Abstract:
Disclosed herein is a module, including: a circuit board; electronic components mounted on the circuit board; a mold resin that insulates and seals the electronic components; a shield conducting film that covers the outside of the mold resin; and shield conducting walls which are so formed in the mold resin as to divide the mold resin into a plurality of regions.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to a module including of a circuit board and electronic components (such as integrated circuits and passive elements) mounted thereon, and also to a portable terminal equipped with the module. 
         [0002]    Any module in which small electronic components mounted on a circuit board constitute circuits usually has its circuits electromagnetically shielded so as to prevent them from interfering with one another in the module or with actions of other electronic machines or from adversely affecting human bodies. In addition, it is common practice to electromagnetically shield those circuits vulnerable to electromagnetic interference so as to provide them with electromagnetic resistance. 
         [0003]      FIG. 7  is a diagram illustrating one example of the method for electromagnetic shielding with shield caps on the module. 
         [0004]    There are shown a circuit board  100  and electronic components  101 ,  102 ,  103 ,  104 , and  105  mounted thereon. The electronic components  101 ,  102 , and  103  are covered with a metal shield cap  106 , and the electronic components  104  and  105  are also covered with a metal shield cap  107 , both intended for EMC (electromagnetic compatibility). The shield caps  106  and  107  are connected to the ground pads formed on the surface of the circuit board  100 , and the ground pads are electrically connected (or grounded) through via through holes to the solid plane ground as an inner layer on the circuit board  100 . 
         [0005]    The foregoing arrangement needs means for preventing the shield caps  106  and  107  from interfering with the electronic components  101 ,  102 ,  103 ,  104 , and  105  mounted on the circuit board  100  on account of their dimensional variation and their erroneous mounting alignment. For this reason it is necessary that the shield caps and electronic components should be positioned sufficiently apart and the shield caps should be sufficiently higher than the electronic components. 
         [0006]    To be more specific, there should be a gap of at least 0.3 mm between the shield cap  106  and the end (or land) of the electronic component  101 . Also, there should be a gap of at least 0.3 mm between the shield cap  106  and the end of the circuit board  100 . This means that the end (or the end of the land) of the electronic component  101  should be at least 0.7 mm away from the end of the circuit board  100  if the shield cap  106  has a thickness of 0.1 to 0.2 mm. 
         [0007]    In addition, there should be an air gap of about 0.1 to 0.2 mm in the vertical direction from the top of the electronic component  102  (which is highest) to the shield cap  106 . Therefore, the distance from the circuit board  100  to the shield cap  106  should be 1.2 to 1.5 mm. It follows that the module would have a height of about 1.6 to 2.2 mm if the circuit board  100  has a thickness of 0.3 to 0.5 mm and the shield cap  106  has a thickness of 0.1 to 0.2 mm. 
         [0008]    Electromagnetic shielding with the shield caps  106  and  107  needs a large area for their mounting as well as a sufficient upward space; therefore, it hinders the size reduction and height reduction of the module. 
         [0009]      FIG. 8  is a diagram illustrating one example of the method for electromagnetic shielding of a resin-sealed module with shield coating. The constituents in  FIG. 8  which are identical with or equivalent to those in  FIG. 7  are given the same reference numbers without repetition of their detailed description. 
         [0010]    The electromagnetic shielding method mentioned above employs a mold resin  108  (for sealing) and a shield conducting film  109  (of conductive paint) applied to the outside of the resin by coating or printing. It saves the area and height for mounting, thereby achieving the size reduction and height reduction of the module. (See Japanese Patent Laid-open No. 2005-79139 and Japanese Patent Laid-open No. 2008-288610, for example.) 
         [0011]    The module shielded in this manner has a minimum gap of 0.3 mm between the end of the circuit board  100  and the end (or the end of the land) of the electronic component  101 . It also has the shield conducting film  109  having a thickness of 0.01 to 0.1 mm, which is electrically connected to the solid plane ground as an internal layer on the circuit board  100 . There is a gap of 0.05 to 0.1 mm between the shield conducting film  109  and the top of the highest electronic component  102 . The shield conducting film  109  has a thickness of 0.01 to 0.05 mm above the top of the mold resin  108 . The mold resin  108  has a thickness of 1.05 to 1.2 mm between the circuit board  100  and the shield conducting film  109 . The circuit board  100  has a thickness of 0.3 to 0.5 mm. Consequently, the module height is limited to about 1.36 to 1.75 mm. 
         [0012]    The module sealed with the mold resin  108  and covered with the shield conducting film  109  by coating or printing offers the advantage of saving the mounting area and reducing the height and increasing the strength. 
