WO2008128016A9

WO2008128016A9 - Metal core circuit boards for light emitting diode applications and methods of manufacture thereof

Info

Publication number: WO2008128016A9
Application number: PCT/US2008/059983
Authority: WO
Inventors: Seung B. Chun; Michael S. White
Original assignee: World Properties Inc.
Priority date: 2007-04-13
Filing date: 2008-04-11
Publication date: 2010-10-28
Also published as: WO2008128016A3; WO2008128016A2

Abstract

An insulated metal substrate laminate includes a metal substrate (104), a dielectric layer (106) disposed upon the metal substrate, wherein the dielectric layer has an aperture (110) formed therein and a thickness of less than or equal to 1 mil, and an electrically conductive layer (108) disposed upon the dielectric layer, wherein the electrically conductive layer has an aperture formed therein, wherein the aperture is coaxially aligned over the aperture of the dielectric layer.

Description

METAL CORE CIRCUIT BOARDS FOR LIGHT EMITTING DIODE APPLICATIONS AND METHODS OF MANUFACTURE

THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Serial No. 60/911,643 filed April 13, 2007, which is incorporated herein by reference in its entirety.

BACKGROUND

[0001] This disclosure relates to metal core circuit boards, and methods of manufacture thereof.

[0002] A light emitting diode (LED) includes a semiconductor chip that emits light and heat in response to the application of an electrical current. In general, both the brightness of the light emitted and the amount of heat generated increases as more electric current is applied to the LED. The heat shedding capacity of the LED defines an upper threshold for the application of more current. Accordingly, the efficiency of the LED to shed heat limits the brightness attainable by the LED. Various LED thermal management systems have been devised to improve the heat transfer from the LED to external heat dissipaters. Such systems typically include an electrically insulating circuit board having opposed first and second surfaces with electrically conductive circuit traces on the first surface of the circuit board. A plurality of LEDs has a pair of electrical leads in electrical engagement with the traces. A heat dissipater is disposed in parallel relationship to the circuit board. For example, conventional LEDs are generally soldered onto a circuit board. To increase the brightness of the illumination, the entire circuit board mounts on a heat sink device to remove the heat generated by the operation of the LEDs. The heat sink device conducts heat away from the LEDs. Moreover, LED thermal management systems can comprise an metal core circuit board (MCCB) laminate. The MCCB laminate includes the traces, circuit board, as well as a metal substrate that is connected to the heat sink device.

[0003] Figure 1 illustrates a conventional LED thermal management system 10. The LED emitter 12 is connected to an MCCB laminate 14 comprising electrically conductive trace layer 16 disposed on top of a dielectric layer 18. The MCCB laminate 14 further comprises a metal substrate 20, which is disposed beneath the dielectric layer 18. The LED emitter 12 has leads 22 that are soldered to the traces 16. In such current LED thermal management systems, the LED exhibits substantial thermal resistance because of poor thermal coupling with the metal substrate 20. hi this system, the majority of the thermal resistance comes from the dielectric layer 18.

[0004] hi Figure 2, a second LED thermal management system 50 is illustrated, wherein the thermal resistance of the dielectric layer 58 is significantly reduced, hi this system, the LED emitter 52 is coupled directly to the metal substrate 60 of the MCCB laminate 54. A hole in the dielectric layer 58 permits the LED emitter 52 to be in direct thermal communication with the metal substrate 60, thereby reducing the thermal resistance of the MCCB laminate 54. Because, however, the LED emitter 52 is in a position lower than if the emitter were disposed on top of the dielectric layer, it is difficult to solder the LED leads 62 to the traces 56. hi fact, for some LED applications, the leads must be manually soldered to the circuit board because an automated soldering process, such a Refiow for example, is too difficult to perform given the thickness of the dielectric layer. As a result, producing the thermal management system 50 is both time consuming and labor intensive.

[0005] Accordingly, there remains a need in the art for improved MCCB laminates capable of being assembled faster, without the need for additional labor, while improving thermal management of LED applications.

