Light emitting device including a leadframe and an insulating material - Patents.com

Abstract

To provide a light emitting diode (LED) package which may serve a purpose of a highly reflective, electrically conductive material.SOLUTION: A package for a light emitting diode (LED) may include a lead frame, an LED, and an optically reflective but electrically non-conductive molding. The lead frame may have a first lead frame part and a second lead frame part electrically isolated from the first lead frame part. Each lead frame part may have at least one raised pillar. The molding may be disposed over the lead frame except over the pillars of the lead frame. The LED may be mounted on at least one pillar and is electrically coupled to at least one pillar.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This application claims the benefit of U.S. Patent Application No. 15 / 652,603, filed July 18, 2017, and European Patent Application No. 17184498.8, filed August 2, 2017, the contents of which are incorporated herein by reference. [Background technology]

[0002] Light emitting diodes ("LEDs") are solid-state devices that emit light when supplied with electrical current. LEDs are packaged in relatively complex housings that incorporate different materials to provide various functions for the LED. One component typically used in the package is a layer of silver. Silver provides good electrical conductivity to the LED semiconductor device while also providing good optical properties, such as high reflectivity and reflection of light at appropriate wavelengths. However, silver suffers from discoloration even when covered by an encapsulant material. Summary of the Invention

[0003] A light emitting diode (LED) package may include a leadframe having a first leadframe portion electrically isolated from a second leadframe portion. The first leadframe portion may include a first pillar that rises above a lower surface of the first leadframe portion. The second leadframe portion may include a second pillar that rises above a lower surface of the second leadframe portion. A molding may cover the lower surface of the leadframe portions. At least a portion of the first pillar and the second pillar may remain exposed. The molding may include a highly optically reflective and electrically insulating material. An LED device may be disposed only on the second pillar. A first contact may be formed on the LED device. The first contact may be electrically coupled to the first pillar via a first wirebond. A second contact may be formed on the LED device. The second contact may be electrically coupled to the second pillar via a second wirebond. [Brief description of the drawings]

[0004] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which like reference characters indicate similar elements and in which: [Figure 1] FIG. 1 is a cross-sectional view of an LED package according to an example. [Diagram 2] 2 and 3 show other configurations of LED packages according to examples. [Diagram 3] 2 and 3 show other configurations of LED packages according to examples. [Figure 4] 4-8 show exploded views of an LED package and a method of manufacturing the same according to an example. [Diagram 5] 4-8 show exploded views of an LED package and a method of manufacturing the same according to an example. [Figure 6] 4-8 show exploded views of an LED package and a method of manufacturing the same according to an example. [Figure 7] 4-8 show exploded views of an LED package and a method of manufacturing the same according to an example. [Figure 8] 4-8 show exploded views of an LED package and a method of manufacturing the same according to an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] Examples of different light emitting diode ("LED") implementations are described more fully below with reference to the accompanying drawings. These examples are not mutually exclusive, and features found in one example may be combined with features found in one or more other examples to achieve further implementations. Accordingly, it is to be understood that the examples shown in the accompanying drawings are provided for illustrative purposes only, and that they are not intended to limit the present disclosure in any way. Like elements are referenced with like numerals throughout.

[0006] It is understood that, although terms such as first, second, etc. may be used herein to describe various elements, the elements should not be limited by these terms. These terms are merely used to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element, without departing from the scope of this specification. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0007] It is understood that when an element, e.g., a layer, region, or substrate, is referred to as being "on" or extending "upon" another element, it may be directly on or extending directly onto the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements present. It is also understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. It is understood that these terms are intended to encompass elements in different orientations in addition to the orientation depicted in the figures.

[0008] Relative terms such as "lower" or "upper" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe the relationship of one element, layer or region to another element, layer or region when depicted in the figures. It is understood that these terms are intended to encompass devices in different orientations in addition to the orientation depicted in the figures.

