Abstract:
A surface mountable and low profile electrical component which can be electrically coupled to the solder side of a PCB, while other electrical components are mounted to a component side of the PCB. The surface mountable electrical component includes a mounting substrate having a diode or LED chip with electrical terminals. The terminals pass through the mounting substrate to be electrically coupled to first and second electrical contacts, which provide an electrical pathway between the terminals and the PCB.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the mounting of electrical components on a printed circuit board. 
     2. Description of the Relevant Art 
     Light emitting diodes (LEDs) are well known. LEDs are commonly used in electrical circuits to indicate the status of a circuit, the change in status of a circuit, and/or to signal an alarm. In operation, LEDs are designed to “light up” when they pass current. Thus, LEDs are most commonly used on faceplates and other displays. 
     In many cases, the circuit or circuits of which the LED is a part, may be contained partially or wholly on a printed circuit board (PCB). Most PCBs typically include an electrically insulating substrate and a copper foil laid out or printed on one surface of the substrate according to a desired electronic circuit pattern. Resistors, capacitors, transistors, diodes and other electronic components are attached to the PCB according to the electronic circuit pattern. 
     In FIG. 1, a portion of a PCB  10  is shown, which has a component side  12 , where components  14 , such as ASICs, LEDS, memory chips, and generic processors, are mounted. The PCB  10  also has a solder side  16 , where electrical connections to components  14  are made Typically, components are attached to PCBs by forming holes  18  through the substrate. At specific component attachment locations, leads or pins  20  from the components can be inserted through holes  18  from component side  12  of PCB  10 , such that the component leads  20  project from solder side  16  of PCB  10 . The projected portions of the component leads are soldered  22  to component-attaching lands  24  formed on solder side  16  of PCB  10 . 
     When mounting components to the PCB it is desirable to keep the overall height profile of the PCB (with components) as thin as possible. This practice permits the greatest number of PCBs to be used together in the confines of a given card-based system, or to be used in miniaturized electronic devices. Typically, to insure a thin profile all components are mounted on a single side of the PCB. However, some components, such as the LED, take up valuable space on the component side of the PCB, which could be used for more valuable components. Accordingly, moving the LED to the solder side of the PCB, can significantly-improve the PCBs capacity. However, using the conventional component mounting method described above causes the LED to protrude out from the solder side of the PCB, significantly increasing the overall thickness of the PCB. 
     For these reasons, a need exists for a surface mountable LED, which may be mounted to the solder side of the PCB without significantly increasing the overall thickness profile of the PCB. 
     SUMMARY OF THE INVENTION 
     The present invention provides a surface mountable and low profile electrical component which can be electrically coupled to the solder side of a PCB, while other electrical components are mounted to a component side of the PCB. Advantageously, the electrical component is surface mounted to maintain a substantially low height profile. 
     As described in greater detail below, the surface mountable electrical component includes a mounting substrate having a diode or LED chip with electrical terminals. The LED chip is integrally mounted into a first side of the mounting substrate. Preferably, the LED chip extends out in a cantilevered arrangement from a first side of the mounting substrate. The terminals pass through the mounting substrate and extend out from an oppositely facing second side of the mounting substrate. The terminals can be electrically coupled to first and second electrical contacts, which provide an electrical pathway between the terminals and the PCB. 
     In operation, as the substrate is mounted to the PCB, the electrical contacts are made to intimately contact electrical conductors printed on the PCB, such that the electrical component becomes functional, which makes the LED chip operative. 
     There are many advantages to the present invention. For example, mounting space is created on the component side of the PCB for additional and potentially more valuable electrical components. As described in detail below, mounting the electrical component to the solder side of the PCB maintains a low thickness profile of the PCB. 
     Using the LED chip mounting technique of the present invention, a light source can be provided sufficiently thin, contributing to reduction in weight and size for portable apparatus or devices in which the electrical component is used. 
     Other uses, advantages, and variations of the present invention will be apparent to one of ordinary skill in the art upon reading this disclosure and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified cross-sectional illustration of a representative PCB with components attached; 
     FIGS. 2A and 2B are illustrations of front and rear perspective views of an embodiment of the present invention; 
     FIGS. 3A,  3 B, and  3 C are illustrations of a front, rear, and bottom view of the embodiment of FIGS. 2A and 2B; and 
     FIG. 4 is a simplified perspective view of an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 2A and 2B are illustrations of a front and rear perspective view of an embodiment of the present invention. As shown, electrical component  30  includes a diode chip  32  and a mounting substrate  34 . In one embodiment, with no intent to limit the invention thereby, mounting substrate  34  is a cube shaped structure having a first side  36 , a second side  38 , a top side  40 , and a bottom side  42 . Diode chip  32  is mounted to first side  36 , such that first terminal  44  and second terminal  46  extend out from an opposite side, side  38 , of mounting substrate  34 . On bottom side  42  are formed first and second electrical contacts  48  and  50  respectively. 
