Abstract:
A universal snap-fit system for interconnecting multiple circuit boards in a stacked relationship is provided. The system allows circuit boards to be stacked with a minimum of assembly time. In addition, the system allows circuit boards of varying thicknesses to be stacked, without requiring the provision of system components in a multitude of sizes. The provided system also allows more than two circuit boards to be interconnected to one another in a stacked relationship without requiring multiple sets of attachment holes in interior circuit boards. In addition, more than two circuit boards can be stacked quickly and easily.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the interconnection of circuit boards. In particular, the present invention relates to a universal snap-fit spacer system for stacking circuit boards, including circuit boards of different thicknesses.  
         BACKGROUND OF THE INVENTION  
         [0002]    Electrical and electronic circuits are often formed on planar circuit boards. Often, it is desirable to interconnect two or more circuit boards to one another in a stacked configuration. When stacking multiple circuit boards, a minimum spacing must be maintained between a first circuit board and the circuit board or boards adjacent to the first circuit board. Such spacing is required for various reasons, including the prevention of electrical shorts between the boards, and the provision of cooling airflow over components interconnected to the circuit boards.  
           [0003]    Systems for interconnecting circuit boards include threaded fasteners in combination with spacers. In such a system, a screw (or bolt) is passed through a hole formed in a first circuit board. Next, the spacer is placed over the screw, before the end of the screw is passed through a hole formed in a second circuit board. Finally, a nut is placed over the end of the threaded fastener to secure the assembly. Although a system of threaded fasteners in combination with spacers is capable of securely fastening a first circuit board to a second circuit board, such a system is not entirely satisfactory for a variety of reasons. For instance, considerable labor is involved in piecing together and securing the assembly, thus resulting in a relatively slow and expensive assembly process.  
           [0004]    In addition, in order to interconnect a third circuit board using such a system, additional holes must be formed in either the first or second circuit board. This is disadvantageous, as space on individual circuit boards is often at a premium. In addition, the assembly of an electrical component having more than two interconnected circuit boards creates additional assembly difficulties, as access to the fasteners used to interconnect additional circuit boards is often limited. Alternatively, stacks of three or more circuit boards may be created by interposing interior circuit boards between two spacers, and using a screw that passes through all of the circuit boards. However, the assembly process for stacking three or more circuit boards in this manner is even more difficult than stacking a pair of circuit boards.  
           [0005]    Another system for interconnecting multiple circuit boards involves the use of threaded spacer members in connection with threaded screws (or bolts). In such a system, the screw is placed through a hole formed in a first circuit board, and is then threaded into the threaded spacer. Next, a second screw or bolt is placed through a hole in the second circuit board, and is then threaded into the opposite end of the threaded spacer. Although such a system can decrease assembly times as compared to systems using spacers having smooth bores in combination with threaded fasteners, the threading of multiple components to one another is still required. Accordingly, the interconnection of multiple circuit boards using such a system remains relatively time consuming and expensive. In addition, such a system may also require the use of additional holes in circuit boards where more than two circuit boards are attached to one another.  
           [0006]    Snap-fit, one piece interconnects have also been used for interconnecting circuit boards. Such one piece interconnects are capable of reducing the time required to interconnect multiple circuit boards. However, such one piece interconnects must be supplied in a variety of sizes, to accommodate different circuit board thicknesses and to accommodate different spacings between interconnected circuit boards. In addition, where more than two circuit boards are interconnected, interior circuit boards must have an additional set of holes formed therein, limiting the area of the circuit board available for electrical componentry  
           [0007]    For the reasons set forth above, there is a need for a method and apparatus for interconnecting multiple circuit boards quickly and inexpensively. In addition, there is a need for a method and apparatus that allows for more than two circuit boards to be interconnected that requires a minimal amount of circuit board area. There also is a need for a method and apparatus for interconnecting multiple circuit boards that is reliable in operation and inexpensive to implement.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to solving these and other problems and disadvantages of the prior art. According to the present invention, a spacer element and a fastener member are provided for interconnecting multiple circuit boards. In operation, a first fastener member is used to interconnect a first circuit board to a spacer element. A second fastener member is then used to interconnect a second circuit board to the spacer element. The interconnections between the circuit board and the fastener member, and between the spacer element and the fastener member are made by a locking assembly provided on either end of the fastener member that allows the fastener member to be snapped together with the spacer element and with a circuit board or a second spacer element.  
