SYSTEM AND METHOD FOR LED PACKAGING
System and method for LED packaging. The present invention is directed to optical devices. More specifically, embodiments of the presentation provide LED packaging having one or more reflector surfaces. In certain embodiments, the present invention provides LED packages that include thermal pad structures for dissipating heat generated by LED devices. In particular, thermal pad structures with large surface areas are used to allow heat to transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations. There are other embodiments as well.
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This application claims priority from U.S. Provisional Patent Application No. 61/241,459, filed Sep. 11, 2009; U.S. Provisional Patent Application No. 61/241,457, filed Sep. 11, 2009; and U.S. Provisional Patent Application No. 61/241,455, filed Sep. 11, 2009, commonly assigned and incorporated by reference herein for all purposes.
BACKGROUND OF THE INVENTIONThis invention is directed to optical devices. More specifically, embodiments of the invention provide LED packaging having reflector surfaces, and in some implementations provide LED packages that include thermal pad structures for dissipating heat generated by the LED devices. In particular, thermal pad structures with large surface areas are used to provide heat transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations.
In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb,” has been used for over one hundred years. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light. Unfortunately, the conventional Edison light bulb dissipates much thermal energy. More than 90% of the energy used for the conventional light bulb dissipates as thermal energy. Additionally, the conventional light bulb eventually fails due to evaporation of the tungsten filament.
Fluorescent lighting overcomes some of the drawbacks of the conventional light bulb. Fluorescent lighting uses an optically clear tube structure filled with a noble gas, and typically also contains mercury. A pair of electrodes is coupled between the gas and to an alternating power source through a ballast. Once the mercury has been excited, it discharges to emit UV light. Typically, the optically clear tube is coated with phosphors, which are excited by the UV light to provide white light. Many buildings use fluorescent lighting and, more recently, fluorescent lighting has been fitted onto a base structure, which couples into a standard socket for household use.
Solid state lighting techniques have also been developed. Solid state lighting relies upon semiconductor materials to produce light emitting diodes, commonly called LEDs. At first, red LEDs were demonstrated and introduced into commerce. Modern red LEDs use Aluminum Indium Gallium Phosphide or AlInGaP semiconductor materials. Most recently, Shuji Nakamura pioneered the use of InGaN materials to produce LEDs emitting light in the blue color range for blue LEDs. The blue LEDs led to innovations such as solid state white lighting, the blue laser diode, which in turn enabled the Blu-Ray™ DVD player (trademark of the Blu-Ray Disc Association), and other developments. Blue, violet, or ultraviolet-emitting devices based on InGaN are used in conjunction with phosphors to provide white LEDs. Other colored LEDs have also been proposed.
To take advantage of LED devices, well designed LED packages that house LED devices and provide electrical connections are essential. Numerous types of conventional LED packages have been used, however, they suffer from various disadvantages.
BRIEF SUMMARY OF THE INVENTIONThis invention is directed to optical devices. More specifically, embodiments of the invention provide LED packaging having reflector surfaces, and in some implementations provide LED packages that include thermal pad structures for dissipating heat generated by the LED devices. In particular, thermal pad structures with large surface areas are used to provide heat transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations.
In one embodiment, this invention provides an optical device with a substrate and an interior surface. The device also includes a conductive layer having a thickness of at least 15 um overlying a portion of the surface. The optical device further includes an LED electrically coupled to the conductive layer, and a layer of insulating material overlaying the interior surface. A reflective layer overlies the insulating material, and preferably has a reflectivity of at least 95%.
According to another embodiment, the invention provides an optical device which includes a substrate with a flat surface. A first conductive region overlies a first portion of the flat surface, and a separate second conductive region overlies a second portion of the flat surface. The optical device includes a first via structure on the first conductive region, and an electrically separated second via structure on the second conductive region. The device additionally includes a thermal pad structure overlaying a third portion of the flat surface. The thermal pad structure is electrically insulated from the first conductive region and the second conductive region. The third portion preferably covers at least 50% of flat surface.
