Abstract:
A Plastic Leaded Chip Carrier (PLCC) package is disclosed. The PLCC package provides a light source that is both high contrast and high brightness. Specifically, the PLCC package includes a reflector cup whose surface area is partially inclusive of a lead frame and partially inclusive of a plastic housing that surrounds the lead frame.

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure is generally directed toward light emitting devices and packages for the same. 
     BACKGROUND 
     Light Emitting Diodes (LEDs) have many advantages over conventional light sources, such as incandescent, halogen and fluorescent lamps. These advantages include longer operating life, lower power consumption, and smaller size. Consequently, conventional light sources are increasingly being replaced with LEDs in traditional lighting applications. As an example, LEDs are currently being used in flashlights, camera flashes, traffic signal lights, automotive taillights and display devices. 
     Two prevalent types of LED form factors are surface-mount LEDs and thru-hole LEDs. Surface-mount LEDs are desirable for applications which require a low LED profile. Among the various packages for surface-mount LEDs, an LED package of interest is the Plastic Leaded Chip Carrier (PLCC) package. Surface mount LEDs in PLCC packages may be used, for example, in automotive interior display devices, electronic signs and signals, and electrical equipment. 
     While the PLCC package does offer a relative low profile as compared to its thru-hole counterpart, currently available PLCC packages cannot simultaneously provide high contrast and high brightness. Specifically, a PLCC package that is designed to provide high contrast (e.g., by using a black plastic as its housing) does not generally provide high brightness because the plastic used for the housing absorbs light rather than reflects light. Conversely, a PLCC package that is designed to provide high brightness (e.g., by using a white plastic as its housing) does not generally provide high contrast. 
     It should also be noted that a thru-hole LED is almost always brighter than a PLCC package, regardless of whether a black or white plastic is used for the housing. This is because the thru-hole LED typically has a metal-plated reflector cup whereas the reflector cup in a PLCC package is traditionally plastic, which is not as reflective as the metal use in thru-hole LEDs. 
     To date, there is no known LED package that combines the low profile nature of a PLCC package as well as simultaneously achieves high contrast and brightness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is described in conjunction with the appended figures: 
         FIG. 1  is a perspective view of a PLCC package in accordance with embodiments of the prior art; 
         FIG. 2  is a perspective view of a lead frame for a PLCC package in accordance with embodiments of the present disclosure; 
         FIG. 3  is a perspective view of a PLCC package without an encapsulant in accordance with embodiments of the present disclosure; 
         FIG. 4  is an exploded perspective view of the light sources contained within a PLCC package in accordance with embodiments of the present disclosure; 
         FIG. 5A  depicts a first stage of a lead frame manufacturing process in accordance with embodiments of the present disclosure; 
         FIG. 5B  depicts a second stage of a lead frame manufacturing process in accordance with embodiments of the present disclosure; 
         FIG. 5C  depicts a third stage of a lead frame manufacturing process in accordance with embodiments of the present disclosure; 
         FIG. 5D  depicts a fourth stage of a lead frame manufacturing process in accordance with embodiments of the present disclosure; and 
         FIG. 6  is a flow diagram depicting a PLCC package manufacturing process in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The ensuing description provides embodiments only, and is not intended to limit the scope, applicability, or configuration of the claims. Rather, the ensuing description will provide those skilled in the art with an enabling description for implementing the described embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the appended claims. 
     Furthermore, although the depicted PLCC package  100  is a conventional C-bend PLCC, embodiments of the present disclosure are not so limited. In particular, embodiments of the present disclosure can be utilized in any type of known PLCC package and/or platform. Specifically, any type of PLCC package and/or platform or similar type of package for a light emitting device that uses a plastic molded lead frame can incorporate one or more features disclosed herein. Suitable types of PLCC packages that may incorporate embodiments of the present disclosure include, without limitation, a Moonstone Package which has one or more leads protruding to its side, an L-bend PLCC, a PLCC with one or more leads protruding from its bottom, and so on. In some embodiments, the PLCC package may be manufactured according to the industry standard PLCC-4. 
