Abstract:
A printed circuit board (PCB) assembly includes a first printed circuit board that includes first circuit traces formed of copper. A second printed circuit board includes second circuit traces that are formed of nickel/gold plated copper and terminations that are soldered to the first circuit traces. An electrical component contacts the second circuit traces.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Ser. No. 61/579,121, filed Dec. 22, 2011, the contents of which are incorporated by reference herein. 
     FIELD 
     The present disclosure relates to construction of electrical printed circuit boards and more particularly to stacked printed circuit boards with different metals used for the traces on respective boards. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Electrical printed circuit boards (PCB) are well known in the art. Generally PCBs comprise an insulating substrate that is glued to a thin layer of conductive metal. The insulating substrate is chosen from a number of materials such as fiberboard, fiberglass, flexible polyamide and the like. The choice of substrate material is generally dictated by temperature specifications, cost, and need for mechanical flexibility such as bending. 
     The conductive metal is generally copper however other metals can also be used depending on the situation. An etching mask is applied to the conductive metal and defines the shape of the circuit traces that will be formed on the PCB. An etching solution then dissolves away the portions of the conductive metal that are not protected by the etching mask. When the etching mask is removed the desired circuit traces are all that remain of the conductive metal. 
     Some applications demand that the metal be resistant to corrosion and wear. In those cases it is common to plate the copper with nickel and gold, however such a coating is undesirably expensive. 
     Referring now to  FIG. 1 , a cross section is shown of a typical PCB  10  of the prior art. PCB  10  includes a substrate  12 . Circuit traces  14 - 1 ,  14 - 2 , and  14 - 3 , collectively referred to as circuit traces  14 , are formed as described above. In this example a pushbutton switch  16  is also shown attached to PCB  10 . Pushbutton switch  16  includes a pliable body  18  and a conductive pill  20 . A user can press the top of switch  16  such that pliable body  18  deforms and allows conductive pill  20  to make a circuit between circuit traces  14 - 1  and  14 - 2 . When the user releases button  16  pliable body  18  returns to its original shape and the circuit is reopened. Such a combination of PCB  10  and switch  16  are commonly used in keypads for devices such a cell phones, automobile radios, and the like. 
     An undesirable characteristic of PCB  10  is that an extra expense in incurred if circuit traces  14 - 1  and  14 - 2  need to be coated with nickel/gold to increase the durability and/or current carrying capacity in combination with switch  16 . The extra expense comes by virtue of having to also coat circuit trace  14 - 3  along with circuit traces  14 - 1  and  14 - 2 . It is impractical to coat a subset of traces  14 . Instead it is more simple to coat all traces  14  simultaneously. 
     SUMMARY 
     A printed circuit board (PCB) assembly includes a first printed circuit board that includes first circuit traces formed of copper. A second printed circuit board includes second circuit traces that are formed of nickel/gold plated copper and terminations that are soldered to the first circuit traces. An electrical component contacts the second circuit traces. 
     In other embodiments the terminations comprise a lead frame. The electrical component can include a pushbutton switch that includes a conductive pill that contacts the second circuit traces. 
     In yet other embodiments the electrical component can include an elastomeric connector with a first termination side that contacts the second circuit traces. A display contacts a second termination side of the elastomeric connector and communicates with the second circuit traces. 
     A PCB assembly includes first printed circuit board means that includes first circuit traces formed of copper, second printed circuit board means that includes second circuit traces that are formed of nickel/gold plated copper and termination means for soldering to the first circuit traces, and electrical component means for contacting the second circuit traces. 
     In other embodiments the termination means includes a lead frame. The electrical component means can include a pushbutton switch that includes a conductive pill for contacting the second circuit traces. 
     In yet other embodiments the electrical component means can include an elastomeric connector means for contacting the second circuit traces. The PCB assembly can also include display means for displaying and means for contacting the elastomeric connector means and communicating with the second circuit traces. 
     A printed circuit board (PCB) assembly includes a first printed circuit board that includes first circuit traces formed of copper. A second printed circuit board includes second circuit traces that are formed of nickel/gold plated copper and a lead frame that is soldered to the first circuit traces. An elastomeric connector includes first and second termination sides that respectively contact the second circuit traces and a display that communicates with the second circuit traces. 
     A method of manufacturing a printed circuit board (PCB) assembly includes providing a first printed circuit board that includes first circuit traces formed of copper, providing a second printed circuit board that includes terminations and second circuit traces that are formed of nickel/gold plated copper, soldering the terminations to the first circuit traces, and applying an electrical component that contacts the second circuit traces. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a cross section of a printed circuit board (PCB) of the prior art; 
         FIG. 2  is a cross section of an improved PCB that includes two types of metallic traces and a pushbutton switch; and 
         FIG. 3  is a cross section of an improved PCB that includes two types of metallic traces and an elastomeric connector. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     Referring now to  FIG. 2 , a cross section is shown of an improved PCB assembly  30 . PCB assembly  30  enables using different types of circuit trace metallurgy in different areas. It therefore avoids unnecessary expense when some portions of PCB assembly  30  use more expensive plating than other areas that do not need the plating. 
     PCB assembly  30  includes a first substrate  32 . First circuit traces  34 - 1  and  34 - 2 , collectively referred to as first circuit traces  34 , are formed of copper using methods that are known in the art and are adhered to first substrate  32 . A single sided assembly is shown for simplicity, however those skilled in the art appreciate that multi-sided and multi-layered substrate/trace assemblies are also within the scope of this invention. 
     PCB assembly  30  also includes a second substrate  36 . Second circuit traces  38 - 1  and  38 - 2 , collectively referred to as second circuit traces  38 , are also formed of copper using methods that are known in the art and are adhered to second substrate  36 . A single sided assembly is shown for simplicity, however those skilled in the art appreciate that multi-sided and multi-layered substrate/trace assemblies are also within the scope of this invention. Second traces  38  are also nickel/gold plated whereas first circuit traces  34  are not. Second substrate  36  also includes a first termination  40 - 1  and a second termination  40 - 2 , collectively referred to as terminations  40 . While only two terminations  40  are shown it is appreciated by those skilled in the art that more can be used based on the number of electrical connections that need to be made between circuits associated with first substrate  32  and second substrate  36 , respectively. While terminations  40  are shown as butted type terminations, it is also appreciated by those skilled in the art that terminations  40  can be formed with a lead frame that provides gullwing leads, J-leads, dual inline package leads, and the like such as are used with integrated circuits. Solder joints  42  connect respective ones of first traces  34  and terminations  40 . 
     In the depicted example a pushbutton switch  46  is also shown attached to second substrate  36 . Pushbutton switch  46  includes a pliable body  48  and a conductive pill  50 . A user can press the top of switch  46  such that pliable body  48  deforms and allows conductive pill  50  to make a circuit between second traces  38 - 1  and  38 - 2 . When the user releases button  46  pliable body  48  returns to its original shape and the circuit is reopened. Such a switch  46  is commonly used in keypads for devices such a cell phones, automobile radios, and the like. 
     Referring now to  FIG. 3 , a second application is shown for improved PCB assembly  30 . In this application nickle/gold plated second traces  38  abut an elastomeric connector strip  60 . Elastomeric connector strips are well know to those skilled in the art. An example includes ZEBRA brand connectors available from Fujipoly America Corp. Elastomeric connector strip  60  makes electrical connections between respective ones of second circuit traces  38 - 1  . . .  38 - 6  and third circuit traces  62 - 1  . . .  62 - 6  that are associated with a display panel  64 . While six connections are shown between second circuit traces  38  and third circuit traces  62  are shown it is appreciated by those skilled in the art that more or less can be used. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.