Abstract:
A system and method is disclosed for allowing a solid substrate, such as a printed circuit board (PCB), to act as the support structure for an electronic circuit. In one embodiment, the LEDs which form a part of a scrambler assembly are constructed on a first substrate and the electrical connections are run to the edges of the substrate and end in electrical contacts positioned thereat. The substrate is then connected to the scrambler package by a series of electrical and mechanical connections to form the LED package. The electrical contacts which are part of the LED package extend from the LED package so as to enable electrical contact with a separate controller substrate.

Description:
BACKGROUND OF THE INVENTION 
     It has become common practice to use light emitting diode (LED) displays for a variety of purposes. Typically such displays are manufactured as seven-segment displays or alphanumeric displays, and, if desired, can be arranged as dot matrix displays. Such displays require multi-color and high brightness and must have a thin profile. 
     In a typical manufacturing process custom display devices use the concept of stretching the light from an LED by diffusion and reflection. The LED chips are mechanically attached onto a printed circuit board (PCB) or lead-frame by using electrically conductive adhesive, e.g. silver epoxy. Gold (or other conductive material, such as aluminum) is used to wire bond the top of the LED die to the PCB. A cone shaped reflecting cavity is cast inside a rectangular package around each LED. A plastic housing, often referred as ‘scrambler’, forms the display package and contains the LED segment cavities. The housing also provides structural integrity to the LED package. Generally, the material used for the scrambler is polycarbonate with TiO 2  sealant to prevent light leakage. Optical grade epoxy fills the top of the cavity and also fills the bottom of the scrambler to form the stretched segment. 
     Presently, these custom LED display packages are predominately through-hole mounted because of economy of manufacture. However, surface mounting assemblies are quickly replacing wave-soldering techniques because wave soldering has reached the limit of its capabilities. Currently, reflow soldering has become the leading technique for soldering components, such as LED packages to PCBs. Miniaturization of control panels and simplified manufacturing processes are requiring LED manufacturers to convert through-hole devices to surface-mountable devices. 
     One manufacturing process now being used for surface mounting LED packages to PCBs is a lead-frame process where a metal frame is folded around a substrate holding the LED. Such processes are time-consuming and cumbersome. An alternate process for surface mounting is to mount the LED onto a PCB for support purposes and to then surface mount the PCB onto a controller PCB board. Because of surface irregularities between the two PCBs, such PCB/PCB mounting is difficult to achieve in a reliable manner. 
     In general, the PCB to PCB or even lead-frame to PCB mating tends to face surface irregularities as a result of PCB warping or lead-frame lead coplanarity issues. In addition, as the customized displays become larger and have more LED segments, the warping becomes more pronounced and adds further complexity to the soldering process. 
     BRIEF SUMMARY OF THE INVENTION 
     A system and method is disclosed for allowing a solid substrate, such as a printed circuit board (PCB), to act as the support structure for an electronic circuit. In one embodiment, the LEDs which form a part of a scrambler assembly are constructed on a first substrate and the electrical connections are run to the edges of the substrate and end in electrical contacts positioned thereat. The substrate is then connected to the scrambler package by a series of electrical and mechanical connections to form the LED package. The electrical contacts which are part of the LED package extend from the LED package so as to enable electrical contact with a separate controller substrate. 