     With reference now to  FIGS. 1-4 , a PLCC package  100  will be described in accordance with at least some embodiments of the present disclosure. Referring initially to  FIG. 1 , a completed PLCC package  100  is depicted in accordance with at least some embodiments of the present disclosure. The PLCC package  100  may comprise a lead frame  104  and a housing  112  that surrounds the lead frame  104 . The lead frame  104  may comprise a plurality of leads  108 . The leads  108  may be provided to supply electrical current to light sources  120  mounted thereto. In some embodiments, the lead frame  104  and housing  112  may comprise a reflector cup  116  which is a depression in the housing  112  that is configured to house the one or more light sources  120  and in some embodiments the reflector cup  116  may be partially or completely filled with an encapsulant  124 . 
     In some embodiments, the housing  112  is made of a plastic material, such as Polyphthalamide (PPA). Of course, the housing  112  may be made of other types of materials such as any other type of polymer or combination of polymers. In some embodiments, the housing  112  may be constructed of any polymer or combination of polymers using extrusion, machining, micro-machining, molding, injection molding, or a combination of such manufacturing techniques. 
     In the embodiment depicted in  FIG. 1 , the leads  108  of the lead frame  104  are exposed in the bottom of the reflector cup  116 . The leads  108  may then extend or pass through part of the housing  112  to an outer surface (e.g., side surface(s) and/or bottom surface) of the housing  112 , thereby facilitating attachment of the PLCC package  100  to an electrical circuit (e.g., bonding pads on a Printed Circuit Board (PCB)). Although the leads  108  of the lead frame  104  extending to the outer surface of the housing  112  are depicted a C-leads, embodiments of the present disclosure are not so limited. In particular, any other type or shape of leads may be utilized such as, for example, SOJ leads, gull wing leads, reverse gull wing leads, and straight cut leads. 
     The reflector cup  116  may be formed as a depression in a top portion of the housing  112 . In some embodiments, the interior cylindrical (or conical) surface of the reflector cup  116  partially comprises the material of the housing  112  (e.g., plastic) and partially comprises the material of the lead frame  104  (e.g., metal). In some embodiments, any path traveled around the circumference of the interior cylindrical (or conical) surface of the reflector cup  116  crosses both the lead frame  104  and the housing  112 . Accordingly, the interior cylindrical (or conical) surface of the reflector cup  116  is configured to increase the brightness of the PLCC package  100  (e.g., by virtue of the fact that the interior cylindrical (or conical) surface of the reflector cup  116  comprises the highly reflective metal of the lead frame  104 ). 
     The material selected for the housing  112  may also be selected to increase the contrast of the PLCC package  100 . In particular, the housing  112  may comprise a black or dark colored plastic that increases the contrast of the PLCC package  100 . Because the housing  112  may include a black plastic and the reflector cup  116  at least partially includes the metal of the lead frame  104 , the PLCC package  100  simultaneously provides both good contrast and brightness properties. 
     The light source(s)  120 , in some embodiments, comprises a single LED, a plurality of LEDs, or an array of LEDs. The embodiment depicted in  FIG. 1  shows a PLCC package  100  that comprises three light sources  120 . Each light source  120  is connected to a different lead  108 ; accordingly, the lead frame  104  may comprise three leads  108  when there are three light sources  120 . As can be appreciated, a greater or lesser number of light sources  120  may be included in the PLCC package  100  without departing from the scope of the present disclosure. Where two or more light sources  120  are provided in the reflector cup  116 , the light sources  120  may have the same or different light-generating properties. As one example, a first light source  120  may generate light at a first wavelength and a second light source  120  may generate light at a second wavelength. Where three light sources  120  are provided, one light source  120  may be configured to emit red light, another light source  120  may be configured to emit green light, and another light source  120  may be configured to emit blue light. Other variations of light source properties can also be accommodated without departing from the scope of the present disclosure. 
     Any number of materials may be suitable for use as the encapsulant  124 . Examples of such materials include, without limitation, epoxy, silicone, a hybrid of silicone and epoxy, phosphor, a hybrid of phosphor and silicone, an amorphous polyamide resin or fluorocarbon, glass, plastic, or combinations thereof. In some embodiments, the encapsulant  124  completely fills the reflector cup  116 . The encapsulant  124  may either be formed to have a lens shape that extends beyond the top surface of the housing  112  or the reflector cup  116  may be flush filled with the encapsulant  124 . 
