Abstract:
One or more embodiments are directed to encapsulating structure comprising: a substrate having a first surface and housing at least one conductive pad, which extends facing the first surface and is configured for being electrically coupled to a conduction terminal at a reference voltage; a cover member, set at a distance from and facing the first surface of the substrate; and housing walls, which extend between the substrate and the cover member. The substrate, the cover member, and the housing walls define a cavity, which is internal to the encapsulating structure and houses the conductive pad. Moreover present inside the cavity is at least one electrically conductive structure, which extends between, and in electrical contact with, the cover member and the conductive pad for connecting the cover member electrically to the conduction terminal.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a shielded encapsulating structure (or package) and to a manufacturing method thereof, and in particular to an encapsulating structure for a MEMS microphone. 
         [0003]    2. Description of the Related Art 
         [0004]    The package of microelectromechanical systems (MEMS), such as, for example, microphones and pressure sensors, provides an electrical shielding between the region of space inside the package itself and the external environment in which the package is set. Said shielding has the function of eliminating, or at least reducing, any possible drifts in the signal of the sensor caused by interference due to electrostatic charges, for example generated by magnetic fields external to the package. Basically, said package operates according to the known principle of the Faraday cage. 
         [0005]    In addition, the package also performs a function of mechanical protection of the sensor, albeit providing, if necessary, a certain degree of accessibility to the sensor from outside. 
         [0006]    The electrical shielding can be obtained with different types of package. 
         [0007]    According to an embodiment of a known type, a substrate faces an internal cavity of the package, and is insulated at the top by means of a planar cap. The internal cavity houses one or more devices, formed on the substrate. In this case, the devices housed in the internal cavity of the package are insulated from the environment external to the package by means of: the substrate; side walls, which extend starting from the substrate in a direction orthogonal to the plane in which the substrate itself lies; and the cap, coupled to the side walls in such a way as to face the substrate and the internal cavity of the package. The internal cavity thus formed is insulated from the environment external to the package. The substrate includes a ground plane, generally made of metal, for example copper. The substrate can moreover be coupled to an integrated-circuit board. Said coupling is obtained, for example, according to the standard technology of manufacturing of a substrate referred to as “ball-grid array” (BGA). In this case, conductive bumps are formed in an area corresponding to the surface of the substrate and are connected to the metal layer by means of conductive vias. Other types of substrate and/or coupling can be used. For example, as an alternative to the use of conductive bumps, it is possible to use conductive pads (or leads) coupled to one another by welding paste. Also in this case, the conductive pads are formed in an area corresponding to the surface of the substrate and connected to the metal layer by means of conductive vias. 
         [0008]    The cap comprises a metal layer, having the function of electrical shielding between the region of space external to the package and the internal space. 
         [0009]    The side walls are glued on the substrate using non-conductive glues or insulating adhesive tape. 
         [0010]    To complete formation of a Faraday cage, the metal layer of the cap is electrically connected to the ground plane of the substrate by means of conductive through vias (for example, filled with resin with conductive filler material), formed on the inside of the side walls. There is thus formed a conductive path between the metal of the cap and the ground plane through the side walls, thus obtaining a Faraday cage. 
         [0011]      FIG. 1  shows a package of the type described previously, comprising: an integrated-circuit board  1 ; a substrate  2 , coupled to the integrated-circuit board  1  by means of a ball-grid array  4  or by means of conductive pads coupled to the integrated-circuit board  1  with welding paste; side walls  6 , coupled to the substrate  2  by means of a non-conductive adhesive layer  8 ; and a cap  10 , coupled to the side walls  6  by means of a further non-conductive adhesive layer  12 . The cap  10 , the side walls  6 , and the substrate  2  define a cavity  14  internal to the package. In addition, the cap  10  comprises, in an area corresponding to the side directly facing the cavity  14 , a metal layer  16 . Formed on the inside of the side walls  6  are conductive through vias  18 , for example filled with resin with conductive filler material, which are adapted to connect the metal layer  16  with a ground plane GND (illustrated schematically), via the ball-grid array  4 . The conductive through vias  18  connect the ground plane GND to the metal layer  16 . Generic devices and/or sensors  19  are housed in the cavity  14 . 
         [0012]    The embodiment of  FIG. 1  has, however, a relatively high manufacturing cost, due to the need to form the through vias. In addition, the presence of the through vias themselves within the side walls  6  imposes a constraint on the minimum dimensions of the side walls  6 , which must have a thickness sufficient to enable formation of the through vias  18 , at the same time guaranteeing structural solidity of the package. For these reasons, moreover, the through vias  18  are formed at a certain distance from one another, leaving portions of the side walls  6  not electrically shielded. The Faraday cage is consequently not complete. 
