Abstract:
Various exemplary embodiments relate to a printed circuit board (PCB) comprising a ball grid array (BGA) of BGA pads on one side of the PCB, arranged in a grid pattern; through-hole vias, including a via pad, arranged in said grid pattern electrically connected to said BGA pads; a solder mask covering the via pad with an opening; a solder pad within said opening electrically connected to said via pad; and a two-lead component attached to said solder pad.

Description:
TECHNICAL FIELD 
       [0001]    Various exemplary embodiments disclosed herein relate generally to surface mount components on a circuit board. 
       BACKGROUND 
       [0002]    Surface mount components are prevalent in many devices today. They allow components to be attached in compact spaces. A ball grid array allows a device to be directly attached to another circuit board without socket mounting, which leads to better performance at high speeds. In order to make smaller devices the spacing of the ball grid array has decreased over time. As technology develops, a way to attach components on increasingly compact grids is necessary. 
       SUMMARY 
       [0003]    A brief summary of various exemplary embodiments is presented below. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various exemplary embodiments, but not to limit the scope of the invention. Detailed descriptions of a preferred exemplary embodiment adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections. 
         [0004]    Various exemplary embodiments relate to a printed circuit board (PCB) comprising a ball grid array (BGA) of BGA pads on one side of the PCB, arranged in a grid pattern; through-hole vias, including a via pad, arranged in said grid pattern electrically connected to said BGA pads; a solder mask covering the via pad with an opening; a solder pad within said opening electrically connected to said via pad; and a two-lead component attached to said solder pad. 
         [0005]    Various embodiments describe the PCB, wherein the grid pattern is square. 
         [0006]    Various embodiments describe the PCB, wherein the grid pattern has 0.65 mm pitch. 
         [0007]    Various embodiments describe the PCB, wherein said solder pad is substantially rectangular. 
         [0008]    Various embodiments describe the PCB, wherein the two-lead component is an Imperial 0201 component. 
         [0009]    Various embodiments describe the PCB, wherein the Imperial 0201 component is a discrete component. 
         [0010]    Various embodiments describe the PCB, wherein the areas are substantially rectangular and each edge makes contact with the corresponding via pad. 
         [0011]    Various exemplary embodiments relate to a method of manufacturing a PCB comprising the steps of selecting two adjacent through-hole vias on a printed circuit board (PCB), wherein the PCB has a ball grid array (BGA) of BGA pads on one side of the PCB arranged in a grid pattern; covering each via with a respective solder mask; removing areas from said solder masks, wherein the areas overlap the holes of the respective through-hole vias; placing solder pads in said areas; and attaching a two-lead component to said two adjacent through-hole vias using said solder pads. 
         [0012]    Various exemplary embodiments relate to A computer aided design tool implemented on a computing device for accommodating a two-lead component on in a 0.65 mm by 0.65 mm pitch ball grid array (BGA) printed circuit board (PCB) comprising a design tool mode configured to select two adjacent through-hole vias on the printed circuit board (PCB) for connection to a two-lead component a design tool mode configured to identify a placement of solder pads and shape of solder pads on the two adjacent through-hole vias, wherein the placement allows a two-lead component to connect to two adjacent through-hole vias, and wherein the solder pads overlap the holes of the respective through-hole vias. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    In order to better understand various exemplary embodiments, reference is made to the accompanying drawings, wherein: 
           [0014]      FIG. 1  illustrates an embodiment of a surface mount component on a very fine pitch array; 
           [0015]      FIG. 2  illustrates an embodiment of a process for attaching a surface mount component on a very fine pitch array; and 
           [0016]      FIG. 3  illustrates a cross sectional view of the surface mount component on a very fine pitch array. 
       
    
    