BRIEF SUMMARY

[0006] Disclosed herein is a metal core circuit board laminate. The laminate includes a metal substrate, a dielectric layer disposed upon the metal substrate, wherein the dielectric layer has an aperture formed therein and a thickness of less than or equal to 1 mil, and an electrically conductive layer disposed upon the dielectric layer, wherein the electrically conductive layer has an aperture formed therein, wherein the aperture is coaxially aligned over the aperture of the dielectric layer.

[0007] A light emitting diode includes a metal core circuit board laminate including, a metal substrate, a dielectric layer disposed upon the metal substrate, wherein the dielectric layer has an aperture formed therein and a thickness of less than or equal to 1 mil, and an electrically conductive layer disposed upon the dielectric layer, wherein the electrically conductive layer has an aperture formed therein, wherein the aperture is coaxially aligned over the aperture of the dielectric layer, a light emitting diode emitter in electrical communication with the electrically conductive layer, and power supply in electrical communication with the electrically conductive layer.

[0008] In another embodiment, a method of assembling a metal core circuit board for supporting and providing electrical communication to a light emitting diode, includes forming an aperture in a dielectric layer, forming an aperture in an electrically conductive layer, placing the dielectric layer upon a metal substrate, wherein the dielectric layer has a thickness of less than or equal to 1 mil, placing the electrically conductive layer upon the dielectric layer, wherein the aperture of the electrically conductive layer is coaxially aligned over the aperture of the dielectric layer, and laminating the electrically conductive layer, the dielectric layer, and the metal substrate together by applying a pressure of at least about 300 pounds per square inch at a temperature of at least about 460 degrees Fahrenheit for at least about 10 minutes to form the metal core circuit board laminate.

BRIEF DESCRIPTION OF THE DRAWING

[0009] Figure 1 is a cross-sectional view of a prior art light emitting diode thermal management system;

[0010] Figure 2 is another embodiment of a prior art light emitting diode thermal management system; and

[0011] Figure 3 is a cross-sectional view of a light emitting diode having an insulated metal laminate as disclosed herein.

DETAILED DESCRIPTION

[0012] The inventors hereof have found that by directly disposing a light emitting diode (LED) onto an metal core circuit board (MCCB) having a thin dielectric layer, the LED will have both improved thermal transfer ability and will be capable of assembly with an automated soldering process, hi one embodiment, the disclosed LED has higher thermal transfer performance, a thinner MCCB laminate, and can be fabricated more easily at lower cost when compared with current LED systems using MCCB laminates, such as those described above. The MCCB laminates, as disclosed herein, are particularly suitable for use in LED applications, such as high brightness LEDs, which can be combined to form an array called a light engine.

[0013] Turning now to Figure 3, a LED 100 is illustrated having an exemplary embodiment of an MCCB laminate 102. The MCCB laminate 102 comprises a metal substrate 104 with a dielectric layer 106 disposed thereon. An electrically conductive layer 108 is arranged on the dielectric layer 106. Both the dielectric layer 106 and the electrically conductive layer 108 form a circuit board and each respectively have an aperture 110, 118, formed therein. The apertures can be centrally located on the MCCB laminate 102. The apertures permit an LED emitter 112 to be disposed in thermal communication with the metal substrate 104. hi other words, the LED emitter 112 extends through each aperture in the conductive layer and dielectric layer to the metal substrate 104. The LED emitter 112 further comprises a pair of electrical leads 114 which are configured to be in electrical communication with the electrically conductive layer 108. The electrically conductive layer 108 is electrically engaged to the electrical leads 114 with solder 116. A power supply 120 is in electrical communication with the electrically conductive layer to provide power to the LED 100.

[0014] The metal substrate 104 generally comprises a material that exhibits excellent thermal conduction. Suitable materials include, without limitation, aluminum, copper, stainless steel, copper-beryllium, tin-plated copper, and the like. The metal substrate can have any shape and thickness suitable for LED applications as would be known to one of skill in the art. m one embodiment, the metal substrate 104 can have a thickness of about 20 mil to about 200 mil.

