Arrangement for modifying electrical printed circuit boards
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of Ser. No. 751,815, filed July 5, 1985, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to printed circuit boards, and, more particularly, it relates to an arrangement for modifying existing printed circuit boards including components mounted thereon such as the type employed in telephone switching applications. 
     In facilities employing telephone switching technology in particular, there is a recurring need to modify existing printed circuit boards of a given type. Such modifications are made predominantly to the electrical conductors. This is accomplished by removing the connections that are no longer necessary and replacing them with additional conductors in the form of insulated leads. These are attached to the relatively thick support plate of the printed circuit module by the linear or spaced application of adhesives. As a rule these modifications are carried out by the user by hand, in accordance with modification instructions provided by the supplier. 
     SUMMARY OF THE INVENTION 
     Broadly, the invention provides an arrangement for making the modification to the modules more simply, more reliably, at lower cost and more quickly. 
     According to one aspect of the invention, the added conductors are applied to the thick support plate at one time by the application thereto of a relatively thin support plate including printed circuit conductors formed thereon. The predetermined pattern of the printed circuit conductors provides the additional conductors in a printed and established form. By this means an incorrect placement of the added conductors is avoided in a dependable way. The connecting leads of the components extend through to the opposite or soldered side of the thick support plate. The thick support plate is made thinner than the height that the protruding ends of the component leads extend beyond the thick support plate. In this way the leads extend beyond the soldering eyelets and clearance holes in the thin support plate. The soldering eyelets of the thin support plate are then joined to the component leads by soldering and the thin support plate is also thereby mechanically fastened to the thick support plate. 
     Through the invention the necessity of connecting wires to the thick support plate is avoided. Such connecting wires are suitable for printed circuits, particularly in view of their mode of insertion which places a definite limit on thickness. 
     The thin support plates used for modifying a printed circuit modules are preferably produced in quantity at a central location and provided to the individual users. Since the placement of the thin support plate on the module to be modified no longer depends on a particular routing of wires, the modification may be carried out by less qualified personnel, e.g., the users. At the same time there is assurance that all added conductors run along predetermined paths so that the intended electrical operation is dependably retained. Subsequent modifications may also be carried out in the same way. 
     In a further aspect of the invention, insulated soldering eyelets are also provided on the thin support plate, in addition to those soldering eyelets that are integral with the added conductors. Insulated soldering eyelets are those that are not electrically connected with the added conductors, i.e., they are insulated from them and hence do not &#34;see&#34; them. Thus, soldering eyelets of this type are sometimes referred to as &#34;blind&#34; eyelets. The blind eyelets are soldered to the component leads of the module. These &#34;blind&#34; insulated soldering eyelets are located particularly at the corners of the thin support plate in order to form a dependable mechanical attachment to the thick support plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features and advantages of this will be more fully understood from the following description of an illustrative embodiment taken in conjunction with the accompanying drawing. 
     The sole FIGURE is a cross-sectional drawing of an illustrative arrangement for modifying printed circuit boards in accordance with the principles of the invention. 
    
    
     DETAILED DESCRIPTION 
     In the sole FIGURE, an illustrative embodiment of the invention is shown. The FIGURE illustrates by means of a schematic cross-section view an already modified electrical printed circuit (PC) board including a relatively thick component support plate 1 having component leads 4 passing therethrough from originally mounted components, the originally mounted components being represented by component 11, and a relatively thin support plate 3 having electrical conductors 8 formed thereon. For simplifying the illustrated embodiment, only one originally mounted component 11 and one added component 2 (to be described later on) are shown, although in practice there may be hundreds of originally mounted components and more than one added component. 
     As originally manufactured, thick component support plate 1 includes electrical signal conductors 7 on the side thereof which is opposite from the side of components 11. Electrical signal conductors 7 include soldering eyelets 12 integral therewith which are aligned with leads 4 of components 11 in order to provide good electrical connections between components 11 and electrical signal 7 and completes the electrical circuit of the unmodified PC board. 
     In accordance with the principles of the invention, the modification of the originally manufactured PC board is accomplished by the mounting on component support plate 1 of added components, the added components being represented by component 2. Components 2 have leads 13 passing through holes 5 drilled or otherwise formed in thick component support plate 1. A relatively thin conductor support plate 3 having electrical conductors 8 formed thereon is then attached to the electrical signal conductor 7 side of thick support plate 1 for providing the modifying, additional conductors between components 2 and/or 11. 
     When mounted on the conductor side of thick component support plate 1, conductors 8 engage aligned ones of leads 4 and/or 13 of components 11 and/or 2 for providing the modifying electrical connections therebetween. 
     Conductors 8 include soldering eyelets 9 therein at each aligned location where there is a connection to a lead 4 and/or 13 of one of components 11 and/or 2, respectively. For purposes of illustration, only one conductor 8 is shown for connecting lead 13 of component 2 to another component lead which is not shown and includes a soldering eyelet 9 which receives aligned leads 13 of components 2. 
     As previously noted, thin conductor support plate 3 is thin enough so that leads 4 and 13 of components 11 and 2 protrude out from thick component support plate 1 by an amount greater than the thickness of thin conductor support plate 3 thereby enabling subsequent soldering of leads 4 and/or 13 to soldering eyelets 9. 
     For the remaining ones of leads 4, i.e., those leads to which added conductors 8 are not to be electrically connected, thin conductor support plate 3 includes either one of a clearance hole 6 therein, so that selected ones of those leads 4 can pass through thin conductor support plate 3 without preventing thin conductor support plate 3 from being positioned approximate to thick component support plate 1 or, an insulated or &#34;blind&#34; soldering eyelet 10 therein, which allows selected ones of leads 4 of originally mounted components 11 to be soldered to the insulated soldering eyelets 10 so as to assist in firmly attaching thin support plate 3 approximate to thick support plate 1 while keeping these leads 4 electrically insulated from (i.e., &#34;blind&#34; to) the added conductors 8 of thin conductor support plate 3. 
     As previously noted, insulated soldering eyelets 10 are preferrably located so as to be aligned with leads 4 which are near the corners of thin conductor support plate 3. 
     For ease and clarity of illustration in the FIGURE, the rightmost lead 4 of component 11 is representative of a group of leads 4 which is aligned with and passes through a group of clearance holes 6 in thin conductor support plate 3, and the leftmost lead 4 of component 11 is representative of a group of leads 4 which is aligned with and is soldered to a group of insulated soldering eyelets 10 on thin support plate 3. 
     There has thus been shown and described a novel arrangement for modifying printed circuit boards which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.