       SUMMARY 
       [0013]    Although the foregoing technology is capable of reducing the size and height of the module by sealing electronic components with a resin and covering the seal resin with a shield conducting material, it involves difficulties in shielding circuit blocks individually on the circuit board. The reason for this is that the resin molding process is carried out while the circuit board is not yet separated into individual modules but is a collection of sub-boards. The molding process carried out in such a state leads to the deterioration of characteristic properties due to cross talk between circuit blocks and EMC noise if there are a plurality of circuit blocks in the module. 
         [0014]    The present disclosure was completed in view of the foregoing. There is a need for the present disclosure to provide a module which permits the electronic components sealed with a mold resin to be shielded for individually divided circuit blocks. 
         [0015]    The main embodiment of the present disclosure resides in a module which includes a circuit board, electronic components mounted on the circuit board, a mold resin that insulates and seals the electronic components, a shield conducting film that covers the outside of the mold resin, and shield conducting walls which are so formed in the mold resin as to divide the mold resin into a plurality of regions. 
         [0016]    The module constructed as mentioned above permits the shield conducting walls formed in the mold resin to shield the circuit blocks each including of electronic components mounted on the circuit board. 
         [0017]    With the module constructed as mentioned above, it is possible to shield the circuit blocks in small units without adverse effects on the module with mold resin sealing and shield coating which has the advantage of being small in size and low in height. Thus the module protects its characteristics from deterioration by crosstalk between circuit blocks and EMC radiation noise. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIGS. 1A and 1B  are diagrams illustrating the structure of the module pertaining to a first embodiment of the disclosure,  FIG. 1A  is a schematic sectional view of the module, and  FIG. 1B  is a schematic plan view of the module; 
           [0019]      FIGS. 2A and 2B  are diagrams illustrating the detailed structure (in side view) of the module pertaining to the first embodiment of the disclosure,  FIG. 2A  is a partial sectional view illustrating the structure (in side view) of the module, and  FIG. 2B  is a partial sectional view illustrating the structure (in side view) of the module in its modified form; 
           [0020]      FIGS. 3A and 3B  are diagrams illustrating the structure of the module pertaining to a second embodiment of the disclosure,  FIG. 3A  is a schematic sectional view of the module, and  FIG. 3B  is a schematic plan view of the module; 
           [0021]      FIGS. 4A and 4B  are diagrams illustrating the structure of the module pertaining to a third embodiment of the disclosure,  FIG. 4A  is a schematic sectional view of the module, and  FIG. 4B  is a schematic plan view of the module; 
           [0022]      FIG. 5  is a block diagram showing an example of the structure of the RF module for a portable terminal; 
           [0023]      FIG. 6  is a schematic diagram showing a portable terminal equipped with the module; 
           [0024]      FIG. 7  is a diagram showing an example of the method for electromagnetic shielding of the module with shield caps; and 
           [0025]      FIG. 8  is a diagram showing an example of the method for electromagnetic shielding of the resin-sealed module with shield coating. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    The embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. 
         [0027]      FIGS. 1A and 1B  are diagrams illustrating the structure of the module pertaining to a first embodiment of the disclosure.  FIG. 1A  is a schematic sectional view of the module.  FIG. 1B  is a schematic plan view of the module.  FIGS. 2A and 2B  are diagrams illustrating the detailed structure (in side view) of the module pertaining to the first embodiment of the disclosure.  FIG. 2A  is a partial sectional view illustrating the structure (in side view) of the module.  FIG. 2B  is a partial sectional view illustrating the structure (in side view) of the module in its modified form. 
         [0028]    The module pertaining to the first embodiment includes of a circuit board  10  and a plurality of electronic components  11 ,  12 ,  13 ,  14 , and  15  mounted thereon. The electronic components  11 ,  12 , and  13  include transistor, diode, resistor, capacitor, inductor, etc. of surface mount type. The electronic components  14  and  15  are integrated circuits. On the circuit board  10  is mounted a conducting part  16  of metal. Incidentally, the circuit board  10  may be a plastic board of glass epoxy or a ceramic board of LTCC (Low Temperature Co-fired Ceramics), alumina, or aluminum nitride. 
         [0029]    The conducting part  16  is mounted on a ground pad  17  formed on the surface of the circuit board  10 , as shown in  FIG. 1A . This ground pad  17  is electrically connected to a solid plane ground  19  (which is an internal layer on the circuit board  10 ) through a via through hole  18 . There are several of the conducting part  16  arranged and mounted on the top surface of the circuit board  10 , as shown in  FIG. 1B . Thus, they form the conducting shield wall that electromagnetically shields the region of the circuit block containing the electronic parts  11 ,  12 , and  14 , and the region of the circuit block containing the electronic parts  13  and  15 . Incidentally, the module pertaining to the first embodiment employs several pieces of the small conducting part  16  arranged at a certain pitch as the shield conducting wall. This design assumes the use of a general-purpose surface mounter for small-sized electronic parts. However, it may be so modified as to replace several pieces (five pieces in  FIG. 1B ) by a single piece if there is available a surface mounter capable of mounting large-sized electronic parts. 