         [0013]    Further embodiments of a known type (not shown in the figure) comprise a package in which the substrate is coupled to a cap that has a recess. Said recess forms, when the cap is coupled to the substrate, the internal cavity of the package. Side walls  6  of the type shown in  FIG. 1  are consequently not necessary in so far as the cap is directly coupled to the substrate. The cap comprises a metal layer formed on the inside of the recess (on the bottom and on the side walls of the recess) and in an area corresponding to the regions of coupling with the substrate. When the cap is coupled to the substrate, there is no need to form through vias of the type described with reference to  FIG. 1  in so far as the walls that define the internal cavity of the package laterally are already metallized. The electrical contact between the cap and the ground plane occurs by means of the metal formed in an area corresponding to the regions that are coupled to the substrate. The substrate has, for this purpose, conductive pads for coupling with the metal of the cap. The Faraday cage that is thus formed is, consequently, complete. 
         [0014]    This further embodiment presents, however, the disadvantage of requiring a machined cap (comprising a recess), which has a cost higher than the cost of a planar cap (for example, of the type shown in  FIG. 1 ). In particular, the cost is typically highest in the case of packages for hermetically sealed pressure sensors, which require caps with a particular shielding of the measurement vias. In addition, due to manufacturing reasons, the depth of the recess is limited, and thus the maximum height (measured along an axis orthogonal to the plane of lie of the substrate) of the internal cavity of the package obtained is consequently limited. This embodiment is consequently suitable for MEMS sensors that require a relatively reduced height of the cavity, for example MEMS microphones in which the volume underlying the membrane of the microphone is smaller than the volume surrounding the sensor itself. 
       BRIEF SUMMARY 
       [0015]    One or more embodiments of the present disclosure are directed to a shielded encapsulating structure and a manufacturing method thereof that will be able to overcome the drawbacks of the known art. 
         [0016]    According to the present disclosure a shielded encapsulating structure and a manufacturing method thereof are provided, as defined in the annexed claims. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    For a better understanding of the present disclosure, preferred embodiments thereof are now described, purely by way of non-limiting example and with reference to the attached drawings, wherein: 
           [0018]      FIG. 1  shows, in cross section, an encapsulating structure (or package) of a shielded type according to an embodiment of a known type; 
           [0019]      FIGS. 2   a  and  2   b  show, respectively in cross section and in top plan view, an encapsulating structure according to an embodiment of the present disclosure; 
           [0020]      FIG. 3  shows, in cross section, an encapsulating structure according to a further embodiment of the present disclosure; 
           [0021]      FIGS. 4   a  and  4   b  show in top plan view and in cross section, respectively, an encapsulating structure according to a further embodiment of the present disclosure; 
           [0022]      FIGS. 5   a  and  5   b  show in top plan view and in cross section, respectively, an encapsulating structure according to a further embodiment of the present disclosure; 
           [0023]      FIGS. 6   a  and  6   b  show in cross section and in top plan view, respectively, an encapsulating structure according to a further embodiment of the present disclosure; 
           [0024]      FIG. 7  shows, in cross section, an encapsulating structure according to a further embodiment of the present disclosure; 
           [0025]      FIGS. 8-13  show, in perspective view, steps of production of the encapsulating structure according to the embodiment of  FIGS. 2   a  and  2   b ; and 
           [0026]      FIG. 14  shows an encapsulating structure formed according to one of the embodiments of the present disclosure housing a MEMS microphone. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 2   a  shows, in cross-sectional view along a line of section II-II of  FIG. 2   b , an encapsulating structure, or package  20  according to one embodiment of the present disclosure.  FIG. 2   b  shows the package  20  of  FIG. 2   a  in top plan view. 
         [0028]    The package  20  comprises a substrate  21  (lying in a plane XZ), comprising one or more metal layers  22  (only one of which is shown by way of example in  FIG. 2   a ), which extend on the inside of the substrate  21  or in areas corresponding to surface regions of the substrate  21 . 
         [0029]    One of said metal layers  22  extends throughout the extension of the substrate  21 , and is connected to a ground plane GND of the package  20 . According to one embodiment, in order to form a complete shield, the metal layer  22  extends throughout the extension of the substrate  21 . Other embodiments, in which the metal layer  22  extends only partially in the substrate  21  are, however, possible. 
