LED package comprising leadframe and two-part heatsink

Description

BACKGROUND

[0001] The present invention relates to the field of packaging semiconductor devices, and more particularly to packaging light emitting diodes.

[0002] Light emitting devices (LEDS) such as light emitting diodes.are often packaged within leadframe packages. A leadframe package typically includes an LED connected to thin metal leads where the LED and most of the leads are completely encapsulated within a plastic body. A part of the plastic body defines a lens. A portion of the leads connected to the LED extends outside the plastic body. The metal leads of the leadframe package serve as the conduit to supply the LED with electrical power and, at the same time, may act to draw heat away from the LED. Heat is generated by the LED when power is applied to the LED to produce light. The portion of the leads that extend out from the package body connects to circuits external to the leadframe package.

[0003] Some of the heat generated by the LED is dissipated by the plastic package body; however, most of the heat is drawn away from the LED via the metal components of the package. The metal leads are typically very thin and have a small cross section. For this reason, capacity of the metal leads to remove heat from the LED is limited. This limits the amount of power that can be sent to the LED. This, in turn, limits the amount of light that can be generated by the LED.

[0004] To increase the capacity of an LED package to dissipate heat, various designs are used in the industry; however, each of these designs results in LED packages with limited heat dissipation capacities while increasing the complexity and the costs of manufacturing the LED packages. For example, in one approach, LED packages are designed to include the LED within a cavity of a heatsink slug. Then, the heatsink slug is surrounded by a plastic body except for its bottom surface. For example, some LUXEON^™ LED packages by Lumileds Lighting, LLC embodies such a design. Here, the heatsink slug increases the capacity of the LED package to dissipate heat; however, LED packages of this design are relatively difficult and costly to manufacture. Further, the heat dissipation is limited because of its limited exposed surface (the bottom surface only).

[0005] In another LED package design, the leads of the leadframe are extended (in various shapes and configurations) beyond the immediate edge of the LED package body. This increases the surface area of the portions of the leads exposed to the surrounding air. The increased exposed surface area of the extended leads increases the capacity of the LED package to dissipate heat; however, the extended leads increase the size of the LED package requiring relatively large area on a circuit board. Circuit board area is a scarce and costly factor in many applications.

[0006] Another undesirable aspect of the current leadframe package designs relates to problems with thermal expansion of the package. When heat is generated, the LED package experiences thermal expansion. Each of the parts of the LED package has a different coefficient of thermal expansion (CTE). For example, the CTE of the LED, the CTE of the package body, the CTE of the leads, and the CTE of lens are different from each other. For this reason, when heated, each of these parts experience different degrees of thermal expansion resulting in mechanical stresses between the parts of the package thereby acversely affecting its reliability.

[0007] EP 0 933 823 A2 describes a thermal expansion compensated opto-electronic semiconductor element and a method of its manufacture. The opto-electronic semiconductor element comprises a leadframe sandwiched by a bottom element and a top frame element of a two-part housing, whose thermal expansion is matched to the leadframe. An inner side of the frame element and/or an inner side of the bottom element may be covered by an aluminium layer.

[0008] WO 02/33756 A1 discloses a LED package comprising a plurality of LED chips on a leadframe, wherein the leadframe is glued on a copper block.

[0009] A light source with an LED embedded in a transparent material filling is described in DE 199 18 370 A1. A converter substance is integrated in the filling for the at least partial wavelength conversion of the light emitting by the LED. A lens is glued over the transparent material filling.

[0010] DE 44 46 566 A1 describes a multi-terminal surface-mounted electronic device. The multi-terminal surface-mounted electronic device comprises an electronic component, which is located in a housing. Both the electronic component and the housing are joined to a base strip. The base strip provides the terminals whose contact surfaces are so formed that they can embrace the entire housing either completely or partially.

[0011] Consequently, there remains a need for an improved LED package that overcomes or alleviates one or more of the shortcomings of the prior art packages.

SUMMARY

[0012] The present invention provides a light emitting die package according to claim 1.