[0015] The MCCB laminate 102 further comprises the dielectric layer 106 disposed on the metal substrate 104. The dielectric layer 106 comprises a solid component comprised of dielectric material, which can be cut and shaped to any suitable size and shape for a given LED application. As used herein, the term "dielectric" is used to describe electrically insulating material having good bond strength with circuit traces and the metal substrate, high breakdown voltage, low moisture absorption, and the like, hi one embodiment, the dielectric layer can have a thickness of less than or equal to 1 mil. By providing a thin film (i.e., less than 1 mil) dielectric layer, the physical constraints that prevent current LED thermal management systems, such as those using thick flame-resistant 4 (FR4) epoxy glass laminates, from passing through an automatic soldering process, are eliminated. As will be described in greater detail below, the dielectric layer as disclosed herein advantageously permits use of the MCCB laminate in an automatic soldering process, such as flow soldering, reflow soldering, and the like. Suitable dielectric materials include polyimide (PI), polyetheretherketone (PEEK), polyetherimide (PEI), polyamidimide (PAI), polyethylene terephthalate (PET), Polyethylene naphthalate (PEN), polycyclohexylene terephthallate (PCT), and other like electrically insulating materials, depending on the intended application of the metal core circuit board. In one embodiment, the dielectric layer 106 can be PI film manufactured by Kaneka, such as Pixeo FC-622. Again, the dielectric layer 106 can have a thickness of less than or equal to 1 mil and can have an aperture 110 formed therein for the LED emitter 112. Moreover, the aperture of the dielectric layer can be formed so that when combined with the electrically conductive layer 108 the like apertures are coaxially aligned on top of one another.

[0016] The electrically conductive layer 108 is arranged on the dielectric layer 106. The electrically conductive layer 108 provides an electrically conductive surface for establishing conductive paths for electrically interconnecting the LED leads 114. The electrically conductive layer 108 is a solid component, which can be cut and shaped to any suitable size and shape for a given LED application. For example, the electrically conductive layer 108 can comprise a metal foil. Suitable metal foils include copper foil, tin-plated copper foil, silver foil, gold foil, and the like. In one embodiment, the electrically conductive layer 108 can be formed of CopperBond® copper foil, commercially available from Olin. Like the dielectric layer 106, the electrically conductive layer 108 has an aperture formed therein for the LED emitter 112.

[0017] An exemplary method of assembling the MCCB laminate and a LED includes forming apertures in the electrically conductive layer and the dielectric layer. As used herein, the term "forming" is used to generally refer to means for creating an aperture, such as without limitation, cutting, drilling, punching, die-cutting, and the like. Also, the apertures as disclosed herein, are not intended to be limited in size or shape. As used herein, the term "aperture" is intended to refer to a portion of the dielectric layer or the electrically conductive layer removed from the top surface to the bottom surface. Exemplary apertures include, without limitation, vias, thru-holes, channels, contacts, and the like. In one embodiment, apertures can be die-cut in both the electrically conductive layer and the dielectric layer simultaneously. The pre-cut electrically conductive layer and dielectric layer are then placed in contact with the metal substrate for all the components to be laminated together to form the MCCB laminate. The MCCB components are laminated together by applying pressure to the components at a pressure and for a period of time appropriate to create a bond between the layers of the MCCB laminate depending on the material chosen for the dielectric layer. In one method, the MCCB laminate is placed in a heated pneumatic platen press. The MCCB laminate is then subjected to a pressure of about 300 pounds per square inch (psi) to about 1200 psi (about 20 bars to about 83 bars) for a period of about 10 minutes to about 40 minutes at a temperature of about 460 degrees Fahrenheit (^"F) to about 660 ^°F (about 238 degrees Celsius (^'C) to about 349 ^°C). hi one exemplary embodiment, laminating the electrically conductive layer, the dielectric layer, and the metal substrate together is done at a pressure of about 600 psi at a temperature of about 610 ^°F for about 25 minutes to form the metal core circuit board laminate. The operating temperature of the heated press will depend upon the dielectric material selected to form the dielectric layer of the MCCB laminate. Also, in one method, the MCCB components are laminated in the heated press under vacuum. The MCCB laminate can then be removed from the press and the LED emitter can be connected to the MCCB laminate via an automatic soldering process, such as reflow soldering.

