U.S. patent application number 12/211256 was filed with the patent office on 2009-01-08 for producing a surface-mountable radiation emitting component.
This patent application is currently assigned to Osram Opto Semiconductors GMBH, a Germany corporation. Invention is credited to Herbert Brunner, Klaus Hohn, Harald Jager, Josef Schmid.
Application Number | 20090011527 12/211256 |
Document ID | / |
Family ID | 7690112 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090011527 |
Kind Code |
A1 |
Brunner; Herbert ; et
al. |
January 8, 2009 |
PRODUCING A SURFACE-MOUNTABLE RADIATION EMITTING COMPONENT
Abstract
A radiation-emitting surface-mountable component has a
light-emitting diode chip mounted on a leadframe. A molding
material encapsulates the leadframe and the light emitting diode
chip.
Inventors: |
Brunner; Herbert;
(Regensburg, DE) ; Hohn; Klaus; (Taufkirchen,
DE) ; Jager; Harald; (Regensburg, DE) ;
Schmid; Josef; (Regensburg, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Osram Opto Semiconductors GMBH, a
Germany corporation
|
Family ID: |
7690112 |
Appl. No.: |
12/211256 |
Filed: |
September 16, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10747703 |
Dec 29, 2003 |
7436002 |
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12211256 |
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PCT/DE02/01514 |
Apr 25, 2002 |
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10747703 |
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Current U.S.
Class: |
438/26 ;
257/E33.059 |
Current CPC
Class: |
H01L 2224/48091
20130101; Y02P 70/50 20151101; H01L 2924/01077 20130101; H01L
2224/4848 20130101; H01L 2224/73265 20130101; H01L 24/32 20130101;
H01L 2924/01021 20130101; H01L 33/486 20130101; Y02P 70/613
20151101; H01L 2924/12041 20130101; H01L 24/73 20130101; H01L
2224/48465 20130101; H01L 2924/01057 20130101; H01L 2924/00014
20130101; H01L 2924/0102 20130101; H01L 2924/181 20130101; H05K
3/3426 20130101; H01L 2224/48247 20130101; H01L 2924/12042
20130101; H01L 2224/32245 20130101; H01L 33/62 20130101; H01L
2924/01078 20130101; H01L 33/54 20130101; H01L 2924/01079 20130101;
H01L 24/48 20130101; H01L 2224/48091 20130101; H01L 2924/00014
20130101; H01L 2224/4848 20130101; H01L 2224/48465 20130101; H01L
2224/48465 20130101; H01L 2224/48247 20130101; H01L 2924/00012
20130101; H01L 2224/48465 20130101; H01L 2224/48091 20130101; H01L
2924/00012 20130101; H01L 2224/73265 20130101; H01L 2224/32245
20130101; H01L 2224/48247 20130101; H01L 2924/00012 20130101; H01L
2224/48465 20130101; H01L 2224/48247 20130101; H01L 2924/00
20130101; H01L 2224/48465 20130101; H01L 2224/48091 20130101; H01L
2924/00 20130101; H01L 2924/00014 20130101; H01L 2224/45099
20130101; H01L 2924/00014 20130101; H01L 2224/05599 20130101; H01L
2924/12042 20130101; H01L 2924/00 20130101; H01L 2924/181 20130101;
H01L 2924/00012 20130101 |
Class at
Publication: |
438/26 ;
257/E33.059 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2001 |
DE |
DE 101 31 698.4 |
Claims
1. A method for producing a surface-mountable, radiation-emitting
component, the method which comprises the following steps: mounting
a radiation-emitting chip on a leadframe; preparing a molding
material from a resin powder prereacted with curing agent, and
optionally added further fillers; and encasing the leadframe and
the radiation-emitting chip with the molding material.
2. The method according to claim 1, wherein the step of preparing
the molding material comprises: mixing a resin powder, prereacted
with curing agent, with a conversion material and, optionally,
further fillers; and blending the mixture to provide a homogeneous
powder mixture.
3. The method according to claim 2, wherein the molding material is
a plastics compression molding material.
4. The method according to claim 1, which comprises encasing the
radiation-emitting chip such that light exit sides of the chip are
surrounded by the molding material.
