profits. However, not all DUTs scrapped are bad. Variability factors in the test method, equipment, and environment plays an essential role in testing accuracy of the DUT. Minimizing these variability factors will lead to better testing process and higher production yield. The present invention focuses on the minimization of the variability in the test environment. 
   Device under test (DUT) are often sensitive to electromagnetic interference, particularly at high frequencies. Proper shielding of a DUT is therefore essential because of potential interference and the effect on the test&#39;s accuracy. In an un-shielded and high interference environment, many DUTs could be falsely rejected because of measurement errors that can be attributed to electromagnetic interference. Reducing this type of interference can be done in two ways. The first way is to eliminate the source of the interference. The second is to shield the DUT. 
   Surprisingly, it can be very difficult to eliminate the source of the high frequency that causes the interference. High frequency devices are abundant. Often time these devices are located in the same environment with the DUT such as switched mode power supplies, computer clocks, laptops, mobile phones, and nearby WLAN access points. 
   Shielding is the second way to reduce electromagnetic interferences. One option is to shield the test room or the test area in which the DUT are being tested; however, this is a prohibitively expensive solution. The other option is to shield the ATE system. This option is also not viable, because ATE system is typically very large. 
   Generally, a compact shielding solution can be developed for an ATE. But there are few, if any, shielding solutions available on the market. Test equipment and socket vendors want to customize and integrate a shielding into their socket base but are not doing so due to high cost which in turn makes the test equipment not very marketable. Moreover, any of these solutions would be specific to that manufacturer and that socket footprint, which is not scalable. 
   Accordingly, what is needed is a low cost testing device that is capable of significantly attenuating interfering signals to a level below the sensitivity of the device under test (DUT). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
     The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
       FIG. 1A  illustrates an isometric top-view of a shielding device according to an embodiment of the present invention. 
       FIG. 1B  illustrates an isometric bottom-view of a shielding device according to an embodiment of the present invention. 
       FIG. 2  illustrates an isometric view of a shielding device according to an embodiment of the invention. 
       FIG. 3  illustrates an isometric top-view of a shielding lid according to an embodiment of the present invention. 
       FIG. 4  illustrates an exploded view of the shielding device assembly according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   This specification discloses one or more embodiments that incorporate the features of this invention. The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. An embodiment of the present invention is now described. While specific methods and configurations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the art will recognize that other configurations and procedures may be used without departing from the spirit and scope of the invention. 
   A shielding device was developed to eliminate electromagnetic waves interference while testing RF products operating in the 2.4 GHz and 5 Ghz industrial, scientific, and medical (ISM) frequency bands. The invention is not limited to the specific frequencies mentioned herein, and can be applied to other frequencies as will be understood by those skilled in the arts. Specific problems that were addressed include bit error rate (BER) failures on Bluetooth devices caused by access points and laptops transceivers operating on nearby 802.1 μg WLAN. Similar problems were also detected while testing receiver gain on 802.11g WLAN parts. 
   Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     FIG. 1A  illustrates a shielding device  100 . Shielding device  100  is made with conductive metals such as copper, aluminum, stainless steel, or nickel-plated aluminum. The type of metal or plated-metal selected to fabricate shielding device  100  is based on several factors such as electromagnetic waves attenuating capability, ease of metal processing, and cost. In an embodiment, device  100  is made of stainless steel. Other suitable metals could also be used to fabricate shielding device  100  as will be understood by one skilled in the art. Shielding device  100  includes a mating surface  105 , a channel  110 , at least one alignment pin  115 , a electromagnetic interference (EMI) gasket  120 , and an opening  130 . 
   Mating surface  105  mates with a corresponding surface of a shield lid in the final assembly of an embodiment of the shielding device. For example,  FIG. 4  illustrates a lid  450 , which will be discussed in detail herein. In an alternative embodiment, surface  105  mates with a surface of a plunger of a device handler. The shield lid and the plunger are preferably made of the same material as shielding device  100 . In a metal to metal contact, there are always tiny gaps between the two mating surfaces. These gaps provide a conduit for electromagnetic waves to enter into the internal area of the shielding device  100 . A way to eliminate these rogue electromagnetic waves is to provide an EMI gasket  120  between the two metal mating surfaces. 
