Abstract:
A printed circuit board includes a busbar applied to a surface of the printed circuit board. The busbar is configured as a sequence of sheet metal conductor pieces which are connected to each other in an electrically conducting manner. The respective ends of the conductor pieces may have a rounded portion and a corresponding cutout, or a point and a corresponding indentation. An electrical controller, a motor vehicle and a printed circuit board configuration having at least one printed circuit board are also provided.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a printed circuit board having a high current-carrying capacity and to a method for producing such a printed circuit board, in particular for electrical control units. 
     In modern electrical control units, in particular for the automotive industry, it is the case with increasing prevalence that high currents are conducted via the printed circuit board. The conductor tracks provided for this purpose are usually designed with appropriate width and over a plurality of layers or levels of the printed circuit board in order to counteract overheating and thus a high voltage drop in the lines. 
     What is disadvantageous about a printed circuit board populated in this way with wide conductor tracks, which are designated hereinafter as busbars or current bridges, is that a large proportion of the area of the printed circuit board cannot be utilized for other devices and this type of printed circuit boards thus becomes very cost-intensive. In some cases it is even impossible to pass the required high current via the printed circuit board. 
     The busbars have hitherto been applied or laminated onto or into the printed circuit board by means of SMD (Surface Mounted Device) or THT (Through-the-hole Technology) soldering methods. These busbars have to be designed specifically for one printed circuit board product having a defined geometry and re-use for other printed circuit board products is therefore virtually ruled out. Consequently, new current bridge layouts always have to be developed for new printed circuit board products. As a result, the production costs increase greatly in the case of layout changes, which is also based on the fact that manufacturing with the population of the printed circuit board has to be adapted anew in the event of such a design change. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, the problem addressed by the invention is that of providing a printed circuit board having a high current-carrying capacity which has busbars which can be flexibly adapted to layout changes of the printed circuit board. The busbar arrangement of the printed circuit board is furthermore intended to be less susceptible to temperature fluctuations and to exhibit lower failure rates in the event of vibrations and deformations of the printed circuit board. Moreover, the problem addressed by the invention is that of specifying a method for producing an improved printed circuit board having a high current-carrying capacity which can be integrated into the primarily automated production method for printed circuit boards and can also be easily adapted in the event of layout changes. 
     The problem is solved according to the invention by means of the features of the independent claims. Advantageous configurations of the invention are specified in the dependent claims. 
     The printed circuit board according to the invention comprises a busbar applied on the surface of the printed circuit board, wherein the busbar is formed by a sequence of sheet metal conductor pieces which are electrically conductively connected to one another. 
     The term sheet metal conductor pieces in the context of the present invention is understood to mean substantially longitudinally and areally extended, metallic, electrically conductive material sections in the form of easily producible, in particular stampable and embossable conductors produced from customary conductor materials such as, for example, copper, silver and gold. 
     The embodiment of the busbar as a sequence of sheet metal conductor pieces makes it possible that high currents can be conducted via the printed circuit board in an area-saving manner. Moreover, as a result of this multipartite embodiment according the invention of the busbar in a sequence of sheet metal conductor pieces, the layout of the printed circuit board can be configured in a manner flexibly adapted to the spatial conditions of the other electrical components, as a result of which cost savings are made possible on account of the current paths that can be fashioned more easily. Furthermore, the printed circuit boards configured according to the invention in this way are less susceptible to temperature fluctuations and exhibit lower failure rates in the event of vibrations and deformations of the printed circuit board. 
     According to the invention, the sheet metal conductor pieces are electrically conductively connected to one another. By way of example, the sheet metal conductor pieces can be connected to one another by soldered joints or by electrically conductive adhesive. The sheet metal conductor pieces are preferably connected by soldered joints. This can be effected in an automatable method in a manner integrated into the method for producing the printed circuit board, in a cost-saving manner. The soldered joints or adhesive bonding locations between the sheet metal conductor pieces of the busbar can function in the manner of an expansion joint, for example, and thus advantageously contribute to the fact that the printed circuit board overall is less susceptible to temperature fluctuations and the printed circuit board exhibits lower failure rates even in the event of vibrations and deformations. 