5. The method according to claim 1, wherein the prereacted resin
powder consists of epoxy novolak or epoxy-cresol novolak.
6. The method according to claim 5, which comprises utilizing epoxy
resin prereacted with at least one of a phenol curing agent and an
anhydride curing agent.
7. The method according to claim 1, wherein the conversion material
is a luminescent pigment powder containing at least one inorganic
phosphor having a phosphor metal center M in a host lattice based
on the general formula A.sub.3B.sub.5X.sub.12.
8. The method according to claim 7, wherein the phosphor is YAG:Ce,
TAG:Ce, TbYAG:Ce, GdYAG:Ce, GdTbYAG:Ce or a mixture formed
therefrom.
9. The method according to claim 1, wherein the conversion material
is a luminescent pigment powder containing at a metal center M in a
sulfide, oxysulfide, borate, aluminate or metal chelate
complex.
10. The method according to claim 1, which comprises pre-drying the
luminescent pigment powder before mixing with the resin powder.
11. The method according to claim 1, which comprises providing a
resin initially in rod or tablet form, and milling the resin to
provide the resin powder.
12. The method according to claim 1, which comprises providing a
resin initially in rod or tablet form and milling the resin, prior
to mixing with the conversion material, to provide the resin
powder.
13. The method according to claim 1, which comprises mixing the
resin powder or the resin and the conversion material, and
optionally the further fillers, by first mixing the components
coarsely and then milling the mixture in a mill to form a very
fine, homogeneous powder.
14. The method according to claim 13, which comprises milling the
mixture in a ball mill.
15. The method according to claim 1, which comprises milling the
resin or the resin powder in a mill prior to mixing with the
conversion material, and optional further fillers.
16. The method according to claim 15, which comprises milling the
resin or the resin powder in a coffee grinder.
17. The method according to claim 1, which comprises mixing an
adhesion promoter with the conversion material.
18. The method according to claim 1, which comprises mixing an
adhesion promoter with the resin powder.
19. The method according to claim 18, which comprises mixing the
adhesion promoter in liquid form with the conversion material.
20. The method according to claim 18, wherein the adhesion promoter
is one of glycidyloxy-propyltrimethoxysilane and further
derivatives based on trialkoxysilane.
21. The method according to claim 1, which comprises mixing a
wetting agent with the conversion material, for improving a
wettability of surfaces of the conversion material
22. The method according to claim 1, which comprises adding at
least one monofunctional and polyfunctional polar agent which has
carboxyl, carboxylic ester, ether and alcohol groups and improves
the wettability of the surfaces of the conversion material for
modifying surfaces of the conversion material.
23. The method according to claim 1, which comprises admixing a
mold release agent or lubricant.
24. The method according to claim 23, which comprises admixing the
mold release agent or lubricant with the resin powder or prior to
mixing with the conversion material.
25. The method according to claim 23, wherein the mold release
agent is a solid wax-based mold release agent or a metal soap with
long-chain carboxylic acids.
26. The method according to claim 25, wherein the mold release
agent is a stearate.
27. The method according to claim 1, which comprises admixing
inorganic fillers for increasing a refractive index of the plastics
compression molding material.
28. The method according to claim 27, which comprises admixing
fillers comprising oxides selected from the group consisting of
TiO.sub.2, ZrO.sub.2, .alpha.-Al.sub.2O.sub.3, and other metal
oxides.
29. The method according to claim 1, which comprises mixing glass
particles with the molding material as filler.
30. The method according to claim 29, which comprises admixing
glass particles having a mean particle size less than 100
.mu.m.
31. The method according to claim 29, which comprises admixing
glass particles having a mean particle size less than 50 .mu.m.
32. The method according to claim 29, wherein a proportion of the
glass particles in the molding material lies between 0% by weight
and 90% by weight.
33. The method according to claim 29, wherein a proportion of the
glass particles in the molding material lies between 10% by weight
and 50% by weight.
34. The method according to claim 1, which comprises admixing an
antioxidant.
35. The method according to claim 34, wherein the antioxidant is
based on one of phosphite and sterically hindered phenols.
36. The method according to claim 1, which comprises admixing a UV
light stabilizer.
