Abstract:
A method and apparatus are provided for preventing warpage of printed circuit boards (PCBs) for the purpose of maintaining proper shape and alignment. A PCB is placed on a base of matching shape and slightly larger size. The PCB is secured to the base by a single fastener, preferably through approximately its center. Inwardly curving brackets are mounted along the outer edges of the base in such a way that their central portions rest on top of the PCB. The brackets are constructed of a solid yet flexible non-conducive material and are fastened to the base and, optionally, to each other. The PCB placed in between the base and the brackets is able to expand without warping significantly. This method is especially effective when used to maintain the shape and alignment of the PCB for an antenna.

Description:
BACKGROUND OF THE INVENTION 
     1 . Field of the Invention 
     The present invention relates generally to the prevention of deformities in circuit boards, such as printed circuit boards, and more specifically to preventing warpage in printed circuit boards in antennas. 
     2 . Description of the Related Art 
     In printed circuit boards (PCBs), integrated circuits, active components, passive components, and wiring are formed and/or placed onto one or both sides of an insulating base according to a predetermined pattern. Such PCBs are found in countless types of electronic equipment, running everything from portable radios to immense super-computers. Sophisticated boards may contain several layers of wiring to enable complex connectivity between the various components. 
     Boards are manufactured from a variety of board materials. The most commonly used material is a composition of glass fabrics or fibers bonded with epoxy resins. Other compositions used are made up of various other materials such as aramid fibers and polymide or polytetrafluoroethylene resins. However, these materials have been known to expand when subjected to heat from, for example wave soldering or exposure to the elements. In addition, such materials may be chipped or dropped and broken while being handled. Any such deformity may cause an electrical device to stop functioning properly. The problem of PCB warpage, or bending, is experienced in both the manufacture and use of PCBs. Since in most cases PCBs are secured in place (by pins or screws placed at the boards edges for example), any expansion will cause the board to bend or warp. Devices such as antennas, which are constantly exposed to the elements, are especially susceptible to this problem. Moreover, in the case of an antenna, any PCB warpage can potentially prevent the antenna from being able to receive transmissions properly, since the proper alignment and shape of the PCB is often essential to the antenna&#39;s proper function. 
     Typically, the problem of PCB warpage or bending is dealt with by providing “board stiffeners”, which are rigid in a direction generally perpendicular to the plane of the board. The fundamental nature of these separate board stiffeners is to act as common mechanical support members secured to the board, much like beams in the shape of an “I”(I-beams) or “L”(L-beams) in larger mechanical structures. Board stiffeners are installed at selected locations, generally both longitudinally and crosswise, to ensure that the board remains planar. A typical board stiffener comprises an elongated metallic bar which is mounted in a fixed relationship onto the upper or bottom surface of the board. To securely affix the stiffener to the board in an appropriate position, typical installation makes use of a conventional fastening technique, such as riveting or soldering, at a plurality of locations on the board. In most cases, the stiffener is constructed of an electrically conductive material. This allows the board stiffener to function as a power distributor or as a common electrical ground for a portion of the circuitry embodied within the board, in addition to providing a mechanical function. There are many different board stiffener structures, such as grooved wrap-around frames. A grooved wrap-around frame is a frame that supports the entire perimeter of a PCB with engaging tabs that fit through the PCB, and are bent over on the opposite side of the board. 
     However, in many cases, the board stiffeners themselves or indeed the entire casing of an electronic device, may be subject to the same aforementioned distortions and deformations. These may result in stress-induced warpage of a PCB. 
     Another solution is to provide PCBs that have low expansion factors, leading to reduced likelihood of PCB warpage. These warp-resistant PCBs, however, tend to be more expensive than typical PCBs. 
     It would be advantageous to have a method and apparatus that would significantly reduce PCB warpage. It would also be advantageous to provide solutions to maintain proper PCB alignment and shape in an antenna despite the PCBs possible expansion due to the influence of the elements. Furthermore, it would be advantageous to provide such solutions with relatively inexpensive PCBs for use in devices, such as antennas, that are exposed to the elements. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for holding in place a printed circuit board (PCB) so as to prevent the PCB from warping. The method entails fastening a PCB to a base structure, placing a frame over the PCB, and securing the frame to the base at a single point in the relative center of the PCB. The apparatus comprises a base to which a PCB is fastened and a frame overlaying the PCB and secured to the base. 
