Abstract:
A land pattern for 1 mm and 0.8 mm pitch arrays has been disclosed for placing two port devices. The land pattern includes a ball grid array (BGA) of BGA pads each connected to a respective through hole via, and a pair of rectangular conductive pads electrically connected to a an adjacent pair of through hole vias, wherein each rectangular pad extends out from its via towards the other via of the pair along a line connecting the centers of said adjacent pair vias. A solder mask is located on the rectangular pad side and has apertures over each rectangular conductive pad. The land pattern is particularly useful for locating two port devices directly underneath a BGA device while minimizing the distance from a BGA ball to the two port device lead.

Description:
FIELD OF THE INVENTION 
     The invention is directed to placement of two-port surface mount components relative to Ball Grid Arrays (BGAs) and in has particular use in placement of decoupling capacitors for grid array components. 
     BACKGROUND OF THE INVENTION 
     This invention relates to the design of electronic circuit cards. Specifically, it may be directed to the problem of electrically decoupling a BGA device with 0201 size surface mount capacitors placed on the opposite side of the circuit card with respect to the BGA device and within the grid of vias and contacts used to route signal traces to and from the BGA device. 
     A number of solutions have been previously developed. These solutions targeted at solving decoupling issues on 1.00 mm pitch BGA devices. However these solutions are not applicable to finer pitch BGA devices (&lt;1.00 mm). Increasing design densities and component miniaturization trends are making the use of 0.80 mm pitch BGAs more common on many designs. 
     One prior art approach uses octagonal land patterns in combination with specifically filled vias underneath fine pitch BGA devices for decoupling applications using 0402 sized capacitors. This approach was disclosed in U.S. Pat. No. 7,602,615 by the assignee hereof and is incorporated herein by reference. 
     A drawback of this approach is the land placements limits application of 0402 decoupling capacitors to between adjacent BGA pins on a grid having a 1.00 mm pitch in at least one grid direction. 
     Therefore, it would be desirable to overcome this limitation so as to increase be able to place decoupling capacitors on a BGA grid pattern having sub-1.00 mm dimensions in both grid directions, thereby enabling more termination and decoupling opportunities. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a land pattern for placement of two port surface mount components relative to BGAs. 
     According to an aspect of the invention there is provided an electronic circuit board (ECB) having a ball grid array (BGA) of BGA pads on a first side of the ECB, arranged in a grid pattern of rows and columns; through hole vias having conductive barrels extending from the first side of the ECB to an opposite second side of the ECB, and wherein each of the through hole vias is offset from a corresponding one of the BGA pads and electrically connected to the corresponding BGA pad by a conductor on the first side; and wherein at least one adjacent pair of the though hole vias having a via pad around the through hole via and electrically connected to the conductive barrel of the through hole via on the second side; each via pad of the adjacent pair extending out from its respective corresponding one of the adjacent pair of through hole vias towards the other via of the adjacent pair of through hole vias along a line connecting the centers of the adjacent pair of through hole vias; a solder mask located on the second side; the solder mask having apertures above and over each via pad of the adjacent pair; and a 0201 size two-port device mounted in electrical connection directly on the via pads through the apertures in a given alignment with the grid pattern. 
     In some embodiments of the invention the pair of via pads is arranged in a direction aligned to the grid pattern of the BGA pads. In other embodiments the pair of via pads is arranged in a direction having diagonal alignment with the grid pattern of the BGA pads. 
     In some embodiments of the invention the two port device is a linear device. The linear device may be a resistor, inductor or capacitor. Advantageously, in some embodiments the linear device is a decoupling capacitor. 
     In some embodiments of the invention the two port device is a non-linear device. The non-linear device may be a diac, a zener diode, and a memristor. Advantageously, in some embodiments the non-linear device is a surge suppressor capacitor. 