37. The method according to claim 1, which comprises providing a
molding material with the following constituents: resin powder
.gtoreq.60% conversion material .gtoreq.0% and .ltoreq.40% adhesion
promoter .gtoreq.0% and .ltoreq.3% mold release agent .gtoreq.0%
and .ltoreq.2% surface modifier .gtoreq.0% and .ltoreq.5%
antioxidant .gtoreq.0% and .ltoreq.5% UV light stabilizer
.gtoreq.0% and .ltoreq.2% glass particles .gtoreq.0% and
.ltoreq.80%.
38. The method according to claim 37, which comprises adjusting the
conversion material in the molding material to >10% and
.ltoreq.25%.
39. The method according to claim 1, wherein the step of encasing
the leadframe comprises injection molding or injection compression
molding.
40. The method according to claim 39, which comprises mounting the
radiation-emitting chip on a leadframe, introducing the
radiation-emitting chip and a portion of the leadframe into an
injection mold, liquefying the molding material, and injecting the
molding material into the injection mold.
41. The method according to claim 39, which comprises preheating
the leadframe prior to the encasing step.
42. The method according to claim 1, wherein the encasing step
comprises encapsulating a plurality of leadframes, each having at
least one radiation-emitting chip mounted thereon, with a cohesive
covering and subsequently dividing into individual components.
43. The method according to claim 42, wherein the dividing step
comprises a process selected from the group consisting of breaking,
sawing, laser cracking, or water jet sawing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/747,703, filed Dec. 29, 2003, which is a continuation
of International Application No. PCT/DE02/01514, filed Apr. 25,
2002, which claims the benefit of priority under 35 U.S.C. .sctn.
119 of German Patent Application No. DE 101 31 698.4, filed Jun.
29, 2001. The disclosure of each prior application is incorporated
herein by reference.
BACKGROUND
[0002] The invention relates to a surface-mountable
radiation-emitting component and a process for its production.
[0003] German published patent application DE 38 04 293 discloses a
white light source based on a semiconductor LED. Described therein
is a configuration which has electroluminescence or a laser diode
and wherein the emission spectrum emitted by the diode is shifted
toward greater wavelengths by means of a plastics element to which
a phosphorescent, light-converting organic dye has been added. The
light emitted by the configuration thus has a color differing from
that of the light emitted by the light-emitting diode. Depending on
the type of dye added in the plastic, light-emitting diode
configurations which luminesce in different colors can be produced
using one and the same light-emitting diode type.
[0004] WO 98/12757 describes a wavelength-converting potting
compound for an electroluminescent component having a body which
emits ultraviolet, blue or green light and is based on a
transparent epoxy resin and to which a phosphor, in particular an
inorganic luminescent pigment powder comprising luminescent
pigments from the group consisting of the phosphors, has been
added. A preferred embodiment described is a white light source
wherein a radiation-emitting semiconductor LED based on GaAlN,
having an emission maximum between 420 nm and 460 nm, is used
together with a phosphor which is chosen so that a blue radiation
emitted by the semiconductor body is converted into complementary
wavelength ranges, in particular blue and yellow, or into additive
color triplets, e.g. blue, green and red. Here, the yellow or the
green and the red light is 20 produced by the phosphors. The hue
(hue in the CIE color table) of white light produced in this manner
can be varied by a suitable choice of the phosphor or phosphors
with regard to mixing and concentration.
[0005] Similarly, published international application WO 98/54929
discloses a semiconductor element emitting visible light and having
a UV/blue LED which is arranged in a depression in a support body
whose surface has a light-reflecting layer and is filled with a
transparent material which surrounds the LED on its light exit
sides. For improving the light output, the transparent material has
a refractive index which is lower than the refractive index of the
optically active region of the LED.
[0006] In these prior art designs, a pre-housed component is first
produced by surrounding a prefabricated leadframe with a suitable
plastics material by injection molding. The plastics material forms
the housing of the component. The component has, at the top, a
depression into which leadframe connections are introduced from two
opposite sides, onto one of which connections a semiconductor LED
is adhesively bonded and electrically contacted. A potting compound
to which the phosphor has been added, as a rule a transparent epoxy
resin, is then introduced into this depression.
