Title: LED package die having a small footprint
Abstract: A light emitting die package and a method of making the light emitting die package are disclosed. The die package includes a stem substrate having grooves, a wire lead attached to the grooves, and a light emitting diode (LED) mounted on the stem substrate. Also coupled to the substrate are a sleeve, a reflector, and a lens. To make the light emitting die package, a long substrate is formed and wire leads attached to the substrate. Then, the substrate including the attached wire leads is cut to predetermine lengths to form individual stem substrates. To each stem substrate, LED, reflector, and lens are coupled.
Patent Number: 6,897,486 Issued on 05/24/2005 to Loh
| Inventors:
|
Loh; Ban P. (8 Trescott Dr., Durham, NC 27703)
|
| Appl. No.:
|
721641 |
| Filed:
|
November 25, 2003 |
| Current U.S. Class: |
257/81; 257/99 |
| Intern'l Class: |
H01L 029/26.7 |
| Field of Search: |
257/81,82,88,99,98,706,707
|
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| Foreign Patent Documents |
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| 2003298117 | Oct., 2003 | JP.
| |
Other References
U.S. Appl. No. 10/446,532, filed May 27, 2003, Ban P. Loh, Power surface mount
light emitting die package, Publication date; Mar. 4, 2004.
U.S. Appl. No. 10/692,351, filed Oct. 22, 2003, Peter Scott Andrews, Ban P. Loh,
Durham, Power surface mount light emitting die package, Published date; Apr. 29, 2004.
U.S. Appl. No. 10/721,654, filed Nov. 25, 2003, Ban P. Loh, Composite leadframe
LED package and method of making the same, Publication date: Jul. 1, 2004.
U.S. Appl. No. 10/861,929, filed Jun. 4, 2004, Ban P. Loh, Gerald H. Negley,
Power light emitting die package with reflecting lens and the method of making
the same, Publication date: Not yet published.
U.S. Appl. No. 10/861,639, filed Jun. 4, 2004, Ban P. Loh, Gerald H. Negley,
Composite optical lens with an integrated reflector, Published date; Not yet published.
|
Primary Examiner: Clark; S. V.
Attorney, Agent or Firm: Silicon Edge Law Group LLP, Chung; D. James
Parent Case Text
PRIORITY
This application claims the benefit of the filing date of U.S. Provisional Patent
Application No. 60/431,501 filed Dec. 6, 2002 entitled "LED package with a long
stem body as heat-spreader and a small footprint" under 35 USC section 119, section
120, or both.
Claims
1. A light emitting die package comprising:
a stem substrate having a first end surface and a second end surface, said stem
substrate defining at least one groove;
a wire lead running along the groove of said stem substrate, the wire lead terminating
at the first end surface; and
a light emitting diode (LED) mounted on the first end surface, the LED making
electrical and thermal contact with said stem substrate, the LED also connected
to the wire lead.
2. The light emitting die package recited in claim 1 wherein said stem substrate
comprises electrically and thermally conductive material.
3. The light emitting die package recited in claim 1 wherein said wire lead is
positioned within the groove but electrically insulated from the stem substrate
by wire lead insulation.
4. The light emitting die package recited in claim 3 wherein a portion of the
wire lead insulation is stripped exposing a portion of the lead wire.
5. The light emitting die package recited in claim 1 further comprising a sleeve
surrounding said stem substrate proximal to the first end surface, said sleeve
defining an opening at the first end surface.
6. The light emitting die package recited in claim 5 wherein said sleeve defines
a ledge adapted to couple a lens that, when mounted on the ledge, aligns the lens
with lights from said LED.
7. The light emitting die package recited in claim 5 further comprising a lens
coupled to said sleeve, said lens adapted for optical imaging function.
8. The light emitting die package recited in claim 7 wherein said lens includes
a bottom surface coated with material for operating on light generated by the LED.
9. The light emitting die package recited in claim 7 wherein the lens encloses
the opening thereby forming a cavity, the cavity at least partially filled by encapsulating material.
10. The light emitting die package recited in claim 5 wherein the opening is
filled with encapsulant and capped with a lens movably coupled to said sleeve on
the encapsulant.
11. The light emitting die package recited in claim 5 wherein said wire lead
is positioned within the groove but electrically insulated from the stem substrate
by wire lead insulation.
12. The light emitting die package recited in claim 11 wherein a portion of the
wire lead insulation is stripped exposing a portion of the lead wire.
13. The light emitting die package recited in claim 5 further comprising a reflector
coupled to said sleeve, said reflector surrounding the opening and is adapted to
reflect light from the LED.
14. The light emitting die package recited in claim 5 wherein said sleeve includes
an integrated reflector surface.