     As best understood with reference to FIG. 2A, portions  48 B and  50 B of electrical contacts  48  and  50  extend out from bottom side  42 . Contact portions  48 B and  50 B are bent or curved upward along second side  38  to form contact portions  48 A and  50 A. In this manner, electrical contact portions  48 A and  50 A can be electrically coupled to first and second terminals  44  and  46 . 
     Mounting substrate  34  may be formed of any suitable insulating material, such as any conventional resin. Mounting substrate  34  can be formed to any dimension or suitable geometric shape, as desired. In embodiment, with no intent to limit the invention, mounting substrate  34  is approximately a cube, which has a length of approximately 0.17 in., a width of approximately 0.19 in., and a height of approximately 0.17 in. These or similar dimensions provide compactness for electrical component  30 . 
     LED chip  32  is a conventional light emitting diode as is known in the art. A typical LED emits light based on a change in the energy levels when holes and electrons combine in the negative region of a positive-negative semiconductor diode. The shifts in energy cause photons to be generated, which are emitted as light energy. LED chip  32  can emit visible colors, such as blue, yellow, green, white, and red. LED chip  32 , can be fabricated into any suitable geometric configuration with any desired dimensions as suited for a particular application. In one embodiment, LED chip  32  occupies a volume envelope as indicated by the rectangular form  37  shown in FIGS. 3A and 3C. In this embodiment, with no intent to limit the invention, shorter side W of LED chip  32  can be a length approximately 0.122 in., while the longer side L can be approximately 0.157 in. The thickness T of LED chip  32  can be approximately 0.075 in. 
     In one embodiment, LED chip  32  may be mounted in a reflector cup of a lead frame, wire bonded to terminals  44  and  46 , and encased in a solid epoxy lens. LED chips for use in the present invention are commercially available from, for example, Dialight, Inc. of Manasquan, N.J. 
     As best understood with reference to FIGS. 3A-3C and FIG. 4, LED chip  32  is integrally mounted into mounting substrate  34 , such that shorter side W of LED chip  32  extends in a direction perpendicular to a surface of PCB  64 , while longer side L can extend in parallel to the surface of PCB  64 . 
     As best understood with reference to FIG. 4, with mounting substrate  34  shown in phantom, LED chip  32  can be mounted at a position on first side  36 , such that terminals  44  and  46  are fixed through mounting substrate  34  and protrude directly out from second side  38 . Again referring to FIGS. 3A-3C, an electrical connection can be made between terminals  44  and  46  of LED chip  32  and portions  48 A and  50 A of electrical contacts  48  and  50 . Connection can be made using conventional techniques, such as through a conductive adhesive including wire-bonding, solder, silver paste, and the like. 
     The electrical connection between terminals  44  and  46  and contact portions  48 A and  50 A, is provided on or proximate to second side  38 , at a position below the height of mounting substrate  34 . This eliminates the need for causing terminals  44  and  46  from extending through PCB  64  to be soldered on solder side  16 (see FIG. 1.) Thus, the height of electrical component  30  may be reduced. 
     Referring, again to FIG. 4, electrical component  30  is mounted to PCB  64  such that contact  48  and  50  directly contact PCB electrical mounts  66  and  68 . A solder paste or a silver paste may be applied to the surface of the electrical contacts  48  and  50  of the electrical component  30  and the surface of PCB electrical mounts  66  and  68  of PCB  64 . The solder paste can then be melted by heating, or the silver paste, if used, is cured, so that contacts  48  and  50  are in electrical connection with associated PCB electrical mounts  66  and  68 , thus fixing electrical component  30  to PCB  64 . Standoffs  60  and  62  may be disposed on bottom side  42 , to provide proper alignment of LED chip  32 , prior to, during, and after solder reflow. 
     In the present invention, LED chip  32  is formed long in the L direction so that the resulting electrical component  30  is reduced in height without narrowing the light emitting area of LED chip  32 . Consequently, the thinning of electrical component  30  is achieved without incurring a reduction in light emission nor any degradation in the performance of electrical component  30 . Furthermore, since LED chip  32  is mounted at a position horizontally long on PCB  64  the terminals  44  and  46  can be directly coupled to contact portions  48 A and  50 A along second side  38  removing the necessity for causing terminals  44  and  46  from pushing through PCB  64 , contributing to the thinning of the electrical component  30 . To this end, it is possible to form electrical component  30  to a thickness no greater than 0.25 in; preferably no greater than 0.2 in. 
     The description of the invention given above is provided for purposes of illustration and is not intended to be limiting. The invention is set forth in the following claims.