     In one preferred configuration of the invention, the sheet metal conductor pieces have an identical geometry. By virtue of the fact that the sheet metal conductor pieces have an identical geometry, they can be manufactured in mass production. This considerably reduces the production costs of the current bridges of a printed circuit board according to the invention in comparison with the previous individual fabrication for a specific printed circuit board layout. Furthermore, the sequence of the sheet metal conductor pieces having an identical geometry can be changed very easily and in a computer-calculated manner in the event of a layout change, such that only a recurring geometry has to be stored in the corresponding software. 
     It is preferably provided that the sheet metal conductor pieces have an angular portion at least at one end. This makes it possible to arrange the current bridges as sequences of the sheet metal conductor pieces including with a plurality of changes in direction, for example by 90°, in a small space. As a result, it is advantageously possible, with regard to further layout requirements of other devices, to embody the busbars in a manner saving as much area as possible and additionally to shorten further signal and current paths or to fashion them more easily. This can contribute to reducing the failure rates of the printed circuit boards. 
     Furthermore, one preferred configuration of the invention provides for sheet metal conductor pieces to have a rounded portion at least at one end. 
     In the context of a further preferred configuration of the invention it is provided that the sheet metal conductor pieces have a rounded portion at least at one end, and at the other end a cutout corresponding to the rounded portion. According to the invention this means that a sheet metal conductor piece can be attached, by the end at which the mounted portion is arranged, to the end having the cutout of a second sheet metal conductor piece. In other words, sheet metal conductor pieces can be arranged like an articulated joint with respect to one another. The cutout and rounded portion of the two sheet metal conductor pieces can preferably be embodied in a manner coordinated with one another in such a way that it would be possible to place them against one another seamlessly or with an equidistantly configured joint. By means of this seam or joint, the two sheet metal conductor pieces can then be electrically conductively connected to one another for example by means of soldering or adhesive bonding. Both the rounded portion and the cutout can be embodied in a semicircular fashion, for example. This embodiment of the sheet metal conductor pieces has the advantage that a particularly good current-carrying capacity can be achieved. Furthermore, the arrangement of the sheet metal conductor pieces to form the busbar can additionally be realized with a large angle bandwidth. This furthermore increases the degree of freedom in the layout design of the printed circuit board according to the invention. 
     In another preferred configuration, the sheet metal conductor pieces can have an indentation at least at one end, and at the other end a point corresponding to the indentation. According to the invention, this means that a sheet metal conductor piece can be attached, by the end at which the point is arranged, to the end having the indentation of a second sheet metal conductor piece. The indentation and the point of the two sheet metal conductor pieces can preferably be embodied in a manner coordinated with one another in such a way that it would be possible to place them against one another seamlessly or with an equidistantly configured joint. By means of this seam or joint, the two sheet metal conductor pieces can then be electrically conductively connected to one another for example by means of soldering or adhesive bonding. The printed circuit board having a busbar embodied in such a way can exhibit lower failure rates in the event of vibrations and deformations and overall can be less susceptible to temperature fluctuations. The printed circuit boards having busbars configured according to the invention in this way can furthermore have a good current-carrying capacity. 
     The invention furthermore relates to a method for producing a printed circuit board according to the invention. The method according to the invention provides for the printed circuit board to be populated with the sheet metal conductor pieces in an automated manner in an SMD method. 
     The abbreviation SMD stands for Surface Mounted Devices and signifies surface-mountable devices. Such devices have no wire connections, but rather are secured by means of connection areas directly on a printed circuit board, for example by being fixedly adhesively bonded and then soldered. Advantageously, therefore, this SMD method does not require complex holes on the printed circuit board or wiring that would be unavoidable in the case of through-the-hole technology (THT) or pin-in-hole technology (PIH). 
     Population with the sheet metal conductor pieces can be effected in an automated manner and with high precision. Moreover, as a result of avoiding connection wires and associated holes, it is possible to use a significantly thinner printed circuit board material, thus advantageously resulting in a weight reduction. A printed circuit board according to the invention can therefore be manufactured significantly more cost-effectively. Furthermore, the automated population of the printed circuit board with the sheet metal conductor pieces by an SMD method makes it possible to achieve not only faster and more expedient production but also a particularly good manufacturing quality. The manufacturing quality can additionally be increased by possible automatic optical inspection (AOI). Overall, it is thus possible, without any problems, to integrate the population of the printed circuit board with the busbar composed of sheet metal conductor pieces and the population of the printed circuit board with further devices of a desired layout in a process and, if appropriate, to carry them out in one method step. 