15. The light emitting die package recited in claim 1 wherein the LED is connected
to the wire lead using a connection selected from a group consisting of bond wire,
solder, and ball-grid-array connection.
16. A light emitting die package array comprising:
an array housing including an external heatsink and reflector bowl, said array
housing defining die package spaces;
a plurality of light emitting die packages mounted in the die package spaces,
each light emitting die comprising:
a stem substrate having a first end surface and a second end surface, said stem
substrate defining at least one groove;
a wire lead mounted on the groove of said stem substrate, the wire lead terminating
at the first end surface; and
a light emitting diode (LED) mounted on the first end surface making electrical
and thermal contact with said stem substrate, the LED also connected to the wire
lead.
17. The light emitting die package array recited in claim 16 wherein the external
heat sink is thermally connected to the mounted light emitting die packages.
18. The light emitting die package array recited in claim 16 wherein, for each
light emitting die package, said wire lead is positioned within the groove but
electrically insulated from the stem substrate by wire lead insulation.
19. The light emitting die package array recited in claim 16 wherein each light
emitting die package further comprises a sleeve surrounding said stem substrate
proximal to the first end surface, said sleeve defining an opening at the first
end surface.
20. The light emitting die package array recited in claim 19 wherein each light
emitting die package further comprises a reflector coupled to said sleeve, said
reflector surrounding the first end surface.
21. The light emitting die package array recited in claim 16 wherein each light
emitting die package further comprises a lens coupled to said sleeve, said lens
covering the opening.
Description
BACKGROUND
The present invention relates to the field of packaging semiconductor devices,
and more particularly to packaging light emitting diodes.
Light emitting diodes (LEDS) such as light emitting diodes are often packaged
within leadframe packages. A leadframe package typically includes a molded plastic
body which encapsulates an LED, a lens portion, and thin metal leads connected
to the LED and extending 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. A portion of the leads extends
out from the package body for connection to circuits external to the leadframe package.
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 thereby limiting the
amount of light that can be generated by the LED.
To increase the capacity of an LED package to dissipate heat, in one LED package
design, the LED is placed 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, the LED-in-cavity design is relatively difficult and costly to manufacture.
Further, the heat dissipation is limited because of its limited exposed surface
(the bottom surface only).
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.
Another undesirable aspect of the current leadframe package designs relates
to problems associated 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 adversely affecting its reliability.
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
The need is met by the present invention. In a first embodiment of the present
invention, a light emitting die package includes a stem substrate, a wire lead,
and a light emitting diode (LED) mounted on the stem substrate. The stem substrate
has a first end surface and a second end surface and defines at least one groove.
The wire lead runs along the groove of the stem substrate, terminating at the first
end surface. The light emitting diode (LED) mounted is mounted on the first end
surface. The LED makes electrical and thermal contact with the stem substrate.
The LED is also connected to the wire lead.
In a second embodiment of the present invention, a light emitting die package
array includes an array housing having an external heatsink and reflector bowl.
The array housing defines die package spaces. A plurality of light emitting die
packages mounted in the die package spaces, each light emitting die having a light
emitting die package includes a stem substrate, a wire lead, and a light emitting
diode (LED) mounted on the stem substrate. The stem substrate has a first end surface
and a second end surface and defines at least one groove. The wire lead runs along
the groove of the stem substrate, terminating at the first end surface. The light
emitting diode (LED) mounted is mounted on the first end surface. The LED makes
electrical and thermal contact with the stem substrate. The LED is also connected
to the wire lead.
In a third embodiment of the present invention, a method of manufacturing a light
emitting die package is disclosed. First, a stem substrate rod having a predetermined
length is fabricated, the stem substrate rod defining at least one groove. Wire
leads are attached on the groove of the stem substrate rod. Next, the stem substrate
rod including the attached wire leads are cut to a predetermined length thereby
forming an individual stem substrate. The individual stem substrate is planarized
to form a first end surface. A light emitting diode (LED) is mounted on the first
end surface, the LED making electrical and thermal contact with the stem substrate,
the LED also connected to the wire lead.
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 way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a light emitting die package according to one
embodiment of the present invention;
FIG. 2 is an exploded perspective view of the light emitting die package of
FIG. 1;
FIG. 3 is a top view of the light emitting die package of FIG. 1;
FIG. 4 is a cut-away side view of the light emitting die package of FIG. 1 cut
along line A—A as illustrated in FIG. 3; and
FIGS. 5A through 5D illustrate, respectively, a top view, side view, bottom
view, and a cutaway side view of the light emitting die of FIG. 1.