[0009] Although silver has good optical qualities, such as reflectance, it is susceptible to tarnishing by environmental factors, and herein provided is a package with physical properties that reduce the need for the use of silver. More specifically, silver has a high affinity for substances such as hydrogen sulfide, halogens, oxygen, water vapor, nitrous oxide, sulfur dioxide, and ozone, which may be found in polluted air, especially in urban or industrial areas. These substances can result in the formation of black silver sulfide or dark yellow silver oxide (known as silver tarnishing), which can significantly and rapidly reduce the reflectance of silver.

[0010] The package includes a metal leadframe, a molding material disposed at least partially over the leadframe to form a well in which a light emitting diode ("LED") component is disposed, and an encapsulant material disposed within the well. The metal leadframe includes pillars on which the LED or other components are disposed and / or which serve as electrical contacts to form an electrical circuit including the leadframe and the components within the well. Areas of the leadframe other than the pillars are covered by a molding that is optically reflective. A top surface of the molding material within the well is flush (or nearly flush) with a top surface of the pillar (or a top surface of an additional layer, e.g., a plated metal layer, formed over the pillar) to form a single, flush, bottom surface of the well. The molding material is a highly reflective material that reflects light from the LED, providing the LED package with good optical properties. A leadframe configuration with raised pillars allows less, or less, of more traditional materials such as silver to be used in the LED package, which reduces the silver tarnish problem. More specifically, whereas in conventional designs silver would cover a large portion of the bottom surface of the well and therefore suffer from tarnishing and degrading the optical properties of the LED package, in the packages of the present disclosure the exposed surfaces are substantially devoid of silver and reflectivity is provided by the reflective molding material which does not suffer from silver tarnishing.

[0011] FIG. 1 is a cross-sectional view of a package 100(1) according to an example. The package 100 includes a leadframe 102 including a first leadframe portion 104(a) and a second leadframe portion 104(b), where the first leadframe portion 104(a) is electrically insulated from the second leadframe portion 104(b). The different leadframe portions 104 of the leadframe 102 provide electrical coupling between components within the package 100 and components outside the package. For example, one leadframe portion 104 is coupled to one terminal of the LED device 112 and one external wire, and another leadframe portion 104 is coupled to another terminal of the LED device 112 and another external wire, such that the LED device 112 is integrated into a circuit. A metal plating layer 106 is disposed on the first leadframe portion 104(a) and the second leadframe portion 104(b) to electrically couple various components, such as the LEDs 112, to the leadframe 102. In conventional designs, the plating layer is made of silver so that the plating layer can serve dual duties as both an electrical conductor and an optical reflector, but in this disclosure, the metal plating layer 106 does not need to be silver since the reflectivity of the LED package 100 is provided by the molding material 120. The metal plating layer 106 may be a technically feasible material other than silver, or it may be silver.

[0012] The leadframe 102 has two raised portions or "pillars" 108 that extend above a bottom surface 110 of the leadframe 102. The pillars 108 serve to provide electrical contacts for electrical components (such as, for example, LEDs 112) within a well 114. The well 114 is formed by sidewalls 118 of a molding 120 of molding compound. The LED 112 is disposed on one of the pillars 108 and is electrically coupled to the pillar 108 of the second leadframe portion 104(b) via a wire bond 116. The LED 112 is also electrically coupled to the pillar 108 of the first leadframe portion 104(a) via a conductive contact 113. The pillars 108 allow electrical connections to be made between the components within the wells 114 and the leadframe 102, for example, while minimizing the amount of exposed metal placed on the leadframe 102. An encapsulant 122 is disposed over the components within the well 114 and fills the space of the well 114 .

[0013] In a conventional leadframe design, two (or more) electrically isolated portions of the leadframe are plated with a metallic material, such as silver, that provides both electrical coupling to the leadframe and high optical reflectivity with good color characteristics of reflected light. In conventional designs, silver is very often used as a particularly good conductive and optically reflective material. However, as mentioned above, silver suffers from tarnishing even when covered by an encapsulant material. The leadframe 102 with pillars 108 of the present disclosure provides the ability to allow the majority of the bottommost surface of the well 114 (also referred to as the "basin 124") to not have silver, but instead have a highly optically reflective non-conductive material, while still allowing electrical connection of the components in the well 114 to the leadframe 102. It should be noted that the basin 124 is comprised of the topmost surface of the metal layer 106 and the topmost surface of the molding 120 at the bottom of the well 114. Although illustrated as being a flush surface, various portions of the basin 124 may be slightly or significantly uneven.