         [0030]    The substrate  21  moreover houses one or more electrical and/or electronic and/or MEMS devices and/or components, such as ASIC  40  and MEMS  41  as illustrated in  FIG. 2   b  but not illustrated in  FIG. 2   a  to more clearly show further aspects of the package  20 . The manufacturing process of said electrical and/or electronic and/or MEMS devices and/or components are known. In particular, the substrate  21  houses an electronic or microelectromechanical device, operation of which can be adversely affected by the presence of magnetic fields or electrostatic charges coming from the environment external to the package  20 . In particular, said device may be a MEMS microphone. 
         [0031]    The substrate  21  is, for example, made of plastic or ceramic material, or FR-4 (fibreglass), or a flexible material adapted to form a substrate of a flexible-printed-circuit (FPC) type. The ground plane GND is, for example, the ground plane of a printed circuit board (PCB) to which the substrate  21  is connected via metal bumps or conductive paste coupled to respective conductive pads, in a way similar to what has already been shown and described with reference to  FIG. 1 . Other materials that can be used for the substrate  21 , and, in general, any structure adapted to carry electrical elements (electronic devices, components, etc.) can be used to form the substrate  21 . 
         [0032]    The package  20  comprises an internal cavity  32 , adapted to house the electrical and/or electronic and/or MEMS devices and/or components. The internal cavity  32  is delimited at the bottom by the substrate  21  and laterally (along planes XY orthogonal to the plane XZ) by walls  24 . 
         [0033]    The substrate  21  has a surface  21   a  and a surface  21   b , opposite to one another. The side walls  24  rest on the surface  21   a  of the substrate  21  (with a coupling interface) and extend vertically in a direction Y orthogonal to the plane XZ, proceeding away from the substrate  21  along the axis Y. As may be noted from  FIG. 2   b , according to one embodiment, the substrate  21  has a quadrangular shape (for example, in  FIG. 2   b  it is shown as having a rectangular shape), and the walls  24  extend throughout the length of the four sides of the substrate  21 , surrounding the internal cavity  32  laterally. 
         [0034]    The side walls  24  are, for example, made of BT (bismaldehyde-trizaine) resin reinforced with fibreglass, plastic, or metals such as aluminium, copper, etc. 
         [0035]    The side walls  24  are coupled to the surface  21   a  of the substrate  21  in such a way as to be fixed with respect to the substrate  21 . The coupling interface between the side walls  24  and the substrate  21  comprises a first coupling region  26  of non-conductive glue or non-conductive biadhesive tape. 
         [0036]    The side walls  24  are moreover coupled to a cap  28 , which extends in a plane substantially parallel to the plane XZ, at a distance from substrate  21 . The cap  28  comprises, according to one embodiment of the present disclosure, a conductive layer  31 , made, for example, of metal such as aluminium or copper or the like, which extends in an area corresponding to a side  28   a  of the cap  28 . The remaining portion of the cap  28  may, for example, be made of plastic material, or fibreglass, or some other material chosen according to the needs. The side  28   a  of the cap  28  is the side that, at the end of the steps of manufacture of the package  20 , directly faces the surface  21   a  of the substrate  21 . 
         [0037]    The cap  28  can comprise (in a way not shown in the figure), one or more through vias, which are adapted to ensure accessibility from the outside of the package towards the internal cavity  32  (see, for example,  FIG. 14  for an embodiment provided by way of non-limiting example of use of a package comprising a perforated cap). 
         [0038]    The side walls  24  are coupled to the side  28   a  of the cap  28  by means of a second coupling region  30 , for example made of non-conductive glue or non-conductive biadhesive tape, or conductive glue or biadhesive conductive tape. 
         [0039]    In this way, the side walls  24  extend between the substrate  21  (in particular, the surface  21   a  of the substrate  21 ) and the cap  28  (in particular, the side  28   a  of the cap  28 ), and maintain the cap  28  in position above the substrate  21 . There is thus formed the internal cavity  32 , delimited by the substrate  21 , by the side walls  24 , and by the cap  28 . The side  28   a  of the cap  28  and the surface  21   a  of the substrate  21  directly face the internal cavity  32 . 
         [0040]    The internal cavity  32  has a height k, measured in the direction of the axis Y between the surface  21   a  of the substrate  21  and the side  28   a  of the cap  28 , given by the sum of the thickness (measured in the direction Y) of the first coupling region  26 , of the side walls  24 , and of the second coupling region  30 . 
         [0041]    As may be seen in  FIG. 2   b , the internal cavity  32  is adapted to house one or more electronic circuits (for example electronic circuits such as microcontrollers or ASICs) and/or electromechanical circuits (for example, microelectromechanical sensors such as microphones produced using MEMS technology), and/or chips, housing in turn electronic circuits, mounted on the substrate  21  in a region corresponding to the surface  21   a . The electronic circuits, and/or the electromechanical circuits, and/or the chips can be electrically connected together by means of conductive wires, obtained with known wire-bonding techniques. The internal cavity  32  can, in general, house any type of electrical, electronic, mechanical, microelectromechanical component and/or device, or components and/or devices of some other type. 
