Abstract:
A method for reducing the fitting thrust of golden finger ( 101,103 ) and a PCB ( 100 ). The method and the PCB ( 100 ) solve the problem of excessive inserting force of the golden finger ( 101,103 ) of the prior art, through modifying the shape of the edge of the PCB ( 100 ), the edge of the PCB open reeds of a connector ( 201, 203 ) at different time. The PCB ( 100 ) has at least one concave edge section or at least one convex edge section or at least one tilt edge section, and the edge can further be beveled. The bonding pads of the golden finger can be assorted, pin ends of a part of golden fingers ( 101, 103 ) can be partially removed or these golden fingers can be completely removed, the pin ends of a part of golden fingers ( 101,103 ) can be preserved. Through the method, the purpose of reducing the fitting thrust upon inserting the PCB ( 100 ) into the connector can be achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national phase application under the provisions of 35 U.S.C. §371 of International Patent Application No. PCT/CN08/72825 filed Oct. 24, 2008, which in turn claims priority of Chinese Patent Application No. 200810006358.X filed Feb. 29, 2008. The disclosures of such international patent application and Chinese priority patent application are hereby incorporated herein by reference in their respective entireties, for all purposes. 
     FIELD OF THE INVENTION 
     The present invention relates to the design and manufacture of the hardware circuit, in particular to a method capable of reducing the fitting thrust of golden finger and a printed circuit board (PCB). 
     BACKGROUND OF THE INVENTION 
     Golden finger is a commonly used method for hardware connection in the computer hardware industry, which is used, for example, in the memory bank, the PC boards and so on, i.e., some bonding pads are made onto a PCB directly, then the PCB is directly inserted to a connector in which the reeds snap to the bonding pads of the PCB, so as to ensure an electrical connection. In order to increase abrasion resistance and stability, a gold plating process is applied on the bonding pads of the PCB, such that the bonding pads are referred to as the golden finger. 
     In recent years, the application of the golden finger is extended to the non-computer industries such as the communication industry. For example, the golden finger as a connection manner has been early or late employed in the AMC (Advanced Mezzanine Card) standard, the ATCA (Advanced Telecommunications Computing Architecture) standard and the MicroTCA (Micro Telecommunications Computing Architecture) standard established by the PICMG (PCI Industrial Computer Manufacturers Group). 
     As the increased application of the golden finger in the non-computer industries, some inherent problems of the golden finger connection emerge, one of which is that, since the number of times of the reliable inserting/removing operations required in the non-computer industries is much greater than that required in the computer industry (for example, the AMC standard specifies the number of times of the reliable inserting/removing operations is 200, while that required by the computer products is normally less than 20), a more tight cooperation between the connector and the golden finger is required, which will result in an excessive inserting/removing force. 
     Although having recognized the problem, what the standard organization can do is only to loose the standard of the allowable inserting force rather than to provide a solution to reduce the inserting/removing force, for example, the AMC standard specifies that as long as the maximum inserting force is less than 100 N, it is regarded as qualified, however, the inserting force for fitting the PCB of the golden finger connector in the prior art is more than 50 N. The inserting force will be doubled for the PCB with two connectors, and tripled for three connectors. According to the MicroTCA standard, there are 4 connectors on the MCH (MicroTCA carrier hub), thus the thrust force will be quadrupled, which has gone beyond the manual operation limitation. As the wide applications of the MicroTCA standard, the problem will emerge definitely. 
     An investigation shows that the reason of the excessive inserting force of the golden finger lies in that the connector reeds (spring leaves) are required to resist the opening force of the reeds of the golden finger when fitting with the golden finger. However, according to the current standards (AMC, MicroTCA, etc.), both the connectors and the PCBs have a right angle structure, and all of the golden fingers are opened at the same time, thus there will generate an extreme peak thrust force at the moment of fitting. For example, for the AMC standard, there are 170 reeds, thus the instantaneous maximum thrust force is 170 times of that of a single reed. 
       FIG. 1  is the schematic diagram showing the fitting between the golden finger and the connector in the prior art, wherein two golden fingers  101  and  103  are shown to be un-overlapped and in different planes for clarity. The two golden fingers  101  and  103  respectively contact with two reeds  201 ,  203  of the connector  200  at the same time, the thrust force at this time is twice of the thrust force of the single golden finger. 
     After the reeds open, the thrust force is used to counteract the sliding friction force, and the required thrust force is substantially reduced at this time. Therefore, as to the problem of the excessive thrust force, it is necessary to solve the tremendous thrust force required when the golden fingers open. 
     SUMMARY OF THE PRESENT INVENTION 
     The main purpose of the present invention is to solve the excessive inserting force of the golden fingers in the prior art by providing a method for reducing the fitting thrust and a PCB. 
     To this end, according to one aspect of the present invention, modifying the shape of a edge of a PCB such that the edge of the PCB do not push open reeds of the connector at the same time, that is to say, different reeds are cleaved at different time so as to reduce the resistance. 