[0013] Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by the way of example the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 

Figures 1A and 1B are perspective views of a light emitting die package according to one embodiment of the present invention;

Figure 1C is a cutaway side view of the light emitting die package of Figure 1A cut along line A-A;

Figure 2 is an exploded perspective view of the semiconductor package of Figure 1A;

Figure 3 is a perspective view of a light emitting die package of Figure 1A during its manufacturing process.

DETAILED DESCRIPTION

[0015] The present invention will now be described with reference to the Figures 1 through 3, which illustrate various embodiments of the present invention. As illustrated in the Figures, the sizes of layers or regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the present invention. Furthermore, various aspects of the present invention are described with reference to a structure or a portion being formed on other structures, portions, or both. As will be appreciated by those of skill in the art, references to a structure being formed "on" or "above" another structure or portion contemplates that additional structure, portion, or both may intervene. References to a structure or a portion being formed "on" another structure or portion without an intervening structure or portion are described herein as being formed "directly on" the structure or portion. Furthermore, relative terms such as "on" or "above" are used herein to describe one structure's or portion's relationship to another structure or portion as illustrated in the Figures. It will be understood that relative terms such as "on" or "above" are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in the Figures is turned over, structure or portion described as "above" other structures or portions would now be oriented "below" the other structures or portions. Likewise, if the device in the Figures is rotated along an axis, structure or portion described as "above" other structures or portions would now be oriented "next to" or "left of" the other structures or portions. Like numbers refer to like elements throughout.

[0016] As shown in the figures for the purposes of illustration, embodiments of the present invention are exemplified by a light emitting die package including a leadframe with leads, a bottom heatsink, and a top heatsink with an opening. A light emitting device (LED) such as a light emitting diode is mounted on the leadframe within the opening. A lens covers the opening. In effect, the light emitting die package according to one embodiments of the present invention comprises a two part heat sink sandwiching a leadframe. Because both the bottom and the top heat sinks draw heat away from the LED, more power can be delivered to the LED, and the LED can produce more light. Furthermore, for the same reason, the light emitting die package of the present invention may not require a separate heat sink slugs or leads that extend away from the package. Accordingly, the LED die package of the present invention may be more compact, more reliable, and less costly to manufacture than the die packages of the prior art.

[0017] Figures 1A and 1B are perspective views of a light emitting die package 10 according to one embodiment of the present invention. Figure 1C is a cutaway side view of the light emitting die package 10 of Figure 1A cut along line A-A. Figure 2 is an exploded perspective view of the semiconductor package 10 of Figures 1A and 1B. Referring to Figures 1A through 2, the semiconductor package 10 includes a leadframe 20, a bottom heatsink 30, and a top heatsink 40.

[0018] The leadframe 20 includes a plurality of leads. In the figures, for illustrative purposes only, leads 22a, 22b, 22c, 22d, and 22e are shown. For convenience, the leads 22a, 22b, 22c, 22d, and 22e are collectively referred to as leads 22 in this document. The leads 22a, 22b, 22c, 22d, and 22e are electrically isolated from each other. To avoid clutter, not all instances of the leads 22 are illustrated with a reference numeral in the Figures. The leadframe 20 includes a top side 24 and a bottom side 26. Further, a portion 28 of the leadframe 20 defines a mounting pad 28. The mounting pad 28 is a portion of the leadframe 20 (including a portion of the first lead 22a) where an LED assembly 50 is mounted. Typically the mounting pad 28 is generally located proximal to center of the top side 24 of the leadframe 20. In alternative embodiments of the present invention, the LED assembly 50 can be replaced by other semiconductor circuits or chips. The leadframe 20 is made of electrically conductive material and is generally thin. In one embodiment the leadframe 20 has thickness in order of thousandths or hundredths of inches, and for example, ranges from 0.005 inches to 0.010 inches.

