Abstract:
A radiation shielding system for protecting an integrated circuit package from ionizing radiation is provided for an integrated circuit package which is substantially planar and has a plurality of package leads extending from at least one surface of the package, substantially perpendicular to a surface of the integrated circuit package. The system comprises a base portion comprising shielding material and defining a well for receiving the integrated circuit package. A lid of shielding material is provided for being attached to the base portion to completely encompass the integrated circuit package. The system also includes means for allowing portions of each of the package leads to exit the well when the integrated circuit package is within the well. The means includes insulating material.

Description:
This application claims the benefit of U.S. provisional patent application No. 60/165,950, filed on Nov. 17, 1999, which is incorporated by reference, herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to radiation shielded carriers for integrated circuit packages. 
     BACKGROUND OF THE INVENTION 
     Electrons trapped in high earth orbits and electrons and protons trapped in low and medium earth orbits cause a high level of ionizing radiation in space. Such ionizing radiation causes an accumulation of charge in electronic circuits which eventually results in a malfunction or failure of the circuits. 
     Shielding is commonly provided to protect radiation sensitive components. Currently, flat slabs of high-Z metal or layers of high-Z and low-Z metals are attached to either the top or top and bottom of electronics packages for shielding. The high Z metals, such as tungsten/copper alloys, absorb ionizing radiation, such as protons and electrons, and reemit the energy from such radiation in the more innocuous forms of light, some heat, and secondary electrons. Secondary electrons have a very short range and are mostly absorbed by high Z metals, as well. The low Z materials, such as aluminum, also absorb secondary electrons, and can improve the efficiency of the shield. However, such configurations do not protect sensitive electronics from radiation entering from the sides of the device, where no shielding material is present. 
     Shielding material is also used to encapsulate the integrated circuit die. Connections are provided within the shield from the integrated circuit die to package leads extending out of the shielding material. The shield encapsulating the integrated circuit die must be vertically sealed. See, example, U.S. Pat. No. 5,635,754. While usually providing better radiation protection, such devices are complex and expensive to manufacture. 
     Another method for protecting sensitive electronics is to design a radiation tolerant integrated circuit die that can withstand high levels of ionizing radiation. These design methodologies can involve redundancy of electronic circuits, suitable doping of the semiconductor material, and spacing of electronic circuits. These methodologies are not normally used in commercially available electronics and require increased cost for redesign and production. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a radiation shielded carrier is provided for protecting an integrated circuit package from ionizing radiation, which completely encapsulates the integrated circuit package. 
     In one embodiment of the present invention, a radiation shielding system for protecting an integrated circuit package from ionizing radiation is provided for an integrated circuit package which is substantially planar and has a plurality of package leads extending from at least one surface of the package, substantially perpendicular to a surface of the integrated circuit package. The system comprises a base portion comprising shielding material and defining a well for receiving the integrated circuit package. A lid of shielding material is provided for being attached to the base portion to completely encompass the integrated circuit package. The system also includes means for allowing portions of each of the package leads to exit the well when the integrated circuit package is within the well. The means includes insulating material. 
     In another embodiment of the invention, a radiation shielded integrated circuit device comprises an integrated circuit package including an integrated circuit die electrically connected to a plurality of package leads. Shielding material completely encompasses the integrated circuit package. The shielding material defines a plurality of openings. The number of openings is at least equal to the number of leads of the integrated circuit package and the locations of the openings correspond to the locations of each of the package leads such that each package lead extends through a respective opening in the shielding material. Insulating material is provided in the openings. 
