Abstract:
An electrical component assembly includes a first printed circuit board (PCB) having a plurality of first-PCB conductive paths communicating with the surface of the first PCB, the assembly also includes at least one additional PCB having a plurality of additional-PCB conductive paths communicating with the surface of the PCB, with the conductive paths located such that when the additional PCBs and the first PCB are positioned one on top of the other, the conductive paths of the PCBs are substantially aligned, the conductive paths being formed from solder-filled vias passing through the PCBs and electrically-conductive junction pads positioned on the surface of the PCBs. The assembly also includes a plurality of electrical circuit components, wherein each component is electrically connected to a conductive path of one of the PCBs at one end and to a conductive path of another of the PCBs at the other end, the assembly also includes a plurality of traces that connect conductive paths. In some assemblies the traces configure some of the electrical components in a series arrangement whereas in other assemblies the traces configure some of the electrical components in a parallel arrangement.

Description:
RELATED APPLICATIONS 
     This application is claiming the benefit of a co-pending provisional application Ser. No. 60/098,447, filed on Aug. 31, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of electrical component integration and more particularly to systems for, and methods of, arranging and connecting electrical components to be used in electrical systems such as surge protective devices (SPDs). 
     2. Description of Related Art 
     Discrete electrical components are typically integrated into an electrical system by means of a printed wiring board (PCB). Components are mounted to a PCB using well known methods such as surface mounted technology and general feedthrough technology. 
     Some electrical systems, such as surge protective devices (SPDs) for use in power and signaling systems, require a large number of electrical components, particularly diodes, in order to provide the voltage, clamp range and energy suppression typically required by such systems. The large number of diodes renders PCB layout design difficult for several reasons. First, the large number of discrete components laid out on the PCB produces a cumulatively large lead length within the circuit formed by the interconnection of the discrete components. A large lead length may have a detrimental effect on the operational characteristics of the circuit. 
     Second, a PCB having a large number of individually mounted discrete components is typically structurally unstable in that the individually mounted components may become disconnected from the PCB. This is especially true for a PCB which is part of a module card that is often removed from and reinstalled into an electrical system. 
     Third, depending on the physical constraints of the electrical system being designed, limitations may be placed on the size of a PCB. A size limitation on the PCB, in turn limits the number of discrete components that may be mounted on the PCB and thereby limits the functional capabilities of the circuitry on the PCB. 
     Hence, those concerned with the development and use of electrical component assemblies have long recognized the need for component assemblies which are relatively compact, structurally sturdy, have minimum lead length between components and are configured to provide multiple paths, thus allowing for a multitude of electronic operating characteristics and functions. The present invention fulfills these needs and others. 
     SUMMARY OF THE INVENTION 
     Briefly, and in general terms, the present invention provides a system for arranging and connecting components used in surge protective devices (SPDs) and the like. The system provides a sturdy matrix array of electrical components having minimal lead lengths and the ability to provide multiple conductive paths, thus allowing for custom circuit design based on desired electronic operating characteristics and functions. 
     By way of example, and not necessarily by way of limitation, the present invention in one aspect provides an electrical component assembly having a first printed circuit board PCB) having a plurality of first-PCB conductive paths communicating with at least one surface of the first PCB. The assembly also has at least one additional PCB having a plurality of additional-PCB conductive paths communicating with at least one surface of the additional PCB. The first-PCB conductive paths and additional-PCB conductive paths are located such that when the additional PCB and the first PCB are positioned so that one PCB overlies the other, the first-PCB conductive paths and the additional-PCB conductive paths are substantially aligned. The assembly also includes a plurality of electrical circuit components, each electrically connected to one of either of the first-PCB conductive paths and the additional-PCB conductive paths at one end and to another of either of the first-PCB conductive paths and the additional-PCB conductive paths at the other end. The assembly further includes at least one trace conductive path connecting at least two of either of the first-PCB conductive paths and the additional-PCB conductive paths 
     Thus the present invention substantially reduces the amount of wire leads within a circuit assembly by creating a unique arrangement of conductive paths, carried by the PCB, that functions as electrical junctions between components. The conductive paths also provide a bonding surface which enhances functional rigidity and electrical performance. The invention also creates a unique circuit configuration in utilizing PCB designs to create a matrix array. The invention creates an electrical junction between discrete components by bonding the components, surface to surface, using solder bonds and the PCB, itself, as a junction carrier. These conductive paths allow for parallel or series configurations in design. 
