Patent Publication Number: US-5291376-A

Title: System for coupling a high voltage, high current wire to a circuit board

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to electric circuit boards and more specifically to circuit boards having high voltage, high current, such as 240 volts, 50 amps, traces thereon. 
     It is conventional to have high voltage, high current lines directly connected to relays and to use a relatively low voltage, low current signal to effect energization of the relay and concomitantly energize or de-energize the high voltage, high current lines. By way of example, in switching loads such as those used for residential heating, high voltage, high current lines are connected through relays to banks of electric heaters with the relays energized by appropriate low voltage signals from a thermostat or the like. 
     A control system for energizing and de-energizing electric heater banks along with associated components such as a fan, in which high voltage, high current lines are directly coupled to traces on a circuit board and to relays mounted on the board is shown in copending application Ser. No. 07/886,274 assigned to the assignee of the present invention. In that application a method and apparatus is disposed in which extended relay contact life is obtained by using a microprocessor, reading the AC input signals when the wave is at a peak, generating an output from the microprocessor to a relay at a time equal to a delay following a zero crossing of the AC line current wave so that contact engagement occurs in the proximity of zero crossing of the AC line current. This near zero crossing of the AC line current is conducive to providing the high voltage, high current traces directly on the board for connection with the relays. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a reliable coupling between a high voltage, high current wire and a trace on a circuit board. Another object is the provision of such a coupling which has improved capability for withstanding torque placed upon it when connecting a wire thereto. 
     Briefly, in accordance with the invention, a block of electrically conductive material is provided for each high voltage, high current trace disposed on the circuit board to which it is desired to couple a high voltage, high current line, the block being formed with a bore laterally extending between opposed sides of the block and being adapted to receive therethrough a high voltage, high current wire. A first threaded bore extends from a surface of the block to the laterally extending bore and is adapted to receive a set screw in order to clamp the wire against the body of the block. The block is formed with a seat which includes at least one portion extending downwardly from the block which is adapted to be received in a mating aperture in the circuit board. In the described embodiment a pair of parallel extending ribs depend downwardly from the bottom surface of the block and are received in a mating pair of slots formed in the circuit board. A second threaded bore is formed in the bottom surface of the block between the pair of ribs and a corresponding bore is formed in the circuit board between the pair of slots so that when the block is placed on a first side of the circuit board with the ribs received in the slots, an electrically conductive threaded member can be inserted through the bore into threaded engagement with the second threaded bore with a radially extending head of the threaded member engaging a trace on the second side of the board. According to a feature of the invention a quantity of solder is then placed over the radially extending head and onto the trace to enhance the current carrying capability thereof. 
     Various additional objects and advantages of the present invention will become apparent from the following detailed description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings in which the preferred embodiment of the invention is illustrated: 
     FIG. 1 is a perspective top view of a circuit board system made in accordance with the invention; 
     FIG. 2 is a perspective bottom view of a portion of the FIG. 1 circuit board system; 
     FIG. 3 is a perspective top view of a coupling block and a portion of a circuit board having a coupling block seat shown with the coupling block spaced above the seat; and 
     FIG. 4 is an elevational view of the coupling block shown in FIGS. 1 and 3. 
     Dimensions of certain parts as shown in the drawings may have been modified or exaggerated for the purpose of clarity of illustration. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to the drawings, a system for coupling high voltage, high current wires to a circuit board comprises a circuit board 12 formed of conventional electrically insulative material having a suitable thickness, typically between 0.045 and 0.062 inches. The particular board shown is intended for use in the control of a heating system such as the type described in application Ser. No. 07/886,274 referenced supra, although the invention is applicable to any circuit board having a trace or conductive path to which it is desired to couple a high voltage, high current wire. Board 12 includes a plurality of relays K1, K2, K3 adapted upon energization to close or open circuit paths between traces 14, 16, 18, 20 and common trace 22. Relays K1, K2, K3 are controlled by low voltage signals provided by other components mounted on circuit board 12 which are not relevant to the coupling system of the invention and therefore will not be further described herein. 
     As shown in FIG. 1, a coupling system 24 comprises a block 26 formed of suitable electrically conductive material generally in the shape of a parallelepiped having, as seen in FIG. 3, an upper surface 28, a lower surface 30 and opposed pairs of sidewalls 32, 34 and 36, 38 respectively. Block 26 is formed with a bore 40 laterally extending between a pair of sidewalls 36, 38 and is adapted to receive therethrough a high voltage, high current wire (not shown). A first threaded bore 42 (FIG. 4) extends from the top surface 28 into communication with laterally extending bore 40 and is adapted to receive a suitable set screw 44 having a generally convex lower distal end 46 adapted to clamp a wire inserted through bore 40 against the lower surface of the body of the block defining bore 40. 
     A pair of generally parallel extending rib members 48, 50 depend downwardly from sidewalls 32, 34, a distance b (FIG. 4) below lower surface 30 of block 24. Distance b is preferably selected to be less than distance a, the thickness of circuit board 12, shown in FIG. 3. 
     Circuit board 12 is formed with a seat located on an area of the board demarked by line 52 which comprises a pair of parallel extending slots 54, 56 respectively adapted to receive ribs 48, 50 therein. A bore 58 is formed through circuit board 12 between slots 54, 56 and is adapted to receive a threaded member, screw 60, therethrough (FIG. 4). Block 24 is formed with a second threaded bore 62 adapted to receive screw 60. Bore 62 is shown to extend to and communicate with laterally extending bore 40; however, if desired, it could be closed ended terminating below the bore. Block 24 is installed by placing it on one side of circuit board 12, as seen in FIG. 3, with ribs 48, 50 received respectively in slots 54, 56 and screw 60 is inserted through bore 58 of board 12 from the opposite side of the board and into threading engagement with second threaded bore 62. Screw 60 is formed of electrically conductive material and has an outwardly radially extending head 62 which is brought into engagement with trace 22 on the circuit board as shown at 64 in FIG. 2. 
     Another block 24 is mounted in the same manner so that the head of corresponding screw is brought into engagement with trace 14 on the circuit board as shown at 66 in FIG. 2. The screw heads shown at 64 and 66 are then preferably covered with a selected quantity of solder 68 which extends onto traces 22, 14 as well, to enhance the current carrying capability thereof. 
     Block 24 formed of suitable material, such as aluminum, may be plated with tin, e.g., 0.0001-0.0004 inches over a copper layer, e.g., 0.00005-0.00012 inches to enhance long term electrical conductivity, if desired. 
     Use of the downwardly depending ribs and mating slots in the circuit board greatly increases the couplings ability to withstand torque subjected, for example, when set screw 44 is tightened onto a wire received in laterally extending bore 40 and enables the system to exceed 45 inch pounds of torque required by accepted standards for high voltage, high current couplings. 
     It will be understood that although a pair of parallel extending ribs are shown, other downwardly depending portions could be used along with mating apertures in the circuit board to provide the required torque resistance, such as short L shape ribs formed at each corner of block 24. Further, although the first threaded bore 42 is shown extending from the top surface 28, the bore could extend from sidewall 34 or 32 to laterally extending bore 40, if desired. 
     Though the invention has been described with respect to a specific preferred embodiment thereof, many variations and modifications will immediately become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.