Abstract:
Connecting a first ( 12 ) and a second ( 14 ) printed circuit board or PCB carrying a LED lighting source ( 10 ) and the associated drive circuitry involves providing board connection pads ( 12   a,    14   a ) at said first ( 12 ) and second ( 14 ) PCBs, and arranging a flex PCB ( 16 ) in a bridge-like fashion between the first ( 12 ) and second ( 14 ) PCBs. The flex PCB ( 16 ) has connection pads ( 16   a ) for bonding with the board connection pads ( 12   a   , 14   a ) of the PCBs ( 12, 14 ). The connection pads ( 16   a ) in the flex PCB ( 16 ) arranged in a bridge-like fashion between the first ( 12 ) and second ( 14 ) PCBs are bonded with the connection pads ( 12   a,    14   a ) of the first ( 12 ) and second ( 14 ) PCBs, so that the first ( 12 ) and second ( 14 ) PCBs are connected.

Description:
FIELD OF THE INVENTION 
     This disclosure relates to connecting Printed Circuit Boards (briefly, PCBs). 
     This disclosure was devised with specific attention paid to its possible use in PCB mounting arrangements for lighting sources such as light-emitting diode (LED) lighting sources. 
     DESCRIPTION OF THE RELATED ART 
     Electrical connection between different PCBs is a critical point in production. 
     For instance, in the case of LED modules, the LED or LEDs (i.e. the light sources) and the related driver electronics are frequently mounted on different PCBs (oftentimes referred to as the LED-PCB and the DRIVER-PCB). This may be the result of e.g. the LED or LEDs being already mounted on a PCB of their own and/or the requirement of thermally insulating the driver electronics from the heat-source represented by the LED or LEDS. Also, the driver electronics may be bulky and the mounting space available in the vicinity of the LED or LEDs may not be sufficient. 
     With such a configuration, connection between the two (or more) PCBs involved may be critical. In fact, automatically soldering wires between the PCBs may be far from easy, while mechanical connectors are usually bulky and may represent an undue additional cost. More generally, connection may be labour- and time-consuming and lends itself poorly to up-scaling in the presence of higher production volumes. 
     OBJECT AND SUMMARY OF THE INVENTION 
     In designing LED modules, use of LEDs already mounted on respective PCBs may sometimes be avoided (for instance, plastic packages or ceramic submounts may be preferred). 
     Also, if using LEDs already mounted on a PCB of their own cannot be avoided, efforts may be made at optimizing the connection process of the LED-PCB to the driver-PCB. 
     While in that way the critical nature of connection between PCBs may be somehow palliated, the need is still felt for improved solutions which may radically dispense with the disadvantages discussed previously. 
     The object of the invention is to provide such a solution. 
     According to the invention, that object is achieved by means of a method as set forth in the claims that follow. The invention also relates to a corresponding arrangement. 
     The claims are an integral part of the disclosure of the arrangement described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE ANNEXED REPRESENTATIONS 
       The invention will now be described, by way of example only, with reference to the annexed representations, wherein: 
         FIG. 1  is an exploded perspective view of the parts involved in an arrangement as described herein, and 
         FIG. 2  represents the operation of connecting the various parts shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
     In  FIG. 1 , reference  10  denotes a LED light source (including one or more LEDs) mounted on a printed circuit board (PCB)  12 . The PCB  12  is intended to be connected with another PCB  14  carrying thereon driver electronics for the LED light source  10 . The two PCBs  12  and  14  are provided with connection pads  12   a ,  14   a  to enable electrical connection therebetween. 
     Unless otherwise detailed in the following, these parts and elements are conventional in the art, which makes it unnecessary to provide a more detailed description herein. 
     Reference  16  denotes as whole a so-called “flex” PCB (namely, a flexible PCB o FCB) carrying respective connection lines as well as pads  16   a  to be soldered to the pads  12   a ,  14   a  of the PCBs  10  and  14  to ensure electrical connection therebetween. 