     In a more detailed facet, the first-PCB conductive paths and the additional-PCB conductive paths include at least one solder-filled via passing through the PCB. In another facet, the first-PCB conductive paths and the additional-PCB conductive paths further include at least one electrically-conductive junction pad communicating with the solder-filled via. The junction pad is positioned at the surface of the PCB. In still another aspect, the junction pad is substantially flush with the PCB. In yet another facet, the trace conductive path is carried on the surface of the PCB. 
     In a second aspect, the invention provides a SPD for electrical circuitry. The device includes first and second terminals for connection to the power and/or signal terminals of a circuit being protected. The device also includes a first printed circuit board (PCB) having a plurality of first-PCB conductive paths communicating with the surface of the first PCB and at least one additional PCB having a plurality of additional-PCB conductive paths communicating with the surface of the additional PCB. The first-PCB conductive paths and the additional-PCB conductive paths are located such that when the additional PCB and the first PCB are positioned so that one PCB overlies the other, the first-PCB conductive paths and the additional-PCB conductive paths are substantially aligned. The device also includes a plurality of electrical circuit components, each electrically connected to one of either of the first PCB conductive paths and the additional-PCB conductive paths at one end and to another of the first-PCB conductive paths and the additional-PCB conductive paths at the other end. The device further includes a plurality of trace conductive paths connecting selected first-PCB conductive paths and additional-PCB conductive paths, the first-PCB conductive paths, additional-PCB conductive paths and trace conductive paths connect the electrical circuit components to provide a means for clamping the voltage across the first and second terminals to a characteristic voltage when energized. The electrical components also provide an energizing circuit having a predetermined voltage threshold of conduction. 
     In a third aspect, the invention provides a SPD coupled between power lines and/or signal circuits. The device includes a first printed circuit board (PCB) having a plurality of first-PCB conductive paths communicating with the surface of the first PCB. Also included is at least one additional PCB having a plurality of additional-PCB conductive paths flush with the surface of the additional PCB. The first-PCB conductive paths and the additional-PCB conductive paths are located such that when the additional PCBs and the first PCB are positioned so that one PCB overlies the other, the first-PCB conductive paths and the additional-PCB conductive paths are substantially aligned. The device also includes a plurality of electrical circuit components, each electrically connected to one of either of the first-PCB conductive paths and the additional-PCB conductive paths at one end and to another of either of the first-PCB conductive paths and the additional-PCB conductive paths at the other end. Also included is a plurality of trace conductive paths connecting select first-PCB conductive paths and additional-PCB conductive paths. The first-PCB conductive paths, additional-PCB conductive paths and trace conductive paths connect the electrical circuit components to provide a means for clamping the voltage across said power line and neutral line to a predetermined voltage. 
     These and other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing, which illustrate by way of example the features of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a three-phase surge protective device including three surge protective modules configured in accordance with the present invention; 
     FIG. 2 is an isometric view of the interior of the surge protective device of FIG. 1 illustrating two surge protective modules or “cards”, one installed and the other removed; 
     FIG. 3 is a side view of the surge protective modules of FIG. 2; 
     FIG. 4 is a block diagram illustrating the interconnection between the surge protective device of FIG. 1 and a power source; 
     FIG. 5 is a plan view of an exemplary interior of the surge protective modules of FIGS. 2,  3 , and  4 , showing the general layout of suppressor assemblies and other circuit components on a main PCB; 
     FIG. 6 a  is a schematic diagram of the three surge protective cards of FIG. 4 configured as a bridge suppressor including two suppressor assemblies in series comprising unipolar suppressor cells; 
     FIG. 6 b  is a schematic diagram of the three surge protective cards of FIG. 4 including two suppressor assemblies in series comprising bipolar suppressor cells; 
     FIG. 7 is a schematic diagram of the three surge protective cards of FIG. 4 including a suppressor assembly comprising bipolar suppressor cells; 
     FIG. 8 a  is an isometric view of an exemplary main PCB subassembly as may be included in the surge protective module of FIG. 5, depicting the arrangement and orientation of unipolar suppressor cells, e.g., diodes; 
     FIG. 8 b  is an isometric view of an exemplary main PCB subassembly as may be included in the surge protective module of FIG. 5, depicting the arrangement of bipolar suppressor cells, e. g. diodes; 
     FIG. 9 a  is an isometric view of a first-layer PCB subassembly which in combination with the main PCB subassembly of FIG. 8 a  forms a portion of the suppressor assemblies of FIG. 5, depicting the arrangement and orientation of unipolar suppressor cells; 
     FIG. 9 b  is an isometric view of a first-layer PCB subassembly which in combination with the main PCB subassembly of FIG. 8 b  forms a portion of the suppressor assemblies of FIG. 5, depicting the arrangement of bipolar suppressor cells; 
