US20140254180A1

US20140254180A1 - Systems and Methods Providing Thermal Spreading for an LED Module

Info

Publication number: US20140254180A1
Application number: US14/286,534
Authority: US
Inventors: Wei-Yu Yeh; Chih-Hsuan Sun
Original assignee: Chip Star Ltd
Current assignee: Epistar Corp
Priority date: 2011-02-09
Filing date: 2014-05-23
Publication date: 2014-09-11
Also published as: US20120201007A1; US8737073B2

Abstract

A Light Emitting Diode (LED) module includes a circuit board having a front side and a back side, a heat sink coupled to the back side of the circuit board, a thermal pad disposed on a front side of the circuit board, an LED disposed on the front side of the circuit board. The LED is in thermal contact with the thermal pad. The module further includes a heat spreading device placed over the thermal pad and in thermal contact with the thermal pad.

Description

PRIORITY DATA

This application is a continuation application of U.S. application Ser. No. 13/024,017, filed Feb. 9, 2011, which is hereby incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates generally to Light Emitting Diode (LED) module manufacturing. Specifically, the present disclosure relates to systems and methods that provide a front-side heat spreading structure for an LED module.
Many conventional systems mount LEDs to circuit boards. Such circuit boards have a front side, where the LEDs are mounted, and a backside opposite the front side. LEDs can produce heat, so some conventional systems include mechanisms to remove the heat. One example of a system to remove the heat is a heat sink mounted to the back side of the circuit board. The heat can be moved from the front side LED to the backside heat sink using a thermal via or a thermal pad and an intermediate layer of thermal conductive material.
However, there are disadvantages to having only a backside heat sink. For instance, structures to move the heat from the front side to the back side take up space on and within the circuit board. Also, removing the heat only through the back side may not provide enough heat dissipation for some applications. More efficient and effective heat dissipation is called for.

SUMMARY

The present disclosure provides for many different embodiments. In a first embodiment, a Light Emitting Diode (LED) module includes a circuit board having a front side and a back side, a heat sink coupled to the back side of the circuit board, a thermal pad disposed on a front side of the circuit board, an LED disposed on the front side of the circuit board, the LED in thermal contact with the thermal pad, and a heat spreading device placed over the thermal pad and in thermal contact with the thermal pad.
In another embodiment, a method for manufacturing an LED module includes creating a circuit layout on a front side surface of a circuit board. The circuit layout includes a metal thermal pad. The method also includes disposing a plurality of LEDs on the circuit layout so that each of the LEDs is in thermal communication with the thermal pad and assembling a heat spreading structure over the front side surface of the circuit board so that the heat spreading structure is in thermal communication with the thermal pad. The heat spreading structure exposes the plurality of LEDs.
In another embodiment, an LED assembly includes a circuit substrate that has a front side and a back side, a thermal pad formed of thermally conductive material on the front side of the circuit substrate, an LED disposed on the front side of the circuit substrate and in contact with the thermal pad, and means for spreading heat produced by the LED, the heat spreading means placed over the front side of the circuit substrate and having a hole to expose the LED.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is an illustration of an exemplary LED module according to one embodiment.

FIG. 2 is a cross-sectional illustration of an exemplary LED package according to one embodiment.

FIG. 3 is an illustration of the exemplary circuit board of FIG. 2, shown with LEDs mounted thereon.

FIG. 4 is an illustration of a port ion of another exemplary circuit board shown as it would appear using Computer Aided Design (CAD), according to one embodiment.

FIG. 5 shows an exemplary LED for use with the circuit board of the embodiment of FIG. 4.

FIG. 6 is an illustration of another exemplary LED package according to one embodiment.

FIG. 7 is an illustration of exemplary method for manufacturing an LED module according to one embodiment.

