Abstract:
An electromagnetic shield for an electronic module includes a surface finish that is applied to the surface of an electronic module so as to minimize the size of the shield. Once the shield is in place, the shield acts to address electromagnetic interference (EMI) concerns associated with the electronic module. An electronic module having a ring of conductive material embedded about its peripheral edge is formed. The electronic module is then sub-diced so as to expose the ring of conductive material. After sub-dicing, a conductive material may be applied through an electroless plating process followed by an electrolytic plating process. Alternatively, a conductive epoxy may be sprayed or painted onto the surface of the electronic module.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a shield for an electronic module, wherein the shield is designed to reduce electromagnetic interference experienced by the electronic module. 
   BACKGROUND OF THE INVENTION 
   Electronic components have become ubiquitous in modern society. The electronics industry proudly, but routinely, announces accelerated clocking speeds and smaller integrated circuit modules. While the benefits of these devices are myriad, smaller and faster electronic devices create problems. In particular, high clock speeds inherently require fast transitions between signal levels. Fast transitions between signal levels create electromagnetic emissions throughout the electromagnetic spectrum. Such emissions are regulated by the Federal Communications Commission (FCC) and other regulatory agencies. Furthermore, fast speed inherently means higher frequencies. Higher frequencies mean shorter wavelengths. Shorter wavelengths mean shorter conductive elements act as antennas to broadcast these electromagnetic emissions. These electromagnetic emissions radiate from a source and may impinge upon other electronic components. If the signal strength of the emission at the impinged upon electronic component is high enough, the emission may interfere with the operation of the impinged upon electronic component. This phenomenon is sometimes called electromagnetic interference (EMI) or crosstalk. Dealing with EMI and crosstalk is sometimes referred to as electromagnetic compatibility (EMC). Other components, such as transceiver modules, inherently have lots of radiating elements that raise EMI concerns. Thus, even electronic modules that do not have high clock speeds may need to address EMI issues. 
   One way to reduce EMI to comply with FCC regulations is to shield the electronic modules. Typically the shield is formed from a grounded conductive material that surrounds the electronic module. When electromagnetic emissions from the module strike the interior surface of the conductive material, the electromagnetic emissions are electrically shorted through the grounded conductive material, thereby reducing emissions. Likewise, when emissions from another radiating element strike the exterior surface of the conductive material, a similar electrical short occurs, and the module does not suffer from EMI from other modules. 
   However, as the electronic modules continue to become smaller from miniaturization, creating effective shields that do not materially add to the size of the module becomes more difficult. Thus, there is a need for an electromagnetic shield that is inexpensive to manufacture on a large scale, does not substantially change the size of the electronic module, and effectively deals with EMI concerns. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a method of making an electromagnetic shield for an electronic module. The shield is a surface finish that is applied to the surface of an electronic module so as to reduce the size of the shield. Once the shield is in place, the shield acts to address electromagnetic interference (EMI) concerns associated with the electronic module. There are two primary embodiments of the present invention. 
   In both embodiments, an electronic module having a groundable ring of conductive material embedded about its peripheral edge is formed. The module is then sub-diced so as to expose the ring of conductive material. The shield is applied to the surface of the electronic module and electrically coupled to the groundable ring of conductive material. In use, the ring of conductive material is grounded, thereby grounding the shield. 
   In the first embodiment, an electroless plating process forms a seed layer of conductive material, such as copper (Cu), over the module. The seed layer then carries current for an electrolytic plating process, which deposits a second conductive layer on the seed layer. A third layer may be applied through a second electrolytic plating process. The third layer is a relatively poor conductor compared to the seed layer and the second conductive layer, and may be formed with a material such as nickel (Ni). The seed layer and second layer form a conductive layer that provides an effective electromagnetic shield around the module. The nickel lay may contribute to the conduction that helps shield the module and may also provide some absorption of electromagnetic signals to further shield the module. It should be appreciated that the side of the module that has the electrical contacts is masked during the plating processes such that the plating does not interfere with the contacts of the module. 
   The second embodiment includes a conductive epoxy paint sprayed on the electronic module. In particular, the epoxy may include copper (Cu) and/or silver (Ag) flecks therein. When the epoxy is sprayed on the electronic module, the flecks form a conductive layer that shields the electronic module. It should be appreciated that the side of the module that has the electrical contacts is masked during the spraying step so that the spray does not interfere with the contacts of the module. 
   Both embodiments are designed to be implemented prior to singulation of the electronic modules. Thus, after the shield is applied, electronic modules may be singulated one from another and further processed as needed or desired. The mask may be removed before or after singulation. 
   Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention. 