     FIG. 10 a  is an isometric view of a mid-layer PCB subassembly which, in combination with the main PCB subassembly of FIG. 8 a  and the first-layer PCB subassembly of FIG. 9 forms a portion of the suppressor assemblies of FIG. 5, depicting the arrangement of and orientation of unipolar suppressor cells; 
     FIG. 10 b  is an isometric view of a mid-layer PCB subassembly which, in combination with the main PCB subassembly of FIG. 8 b  and the first-layer PCB subassembly of FIG. 9 forms a portion of the suppressor assemblies of FIG. 5, depicting the arrangement of bipolar suppressor cells; 
     FIG. 10 c  is an isometric view of a cap PCB which, in combination with the main PCB subassembly of FIG. 8 a  or  8   b,  the first-layer PCB subassembly of FIG. 9 a  or  9   b  and the mid-layer PCB subassembly of FIG. 10 a  or  10   b  forms the suppressor assemblies of FIG. 5; 
     FIG. 11 depicts two suppressor cells positioned between two PCBs and connected in series; 
     FIGS. 12 a  and  12   b  are side views of two of many possible configurations of the suppressor assemblies of FIG. 5 having two mid-layer PCB subassemblies and one cap PCB with a plurality of suppressor cells positioned between the PCBs and adjacent stacks of suppressor cells connected in series; 
     FIG. 13 depicts two suppressor cells positioned between two PCBs and connected in parallel; 
     FIGS. 14 a  and  14   b  are side views of two of many possible configurations of the suppressor assemblies of FIG. 5 having two mid-layer PCB subassemblies and one cap PCB with a plurality of suppressor cells positioned between the PCBs and adjacent stacks of suppressor cells connected in parallel; 
     FIG. 15 a  is a plan view of a mid-layer PCB depicting a plurality of junction pads and solder junctions onto which suppressor cells are attached; 
     FIG. 15 b  is a plan view of a cap PCB depicting a plurality of junction pads onto which suppressor cells are attached and a plurality of trace paths between adjacent junction pads so as to provide a series connection across each row of suppressor cells; 
     FIG. 15 c  is a plan view of a cap PCB depicting a plurality of junction pads onto which suppressor cells are attached and a plurality of trace paths across the rows of junction pads so as to provide a parallel connection across adjacent columns of suppressor cells; 
     FIG. 16 is an isometric view of a PCB assembly depicting circuit components including two suppressor assemblies mounted parallel to the PCB; 
     FIG. 17 is a schematic of the PCB assembly of FIG. 16 including two suppressor assemblies comprising bipolar suppressor cells; 
     FIG. 18 is an isometric view of a PCB assembly depicting circuit components including two suppressor assemblies mounted perpendicular to the PCB; 
     FIG. 19 is a schematic of the PCB assembly of FIG. 18; 
     FIG. 20 is a detailed schematic of the suppressor assembly ZS 1  of FIG. 19; 
     FIG. 21 a  is an isometric view of a first-layer PCB, a mid-layer PCB and a cap PCB in stacked arrangement on a main PCB, for clarity, the PCBs are shown without suppressor cells; 
     FIG. 22 is plan view of the main PCB of FIG. 21 depicting junction pads and trace paths, for clarity, suppressor cells are not shown; 
     FIG. 23 is an isometric view of either a first-layer PCB subassembly or a mid-layer PCB subassembly of FIG. 22 a  depicting the arrangement and orientation of suppressor cells; 
     FIG. 24 is a schematic of a dc surge suppressor circuit which incorporates a suppressor assembly configured in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals denote like or corresponding parts throughout the drawing figures, an surge protective device (SPD)  2  incorporating surge protective modules configured in accordance with the present invention is shown in FIG.  1 . As best observed in FIGS. 2 and 3, the interior of the surge protective device  2  reveals a plurality of surge protective modules (SPMs)  4 . The SPMs  4  are modular cards which may be installed into and removed from a back panel  6 . The back panel  6  also provides a plurality of lugs  8  for hook up of one, two or three phase lines, a neutral line and a ground line. 
     With reference to FIG. 4, a three-phase SPD  2  is shown connected to a three-phase power source  3 . A phase  1  surge protective module  10 , a phase  2  surge protective module  12 , and a phase  3  surge protective module  14  are installed in their respective slots on the back panel  6 . The three phase lines L 1 , L 2 , and L 3  of the power source  3  are connected to the phase L 1 , L 2 , and L 3  lugs  8  respectively through a disconnect/main breaker  5  and a disconnect  7 . The ground GND and neutral N lines are connected to an external ground GND and neutral N. 
     The interior of each of the SPMs  10 ,  12 ,  14 , as shown in FIG. 5, includes a “main” or “bottom” printed circuit board (PCB)  16 . Mounted on the main PCB are a relay  18 , a relay  3 -pin plug  20 , a green LED  22 , a red LED  24 , two suppressor assemblies  26  and various other components. Extending from the PCB are a ground pin  28 , a neutral pin  30 , a line- 3  pin  32 , a line- 2  pin  34  and a line- 1  pin  36 . These pins extend through the rear of the cards housing  38  and provide for the interconnection between the cards and the back panel  6  (FIG.  3 ). 
     Depending on the design of the SPMs  10 ,  12 ,  14 , the operating characteristics of the SPD  2  may vary. For example, different suppressor assemblies  26  designs may provide different voltage, clamp range and energy suppression capabilities to an electric panel box  2 . SPM  10 ,  12 ,  14  components, including suppressor assemblies  26 , can be of varying sizes and shapes defined by circuitry requirements. Thus, the overall size of a SPM can change due to packaging and performance requirements. In one exemplary configuration, as shown in FIG. 6 a,  the SPMs  10 ,  12 ,  14 , include the circuitry listed below. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ref. Des. 
                 Component 
               