     In the embodiment shown, the pads  12   a ,  14   a  of the PCBs  12  and  14  face “upwardly” while the connection pads  16   b  of the flex  16  face downwardly. The flex  16  can thus be arranged in a bridge-like arrangement above and across the PCBs  10  and  14  while bonding (e.g. soldering) of the pads  12   a , respectively  14   a  with the pads  16   a  of the flex  16 . This result—can be achieved—in a known manner—by means of a hot bar HB which is temporally superposed to the flex  16  (or at least the ends thereof) to produce soldering of the pads  12   a ,  14   a  and  16   a.    
     For facilitating the soldering process, the pads  12   a  and  14   a  can be partially left uncovered by the flex allowing the direct contact between the hot bar HB and the metal pads. 
     The bonding process can be also carried out by means of laser soldering techniques. In that case the pads  12   a  and  14   a  may be left partially uncovered in order to allow the laser beam to reach the soldering area. 
     A “flex” is a well known component adapted for connecting electrical/electronic components expected to move mutually during operation (e.g. in hard disk drives) and/or components of apparatus whose mutual positions are changed during assembly of the apparatus. 
     In the embodiment shown, connecting the PCBs  12 ,  14  via the flex involves a base plate  20 . 
     In the embodiment shown, the metal plate  20  includes three recessed areas  120 ,  140  and  160 . 
     These recesses can be easily produced when manufacturing the plate  20  and are intended to house:
         the PCB  12  (recess  120 ),   the PCB  14  (recess  140 ); and   the “flex”  16  (recess  160 ).       

     In the embodiment shown, the recesses  120 ,  140  and  160  are generally “shallow” recesses having thicknesses substantially equal to the “height” or “depth” of the element intended to be received therein. 
     As a result of this (and as better appreciated in  FIG. 2 ) the PCBs  12  and  14  may be arranged in the recesses  100 ,  140  and the flex  16  arranged in a bridge-like arrangement therebetween in such a way that the upper surface of the flex  16  lies at least approximately “flush” with the upper surface of the plate  20 . 
     In that way, when the hot bar HB or the soldering laser is applied, the flex  16  (or at least the ends of the flex  16 ) are very precisely positioned, with the pads  16   a  exactly facing and abutting against the pads  12   a ,  14   a . The desired bonding action may be achieved in a rapid and reliable manner by minimising the amount of the heat energy applied. 
     The arrangement described herein completely dispenses with the need of using wires and/or mechanical connectors and is ideally adapted for an automated soldering process. The fixed shape of the flex  16  derives from the layout design, related cut and mechanical properties while the flat bonding pads ( 12   a ,  14   a ,  16   a ) provide a wide contact surface thus facilitating an automated bonding process. The bonding process may be automated by resorting to simple machinery (essentially a metal base properly shaped and a movable hot bar or laser soldering head). 
     The layout of the flex PCB  16  can be selected to match the relative expected positions of the two PCBs  12  and  14  in the final application. Exact positioning on the three components involved in the connection process ( 12 ,  14  and  16 , in the drawings herein) permits the hot bar HB (or the laser soldering beam) to move in correspondence with the pads to be soldered and apply the thermal profile required for the bonding process. Manual work is completely dispensed with in the production of lighting modules since no manual soldering is being resorted to thus giving rise to a completely automated process. No additional components are introduced by rendering the production process a very fast one. Also, the arrangement described herein lends itself to a semi-automatic implementation in the case of small volumes to be produced. 
     Of course, without prejudice to the underlying principles of the invention, the details and embodiments may vary, even significantly, with respect to what has been described and illustrated by way of example only, without departing from the scope of the invention as defined by the annexed claims. For instance, the method described in the foregoing can be extended to connecting more than two PCBs. Also, at least one of the PCBs involved may already include a flexible part providing the bridge-like function (i.e. the flex PCB).