DETAILED DESCRIPTION

The present disclosure relates generally to LED modules. Specifically, the present disclosure relates to a front side heat spreading structure for an LED module. While the examples herein discuss applying the techniques to a Metal Core Printed Circuit Board (MCPCB), it is understood that the scope of embodiments is not limited to MCPCBs or even PCBs generally. The scope of embodiments includes all kinds of substrates for circuit layouts, including ceramic, FR-4, and the like.
The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
With reference now to the figures, FIG. 1 is an illustration of an exemplary LED module 100 according to one embodiment. LED module 100 has LEDs 105, which are disposed upon circuit board 120 by, e.g., Surface Mount Technology (SMT) or through-hole mounting. Circuit board 120 in this example has a front side (top) and back side (contacting heat sink 130). The front side, and perhaps other intermediate layers, has metal conductive paths formed of copper (Cu) or other metal. Some of the conductive paths are for power, ground, or signals and are referred to herein as electrical conductive paths. Others of the conductive paths are thermal conductive paths. The thermal conductive paths are isolated from the electrical conductive paths and are arranged to create pathways for heat to travel from LEDs 105 to heat spreading structure 110 and/or heat sink 130. In some embodiments, electrical conductive paths are used as thermal conductive paths so long as placement of heat spreading structure 110 over the electrical conductive paths does not cause short circuits. For instance, when electrical conductive paths are used as thermal conductive paths, various embodiments add electrically-insulative thermal conductive material to be the interface between the electrical conductive path and heat spreading structure. Thermal conductive paths are shown and described in more detail with respect to FIG. 4.
Of note in module 100 is the placement of heat spreading structure 110 on the front side of module 100. Heat spreading structure 110 has holes that expose LEDs 105 but otherwise heat spreading structure 110 covers substantially all of the front side of circuit board 120. Together, heat spreading structure 110 and heat sink 130 spread heat from top to bottom and side to side of module 100, as shown by the arrows.
FIG. 2 is a cross-sectional illustration of exemplary LED package 200 according to one embodiment. Package 200 includes MCPCB 220, upon which LEDs 205 are mounted using solder pads (e.g., solder pad 226). PCB 220 includes Cu layer 221 with etched electrical paths (not shown), solder mask 222, thermally conductive material 223, and aluminum (Al) layer 224. Thermally conductive material 223 includes in this example electrically insulative gel. LED package 200 also includes heat spreading structure 210 disposed over the front side of LED package 200. The interface 225 of heat spreading structure 110 and PCB 220 includes a thermally conductive material, such as thermal grease or tape (not shown) to ensure reliable contact and heat transfer between the surface of PCB 220 and heat spreading structure 210. Heat spreading structure 110 may be electrically isolated from circuitry (not shown) at interface 225 by use of grease, tape, or even ink.
PCB 220 in this example can be manufactured using conventional methods. Further, in this example, heat spreading structure 110 is formed of Al as a separate component that is positioned over PCB 220 and attached thereto using screws or tape. However, other techniques now known or later developed for manufacturing PCB 220 and structure 210 and for attaching structure 210 may be employed in some embodiments. Furthermore, while not shown in FIG. 2, it is understood that LED package 200 may include a back side mounted heat sink as well.
FIG. 3 is an illustration of exemplary circuit board 220 of FIG. 2, shown with LEDs mounted thereon. FIG. 3 provides a view of thermal path 310, which in this example includes a metal layer on the front side surface that contacts the bottoms of the respective LEDs. Thermal path 310 has thin portions (e.g., portions 310 a and 310 b) that contact the LEDs and wider portions ( portions 310 c and 310 d) arranged laterally on the front surface. Electrical contact pads 315, 316 provide for an interface to a power supply and ground and distribute the power through electrical paths (not shown) underneath the layer illustrated in FIG. 3.
FIG. 4 is an illustration of a portion of another exemplary circuit board 400 shown as it would appear using Computer Aided Design (CAD). Circuit board 400 includes power paths 410-404, which are in electrical communication with power (LED+, path 404) and ground (LED−, path 403). Power paths 401-404 are also in electrical communication with solder pads 410, 420. Circuit board 400 also includes thermal pads 405, 406, which are electrically isolated from power paths 401-404. It should be noted that in some embodiments, the Cu that makes up paths 401-404 is covered in electrically insulative, thermally conductive ink from a PCB etch process (except for the portions under pads 410, 420).