               
                   
                   
               
             
             
               
                   
                 B1 
                 Discrete bridge 
               
               
                   
                 D1 
                 blocking diode 
               
               
                   
                 D7 
                 blocking diode 
               
               
                   
                 F1 
                 fuse link 
               
               
                   
                 D5 
                 LED 
               
               
                   
                 D3 
                 LED 
               
               
                   
                 R3 
                 resistor 
               
               
                   
                 R2 
                 resistor 
               
               
                   
                 ZS1 
                 Unipolar suppressor cells in series and in parallel 
               
               
                   
                 ZS2 
                 Unipolar suppressor cells in series and in parallel 
               
               
                   
                 RLY1 
                 Relay 
               
               
                   
                 J1-14 
                 Jumper, phase select 
               
               
                   
                   
               
             
          
         
       
     
     In another exemplary configuration, as shown in FIG. 6 b,  the SPMs  10 ,  12 ,  14 , include circuitry similar to that listed for FIG. 6a except that ZS 1  and ZS 2  comprise bipolar suppressor cells in series and in parallel and the discrete bridge B 1  is eliminated. These configurations maybe used in 120V single-phase or three-phase power systems. 
     In another exemplary configuration, as shown in FIG. 7, the SPMs  10 ,  12 ,  14 , include the circuitry listed below. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ref. Des. 
                 Component 
               
               
                   
                   
               
             
             
               
                   
                 D1 
                 blocking diode 
               
               
                   
                 D7 
                 blocking diode 
               
               
                   
                 F1,2 
                 fuse link 
               
               
                   
                 D5 
                 LED 
               
               
                   
                 D3 
                 LED 
               
               
                   
                 R3 
                 resistor 
               
               
                   
                 R2 
                 resistor 
               
               
                   
                 R1 
                 resistor 
               
               
                   
                 ZS1 
                 Bipolar suppressor cells in series and in parallel 
               
               
                   
                 RLY1 
                 Relay 
               
               
                   
                 J1-14 
                 Jumper, phase select 
               
               
                   
                 J17 
                 Jumper, neutral/ground select 
               
               
                   
                   
               
             
          
         
       
     
     This configuration is used in a three-phase power system. 
     In yet another exemplary configuration, as shown in FIG. 17, a SPM includes the circuitry listed below. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ref. Des. 
                 Component 
               
               
                   
                   
               
             
             
               
                   
                 F1,2 
                 Fuse links 
               
               
                   
                 D1-4 
                 Rectifier diode 
               
               
                   
                 R1-4 
                 Resistor 
               
               
                   
                 LED1,3 
                 LED 
               
               
                   
                 LED2,4 
                 LED 
               
               
                   
                 ZS1,2 
                 Bipolar suppressor cells in series and in parallel 
               
               
                   