[0019] The bottom heatsink 30 is coupled to the bottom side 26 of the leadframe 20 at least under the mounting pad 28. The bottom heatsink 30 is made of thermally conductive material and is thermally coupled to the bottom side 26 of the leadframe 20 but is electrically separated from the leadframe 20. The bottom heatsink 30 has a top surface 32 thermally coupled to but is electrically separated from the leadframe 20, the electrical separation can be accomplished by using a dielectric layer between the leadframe 20 and the bottom heatsink 30, for example, adhesive filled with ceramic particles. The bottom heatsink 30 has a bottom surface 34 defining a bottom plane for the light emitting die package 10. The bottom surface 34 of the bottom heatsink 30 can include a metalized bottom as illustrated in Figure 1B. As illustrated, the leads 22 are bent toward the bottom plane, terminating proximal to the bottom plane.

[0020] The top heatsink 40 is coupled to the top side 24 of the leadframe 20. The top heatsink 40 defines an opening 42, the opening 42 generally surrounding the mounting pad 28. The top heatsink 40 is made of thermally conductive material and is thermally coupled to the top side 24 of the leadframe 20 but is electrically separated from the leadframe 20, the electrical separation can be accomplished by using a dielectric layer between the leadframe 20 and the bottom heatsink 40. The bottom heatsink 30 and the top heatsink 40 have generally similar lateral dimensions, or extents, and substantially overlap each other sandwiching the leadframe 20 between them. The top heatsink 40 and the bottom heatsink 30 are made with thermally conductive material such as, for example only, copper, aluminum, or ceramics material.

[0021] The light emitting die package 10 includes the LED assembly 50 including at least one light emitting device (LED) mounted on the mounting pad. In Figure 2, the LED assembly 50 is illustrated as having four light emitting diodes. The LEDS are adapted to generate light when energized.

[0022] The light emitting die package 10 includes a reflector 60 coupled to the top heatsink 40, the reflector 60 surrounding the mounting pad 28. In an alternative embodiment, the reflector 60 is not a separate component but is integrated with and is a portion of the top heatsink 40. The reflector 60 is adapted to reflect light from the LED assembly 50 toward a lens 70.

[0023] The light emitting die package 10 includes the lens 70 coupled to the top heatsink 40, the lens 70 coupled generally over the opening 42, the mounting pad 28, and over the reflector 60. When the lens 70 is placed over the opening 42, an enclosed cavity 44 is defined by the leadframe 20, the opening 42 of the top heatsink 40, and the lens 70. The lens 70 operates on the light generated by the LED assembly 50 by, for example, reflecting, directing, focusing, and alter wavelength. For example, a bottom surface 72 of the lens 70 can be coated with calcium carbonate to diffuse the light. Alternately, the bottom surface 72 of the lens 70 can be coated with phosphors to alter wavelengths of light from the LED assembly 50.

[0024] The enclosed cavity 44 is filled by clear encapsulant such as Silicone. The encapsulant affixes the LED assembly 50 to the mounting pad 28. The enclosed cavity 44 need not be completely filled with the encapsulant. In fact, partially filling the cavity 44 with encapsulant while leaving gaps within the cavity 44 allows the encapsulant to expand (when heat is generated by the LED assembly 50) without separating the lens 70 from the top heatsink 40.

[0025] The method of manufacturing the light emitting die package 10 of Figures 1A through 2 can be discussed using Figure 3. Figure 3 illustrates the light emitting die package 10 of Figure 1A before it is manufactured. To manufacture the light emitting die package 10 of Figure, a leadframe die 80 is fabricated. For illustratively purposes, in Figure 2, the leadframe die 80 is fabricated for manufacturing of two light emitting die packages. In fact, a leadframe die can be fabricated to manufacture multiple light emitting die packages simultaneously. The leadframe die 80 includes a plurality of leads, for example, the leads 22a, 22b, 22c, 22d, and 22e (collectively, "leads 22") and a die frame 82 surrounding the leads 22. The leadframe die has a top side 24 (that is the same side as the top side 24 of leadframe 20 of Figure 2) and a bottom side 26 (that is the same side as the bottom side 26 of leadframe 20 of Figure 2). The leadframe die 80 is fabricated by stamping a sheet of die material such as metal. The thickness of the die material may vary greatly depending on the desired application, for example, the thickness may be in the order of fractions of millimeters (mm), for example, ranging from 0.13 mm to 0.25 mm. Alternately, the leadframe die 80 can be fabricated using etching processes.