DETAILED DESCRIPTION
The present invention will now be described with reference to the FIGS. 1 through
4, which illustrate various embodiments of the present invention. As illustrated
in the Figures, some sizes of structures or portions are exaggerated relative to
other structures or portions 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.
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 stem substrate,
wire leads, and a light emitting diode. The stem substrate has a first end surface
and a second end surface and defines at least one groove. The wire leads are attached
to the groove of the stem substrate, terminating at the first end surface. The
light emitting diode is mounted on the first end surface and makes making electrical
and thermal contact with the stem substrate. The LED is also connected to the wire lead.
The stem substrate forms the body of the die package and draws heat away from
the LED (as opposed to merely the wire leads drawing heat away from the LED as
implemented in the prior art). Because the stem substrate is relatively much thicker
than the wire leads, the heat dissipation capacity is greater than the prior art
designs. The stem substrate provides for a relatively huge thermal mass and effective
heat-spreading capability along its entire length. Accordingly, 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 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.
Furthermore, whereas much of the prior art LED packages are flat and
all their leads and heat sink are connected in the top face or in the same plane
as the optical system. This has a disadvantage of occupying valuable area, or "real
estate" on a printed circuit board that drive a package. The light emitting die
package of the present invention has a step shape with a relatively long body and
a relatively small footprint. The small footprint allows more units be packed as
cluster to produce high intensity light source for illumination applications similar
to conventional light sources such as incandescent light or halogen light bulbs.
FIG. 1 is a perspective view of a light emitting die package
10 according
to one embodiment of the present invention. FIG. 2 is an exploded perspective view
of the light emitting die package
10 of FIG.
1. FIG. 3 is a top view
of portions of the light emitting die package
10. Specifically, FIG. 3 illustrates
a top view of the light emitting die package through a clear lens
70. FIG.
4 is a cut-away side view of the light emitting die package of FIG. 1 cut along
line A—A as illustrated in FIG.
3. Referring to FIGS. 1 through 4,
the light emitting die package
10 includes a stem substrate
20, wire
leads
30, and light emitting diode (LED) assembly
50.
The stem substrate
20 has a first end surface
22 and a second end
surface
24 and is made of electrically and thermally conductive material
such as, for example only, copper, aluminum, or ceramic materials. In some embodiments,
the first end surface
22 can be plated with precious metal to enable or
improve bonding with the LED assembly
50, but this is not required. The
stem substrate
20 defines at least one groove
26. In the Figures,
four grooves
26 are illustrated. The stem substrate can be formed by machining
or extrusion of copper, aluminum, or ceramics. The first end surface
22
can be plated or finished with metal that allows LED chip to attach and to bond.
The second end surface
24 may be plated, finished, or otherwise configured
for connecting to an external heat sink, external circuits, or both.
Each of the wire leads
30 runs along one of the grooves
26 defined
by the stem substrate
20. The wire leads terminate at the first end surface
22. In fact, as illustrated, the wire leads
30 may be positioned
within the grooves
26 since the grooves
26 in the illustrated embodiment
are sufficiently deep; however, the wire leads
30 are electrically isolated
from the stem substrate
20 by wire lead insulation material such as polyimides
wrapping each of the wire leads. A portion of the wire lead insulation of each
of the wire leads
30 are stripped, exposing a portion (exposed portion
32)
of the wire lead for electrical connection to external circuit. The wire leads
30 can be bonded to the stem substrate
20 using high-temperature
adhesive. The first end surface of the wire leads can be metalized, by plating
for example, for bonding by bond wires connecting it to the LEDS. In some embodiments,
depending on the size and the shape of the grooves
26, the wire leads
30
may require roll-forming. For example, the wire leads
30 may be magnet wires
which are insulated by plastic dielectric materials.
The LED assembly
50 includes at least one light emitting diode (LED) and
is mounted on the first end surface
22, the LEDS making electrical and thermal
contact with the stem substrate
20. In the Figures, for the purposes of
illustration, the LED assembly
50 is show with four LEDS. Each of the LEDS
is connected to one of the wire leads
30 using a bond wire
52. The
bond wires
52 are illustrated also in FIG.
3. Alternatively, the
LED may be connected to the wire lead using solder or ball-grid-array connections.
Continuing to refer to FIGS. 1 through 4, the light emitting die package
20 further includes a sleeve
40 surrounding the stem substrate
20
proximal to the first end surface
26. The sleeve
40 defines an opening
42 at and surrounding the first end surface
26. The sleeve includes
a ledge
46 adapted to couple the lens
70, when mounted on the ledge
46, aligns the lens
70 with light from the LED assembly
50.
The ledge
46 is also illustrated in FIG. 4 illustrating a cut-away side
view of the light emitting die package
10 of FIG. 1 cut along line A—A
as illustrated in FIG.