                 RLY1,2 
                 Relay 
               
               
                   
                 LMP1,2 
                 Lamp 
               
               
                   
                   
               
             
          
         
       
     
     This configuration is used in a 120V/240V single-phase, three-wire system. 
     In each of the exemplary configurations depicted in FIGS. 6 a,    6   b,    7  and  17  the suppressor assemblies are represented schematically as including diode suppressor cells. Suppressor cells may, however, encompass other circuit technology such as metaloxide varistors (MOVs). In addition, suppressor assemblies may also include filtering features provided by other circuit technology such as capacitors. 
     In accordance with the present invention, the operating characteristics, e.g., voltage, clamp range, suppression capabilities, of the SPMs  10 ,  12 ,  14 , are obtained using unique circuit board component stacking technologies which allow for a multitude of suppressor designs. In general, the SPMs  10 ,  12 ,  14  are comprised of several PCB subassemblies which are individually manufactured and later assembled, in a stacked layer fashion as shown for example, in FIG. 16, to produce a suppressor assembly  26 . Mounted on the subassemblies and positioned between the layers of an assembly are suppressor cells  40 , e.g. diodes MOVs, capacitors, etc. The stacked portion of the SPMs  10 ,  12 ,  14  form the suppressor assemblies  26 . 
     The pattern of each PCB defines a routing of electrical connection that allows suppressor cells  40  to be vertically stacked and bonded to the PCB in individual layers. With reference to FIGS. 15 a-   15   c,  traces  50 ,  52  i.e., electrical connections, are created using unique circuit board technologies. The PCBs  44   a,    44   b,    46  have through holes, i. e. vias  43 , to allow for electrically conductive bonding agents to flow from one side of the PCB to the other. The PCBs  44   a,    44   b,    46  also have junction pads  45  that are strategically positioned for each suppressor design. 
     With reference to FIGS. 12 a,    12   b,    14   a,    14   b  a multitude of vias  43  are formed through junction pads  45  located on the surface of the PCBs  42 ,  44   a,    44   b,    46 . The vias  43  are then filled with solder. The combination of solder-filled vias and junction pads  45  create a conductive path through the PCB. Connection is made with a cell  40   a,    40   b,    40   c  with electrical surfaces parallel to the PCB conductive paths. The conductive paths are designed to carry the correct current required to maximize performance of the device. The arrangement of the cells  40   a,    40   b,    40   c  and interconnections are such as to create a tight matrix array. 
     Typically, a PCB  42 ,  44   a,    44   b,    46  is created with several unique vias  43 , each communicating with a solid junction pad  45  on one or both sides of the PCB. Other traces  50 ,  52  are created at the surface of the PCB. During assembly of a PCB subassembly, a solder bonding agent is applied to the PCB to fill the vias  43  while a cell  40   a,    40   b,    40   c  is placed on top of the junction pad  45 . This may be repeated for any number of PCBs. A cap PCB  46  and bottom PCB  42  complete the suppressor assembly  26 . As explained in detail below, the combination of stacked cells, conductive paths and surface traces allow for parallel or series connections of cells which allow for a great variety of suppressor assembly  26  designs. 
     As shown in FIGS. 8 a  through  10   b,  and  23 , the suppressor assemblies  26  may include individual rectifier and avalanche diode cells  40 . These diodes may be unipolar or bipolar. For unipolar diodes, as shown in FIGS. 8 a,    9   a  and  10   a  the diodes  40  may be oriented either positive side up  54 , as indicated by those diodes with a line on top, or positive side down  56 . As further shown in FIGS. 12 a,    12   b,    14   a  and  14   b,  a plurality of diode cells  40   a,    40   b,    40   c,  are stacked vertically between a plurality of PCBs  42 ,  44   a,    44   b,    46 . The bottom surface of a first diode cell  40   a  is bonded to a junction pad  43  on the top surface of a bottom PCB  42  while the top of the diode is bonded to a junction pad on the bottom surface of a first mid-layer PCB  44   a.  In turn, the bottom surface of a second diode cell  40   b  is bonded to a junction pad  43  on the top of the first mid-layer PCB  44   a  while its top surface is bonded to junction pad on the bottom of a second mid-layer PCB  44   b.  Similarly, the bottom surface of a third diode cell  40   c  is bonded to junction pad  43  on the top of the second mid-layer PCB  44   b  while its top surface is bonded to a junction pad on the bottom of a top or “cap” PCB  46 . 
     These diode cells  40   a,    40   b,    40   c  are strategically placed to form suppressor assemblies  26  of known performance in regard to voltage, clamp range and energy suppression. As indicated in FIGS. 12 b  and  13   b,  diodes  40   a,    40   b,  and  40   c  need not be present in each column. The stacking of PCBs  42 ,  44   a,    44   b,    46  can be any number over two boards in height. Traces  50 ,  52  are used to connect stacks of diode cells  40  in either a series or parallel configuration to provide for customized voltage and energy levels. Other traces (not shown) are used to mount discrete components such as resistors, lights, relays, etc. 