       FIG. 1  illustrates a perspective view of a typical electronic module; 
       FIG. 2  illustrates a top plan view of an electronic module with an embedded periphery of conductive material; 
       FIG. 3  illustrates a strip of electronic metamodules prior to implementation of the present invention; 
       FIG. 4  illustrates the strip of electronic metamodules of  FIG. 3  after a sub-dicing operation; 
       FIG. 5  illustrates a top plan view of part of a metamodule of  FIG. 3  with the singulation cuts illustrated; 
       FIG. 6  illustrates as a flow chart exemplary steps of the first embodiment of the present invention; 
       FIG. 7  illustrates an exemplary electronic module constructed according to the first embodiment of  FIG. 6 ; 
       FIG. 8  illustrates as a flow chart exemplary steps of the second embodiment of the present invention; and 
       FIG. 9  illustrates an exemplary electronic module constructed according to the second embodiment of  FIG. 8 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
   The present invention is directed to providing improved manufacturing techniques to shield an electronic module. While the present invention is particularly contemplated as being appropriate for a transceiver module, the present invention could be used with any number of different electronic modules. The manufacturing techniques of the present invention insert a conductive element around the periphery of the electronic module. After a sub-dicing step is performed to expose the conductive element around the periphery of the module, the top surface of the module is roughened. In one embodiment, an electroless plating process deposits a conductive seed layer on the module. Then an electrolytic plating process is used to deposit a second conductive layer on the seed layer. A final layer of a material such as nickel is then deposited on top of the second conductive layer through another electrolytic plating process. In a second embodiment, after the sub-dicing and roughening steps, a conductive epoxy or paint is applied to the module. In both embodiments, the conductive layers formed by the process form an electromagnetic shield around the electronic module so as to reduce electromagnetic interference (EMI). 
   The present invention is well suited for use with an electronic module for transceivers, such as the RF6001 sold by RF Micro Devices of 7628 Thorndike Road, Greensboro, N.C. 27409-9421. The datasheet for the RF6001 can be found online at http://www.rfmd.com/DataBooks/db97/6001 — 2pg.pdf, is herein incorporated by reference in its entirety, and is enclosed in the Information Disclosure Statement accompanying the present application. When the present invention is applied to an electronic module, such as the RF6001, certain changes must be made to the electronic module as will become clear from the discussion presented below. It should be appreciated that other electronic modules, such as power amplifier modules, receiver modules, transmitter modules, and the like, could also benefit from the present invention, and the present invention is not limited to a particular type of electronic module. 
   A conventional electronic module  10  is illustrated in  FIG. 1 . The electronic module  10  includes a body  12  made from a dielectric material molded into a desired shape with several contacts  14  positioned on an input/output (I/O) face  16  of the electronic module  10 . Conceptually the I/O face  16  is the bottom face of the electronic module  10 . Electrical components (not particularly illustrated) are embedded inside the body  12 , as is well understood. The electronic module  10  may include a plurality of conductive layers and a plurality of dielectric layers sandwiched one on top of the other within the body  12 , as is conventional. Conductive vias (also not illustrated) electrically couple the conductive layers one to the other as needed or desired. In practice, the vias act as a shield for lateral electromagnetic emissions from the electronic module  10 . However, a top surface  18  of the electronic module  10  is not protected by the vias and thus allows electromagnetic emissions to escape from the electronic module  10 . While the contacts  14  are illustrated as pins, it should be appreciated that the electronic module  10  may also use a land or ball grid array as the contact points for the electronic module  10 . For an example of a ball grid array, see  FIGS. 7 and 9 . The thin nature of the land grid array makes it well suited for certain applications, but makes the illustration of the contacts  14  difficult. However, land grid array contacts are well understood in the art and a further illustration thereof is not specifically required to understand the invention. 
   The present invention provides a technique to shield electronic modules. An electronic module  20 , as illustrated in  FIG. 2 , has been manufactured according to an exemplary embodiment of the present invention. The electronic module  20  has a peripheral edge  22 . A conductive element  24  is positioned around the periphery of the electronic module  20  proximate the peripheral edge  22 . In an exemplary embodiment, the conductive element  24  is formed on one of the conductive layers within the electronic module  20  and is electrically grounded as better explained below. As used herein, the term “periphery” is defined to be the outermost part or region within a precise boundary, in particular, the boundary formed by the peripheral edge  22 . While the conductive element  24  is illustrated as a line in  FIG. 2 , it should be appreciated that the conductive element  24  has some width and may extend laterally from a point inside the peripheral edge  22  all the way to the peripheral edge  22  if needed or desired (see  FIGS. 5 ,  7  and  9 ). 