According to another embodiment, the invention provides an optical device. The device includes a substrate with an interior surface and a bottom side. A top conductive layer, preferably having a thickness of at least 15 um overlies a portion of the interface surface. A bottom conductive layer overlies a portion of the bottom side of the substrate. An LED is electrically coupled to a location of the top conductive layer, and a reflective layer overlies the top conductive layer. The reflective layer preferably has a reflectivity of at least 95%.
The device and method of manufacture provide for improved lighting with improved efficiency. They are easier to manufacture using conventional technologies. In certain embodiments, thermal management structures are able to greatly improve thermal conductivity of the LED package. In a specific instance, thermally conductive material as a part of the conductive layer can improve thermal conductivity by almost 50%. For example, the thermal conductivity of a conventional LED package is about 13° C./W. By increasing the thickness of conductive layers according to an embodiment of the present invention (e.g., 50 microns of copper material illustrated in
A further understanding of the nature and advantages of the present invention may be realized by reference to following portions of the specification and attached drawings
The patent application file contains at least one drawing executed in color. Copies of this patent application publication with color drawings will be provided upon request and payment of the necessary fee.
As explained above, LED chips are often used as a light source. For LED chips to function, they are secured into a package and electrically coupled to an energy source. The optical efficiency of an LED package is related the reflectivity of the cavity surfaces.
According to an embodiment, the invention provides an improved reflector.
It is to be appreciated that embodiments of the present invention provides other ways to enhance reflectivity, thereby improving overall LED package performance. In certain embodiments, reflectivity of an LED package is enhanced by increasing the coverage of reflective areas.
In certain embodiments, the present invention provides thermal management means for the LED packages. More specifically, thermal management pads are provided for surface mount LED packages. For surface mount LED packages, the mounting surfaces typically have three contacts: two electrical contacts and an electrically isolated thermal contact. For example, an LED device is mounted onto a circuit board (such as a metal clad PCB) with matching contact pads. In operation, the LED device often generates a large of heat that needs to be dissipated, as the heat might cause problem even device break down.
In an embodiment, the heat generated by the LED package is conducted across one or more thermal pad structures. More specifically, the thermal pad structures with relatively large surface area are positioned in proximity of the electrical contacts. In principle, the area of the thermal pad directly affects the contact resistance. For example, a larger the thermal pad area translates a lower the thermal resistance, as heat can dissipate through the large area.
In an LED package that is mounted onto a metal clad PCB, the metal clad PCB has a dielectric layer that electrically isolates the electrical circuits from the base metal. For example, the base metal can be aluminum or copper. Unfortunately, the dielectric layer often has a very low thermal resistance of about 2.2° C./W compared to thermal resistance of copper at 400° C./W. As a result, the dielectric layer can be a thermal choke point. In particular for silicon packages where the VIA structures for the electrical contacts are formed by etching silicon substrate material, the VIA location can limit the size of the thermal pad.
It is therefore to be appreciated that embodiments of the present invention provide improved thermal management structures, such as thermal pad structure with large surface area.
It is to be appreciated that the increase thermal pad area greatly increases the rate of heat dissipation by the thermal pad structure.
In comparison, thermal pad structures according to embodiments of the present invention reduces thermal resistance by a substantial amount.
It is to be appreciated that the specific designs of the thermal pad can be varied depending on the application. In certain embodiments, heat dissipation is accomplished by increasing the thickness of thermal conductive material.
Usually, silicon based LED packages are advantageous as they can processed in large wafer scaled formats. For example, up to 8″ silicon wafers are being processed today verses only 2″×4″ ceramic tiles used in the early days. However, the conductivity of silicon (80-140 W/m/k) is relatively low when compared to copper (3090 W/m/k) and other metal materials. Further, in some implementations, the thickness of silicon on which the LED is bonded can be rather thin. Sometimes, the thickness of the silicon material can be as low as 150 um. As a result, the thickness and the thermal conductivity of the silicon material limit the thermal spreading and increase thermal resistance, which is highly undesirable for high power densities applications.