     According to another aspect of the invention there is provided a computer aided design tool for accommodating a two-port device in an 0.8 mm by 0.8 mm pitch ball grid array (BGA) electronic circuit board (ECB) having a design tool mode to identify, in an ECB configuration of BGA pads in a grid pattern on a first side of the ECB and through hole vias adjacent to the BGA pads, each of the through holes vias connected to a corresponding BGA pad by a corresponding trace on the first side of the ECB, at least one adjacent pair of the though hole vias having a via pad around the through hole via and electrically connected to the conductive barrel of the through hole via on the second side; the via pad pair for directly mounting of and connection to a corresponding one of the two port devices; a first design tool mode to configure the via pad pairs to have a configuration that configures each pair of via pads to extend out from its respective corresponding one of the adjacent pair of through hole vias towards the other via of the adjacent pair of through hole vias along a line connecting the centers of the adjacent pair of through hole vias; a second design tool mode to configure a solder mask located on the second side to have apertures above and over each via pad. 
     Note: in the following the description and drawings that follow merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments, as illustrated in the appended drawings, where: 
         FIG. 1  illustrates a first embodiment of the invention; 
         FIG. 2  illustrates a second embodiment of the invention; 
         FIG. 3  illustrates a third embodiment of the invention; and 
         FIG. 4  illustrates an exploded diagram of a through hole via pad pair connected to BGA lands, a pair of component lands, a solder mask, and a 0201 component according to an embodiment of the invention. 
     
    
    
     The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there may be seen a section of an electronic circuit board  100  which has an array of BGA pads  110 . The BGA pads  110  are on the side of the circuit board opposite to which the two port device would be placed, and in this embodiment are distributed on a 0.8 mm grid. Also visible are a grid of through hole vias  112  which are each connected to a respective BGA pad  110  by a trace  114 . The through hole vias  112  have via pads  113  which surround the barrel of the via on the non-BGA side of the electronic circuit board. The through hole vias  112  go through electronic circuit board  100  with the hole inside the conductive barrel of the via generally being filled with conductive or non-conductive material. 
     In  FIG. 1 , some of the via pads have been extended so as to provide a land for a two port component. As may be seen by via pad pair  116  having left hand pad  117  and right hand pad  118 , the generally circular pads  113  have been extended by a generally rectangular extension which extends along a line connecting the centers of the paired vias towards the respective opposite via pad of the pair. 
     Also apparent in  FIG. 1  is a section of solder resist layer  120 . This solder resist is applied to the surface of electronic circuit board  100  to delimit areas wherein solder may adhere to the board. For ease of understanding, only a portion of solder resist is shown so that the circuit board features elsewhere in  FIG. 1  are not obscured. Visible in solder resist layer section  120  are apertures  122  and  124 . Each aperture corresponds with a respective portion of the via pad pair underlying the solder mask which serves as a land for a respective end of a two port component. 
     A 0201 size two port component  130  may be seen in position on via pad pair  136 . The solder resist layer has not been included in this section so that the portion of via pad pair  136  not covered by two port component  130  remains visible. 
       FIG. 1  thus depicts the placement of a 0201 sized component according to a horizontal direction of the BGA grid. 
     Referring now to  FIG. 2 , there may be seen an embodiment of the invention wherein a 0201 sized component is placed according to a vertical direction of the BGA grid. There may be seen a section of an electronic circuit board  200  which has an array of BGA pads  210 . The BGA pads  210  are on the side of the circuit board opposite to which the two port device would be placed, and in this embodiment are distributed on a 0.8 mm grid. Also visible are a grid of through hole vias  212  which are each connected to a respective BGA pad  210  by a trace  214 . The through hole vias  212  have via pads  213  which surround the barrel of the via on the non-BGA side of the electronic circuit board. The through hole vias  212  go through electronic circuit board  200  with the hole inside the conductive barrel of the via generally being filled with conductive or non-conductive material. 
     In  FIG. 2 , some of the via pads have been extended so as to provide a land for a two port component. As may be seen by via pad pair  216  having upper pad  217  and lower pad  218 , the generally circular pads  213  have been extended by a generally rectangular extension which extends along a line connecting the centers of the paired vias towards the respective opposite via pad of the pair. 
     Also apparent in  FIG. 2  is a section of solder resist layer  220 . This solder resist is applied to the surface of electronic circuit board  200  to delimit areas wherein solder may adhere to the board. For ease of understanding, only a portion of solder resist is shown so that the circuit board features elsewhere in  FIG. 2  are not obscured. Visible in solder resist layer section  220  are apertures  222  and  224 . Each aperture corresponds with a respective portion of the via pad pair underlying the solder mask  220  which serves as a land for a respective end of a two port component. 