[0018] Advantageously, the method as disclosed herein requires less time, labor, and energy when compared to existing methods of producing MCCB laminates for LED systems. As a result, the cost of producing the disclosed MCCB laminate comprising a thin film dielectric layer is lower than MCCB laminates produced by current methods. Specifically, producing MCCB laminates by the method as disclosed herein eliminates the need for dielectric and metal etching processes, since the electrically conductive layer and dielectric layer can have pre-cut apertures for the LED emitter. Likewise, the dielectric layer further provides for a faster assembly time over current methods because the MCCB laminate as disclosed herein can be used in automated soldering processes.

[0019] The following example, which is meant to be exemplary, not limiting, illustrates a method of manufacturing the MCCB laminates described herein. Example 1.

[0020] In order to find suitable press conditions for the laminates, MCCB laminates were made by various methods in the following table and the copper peel strength was measured. A Pixeo FC622 PI bond dielectric film made by Kaneka was placed between a 2 ounce copper film layer made by Olin and 1.6 mm 5052H32 aluminum plate produced by Bralco. The MCCB laminates were produced in a vacuum press to prevent the copper film layer from tarnishing, and to prevent possible degradation that could occur at the high temperatures. Table 1 illustrates the various press conditions that were tried and the resulting bond strength of the laminate as a result.

Table 1.

Example 2

[0021] An MCCB laminate was made from a 2 oz copper foil layer and a 1.6 mm 5052H32 aluminum plate substrate. The layers were placed under pressure as described for sample 1, as shown in Table 1. To make a patterned circuit, the copper foil removed by chemical etching in the desired areas. The aperture for connection of, for example, a diode, was created by a CO₂ laser. The laser created the aperture at an intensity of 32 kilovolts at 100 pulses/second, with a 32 mil beam spot size. Both circular and rectangular apertures were formed and no damage to aluminum plate substrate surface was observed. The resulting apertures had clean edges and were formed completely through with no PI residue left on the substrate..

Example 3

[0022] An MCCB laminate was produced by the following method. A l- ounce CopperBond® copper foil was placed on top of a Pixeo FC-622 PI thin film layer. The foil and thin film layer were then punched to create apertures of 0.25 inches in diameter. The punched foil and thin film were then placed on a 40-mil 6061T6 aluminum plate. The three-layer assembly was then placed in a heated press. The press was closed and a pressure of 600 psi at a temperature of 590 ^°F was placed on the MCCB layers in vacuum to produce the MCCB laminate.

[0023] The terms "first," "second," and the like as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). Further as used herein "disposed" means that the recited elements are in direct contact with, and fully or partially cover each other. All ranges disclosed within this specification that are directed to the same component or property are inclusive of the stated endpoint, and are independently combinable. All references are incorporated herein by reference in their entirety.

[0024] While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention.

Claims

CLAIMS What is claimed is:

1. A metal core circuit board laminate, comprising: a metal substrate; a dielectric layer disposed upon the metal substrate, wherein the dielectric layer has an aperture formed therein and a thickness of less than or equal to 1 mil; and an electrically conductive layer disposed upon the dielectric layer, wherein the electrically conductive layer has an aperture formed therein, wherein the aperture is coaxially aligned over the aperture of the dielectric layer.

2. The metal core circuit board laminate of Claim 1, wherein the electrically conductive layer comprises copper, tin-plated copper, silver, gold, or a combination comprising at least one of the foregoing.