         [0042]    In order to guarantee an electrical connection between the ground plane GND and the cap  28  (in particular, the conductive layer  31  of the cap  28 ), the package  20  further comprises conductive columnar elements  34 , which extend between the substrate  21  and the cap  28 , on the inside of the cavity  32 , to connect the substrate  21  electrically with the cap  28 . For this purpose, the substrate  21  further comprises a plurality of conductive pads  36 , formed in an area corresponding to the surface  21   a  and adapted to define a conductive region for the electrical contact with respective conductive columnar elements  34 . In turn, the conductive pads  36  are in electrical connection with the metal layer  22 , and hence with the ground plane GND, by means of conductive vias  38 . In this way, the cap  28  is in electrical connection with the ground plane GND via the conductive columnar elements  34 . 
         [0043]    The conductive columnar elements  34  have a height h (measured in the direction of the axis Y) given by the sum of the thickness (once again measured in the direction Y) of the first coupling region  26 , of the side walls  24 , and of the second coupling region  30 , minus the possible thickness of the conductive pad  36  above the surface  21   a  of the substrate  21 , in the case where the conductive pad  36  projects beyond the surface  21   a.    
         [0044]    The conductive columnar elements  34  may be or include electrically conductive glue, for example a glue (or resin) with epoxy base comprising silver or some other electrically conductive material. 
         [0045]    The type of glue to be used is chosen case by case, according to the needs. For example, to form conductive columnar elements  34  with a high ratio between the base area and the height (high aspect ratio), in particular having a height h comprised between 0.3 mm and 0.8 mm, it may be desired to use a glue with high viscosity, for example with a value of viscosity of 30,000 centipoise (cps) (30,000 millipascal-second (mPa·s)) or more. 
         [0046]    Instead, to form conductive columnar elements  34  having a low value of aspect ratio, in particular having a height h lower than 0.3 mm, it is possible to use a glue with a viscosity lower than the previous case. 
         [0047]    In any case, the viscosity of the glue is such as to enable formation of conductive columnar elements  34 , the base area of which is entirely contained within the respective pad  36 . Each pad  36  has a quadrangular shape, typically square, with base side may be between 0.3 mm and 1 mm. It is evident that, if necessary, the values indicated can vary; for example, the pads  36  may have a base side greater than 1 mm and a different shape from the square one. 
         [0048]    According to one embodiment of the present disclosure, the conductive columnar elements  34  are formed in direct contact with the side walls  24 . However, according to other embodiments (not shown), the conductive columnar elements  34  can be formed at a distance from the side walls  24 . 
         [0049]    As may be noted from  FIG. 2   b , the substrate  21  and the cap  28  have a substantially quadrangular shape (but any other geometrical shape is possible). The internal cavity  32  houses, for example, an ASIC  40  and a MEMS sensor  41  (for example, a microphone). The side walls  24  extend in a peripheral area of the substrate  21 , surrounding and defining the internal cavity  32 . 
         [0050]      FIG. 2   b  shows four conductive pads  36 . However, the number of conductive pads can be different from four (greater or smaller). Also the number of conductive columnar elements  34  may be different from four (greater or smaller). 
         [0051]      FIG. 3  shows a further embodiment of the present disclosure.  FIG. 3  shows, in cross-sectional view, a package  45  similar to the package  20  of  FIGS. 2   a  and  2   b . The package  45  differs from the package  20  in that the package  45  comprises a cap  46  similar to the cap  28  of the package  20 , but without the conductive layer  31 . Instead, the cap  46  is itself made of conductive material, for example metal, such as aluminium, copper, stainless steel, or the like. 
         [0052]    Other elements of the package  45  that are in common with the package  20  of  FIGS. 2   a  and  2   b  are designated by the same reference numbers and are not described any further here, for reasons of brevity. 
         [0053]      FIG. 4   a  shows, in top plan view, a package  50  according to a further embodiment of the present disclosure. 
         [0054]      FIG. 4   b  shows a cross-sectional view of the package  50  along the line of section IV-IV of  FIG. 4   a.    
         [0055]    Elements of the package  20  of  FIGS. 2   a  and  2   b  that are in common with those of the package  50  of  FIGS. 4   a  and  4   b  are identified by the same reference numbers and are not described any further, for reasons of brevity. 