     In accordance with another embodiment of the invention, a radiation shielded integrated circuit device comprises an integrated circuit package including first and second substantially planar surfaces and two rows of package leads extending from opposing edges of the first surface, substantially parallel to the first surface. Each row extends in opposite directions. Shielding material is provided including first and second substantially planar surfaces opposing the first and second surfaces of the integrated circuit die, respectively. Four side walls of shielding material connect the first and second planar surfaces of shielding material. Insulating material is disposed along two opposing side walls of shielding material. The insulating material defines a plurality of openings corresponding to the number and location of the package leads. Each of the package leads extends through a respective opening. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described with reference to the accompanying drawings, wherein: 
     FIGS. 1 a  and  1   b  are cross-sectional views of integrated circuit (“IC”) packages; 
     FIGS. 2-4 are cross-sectional views of a radiation shielded carrier; 
     FIG. 5 is a top perspective view of an assembled radiation shielded carrier; 
     FIG. 6 is a portion of a lid including a layer of high Z material over low Z material; 
     FIG. 7 is a perspective view of a radiation carrier shield; 
     FIG. 8 is a cross-sectional, diassembled view of a radiation carrier shield; 
     FIG. 9 is view of the upper and lower sections of a radiation carrier shield; 
     FIG. 10 is a cross-sectional view through one opening of a radiation shielded carrier; 
     FIG. 11 is a cross-sectional view of a radiation shielded carrier; 
     FIG. 12 a  is a side view of a lid; 
     FIG. 12 b  is a bottom view of a lid; 
     FIG. 13 a  is a side view of a base; and 
     FIG. 13 b  is a top view of a base. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 a  is a cross-sectional view of a typical integrated circuit (“IC”) package  10  which may be shielded in accordance with the present invention. An IC die  12 , which includes the silicon substrate and the IC components providing the functionality of the circuit, is mounted in a well  14  of a ceramic base  16 . Wire bands  18   a ,  18   b  connect the integrated circuit die  12  to wire band pads  20   a ,  20   b , respectively. While only two wire bands  18   a ,  18   b  are shown in the cross-sectional view of FIG. 1, it is understood that a plurality of wire bands are typically provided. The wire band pads are electrically connected to package leads, such as package leads  22   a ,  22   b , as is known in the art. A lid  24  is provided to hermetically seal the well  14  to protect the integrated circuit die  12 . The lid may be a metal, such as Kovar, or a ceramic. Modem IC packages are typically rectangular. 
     In the configuration of FIG. 1 a , the package leads  22   a ,  22   b  extend downwardly from the side walls of the IC package  10 , perpendicular to the bottom of the base of the IC package  10 . FIG. 1 b  is a cross-sectional view of an IC package  24  which is identical to the IC package  10  of FIG. 1 a , except that the package leads  24   a ,  24   b  extend outwardly from opposing edges of the bottom of the base of the IC package  24 , substantially perpendicular to the side walls of the IC package  24 . While only one pair of package leads  22   a ,  22   b  and  24   a ,  24   b  are shown in the views of FIGS. 1 a  and  1   b , it is understood that a plurality of package leads parallel to the package leads shown, extend along the side walls or along the bottom of the IC packages  10  and  24 , respectively. In addition, the package leads may be provided in an array of rows and columns extending through the bottom of the base of the IC package, perpendicular to the bottom of the base. 
     FIG. 2 is a cross-sectional, side, disassembled view of two components of a radiation shielded carrier  100  for encompassing an IC package, such as IC package  10  in FIG. 1 a , in accordance with one embodiment of the invention. A base  102  of shielding material includes a base wall  103  and a side wall  104  extending from the base wall  103 , defining a well  106 . The wall may comprise four walls  104   a ,  104   b ,  104   c ,  104   d , substantially perpendicular to the base  102 . Two of the side walls  104   a ,  104   b  are shown in FIG.  1 . 
     Returning to FIG. 2, a lid  108  of shielding material is provided for attachment to the side walls  104   a - 104   d  of the base  12 . The base  102  and lid  108  are typically rectangular. The shape and dimensions of the shielded carrier may vary based on environment where the shielded carrier will be mounted. The outer diameter of the base and the lid  108  are substantially the same, so that the lid  108  completely covers the well  106 . 