     The spring-loaded electrical contacts allow for flexible mating between the LED package and the electronic circuit thereby allowing the LED package to become surface mounted to the separate controller substrate. In one embodiment, both substrates are PCBs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a plan view of one embodiment of a multi-LED display device; 
         FIG. 2  is a side view of the device shown in  FIG. 1  without the electrical contacts and without the LED substrate; 
         FIG. 3  is a side view of the device of  FIG. 1  shown with electrical contacts and without an LED substrate; 
         FIG. 4  is a side view of the device of  FIG. 1  shown mated to a controller PCB; 
         FIGS. 5 and 6  are alternative embodiments of the device of  FIG. 4  shown prior to mating with a controller PCB; and 
         FIGS. 7 and 8  show prior art LED devices. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Surface mountable (SMT) devices are used when reflow soldering is employed. Since manufacturing techniques now favor reflow soldering, it is important for devices to have surface mounting capability.  FIG. 7  shows prior art LED display  70  adapted for surface mounting on a PCB, such as PCB  74 , using electrical contacts  72 - 1 ,  72 - 2  which are part of lead-frame  72  to make electrical contact with PCB  74 . Lead-frame  72  is folded around scrambler portion  75  of the LED package. The lead-frame serves to hold the LED, such as LED  700 , in position within scrambler portion  73 . Wire bond  76  connects LED  700  to the lead-frame. When such a lead-frame is used, the manufacturing processes are tedious and result in limited package design capability. Lead-frame based custom LED packages are thus relatively expensive and are not viable for small-scale and medium-scale production. In addition, lead-frame based custom LED modules do not allow for cross-linking circuitry as the stamping tools are not able to stack layers of conductive traces in the lead-frame to create the tightly bound network that is necessary in multi-layer printed circuit boards. Such a handicap limits lead-frame based custom LED modules to only single or dual digit display. Further, it is difficult to integrate ICs or other electrical components into the display to make an intelligent package. 
       FIG. 8  shows a prior art LED display using a PCB, such as PCB  81 , as a substrate for the LED. The manufacturing process requires securing the plastic casing, such as casing  71 , onto PCB  81  either by using adhesive, epoxy filling or heat staking. LED  800  is constructed on PCB  81  and wire bond  86  connects the top of LED  800  to the PCB. It is critical to ensure that bottom plane  82  of PCB  81  is precisely planar to top surface  83  of controller substrate  84 , otherwise there could be soldering problems, such as poor wetting, opens, solder bridging, solder joint deformation, etc., between electrical contacts (not shown) on bottom surface  82  of PCB  81  and solder pads (not shown) on top surface  83  of PCB  84 . 
     Heat staking casing  71  to PCB  81  leaves a lump of melted thermoplastic with a shape that is not easily controlled. Thus, an additional process must be carried out to file and clean residue from the heat-staking process. Relying on heat staking alone presents a danger as heat staking has a tendency to produce cross-talk if there&#39;s a gap between the PCB and reflector  71 . Such a gap allows light to leak between luminous segments. When the lump of thermoplastic is removed, the holding strength between the casing plastic and the PCB is weakened. 
       FIG. 1  shows one embodiment  10  of an LED display having multiple LEDs (such as LEDs  100 - 1  to  100 -N) constructed on substrate  13 . Substrate  13  is mated into area  16  of top structure  12  to form LED package  10 . A plurality of electronic devices, such as LEDs  100 , can be constructed on substrate  13  and electrically connected, for example by bond wire  12 - 1 , to the substrate. Constructed on the sides (or on the top or bottom surface) of substrate  13  are a plurality of electrical contact pads  101  adapted to mate with contacts, such as contacts  31  (to be discussed with respect to  FIGS. 5 and 6 ), which are positioned on the inside of edges  110  of structures  12 . These contact pads are for the purpose of communicating electrical signal power from a controller PCB (shown in  FIG. 4 ) to control the respective LEDs contained thereon. Openings  23 - 1 ,  23 -N fit around LEDs  100 - 1 ,  100 -N, respectively, and are constructed as shown in  FIG. 2 . These need not be actually “opened” to the surface so long as light from each LED is visible outside LED package  10 . 
       FIG. 2  shows a side view of device  10  (shown in  FIG. 1 ). Shown in phantom is LED  100 - 1  with wire bong  12 - 1 . LED  100 - 1  is mounted on a substrate which mates within area  16 , such that when the substrate is mated the LED becomes positioned within reflector area  23 - 1  defined by barriers  24 . 
     Area  16  of scrambler  10  is defined by edges  110  of scrambler top structure  12  which edges protrude below bottom surface  21 . As discussed, substrate  13  mates to top structure  12  within the peripheral confines of edges  110  of scrambler  12 . 
       FIG. 3  is a side view of device  10  (without substrate  13 ) showing one embodiment of contacts  31 - 1  and  31 - 2  which are “spring-loaded” and insert-molded into peripheral edges  110  of top structure  12 . Each contact has a bottom surface  32 - 1 ,  32 - 2  which, as will be seen in  FIG. 4 , mate with contacts on the top surface of a controller substrate. Different electronically conductive materials, for example, beryllium copper, copper alloy, etc., can be used to create the desired contact areas. In some situations, the contacts can be spring-loaded and such spring-loaded contacts may also act as mechanical locks to maintain substrate  13  in mechanical contact with top structure  12 . The height and shape of the contacts can be tailored to meet individual device requirements and need not be the same dimension or construction for all contacts on a device. 