     SMD technology is furthermore advantageous since it enables a small device spacing and optimum miniaturization and the signal and current paths can thus be shortened. This enables, if appropriate, the improvement of radio-frequency properties and smaller ohmic losses and reduces the susceptibility to faults and the failure rate of the printed circuit board. Furthermore, in the SMD method, printed circuit boards can be populated with devices on both sides. 
     In a further configuration of the method according to the invention, the sheet metal conductor pieces can be mechanically and electrically conductively connected to one another and/or to conductor tracks of the printed circuit board by means of a reflow soldering step and/or by means of an adhesive bonding step using an electrically conductive adhesive. The sheet metal conductor pieces are preferably connected by means of soldering. Reflow soldering affords the advantage that, by means of a relatively simple populating method, for example simple Pick &amp; Place, devices can be positioned on the printed circuit board and can subsequently be soldered jointly in a furnace in a batch process. In addition, a self-alignment effect can be used during reflow. Advantageously, therefore, for example small positioning errors during SMD device placement can be automatically corrected during reflow soldering by means of the surface tension of the liquid solder. 
     The invention furthermore relates to the use of a printed circuit board according to the invention, such as has been described above in various configurations, in an electrical controller, in heavy-current electronics, in particular in on-board power supply system controllers, fuse boxes, HEV (hybrid electric vehicles), and in non-automotive high-current applications. In other words, the invention also encompasses an electrical controller, heavy-current electronics or high-current application containing one or more printed circuit boards according to the invention. Owing to the use of the printed circuit boards according to the invention, the components, units and devices manufactured therewith are also less susceptible to temperature fluctuations and also exhibit lower failure rates in the event of vibrations, for example engine vibrations, and deformations of the printed circuit board. 
     In one preferred embodiment, the electrical controller can be a transmission or engine controller of a motor vehicle. In other words, the invention also encompasses an electrical transmission or engine controller containing one or more printed circuit boards according to the invention. With regard to the advantages, reference is hereby subsequently made explicitly to the explanations concerning the printed circuit board according to the invention in its possible configurations and to the method according to the invention. 
     The invention furthermore relates to a motor vehicle, comprising at least one electrical controller according to the invention or at least one printed circuit board according to the invention. With regard to the advantages, reference is hereby subsequently made explicitly to the explanations concerning the printed circuit board according to the invention in its possible configurations and to the method according to the invention. 
     The invention is explained by way of example below with reference to the accompanying drawings on the basis of preferred exemplary embodiments, without being restricted thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1 : shows a schematic plan view of a sheet metal conductor piece for a printed circuit board according to the invention; 
         FIGS. 2 a -2 b   : show a schematic plan view and a schematic side view of a printed circuit board according to the invention; and 
         FIGS. 3 a -3 d    show a schematic plan view of sheet metal conductor pieces having four different geometries for a printed circuit board according to the invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a schematic plan view of a sheet metal conductor piece  14  for a printed circuit board  11  according to the invention. The sheet metal conductor piece  14  has an angular portion with an angle X°. This angle X° can be 45°, for example, but is not restricted thereto. Advantageously, by virtue of the angular portion of the sheet metal conductor piece  14 , in the production of a busbar  13  made from a plurality of such sheet metal conductor pieces  14 , it is possible to achieve desired direction changes required for example as a result of a predefined layout of circuits and/or of the arrangement of the further devices on the printed circuit board  11 . As a result, it is therefore advantageously possible, with regard to further layout requirements of other devices, to embody the busbars  13  in a manner saving as much area as possible and additionally to shorten signal and current paths or to fashion them more easily. This can contribute to reducing the failure rates of the printed circuit boards  11 . 
       FIG. 2 a    shows a schematic plan view of a printed circuit board  11  according to the invention with a busbar  13 . The busbar  13  is composed of a plurality of sheet metal conductor pieces  14  having an angular portion, as illustrated in  FIG. 1 . In this embodiment, the sheet metal conductor pieces  14  used have an identical geometry. The sheet metal conductor pieces  14  can advantageously be produced in mass production. This considerably reduces the production costs of the busbars  13  of a printed circuit board  11  according to the invention in comparison with the previous individual fabrication for a specific printed circuit board layout. Furthermore, the sequence of the sheet metal conductor pieces  14  having an identical geometry can be changed very easily and in a computer-calculated manner in the event of a layout change, such that only a recurring geometry has to be stored in the corresponding software. 