In various embodiments, the present invention provides LED packages with thick conductive layers that help dissipate heat from the LED package.
It is to be appreciated that other variations of thermal management structures are available as well.
LED packages with thermal management structures as shown in
In one or more preferred embodiments, the thermal management structures such as thermal pad and conductive layers can be arranged different or constructed using different types of materials. Similarly, various types of material may be used for the insulating later to improve the reflectivity of the reflective layer. Of course, there can be other variations, modifications, and alternatives. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.
Claims
1-20. (canceled)
21. An LED device comprising:
- a silicon substrate, the silicon substrate having a first flat surface and a second flat surface, wherein the second flat surface is opposite the first flat surface;
- a conductive layer having a first portion and a second portion, wherein the second portion is electrically insulated from the first portion and wherein the first portion and the second portion overly the first flat surface;
- a first via structure provided on the first portion;
- a second via structure provided on the second portion, the second via structure being electrically insulated from the first via structure; and
- a thermal pad structure in thermally-conductive contact with the second flat surface,
- wherein the thermal pad structure is electrically insulated from the first portion and the second portion, and
- wherein the a portion of the thermal pad structure overly the second flat surface, and cover more than 30% of the second flat surface.
22. The device of claim 21, further comprising an LED electrically coupled to the first portion.
23. The device of claim 21, wherein the thermal pad structure comprises a reflective surface.
24. The device of claim 21, wherein the thermally-conductive contact is characterized by a thermal resistance of less than about 25° C./W.
25. The device of claim 21, further comprising a reflective layer overlying at least a portion of the first flat surface, the reflective layer defining an opening for a bond pad.
26. The device of claim 21, further comprising an insulation region between the first portion and the second portion, wherein the insulation region comprises titanium oxide.
27. The device of claim 21, further comprising an insulation region between the first portion and the second portion, wherein the insulation region comprises silicon oxide.
28. A light source comprising:
- a silicon substrate, the silicon substrate having a first flat surface and a second flat surface;
- a conductive layer having a first portion and a second portion, wherein the second portion is electrically insulated from the first portion and wherein the first portion and the second portion are juxtaposed on a plane parallel to the first flat surface;
- a first via structure provided on the first portion;
- a second via structure provided on the second portion, the second via structure being electrically insulated from the first via structure; and
- a thermal pad structure in thermally-conductive contact with the second flat surface,
- wherein the thermal pad structure is electrically insulated from the first portion and the second portion, and
- wherein a portion of the thermal pad structure overlies the second flat surface, and covers more than 30% of the second flat surface.
29. The light source of claim 28, further comprising an LED electrically coupled to the first portion.
30. The light source of claim 28, wherein the thermal pad structure comprises a reflective surface.
31. The light source of claim 28, wherein the thermally-conductive contact is characterized by a thermal resistance of less than about 25° C./W.
32. The light source of claim 28, further comprising a reflective layer overlying at least a portion of the firs flat surface, the reflective layer defining an opening for a bond pad.
33. The light source of claim 32, wherein the reflective layer comprises a metal.
34. The light source of claim 28, further comprising an insulation region between the first portion and the second portion, wherein the insulation region comprises titanium oxide.
35. The light source of claim 28, further comprising an LED package.
36. The light source of claim 35, wherein the LED package is a surface mount package.
Type: Application
Filed: Feb 4, 2014
Publication Date: May 29, 2014
Applicant: SORAA, INC. (Fremont, CA)
Inventor: FRANK TIN CHUNG SHUM (Sunnyvale, CA)
Application Number: 14/171,885
International Classification: H01L 33/60 (20060101); H01L 33/64 (20060101);