3.
The lens
70 is adapted for optical imaging functions such as, for example
only, diffusion, focusing, and wavelength shifting. The lens
70 operates
on the light generated by the LED assembly
50 by, for example, reflecting,
directing, focusing, and shifting wavelengths. 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 absorb light having a first wavelength and reemit the light at a second
wavelength. In fact, the bottom surface
72 of the lens
70 can be
configured for various optical operations. For example, it can be grooved to reflect
or refract light from the LED assembly
50. Likewise, the top dome surface
can also be used to operate on the light resulting in a predetermined radiation
pattern of the die package
10. The lens
70 can be made with high
temperature plastic or glass.
When the lens
70 is placed on the ledge
46 over the opening
42,
an enclosed cavity
44 is formed by the first surface
22 of the stem
substrate
20, the opening
42, and the lens
70. The enclosed
cavity
44 is at least partially filled by clear encapsulant such as Silicone.
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 sleeve
40. Further, the lens
70 is slightly movably coupled
to the sleeve
40 to allow the encapsulant to expend even further than the
expansion allowed by the gap. In an alternative embodiment, the cavity
44
is completely filled by the encapsulant so that there is no gap or air bubble within
the cavity
44. In this case, as the encapsulant expands due to heat generated
by the LED assembly
50, the lens is allowed slight up and down movements
to relieve the pressure caused by the expansion. The encapsulant is selected for
predetermined refractive index and other optical properties, physical properties,
or both.
The light emitting die package
10 includes a reflector
60 coupled
to the sleeve
40, the reflector
60, the reflector
60 surrounding
the opening
42 and is adapted to reflect light from the LEDS of the LED
assembly
50 by having a reflective surface angled such that the reflector
60 reflects light from the LED assembly
50 toward the lens
70.
The sleeve
40 operates to align both the reflector
60 and the lens
70 relative to the stem substrate
20. The reflector
60 can
be made of any reflective material or non-reflective material but with a high reflective
finish such as silver plating. The reflector
60 is electrically isolated
from the stem substrate
20. The reflector cup is mounted proximal to the
LED assembly
50 to direct all the light emitted by LED towards the lens.
In FIG. 4, measurements of the sample light emitting die package
10 are
illustrated. In the illustrated embodiment, the light emitting die package
10
has a height
28 in the order of millimeters (mm) or tens of mm, for example
13.25 mm and width, or diameter
29 in the example, in the order of mm, for
example, 5.6 mm.
The light emitting die package
10 can be grouped to form light emitting
die array
80 illustrated in FIGS. 5A through 5D where FIGS. 5A through 5D
illustrate, respectively, a top view, side view, bottom view, and a cutaway side
view of the light emitting die array
80.
Referring to FIGS. 5A through 5D, the light emitting die array
80
includes an array housing including an external heatsink
82 and reflector
bowl
84, the array housing defines die package spaces, or "holes," to receive
light emitting die packages
10. In the Figures, four light emitting die
packages
10 fill these reception holes. Each of these light emitting die
packages
10 are configured as illustrated in FIGS. 1-4.
FIGS. 1-4 can be used to describe the method of manufacturing the light emitting
die package
10. Referring again to FIGS. 1-4, to manufacture the light emitting
die package
10 of FIGS. 1-4, a relatively long piece of stem substrate rod
(not illustrated) is fabricated, the stem substrate rod defining at least one groove.
Relatively wire leads are attached to the grooves of the stem substrate rod. Then,
the stem substrate rod including the attached wire leads such as magnet wires are
cut to a predetermined length thereby forming an individual stem substrate
20
including the attached wire leads
30 as illustrated in FIGS. 1-4, the wire
leads already attached to the stem substrate
20. The individual stem substrate
including the attached wire leads
30 are planarized to form the first end
surface
22.
Then, the LED assembly
50 including at least one light emitting device
(LED) such as a light emitting diode is mounted on the first end surface
22,
the LED assembly
50 making electrical and thermal contact with the stem
substrate
20, the LED also connected to the wire lead via wire bonds
52.
The LED can be encapsulated in an encapsulant as discussed above. The sleeve
40
is attached to the stem substrate
20 proximal to the first end surface
22.
The sleeve defines the opening
42 at and around the first end surface
22.
The reflector
60 is then coupled to the sleeve
40, the reflector
surrounding the opening
42. Finally, the lens
70 is coupled to the
opening
42 of the sleeve
40. The exact order of these manufacturing
steps may vary and still be within the scope of the present invention.
From the foregoing, it will be apparent that the present invention is novel
and 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. For
example, differing configurations, sizes, or materials may be used to practice
the present invention. The invention is limited by the claims that follow.
*