   As further illustrated, the electronic module  20  has a plurality of contacts  26  proximate the peripheral edge  22  of the electronic module  20 . The plurality of contacts  26  allows electrical connection to one or more electronic components  28  within the electronic module  20 . Electronic components  28  may include, but are not limited to: Analog to Digital Converters (ADC), Digital to Analog converters (DAC), low pass filters (LPF), filters, voltage controlled oscillators (VCO), multiplexers, and other electronic components as needed or desired based on the function of the electronic module  20 . In an exemplary embodiment, all the electronic components  28  are positioned inside the boundary formed by the conductive element  24 . The particular electronic components  28  illustrated in  FIG. 2  correspond to the components within the RF6001 discussed above. For a more detailed explanation of the electronic components  28 , reference is made to the previously incorporated data sheet. However, as is readily understood, the precise electronic components  28  and their precise arrangement are not material to the present invention. 
   It should be appreciated that during the manufacturing of the electronic module  20 , the conductive element  24  is encased within the molding material of the electronic module  20 . The molding material may be a plastic dielectric material or the like, as is conventional. 
     FIG. 3  illustrates a plurality of electronic metamodules  30  ready to be used in the methodology of the present invention. In particular, the plurality of electronic metamodules  30  is formed from a plurality of electronic modules  20  within a single molding body  32 . The molding bodies  32  are positioned on a strip of laminate  34 . The strip of laminate  34  may include apertures  36  (sometimes called fiducials) that may assist in aligning the strip of laminate  34  for the following steps. 
     FIG. 4  illustrates the electronic metamodules  30  after the sub-dicing step of the present invention. In particular, each metamodule  30  has been cut such that each of the electronic modules  20  is distinct from one another. The sub-dicing step cuts into each electronic module  20  to expose the conductive element  24 , but does not cut through the strip of laminate  34 . While not shown, it should be appreciated that dicing tape is positioned on the bottom side of the strip of laminate  34 , and may be left in place during the process that follows. Dicing tape is a well known tape that is designed to hold diced components together during submersion in fluids and other processing steps. Exemplary dicing tape is sold by AI Technology Inc. of 70 Washington Road, Princeton Junction, N.J. 08550. 
     FIG. 5  illustrates a top plan view of part of an electronic metamodule  30  after subdicing, but before singulation. As is readily apparent, the conductive element  24  is exposed around the periphery of each electronic module  20 . Dotted lines  38  represent the cuts made in a singulation process. The singulation process effectively turns the dotted lines  38  into peripheral edges  22  ( FIG. 2 ) of the electronic modules  20 . 
     FIG. 6  illustrates a first exemplary embodiment of the methodology of the present invention. In particular, an electronic metamodule  30  is manufactured, wherein each electronic module  20  within the electronic metamodule  30  has its own conductive element  24  around the periphery of the respective electronic module  20  (block  100 ). A blade is used to sub-dice each electronic module  20  (block  102 ) within the electronic metamodule  30 . In an exemplary embodiment, the blade is 31 mil (.0787 cm) thick. The sub-dicing step of block  104  exposes the conductive element  24  within the electronic module  20  (see also  FIG. 5 ). As used herein, a “sub-dice” is defined as a cut that does not cut all the way through the element being cut. Thus, “sub-dicing” is cutting an element in such a manner that the cut does not extend all the way through the element being cut. After sub-dicing, the top surface of the electronic metamodule  30  is roughened (block  104 ). This roughening may be done through an abrasion process, a desmear technique, or other process as needed or desired. 
   After roughening, an electroless plating process is performed to deposit a seed layer  40  ( FIG. 7 ) of a conductive material on the electronic module  20  (block  106 ). In an exemplary embodiment, the seed layer  40  of conductive material is copper (Cu), although other conductive materials such as aluminum (Al), silver (Ag), gold (Au), or other conductive material could be used if needed or desired. An electroless plating process is defined herein to be a chemical deposition of metal instead of electrodeposition. 
   An exemplary electroless plating process of Cu on a dielectric substrate requires the prior deposition of a catalyst such as a palladium-tin (Pd-Sn) colloid consisting of a metallic Pd core surrounded by a stabilizing layer of Sn ions. The activation step (deposition of the colloid) is usually followed by an acceleration step (removal of excess ionic tin). Adhesion of the deposit to the substrate is improved by mechanical and chemical pretreatment steps. Other electroless plating processes could also be used and are considered within the scope of the present invention. 
   After the seed layer  40  of conductive material is created on the electronic module  20 , an electrolytic plating process is performed to deposit a second layer  42  ( FIG. 7 ) of conductive material on the electronic module  20  (block  108 ). In an exemplary embodiment, the second layer  42  of conductive material may be Cu, Al, Ag, Au, or other material as needed or desired. It should be appreciated that the conductive element  24  is electrically coupled to the seed layer  40 , and the seed layer  40  then carries the current for the electrolytic plating process. 