           [0009]    In accordance with an embodiment of the present invention, the locking assembly of the fastener member comprises a plurality of adjacent locking members interconnected to the body of the fastener member by a resilient portion. The resilient portion biases the locking members such that in a nominal position the distance between the outer edge of a first locking member and the outer edge of a second locking member adjacent to the first locking member is a first amount. When a force sufficient to overcome the biasing force is presented in a direction tending to draw adjacent locking members towards one another, the distance between the outer edge of the first locking member to the outer edge of the second locking member can be reduced to a second amount, that is less than the first amount.  
           [0010]    In accordance with an embodiment of the present invention, the surface of the locking member proximate to the ends of the fastener member may be angled, to present a camming surface. Thus, when the fastener members are pressed into a hole having a diameter that is about equal to or slightly greater than the second distance, the locking members are pressed towards one another and the fastener can be inserted into the hole.  
           [0011]    The biasing force provided by the resilient portion of the fastening member causes the distance between the outer edges of the locking members to return to the first or nominal amount after the locking members have passed through the hole, or have reached a recess in the interior of the spacer element. The surface of the locking members adjacent to the body portion of the fastener member may be perpendicular to the longitudinal axis of the fastening member, to form a locking surface that prevents the fastener member from being removed from the hole once the resilient members have returned the locking members to their nominal position. In a typical assemblage, a first fastener member is used to secure a first circuit board to a spacer element, while a second fastener member is used to interconnect a second circuit board to the spacer element.  
           [0012]    In accordance with an embodiment of the present invention, the spacer element has an interior bore diameter about equal to the distance between the outer edges of the locking members when the locking members are compressed. Along the interior bore, multiple recesses may be formed. These recesses may be spaced at predetermined intervals, allowing a fastener member to be locked at varying depths within the spacer element.  
           [0013]    According to still another embodiment of the present invention, depth control holes may be formed in the spacer element that intersect the interior bore and that are transverse to the longitudinal axis of the spacer element. Depth control rods may then be inserted in the depth control holes to prevent fastener members from being inserted into the spacer element further than the position of the depth control rod.  
           [0014]    According to an embodiment of the present invention, multiple circuit boards may be interconnected to one another. In such an embodiment, a first fastener member is inserted into a hole formed in a first circuit board. A first end of the fastener member may be inserted into a first spacer element, and a second end of the fastener member may be inserted into a second spacer element such that the circuit board is held between the two spacer elements. A second circuit board may then be interconnected to the first spacer element by inserting a second fastener member into a hole in the second circuit board, and by inserting the second fastener member into an end of the first spacer element opposite the first fastener member. Similarly, a third circuit board may be stacked with the first two circuit boards by inserting a third fastener member through a hole in the third circuit board, and by inserting the third fastener member into an end of the second spacer element opposite the first fastener member.  
           [0015]    According to yet another embodiment of the present invention, different thicknesses of circuit boards may be accommodated by a single fastener member and spacer element combination. For instance, a first circuit board thickness maybe accommodated by inserting the fastener member into the spacer element up to a first depth, while a second circuit board thickness may be accommodated by inserting the fastener member into the spacer element up to a second depth. According to still another embodiment of the present invention, spacer members may be used in combination with spacer elements to accommodate different circuit board thicknesses.  
           [0016]    These and other advantages and features of the invention will become more apparent from the following description of illustrative embodiments of the invention, taken together with the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is an exploded perspective view of a universal snap-fit spacer system in accordance with an embodiment of the present invention;  
         [0018]    [0018]FIG. 2A is an elevational view of the universal snap-fit spacing system of FIG. 1 interconnecting first and second circuit boards;  
         [0019]    [0019]FIG. 2B is a cross-sectional view taken along section line A-A of FIG. 2A;  
         [0020]    [0020]FIG. 2C is a cross-sectional view of the universal snap-fit spacing system of FIG. 1 with a fastener member partially inserted in a spacer element;  
         [0021]    [0021]FIG. 3A is an elevational view of a universal snap-fit spacer system in accordance with an embodiment of the present invention, interconnecting first, second and third circuit boards;  
         [0022]    [0022]FIG. 3B is a cross-sectional view taken along section line B-B of FIG. 3A;  
         [0023]    [0023]FIG. 4A is an elevational view of a universal snap-fit spacer system in accordance with an embodiment of the present invention, interconnecting a first circuit board having a first thickness and a second circuit board having a second thickness; and  
         [0024]    [0024]FIG. 4B is a cross-sectional view taken along section line C-C of FIG. 4A. 