3. The metal core circuit board laminate of Claim 1 , wherein the dielectric layer comprises a polyimide, a polyetheretherketone, a polyetherimide, a polyamidimide, a polyethylene terephthalate, polyethylene naphthalate, polycyclohexylene terephthallate, or a combination comprising at least one of the foregoing.

4. The metal core circuit board laminate of Claim 1, wherein the metal substrate comprises aluminum, copper, tin-plated copper, copper-beryllium, stainless steel, or a combination comprising at least one of the foregoing.

5. A method of assembling a metal core circuit board laminate for supporting and providing electrical communication to a light emitting diode, comprising:

forming an aperture in a dielectric layer, wherein the dielectric layer has a thickness of less than or equal to 1 mil; forming an aperture in an electrically conductive layer; placing the dielectric layer upon a metal substrate; placing the electrically conductive layer upon the dielectric layer, wherein the aperture of the electrically conductive layer is coaxially aligned over the aperture of the dielectric layer; and laminating the electrically conductive layer, the dielectric layer, and the metal substrate together by applying a pressure of at least about 300 pounds per square inch at a temperature of at least about 460 degrees Fahrenheit for at least about 10 minutes to form the metal core circuit board laminate.

6. The method of Claim 5, wherein forming the aperture in the dielectric layer and forming the aperture in the electrically conductive layer comprises simultaneously forming the apertures.

7. The method of Claim 5, wherein forming the aperture in the dielectric layer and forming the aperture in the electrically conductive layer occurs prior to placing the dielectric layer and electrically conductive layer upon the metal substrate

8. The method of Claim 5, further comprising soldering a light emitting diode emitter to the electrically conductive layer of the metal core circuit board laminate.

9. The method of Claim 8, wherein soldering the light emitting diode emitter comprises feeding the light emitting diode emitter and metal core circuit board through an automated reflow soldering process.

10. The method of Claim 5, wherein the electrically conductive layer comprises copper, tin-plated copper, silver, gold, or a combination comprising at least one of the foregoing.

11. The method of Claim 5, wherein the dielectric layer comprises a polyimide, a polyetheretherketone, a polyetherimide, a polyamidimide, a polyethylene terephthalate, polyethylene naphthalate, polycyclohexylene terephthallate, or a combination comprising at least one of the foregoing.

12. The method of Claim 5, wherein the metal substrate comprises aluminum, copper, tin-plated copper, copper-beryllium, stainless steel, or a combination comprising at least one of the foregoing.

13. A light emitting diode made by the process of Claim 5.

14. A light engine employing the light emitting diode of Claim 13.

15 A light emitting diode comprising: a metal core circuit board laminate comprising a metal substrate; a dielectric layer disposed upon the metal substrate, wherein the dielectric layer has an aperture formed therein and a thickness of less than or equal to 1 mil; and an electrically conductive layer disposed upon the dielectric layer, wherein the electrically conductive layer has an aperture formed therein, wherein the aperture is coaxially aligned over the aperture of the dielectric layer; and a light emitting diode emitter in electrical communication with the electrically conductive layer; and a power supply in electrical communication with the electrically conductive layer.

16. The light emitting diode of Claim 15, further comprising solder configured to connect the light emitting diode emitter to the electrically conductive layer.

17. The light emitting diode of Claim 15, wherein the electrically conductive layer comprises copper, tin-plated copper, silver, gold, or a combination comprising at least one of the foregoing.

18. The light emitting diode of Claim 15, wherein the dielectric layer comprises a polyimide, a polyetheretherketone, a polyetherimide, a polyamidimide, a polyethylene terephthalate, polyethylene naphthalate, polycyclohexylene terephthallate, or a combination comprising at least one of the foregoing.

19. The light emitting diode of Claim 15, wherein the metal substrate comprises aluminum, copper, tin-plated copper, copper-beryllium, stainless steel, or a combination comprising at least one of the foregoing.

20. The light emitting diode of Claim 16, wherein the solder connects the light emitting diode emitter to the electrically conductive layer with an automated reflow soldering process.