       FIG. 4  shows one embodiment of the side view of device  40  comprising device  10  positioned for mating with a controller substrate, such as PCB  45 . Device  10  has scrambler structure  12  mated with PCB  13  with electrical contact between scrambler structure  12  and PCB  13  being accomplished by spring-loaded contacts  31 - 1 ,  31 - 2 . PCB  13  is mated with scrambler top structure  12  by snapping onto spring-loaded contacts  31 - 1 ,  31 - 2 . Electrical connection is established when the contacts and the corresponding metal pads ( 101  in  FIG. 1 ) on PCB  13  are in contact. The pads on the PCB can be easily formed by using any well-known metallization process. When substrate  13  is mated with structure  12 , LED  100 - 1  is positioned within reflector section  23 - 1  of top structure  12  of LED display  10 . Electrical control of the LED is by voltage being applied to areas  32 - 1  and  32 - 2  of contacts  31 - 1  and  31 - 2 , respectively. Current then flows via wires (or current paths  45 - 1 ,  45 - 2 ) to the respective LEDs. Areas  32 - 1  and  32 - 2 , as well as areas of other contacts (not shown), are designed to mate with electrical contacts, such as contacts  44 - 1 ,  44 - 2 , of substrate  45 . Substrate  45  can be, for example, a controller PCB having constructed thereon other electronic circuitry for controlling LED display  10 . 
     Contacts  44 - 1 ,  44 - 2 , in one embodiment, are designed for surface soldering onto PCB  45 . Using this arrangement, PCB  13  is free to flex so long as it makes electrical contact with spring-loaded contacts  31 - 1 ,  31 - 2  which, in turn, makes contact with the top surface of PCB  45 . Note that while the contacts are shown as being individual, they can each carry multiple signals and they need not be spaced on different sides of the device provided only that individual control of each LED (or other electrical device) can be achieved. Also note that bottom surface  21  of substrate  13  can be above bottom surfaces  23  of the peripheral edges of device  10  which define area  16  for receiving substrate  13 . While the edges defining receiving area  16  ( FIG. 1 ) have been shown to be on only two sides of substrate  13 , such edges can surround the substrate, if desired. One edge of substrate  13  may be directly abutting edge  110 , the scrambler top structure and the spring-loaded contacts could apply force from an opposite edge, if desired. In such a configuration, all of the electrical contacts would be on the same side of substrate  13 . 
     There is no limit on the dimensions of the spring-loaded contacts. Practically, electrically conductive contacts with larger surface area will enhance the contact force to ensure good electrical connection between PCB  13  and structure  12 . It should be noted that there is also no limit on the number of contacts that can be insert-molded on structure  12 . Also, the spring-loaded contacts can be any shape desired. Along that line,  FIG. 5  shows device  50  having “folded” contacts  51  yielding longer spring distances. As discussed above, any electrically conducting materials or metals can be used as the contacts to be insert-molded into the scrambler. By the same token, metal printing along the edges of  110  (along the receiving area) can also be used in place of (or in addition to) the insert-molded contacts. 
       FIG. 6  shows one embodiment of a “stepped” contact, such as contact  61 . which can be used to contact the bottom surface  62  of PCB  13 . Different electrically conducting materials, for example, beryllium copper, copper alloy, etc., can be used to create the spring-loaded contacts. Also, as discussed above, such electrically conductive material can be printed or plated on to the sides of the respective devices. 
     Using the concepts discussed herein only a small process deviation adapted to an existing manufacturing process produces devices which can easily be surface soldered together. 
     The height and shape of the contacts can be tailored to meet individual device requirements and need not be the same dimension or construction for all contacts on a device. 
     The construction discussed herein is applicable for different device types, for example, for air-gap devices or silicon protection SMT devices. Using the concepts taught herein, either the top scrambler structure or the PCB can be easily replaced leading to higher yields. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.