Abstract:
A circuit board that is to be mounted in a connector socket includes a plurality of electrical connectors located along a side edge of the circuit board. Retention bosses are formed on first and second opposite sides of the circuit board, each of the retention bosses protruding from a surface of the circuit board and extending parallel to and adjacent to the first edge of the circuit board. When the first edge of the circuit board is inserted into a slot of a connector socket, contact surfaces of the first and second retention bosses contact top surfaces of the connector socket to help immobilize the circuit board with respect to the connector socket. Adhesive layers on the contact surfaces of the first and second retention bosses may adhere to the top surfaces of the connector socket to help hold the circuit board immobile with respect to the connector socket.

Description:
BACKGROUND 
     This application relates to methods of manufacturing and mounting a printed circuit board in a receiving socket such that electrical leads on the printed circuit board maintain good electrical connections with pins in the receiving socket. In particular, the application is concerned with creating a mounting structure that will ensure good electrical connections are maintained even when the assembly is subjected to significant levels of shock and vibration. 
     A printed circuit board (PCB) both mechanically supports and electrically connects electronic components. A PCB may include one or more non-conductive layers which provide mechanical support and electrical separation/insulation for one or more conductive layers. The one or more conductive layers, for example, may include any electrically conductive material such as copper, silver, aluminum, etc. The conductive layers may be formed on the PCB in patterns that allow leads of selected electrical components that are mounted on the PCB to be electrically connected to one another. 
       FIGS. 1A and 1B  illustrate a related art PCB  1 , and a mounting socket  2  that receives the PCB. The PCB  1  includes a substrate  11 , electronic components  12 , and a plurality of electrical leads  13  formed along the lower edge of the substrate  11 . Electrical components  12  can be formed on both sides of the substrate. Likewise, separate electrical leads  13  may be formed on opposite sides of the substrate. Conductive layers or traces on the substrate electrically connect leads of the electrical components  12  to the electrical leads  13  on the bottom edge of the substrate. 
     The PCB is mounted in the socket  2  by pushing the lower edge of the PCB into a slot  22  formed between sidewalls  25  of the socket  2 , as illustrated in  FIG. 1B . Electrical contacts or pins in the slot  22  couple to the electrical leads  13  on sides of the bottom edge of the PCB  1 . The socket may also include pivoting locking clips  21  that engage slots  15  on side edges of the PCB to hold the PCB  1  in the socket  2 . When the locking clips  21  are pivoted outward away from the side edges of the PCB  1 , they may exert an upward force on the bottom edge of the PCB  1  that tends to push the PCB  1  out of the slot  22  of the socket  2 . 
     Unfortunately, when a PCB  1  and mounting slot  2  arrangement as shown in  FIGS. 1A and 1B  are subjected to significant levels of shock and vibration, the PCB  1  can move with respect to the mounting socket  2 . This movement of the PCB  1  can cause an electrical connection between the electrical leads  13  on the bottom edge of the PCB  1  and contacts in the slot  22  to be broken temporarily broken or impaired. Although contact between the electrical contacts  13  and the leads in the slot  22  may not be completely broken, movements of the PCB  1  with respect to the mounting slot  22  may cause the electrical resistance of the connection to vary over time. And this change in electrical resistance alone could cause problems for signals traversing the connection. As a result of these factors, when such an assembly is subjected to significant shock and vibration, it is common for an electrical computing system using this arrangement to report faults or errors, or completely stop responding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrated a background art PCB and mounting socket; 
         FIGS. 2A and 2B  are perspective views of opposite sides of a first embodiment of a PCB having retention bosses that is positioned above a mounting slot; 
         FIG. 3  is a side view of PCB having retention bosses mounted in a mounting slot; 
         FIG. 4  is a cross-sectional view of a PCB having retention basses mounted in a mounting slot; 
         FIG. 5  is a perspective view of a PCB with discontinuous sections of a retention boss; 
         FIG. 6A-6C  are cross-sectional views illustrating alternate cross-sectional shapes of retention bosses; and 
         FIG. 7  illustrates steps of a method of forming a PCB with retention bosses. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A detailed description of exemplary embodiments is provided with reference to the accompanying drawings. Like reference numerals indicate like parts throughout the drawings. 