     
    
     DETAILED DESCRIPTION  
       [0025]    With reference now to FIG. 1, various components of a universal snap-fit spacer system  100  are illustrated. In general, the system  100  includes a fastener member  104  and a spacer element  108 . In FIG. 1, two fastener members  104   a  and  104   b  are illustrated.  
         [0026]    The fastener member  104  generally includes a body portion  110 , and a resilient portion  112 . A locking assembly  116  is interconnected to the body portion  108  of the fastener member  104  by the resilient portion  112 . In the embodiment of the fastener member  104  illustrated in FIG. 1, a locking assembly  116  is formed at each end of the fastening member  104 . According to the embodiment illustrated in FIG. 1, each locking assembly  116  includes a pair of locking members  120  that comprise a camming surface  124  and a locking surface  128 . In general, the locking members  120  are interconnected to the body portion  110  of the fastener member  104  by a pair of stem members  132  that comprise the resilient portion  112 . A gap  136  is formed between the stem members  132 .  
         [0027]    The spacer element  108  comprises a cylindrical member  144  with an interior bore  148  formed concentrically with the longitudinal axis of the cylindrical member  144 . Depth control holes  152  are formed through the cylindrical member  144 , such that they are transverse to the longitudinal axis of the cylindrical member  144  and intersect the interior bore  148 . Exterior grooves  156  may be formed about the circumference of the cylindrical member  144  at predetermined intervals. Depth control rods  160 , sized to be received by the depth control holes  152  may also be provided as part of the system  100 . According to an embodiment of the present invention, the depth control rods are held in the depth control holes  152  by friction.  
         [0028]    When no external force is applied to the locking assembly  116 , the locking assembly  116  is in a first or nominal state. In this first state, the distance between the outer extent of a pair of locking surfaces  128  is a first, or maximum amount (e.g., as illustrated in FIG. 1). The distance across the outer extent of the locking surfaces  128  may be reduced to a second, minimal amount, by providing a force that brings the pair of locking members  120  together, closing the gap  136  at an end of the fastener member  104 . In general, the edges of the camming surfaces  124  opposite the locking surfaces  128  present a maximum diameter that is less than the diameter of the bore  148 . As the locking members  120  are pressed into the interior bore  148 , the camming surfaces  124  force the locking members  120  together, across the gap  136 . Thus, the gap  136  allows the maximum distance across the locking members  120  to be about equal to the diameter of the interior bore  148 . Accordingly, the fastener member  104  is free to enter the spacer element  108 . When a first recess, such as recess  208   a  (see FIG. 2B), is encountered, the biasing force provided by the resilient portion  112  causes the locking members  120   b  to return to their nominal position. In this nominal position, the locking members  120  present a maximum diameter, and the locking edge  140  of the locking members  120  is engaged with the latching surface  216  (see FIG. 2B) of the recess  208 . Accordingly, the fastener member  104  is prevented from being withdrawn from the spacer element  108 . If engagement with a next recess (e.g., recess  208   b ) is desired, the fastener member  104   a  can be pressed further into the spacer element  108 . Forcing the fastener member  104  further into the spacer element  108  causes the tapered surface  212  of the recess  208  to act on the camming surface  124  of the locking members  120 , bringing the locking members  120  closer together across the gap  136 . Accordingly, it can be appreciated that the fastener member  104  can be moved further into the spacer element  108  to engage a next recess, but cannot be withdrawn from the interior bore  148  of the spacer element  108  after a first recess  208  has been engaged.  
         [0029]    With reference now to FIG. 2A, first  200   a  and second  200   b  circuit boards, held together by a snap-fit spacer system  100  in accordance with an embodiment of the present invention are illustrated. From FIG. 2A, it can be appreciated that the first circuit board  200   a  is held between the locking assembly  116  at an end of a first fastener member  104   a  and a first end of the spacer element  108 . Furthermore, it is apparent that the second circuit board  200   b  is held between the locking assembly  116  at an end of a second fastener member  104   b  and the second end of the spacer element  108 .  
         [0030]    With reference now to FIG. 2B, the spacer system  100  and circuit boards  200   a - b  are shown in cross-section, the cross-section being taken along section line A-A in FIG. 2A. In FIG. 2B, the interior features of the spacer element  108  are clearly illustrated. In particular, annular recesses  208  formed within the interior bore  148   b  are visible. In general, the recesses  208  have a maximum diameter that is about equal to or greater than the maximum distance between the edges of the locking surfaces  128  when the locking assembly  116  is in the nominal position. As shown in FIG. 2B, the recesses  208  may include tapered surfaces  212  on a side of the recesses  208  proximal to the center of the spacer element  108  to assist the camming surfaces  124  in forcing the pair of locking members  120  towards one another, allowing the fastener members  104  to be pushed towards a recess  208  deeper within the interior bore  148 . A latching surface  216  may be formed perpendicular to the longitudinal axis of the interior bore  148  and on a side of the recess proximal to the nearest end of the spacer element  108 .  