     Preferably, said PCB comprises at least one concave edge section, or at least one convex edge section, or at least one tilted edge section. Herein, a recess shape is used to guide a single connector, or in the case that there is a plurality of connectors, these connectors are guide through the positioning relationships among them. In addition, the convex or concave edge can be utilized to provide pre-reserved buffer regions. Furthermore, for example, these buffer regions can be made have beveled shape. 
     Preferably, said edge of said PCB comprises two concave edge sections with the same shape, or two convex edge sections or two tilted edge sections, and said two concave edge sections (also referred as depressed or recessed sections) or said two convex edge sections or tilted edge sections are symmetrical with respect to the locating part of the PCB. The two edge sections may be, for example, the two concave edge sections, the two convex edge sections or the two tilted edge sections or the combination thereof. 
     Preferably, the PCB may comprise at least two edge sections, and the edge of the PCB is arranged in a staircase shape. 
     Preferably, the golden finger bonding pads can be assorted, i.e., the pin ends of some golden fingers being removed, and the pin ends of some golden fingers being reserved. For example, as to the case that the PCB contraction affects the original end portion of the golden finger bonding pads, in order to ensure the communication performance of the signal, rather than removing all golden finger ends, the end portion of the longer golden finger bonding pads on the same PCB are reserved. 
     According to another aspect of the present invention, the PCB edge is beveled, i.e., the beveling is performed in the vertical section of the PCB, so as to the reeds open gradually rather than suddenly, to reduce the maximum thrust. The beveling may extend to the golden finger bonding pads or extend on the edge area outside of the edge of the golden finger bonding pads. 
     According to another aspect of the present invention, the golden finger bonding pads can be assorted, i.e., the portion of the pin ends of some golden fingers being removed or these golden fingers being totally removed, and the portion of the pin ends of some golden fingers being reserved. By assorting the golden fingers, a part of the pins need not to be firstly contact are selected and the golden finger portion on the ends of these pins are removed, so as to reduce thickness and thus the friction force. Since the golden fingers have different lengths, they subject to forces at different time when fitting with the connectors, thus the maximum thrust is reduced. 
     The present invention also provides a PCB used for above method, in the PCB, the golden finger ends on the edge of the PCB are positioned at different inserting locations in order to open reeds of a connector at different time. In particular, the PCB may have at least one concave edge section or at least one convex edge section or at least one tilted edge section. Said edge can be further beveled. However, it should be understood that the definition to the shape of the edge throughout the context means that these edges are mainly used to reduce or decrease the fitting thrust and also used for the purpose of locating, therefore, which are different from the shapes of the edge for locating in the PCB of the prior art. 
     It is to be understood that the general description above and the detailed description below are intended to exemplify and illustrate, so as to provide a further explanation to the present invention to be protected. 
     Other features and advantages of the present invention will be detailed in the description, and partly obvious from the description, or can be understood through implementing the present invention. The purposes and other advantages can be achieved and obtained through the structure specified by the specification, claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Drawings are provided for the further understanding of the present invention and form a part of the specification, which are used to illustrate some embodiments of the present invention and explain the principle of the present invention together with the specification, wherein 
         FIG. 1  is a schematic diagram showing the fitting between the golden finger and the connector of the prior art; 
         FIG. 2  is the top view of the PCB with the gold fingers of the prior art; 
         FIGS. 3-1  to  3 - 9  are top views of the PCB improved according to the present invention; 
         FIGS. 4-1  to  4 - 3  are section views showing the process of inserting the golden fingers of the PCB improved according to the present invention; 
         FIG. 5  is a graph plotting the thrusts in different edge shapes; 
         FIGS. 6-1  to  6 - 3  are diagrams showing plugging/unplugging guide of the PCB improved according to the present invention; 
         FIG. 7  shows a staircase-like edge; 
         FIGS. 8-1  and  8 - 2  are top views respectively showing the PCB with flushed golden fingers and the PCB with un-flushed golden fingers; 
         FIGS. 9-1  and  9 - 2  are section views showing the contacting between the connector reeds and the flushed golden fingers and the un-flushed golden fingers; 
         FIG. 10  is a schematic diagram showing the PCB with a un-golden finger pin area; 
         FIGS. 11-1  and  11 - 2  are sectional schematic views showing the beveled PCB being inserted into the connector reeds. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be described in detail by referring to drawings. 
     Considering the problem of the excessive inserting force, there is provided an improved solution which makes the resistance of opening each reed impose to the PCB at different time, so as to reduce the instantaneous maximum resistance. 
