Abstract:
An electronic device protected against electromagnetic disturbances comprising: a support structure having a first and second electronic component, wherein the support structure includes a conductive means surrounding each of the first and second electronic components; a first and second insulating block formed overlying the first and second electronic components on the support structure; and a metal layer overlying the first and second insulating blocks that are formed over the first and second electronic components, wherein the metal layer is electrically connected to the support structure through the conductive means to protect the first and second electronic components from the electromagnetic disturbances irradiating from each of the first and second electronic components.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a device for protecting an electronic circuit and a method for forming such a device.  
         [0003]     2. Description of the Related Art  
         [0004]     Many electronic circuits, for example for cell phones, are formed by attaching to a main support, generally called a motherboard, elementary electronic circuits formed separately, each fulfilling a specific function. As an example, for a cell phone, an elementary electronic circuit corresponds to a radio transceiver circuit, to be connected to the cell phone antenna, which demodulates the signals received at the antenna level and modulates the signals to be transmitted. Another elementary electronic circuit corresponds to a power amplifier circuit for amplifying the signals to be transmitted provided by the radio transceiver circuit. Each elementary electronic circuit is formed on a distinct support, for example, a ball grid array (BGA) or a land grid array (LGA) casing.  
         [0005]     Some elementary electronic circuits may be sensitive to electromagnetic disturbances. Such is the case, for example, for the radio transceiver circuit of a cell phone which is generally attached to the motherboard, like the power amplifier circuit, close to the antenna. In particular, the proper operation of the radio transceiver circuit may be disturbed by the electromagnetic disturbances transmitted by the power amplifier circuit and other external circuits.  
         [0006]      FIG. 1  shows a conventional example of protection of an elementary electronic circuit against electromagnetic disturbances. In  FIG. 1 , a portion of a motherboard  10  on which an elementary electronic circuit  12  is welded has been shown in cross-section view. As an example, elementary electronic circuit  12  is formed of a BGA package  14 , welded to motherboard  10  via bumps  16 . Elementary electronic circuit  12  comprises an integrated circuit  18 , attached to package  14  by a glue layer  20 . Electric wires  22 , for example, made of gold, ensure an electric connection between chip  18  and BGA package  14 . A resin block  24  covers integrated circuit  18  and protects it against mechanical shocks.  
         [0007]     To protect integrated circuit  18  against electromagnetic disturbances, a metal cover  26 , welded to motherboard  10  and which encapsulates circuit  12 , is provided. Cap  26  is grounded via motherboard  10 . Generally, it is necessary to provide a metal cover such as described in  FIG. 1  for each elementary electronic circuit to be protected against electromagnetic disturbances.  
         [0008]     The current tendency is to integrate on a same elementary electronic circuit several functions previously performed by separate elementary circuits. As an example, in mobile telephony, it may be desirable to form a single elementary electronic circuit which integrates the functions previously performed by the transceiver circuit and the power amplifier circuit. This may be obtained by arranging several integrated circuits on a same BGA package, a same LGA package, or another type of package.  
         [0009]     A difficulty then is to protect certain components of such an elementary electronic circuit against electromagnetic disturbances transmitted by other components of the same elementary electronic circuit. Indeed, the arranging of metal covers directly at the level of the elementary electronic circuit is generally incompatible with conventional methods for manufacturing such circuits.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     One embodiment of the present invention protects a portion of an electronic circuit, comprising at least one integrated circuit, against electromagnetic disturbances transmitted by another portion, comprising at least another integrated circuit, of the same electronic circuit and against electromagnetic disturbances originating from other electronic circuits.  
         [0011]     One embodiment of the present invention provides a device of connection of an electronic circuit to an external element having a manufacturing process compatible with current methods for manufacturing electronic circuits.  
         [0012]     One embodiment of the present invention is to provide a device of connection of an electronic circuit to an external element having a manufacturing process which only slightly modifies current electronic circuit manufacturing processes.  
         [0013]     For this purpose, one embodiment of the present invention provides a device for protecting an electronic circuit, comprising a support to which are attached at least two circuit portions, each comprising at least one integrated circuit chip. Each circuit portion is covered with an insulating block, itself covered with a metal layer connected to the support.  
         [0014]     According to an embodiment of the present invention, the support is intended to be attached to a base, the support comprising means of electric connection of the metal layers to a terminal at the base reference voltage.  
         [0015]     According to another embodiment of the present invention, the device comprises conductive strips attached to the support and surrounding each circuit portion, the metal layers being connected to the support via conductive strips.  
         [0016]     According to yet another embodiment of the present invention, the support comprises a planar insulating portion and means, contained in the planar portion, for connecting first conductive tracks arranged on a surface of the planar portion and second conductive tracks arranged on the opposite surface, the conductive strips being in contact with at least one conductive track, among the first conductive tracks, connected to a conductive track, among the second conductive tracks, intended to be connected to a source of a reference voltage.  