[0007] The advantage of the prior designs is that very directed
emission can be achieved by virtue of the fact that the side walls
formed by the plastics housing can be in the form of inclined
reflectors. In the applications wherein, however, such directed
emission is not absolutely essential or is achievable in another
way, the production process is relatively complicated and
multistage, since the housing plastic and potting compound are
formed from two different materials and have to be shaped in
separate process steps. In addition, the problem of sufficient and
thermally stable adhesion between the potting compound and the
housing plastic always has to be solved. In practice, this
constantly leads to problems, particularly with the use of high
light powers.
[0008] In many potential applications for light-emitting diodes,
such as, for example, in display elements in the automobile
dashboard area, lighting in aircraft and automobiles and in
full-color LED displays, there is increasingly a need for
light-emitting diode configurations by means of which multicolored
light, in particular white light, can be produced. As large an area
of the color space as possible should be covered with regard to the
color of the light produced. There is often a need for lighting and
display elements which emit light having an exactly predetermined
color location and an exactly predetermined color saturation.
SUMMARY
[0009] It is accordingly an object of the invention to provide a
surface-mountable radiation emitter component and a corresponding
production method which overcome the abovementioned disadvantages
of the heretofore-known devices and methods of this general
type.
[0010] With the foregoing and other objects in view there is
provided, in accordance with the invention, a surface-mountable
radiation-emitting component with a commonly encased leadframe and
a radiation-emitting chip. The component comprises:
[0011] a leadframe and a radiation-emitting chip mounted on the
leadframe;
[0012] a molding material encasing the leadframe and the
radiation-emitting chip and having a shape defining a mounting
surface of the component, the mounting surface extending at a first
predetermined angle relative to a main emission direction of the
component;
[0013] the leadframe having leadframe connections protruding out of
the molding material and having connection surfaces enclosing a
second predetermined angle with the mounting surface.
[0014] With the above and other objects in view there is also
provided, in accordance with the invention, a method for producing
a surface-mountable, radiation-emitting component, the method which
comprises the following steps:
[0015] mounting a radiation-emitting chip on a leadframe;
[0016] preparing a molding material from a resin powder prereacted
with curing agent, and optionally added further fillers; and
[0017] encasing the leadframe and the radiation-emitting chip with
the molding material.
[0018] Accordingly, the invention describes a surface-mountable
radiation-emitting component having a radiation-emitting chip which
is mounted on a leadframe, the leadframe and the radiation-emitting
chip being surrounded by a molding material which is shaped in such
a way that the component has a mounting surface which is arranged
at a first predetermined angle relative to a main emission
direction of the component. The leadframe has leadframe connections
which lead out from the molding material and have connection
surfaces which are arranged at a second predetermined angle
relative to the mounting surface.
[0019] The radiation-emitting chip may be a light-emitting diode
chip such as, for example, a semiconductor LED or a semiconductor
laser. Preferably, this chip emits electromagnetic radiation in the
ultraviolet or blue spectral range.
[0020] In a preferred embodiment of the invention, the main
emission direction and the mounting surface are arranged parallel
so that the first angle is O.degree.. The component is in the form
of a so-called lateral emitter which emits predominantly parallel
to the mounting surface or, in the installed state, to a support
plate, for example a circuit board, on which the component is
fastened. Such an emission characteristic is advantageous,
particularly for lateral light input into a display to be
illuminated, for example an LCD display, and permits a very flat
design. The leadframe is preferably arranged so that the connection
surfaces of the leadframe connections are perpendicular to the
mounting surface or are arranged at approximately a right angle to
the mounting surface, so that the second predetermined angle is
90.degree. or, for example, is between 70.degree. and 90.degree..
Furthermore, the first predetermined angle may also be, for
example, between O.degree. and 20.degree., so that the component
emits laterally without the main emission direction being oriented
parallel to the mounting surface.
[0021] Alternatively, the main emission direction may also be
arranged perpendicular to the mounting surface so that the first
predetermined angle is 90.degree.. A similar configuration having a
first predetermined angle between 70.degree. and 90.degree. is
likewise possible. In this case, a parallel or approximately
parallel configuration of the connection surfaces of the leadframe
relative to the mounting surfaces with a second predetermined angle
between O.degree. and 20.degree. is advantageous. Said angle ranges
do not of course restrict the invention.