     With reference now to  FIG. 2 , additional details of the lead frame  104  will be described in accordance with at least some embodiments of the present disclosure. As noted above, the lead frame  104  may be configured to carry current to the light source(s)  120  as well as reflect light emitted by the light source(s)  120 . By incorporating the lead frame  104  into the interior walls of the reflector cup  116 , the reflectivity of the reflector cup  116  can be enhanced without requiring an additional step of applying a reflective material to the interior surface of the reflector cup  116 . This is advantageous because additional manufacturing steps increase product cost and extend the amount of time required for manufacturing. 
     As discussed above, the lead frame  104  may comprise a plurality of leads  108  and each lead  108  may be configured to carry electrical current to a light source  120 . Each lead  108  may comprise a first portion  128   a  and a second portion  128   b  that is physically separated from the first portion  128   a . Surfaces of both the first and second portions  128   a ,  128   b  may be exposed in the bottom of the reflector cup  116 . 
     Where an LED or similar light source is used, one or more bonding wires  140   a ,  140   b  may be used to connect each light source  120  to the different portions of the leads  108 . One surface of the light source  120  may correspond to an anode of the light source  120  and another surface of the light source  120  may correspond to a cathode of the light source  120 . Alternatively, as displayed in  FIG. 2 , both the anode and cathode may be on the same surface of the light source  120 . 
     By connecting the light source  120  to two different portions  128   a ,  128   b  of a lead  108 , an electrical potential can be applied to the anode and cathode of the light source  120  thereby energizing the light source  120  and causing it to emit light. A light source  120  comprising both an anode and cathode on a common surface may be constructed using known flip-chip manufacturing processes or any other known method for establishing both an anode and cathode on a common side of a light source  120 . In such an embodiment, multiple bonding wires  140   a ,  140   b  may be used to connect to the anode and cathode separately to the first portion  128   a  of the lead  108  and the second portion  128   b  of the lead  108 . Alternatively, where the cathode and anode are on opposite surfaces of the light source  120 , it may be possible to utilize only one bonding wire (to bridge the gap between portions  128   a ,  128   b ) as the bottom surface of the light source  120  may be physically and electrically connected to the lead  108 . 
     In some embodiments, the light source(s)  120  is configured to emit light from its top surface. Light emitted by the light source(s)  120  may be coherent or incoherent in nature. In some embodiments, incoherent light is emitted by the light source(s)  120  and is scattered within the reflector cup  116 . The emitted light may reflect off the interior walls of the reflector cup  116  that rise above the light source(s)  120 . 
     As noted above, the interior walls of the reflector cup  116  may comprise both the lead frame  104  and the housing  112 . As can be seen in  FIG. 2 , the lead frame  104  may be configured with one or more raised portions that are integrated into the interior walls of the reflector cup  116 . The embodiment of  FIG. 2  includes a first lead frame portion of reflector cup  144   a  and a second lead frame portion of reflector cup  144   b . The first lead frame portion of the reflector cup  144   a  may be integrally connected to one of the leads  108  via a connector  156 . Likewise, the second lead frame portion of the reflector cup  144   b  may be integrally connected to another one of the leads  108  via another connector  156 . 
     It should be appreciated that more than one raised portion may be connected to a single lead  108 . Accordingly, the number of raised portions of the lead frame  104  that are integrated into the interior walls of the reflector cup  116  are not necessarily limited by the number of leads  108  in the lead frame  104 . Moreover, one, two, three, four, or more different portions of the lead frame  104  may be raised above the light source(s)  120  and integrated into the interior walls of the reflector cup  116 . In some embodiments, the raised lead frame portions of the reflector cup  144   a ,  144   b  are physically separated from one another to preclude electrical shorts between the leads  108 . 