   EMI gasket  120  is disposed inside of channel  110 . The EMI gasket  120  is configured such that it fits inside channel  110 , but also with adequate room for expansion due to compression. EMI gasket  120  is also configured such that when the shield lid (not shown) mates surface  105 , gasket  120  compresses and creates a tight seal that would effectively block out electromagnetic waves. The EMI gasket  120  is preferably made with material that can withstand many compression cycles (compressive durability) such as a silicon sponge type gasket fortified with vertical wire. Other type of gaskets could also be used such as elastomer or foam gasket as long as the gasket has high shielding effectiveness (100 dB from 100 MHz to 10 GHz) and high compressive durability. For example, EMI gasket  120  can be an Elastofoam® gasket made by Tecknit Corporation of New Jersey. A brochure of available Elastofoam® gaskets is available at http://www.tecknit.com. The Elastofoam® gasket consists of scores of individual fine wires embedded and bonded in a soft closed cell silicone sponge elastomer. In an embodiment, the Elastofoam® gasket with Tecknit part No. 88-12057 is used. The invention is not limited to the EMI gasket described herein, other suitable type of gaskets could be used as long as there is proper compressive durability and electromagnetic waves attenuation. 
   Further, shielding device  100  includes at least one alignment pin  115 . Alignment pin  115  is used to align shielding device  100  with a test interface (not shown) which is aligned to a test board that eventually goes onto a test bed (also not shown) of an ATE for testing. Alignment between these various components is critical, especially during production where millions of devices are precisely positioned in the test sockets by device handlers. Normally, shielding device  100  has to be manufactured to certain specification in order for proper mating with the test socket. This task itself is usually not an issue; however, the design of the test socket varies by the type of ATE machine, products, and manufacturers. Therefore, it becomes impractical to fabricate various versions of shielding device  100  to accommodate all of the different test socket footprint designs. To overcome this problem, two alignment pins  115  are provided on shielding device  100 . Alignment pins  115  can be used to properly align shielding device  100  to the test socket of the test board or bed of various type of ATEs. As shown in  FIG. 1A , pins  115  are flushed with a surface  137  of device  100 . Pins  115  extend beyond the surface opposing (not shown) surface  137 . In this way, proper alignment may be provided. Additionally, alignment hole  135  could also be used to align a shielding lid or plunger (not shown) of a device handler. Shielding device  100  also includes an opening  130  to accommodate for an integrated circuit die, a circuit board, a semiconductor device, or any electrical device under test. 
     FIG. 1B  illustrates the same shielding device  100  as shown in  FIG. 1A  but from a bottom view. Although device  100  as shown has a general rectangular shape, device  100  could take the form of any other shapes such as a circle, a square, or even a triangle. In an embodiment, shielding device  100  includes a mating surface  155 , a channel  160 , a cavity or slot  165 , a gasket  170 , and an opening  130 . Mating surface  155  mates with a corresponding surface of a test board of an ATE (not shown). Again, a gasket is needed between two contacting metal surfaces to effectively block out electromagnetic waves interference. 
   In an embodiment, a channel  160  is provided along the circumference of device  100 . Channel  160  completely encloses cavity  165  in which a DUT rests (not shown). Further, gasket  170  is disposed inside of channel  160  to provide for a tight seal and to protect the DUT located inside of cavity  165 . Gasket  170  is made from an foam or elastomer gasketing materials such as silver plated copper in silicone. Other suitable materials could also be used as long as it provides for attenuation of high frequency electromagnetic waves (120 dB at 10 GHz) and tight seal between two contacting metal surfaces. For example, gasket  170  is a Cho-Seal® conductive elastomer made by Chomerics, an entity of Parker Hannifin Corporation of Massachusetts. A brochure of available Cho-Seal® conductive elastomers is available at http://www.chomerics.com. In an embodiment, Cho-Seal® gasket with Chomerics part No. 10-05-1362-1215 is used. Although certain frequencies are recited as guideline for selecting a suitable gasket, the invention is not limited to the specific frequencies mentioned herein, and can be applied to other frequencies as will be understood by those skilled in the arts. 
   Further, cavity  165  may take any shape and size as long as it is completely enclosed by channel  160 . Cavity  165  is configured such that its size will accommodate for various IC device&#39;s size and geometry. The depth of cavity  165  is designed such that there is a minimum clearance of one tenth of an inch (0.1″) between the base of the cavity (or roof of the shield) to any components or circuit board traces under the shield. In this way, the shield does not interfere with the operation of any microstrip traces or high frequency components such as capacitors, inductors, etc. 
   Shielding device  100  eliminates the need for the test socket vendor to integrate shielding solution into their socket body. There are some dimensional restrictions that the test socket must be designed to in order to accommodate shielding device  100 . However, specifying height, width, and length of test sockets is every day practice in the industry. The only added requirement of the socket vendor is that their lid must mount to shielding device  100  instead of the test board or the test socket, and their plunger must accommodate the added plunge depth due to the height of shielding device  100 . Additionally, the socket vendor must configure their plunger to seal against the gasketed perimeter created by channel  110  and gasket  120 . But this is not burdensome to the test socket vendor because every socket must be designed to accommodate for the height of the DUT package and the plunger design is an ordinary step of the socket design process. 