[0014] 2 and 3 show other configurations of package 100 according to examples. More specifically, FIG. 2 shows package 100(2) in which LED 112 is coupled to leadframe 102 via two wirebonds 116, and FIG. 3 shows package 100(3) in which two contacts 119 on the bottom surface of LED 112 couple LED 112 to leadframe 102. FIG. 2 is a cross-sectional view of package 100(2) according to another example. Package 100(2) is similar to package 100(1) except that in package 100(2), LED 112 is coupled to leadframe 102 via two wirebonds 116 (which are coupled to LED 112 via contact 117) instead of via contact 113 on the bottom surface of LED 112 and a single wirebond 116. LED 112 is mounted on pillar 108, but does not have an electrical coupling to the pillar via the bottom surface of LED 112. 3 is a cross-sectional view of a package 100(3) according to yet another example embodiment. In package 100(3), an LED 112 is coupled to a leadframe 102 via two contacts 119 without wire bonds 116. The LED 112 is mounted on both of the leadframe portions 104 shown, allowing the two contacts 119 to be coupled to the two leadframe portions 104 when the LED 112 is directly above them.

[0015] While a particular configuration of components within the well 114 is shown, it should be understood that various configurations not shown are within the scope of the teachings of the present disclosure. The configuration of the basin 124 varies depending on the shape, size, and number of the pillars 108. In various embodiments, the basin 124 is mostly non-conductive material, such as the material of the molding compound 120. In such embodiments, the basin 124 is 50% non-conductive material, 85% non-conductive material, or 95% non-conductive material. The portions of the basin 124 that are not non-conductive material comprise the conductive material of the leadframe 102 and / or metal layer 106.

[0016] In the example package 100 shown above, the molding 120 comprises a highly reflective material. For example, the molding 120 comprises a silicone molding compound with high thermal, mechanical, electrical, and photochemical stability, such as, but not limited to, thermosetting polysiloxane and its derivative compounds. In various embodiments, the molding 120 is formed from an electrically insulating material, such as, for example, plastic, thermosetting material, thermoplastic material, polymer, epoxy polymer resin, silicone-based composite material, composite molding compound silicone, polycyclohexylene, polycyclohexylene terephthalate, epoxy molding compound, liquid crystal polymer, mixtures thereof, or other suitable materials. The material forming the molding 120 may include a filler, such as, for example, an organic material or an inorganic material. The filler may adjust the physical properties of the material of the molding 120 to improve the integrity and reliability of the material under the application conditions of the LED device and to achieve the desired light reflectance of the molding 120. The material used for molding 120 is durable, substantially non-yellowing, mechanically suitable, compatible with appropriate manufacturing processes, and highly reflective. Preferably, molding 120 has a similar coefficient of thermal expansion as leadframe 102, where "similar" means that the coefficients of thermal expansion are within 10% of each other. Although certain possible materials for molding 120 are listed above, any suitable material may be used.

[0017] Although the metal plating layer 106 is shown disposed over the top surface of the leadframe 102, in various examples, the metal plating layer 106 is disposed over only a portion of the top surface of the leadframe 102, such as over the pillars 108. Additionally, the metal plating layer 106 may be any conductive material. In some embodiments, both the metal plating 106 and the molding 120 forming the basin 124 are materials that are stable at high temperatures, stable at high doses of short wavelength (blue and UV) light, and inert to corrosive gases, such as sulfur and / or its compounds, chlorine and / or its compounds, nitrogen oxides, ozone, water vapor, oxygen, and other contaminants in the environment of the intended use of the LED 112. The leadframe 102 in the example package 100 is shown as having a metal layer 106 disposed over its top surface to provide compatibility for the wire bonds 116 of FIGS. 1 and 2 or the contacts 119 of FIG. 3 as well as protection to the base material of the leadframe 102. In some embodiments, for example when such compatibility and / or protection is not required, such metal layer 106 is not present.