     A 0201 size two port component  230  may be seen in position on via pad pair  236 . The solder resist layer has not been included in this section so that the portion of via pad pair  236  not covered by two port component  230  remains visible. 
       FIG. 2  thus depicts the placement of a 0201 sized component according to a vertical direction of the BGA grid. 
     Now referring now to  FIG. 3 , there may be seen an embodiment of the invention wherein a 0201 sized component is placed according to a diagonal direction relative to the BGA grid. There may be seen a section of an electronic circuit board  300  which has an array of BGA pads  310 . The BGA pads  310  are on the side of the circuit board opposite to which the two port device would be placed, and in this embodiment are distributed on a 0.8 mm grid. Also visible are a grid of through hole vias  312  which are each connected to a respective BGA pad  310  by a trace  314 . The through hole vias  312  have via pads  313  which surround the barrel of the via on the non-BGA side of the electronic circuit board. The through hole vias  312  go through electronic circuit board  300  with the hole inside the conductive barrel of the via generally being filled with conductive or non-conductive material. 
     In  FIG. 3 , some of the via pads have been extended so as to provide a land for a two port component. As may be seen by via pad pair  316  having upper-right pad  317  and lower-left pad  318 , the generally circular pads  313  have been extended by a generally rectangular extension which extends along a line connecting the centers of the paired vias towards the respective opposite via pad of the pair. 
     Also apparent in  FIG. 3  is a section of solder resist layer  320 . This solder resist is applied to the surface of electronic circuit board  300  to delimit areas wherein solder may adhere to the board. For ease of understanding, only a portion of solder resist is shown so that the circuit board features elsewhere in  FIG. 3  are not obscured. Visible in solder resist layer section  320  are apertures  322  and  324 . Each aperture corresponds with a respective portion of the via pad pair underlying the solder mask  320  which serves as a land for a respective end of a two port component. 
     A 0201 size two port component  330  may be seen in position on via pad pair  336 . The solder resist layer has not been included in this section so that the portion of via pad pair  336  not covered by two port component  330  remains visible. 
       FIG. 3  thus depicts the placement of a 0201 sized component according to a diagonal direction relative to the BGA grid. 
     Referring to  FIG. 4 , there may be seen an exploded diagram  400  of a pair of 0.8 mm separation BGA pads  410  connected by respective links  414  to respective through hole vias  412 . Extended via pad pair  416  is positioned atop and electrically connected to through hole vias  412 . Left hand extended via pad  417  has a generally rectangular protrusion extending along its line of symmetry towards right hand extended via pad  418 . Likewise, right hand extended via pad  418  has a generally rectangular protrusion extending along its line of symmetry towards left hand extended via pad  417 . 
     Surmounting the same side of the board as extended via pad pair  416  is solder mask  420  having apertures  422  and  424 . Apertures  422  and  424  are positioned atop extended via pad pair  416  to define a pair of lands for attachment of a two port device. Aperture  422  defines an electrical connection land on left hand extended via pad  417 , and aperture  424  defines an electrical connection land on right hand extended via pad  418 . Two port device  430  is positioned atop the lands defined by the apertures on extended via pad pair  416  and electrically connected. 
     The aforesaid embodiments assist with densification of electric wiring board design by placing the decoupling and termination devices directly beneath the BGA device. Such a placement helps in enhancing the electrical performance of the decoupling and termination devices by minimizing the distance from the BGA device ball to the lead of the two port device. 
     While the embodiments have generally been described in conjunction with decoupling capacitors, further functionality would include the use of alternate two port devices. Such devices may include linear devices such as resistors or inductors, useful for termination and waveform shaping purposes. Alternatively, such devices may include non-linear devices such as zener diodes, diacs, or varistors; useful for signal clamping and device protection purposes. Other two port devices, such as memristors or light emitting diodes are also contemplated for some applications. 
     Numerous modifications, variations and adaptations may be made to the embodiment of the invention described above without departing from the scope of the invention, which is defined in the claims.