     A series trace  50 , as shown in FIG. 11, connects adjacent diodes  40  in series. An arrangement of series traces  50  (FIGS. 12 a  and  12   b ) on the cap PCB  46 , in combination with an arrangement of series traces  50  on the bottom PCB  42  may be staggered, relative to each other, to produce a series of diodes cells  40  as indicated by the dashed line through FIG. 12 a.  The series trace  50  may be arranged in order to produce a great variety of series arrangement of diode cells  40 . An example of another arrangement is shown in FIG. 12 b.    
     A parallel trace  52 , as shown in FIG. 13, connects adjacent diodes  40  in parallel. A pair of parallel traces  52  on the cap PCB  46  such as shown in FIG. 15 c,  in combination with a pair of parallel traces on the bottom PCB  42  (FIG. 14 a ) produces a plurality of serially stacked diodes connected in parallel, as indicated by the dashed lines through FIGS. 14 a  and  14   b.    
     FIGS. 8 a  through  10   b  illustrate various PCB subassemblies  42 ,  44   a,    44   b,    46 . As previously mentioned, a subassembly is a PCB with components  40  stacked vertically and through-hole or surface-mount components installed as required. Theses subassemblies  42 ,  44   a,    44   b,    46  are manufactured using vertically mounted components in a defined pattern and are eventually assembled to form a PCB assembly, such as shown in FIGS. 16 and 18. As previously mentioned, components  40  may include diodes, MOVs, capacitors and other micro circuitry. 
     The subassemblies  42 ,  44   a,    44   b,    46  are assembled using surface mounting technologies. Assembly of the subassemblies  42 ,  44   a,    44   b,    46  requires a controlled manufacturing process including temperature, time, oven profiling and materials. The temperature requirements are defined by the material selected and the mass of the material. The temperature at which the oven operates is defined by the oven profile. An oven profile is defined as time in feet per minute and temperature per zone. In one theory of oven profile, the oven profile allows for solder reflow to occur after the thermal mass of the complete assembly raises above 190° C. Solder paste reflows at 185° C. In another theory, thermal transfer occurs over a long rise time to the innermost components. The time it takes to process a subassembly varies depending on the size of the suppressor assembly, the thermal mass and heat transfer to the innermost components of the stacked suppressor assembly. 
     A suppressor assembly  26  is formed from a group of PCB subassemblies  42 ,  44   a,    44   b,    46  which are assembled under a controlled process. One of the unique features of modules assembled in accordance with the invention is that a group of PCB subassemblies  42 ,  44   a,    44   b,    46  may be stacked vertically, as shown in FIG. 21, and bonded together with components added as required. In addition, assemblies may be potted using various materials to protect from shock and provide thermal conduction for the suppressor. 
     Following is a list of materials, and material requirements, which may be used to manufacture a SPM: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Circuit boards: 
                   
               
               
                 Board material: 
                 Laminated glass epoxy sheet, copper clad 
               
               
                 Components: 
               
               
                 Diodes: 
                 Silicon avalanche suppressor diodes in cell form. 
               
               
                 Rectifier diodes: 
                 Silicon rectifier blocking diodes in cell form. 
               
               
                 Resistors: 
                 Standard electronic components used. 
               
               
                 LEDs: 
                 Standard electronic components used. 
               
               
                 Relays: 
                 Standard electronic components used. 
               
               
                 Miscellaneous: 
                 Standard electronic components used. 
               
               
                   
               
             
          
         
       
     
     While the present invention has thus far been described within the context of surge protective devices for use in power or signaling systems, it may also find application in other electrical systems which operate in environments which render such systems relatively vulnerable to the deleterious effects of electrical transients. Such systems include control circuitry, computers and other circuits employing semiconductor devices. The present invention is of benefit to such systems as described in U.S. Pat. Nos. 3,475,653; 3,573,550 and 4,797,773, the disclosures of which are hereby incorporated by reference. 
     While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.