         [0056]    The package  50  differs from the package  20  in that it does not comprise the plurality of conductive columnar elements  34 . Instead, the package  50  comprises a conductive structure  52 , which extends in a continuous way along the side walls  24 , on the inside of the cavity  32 . The conductive structure  52  extends in contact with the side walls  24 , between the substrate  21  and the cap  28 . The conductive structure  52  is in direct electrical contact with the conductive pads  36  and, via the latter and the vias  38 , with the ground plane GND. 
         [0057]    With joint reference to  FIGS. 4   a  and  4   b , the conductive structure  52  has a height h′ (measured in the direction of the axis Y) equal to the height h of the conductive columnar elements  34 , and in any case such as to form an electrical contact between the cap  28  and the conductive pads  36 . The conductive structure  52  substantially has a height h′ given by the sum of the thickness, measured in the direction Y, of the first coupling region  26 , of the side walls  24 , and of the second coupling region  30 , minus the possible thickness (above the surface  21   a  of the substrate  21 ) of the conductive pad  36  in the regions in which the latter are present. 
         [0058]    The conductive structure  52  extends moreover starting from the side walls  24  towards the inside of the cavity  32 , parallel to the plane XY (on top of and in contact with the surface  21   a ). The extension of the conductive structure  52  from the side walls  24  towards the inside of the cavity  32  defines the thickness b of the conductive structure. According to one embodiment, the thickness b is such that, in an area corresponding to the conductive pads  36 , the conductive structure  52  remains confined within the base area of the conductive pads  36 . The thickness b is moreover substantially uniform throughout the extension of the conductive structure  52 . For example, b is may be between h/2 and h. 
         [0059]    It is evident that, according to alternative embodiments, or on account of imprecision during dispensing of the glue, the thickness b may not be uniform throughout the extension of the conductive structure  52 , and/or exceed the sides that define the base area of the conductive pads  36 . However, in this case, there is a corresponding reduction of the usable volume of the internal cavity  32 . 
         [0060]    The conductive structure  52  is a layer of electrically conductive glue, in particular of the same type as the one described with reference to  FIGS. 2   a ,  2   b  for the package  20 . The same considerations made above apply here as regards the choice of the viscosity of the glue, which depends upon the specific application and upon the height h′ of the conductive structure  52  that is to be obtained. 
         [0061]    The embodiment of  FIGS. 4   a ,  4   b  presents the advantage of enabling formation of a complete Faraday cage in so far as the internal cavity  32  is completely shielded with respect to the environment external to the package  50 . However, the volume of the internal cavity  32  is reduced with respect to the embodiment of  FIGS. 2   a ,  2   b.    
         [0062]    According to a further embodiment (not shown in the figure), the package  50  comprises a cap  46  of the type described with reference to  FIG. 3 . 
         [0063]      FIGS. 5   a  and  5   b  show a package  60  in lateral section and in top plan view, respectively, of a further embodiment of the present disclosure. 
         [0064]      FIG. 5   a  is a view along the line of section V-V of  FIG. 5   b . Elements of the package  60  that are common to the package  20  of  FIGS. 2   a ,  2   b  and/or to the package  50  of  FIGS. 4   a ,  4   b  are designated by the same reference numbers and are not described any further. 
         [0065]    According to the embodiment of the package  60 , the electrical contact between the cap (which may be indifferently of the type shown in  FIG. 2   a  or of the type shown in  FIG. 3 ) and the ground plane GND is obtained by means of a conductive structure  62  that extends in an area corresponding to a portion of the side walls  24 , on the inside of the cavity  32 , leaving the remaining portion of the side walls  24  exposed. Unlike what is shown in  FIGS. 4   a  and  4   b , the conductive structure  62  does not cover completely the side walls  24  within the cavity  32 , but coats them only partially. The advantage, in this case, lies in the possibility of obtaining an internal cavity  32  of oversized volume with respect to the embodiment of  FIG. 4   a , at the expense of a non-complete electrical shielding. 
         [0066]    The conductive structure  62  may be or include conductive glue of the same type as the one described with reference to the embodiments of  FIGS. 2   a ,  2   b  and  4   a ,  4   b.    
         [0067]      FIGS. 6   a  and  6   b  show a further embodiment of a package  70 , in which the surface of the substrate  21  has one or more deep regions (or recesses)  71 , which extend to a height, measured along the axis Y, may be between the height at which the surface  21   a  extends and the height at which the surface  21   b  extends. A substrate that has a deep region  71  can be used for housing chips of electronic circuits and chips of MEMS devices set on top of one another, each at a respective height. 
         [0068]      FIG. 6   a  is a cross-sectional view of  FIG. 6   b , along the line of section VI-VI of  FIG. 6   b .  FIGS. 6   a  and  6   b  show a single deep region  71 . The deep region  71  has a substantially quadrangular shape (but any other shape is possible), and is laterally delimited by walls  72 . The deep region  71  comprises one or more conductive pads  74  (just one is shown in the figure), connected, through a conductive via  75 , to the metal layer  22 , and hence to the ground plane GND. 