         [0031]    With reference now to FIG. 2C, a first fastener member  104   a  is shown being inserted into a spacer element  108 . As illustrated in FIG. 2C, the camming surfaces  124  force the stem members  132  towards one another, closing or reducing the gap  136  at the end of the fastener member  104   a as the fastener member is inserted into the hole  202   a  in the circuit board  200   a  or the interior bore  148  of the spacer element  108 . With the stem members  132  forced together, the distance across the opposite locking surfaces  128  of the locking assembly  116  is reduced to an amount about equal to the diameter of the hole  202   a  or of the interior bore  148 .  
         [0032]    In FIG. 2B, the fastener members  104  are each shown with the locking surfaces  128  of a locking assembly  116  engaged with the latching surface  216  of recesses  208 . Therefore, it is apparent that the locking assembly  116  at a first end of the first fastener member  104   a  was pushed past the first  208   a  and second  208   b  recesses before coming into engagement with the third recess  208   c . It will further be noted that the locking surfaces  128  of the locking members  120  are engaged with the latching surface  216  of the third recess  208   c . This engagement prevents the fastener member  104   a  from being withdrawn from the spacer element  108 . Depth control rods  160   a,b  can be seen in position in depth control holes  152 . The first depth control rod  160   a  prevents the first fastener member  104   a  from being pushed past the third recess  208   c , and the second depth control rod  160   b  prevents the second fastener member  104   b  from being pushed past the fourth recess  208   d.    
         [0033]    At a second end of the first fastener member  104   a , the locking assembly  116  can be seen in engagement with a surface of the first circuit board  200   a . In particular, the locking surfaces  128  of the locking members  120  at the second end of the first fastener member  104   a  hold the first circuit board  200   a  against the first end of the spacer element  108 . Likewise, at the second end of the spacer element  108 , the second fastener member  104   b  affixes the second circuit board  200   b  against the spacer element  108 . The locking members  120  at the first end of the second fastener member  104   b  can be seen in engagement with a fourth recess  208   d . In order to position the locking members  120  of the first end of the second fastener member  104   b  in that recess  208   d , fifth  208   e  and sixth  208   f  recesses were passed. In general, the recesses  208   d,e,  and  f  are the mirror images of  208   a, b  and  c . In particular, the recesses  208   d, e  and  f  have tapered surfaces  212  oriented to cooperate with the camming surfaces  124  in reducing the effective diameter of the locking members  120  of fastener members  104  inserted into the second end of the spacer element  108 , for example while the fastener member  104   b  is being brought into engagement with the fourth recess  208   d , as explained above.  
         [0034]    With reference now to FIG. 3A, the fastening system  100  of the present invention is shown in an additional embodiment, interconnecting three circuit boards  300 ,  300   a  and  300   b  together in a stacked relationship. In particular, a first spacer element  108   a  is interposed between the first  300   a  and second  300   b  circuit boards, while a second spacer element  108   b  is interposed between the second  300   b  and third  300   c  circuit boards. In addition, a spacer member  304  is shown interposed between a second end of the first spacer element  108   a  and the second circuit board  300   b.    
         [0035]    With reference to FIG. 3B, it can be appreciated that the depth control rod  160  inserted in the depth control hole  152   a  of the second spacer element  108   b  is useful to prevent the second fastener member  104   b  from passing the first recess  208   g  of the second spacer element  108   b  to engage a recess  208   h  or  208   i  deeper within the second spacer element  108   b . Accordingly, the fastener member  104   b  can be inserted in the second spacer element  108   b , through the second circuit board  300   b , through the spacer member  304 , and in the first spacer element  108   a , without causing the second fastener member  104   b  to travel too deeply into the second spacer element  108   b . Furthermore, it can be appreciated that if a depth control rod  160  is inserted in the depth control hole  152   a  of the first spacer element  108   a , the order of assembly of the interconnection between the first  108   a  and second  108   b  spacer elements, the second circuit board  304  and the spacer member  312  is not important. Without a depth control rod in the depth control hole  152   a  of the first spacer element, the second fastener member should first be inserted in the second spacer element  108   b , through the circuit board  300   b , through the spacer member  304 , and finally inserted in the first spacer element  108   a.    