     In some embodiments, each raised lead frame portion of the reflector cup comprises an inner reflective surface  148  and a top surface  152 . The inner reflective surface  148  may be curved to conform with the desired radius of curvature of the inner walls of the reflector cup  116 . The top surface  152  may be located above the top of the light source(s)  120 . 
     In some embodiments, portions of the lead frame  104  may be provided with fastening features which facilitate a better bond between the metal of the lead frame  104  and the plastic of the housing  112 . Examples of such fastening features include, without limitation, one or more fastening holes  132  and one or more fastening grooves  136 . Each of these features are provided to help the material of the housing  112  secure itself to the material of the lead frame  104  and prevent relative movement of the two components after the housing  112  has been established around the lead frame  104 . 
     The locations for the fastening features depicted in  FIG. 2  are intended to be only one example of suitable locations for the fastening features. In particular, it may be perfectly suitable to provide one or more fastening holes  132  in the lower extremities of the leads  108  or on the sides of the leads  108 . Likewise, the fastening grooves  136  do not necessarily need to be provided on the top surface of the leads  108 . Instead, the fastening grooves  136  can be provided on any of the surfaces of the leads  108  to facilitate a superior bond between the housing  112  and the lead frame  104 . 
     Another possible fastening feature that is depicted in  FIG. 2  is a notch or set of notches that are established between the connector  156  and the inner reflective surface  148  of the lead frame  148 . These notches may help ensure that the raised portions of the lead frame  144  can be bent and shaped as desired without breaking as well as ensure that the housing  112  securely fixes the raised portions of the lead frame  144 . 
     As can be seen in  FIG. 3 , the housing  112  may be formed around the lead frame  104  to establish the reflector cup  116 . Specifically, the housing  112  may be formed to include a reflective surface  160  which conforms with the radius of curvature established for the inner reflective surface of the lead frame  148 . Stated another way, any circumference traveled along the interior wall of the reflector cup  116  may comprise smooth transitions between the lead frame  104  and the housing  112 . This helps maintain the uniformity the light reflected by the reflector cup  116 . 
     The housing  112  may also be fashioned to have a top surface that is either flush with the top surface of the raised portion of the lead frame  152  or slightly higher than the top surface of the raised portion of the lead frame  152 . In some embodiments, the top surface of the raised portion of the lead frame  152  may be slightly recessed with respect to the top surface of the housing  164  and that recess may be provided to help the encapsulant  124  bond with the housing  112  and lead frame  104 . The recess may also be used to help form a lens with the encapsulant  124  that rises above the top surface of the housing  164 . 
     Referring now to  FIG. 4 , an exploded view of the reflector cup  116  is depicted in accordance with embodiments of the present disclosure.  FIG. 4  helps depict how the light source(s)  120  are positioned within the bottom of the reflector cup  116  and connected to the leads  108  of the lead frame  104 .  FIG. 4  also shows that an adhesive  168  may be used to physically connect a light source  120  to one portion of a lead frame  128 . In some embodiments, the adhesive  168  may correspond to a die attach glue or any other substance suitable for fixing the material of the light source  120  to the material of the lead  108 . 
     In some embodiments where an anode or cathode is provided on the bottom of the light source  120 , the adhesive  168  may also have properties which enable it to conduct electricity. In other words, the adhesive  168  may be configured to physically and electrically connect the light source  120  to the lead frame  108 . In this configuration, the adhesive  168  may actually comprise solder or some other conductive material. 
     With reference now to  FIGS. 5A-D , a process for manufacturing a lead frame  104  will be described in accordance with at least some embodiments of the present disclosure.  FIG. 5A  depicts a first processing stage where a flat plate of material  500  is provided with a number of cut-outs that establish the leads  108  and the lead frame portions of the reflector cup  144   a ,  144   b  in the common plane of the plate  500 . The cut-outs may be established by machining the plate  500 , etching the plate  500 , carving the plate  500 , or using any other known technique for removing portions of material in a common plane. 
     In some embodiments, the plate  500  may comprise a metal, metal alloy, aluminum, combinations thereof, or any material capable of conducting electricity. In this processing stage, both portions of each lead  128   a ,  128   b  are physically connected to carrying portions of the plate  500  and these physical connections serve as the only physical connection between the lead frame  104  and the rest of the plate  500 . 