         [0069]    In this case, the electrically conductive connection between the cap  28  (but what has been described here applies also with reference to a cap  46  of the type of  FIG. 3 ) and the ground plane GND is obtained through a first conductive structure  76  and a second conductive structure  78 . The first conductive structure  76  is similar to the conductive structure  62  described with reference to  FIGS. 5   a  and  5   b ; the second conductive structure  78  extends along a portion of the walls  72 , overlapping the first conductive structure  76  so as to be in direct contact with the first conductive structure  76  and with the conductive pad  74 . 
         [0070]    The first and second conductive structures  76 ,  78  may be or include electrically conductive glue, of the type described previously, with reference to the embodiments of  FIGS. 2   a ,  2   b ,  4   a ,  4   b ,  5   a ,  5   b.    
         [0071]    There is thus obtained an electrical connection between the cap  28  and the ground plane GND, through the first and second conductive structures  76 ,  78 . 
         [0072]      FIG. 7  shows, in lateral section, a package  80  according to a further embodiment. 
         [0073]    Elements of the package  80  that are in common with elements of the package  20  are designated by the same reference numbers and are not described any further. 
         [0074]    The package  80  comprises, unlike the package  20 , side walls  24  coated by a conductive layer  81 , for example made of conductive metal material, in particular aluminium, copper, or nickel, or gold, or a metal multilayer including copper, nickel, and gold, or the like. 
         [0075]    In addition, the second coupling region  30  is of an electrically conductive type, obtained by means of a conductive glue, or a conductive adhesive tape, or the like. 
         [0076]    The package  80  further comprises an electrical-connection structure  84 , which extends starting from each towards the side walls  24 , in direct electrical contact with the respective conductive pad  36  and with the conductive layer  81 . The electrical-connection structure  84  may be or include electrically conductive glue, of the same type as the one described with reference to the previous embodiments (see, for example, what has been described with reference to  FIGS. 2   a  and  2   b ). However, since the conductive layer  81  is in electrical connection with the cap  28  via the second coupling region  30 , the conductive glue that forms the electrical-connection structure  84  does not necessarily have to contact directly the cap  28 . It is, instead, sufficient for the electrical-connection structure  84  to be in contact with the conductive layer  81 . In this way, since the conductive layer  81  is in electrical contact with the cap  28 , there is formed an electrical connection between the cap  28  and the ground plane GND through the second coupling region  30 , the conductive layer  81 , the electrical-connection structure  84 , the conductive pad  36 , the conductive via  38 , and the metal layer  22 . 
         [0077]    The second coupling region  30  is formed, for example, using the same conductive glue as the one used to form the electrical-connection structure  84 . 
         [0078]    It is evident that variations may be made to the embodiment described for the package  80 . For example, the cap may be of the type shown in  FIG. 3  and described with reference to said figure. In addition, the electrical-connection structure  84  can be of a columnar type ( FIGS. 2   a ,  2   b ), or extend throughout the extension of the side walls  24  (in a way similar to what is shown in  FIGS. 4   a  and  4   b ) in electrical contact with the conductive layer  81 . Alternatively, the electrical-connection structure  84  extends for a limited portion of the side walls  24  (in a way similar to what is shown in  FIGS. 6   a  and  6   b ). Finally, there may be present a plurality of electrical-connection structures made of conductive glue, which extend at different heights from one another, in the case where the substrate  21  presents deep regions of the type shown in  FIGS. 6   a  and  6   b . In any case, irrespective of the embodiment, the conductive glue is in electrical contact with the conductive layer  81 , and a direct contact between the conductive glue and the cap is not necessary. 
         [0079]    With reference to  FIGS. 8-13  a method for manufacturing an encapsulating structure, or package, according to the present disclosure is now described. 
         [0080]    Referring to  FIG. 8 , a substrate  21  is provided, for example, made of plastic or ceramic material, or FR-4 (fibreglass), or flexible material adapted to form a substrate of a flexible-printed-circuit (FPC) type. The substrate  21  is of a previously machined type, and comprises, for example, the ASIC  40  and the MEMS sensor  41 , housed in a region corresponding to the surface  21   a . The substrate  21  hence comprises, in a way not shown in detail, a number of layers set on top of one another made of semiconductor material, dielectric material, conductive material (in particular the metal layer  22 ). The substrate  21  further comprises the conductive via  38  and the conductive pads  36 , formed in a known way. 