Thermal pad 405 is in thermal communication with solder pad 410, and thermal pad 406 is in thermal communication with solder pad 420. Thus, thermal pads 405, 406 are configured to distribute heat away from LEDs (not shown) mounted upon respective solder pads 410, 420. While not shown in FIG. 4, it is noted that a front side-mounted heat spreading structure (such as heat spreading structure 110 of FIG. 1) may be mounted upon circuit board 400 so that it is in thermal communication with thermal pads 405, 406 and can dissipate heat to another structure or to the atmosphere.
FIG. 5 shows exemplary LED 500 for use with circuit board 400 of the embodiment of FIG. 4. In FIG. 5, LED 500 is shown in a variety of views for a better understanding of this particular embodiment. In one example, the bottom surface of LED 500 is mounted to solder pad 410 so that middle contact 501 is coupled to thermal pad 405, contact 502 is coupled to power path 401, and contact 503 is coupled to power path 402.
FIG. 6 is an illustration of another exemplary LED package 600 according to one embodiment. In the embodiment of FIG. 6, heat spreading structure 620 is mounted upon circuit board 220 so that heat spreading structure 620 is in thermal communication with the LEDs through solder pads 610. While not shown in FIG. 6, solder pads 610 are in thermal communication with one or more thermal pads that distribute heat from the LEDs. Interface 625 between solder pads 610 and heat spreading structure 620 may or may not include a thermal grease or tape. In fact, in some embodiments, the solder pads 610 act as thermal spreading surfaces that make reliable contact with heat spreading structure 620 so that thermal grease and tape can be omitted. Some embodiments may also include a back side mounted heat sink (not shown) as well.
FIG. 7 is an illustration of exemplary method 700, for manufacturing an LED module, according to one embodiment. Method 700 may be performed in some instances by one or more persons and/or machines in a single manufacturing site or multiple manufacturing sites.
In block 710, a circuit layout is created on a front side surface of a circuit board. In one example, the circuit board includes a thin layer of metal, such as Cu, on its surface. The layer of metal is then patterned using a mask and etchant. However, any technique now known or later developed may be used to create the circuit layout.
Further in this example, the circuit layout includes electrical conductive paths for power, ground, and signals and thermal conductive paths for distributing heat. The thermal conductive paths may be different from the electrical paths. An example of a circuit layout is shown in FIG. 4.
In block 720, a plurality of LEDs are disposed in the circuit layout so that each of the LEDs is in thermal communication with a thermal pad in the circuit layout. FIGS. 4 and 5 above illustrate how an LED can be arranged upon a circuit layout in one embodiment to be in thermal communication with appropriate components.
In block 730, a heat spreading structure is assembled over the front side surface of the circuit board so that the heat spreading structure is in thermal communication with the thermal pad. The heat spreading structure may be thermally coupled to the thermal pad using a solder pad or not using a solder pad. Furthermore, some embodiments may or may not employ a heat-conductive thermal insulating material, such as thermal grease or tape or ink, at an interface of the heat spreading structure and the circuit layout.
Block 730 includes in some embodiments arranging the heat spreading structure so that it covers substantially all of the circuit board, covering the entire circuit layout, while including one or more apertures to expose the LEDs. In other examples, the heat spreading structure may leave some areas of the circuit layout exposed.
The heat spreading structure can be assembled in any manner appropriate for a given application. Some embodiments employ screws, tape, and/or adhesive to secure the heat spreading structure to the circuit board.
Method 700 is exemplary, and the scope of embodiments is not limited only to that shown in FIG. 7. Other embodiments may add, omit, modify, or rearrange actions. For instance, some embodiments further include mounting a heat sink on the back side of the circuit board. Moreover, some embodiments may further include deploying the LED module in an application, such as an LED display or LED lighting fixture. The application may include a control system that uses sophisticated algorithms to drive the LEDs to provide desired results, such as outputting a desired color of light, outputting a desired pattern, and/or the like.
Table 1 includes examples of various embodiments using a variety of substrates and other materials. Table 1 is exemplary, as the scope of embodiments may include other materials adapted for use in some applications.