         [0036]    With reference now to FIG. 4A, the fastening system  100  of the present invention is shown in yet another embodiment, interconnecting a first circuit board  400   a  having a first thickness, to a second circuit board  400   b  having a second thickness.  
         [0037]    With reference now to FIG. 4B, the fastening system  100  illustrated in FIG. 4A is shown in a cross-sectional view taken along section line C-C. In FIG. 4B, the first fastening member  104   a  can be seen with a first locking assembly  116   a  engaged with the third recess  208   c  of the spacer element  108 . This configuration allows the second locking assembly  116   b  to hold the first circuit board  400   a  between the locking surfaces  128  of the second locking assembly  116   b  and the first end of the spacer element  108 . The second fastener member  104   b  can be seen with a first locking assembly  116   c  engaged with a sixth recess  208   f . The locking assembly  116   d  at a second end of the second fastener member  104   b  holds the second circuit board  400   b  against the second end of the spacer element  108 . Accordingly, as illustrated in FIG. 4B, by engaging different recesses  208 , along the interior bore  148  of the spacer element  108  with a locking assembly  116  of a fastener member  104 , the system  100  of the present invention is capable of interconnecting circuit boards  400  of different thicknesses to one another in a stacked relationship.  
         [0038]    As an illustration of how the fastener members  104  and spacer elements  108  may be dimensioned in a system  100 , the following is provided as an example. However, it should be appreciated that other spacings and relationships may be used. In general, fastener members  104  and spacer elements  108  should be dimensioned to accommodate the thickness of circuit boards that the system  100  is likely to be used to interconnect. According to this example, the recesses  208  adopted for receiving the locking members  120  of a fastener member  104  inserted in an end of a spacer element  108  are spaced apart from one another by a distance x. The distance from an end of the spacer element  108  to the latching surface  216  of the recess  208  nearest that end of the spacer element  108  is equal to x less the thickness of the thickest circuit board of those circuit boards having a thickness y that is less than x adapted for interconnection using the system  100 . Furthermore, the distance between the locking surfaces  128  of opposite locking assemblies or a fastener member  104  is equal to 3x. Accordingly, as shown in FIG. 1B, a circuit board having a thickness y at an end of a stack of circuit boards, can be interconnected to a spacer element  108  by inserting a fastener member  104  through a hole in the circuit board into the interior bore  148  of the spacer element  108  such that the third recess (e.g., recess  208   c ) is engaged by the locking members  120  at a first end of the fastener member  104 . As a further example, as shown in FIG. 4B, a circuit board  400   b  having a thickness equal to y+2x can be interconnected to another circuit board  400   a  using a fastener member  104   b  inserted through the second circuit board  400   b  and engaged with the sixth recess  208   f.    
         [0039]    Where a circuit board is to be stacked such that it is positioned between two other circuit boards, as illustrated in FIGS. 3A and 3B, a spacer member  304  having a thickness y is provided such that the distance between recesses at the second end of the first spacer element  108   a  is an integer multiple of the distance x from the recesses at the first end of the second spacer element  108   b.    
         [0040]    If a spacer element  108  having a shorter length is desired, it can be cut at a groove  156 . Each groove  156  is positioned so that it lies in or near a plane that includes a latching surface  216  of a recess  208 .  
         [0041]    In accordance with an embodiment of the present invention, the components (e.g., fastener member  104 , spacer element  108  and depth control rods  160 ) are formed from nonconductive materials. For example, the components of the present invention may be formed from nylon, polypropylene or plastic. In accordance with yet another embodiment of the present invention, only the spacer element  108  is formed from non-conductive materials. Where the conduction of electricity between interconnected circuit boards is not a required or desired characteristic, the spacer element  108  may be formed from a conductive material.  
         [0042]    Although the above description discusses the interconnection of circuit boards, the invention is not so limited. For example, the present invention may be utilized whenever a flexible system for quickly interconnecting components is desired. In addition, it should be appreciated that the present invention may be used to interconnect circuit boards to assemblies or components other than additional circuit boards. For example, the present invention may be used to interconnect a circuit board to an enclosure.  
         [0043]    The foregoing discussion of the invention has been presented for purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, within the skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain the best mode presently known of practicing the invention and to enable others skilled in the art to utilize the invention in such or in other embodiments and with various modifications required by their particular application or use of the invention. It is intended that the appended claims be construed to include the alternative embodiments to the extent permitted by the prior art.