[0026] Referring to Figures 2 and 3, the top heatsink 40 is coupled to the leadframe die 80. As already described, the top heatsink 40 defined the opening 42. The bottom heatsink 30 is coupled to the bottom side of the leadframe die 80. The bottom heatsink 30 has a top surface 32 thermally coupled to but is electrically separated from the leadframe die 80. As illustrated in Figure 1B, the bottom heatsink 30 has a metalized bottom surface 34 defining a bottom plane for the light emitting die package 30. Dielectric but thermally conductive adhesive layer 38 of Figure 3 may be used to separate the bottom heatsink 30 from the leadframe 20.

[0027] The top heatsink 40 and the bottom heatsink 30 have similar lateral extents and substantially overlap each other. For example, the later extents 33 and 35 of the bottom heatsink 30 may vary widely depending on the implementation, for example only, the lateral extents 33 and 35 may be in the order of mm or centimeters (cm), and may range from, for example, seven mm to 20 mm. The bottom heatsink 30 and the top heatsink 40 may have thicknesses in the order of mm or cm, and may range from, for example, 1.5 mm to three mm. These measurements may vary greatly depending on various desired characteristics and applications.

[0028] Referring to Figures 2 and 3, the method of manufacturing the light emitting die package 10 is further discussed. The LED assembly 50 including at least one light emitting device (LED) such as a light emitting diode is mounted on at least one lead, such as the lead 22a, within the opening 42. Then, the reflector 60 and the lens 70 are attached on the top heatsink 40, the lens 70 covering the opening 42. The reflector 60 surrounds the opening 42. The reflector 60 may be integrated with the top heatsink 40 in which case there is no need for a separate step of coupling the reflector 60 with the top heatsink 40.

[0029] Finally, the leadframe die 80 is stamped to cut away the die frame 82. During the stamping, the leads 22 are bent towards the bottom plane as illustrated in Figures 1A through 2.

[0030] From the foregoing, it will be apparent that the present invention offers advantages over the current art. Although specific embodiments of the invention are described and illustrated above, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The invention is limited by the claims that follow.

Claims

1. A light emitting die package (10) comprising:

a leadframe (20) including a plurality of leads, said leadframe (20) having a top side (24) and a bottom side (26), and a portion of said leadframe (20) defining a mounting pad (28);

wherein the package body is a two-part heatsink, the two parts sandwiching said leadframe (20), the two-part heatsink comprising:

a first part being a bottom heatsink (30) made of a thermally conductive material and coupled to the bottom side (26) of said leadframe (20), said bottom heatsink (30) having a top surface (32) thermally coupled to but electrically separated from said leadframe (20); and

a second part being a top heatsink (40) made of a thermally conductive material and thermally coupled to the top side (24) of said leadframe (20), said top heatsink (40) defining an opening (42), the opening (42) extending from a main surface of the top heatsink (40) to the opposite main surface of the top heatsink (40) and generally surrounding the mounting pad (28);

wherein said top heatsink (40) and said bottom heatsink (30) have similar lateral extents and substantially overlap each other;

characterized in that

at least one of said top heatsink (40) and said bottom heatsink (30) is made of copper or aluminum.

2. The light emitting die package (10) of claim 1 further comprising a lens (70) covering said mounting pad (28).

3. The light emitting die package (10) of claim 1 wherein said leadframe (20) has lateral dimensions that are approximately a same dimension as said top heatsink (40) and said bottom heatsink (30) in a first direction and that are a larger dimension than said top heatsink (40) and said bottom heatsink (30) in a second direction.

4. The light emitting die package (10) of claim 1 wherein said top heatsink (40) is electrically separated from said leadframe (20) by a dielectric layer positioned between said leadframe (20) and said top heatsink (40).

5. The light emitting die package (10) of claim 1 wherein said bottom heatsink (30) is electrically separated from said leadframe (20) by a dielectric layer (38) positioned between said leadframe (20) and said bottom heatsink (30).