   After the second layer  42  is generated, a third layer  44  ( FIG. 7 ) is created on the electronic module  20  through a second electrolytic plating process (block  110 ). The third layer  44  is comparatively a poor conductor, and may be a layer of low stress nickel (Ni) or the like. Nickel serves to protect the conductive layers so that they do not tarnish or otherwise suffer from environmental effects. Likewise, nickel may contribute to the shielding function by absorbing electromagnetic radiation. In an exemplary embodiment, the seed layer  40 , the second layer  42 , and the third layer  44  form a sandwich of shielding material approximately 20 μm thick. This sandwich is labeled shield  46  ( FIG. 7 ). Greater or lesser thicknesses may also be generated. The shield  46  may be positioned on a top surface  48  of the electronic module  20 . Additionally, while not specifically illustrated, the shield  46  may be formed on side surfaces  50  of the electronic module  20 . Alternatively, vias  58  may form an interior shield for the side surfaces  50  of the electronic module  20 . At least one via  58  electrically couples the conductive element  24  to a ground plane  60  within the electronic module so that the conductive element  24  and the shield  46  are electrically gournded. 
   After the second electrolytic plating process of block  110 , each electronic module  20  is singulated (block  112 ). As used herein, the term “singulation” is defined to be the process wherein the individual electronic modules are separated one from the other such that each module is a single module. Finally, the mask on the underside of the strip of laminate  34  may be removed from an input/output side  52  ( FIG. 7 ) of the electronic module  20  (block  114 ). It should be appreciated that some steps may be rearranged in the present process. For example, the mask may be removed prior to singulation. Likewise, if a layer  40 ,  42 , or  44  is too thick, the layer may be ground down to a desired thickness. The end result of this embodiment is the electronic module  20  as illustrated in  FIG. 7 . 
     FIG. 8  illustrates a second embodiment of the methodology of the present invention. The second embodiment starts in a manner similar to the first embodiment, wherein the electronic metamodule  30  is manufactured, with each electronic module  20  within the electronic metamodule  30  having its own conductive element  24  around the periphery of the respective electronic module  20  (block  100 ). A blade is used to sub-dice each electronic module  20  (block  102 ). In an exemplary embodiment, the blade is 31 mil (.0787 cm) thick. The sub-dicing step of block  104  exposes the conductive element  24  within the electronic module  20 . After sub-dicing, the top surface of the electronic metamodule  30  is roughened (block  104 ). This roughening may be done through an abrasion process, a desmear technique, or other process as needed or desired. 
   After roughening, a conductive fleck filled epoxy is sprayed on each of the electronic modules  20  (block  150 ). In an exemplary embodiment, the conductive fleck filled epoxy is CHO-SHIELD 610 sold by Chomerics of 77 Dragon Court, Woburn, Mass. 01801. More information can be found in the datasheet for CHO-SHIELD 610 available online at http://vendor.parker.com/Groups/Seal/Divisions/Chomerics/Chomerics %20Product %20Libra ry.nsf/24eb4985905ece34852569580074557a/d93045d8cf22cc0f85256bd700509031/$FILE/pg140_choshield_conductive_coatings.pdf, which is hereby incorporated by reference in its entirety, and a copy of which is included in the Information Disclosure Statement filed concurrently with the present application. The conductive flecks of the conductive fleck filled epoxy may be Cu, Ag, a mixture of Cu and Ag, a tin/zinc (Sn/Zn) alloy, or other conductive material as needed or desired. 
   After application of the conductive fleck filled epoxy, each electronic module  20  is singulated (block  152 ), and the mask is removed from the input/output side  52  of the electronic module  20  (block  154 ). Again, it should be appreciated that the mask may be removed before singulation if needed or desired. Likewise, while CHO-SHIELD  610  has an epoxy to carry the conductive flecks, other materials such as polyurethane, acrylic, urethane, or the like could be the vector in which the conductive flecks are carried. 
   An electronic module  20  made according to the process of  FIG. 8  is illustrated in  FIG. 9 . A layer of fleck vector  54  is disposed on the top surface  48  of the electronic module  20 . Conductive flecks  56  “float” within the fleck vector  54  and form a barrier that stops electromagnetic emissions. Additionally, while not specifically illustrated, the fleck vector  54  may be sprayed on the side surfaces  50  of the electronic module  20 . Alternatively, the vias mentioned above may form an interior shield (not shown) for the side surfaces  50  of the electronic module  20 . 
   Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.