         [0017]     According to an embodiment of the present invention, the metal layers have at least one common wall.  
         [0018]     According to an embodiment of the present invention, the metal layers have opposite walls.  
         [0019]     According to an embodiment of the present invention, the support is a ball grid array.  
         [0020]     One embodiment of the present invention provides a method for manufacturing an electronic circuit, comprising the steps of:  
         [0021]     (a) providing a wafer;  
         [0022]     (b) attaching to the wafer circuit portions, each containing at least one integrated circuit chip;  
         [0023]     (c) covering with an insulating layer;  
         [0024]     (d) forming, in the insulating layer, recesses which surround each circuit portion and delimit an insulating block covering each circuit portion;  
         [0025]     (e) covering the obtained structure with a metal layer; and  
         [0026]     (f) delimiting electronic circuits, each comprising at least two adjacent circuit portions.  
         [0027]     According to an embodiment of the present invention, step (b) is preceded or followed by a step of forming conductive strips on the support surrounding each circuit portion, the recesses being formed at step (d) to expose the conductive strips, whereby, at step (e), the metal layer is in contact with the conductive strips.  
         [0028]     According to an embodiment of the present invention, the recesses are formed by sawing.  
         [0029]     According to one embodiment, the electronic device protected against electromagnetic disturbances includes: a support structure having an electronic circuit, wherein the support structure includes a conductive means surrounding the electronic circuit; an insulating block formed overlying the electronic circuit on the support structure; and a metal layer overlying the insulating block that is formed over the electronic circuit, wherein the metal layer is electrically connected to the support structure through the conductive means and is protected from electromagnetic disturbances.  
         [0030]     According to another embodiment the electronic device protected against electromagnetic disturbances includes: a support structure having a first and second electronic component, wherein the support structure includes a conductive means surrounding each of the first and second electronic components; a first and second insulating block formed overlying the first and second electronic components on the support structure; and a metal layer overlying the first and second insulating blocks that are formed over the first and second electronic components, wherein the metal layer is electrically connected to the support structure through the conductive means to protect the first and second electronic components from the electromagnetic disturbances irradiating from each of the first and second electronic components.  
         [0031]     The foregoing and other features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0032]      FIG. 1 , previously described, shows a conventional device for protecting an electronic circuit, attached to a support, against electromagnetic disturbances, according to one illustrative embodiment.  
         [0033]     FIGS.  2  to  8  illustrate successive steps of a first example of a method for protecting an electronic circuit against electromagnetic disturbances, according to one illustrative embodiment.  
         [0034]     FIGS.  9  to  13  illustrate successive steps of a second example of a method for protecting an electronic circuit against electromagnetic disturbances, according to one illustrative embodiment.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     For clarity, same elements have been designated with same reference numerals in the different drawings and, further, as usual in the representation of integrated circuits, the various drawings are not to scale.  
         [0036]     FIGS.  2  to  8  illustrate successive steps of a first example of embodiment of a method according to the present invention for manufacturing an electronic circuit protected against disturbances.  
         [0037]      FIG. 2  is a cross-section view of a support  30  from which Ball Grid Array (BGA) packages on which electronic circuits will be formed must be obtained. At such a step of the manufacturing method, support  30  has the shape of a wafer formed of a central layer  35  made of an insulating material. Metal tracks  36 ,  37  are arranged on each surface of central layer  35  and are covered with an insulating layer  38 ,  39 . Metal vias  40  are formed in central layer  35 , each via  40  connecting a metal track  36  arranged on a surface of central layer  35  with a metal track  37  arranged on the other surface of central layer  35 .  
         [0038]      FIGS. 2 and 3  respectively are a cross-section view and a top view of the structure obtained after having locally etched insulating layer  38  to expose portions of metal tracks  36  and after having formed on support  30  conductive tracks  41  in contact with exposed metal tracks  36 . In top view, conductive strips  41  form a grid on support  30  delimiting locations  42 , one or several integrated circuits being intended to be attached to support  30  at the level of each location  42 . As an example, conductive strips  41  are made of a welding paste and have a thickness of approximately 60 μm and a width of some hundred micrometers. As an example, conductive strips  41  may be formed by spreading welding paste on a mask arranged opposite to support  30 . In this case, conductive strips  41  may be locally interrupted to ease the forming of such a mask. When openings are present at the level of conductive strips  41 , the number and the dimensions of such openings depend on the nature of the expected electromagnetic disturbances.  
         [0039]     Simultaneously to the forming of conductive strips  41 , insulated welding paste pads (not shown) may be formed on support  30 , such pads being in contact with metal tracks  36 . Such insulated pads enable, conventionally, arranging discreet electronic components, generally called SMDs (Surface Mounted Device). Such components correspond, for example, to capacitors or to resistors which cannot be made in integrated form.  