         [0081]    According to one embodiment, the substrate  21  is of a ball-grid-array (BGA) type, of a known type as shown for example in  FIG. 1 . In this case, conductive bumps are formed in an area corresponding to the surface  21   b  of the substrate  21  and connected to the metal layer  22  by means of conductive vias. Other types of substrate and/or connections may be used, for example, employing a conductive paste for coupling conductive pads together. 
         [0082]    As shown in  FIGS. 9   a  and  9   b , the walls  24  are formed. The walls  24  are formed by means of a milling method, in which a cutting tip is moved on a block of solid material for removing portions of the block of solid material in order to obtain a certain desired structure. In this case, the material is BT (bismaldehyde-trizaine) resin, reinforced with fibreglass. 
         [0083]      FIG. 9   a  shows a block  100 , in which scribe lines  101  are shown with a dashed line. The cutting tip is moved along the scribe lines  101  to cut into the block  100  throughout its depth. The portions  100   a  and  100   b  are removed ( FIG. 9   b ) to obtain a wall structure  103  having a quadrangular shape, which has an opening  102 . 
         [0084]    Referring to  FIG. 10 , a first adhesive layer  104  and a second adhesive layer  105  are formed on mutually opposite sides  103   a ,  103   b  of the wall structure  103 , and in particular on the sides  103   a ,  103   b , which are, in subsequent steps, coupled to the substrate  21  and to the cap  28 . The step of forming the first and second adhesive layers  104 ,  105  comprises, for example, applying a layer of non-conductive glue; alternatively, it comprises applying a non-conductive biadhesive tape. 
         [0085]    Referring to  FIG. 11 , the wall structure  103  is set in contact with the substrate  21  in such a way that the first adhesive layer  104  will form a coupling interface between the wall structure  103  and the surface  21   a  of the substrate  21 . When the wall structure  103  and the surface  21   a  of the substrate  21  are coupled as described and shown, the first adhesive layer  104  forms the first coupling region  26  of  FIG. 2   a . The wall structure  103  is set so as to surround the ASIC  40 , the MEMS sensor  41 , and the conductive pads  36 . The wall structure  103 , when it is set on the substrate as described and shown, forms the side walls  24  described with reference to  FIGS. 2   a ,  2   b.    
         [0086]    Referring to  FIG. 12 , the conductive columnar elements  34  for dispensing the conductive glue, of a type chosen as already described with reference to  FIGS. 2   a ,  2   b , are formed. The conductive glue is dispensed, for example, by means of jet dispensing systems of a known type and widely used in micromachining of integrated circuits and packages. 
         [0087]    The conductive glue is dispensed in areas corresponding to the conductive pads  36 , until a height, along the axis Y, is reached greater than the height k, measured along the axis Y. In this way, it is ensured that the cap  28 , when set in a position above the wall structure  103 , is in contact with the conductive glue. The glue can be dispensed by means of a jet dispensing machine, of a known type, adapted to dispense drops of glue having controlled size that can possibly be set according to the need. 
         [0088]    Referring to  FIG. 13 , the conductive cap  28  is set above of the wall structure  103  in such a way as to contact the second adhesive layer  105  that functions as coupling interface between the wall structure  103  and the cap  28 . 
         [0089]    A thermal processing step in oven, at a temperature between 150° C. and 170° C., enables polymerization of the conductive glue that forms the conductive columnar elements  34 , and provides solidification and a good adhesion thereof to the cap  28  and to the conductive pads  36 . The oven for the thermal-processing step is, for example, a tunnel static or dynamic oven, or a tower oven. 
         [0090]    According to a further embodiment, the second adhesive layer  105  is made of or includes conductive glue and is formed on the wall structure  103  simultaneously with formation of the conductive columnar elements  34 . In this case, the conductive glue is dispensed in regions corresponding to the conductive pads  36  and also above the wall structure  103 , in such a way as to contact the side  28   a  of the cap  28 , thus forming the second coupling region  30 . In the case where the same conductive glue is used to form the columnar elements  34  and the second adhesive layer  105 , the thermal-processing step causes polymerization also the second adhesive layer  105  (to form the second coupling region  30 ). 
         [0091]    According to an alternative embodiment, the second coupling region  30  is formed by applying a non-conductive biadhesive tape in an area corresponding to the side  28   a  of the cap  28 , and then the cap  28  is coupled to the wall structure  103 . 