     As shown in the cross-sectional view of FIG. 3, a plurality of holes  120  are defined through the base wall  103  for receiving the package leads  22   a ,  22   b  of the IC package  10  placed in the well  106 . Each of the holes  120  have a diameter slightly larger than the diameter of the package leads. For example, where the pin diameter is about 20 millimeters, the hole diameter is preferably about 20.2 mm. Each hole is filled with insulation material  122  such as glass. Epoxies and plastics may be used, as well. In this case, the shielded carrier  100  is adapted to accommodate an integrated circuit package having two rows of  10  package leads extending from the side walls of the IC package, as in the IC package  10  of FIG. 1 a . Other pin arrangements, such as array of  10  rows of  10  package leads each, can be readily accommodated, as well, by providing a suitable number of holes in suitable locations through the base wall  103  of the base  102 . 
     To assemble the shielded carrier, the IC package  24  is placed in the well  106  of the base  102 , so that the pins  126  extend through the holes  120 . The lid  104  is then connected to the top of the four side walls  104   a - 104   d  of the base  102  by epoxy, solder, braze, welding, or a clamp. One edge of the lid and base may also be connected through a hinge to allow the lid to pivot into open and closed positions. A clip may be provided on the lid to engage the base in the closed position. The IC package  10  may be connected to the base by epoxy or solder, as well. The IC package  10  is completely surrounded by the shielded carrier  100 , except for the portions of the package leads  22   a ,  22   b  extending through the carrier  100 . 
     The package leads  22   a ,  22   b  are not themselves susceptible to ionizing radiation. The package leads  22   a ,  22   b  preferably substantially fill the holes  120 . In addition, the insulation material  122  is somewhat radiation resistant. The amount of ionizing radiation which can enter the radiation shielded carriers of the present invention is therefore minimal. Since the IC die  12  is hermetically sealed in the IC package.  10 ,  10   a , the radiation shielded carriers of the present invention need not be hermetically sealed. 
     FIG. 5 is a top perspective view of an assembled radiation shielded carrier  100  containing an IC package  10   a , showing a row of package leads  22   a  and one of the row of package leads  22   b.    
     FIG. 4 is a cross-sectional view of an assembled shielded carrier, including an IC package  10  received in the well  106 , showing a row of package leads  22   a  of the IC package  10  extending through the holes  120  and insulative material  122 . 
     The base  102  and lid  108  of the shielded carrier  100  are made of a high Z material, preferably a copper/tungsten alloy. An alloy of approximately 90% tungsten/10% copper, which has a density of about 18.31 g/cm 3 , is preferred. Suitable alloys, in the desired shapes, may be obtained from NEC Corporation, Japan and Kyocera Corporation, Japan, for example. The shield may also be of a combination of an outer layer of a high Z material, such as the tungsten/copper alloy, and a low Z material, such as aluminum. FIG. 6 is a portion of a lid  108   a  including a layer of high Z material  108   a  over low Z material  108   b . Such multiple layer material may also be provided by NEC Corporation and Kyocera Corporation. Kovar may be used, as well. Kovar is an inert metal alloy consisting of manganese, silicon, nickel and cobalt, with a density of about 8.36 g/cm 3 . 
     The thickness of the walls of the base  102  and lid  108  is determined by the amount of shielding required in the ionizing environment. In high earth orbits, including geosynchronous orbit, 0.5 to 1.5 g/cm 2  of shielding material is sufficient. For low to medium earth orbits, 2 to 3 g/cm 2  of shielding material is required. These loading requirements translate to a 10% tungsten/90% cooper alloy thickness of about 0.026 to 0.078 cm for high earth orbits and about 0.10 to 0.16 cm for low to medium earth orbits. If Kovar is used, thicker shielding walls are required. 
     FIG. 7 is a perspective view of a radiation carrier shield  200  of a second embodiment of the present invention, showing one row of package leads  24   b  and two of the row of package leads  24   a  extending out of the side walls of the radiation carrier shield  200 . 