       FIGS. 2A and 2B  illustrate a printed circuit board (PCB)  100  positioned above a mounting socket.  FIG. 2A  shows a first side  110  of the PCB  100 , and  FIG. 2B  shows a second, opposite side  120  of the PCB  100 . As described above, a variety of electrical components would be mounted on one or both of the first and second sides  110 ,  120  of the PCB  100 . Electrically conductive layers or traces would couple those electrical components to electrical leads  130  formed on the bottom edge of the PCB  100 . For ease of illustration, however, the electrical components and electrically conductive leads and traces are not shown. 
     One or more retention bosses are formed on the sides of the PCB  100 . In the embodiment illustrated in  FIGS. 2A and 2B , a first retention boss  30  is formed on the first side  110  of the PCB  100 , and a second retention boss  40  is formed on the second side  120  of the PCB. The first and second retention bosses  30 ,  40  are formed adjacent the lower edge of the PCB, above the electrical leads  130 .  FIG. 3  shows the PCB  100  after it has been inserted into the mounting slot  22  of a mounting socket  2 . Once the PCB  100  is inserted into the mounting slot  22 , lower surfaces  35 ,  45  of the first and second retention bosses  30 ,  40  abut upper surfaces  25  of the mounting socket  2  on opposite sides of the mounting slot  22 . 
     The presence of the first and second retention bosses  30 ,  40  helps to stabilize the PCB  100  with respect to the mounting socket  2  when the assembly is subjected to shock and vibration. Because bottom surfaces  35 ,  45  of the first and second retention bosses  30 ,  40  abut the upper surfaces  25  of the mounting socket  2 , the PCB is less likely to wobble in the slot  22 , or to rotate around the lower edge of the PCB, when the assembly is subjected to shock and vibration. Any rotation of the PCB that does occur is likely to be a pivoting movement around the upper surfaces  25  of the mounting socket  2 , instead of a point lower down where the electrical leads  130  on the PCB are located. As a result, the bottom edge of the PCB and the electrical leads tend to move laterally from side to side against the bias of the electrical contacts  27  in the receiving slot  22  of the mounting socket  2 . These aspects of the design cause any movements of the bottom edge of the PCB to smaller than movements that would occur if the retention bosses  30 ,  40  were not present. As a result, the electrical connections between the electrical leads  130  on the PCB and the electrical contacts  27  in the mounting socket  2  are better maintained when the assembly is subjected to shock and vibration. 
     The retention bosses  30 ,  40  may be any length. In some embodiments, the retention bosses may run along substantially the entire length of the PCB. In alternate embodiments, the retention bosses may only extend along a portion of the length of the PCB. In still other embodiments, two or more discontinuous segments of a retention boss may be formed along a single side of the PCB. 
     For example,  FIG. 5  illustrates a PCB  100  with three discontinuous segments  50 ,  52 ,  54  of a retention boss formed on one side of the PCB. The retention boss may be made discontinuous to avoid covering up an electrical component that requires air cooling for proper operation. Alternatively, it may be advantageous to form only a few segments of the retention boss along the length of the PCB to minimize the weight of the assembly, or to reduce material consumption. Several separate segments of a retention boss formed along the length of the retention boss may provide most of the immobilizing benefits as a continuous retention boss formed along the entire length of the PCB. 
     In some embodiments, the length of the first retention boss  30  is controlled such that first and second end surfaces  34 ,  36  of the first retention boss  30  engage corresponding inner surfaces  24 ,  26  of the mounting socket. Likewise, a length of the second retention boss  40  is controlled such that first and second end surfaces  44 ,  46  of the second retention boss  40  engage corresponding inner surfaces  24 ,  26  of the mounting socket. The engagement between the first and second end surfaces of the retention bosses and the corresponding inner surfaces of the mounting socket  2  may also help to keep the PCB  100  from moving with respect to the mounting socket  2 . 
     In some embodiments, an adhesive layer may be formed along the bottom surfaces  35 ,  45  of the first and second retention bosses  30 ,  40 . When a PCB  100  having this configuration is mounted in a mounting slot  22  of a mounting socket  2 , the adhesive layer bonds to the upper surfaces  25  of the mounting socket  2  on opposite sides of the mounting slot  22 , which helps to further immobilize the PCB with respect to the mounting socket.  FIG. 4  shows a cross-sectional view of a PCB  100  having this configuration. 