         [0030]    The electronic parts  11  to  15  and the conducting part  16 , which are mounted on the circuit board  10 , are sealed with an insulating mold resin  20  such as epoxy resin, and the surface of the mold resin  20  is coated with a shield conducting film  21 . Resin sealing is accomplished by flowing the mold resin  20  over the circuit board  10  (in the form of an aggregate of individual circuit boards) on which are mounted the electronic parts  11  to  15  and the conducting part  16  constituting each module. Coating with the shield conducting film  21  is accomplished by printing with a conductive paste (such as silver paste) or by spraying with a conductive paint (such as silver paint, copper paint, and copper-silver paint). 
         [0031]    Coating with the shield conducting film  21  is preceded by forming a half-cut groove (reaching the ground pattern on the circuit board  10 ) in the mold resin  20  with the help of a wide dicing saw moving along the cut line to separate the large circuit board into individual small circuit boards. Coating in this way forms the shield conducting film  21  on the top of the mold resin  20  and on the inner wall of the half-cut groove. The shield conducting film  21  formed on the inner wall of the half-cut groove serves as the conducting film on the side of the mold resin  20  after the large circuit board has been cut into small circuit boards for individual modules. Incidentally, the conducting part  16  will come into electrical contact with the shield conducting film  21  after coating if it is high enough to expose itself from the top of the mold resin  20 . 
         [0032]    The shield conducting film  21  (which is formed on the side of the mold resin  20 ) conducts to the ground of the circuit board  10  at a different position depending on the depth of the half-cut groove. In the case shown in  FIG. 2A , the half-cut groove is so formed as to reach the solid plane ground  19  as an inner layer on the circuit board  10 , so that the shield conducting film  21  conducts to the solid plane ground  19 . Likewise, in the case shown in  FIG. 2B , the half-cut groove is so formed as to reach the ground pad  17 , so that the shield conducting film  21  conducts to the ground pad  17 . 
         [0033]    The large circuit board is completely cut and separated into small circuit boards for individual modules by means of a narrow dicing saw after the mold resin  20  has been coated with the shield conducting film  21  and the half-cut groove has been filled with the conductive paste. Incidentally, the shield conducting film  21  on the side of the mold resin  20  may also be formed by printing with a conductive paste after cutting into small circuit boards, or by spraying with a conducting paint, with the bottom of the module masked, after cutting into small circuit boards. 
         [0034]    The module pertaining to the first embodiment of the present disclosure can be produced in substantially the same way as the existing one except for the additional step of mounting the conducting part  16  on the circuit board  10 . According to the fabricating method employed in the embodiment, the shield conducting wall is formed as the conducting part  16  (in several pieces) is mounted on the circuit board  10 . Therefore, the shield conducting wall may be formed in any pattern on the circuit board  10  by properly arranging the conducting part  16 . For example, the pattern may include L-shape, T-shape, π-shape, and cross-shape. In addition, they may be arranged straight or zigzag (to get out densely mounted electronic parts), continuously or intermittently. 
         [0035]      FIGS. 3A and 3B  are diagrams illustrating the structure of the module pertaining to a second embodiment of the disclosure.  FIG. 3A  is a schematic sectional view of the module.  FIG. 3B  is a schematic plan view of the module. The constituents in  FIGS. 3A and 3B  which are identical with or equivalent to those in  FIGS. 1A and 1B  are given the. same reference numbers without repetition of their detailed description. 
         [0036]    The module pertaining to the second embodiment has the shield conducting wall which is formed by the same method (coating) as shown in  FIG. 2B . That is, the half-cut groove reaching the ground pad  17  on the circuit board  10  is formed by means of a dicing saw at a prescribed position of the mold resin  20 . Then, the half-cut groove is filled with a conductive paste or paint to form a shield conducting wall  22 . The resulting shield conducting wall  22  conducts to the shield conducting film  21  formed thereon. The filling of the half-cut groove with a conductive paste or paint may be accomplished in the same way as that for covering the top of the mold resin  20  with the shield conducting film  21 , so that the shield conducting wall  22  is formed integrally with the shield conducting film  21 . 
         [0037]    In the case where it is difficult to completely fill the half-cut groove (down to the ground pad  17 ) with a conductive paste or paint that forms the shield conducting film  21  on the mold outer surface, it is necessary to form the shield conducting wall  22  before the shield conducting film  21  is formed. To this end, it is desirable to properly select the slit width of the half-cut groove and the viscosity of the conductive paint to be used for filling. For example, if the slit width of the half-cut groove is 0.3 mm, the conductive paint should have a viscosity of about 25 to 40 Pa/s and should optionally be defoamed by evacuation. 