     The advantage of this invention is that a PCB may expand in the XY plane without the expansion causing the PCB to warp. Only expansion in the Z direction is substantially restricted. Also, since the PCB is allowed to expand, the PCB may be constructed of materials that are cheaper than those materials that are more resistant to warpage. Moreover, a board stiffener need not be attached to the PCB. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Objects, features and advantages of the invention will be more readily apparent from the following detailed description of a preferred embodiment of the invention in which: 
     FIGS. 1A and 1B depict an exemplary embodiment of connected brackets holding a PCB; 
     FIGS. 2A and 2B depict an exemplary bracket design; FIG. 2C depicts an alternative design; 
     FIG. 3 depicts an example of the placement of two adjacent brackets; 
     FIG. 4 depicts a flow-chart of a method for holding a PCB to a base using brackets in accordance with the disclosed invention; 
     FIG. 5 depicts an exemplary embodiment of non-connected brackets holding a PCB; 
     FIG. 6 depicts another exemplary embodiment of connected brackets holding a PCB; 
     FIG. 7 depicts another exemplary bracket design; and 
     FIG. 8 depicts an exemplary embodiment of a base and top holding a PCB. 
     Like drawing numerals refer to corresponding parts throughout the several views of the drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention provides a method and apparatus for significantly limiting warpage of a printed circuit board (PCB), such that the PCB maintains its proper shape, form, and alignment. This is especially useful in an antenna implemented on top of a PCB, so as to ensure the antenna&#39;s proper function despite exposure to the elements. 
     PCBs are known to expand when exposed to heat. Therefore, attempting to hold them in place in a constant shape and size may cause them to bend or warp. The invention disclosed is a method and apparatus for allowing a PCB to expand freely in the x-y plane, thus significantly reducing PCB warpage. The invention further allows the board to maintain its relative shape, form, and alignment. This is achieved by use of a specialized apparatus, several embodiments of which are described in detail herein. 
     Reference is now made to FIGS. 1A and 1B where diagrams of an exemplary embodiment of the invention are provided. FIG. 1A shows a top view of apparatus  100  and FIG. 1B shows a cross-section of apparatus  100  along line A—A of FIG.  1 A. FIGS. 1A and 1B show a base  110 , a PCB  120 , brackets  130 - 1  to  130 - 4 , and a fastener  140 . The PCB  120  is placed on the base  110 , which supports PCB  120 . The PCB  120  is secured to base  110  by a single fastener  140  through approximately the center of PCB  120 . Fastener  140  may be a screw, a pin, or another fastening device capable of attaching PCB  120  to base  110 . Base  110  is preferably made of a solid non-conducive material such as plastic, and is preferably of similar shape, but slightly larger than PCB  120 . Alternatively, base  110  may be made of a conducting material. Brackets  130 - 1  through  130 - 4  are connected to base  110  in such a way that they are bent inward, and apply downward pressure on PCB  120 . 
     A representation of an exemplary bracket  130  is provided in FIGS. 2A and 2B wherein FIG. 2A shows a side view of bracket  130  and FIG. 2B shows a top view of bracket  130 . Bracket  130  is preferably made of a solid, flexible non-conducive material. Bracket  130  preferably has a central portion  131 , a first end  132  with an aperture  134  opening vertically therethrough, and a second end  136  with an aperture  138  opening vertically therethrough. The first end  132  and second end  136  are vertically displaced such that when the aperture  134  of a first bracket, e.g.,  130 - 1 , is vertically aligned with the aperture  138  of a second bracket, e.g.,  130 - 2 , the central portions  131  of the first bracket  130 - 1  and second bracket  130 - 2  are substantially horizontally aligned. The brackets are secured together by a fastener that fits through the apertures  134  and  138 . The same fastener may be used to secure the brackets  130 - 1  and  130 - 2  to the base  110  (FIG.  1 A). 
     In an alternative embodiment, a fastener (not illustrated) protrudes from base  110  while a first bracket and a second bracket are placed over the base  110  such that the protruding fastener extends through aperture  138  of the first bracket and aperture  134  of the second bracket, securing the first and second brackets to the base  110 . In yet another embodiment, bracket  130  may have a fastener as part of its structure, protruding downwards from its higher edge  132 . A fastener may be a screw, a pin, or another fastening device capable of connecting the bracket  130  to the base  110 . 
     In another embodiment shown in FIG. 2C, a bracket  130 A is used instead of bracket  130 . In this embodiment, only areas  139 B touch the PCB  120  and thereby hold it in place. The remainder of bracket  130 A has an indentation  139 A that prevents that part of bracket  130 A from touching the PCB  120 . 