TABLE 1

Item	Material 1	Material 2	Material 3	Material 4

substrate	Al-MCPCB	Cu-MCPCB	Ceramic	FR4
Heat sink	Al	Cu	Fe	Ag
(back side)
PCB pad for	Chemical	Sn solder	OSP solder	OSP solder
process	gold solder
Heat spreading	Al	Cu	Fe	Ag
structure (front
side)
Thermal	Grease	Tape	gel
interface
material

Various embodiments may include advantages over other techniques that employ only a back side heat spreading structure. For instance, some embodiments improve the performance of the LED module by shortening the thermal path from the LEDs to a heat spreading structure, which makes for more effective use of the heat spreading structure. Furthermore, embodiments that employ heat spreading structures on both the front side and back side of the circuit board double the paths for thermal spreading. Increased thermal spreading may enhance reliability in applications where heat dissipation is crucial, such as in high-power LED lighting fixtures.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.

Claims

What is claimed is:

1. A device comprising:

a substrate having a first side and an opposing second side;

a heat sink coupled to the second side of the substrate;

a thermal pad disposed on the first side of the substrate;

a Light Emitting Diode (LED) disposed on the first side of the substrate, the LED in direct contact with the thermal pad; and

a heat spreading structure placed over the thermal pad and in thermal contact with the thermal pad.

2. The device of claim 1, wherein the substrate includes a circuit board.

3. The device of claim 1, wherein the heat spreading structure surrounds the LED.

4. The device of claim 1, wherein the heat spreading structure is coupled to the thermal pad using a thermal interface material that includes at least one of a thermal conductive gel and a thermal conductive tape.

5. The device of claim 1, wherein the thermal pad includes a metal layer.

6. The device of claim 5, wherein the metal layer of the thermal pad is in direct contact with the LED.

7. The device of claim 1, wherein the heating spreading structure surround the LED and includes an opening to thereby expose the LED through the heat spreading structure.

8. A device comprising:

a thermal pad disposed over a first side of a substrate;

a Light Emitting Diode (LED) disposed over the thermal pad on the first side of the substrate and in direct contact with the thermal pad; and

a heat spreading structure disposed over the first side of the substrate and having an opening to expose the LED.

9. The device of claim 8, further comprising a heat sink disposed over a second side of the substrate, the second side of the substrate being opposite the first side.

10. The device of claim 8, wherein the heating spreading structure surrounds the LED.

11. The device of clam 8, wherein the heat spreading structure includes at least one of aluminum, copper, iron, and silver.

12. The device of claim 8, further comprising a solder pad disposed over the first side of the substrate, wherein the LED is in direct contact with the solder pad.

13. The device of claim 12, wherein the solder pad is in thermal communication with the thermal pad.

14. The device of claim 12, wherein the heat spreading structure is in direct contact with the solder pad.

15. The device of claim 12, wherein the heat spreading structure is coupled to the solder pad using a thermal interface material that includes at least one of a thermal conductive gel and a thermal conductive tape.

16. A method comprising:

forming a thermal pad on a first side of a substrate;

coupling a Light Emitting Diode (LED) to the first side of the substrate such that the LED is in direct contact with the thermal metal pad; and

forming a heat spreading structure over the first side of the substrate such that the heat spreading structure is in thermal communication with the thermal pad and surrounds the LED.

17. The method of claim 16, further comprising forming a heat sink structure over a second side of the substrate that is opposite the first side of the substrate.

18. The method of claim 16, wherein coupling the LED to the first side of the substrate includes coupling the LED to a solder pad disposed on the first side of the substrate.

19. The method of claim 16, wherein forming the heat spreading structure over the first side of the substrate such that the heat spreading structure is in thermal communication with the thermal pad and surrounds the LED includes coupling the heat spreading structure to the thermal pad using a thermal interface material that includes at least one of a thermal conductive gel and a thermal conductive tape.

20. The method of claim 16, wherein heat spreading structure is electrically isolated from electrical connections on the substrate.