       FIG. 2  shows the PCB  100  which is manufactured strictly according to related standards, wherein all the golden fingers  101 ,  103  and each part of these golden fingers are flushed, therefore an instantaneous maximum resistance will occur when the golden fingers are connecting with a standard connector. 
     It is to be noted that although  FIG. 1  only shows the case of two golden fingers connectors, the cases of one golden finger, three golden fingers, or more golden fingers are similar. It is the same hereinafter. 
     In addition,  FIG. 2  only shows the case that a plurality of golden fingers arranged in one plane, but it is also similar for the case that the golden fingers are arranged in different planes (in particular, for example, the definition for the MCH connector in the MicroTCA standard). It is the same hereinafter. 
       FIGS. 3-1  to  3 - 9  show the embodiments of the un-flushed golden fingers according to the present application. It is to be noted that, the profiles which could be employed comprise but not limit to above listed shapes, and are all contained in the protection scope of the present application, as long as the edge of the PCB contact with the connectors at different time. 
     In  FIG. 3-1 , the PCB  100  comprises a first edge section  110  which is straight, a second edge section  120  which is straight and a locating portion  130 , wherein the first edge section  110  and the second edge section  120  are arranged in a staircase form, such that the golden fingers  103  on the second edge section  120  contact the connector reeds firstly, and then the golden fingers  101  on the first edge section  110  contact the connector reeds secondly when the PCB is inserted into the connector, so as to reduce the maximum fitting thrust. 
     In  FIG. 3-2 , both the first edge section  110  and the second edge section  120  are tilted and symmetrical with respect to the locating portion  130 , and the first edge section and the second edge section present a convex shape as a whole. 
     In  FIG. 3-3 , the first edge section  110  and the second edge section  120  respectively have a convex angle shape, and the first edge section  110  extends outward more than the second section  120  as a whole. 
     In  FIG. 3-4 , both the first edge section  110  and the second edge section  120  are tilted, and the second edge section  120  extends outward more than the first section  110  as a whole. 
     In  FIG. 3-5 , the first edge section  110  is tilted, while the second section  120  is straight. 
     In  FIG. 3-6 , both the first edge section  110  and the second section  120  are tilted, and the first edge section and the second section present a concave shape as a whole. 
     In  FIG. 3-7 , the first edge section  110  and the second section  120  respectively have a concave angle shape, and the first edge section  110  and the second edge section  120  are symmetrical with respect to the locating portion  130 . 
     In  FIG. 3-8 , the first edge section  110  and the second section  120  respectively have a concave arc shape, and the first edge section  110  and the second edge section  120  are symmetrical with respect to the locating portion  130 . 
     In  FIG. 3-9 , the first edge section  110  and the second section  120  respectively have a tilted shape, and the first edge section  110  and the second edge section  120  present a staircase shape. 
     The principle of the method of the present application can be explained by the sectional views shown in  FIGS. 4-1  to  4 - 3 . The two golden fingers in  FIGS. 4-1  to  4 - 3  are shown as un-overlapped and in different planes for the purpose of clarity. In the first travel ( FIG. 4-1 ), the connector reeds  201 ,  203  only contact with the longer PCB and the golden finger  101 , that is to say, only part of the opening resistance is added. In the second travel ( FIG. 4-2 ), the reeds  201  in the protruded area have been opened and entered into a sliding state, while the reeds  203  in the recessed area are to be opened and there exists an opening force, thus in this travel, the total resistance=part of the opening force+sliding friction force. In the third travel ( FIG. 4-3 ), all of the reeds  201 ,  203  are opened, and the resistance=sliding friction force. 
     Therefore, in all of the travels, the resistance in the second travel is maximum, however, which is far less than the traditional instantaneous maximum resistance. 
     The improved effects are different for different profiles. Among various shapes shown in  FIG. 3 , the shape shown in  FIG. 3-1  (right angle 2-step staircase shape edge) can improve the effect by approximately 50%, and the shapes shown in  FIGS. 3-2  to  3 - 9  (tilted edge) can improve the effect by more than 50%. 
     In  FIGS. 4-1  to  4 - 3 , the edge  141  of the PCBs  100  is beveled, which is helpful to further reduce the maximum fitting thrust. 
       FIG. 5  shows a graph for comparing and analyzing the thrusts in different shapes. As seen from the figure, T 1  represents the resistance curve of the PCB with a straight edge in the prior art when being fit, T 2  represents the thrust curve of the PCB with a 2 mm tilted edge, T 3  represents the resistance curve of the PCB with a 1 mm right-angled 2-step staircase edge, T 4  represents the resistance curve of the PCB with a 1.9 mm right-angled 2-step staircase edge, and T 5  represents the resistance curve of the PCB with a 3 mm right-angled 2-step staircase edge. From which, the following can be concluded:
         (1) all of the edge shapes have improved effects regarding the maximum thrust, and the levels of improvement are different for different shapes. It is because that all the solutions can distract the traditional concentrated energy.   (2) for right-angled staircase edge, the distance between 2 or more steps of staircase can be optimized according to actual thrust distribution graphs, so as to obtain one or more optimal values.   (3) theoretically, the tilted edge has a greater improvement than the right-angled edge.       

