Patent Publication Number: US-9420685-B2

Title: Electronic device comprising a substrate board equipped with a local reinforcing or balancing layer

Description:
PRIORITY CLAIM 
     This application claims priority from French Application for Patent No. 1357515 filed Jul. 30, 2013, the disclosure of which is incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to the field of electronic devices that comprise substrate boards equipped with electrical connection networks and integrated-circuit chips mounted on these substrate boards and connected to these networks. 
     BACKGROUND 
     Generally, electrical connection networks comprise metal electrical connection tracks, local metal connection zones, and possibly metal vias passing through the substrate boards. These electrical connection networks, and optionally other metal portions, form metal masses that are irregularly distributed over the surface and possibly in the interior of the substrate boards. 
     In the case where certain connections of the electrical connection networks are intended to transfer high-frequency signals, such as video signals, zones near these connections must be free from metal portions in order to prevent electromagnetic interference. The irregularity of the distribution of these metal portions over the substrate boards is then further accentuated. 
     This results in such substrate boards deforming (warping or sagging), causing planarity defects that result in local electrical connection zones not being coplanar. Integrated-circuit chips mounted on the substrate boards, by way of electrical connection elements such as balls, metal pads or electrical connection wires, in these local electrical connection zones, run the risk of having electrical connections that are defective or missing. 
     There is a need in the art to reduce the above drawbacks. 
     SUMMARY 
     An electronic device is provided, which device comprises a substrate board equipped with an electrical connection network and at least one integrated-circuit chip mounted on said substrate board, the substrate board being equipped with an electrical connection network with a view to making electrical connections between said integrated-circuit chip and the exterior. 
     In such an electronic device, at least one face of the substrate board is equipped with at least one local reinforcing or balancing layer made of a non-metallic material added to at least one local zone free from metal portions. 
     Said local reinforcing or balancing layer may be placed in at least one local zone of the substrate board adjacent to a portion of the electrical connection network and free from metal portions. 
     Said local reinforcing or balancing layer may comprise a plurality of points of non-metal material bonded from above to the substrate board. 
     Said local reinforcing or balancing layer may comprise at least one line or bead of non-metallic material bonded from above to the substrate board. 
     Said local reinforcing or balancing layer may comprise at least one non-metallic film bonded to the substrate board. 
     Said substrate board may be equipped with a superficial passivating layer on which said local reinforcing or balancing layer is placed. 
     Said substrate board may be equipped with a superficial passivating layer containing at least one hole, said local reinforcing or balancing layer being engaged in this hole. 
     A process for fabricating an electronic device is also provided, which process comprises: adding a local reinforcing (or balancing) layer made of a non-metallic material to a zone free from metal portions of a substrate board equipped with an electrical connection network, then mounting an integrated-circuit chip onto the substrate board by way of electrical connection elements placed in metal zones of said electrical connection network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Electronic devices will now be described by way of non-limiting example, and illustrated by the appended drawings, in which: 
         FIG. 1  shows a top view of an electronic device; 
         FIG. 2  shows a cross-sectional view of the electronic device, according to one embodiment; 
         FIG. 3  shows a cross-sectional view of the electronic device, according to another embodiment; 
         FIG. 4  shows a cross-sectional view of the electronic device, according to another embodiment; and 
         FIG. 5  shows a cross-sectional view of the electronic device, according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  illustrate an electronic device  1  that comprises a substrate board  2  made of an insulator, and an integrated-circuit chip  3  placed flat a small distance above one face  4  of the substrate board  1 . 
     The substrate board  2  is equipped with an electrical connection network  5  allowing electrical connections to be made between the integrated-circuit chip  3  and the exterior. 
     The electrical connection network  5  comprises a plurality of electrical connections  6 , for example for transferring video signals, and a plurality of electrical connections  7  for transferring all the other signals and supplying electrical power to the integrated-circuit chip  3 . 
     The electrical connections  6  comprise, on the face  4  of the substrate board  2 , metal connection lines  8 , metal connection elements  9  that are interposed and soldered between the integrated-circuit chip  3  and the substrate board  2  and that electrically connect internal ends of the connection lines  8  to the integrated-circuit chip  3 , and metal electrical connection vias  10  that pass through the substrate board  2  and that, by way of their end located on the face  4  side, are connected to external ends of the connection lines  8 . 