       FIG. 2 b    shows a schematic side view of a printed circuit board  11  according to the invention with a busbar  13 , which is arranged on the surface  12  of the printed circuit board  11 . The busbar  13  is formed as a sequence of a plurality of sheet metal conductor pieces  14 , wherein only three sheet metal conductor pieces  14  are shown by way of example and in order to simplify the illustration. The soldering and/or adhesive-bonding connection of the sheet metal conductor pieces  14  for mechanical and electrical connection is not illustrated. The soldered joints or adhesive bonding locations between the sheet metal conductor pieces  14  of the busbar  13  can function in the manner of an expansion joint, for example, and thus advantageously contribute to the fact that the printed circuit board  11  overall is less susceptible to temperature fluctuations and the printed circuit board exhibits lower failure rates even in the event of vibrations and deformations. 
       FIGS. 3 a  to 3 d    show sheet metal conductor pieces  14  in a schematic plan view with four different geometries. 
       FIG. 3 a    shows a sheet metal conductor piece  14  having two rounded portions at opposite ends. 
       FIG. 3 b    shows a sheet metal conductor piece  14  having a rounded portion  18  at one end, and at the other end a cutout  19  corresponding to the rounded portion  18 . This means that a sheet metal conductor piece  14  can be attached, by the end at which the rounded portion  18  is arranged, to an end having the cutout  19  of a second sheet metal conductor piece  14  configured in such a way. Such sheet metal conductor pieces  14  can be arranged for example like an articulated joint with respect to one another. In this configuration, both the rounded portion  18  and the cutout  19  are embodied in a semicircular fashion. This embodiment of the sheet metal conductor pieces  14  has the advantage that a particularly good current-carrying capacity can be achieved. Furthermore, an arrangement of the sheet metal conductor pieces  14  to form a busbar  13  can additionally be realized as a sequence with a large angle bandwidth. This furthermore increases the degree of freedom in the layout design of a printed circuit board  11  according to the invention. 
       FIG. 3 c    shows a sheet metal conductor piece  14  having an indentation  16  at one end, and at the other end a point  17  corresponding to the indentation  16 . According to the invention, this means that a sheet metal conductor piece  14  can be attached, by the end at which the point  17  is arranged, to the end having the indentation  16  of an identically configured second sheet metal conductor piece  14 . The two sheet metal conductor pieces  14  can then be electrically conductively connected to one another for example by means of soldering or adhesive bonding. The printed circuit board  11  having a busbar  13  embodied in such a way can exhibit lower failure rates in the event of vibrations and deformations and overall can be less susceptible to temperature fluctuations. The printed circuit boards  11  having busbars  13  configured according to the invention in this way can furthermore have a good current-carrying capacity. 
       FIG. 3 c    shows a sheet metal conductor piece  14  having an angular portion at two mutually opposite ends, thus resulting in a trapezoidal shape in the configuration shown. Advantageously, as a result of the angular portions of the sheet metal conductor piece  14  and the trapezoidal shape thereof, desired direction changes can be achieved in the production of a busbar  13  made from a plurality of such sheet metal conductor pieces  14 . As a result, it is advantageously possible, with regard to further layout requirements of other devices, to embody the busbars  13  in a manner saving as much area as possible and additionally to shorten further signal and current paths or to fashion them more easily. This can contribute to reducing the failure rates of the printed circuit boards  11 . 
     To summarize, the invention provides a printed circuit board having a high current-carrying capacity which has at least one busbar formed from a sequence of sheet metal conductor pieces, wherein the sheet metal conductor pieces are electrically conductively connected to one another and can be flexibly adapted to layout changes of the printed circuit board. The printed circuit board having the busbar arrangement according to the invention is furthermore less susceptible to temperature fluctuations and exhibits a lower failure rate in the event of vibrations and deformations. In addition, a method for producing such an improved printed circuit board having a high carrying capacity is provided, which method can be integrated into the primarily automated production method for printed circuit boards and can also be easily adapted in the event of layout changes.