     Due to the above modification, a poor guide effect may occur in the case of a single connector, as shown in  FIGS. 6-1  to  6 - 3 , wherein  FIG. 6-1  shows a unidirectional tilted edge, therefore a fitting error may occur when the connector  200  and the PCB  100  begin to contact due to the freedom in vertical direction. By employing a concave shape, the fitting error may be avoided, as shown in  FIGS. 6-2  and  6 - 3 . 
     If there is a plurality of connectors, as shown in  FIGS. 3-1  to  3 - 9 , the locating relationships among the plurality of connectors can be used for locating. 
     The method requires some space in the right-left direction to realize the buffer action to the thrust. The above space is obtained by extending outside and contracting inside. Take the shape shown in  FIG. 3-1  as an example, the schematic diagram as shown in  FIG. 7  can be derived, wherein P 1  is the boundary of the connector, P 2  is the force applied point of the reeds. Dimension A is the extension with respect to the standard dimension, and dimension B is the contraction with respect to the standard dimension. Herein, only the shape shown in  FIG. 3-1  is explained as an example, and the extending and the contracting of the other shapes are similar. 
     There arises a problem to realize the contraction, according to the definition of the standards, any contraction will impair the definition of the signal due to the removal of the part of the ends of the golden fingers by the contraction. Therefore, the following solution is provided according to the inherent electrical characteristics of the golden finger signal. 
     The golden fingers may contact with the reeds of the connector at different time, for example, the ground line can be firstly connected, then the power, and then the signal. However, the connections of the power and the ground are to ensure the safety of the device, and there is no large electrical current before all signals being in good connection. Based on this property, it is proposed that one PCB only reserves a few full travel golden finger bonding pads, and the rest of the golden finger bonding pads may contract, which makes it possible to provide a contracting space B. 
     As to the selection to the shapes of the PCB, such as tilted edge or right-angled edge, the improvement effect to the thrust, the machining difficulty, the guiding, the machining efficiency and so on may be taken into account. 
       FIG. 8  and  FIG. 9  show another method for reducing the thrust, wherein  FIG. 8  is a top view, while  FIG. 9  is a sectional view. The standard golden fingers of the prior art shown in  FIG. 8-1  and  FIG. 9-1  have flushed ends. As shown in  FIGS. 8-2  and  9 - 2 , the golden fingers are assorted according to the electrical characteristics, wherein some of the pin ends, which need not to be contacted firstly, are not manufactured to be the golden fingers. 
     Thus, the reeds will contact the golden finger coatings of different length at different time rather than at the same time. 
     At the same time, the competitive thickness is reduced due to without applying coatings, which is helpful for reducing the thrust. 
     For a golden finger which is not used in the current circuits, the whole golden finger can be omitted, as shown in  FIG. 10  by reference number  150 , which will further reduce the thrust. 
       FIGS. 11-1  and  11 - 2  show the schematic sectional views of the PCB  100  with beveled edge being inserted into the connector reeds. As shown in the figures, the PCB edge has a beveled angle  141  at its longitudinal section, which increase the opening travel for the connector, and the energy releases slowly, and thus the maximum thrust decreases. The beveling may only comprise the PCB  100  without the golden finger portion  101  (as shown in  FIG. 11-1 ), or may comprise both the PCB  100  and the golden finger portion  101 . 
     The methods according to the application described in the context may be utilized separately, or in combination. A superposed improvement effect will be obtained when used in combination. 
     Above description is to illustrate the preferred embodiments not limit the present invention. Various alterations and changes to the present invention are apparent to those skilled in the art. The scope defined in claims shall comprise any modification, equivalent substitution and improvement in the spirit and principle of the present invention. 
     Explanation to the reference numbers in drawings 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 100 
                 PCB 
               
               
                 101 
                 golden finger 
               
               
                 103 
                 golden finger 
               
               
                 200 
                 connector 
               
               
                 201 
                 reed 
               
               
                 203 
                 reed 
               
               
                 110 
                 first edge section 
               
               
                 120 
                 second edge section 
               
               
                 130 
                 locating portion 
               
               
                 141 
                 beveled edge 
               
               
                 150 
                 blank area