         [0040]      FIG. 4  is a cross-section view of the structure obtained after attachment of electronic circuits  43 ,  44  at the level of locations  42 . In  FIG. 4 , the two shown circuits  43 ,  44  are attached at the level of two adjacent locations  42  and are intended, at the end of the manufacturing process, to be on a same portion of support  30 . However, at the present step of the manufacturing process, circuits  43 ,  44  are reproduced many times on support  30 . As an example, circuit  43  is a transceiver circuit formed of a first integrated circuit chip  45  and of a second integrated circuit chip  46  attached to the first integrated circuit chip  45  according to a flip/chip-type connection, and circuit  44  is a power amplifier circuit formed of an integrated circuit chip  47 . The attachment of circuits  43 ,  44  to support  30  is obtained by depositing glue portions  48  on support  30 , by laying circuits  43 ,  44  at the level of glue portions  48 , and by polymerizing glue portions  48 . The electric connections between circuits  43 ,  44  and support  30  are obtained via electric wires  49 , for example, made of gold, connected to metal tracks  36  through insulating layer  38 . It should be clear that the structures of circuits  43 ,  44  are given as an illustration only, since circuits  43 ,  44  may comprise a greater or smaller number of integrated circuit chips.  
         [0041]      FIG. 5  illustrates the circuit obtained after having deposited a resin layer  52 , for example, an epoxy resin, on support  30  and electronic circuits  43 ,  44  and after having formed bumps  54 , for example, made of tin, on the surface of support  30  opposite to circuits  43 ,  44 . As an example, resin layer  52  has a thickness of approximately 0.8 mm. Some bumps  54  are connected to metal tracks  37  of support  30 , through resin layer  39 , enabling forming of electric connections between bumps  54  and electric wires  49  and between bumps  54  and conductive strips  41 .  
         [0042]      FIG. 6  shows the structure obtained after having formed recesses  53  in resin layer  52  exposing the upper portion of conductive strips  41 . Recesses  53  thus follow the distribution of conductive tracks  41  and delimit distinct resin blocks  55  at the level of each circuit  43 ,  44 . Recesses  53  have a width greater than the width of conductive tracks  41 . As an example, recesses  53  may be formed by sawing of resin layer  52  down to part of the depth of resin layer  52 , for example, by means of a circular saw having a thickness of approximately 250 μm. In  FIG. 6 , recesses  53  are shown with a constant cross-section. According to an alternative embodiment, recesses  53  having a cross-section comprising several successive stages or a “V”-shaped cross-section, the bottom of a recess  54  exposing the upper portion of a conductive strip  41 .  
         [0043]      FIG. 7  illustrates the structure obtained after having covered resin blocks  55  with a metal layer  56  which penetrates into recesses  53  and comes into contact with conductive strips  41 . Metal layer  56  may be formed by a metal deposition, for example, by a cathode sputtering. The metal forming metal layer  56  may be gold or silver. Generally, it is a metal or a metal alloy that can be only weakly oxidized, or the oxidation of which only slightly affects the conduction properties. The thickness of metal layer  56 , on the order of a few micrometers, depends on the used material and on the nature of the electromagnetic disturbances against which a protection is desired to be obtained. Further, the thickness of metal layer  56  may not be constant, in particular at the level of recesses  53 .  
         [0044]     According to an alternative embodiment of the present invention, after deposition of metal layer  56 , an additional step of filling of recesses  53  with an insulating material, for example, a resin, is provided. According to another alternative embodiment, recesses  53  are completely filled with metal.  
         [0045]      FIG. 8  shows the structure obtained after sawing of support  30 , of some conductive strips  41 , and of metal layer  56  to obtain distinct electronic circuits  60 , a single circuit  60  being shown. Each electronic circuit  60  is formed, in the present example, of a portion  62  of support  30  on which are attached circuits  43  and  44 , each circuit being completely surrounded with a metal cage  64 ,  66  corresponding to a portion of metal layer  56 . The sawing of circuits  60  may be performed by means of a circular saw having a thickness smaller than the thickness of the circular saw used to form recesses  53 , for example, on the order of 100 μm.  
         [0046]     Electronic circuit  60  is, for example, intended to be attached to a motherboard. Metal cages  64 ,  66  may then be grounded via conductive strips  41  connected to bumps  54 , themselves grounded via the motherboard. Each metal cage  64 ,  66  then protects the electronic circuit  43 ,  44  that it contains against external electromagnetic disturbances, especially electromagnetic disturbances originating from the other circuit  43 ,  44  attached to the same portion  62  of support  30 .  
         [0047]     FIGS.  9  to  13  illustrate successive steps of a second example of embodiment of the protection method according to the present invention.  