     Equivalently, the electrical connections  7  comprise metal connection lines  11 , metal electrical connection elements  12 , and metal electrical connection vias  13 . 
     The metal vias  10  and  13  are placed between the integrated-circuit chip  3  and the peripheral edges of the substrate board  2 . By way of their end located on the bottom face side, opposite the face  4  of the substrate board  2 , the vias  10  and  13  may be connected to another electronic device (not shown) by way of connection elements (not shown). 
     In the example illustrated, the electrical connections  6  are distributed on one side of the integrated-circuit chip  3  and the electrical connections  7  are distributed over the three other sides of the integrated-circuit chip  3 . 
     The metal connection lines  8  of the electrical connections  6  lie next to one another, and the metal vias  10  are aligned in a row parallel to the corresponding edge  2   a  of the substrate board  2 . 
     Except from the metal from which they are made, the electrical connections  6  are formed in a region  14  of the substrate board free from other metal portions in order to prevent the signals transferred by the connections  6  from being distorted. 
     Furthermore, the substrate board  2  is optionally equipped with metal regions  15  located on its face  4  or incorporated between the layers. 
     A superficial passivating layer  16  made of an insulator extends over the face  4  of the substrate board  2 . 
     In a zone  14   a  of the region  14  free from metal portions, which is located between the metal vias  10  and the corresponding edge  2   a  of the substrate board  2 , the passivating layer  16  has been removed and the substrate board  2  is equipped, on its face  4 , with an added local reinforcing or balancing layer  17  made of a non-metallic material that does not distort the signals transferred by the connections  6 . 
     In the embodiment illustrated in  FIG. 2 , the local reinforcing or balancing layer  17  is formed by at least one line or bead  17   a  of a deposited non-metallic material, or by a non-metallic film bonded to the face  4  of the substrate board  2 . 
     In another embodiment illustrated in  FIG. 3 , the local reinforcing or balancing layer  17  is formed by a plurality of points  17   b  of a deposited non-metallic material. These points  17   a  may be located near one another and be regularly or irregularly distributed. For example, these points  17   a  may be deposited through a removable perforated mask (not shown). 
     In another embodiment illustrated in  FIG. 4 , the passivating layer  16  has not been removed from the zone  14   a  of the region  14  free from metal portions, and the added local reinforcing or balancing layer  17  comprises at least one portion  17   c  formed directly on this passivating layer  16 , this time without strict limitation to the zone  14   a.    
     In another embodiment illustrated in  FIG. 5 , the added local reinforcing or balancing layer  17  of  FIG. 4  contains portions  17   d  inserted in holes  16   a  produced in the passivating layer  16 . 
     As a result of the above the substrate board  2  is equipped with metal portions that are not regularly distributed over its surface, especially due to the existence of the specific region  14  in which the electrical connections  6  are exclusively provided. 
     Adding the local reinforcing or balancing layer  17  to the region  14  allows this irregularity to be compensated for in order for the substrate board  2  not to exhibit warping and/or sagging that could hinder the mounting of the integrated-circuit chip  3  by way of the electrical connection elements  9  and  12  and the mounting of the substrate board  2  on another electronic device, as mentioned above. 
     According to another embodiment, one or more added local reinforcing or balancing layers, equivalent to the local layer  17 , could be provided in other locations on the substrate board  2  and for the same purpose. 
     The electronic device  1  may be fabricated in the following way. 
     Having previously produced the substrate board  2  equipped with the desired electrical connection network  5 , the reinforcing layer  17  is produced. The shape, position and material of this reinforcing layer  17 , which may comprise one or more portions, are chosen so as to prevent any warping and/or sagging of the substrate board  2 . 
     In the case where the reinforcing or balancing layer  17  is formed by at least one deposited line, bead or droplet, the material from which it is made may be a thermosetting epoxy adhesive. In the case where the reinforcing or balancing layer  17  is formed by a bonded film, the material may be an acrylic, epoxy or polyester resin. 
     Next, the integrated-circuit chip  2  is positioned and mounted on the substrate board  2  by way of the electrical connection elements  9  and  12 . 
     The present invention is not limited to the example described above. Variant embodiments are possible without departing from the scope of the invention.