         [0092]    The manufacturing process described with reference to  FIGS. 8-13  can be applied to all the embodiments described according to the present disclosure, by simply modifying the modalities of dispensing of the conductive glue (for example, instead of forming columnar elements, it is possible to dispense the conductive glue along the entire extension of the side walls,  FIG. 4   a ; or else along a portion of the side walls,  FIG. 5   b ; or else on a number of levels in the case where the substrate  21  presents areas at different heights with respect to one another,  FIG. 6   b ; or else reducing the amount of glue dispensed in order to provide electrical contacts between conductive side walls  24  and pads  36 ,  FIG. 7 ). 
         [0093]    It is to be appreciated that the one or more of the steps of the described method may be performed sequentially, in parallel, omitted, or in an order different from the order that is illustrated. 
         [0094]      FIG. 14  shows, in cross-sectional view, a package  200  for a MEMS microphone  201 , according to the present disclosure. The package  200  is formed according to any one of the embodiments described previously, and comprises regions of conductive glue forming part of an electrical connection between the cap  28  (or cap  46 , with reference to the embodiment of  FIG. 3 ) of the package  200  and conductive pads  36  formed on the substrate  21  of the package  200 . Said regions of conductive glue can be columnar elements of the type shown in  FIG. 2   b , or strips of conductive glue of the type shown in  FIGS. 4   a ,  5   b ,  6   b , for creating a direct electrical contact between the cap  28  or  46  and the substrate  21 . Alternatively, the regions of conductive glue are extensive columnar elements or strips adapted to create an electrical contact between side walls provided with a conductive layer and the conductive pads of the substrate  21  according to what is described with reference to  FIG. 7 . 
         [0095]    The MEMS microphone  201  is formed according to known micromachining steps, for example silicon etching, in an area corresponding to the surface  21   a  of the substrate  21 . 
         [0096]    The internal cavity  32  is an acoustic cavity for the MEMS microphone  201 . Formed in an area corresponding to the surface  21   a  of the substrate  21 , an integrated circuit  202  is moreover present, connected to the MEMS microphone  201  by means of conductive wires  203 , for operating the MEMS microphone  201 . 
         [0097]    The cap  28  or  46  further comprises one or more through vias  205  (only one of which is shown in the figure) to enable the passage of acoustic signals from the environment external to the package towards the internal cavity. The through hole  205  may be formed in a location not vertically aligned (i.e., not aligned along the axis Y) with the MEMS microphone  201  so as to protect the MEMS microphone  201  from possible entry of dust or agents that might damage the MEMS microphone  201  or vitiate operation thereof. 
         [0098]    From an examination of the characteristics of the disclosure provided according to the present disclosure, the advantages that it affords are evident. 
         [0099]    The package provided according to any one of the embodiments described presents numerous advantages. The package may be hermetically sealed, and can consequently be used also in situations in which it is desired to protect the sensors housed in the internal cavity  32  from moisture or liquids. 
         [0100]    In addition, the embodiments described envisage a cap of a planar type, which is less expensive than machined caps that themselves comprise one or more cavities. 
         [0101]    According to the present disclosure, the packages described form respective Faraday cages, adapted to eliminate or at least reduce the negative effects that electrostatic charges and magnetic fields external to the package might have on operation of the sensors and devices housed in the internal cavity. 
         [0102]    According to the embodiment of  FIGS. 2   a  and  2   b  the Faraday cage is not complete, but the internal cavity  32  is wide. According to the embodiment of  FIGS. 4   a  and  4   b  the Faraday cage is complete (complete shielding), but the residual space of the internal cavity  32  is smaller than in the case of  FIGS. 2   a ,  2   b . The embodiment of  FIGS. 5   a  and  5   b  is a compromise between the two conditions set forth above. 
         [0103]    In addition, when required, the package according to all the embodiments described may provide mechanical protection of the devices housed in the internal cavity but also accessibility from outside (when the cap is provided with through vias). 
         [0104]    In addition, the package according to the embodiments described has a low production cost, and enables containment of the overall dimensions. 
         [0105]    In addition, the teaching according to the present disclosure can be applied also to non-standard packages, thus enabling a high flexibility of application. 
         [0106]    Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein without thereby departing from the sphere of protection of the present disclosure, as defined in the annexed claims. 
         [0107]    For example, the package according to all the embodiments of the present disclosure can be used to house any device or sensor, not limited to the MEMS microphone of  FIG. 14 . For example, the sensor can be a pressure sensor, in particular provided in MEMS technology. 
         [0108]    As an alternative to what is shown in  FIG. 14 , the opening  205  can be formed in the substrate  21  and not in the cap  28 ,  46 . 
         [0109]    In addition, in order to improve the impermeability of the encapsulating structure according to the present disclosure, in particular in the case where the cap presents vias for access to the internal cavity, the cap can be coated with an impermeable tape. 
         [0110]    The various embodiments described above can be combined to provide further embodiments. 
         [0111]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.