     FIG. 8 is a cross-sectional, disassembled view of the second embodiment of the invention. The radiation shielded carrier  200  comprises a first section  202  and a second section  204 , each defining a portion of a well  206 , as shown in FIG.  9 . FIG. 9 is view of the upper and lower sections of FIG. 5 along line  9 — 9  of FIG.  7 . Matching semi-circular recesses  208  are provided in opposing walls of the first and second sections  202 ,  204 , such that, when the first and second sections  202 ,  204  are mated, as in FIG. 7, circular openings  210  are formed. The semicircular recesses contain insulative material such as glass. The package leads  24   a ,  24   b  of the IC package  24  extend through the openings  210  when the radiation carrier shield  200  is assembled. 
     FIG. 10 is a cross sectional view through one opening of the radiation shielded carrier  200  of FIG. 7, including the IC package  24 . One pair of package leads  24   a ,  24   b  are shown extending through the openings  210 . The internal details of the IC package  24  are not shown in this view. 
     As above, after placement of the IC package  24  into the position of the well  206  of one of the sections  202 ,  204 , the first and second sections may be connected through epoxy, solder, braze or welding, screw, clamp, a hinge or a clip. Preferably, the IC package is attached to one of the sections through epoxy, solder or brace, as well. 
     FIG. 11 is a cross-sectional view of another radiation shielded carrier  300  for an IC package  24 , as in FIG. 1 a . A base  302  with a base wall  304  and a side wall  306  of shielding material defines a well  308  for receiving the IC package  24 . Insulating material  314  extends along a portion of the side wall  306 . A lid  310  covers the well  308 . The package leads  24   a ,  24   b  extend through the side wall  306  of the radiation shielded carrier  300 , through openings  312  in the insulating material. The openings  312  in the shielding material are shown in FIG. 13 a.    
     FIG. 12 a  is a side view of the lid  310 , showing shielding  316  material and a strip  318  of insulating material, such as glass. The strip  318  of insulating material is connected to the shielding material  316  by epoxy, or other glass adherence techniques known in the art. The insulating material  318  preferably extends between the wall portions  319  of shielding material. 
     FIG. 12 b  is a bottom view of the lid  316 , showing the strips  318  of insulating material and the wall portions  319  of shielding material. 
     FIG. 13 a  is a side view of the base  302 , showing the side walls  306  of shielding material and a strip of insulating material  314  in a sawtooth pattern including openings  322 , between the side walls  306 . The strip  314  of insulating material is also connected to the base wall  304  and side walls  306  by epoxy or other known glass adherence techniques. As with the lid  310 , the strip of insulating material  314  on the base preferably extends between the walls  306  of shielding material. 
     To assemble the radiation shielded carrier  300 , the IC package is placed in the well  308  such that the package leads  24   a ,  24   b , extend through the recesses  322  in the insulation wall  320 . The lid  310  is then attached to the top of the wall  305  and the insulating material  320 . 
     FIG. 13 b  is a top view of the base  304 , showing the walls  314  of insulation and the tops of the walls  306 . The sawtooth pattern of the insulation is not indicated in this view. 
     As in the embodiments above, since the package leads  24   a ,  24   b  substantially fill the recesses  322  and the insulation is somewhat radiation resistant, only a minimal amount of radiation may enter along the sides of the radiation shielded carrier  300 . Also as above, the shielding material may be a single layer of high Z material, or a double layer of high Z material and low Z material. The copper tungsten alloy described above is the preferred high Z material. 
     The radiation shielded carrier of the present invention can be used with any plastic and ceramic standard IC packages. 
     Because the shielding material completely surrounds the IC package, the present invention is useful in applications where an anisotopic radiation environment, as well as an isotropic radiation environment exists. 
     It is understood that variations may be introduced to the embodiments discussed above without departing from the scope of the invention, which is defined in the claims below.