       [0017]    To facilitate understanding, identical reference numerals have been used to designate elements having substantially the same or similar structure and/or substantially the same or similar function. 
       DETAILED DESCRIPTION 
       [0018]    The description and drawings 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 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 inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Additionally, the term, “or,” as used herein, refers to a non-exclusive or (i.e., and/or), unless otherwise indicated (e.g., “or else” or “or in the alternative”). Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments. 
         [0019]    Referring now to the drawings, in which like numerals refer to like components or steps, there are disclosed broad aspects of various exemplary embodiments. 
         [0020]      FIG. 1  illustrates an embodiment of a surface mount component on a very fine pitch array. This includes a portion of a circuit board  100 , which contains a ball grid array (BGA) of BGA pads  101  on one side. Two BGA pads  101  are labeled ( 101   a  and  101   b ), but others are present in the grid pattern as illustrated in  FIG. 1 . In an exemplary embodiment BGA pads  101  form a 0.65 mm pitch grid, meaning that BGA pads  101   a  and  101   b  are spaced 0.65 mm center-to-center apart in a square grid. However, BGA pads  101  may also form a substantially rectangular grid, where the BGA pads  101  are spaced 0.65 mm apart or another spacing. The grid may also be varied in its arrangement. BGA pad  101  is connected to corresponding via  110  by way of trace  102 . 
         [0021]    The standard structure of via  110  includes via pad  111  and through-hole via  114 , having via barrel  112  and epoxy fill  113 . Typically, via pad  111  will be substantially circular in shape and have a diameter of 0.46 mm, through-hole via  112  will be substantially circular in shape and have a radius of 0.25 mm, and epoxy fill  113  will be substantially circular in shape and have a radius of 0.2 mm. All dimensions may have a tolerance of ±10%. Via barrel  112  has an outer radius to fit in through-hole via  114  and contain epoxy fill  113 . 
         [0022]    On the side of circuit board  100  opposite BGA pad  101 , component  121  is mounted to two adjacent through-hole vias using solder pad  120  on each via. Vias  110  also form a 0.65 mm pitch center-to-center grid, which is offset from the BGA pad grid, such that they do not overlap. 
         [0023]    In an exemplary embodiment, component  121  is a two-lead 0201 component, having a length of 0.5 mm and a width of 0.25 mm. In the embodiment component  121  is a discrete component. In some cases, the component  121  is a capacitor that can be used for decoupling. Solder pad  120  is used to extend the conductive area of via pad  111  to connect component  121  between two BGA pads due to the dimensions of via  110  on a 0.65 pitch BGA. 
         [0024]      FIG. 2  illustrates an embodiment of a process for attaching a surface mount component on a very fine pitch array. The method generally consists of steps  210 ,  220 ,  230 ,  240 , and  250 . The final product results in the structure depicted in  FIG. 3 . 
         [0025]    At step  210 , two adjacent vias are selected. The structure of each via includes via pad  211  and through-hole via  212 , which initially has epoxy fill  213 . Typically, a hole is drilled and then coated with a conductive material, such as copper. Other via construction methods are recognized by those skilled in the art. 
         [0026]    At step  220 , two adjacent vias are entirely covered with solder mask  221 . In an exemplary embodiment, solder mask  221  is a thin layer of a nonconductive polymer. Solder mask  221  prevents the copper portions of the via from oxidizing and prevents unintended solder bridges from accidentally forming on the circuit board. Solder mask may be applied using a silkscreen process. 
         [0027]    At step  230 , identified landing area  231  is identified in relation to the via and solder mask  242 . Identified landing area  231  is placed such that component  253  may be conductively attached to two adjacent vias. Typically, this will require identified landing area  231  to extend beyond solder mask  232 . However, in an exemplary embodiment, solder mask  232  will touch each side of identified landing area  231 , as depicted in  FIG. 2 . 
         [0028]    At step  240 , a portion of solder mask  232  corresponding to identified landing area  231  is removed to form landing area  241 . This may be accomplished by etching the solder mask to remove material. In an exemplary embodiment solder mask  232  is modified using photolithography. However, other processes may be used to remove a portion of solder mask  232 . 
         [0029]    At step  250 , component  253  is attached using solder pad  252  to two adjacent vias, which are partially covered by solder mask  251 . Solder pad  252  has length  255  and width  254  to substantially fit within landing area  241 . In an exemplary embodiment, solder pad  252  is substantially rectangular in shape. However, solder pad  252  may have other shapes such that an electrical connection can be made with component  253 . 
         [0030]    The steps  210 ,  220 ,  230 ,  240 , and  250  may be carried out by a computer controlled machine. In an exemplary embodiment, a computer aided design tool allows the selection of vias and arrangement of the solder mask, solder pad, and component to be substantially automated. The computer aided design tool may automatically identify appropriate spacing and shape of the solder pad to place standard components on a BGA. A computer aided design tool may also provide instructions to control a machine to manufacture the modified circuit board. Instructions may be exported to the machine or the design tool may directly control the machine. 
         [0031]      FIG. 3  illustrates a cross sectional view of finished assembly  300  of a surface mount component on a very fine pitch array. This view applies to both the device formed at step  250  of  FIG. 2  and attached component  121  of  FIG. 1 . 
         [0032]    Printed Circuit Board (PCB)  301  has vias with filled via barrels  320  attached to backside via  321  on the back side of PCB  301  and extended landing areas  322  that are formed on the front side of PCB  301 . Extended landing areas  322  are formed by the original via structure and the added solder pad which is used to attach component  310  to PCB  301 . Extended landing areas  322  protrude away from filled via barrels  320  such that ports  311  of component  310  may be conductively attached to backside vias  321  through filled via barrels  320 . In an exemplary embodiment extended landing area  322  extends such that it ends to the inner side of ports  311 . Extended landing area  322  is partially covered by solder mask  302  such that conductive portions are not unnecessarily exposed. 
         [0033]    While the figures and descriptions may depict regular circular or rectangular shapes of different elements in exemplary embodiments, it should be understood that alternative shapes may be used such as imperfect polygons and rounded forms. These alternative shapes may be substantially similar to the depicted shapes in area and outline. 
         [0034]    Although the various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be effected while remaining within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the invention, which is defined only by the claims.