Abstract:
Printed circuit boards (PCB&#39;s) with edge connectors undergo bending stresses whenever the edge connectors are plugged into mating connectors. The bending stresses causes deformation of the printed circuit board, which can have deleterious effects on electrical components thereon. Slots are provided on the PCB to enable the portion of the PCB surrounding the edge connector to bend relative to the remainder of the PCB, thereby confine the bending to a localized area between the ends of the slots, and isolate the electrical components from any stresses caused thereby.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims priority from U.S. Provisional Application No. 60/938,044, filed May 15, 2007, entitled “Isolating Stress On A Printed Circuit Board”, by Chamy et al., which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to localizing bending on a printed circuit board (PCB) for minimizing stress on components on the PCB, and in particular to the isolation of specific components on the PCB from bending stresses caused by the interconnection of an edge connector to a mating connector. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional printed circuit boards (PCB)  1  often include a PCB edge connector  2  to provide connectivity to adjacent or superposed PCBs or other electrical connectors. Spacers  3  with fasteners  4  are provided for separating the PCB  1  from adjacent mechanical components, e.g. housing, or other electrical components, e.g. other PCBs. In many cases, due to tolerance variations of supporting mechanical components and connectors, the connection of the electrical connectors  2  forces some displacement (see  FIG. 1 ) of the connector  2 , which causes bending of the PCB  1  located between lines  5  and  6 . The amount of force applied permanently to connector  2  and the amount of bend are proportional to the amount of the displacement of the connector  2 . Unfortunately, the bending of the PCB  1  is harmful to other components, such as ceramic capacitors, integrated circuits (IC&#39;s) in a ball grid array (BGA) and similar packages, and other electronic components in rigid packages. 
         [0004]    Traditionally, designers used cables to eliminate PCB bend. The disadvantage of a cabled solution is that it adds complexity, reduces reliability, adds one or more additional connectors or soldered wires, and requires additional space which is not always available. 
         [0005]    An object of the present invention is to overcome the shortcomings of the prior art by providing a PCB with a slot to ensure the PCB bends in a desired position, thereby isolating specific components on the PCB from stress and minimizing the harmful effects of the displacement of the PCB edge connector by localizing the area of the PCB bend. 
       SUMMARY OF THE INVENTION 
       [0006]    Accordingly, the present invention relates to a printed circuit board device comprising: 
         [0007]    a printed circuit board including a plurality of electrical components; 
         [0008]    an edge connector mounted on a first edge of the printed circuit board, and electrically coupled to the plurality of electrical components via trace leads; 
         [0009]    a first slot extending from an edge of the printed circuit board on one side of the edge connector to a first end; and 
         [0010]    a second slot extending from an edge of the printed circuit board on an opposite side of the edge connector to a second end; 
         [0011]    wherein the first and second slots define an isolated area of the printed circuit board, which supports the edge connector, 
         [0012]    wherein the isolated area is connected to a main section of the printed circuit board, which supports the plurality of electrical components, via a neck, through which the trace leads extend; and 
         [0013]    wherein ends of the first and second slots define an axis about which the isolated area is bendable relative to the main section of the printed circuit board; 
         [0014]    whereby any bending caused by the connection of the edge connector to a mating connector will be localized in the area between the first and second ends, thereby isolating the electrical components from any stresses caused thereby. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein: 
           [0016]      FIG. 1  is an isometric view of a conventional printed circuit board with an edge connector therein; 
           [0017]      FIG. 2  is an isometric view of a printed circuit board with an edge connector in accordance with the present invention; 
           [0018]      FIG. 3  is an isometric view of a printed circuit board with an edge connector in accordance with another embodiment of the present invention; and 
           [0019]      FIG. 4  is an isometric view of a printed circuit board with an edge connector in accordance with another embodiment of the present invention with angled slots. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    With reference to  FIG. 2 , a printed circuit board (PCB)  11 , according to the present invention, includes an electrical, or other form of, edge connector  12  mounted on a first edge of the PCB  11  to provide connectivity to adjacent or superposed PCBs, and/or another electrical, or other form of, connector. Spacers  13  extend from the PCB  11  for separating the PCB  11  from adjacent mechanical, e.g. a housing, or electrical, e.g. other PCBs, components, and are connected to the PCB  11  with threaded fasteners  14  (or other suitable means). Electrical trace leads  15  extend from the edge connector  12  through a confined area or neck  16  to electrical or electro-optical components  17 . 
         [0021]    While the edge connector  12  is connected to other connectors, any bending of the PCB  11  is localized to the confined area  16  by providing, e.g. cutting, slots  18   a ,  18   b ,  19   a  and  19   b  in the PCB  11  adjacent to, e.g. surrounding, connector  12  in first (longitudinal) and second (lateral) perpendicular directions defining an isolated section  20 , which includes the connector  12 . The geometry of the slots  18  and  19  enables the isolated section  20  to bend relative to the remainder of the PCB  11 , which contains components  17 , and confines the area of the bend to the confined area  16 , thereby isolating and protecting the components  17  from stress caused by the bending of the connector  12 . 