     As shown in  FIG. 4 , an adhesive layer  37  is formed on the lower surface of the first retention boss, and an adhesive layer  47  is formed on a bottom surface of the second retention boss  40 . The adhesive layers  37 ,  47  bond to the top surfaces  25  of the mounting socket  2  located on opposite sides of the mounting slot  22 .  FIG. 4  also illustrates how electrical contacts  27  in the mounting slot  22  contact electrical leads on the bottom edge of the PCB  100 . 
     Adhesive layers may also be provided on the end surfaces  34 ,  36 ,  44 ,  46  of the retention bosses. Such adhesive layers would bond to the corresponding inner side surfaces  24 ,  26  of the mounting socket  2  to help keep the PCB immobilized with respect to the mounting socket. 
     When adhesive layers are provided on surfaces of the retention bosses, the adhesive layers may initially be covered by a removable protective film. When one wishes to mount the PCB in a mounting socket, one would remove the protective film, then insert the PCB  100  into the mounting slot of the mounting socket until the adhesive layers contact and adhere to corresponding surfaces of the mounting socket. 
     The width of the bottom surfaces  35 ,  45  of the retention bosses  40 ,  50 , may be greater than, equal to, or less than a width of the upper surfaces  25  of the mounting socket located on opposite sides of the slot  22  of the mounting socket  2 . 
     As illustrated in  FIG. 4 , a cross-sectional shape of the retention bosses  30 ,  40  may be square or rectangular. However, the retention bosses could also have many other cross-sectional shapes. 
     For example,  FIG. 6A  shows a PCB  100  with retention bosses  60 ,  62  having a triangular cross-sectional shape.  FIG. 6B  illustrates a PCB  100  with retention bosses  64 ,  66  having convex side surfaces.  FIG. 6C  illustrates a OCB  100  having retention bosses with concave side surfaces. Of course, many other cross-sectional shapes are also possible. 
     The retention bosses can be formed of any suitable material which does not interfere with the proper operation of the PCB  100 . In some embodiments, it may be desirable for the material of the retention bosses to be electrically insulative, such that the retention bosses do not interfere with or short circuit any of the electrical components, conductive layers or traces that are formed on the PCB. 
     In some embodiments, the retention bosses may be formed of a molding resin, such as an epoxy resin. The resin preferably has a relatively high electrical resistivity, which helps to prevent any short circuiting of any electrical components, leads or metal traces covered by the resin. 
     In some embodiments, the retention bosses may be formed of a material that is semi-rigid. In these embodiments, it may be desirable to form the retention bosses such that they have a length that is slightly longer than the distance between the interior side surfaces  24 ,  26  of the mounting socket. As a result, the retention bosses will be slightly compressed and deformed when the PCB is inserted into the mounting socket. This will provide an interference fit that helps to keep the PCB immobilized with respect to the mounting socket. 
     In the embodiments described thus far, retention bosses are formed on opposite sides  110 ,  120  of a PCB  100 . However, in alternate embodiments, a retention boss may be formed on only one side of a PCB. Further, if retention bosses are formed on opposite sides of a PCB, the retention boss on a first side of the PCB may have a different configuration than a retention boss on the opposite side of the PCB. 
       FIG. 7  illustrates steps of forming a PCB having retention bosses. The method begins in step S 702 , when a PCB is inserted into a mold having one or more cavities that are configured to form the retention bosses. In step S 704 , a molding resin is inserted into the mold cavities. In step S 706 , the resin is allowed to cure. The PCB with the cured resin retention bosses is then removed from the mold. 
     In an optional final step S 708 , an adhesive is applied to selected surfaces of the retention bosses. As noted above, the surfaces of the adhesive opposite the retention bosses may be covered with a removable protective film. 
     The forgoing exemplary embodiments are intended to provide an understanding of the disclosure to one of ordinary skill in the art. The forgoing description is not intended to limit the inventive concept described in this application, the scope of which is defined in the following claims.