6. The light emitting die package (10) of claim 5 wherein the dielectric layer (38) positioned between said leadframe (20) and said bottom heatsink (30) comprises a dielectric but thermally conductive adhesive layer.

7. The light emitting die package (10) of claim 1 further comprising at least one light emitting device (50) mounted on the mounting pad (28).

8. The light emitting die package (10) of claim 7 wherein at least a portion of the top heatsink (40) comprises a reflector (60) adapted to reflect light from the at least one light emitting device (50) towards a lens (70).

9. The light emitting die package (10) of claim 8 wherein a bottom surface (72) of the lens (70) is coated with a phosphor.

Ansprüche

1. Gehäuse für Licht emittierenden Chip (10), das Folgendes umfasst:

einen Leiterrahmen (20), der mehrere Anschlussdrähte umfasst, wobei der Leiterrahmen (20) eine Oberseite (24) und eine Unterseite (26) aufweist, und wobei ein Abschnitt des Leiterrahmens (20) ein Montage-Pad (28) definiert;

wobei der Gehäuse-Korpus eine zweiteilige Wärmesenke ist, wobei die zwei Teile den Leiterrahmen (20) zwischen sich aufnehmen, wobei die zweiteilige Wärmesenke Folgendes umfasst:

einen ersten Teil, der eine untere Wärmesenke (30) ist, die aus einem wärmeleitfähigen Material besteht und mit der Unterseite (26) des Leiterrahmens (20) gekoppelt ist, wobei die untere Wärmesenke (30) eine Oberseite (32) aufweist, die thermisch mit dem Leiterrahmen (20) gekoppelt, aber elektrisch von diesem getrennt ist; und

einen zweiten Teil, der eine obere Wärmesenke (40) ist, die aus einem wärmeleitfähigen Material besteht und thermisch mit der Oberseite (24) des Leiterrahmens (20) gekoppelt ist, wobei die obere Wärmesenke (40) eine Öffnung (42) definiert, wobei sich die Öffnung (42) von einer Hauptfläche der oberen Wärmesenke (40) zu der gegenüberliegenden Hauptfläche der oberen Wärmesenke (40) erstreckt und allgemein das Montage-Pad (28) umgibt;

wobei die obere Wärmesenke (40) und die untere Wärmesenke (30) ähnliche seitliche Erstreckungen haben und sich einander im Wesentlichen überlappen;

dadurch gekennzeichnet, dass mindestens eine der oberen Wärmesenke (40) und der unteren Wärmesenke (30) aus Kupfer oder Aluminium besteht.

2. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 1, das des Weiteren eine Linse (70) umfasst, die das Montage-Pad (28) bedeckt.

3. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 1, wobei der Leiterrahmen (20) seitliche Abmessungen hat, die ungefähr eine gleiche Abmessung sind wie die obere Wärmesenke (40) und die untere Wärmesenke (30) in einer ersten Richtung, und die eine größere Abmessung als die obere Wärmesenke (40) und die untere Wärmesenke (30) in einer zweiten Richtung sind.

4. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 1, wobei die obere Wärmesenke (40) elektrisch von dem Leiterrahmen (20) durch eine dielektrische Schicht getrennt ist, die zwischen dem Leiterrahmen (20) und der oberen Wärmesenke (40) positioniert ist.

5. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 1, wobei die untere Wärmesenke (30) elektrisch von dem Leiterrahmen (20) durch eine dielektrische Schicht (38) getrennt ist, die zwischen dem Leiterrahmen (20) und der unteren Wärmesenke (30) positioniert ist.

6. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 5, wobei die dielektrische Schicht (38), die zwischen dem Leiterrahmen (20) und der unteren Wärmesenke (30) positioniert ist, eine dielektrische, aber wärmeleitfähige Klebeschicht umfasst.

7. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 1, das des Weiteren mindestens eine Licht emittierende Vorrichtung (50) umfasst, die auf dem Montage-Pad (28) montiert ist.

8. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 7, wobei mindestens ein Abschnitt der oberen Wärmesenke (40) einen Reflektor (60) umfasst, der dafür ausgelegt sind, Licht von der mindestens einen Licht emittierenden Vorrichtung (50) in Richtung einer Linse (70) zu reflektieren.