         [0038]    The module pertaining to the second embodiment may have the shield conducting wall  22  formed straight or crosswise (across the module) as shown in  FIGS. 3A and 3B . However, it should not have the half-cut groove formed in L-shape, T-shape, or π-shape because the dicing saw to make the half-cut groove is circular and the half-cut groove in one module should be continuous with the one in the adjoining module. 
         [0039]      FIGS. 4A and 4B  are diagrams illustrating the structure of the module pertaining to a third embodiment of the disclosure.  FIG. 4A  is a schematic sectional view of the module.  FIG. 4B  is a schematic plan view of the module. The constituents in  FIGS. 4A and 4B  which are identical with or equivalent to those in  FIGS. 3A and 3B  are given the same reference numbers without repetition of their detailed description. 
         [0040]    The module pertaining to the third embodiment has the shield conducting wall which includes of several pieces of conducting column  23  formed in the mold resin  20  at a prescribed pitch along the boundary separating the mold resin  20 . The conducting column  23  is formed by filling a conductive paste into a non-through hole which has been made in the mold resin  20  by laser beam machining. Immediately under the non-through hole is the ground pad  17  on the circuit board  10 . The ground pad  17  appreciably reflects the laser beam, so that the conducting column  23  reaches an adequate depth if the laser bean is properly controlled in its intensity. The laser beam machining in this manner permits the shield conducting wall to be formed in T-shape or π-shape. The conducting column  23  includes of a cylindrical non-through hole and a conductor filled therein, and hence it resembles a kind of blind via hole. Therefore, the resulting shield conducting wall is not continuous but is capable of preventing EMC leakage if the conducting columns  23  are arranged at proper intervals. 
         [0041]      FIG. 5  is a block diagram showing an example of the structure of the RF module for a portable terminal.  FIG. 6  is a schematic diagram showing a portable terminal equipped with the module. 
         [0042]    The portable telephone as one of portable terminals is usually equipped with modules for different communication systems, and it is capable of switching them from one to another according to need. For example, an RF (high-frequency) module  30  for the portable telephone shown in  FIG. 5  has a CDMA (Code Division Multiple Access) receiving circuit  31 , a CDMA transmitting circuit  32 , a power amplifier  33 , and a duplexer  34 . It also has a GSM (Global System for Mobile Communications) transmitting-receiving circuit  35  and a power amplifier  36 . The duplex  34  and the power amplifier  36  are connected to an antenna change-over switch  37 , which is connected to the antenna terminal. The CDMA receiving circuit  31 , the CDMA transmitting circuit  32 , and the GSM transmitting-receiving circuit  35  are connected to a main CPU (Central Processing Unit)  38  of the portable telephone. 
         [0043]    The portable telephone may have the possibility of establishing electromagnetic shielding between the circuit block for the transmitting signal system and the circuit block for the receiving signal system, or establishing electromagnetic shielding between circuit blocks for individual communication systems, or establishing electromagnetic shielding between circuit blocks for individual frequency bands. The RF module  30  shown in  FIG. 5  has the circuit block (containing the CDMA receiving circuit  31 , the duplexer  34 , and the antenna change-over switch  37 ) shielded by the shield conducting wall indicated by a broken line. This shield conducting wall is realized by any one of the shield conducting walls pertaining to the first to third embodiments mentioned above. The shield conducting wall is also provided for the circuit block for the CDMA transmitting circuit  32 , the circuit block for the GSM transmitting-receiving circuit  35 , and the circuit block containing the power amplifier  33  and the power amplifier  36 . 
         [0044]    An example of the RF module  30  mounted in a portable telephone is shown in  FIG. 6 . This portable telephone is made up of two enclosures  40  and  41  joined together by a hinge  42 . One enclosure  40  holds a liquid crystal display  43  and a circuit board  44  for the liquid crystal display  43 . The other enclosure  41  holds a keyboard  45 , a reinforcing metal plate  46 , a main circuit board  47 , a sub-circuit board  48 , and an antenna  49 . The main circuit board  47  contains the main CPU  38 , the main memory, the RF circuit, etc. In the main circuit board  47  is mounted the RF module  30  shown in  FIG. 5 . 
         [0045]    The RF module  30  is constructed such that the mold resin  20  is divided by the shield conducting wall; therefore, it offers the advantage of being small in size and low in height as in the case of the module with mold resin sealing and shield coating. Moreover, the fact that the circuit block is shielded in small units is effective in preventing the characteristic properties from being deteriorated by crosstalk between circuit blocks and EMC radiation noise. 
         [0046]    The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2010-155903 filed in the Japan Patent Office on Jul. 8, 2010, the entire content of which is hereby incorporated by reference. 
         [0047]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.