       FIG. 5B  depicts a second processing stage where the lead frame portions of the reflector cup  144   a ,  144   b  are simultaneously raised out of the plane of the plate  500 . In some embodiments, an anvil  504  may be positioned one or proximate to one surface of the plate  500  and forces may be applied on the opposite surface of the plate  500  causing the lead frame portions of the reflector cup  144   a ,  144   b  to move toward the anvil  504  until contact is made with the anvil  504 . 
     As can be seen in  FIG. 5C , after contact is made between the lead frame portions of the reflector cup  144   a ,  144   b  and the anvil  504 , the lead frame portions of the reflector cup  144   a ,  144   b  may be bend to conform with the outer surface of the anvil  504 . This particular processing step establishes the curvature of the cylindrical (or conical) interior walls of the reflector cup  116 . This processing step may also cause the extremities of the lead frame portions of the reflector cup  144   a ,  144   b  to be thinned or tapered. Specifically, the thickness of the top surface  152  may be larger than the thickness of the lower segments of the lead frame portions of the reflector cup  144   a ,  144   b.    
       FIG. 5D  depicts a fourth processing step that occurs after the lead frame portions of the reflector cup  144   a ,  144   b  have been curved. In this processing step the anvil  504  is moved away from its position that was proximate to the plate  500 . At this point the connections between the leads  108  of the lead frame  104  and the plate  500  can be severed and the leads  108  can be bent as desired until the lead frame  104  of  FIG. 2  is created. Additionally, the light source(s)  120  can be attached to the leads  108 . 
     With reference now to  FIG. 6 , a process of constructing a PLCC package  100  will be described in accordance with at least some embodiments of the present disclosure. Although the steps depicted in  FIG. 6  are shown in a particular order, those of ordinary skill in the LED manufacturing arts will appreciate that certain steps may be combined and/or the order of steps may be altered without departing from the scope of the present disclosure. 
     Initially, a lead frame  104  having one or more leads  108  may be formed (step  604 ). The sub-steps of this processing step are depicted and described in more detail in connection with  FIGS. 5A-D . 
     Once the lead frame  104  has been created, the light source(s)  120  may be mounted or connected to the leads  108  of the lead frame  104  (step  608 ). The manner in which the light source(s)  120  are mounted to the leads  108  may depend on the nature of the light source  120  (e.g., depending upon the relative position of the anode and cathode of the light source  120 ). 
     The housing  112  may then be formed around the lead frame  104  (step  612 ). In some embodiments, the housing  112  may be formed with a plastic injection molding process, in which case the plastic housing  112  may comprise a single piece of plastic. However, it may also be possible to construct the housing  112  with one, two, three, or more separate parts that are connected to one another using a bonding or fusing process or agent. In some embodiments, the reflector cup  116  may be formed in the top portion of the housing  112  as part of the injection molding process. Alternatively, the reflector cup  116  may be formed after the housing  112  has been by established around the lead frame  104  by using, for example, a machining, etching, and/or stamping process. Different manufacturing alternatives may be more desirable for different types of PLCC packages  100 . In some embodiments, a white plastic material may be used to form some or all of the housing  112  to improve the brightness of the PLCC package  100 . In other embodiments, a black plastic material may be used to form some or all of the housing  112  to improve the contrast of the PLCC package  100 . 
     After the housing  112  has been attached to the lead frame  104 , the method continues by filling the opening of the reflector cup  116  with an encapsulant  124  (step  616 ). It should be appreciated that this particular step may be optional if no encapsulant  124  is desired. The encapsulant  124  may be provided into the reflector cup  116  using known injection techniques. In some embodiments, the encapsulant  124  hermetically seals the light source(s)  120  in the reflector cup  116  and protects the bonding wires  140   a ,  140   b  from shifting and/or breaking. 
     As can be appreciated, the PLCC package  100  may be manufactured individually or in a batch manufacturing process where each step described above is simultaneously performed on a plurality of PLCC packages  100 . 
     Specific details were given in the description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
     While illustrative embodiments of the disclosure have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.