[0018] The leadframe, including the pillars 108, comprises a conductive material which may be, for example, a metal such as copper, silver, gold, nickel, palladium, combinations thereof, alloys thereof, multi-layer stacks of the same or different metals, or other suitable materials.

[0019] Although wire bonds are shown in some embodiments, any suitable configuration may be used for electrically connecting the LEDs 112 to the leadframe 102. For example, in any of the illustrated packages 100, metal bridge(s), solder, conductive epoxy, or other suitable connections may be used in place of wire bonds.

[0020] 1-3 , molding 120 forms wells 114 into which various components are placed. In other embodiments, only enough material is used to form molding 120 to structurally secure the relative positions of leadframe portions 104 without forming wells 114. In other embodiments, molding 120 forms wells 114 with shallow sidewalls 118, for example, only deep enough to accommodate LEDs 112, wirebond(s) 116 (if present), or other components within well 114.

[0021] Shown is an encapsulant 122 disposed within well 114. In some embodiments, encapsulant 122 comprises a transparent material that protects LED 112 and other components within well 144, such as, for example, wire bonds if present. In some embodiments, encapsulant 122 includes a material, such as, for example, a wavelength converting material, a material that improves the thermal performance of encapsulant 122, a material that creates or reduces light scattering, a material that acts as a filter, or other suitable material.

[0022] Although an LED 112 is described, in various embodiments the LED 112 may be replaced with other types of light emitting devices, such as, for example, laser diodes, and semiconductor light emitting devices made of other material systems may be used, such as, for example, other III-V materials, III-phosphides, III-arsenides, II-VI materials, ZnO, or Si-based materials. Often blue or UV emitting light emitting devices are combined with one or more wavelength converting materials to produce light of different colors, such that the combined light from the light emitting device and wavelength converting material appears white or other color required for a given application.

[0023] Figures 4-8 illustrate a method of forming the package 100(1) of Figure 1, along with an exploded view of the package 100(1) of Figure 1. It should be understood that for clarity, some components have been omitted from the views shown in Figures 4-8. For example, metal layer 106 is not shown.

[0024] In FIG. 4, a leadframe 102 is formed. The posts 108 of the leadframe 102, which will be exposed after forming the molding 120, are at a higher height than other portions of the leadframe 102, which will be covered by the molding 120 when the molding 120 is formed. The leadframe may be formed, for example, by shaping a metal sheet by molding, folding, stamping, punching, etching, or other suitable techniques. After forming the leadframe 102, a metal layer 106 (not shown) may be formed, for example, over the entire surface of the leadframe 102 or only at certain locations, such as the portions of the leadframe that will be exposed after forming the molding 120. The metal layer 106 may be formed by plating, sputtering, evaporation, or other suitable techniques.

[0025] In FIG. 5, a molding 120 is formed on and around the leadframe 102. The molding 120 may be formed, for example, by molding, injection molding, transfer molding, or other suitable techniques. The molding 120 may be shaped to form sidewalls 118 that form wells 114 suitable for enclosing the encapsulant 122 formed in FIG. 8 described below. After forming the insulator 120, only a portion of the leadframe 102, such as the pillars 108, is exposed. The other portions of the leadframe 102 are covered by the molding 120. Most of the bottom surface ("basin") 124 of the well 114, but not the pillars 108, is covered by the molding 120. After forming the molding 120, other processing steps may be performed to expose areas that should not be covered by the molding 120 in the final device, such as the pillars 108. Suitable processing steps include wet or dry bead blasting, chemical etching, electrolysis, or other suitable techniques to clean the surfaces of the pillars 108. After such cleaning, another metal layer may be deposited on the pillars 108, such as, for example, silver, gold, nickel, palladium, or other suitable material.

[0026] 6, LEDs 112 and other components, such as electrostatic discharge protection chips or other suitable components, are attached to the exposed leadframe pillars 108. The LEDs 112 and other components may be attached, for example, by soldering or other suitable techniques.

[0027] 7, one or more wire bonds 116 are formed, if used. Other electrical connections may be formed in addition to or in place of the wire bonds 116 to provide electrical connection between the LEDs 112 and the pillars 108.