9. Gehäuse für Licht emittierenden Chip (10) nach Anspruch 8, wobei eine Unterseite (72) der Linse (70) mit einem Phosphor beschichtet ist.

Revendications

1. Boîtier de puces électroluminescentes (10) comprenant :

une grille de connexion (20) comportant une pluralité de conducteurs, ladite grille de connexion (20) présentant un côté supérieur (24) et un côté inférieur (26), et une partie de ladite grille de connexion (20) définissant une plage d'accueil (28) ;

dans lequel le corps du boîtier est un dissipateur thermique en deux parties, les deux parties prenant en sandwich ladite grille de connexion (20), le dissipateur thermique en deux parties comprenant :

une première partie qui est un dissipateur thermique inférieur (30), constitué d'un matériau thermoconducteur et couplé au côté inférieur (26) de ladite grille de connexion (20), ledit dissipateur thermique inférieur (30) présentant une surface supérieure (32) couplée thermiquement à ladite grille de connexion (20), mais séparée électriquement de celle-ci ; et

une seconde partie qui est un dissipateur thermique supérieur (40), constitué d'un matériau thermoconducteur et couplé thermiquement au côté supérieur (24) de ladite grille de connexion (20), ledit dissipateur thermique supérieur (40) définissant une ouverture (42),

l'ouverture (42) s'étendant d'une surface principale du dissipateur thermique supérieur (40) à la surface principale opposée du dissipateur thermique supérieur (40) et entourant sensiblement la plage d'accueil (28) ;

dans lequel ledit dissipateur thermique supérieur (40) et ledit dissipateur thermique inférieur (30) ont des étendues latérales similaires et se chevauchent sensiblement ;

caractérisé en ce que :

au moins l'un dudit dissipateur thermique supérieur (40) et dudit dissipateur thermique inférieur (30) est constitué de cuivre ou d'aluminium.

2. Boîtier de puces électroluminescentes (10) selon la revendication 1, comprenant en outre une lentille (70) recouvrant ladite plage d'accueil (28).

3. Boîtier de puces électroluminescentes (10) selon la revendication 1, dans lequel ladite grille de connexion (20) a des dimensions latérales qui sont sensiblement identiques à la dimension dudit dissipateur thermique supérieur (40) et dudit dissipateur thermique inférieur (30) dans une première direction, et qui sont sensiblement plus grandes que ledit dissipateur thermique supérieur (40) et ledit dissipateur thermique inférieur (30) dans une seconde direction.

4. Boîtier de puces électroluminescentes (10) selon la revendication 1, dans lequel ledit dissipateur thermique supérieur (40) est séparé électriquement de ladite grille de connexion (20) par une couche diélectrique positionnée entre ladite grille de connexion (20) et ledit dissipateur thermique supérieur (40).

5. Boîtier de puces électroluminescentes (10) selon la revendication 1, dans lequel ledit dissipateur thermique inférieur (30) est séparé électriquement de ladite grille de connexion (20) par une couche diélectrique (38) positionnée entre ladite grille de connexion (20) et ledit dissipateur thermique inférieur (30).

6. Boîtier de puces électroluminescentes (10) selon la revendication 5, dans lequel la couche diélectrique (38) positionnée entre ladite grille de connexion (20) et ledit dissipateur thermique inférieur (30) comprend une couche adhésive diélectrique mais thermoconductrice.

7. Boîtier de puces électroluminescentes (10) selon la revendication 1, comprenant en outre au moins un dispositif électroluminescent (50), monté sur la plage d'accueil (28).

8. Boîtier de puces électroluminescentes (10) selon la revendication 7, dans lequel au moins une partie du dissipateur thermique supérieur (40) comprend un réflecteur (60) adapté pour réfléchir la lumière provenant dudit au moins un dispositif électroluminescent (50) vers une lentille (70).

9. Boîtier de puces électroluminescentes (10) selon la revendication 8, dans lequel une surface inférieure (72) de la lentille (70) est revêtue d'un phosphore.

Drawing