         [0048]      FIGS. 9 and 10  are similar to  FIGS. 2 and 3  since conductive strips  70  are distributed on support  30  in the form of a grid which delimits locations  72 . Like in the first example of embodiment, two adjacent locations  72  at the level of which circuits intended to be located on a same portion of support  30  will be attached are separated by a single conductive strip  70 . However, unlike the first example of embodiment, two adjacent locations  72  at the level of which circuits intended to be on two distinct portions of support  30  will be attached are separated by two parallel conductive strips  70 , separated by an interval  74 .  
         [0049]     The next steps of attachment of circuits  43 ,  44  and of deposition of resin layer  52  are identical to what has been previously described for the first example of embodiment.  
         [0050]      FIG. 11  shows the structure obtained after having formed recesses  76  in resin layer  52  partially penetrating into conductive strips  70 . Recesses  76  thus follow the distribution of conductive strips  70  and delimit resin blocks  77  at the level of each circuit  43 ,  44  and resin blocks  78  at the level of intervals  74  between two adjacent conductive tracks  70 . As an example, recesses  76  may be formed by sawing of resin layer  52  down to part of the depth of resin layer  52 , for example, by means of a circular saw having a thickness of approximately 100 μm.  
         [0051]      FIG. 12  illustrates the structure obtained after having covered resin blocks  77 ,  78  with a metal layer  79 , which penetrates into recesses  76  and comes into contact with conductive strips  70 . The determination of the thickness and of the nature of metal layer  79  follows what has been previously discussed for metal layer  56 .  
         [0052]      FIG. 13  shows the structure obtained after sawing of support  30 , of resin blocks  78 , and of metal layer  79  to obtain distinct electronic circuits  60 , a single circuit  60  being shown. The sawing of support  30  may be performed by means of a circular saw having a thickness, for example, on the order of 100 μm. The sawing is performed at the level of intervals  74 , between two adjacent conductive strips  70 . As for the first example of embodiment, each electronic circuit  60  is formed of a portion  62  of support  30  on which are attached circuits  43  and  44 , each circuit being surrounded with a metal cage  80 ,  82  corresponding to a portion of metal layer  78 . In the second example of embodiment, metal cages  80 ,  82  have a common wall  84  between the two circuits  43 ,  44 .  
         [0053]     For the two previously-described examples of embodiment, the protection of circuits  43 ,  44  formed on the same portion  62  of support  30  being performed by metal cages  64 ,  66 ,  80 ,  82 , it is then no longer necessary, when portion  62  of the support is subsequently attached to a motherboard, to provide a metal cover encapsulating portion  62  of the support, which anyway would not protect each circuit  43 ,  44  attached to support portion  62  against electromagnetic disturbances transmitted by the other circuit  43 ,  44  attached to the same support portion  62 . For a circuit  60  of given dimensions, the implementation of the protection device according to the present invention results in a smaller bulk than that which results from the use of a distinct metal cover. Indeed, the bulk of the protection device according to the present invention results from the addition of metal layer  56 ,  79 , generally having a thickness on the order of a few micrometers. When a distinct metal cover is used, it is generally necessary to provide a free space greater than one millimeter above circuit  60  to enable arrangement of the protection metal cover.  
         [0054]     Further, the present invention enables proper setting of metal cages  64 ,  66 ,  80 ,  82  to the motherboard ground. Indeed, conductive strips  41 ,  70  may be connected to conductive tracks  36  at many points distributed along their entire length, and especially at the level of the conductive track which separates circuits  43 ,  44 , enabling balanced distribution of the voltages.  
         [0055]     In the first example of embodiment a free space may further be left between metal cages  64 ,  66  which then only are in contact at the level of conductive strip  41  extending between circuits  43 ,  44 . Such a structure advantageously enables for resin blocks  55  to deform differently. Such a difference may then be due to differential expansions of resin blocks  55  when the amounts of heat released by circuits  43 ,  44  are different.  
         [0056]     The present invention provides a method for protecting electronic circuits which advantageously causes few modifications with respect to a conventional electronic circuit manufacturing method. Indeed, the only step which requires using specific means is the step of forming of metal layer  56 ,  79  on resin layer  52 . Conductive strips  41 ,  70  may be formed at the step, generally already present, of forming pads intended to be connected to discreet components. Further, the step of forming recesses  53 ,  76  may be implemented by sawing by means of a circular saw, such a sawing method being already conventionally implemented for the delimiting of circuits  60  by sawing of support  30 .  
         [0057]     Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, the present invention has been described for the protection of electronic circuits formed on a same BGA package. However, the present invention also relates to the protection of electronic circuits formed on a same LGA package and, more generally, to the protection of electronic circuits formed on a same support.  
         [0058]     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.