[0028] In FIG. 8, an encapsulant 122 is disposed within the well 114 over the LED 112. The encapsulant 122 may be formed, for example, by molding, dispensing, or other suitable techniques. In some embodiments, the encapsulant 122 is disposed within the well 114 in liquid or gel form and then cured to a solid. The encapsulant 122 may include a wavelength conversion material that converts the light emitted by the LED chip to light of another color. The combination of the light from the LED chip and the light emitted from the wavelength conversion material forms the final color light of the LED device.

[0029] 1-8, or any of the devices described above, can be used in any suitable application, such as, for example, general lighting, backlighting for displays, or specialty lighting applications. In some embodiments, the devices described above can be incorporated into a mobile phone.

[0030] Although the embodiments have been described in detail, it will be understood by those skilled in the art that, given this disclosure, modifications may be made without departing from the spirit of the inventive concepts described herein. In particular, different features and components of different devices described herein may be used in any of the other devices, or features and components may be omitted from any of the devices. Structural features described in the context of one embodiment may be applicable to any of the embodiments. Thus, it is not intended that the scope of the description be limited to the specific embodiments shown and described.

[0031] Although features and elements are described above in specific combinations, one skilled in the art will understand that each feature or element can be used alone or in combination with other features and elements. Also, the methods described herein can be implemented in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs).

Claims

1. a first portion of a leadframe having a first pillar with a first surface that is elevated above a bottom surface of the first portion of the leadframe; a second portion of the leadframe electrically insulated from the first portion of the leadframe, the second portion of the leadframe having a second pillar with a second surface elevated above a lower surface of the second portion of the leadframe; a molding comprising an optically reflective and electrically insulative material on the first portion of the leadframe and the second portion of the leadframe, the molding adjacent a sidewall of the first pillar and a sidewall of the second pillar, the molding having sidewalls shaped to form a well; an LED device on the first surface; a plated metal layer between the lead frame and the molding and between the lead frame and the LED device; a further metal layer deposited on the first surface and the second surface exposed from the molding; having The first pillar and the second pillar are configured such that 50% or more of the surface exposed to the bottom of the well is the surface of the molding. Light emitting diode (LED) packages.

2. a first wire bond electrically coupling the LED device to the first surface; The LED package of claim 1 further comprising:

3. a second wire bond electrically coupling the LED device to the second surface; The LED package of claim 1 further comprising:

4. an encapsulant within the well, the encapsulant configured to physically protect the LED device; The LED package of claim 1 further comprising:

5. The LED package of claim 1 , wherein the first pillar has a width greater than a width of the LED device.

6. The LED package of claim 1 , wherein the molding comprises a silicone material.

7. 1. A method of forming a light emitting diode (LED) package, comprising: forming a first portion of a leadframe, the first portion of the leadframe having a first pillar having a first surface elevated above a bottom surface of the first portion of the leadframe; forming a second portion of the leadframe, the second portion of the leadframe being electrically insulated from the first portion of the leadframe, the second portion of the leadframe having a second pillar having a second surface elevated above a lower surface of the second portion of the leadframe; forming a plated metal layer on the lead frame, including on the first surface and the second surface; forming a molding on the first portion of the leadframe and the second portion of the leadframe, the molding adjacent a sidewall of the first pillar and a sidewall of the second pillar, the molding having sidewalls shaped to form a well; cleaning the first surface and the second surface exposed from the molding; depositing a further metal layer on the first surface and the second surface after said cleaning; forming an LED device on the first surface; Having said that, The first pillar and the second pillar are configured such that 50% or more of the surface exposed to the bottom of the well comprises the surface of the molding. method.

8. electrically coupling the LED device to the first surface via a first wire bond; The method of claim 7 further comprising:

9. electrically coupling the LED device to the second surface via a second wire bond; The method of claim 7 further comprising:

10. forming an encapsulant within the well; The method of claim 7 further comprising:

11. The method of claim 7 , wherein the first surface has a width greater than a width of the LED device.

12. The method of claim 7 , wherein the molding comprises a silicone material.

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