     FIG. 3 shows a three-dimensional rendering of an exemplary placement of two adjacent brackets  130 . Bracket  130 - 2  is placed perpendicular to bracket  130 - 1 , with the higher end  132 - 2  of bracket  130 - 2  placed on the lower end  136 - 1  of bracket  130 - 1 . Similarly, the higher end (not illustrated) of a third bracket is placed on the lower end of bracket  130 - 2 . A fourth bracket (not illustrated) is placed so that its higher end is on the third bracket&#39;s lower end, and its lower end is beneath the higher end  132 - 1  of bracket  130 - 1 , forming a rectangular perimeter of four brackets. This method for placing the brackets preferably results in the brackets holding each other downward, thus increasing the downward pressure applied by the combined brackets. It should be noted that a rectangular shape is shown for convenience only; other shapes may be used. It should be further noted that a person skilled in the art could construct connected brackets  130  as one or more monolithic structures for use with the invention as a single bracket frame, and maintain some of the anti-warp qualities described above. 
     Returning to FIGS. 1A and 1B, brackets  130 - 1  through  130 - 4  are placed on base  110  around PCB  120  according to the method described above and are secured to the base by a fastener in a position that has them at least slightly bent inward towards PCB  120 . This has the effect of placing the central portion of each bracket in a position that applies downward pressure on PCB  120 . In essence, while PCB  120  is able to expand outward (between base  110  and brackets  130 ), it is denied vertical movement that would alter its relative alignment in the overall system. Since PCB  120  is able to expand freely in the x-y plane and is not physically restricted to a certain size and shape, no, or significantly reduced, PCB warpage occurs as a result of this expansion. This allows for the use of low cost PCBs for demanding applications rather than the more expensive PCBs made from materials that are more resistant to warpage. 
     Reference is now made to FIG. 4 where a flow chart is shown describing illustrative steps for securing a PCB to a base in accordance with the disclosed invention. In step S 410 , the PCB is placed on the base. This placement should be done such that a hole through the PCB, preferably located at approximately its center, is placed at a location on the base where a fastener can be inserted. In step S 420 , the PCB is fastened to the base by use of a fastener. The fastener may be a screw, pin, nail or any other type of fastener capable of securing the PCB to the base. At step S 430 , a determination is made whether the brackets are to be interconnected. If in step S 430  it is determined that brackets are to be connected to each other, this step takes place at step S 440  and the process continues to step S 450 ; otherwise, the process continues directly to step S 450 . At step S 450 , the brackets are placed on top of the PCB; and subsequently, in step S 460 , the brackets are fastened to the base by using fasteners as may be necessary. 
     In another embodiment of this invention, schematically shown in FIG. 5, downward pressure on PCB  120  is supplied by only two brackets  510 - 1  and  510 - 2  on opposite sides of the PCB that are not connected to each other. Similarly to bracket  130 , brackets  510 - 1  and  510 - 2  are preferably made of a solid, flexible non-conductive material. This embodiment provides essentially the same anti-warp qualities explained above. A person skilled in the art could use any number of brackets, where the number is equal to or larger than two. Such a person could place additional non-connecting brackets on the same side as a first bracket. 
     Reference is now made to FIG. 6, where a diagram of yet another exemplary embodiment of the invention is provided. The difference between this embodiment and the one depicted in FIG. 1 is in the brackets. Brackets  630 - 1  through  630 - 4  each have two notches  631 ,  632  at the same locations, one on the top at one end of the bracket and the other on the bottom at the other end, as can be seen in a side view of a bracket  630  in FIG.  7 . These notches facilitate the connection of the brackets to each other with a notch on the top side of one bracket mating with a notch on the bottom side of another bracket. Bracket  630  further has apertures  635 ,  636  at both its edges. Fasteners may be fitted through the aforementioned apertures in order to secure bracket  630  to base  110 . A portion of each bracket  630  is placed on top of PCB  120 . Once fastened to base  110 , brackets  630 - 1  through  630 - 4  apply downward pressure on PCB  120 . Thus, this embodiment also provides essentially the same anti-warp qualities described above. It should be noted that a person skilled in the art could construct any number of connected brackets  630  as a single structure for use with the invention, and maintain all of the aforementioned anti-warp qualities. 
     Reference is now made to FIG. 8, where a cross section of another exemplary embodiment of the invention is shown. A PCB  820  is placed on base  810  and secured to base  810  by means of a fastener through hole  840  where a corresponding hole is available through PCB  820 . A top  830  is placed on base  810  and secured to base  810  with fasteners that are inserted through holes  850 . The top  830  has two spaced apart parallel brackets  860  (only one of which is shown) running in one direction and two spaced apart parallel brackets  870  running in a perpendicular direction. The four brackets extend downward toward base  810  and are designed to hold PCB  820  in its planar position while allowing movement in the XY plane. As a result, the PCB  820  is essentially held floating and the structure accomplishes the desired results of avoiding warpage in the Z direction. 
     While the present invention has been described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.