         [0022]    The longitudinal slots  18   a  and  18   b  extend from the first edge of the PCB  11 , on either side of the connector  12 , perpendicular to the direction of the applied force and resulting displacement, indicated by the arrows in  FIG. 2 . The lateral slots  19   a  and  19   b  localize any bending caused by the applied force to the confined area  16  between the ends thereof, and isolate the components  17 , which are outside of the confined area  16 , from the stress in the confined area  16  caused by the bending of the connector  12 . The longitudinal slots  18   a  and  18   b  enable the isolated section  20  to bend relative the remainder of the PCB  11  about an axis extending between the ends of the longitudinal slots  18   a  and  18   b  and along the lateral slots  19   a  and  19   b  parallel to the first edge of the PCB  11 . 
         [0023]    The lateral slots  19   a  and  19   b  extend from the longitudinal slots  18   a  and  18   b , substantially perpendicular thereto, whereby the closed ends of the slots  19   a  and  19   b  define the boundaries of the confined area  16 . The lateral slots  19   a  and  19   b  enable the isolated section  20  to rotate slightly about a longitudinal axis LA parallel to the longitudinal slots  18   a  and  18   b . When the lengths of the lateral slots  19   a  and  19   b  are significant, the bend of the PCB  11  is localized to the confined area  16  remote from the connector  12  and the components  17 . When the lengths of slots  19   a  and  19   b  are equal to zero, the bend of the PCB  11  is localized between longitudinal slots  18   a  and  18   b  and extends longitudinally farther, e.g. to the connector  12 . Accordingly, the slots  18   a ,  18   b ,  19   a  and  19   b  also reduce the force applied to connector  12  for the same displacement as compared to a solid PCB, thereby reducing stresses on the connector  12 . The slots  18   a ,  18   b ,  19   a  and  19   b  are constrained to longitudinal and lateral directions, but can have any trajectory. 
         [0024]      FIG. 3  illustrates another embodiment of the present invention in which a PCB  21  includes an electrical (or other form of) edge connector  22  mounted on a first edge thereof with electrical traces leads  25  extending therefrom through a neck or confined area  26  to electrical or electro-optic components  27 . First lateral slots  29   a  and  29   b  extend from second and third sides of the PCB  21 , respectively, which are substantially perpendicular to the first side (although other embodiments are within the scope of the invention), while longitudinal slots  28   a  and  28   b  extend perpendicularly from the ends of the first lateral slots  29   a  and  29   b , respectively. Second lateral slots  29   c  and  29   d  extend perpendicularly from the ends of the longitudinal slots  28   a  and  28   b , respectively, generally parallel to the first edge. The longitudinal and lateral slots  28   a ,  28   b  and  29   a  to  29   d  form an isolated section  31  with a stepped or saw toothed upper edge, which enables the isolated section  31  to rotate about an axis defined by second lateral slots  29   c  and  29   d  and the ends of the longitudinal slots  28   a  and  28 b. The saw-toothed edges also enable the isolated section  31  to more easily rotate about a longitudinal axis LA. Moreover, the stepped edges minimizes the area of the isolated section  31  and thereby reduce the amount of bending stress applied to the confined area  26 . Additional longitudinal and lateral slots are also within the scope of this invention, as well as slots extending at an acute angle to the longitudinal and lateral axes and edges, as illustrated in  FIG. 4 . 
         [0025]      FIG. 4  illustrates another embodiment of the present invention in which a PCB  41  includes an electrical (or other form of) edge connector  42  mounted on a first edge of the PCB  41  with electrical traces leads  45  extending therefrom through a neck or confined area  46  to electrical or electro-optic components  47 . First lateral slot sections  49   a  and  49   b  extend from second and third sides of the PCB  41 , respectively, which are substantially perpendicular to the first side (although other embodiments are within the scope of the invention), while longitudinal slot sections  48   a  and  48   b  extend from the ends of the first lateral slot sections  49   a  and  49   b , respectively, at some angle, e.g. acute, obtuse or right angle. Second lateral slot sections  49   c  and  49   d  extend from the ends of the longitudinal slot sections  48   a  and  48   b , respectively, generally parallel to the first slot sections  49   a  and  49   b , but not necessarily. The second lateral slot sections  49   c  and  49   d  extend from the ends of the longitudinal slot sections  48   a  and  48   b , respectively, at some angle, e.g. acute, obtuse or right angle. The longitudinal and lateral slot sections  48   a ,  48   b  and  49   a  to  49   d  form an isolated section  51  with a stepped or saw toothed upper edge, which enables the isolated section  51  to rotate about an axis defined by the ends of the second lateral slot sections  49   c  and  49   d . The saw-toothed edges also enable the isolated section  51  to more easily rotate about a longitudinal axis LA. Moreover, the stepped edges minimizes the area of the isolated section  51  and thereby reduce the amount of bending stress applied to the confined area  46 .