   In one embodiment, shielding device  100  has an outer dimension of 78 mm×58 mm, designed to accommodate standard 2×2 configuration on most device handlers (80 mm centers X, 60 mm centers Y) so quad site testing can be performed. Nominal test socket dimensions support DUT&#39;s up to 12 mm×12 mm in size, which incorporates current RF, WLAN, and Bluetooth solutions. However, tradeoffs in area under the shield can be made for even larger devices while maintaining the same 78 mm×58 mm footprint. For larger VLSI devices, the dimensions can be scaled. The present invention is not limited to the dimensions described herein. Other dimensions could be used for the electromagnetic waves shield, as will be understood by those skilled in the arts. 
     FIG. 2  illustrates a top isometric view of an alternative embodiment of shielding device. The shielding device  200  includes an opening  210 , a surface  220 , alignment hole  235 , and at least one alignment pin  230 . In an embodiment, shielding device  200  includes two alignment pins  230 . Noticeably missing from device  200  is a channel and a gasket on surface  220 . In an alternative embodiment, these two features are located in the respective lid or plunger as will be described herein. Although not shown, shielding device  200  has the exact same features of shielding device  100  from the bottom view, see  FIG. 1B . In an yet another embodiment, shielding device  200  incorporates every features of shielding device  100 , as shown in  FIG. 1B , except for channel  160  and gasket  170 . In this embodiment, the gasket and channel assembly would be part the ATE interface board. 
     FIG. 3  illustrates a lid or plunger  300 . Lid  300  includes a surface  305 , a protrusion  310 , a channel  320 , a gasket  330 , and alignment pin  335 . Surface  305  is configured to mate with opposing surface  220  on device  200 . Alignment pin  335  is configured to align and mate with alignment hole  235  on device  200 . When the two surfaces mate, gasket  330  compresses and creates a tight seal along channel  320 . Channel  320  is configured to hold gasket  330  in place but also to give gasket  330  sufficient space for expansion due to the compression that occurred during the mating process. Further, lid  300  includes a protrusion  310  which may or may not exhibit a step-like feature. The protrusion  310  is configured to fit in opening  210 . The height of protrusion  310  is also configured to account for the size and height of the DUT and also for the size and height of shielding device  200 . In an embodiment, the lid  300  is a plunger configured to pick and place an IC device into opening  210  for testing. This could be accomplished using mechanical means or suction means. Additionally, the plunger serves as a lid that once mated with surface  220  on device  200  provides a shielding enclosure for the IC device from external electromagnetic waves interference. 
     FIG. 4  illustrates an exploded view of a shielding device assembly  400  according to an embodiment of the present invention. Assembly  400  is designed for manual testing of an IC device. Assembly  400  includes a shielding device  405 , a lid and plunger assembly  450 , and a test interface  480 . Shielding device  405  comprises a surface  410 , alignment hole  417 , alignment pin  420 , and an opening  415 . Shielding device  405  further includes all of the features of shielding device  200  as shown on  FIG. 2 . The lid/plunger assembly  450  comprises a lid/plunger base  455  and a lid  460 . In lid  460 , the side not shown (opposite side) incorporates all of the features of plunger  300 , including the channel  320  and the gasket  330 . 
   In assembly  400 , surface  410  is mated with surface  465 . During the mating process, alignment holes  417  could be used to properly guide the lid/plunger assembly  450  into place. Once the two pieces are mated, the gasket on surface  305  tightly seals the assembly and blocks electromagnetic interference from reaching opening  415  where test interface  480  rests. Further, shielding device  405  is aligned to a test socket using pin  420  and is gasketed against a test board surface (not shown) to create a tight seal. The test interface  480  that rests in opening  415  can be accessed using lid  460  which opens up at pivot points  465 . In an embodiment, a plunger of a device handler could be configured to pick and place an IC device (not shown) into opening  415  and onto test interface  480  for testing. The plunger may be configured to pick and place IC device with mechanical means or suction means. Additionally, the plunger serves as a lid that once mated with the surface  410  on device  405  provides a shielding enclosure for the IC device and the test interface  480  from external electromagnetic waves interference. Further, the plunger may incorporate all of the features of plunger  300 , including channel  320  and gasket  330 . 
   In an alternative embodiment, assembly  400  uses shielding device  100  in place of shielding device  200 . Further, lid  460  incorporates all of the features of plunger  300  except for channel  320  and gasket  330 . In yet another embodiment, a plunger that is part of a device handler could be used with shielding device  100 . Further, the plunger may incorporate all of the features of plunger  300  except for channel  320  and gasket  330 . 
   While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.