[0022] A further advantage of a component which has a
radiation-emitting chip mounted on a leadframe and is surrounded by
a molding material is a very compact design and very little space
requirement of the component in combination with good heat removal.
Very tightly packed modules with a multiplicity of such components
can thus be realized with such components.
[0023] The molding material is preferably resin-based, in
particular formed from a prereacted resin. The molding material is
particularly preferably prepared by mixing and blending a
radiation-permeable plastics compression molding material with a
conversion material.
[0024] In a preferred embodiment, the leadframe connections led out
laterally extend up to the mounting plane determined by the
mounting surface or to the vicinity thereof. This ensures that a
support plate having corresponding conductor track structures can
simultaneously serve for electric supply to the component. The
leadframe connections may also end a slight distance away from the
mounting plane. Contact points produced on the support plate, for
example solder contact surfaces, are as a rule slightly dome-shaped
and thus compensate the distance between the leadframe connections
and a support plate.
[0025] Preferably, the leadframe as a whole is flat. This
simplifies the production since no additional bends have to be
made. In addition, mechanical stresses which might occur as a
result of such bends are avoided. Furthermore, a flat leadframe is
a planar, exactly defined mounting platform for mounting the
radiation-emitting chip. This facilitates the automatic equipping
and contacting with these chips. In particular, the optical
recognition and control systems used for this may be confused by
non-plane-parallel mounting surfaces, as may occur in prebent
leadframes, for example as a result of bending tolerances. This
leads to malfunctions, which are reduced in the case of flat
leadframes.
[0026] Furthermore, it is advantageous to provide passages or
lateral recesses in the leadframe. These passages or recesses are
filled by the plastics compression molding material, resulting in
mechanically stable anchoring of the leadframe in the plastics
compression molding material.
[0027] In a particularly preferred embodiment, the component has a
top surface parallel to the mounting surface. This permits the use
of the component in so-called pick & place processes,
preferably in combination with automatic equipping apparatuses. The
component is sucked on a surface by a suction arm, transported to
its intended equipping location and mounted there. This requires as
a rule parallel and flat suction and mounting surfaces.
[0028] An advantageous further development of the invention
comprises shaping the covering in such a way that the component is
bounded in the emission direction by a curved surface. The covering
thus simultaneously performs the function of an optical element,
for example of a lens. Depending on the curvature and direction of
curvature, both focusing and extension of the emission
characteristic can be achieved. Depending on the matching of the
conversion material with the radiation produced by the
radiation-emitting chip, the invention is suitable as a white light
source or as a colored light source, it being possible for color
location and color saturation to be freely established within wide
limits when suitable conversion materials are used. Owing to a
certain proportion of white light, the optical impression of an
unsaturated emission color may be evoked in the case of a colored
light source.
[0029] However, the invention is not restricted to the visible
optical spectral range. The radiation-emitting chip and/or the
conversion element can also be provided for ultraviolet or infrared
radiation emission. Thus, for example, mixed-"color" infrared or
ultraviolet radiation, i.e. infrared or ultraviolet radiation
having two or more spectral components, can be produced.
[0030] With regard to shaping, the component advantageously
dispenses with the formation of a depression and the use of two
different materials and instead envisages the use of a single
transparent molding material which is optionally first mixed with
the conversion material and then shaped, preferably injection
molded, around the leadframe. The cured molding material thus
simultaneously serves as a component housing and as a transparent
conversion material matrix. Thus, on the one hand, the production
process is considerably simplified since the housing is formed in a
single shaping process, in particular an injection molding process.
At the same time, the molding material may serve as the matrix for
the conversion material.
[0031] Furthermore, a component is produced which has improved
stability properties since the problem of adhesion between two
surrounding materials, such as, for example, a basic housing body
and an encapsulation, which moreover, may have different
coefficients of thermal expansion, no longer occurs.
[0032] The color locations are established in a reproducible and
specific manner within narrow limits by virtue of the fact that the
sedimentation of the conversion materials during storage and
processing, in particular through rapid curing steps, is very
substantially ruled out. The quality of the conversion materials is
increased by simple process steps with simpler metering
possibilities in the resin preparation, mixing and metering.
[0033] The use of only a single material for the housing form and
the conversion material matrix results in latitude for further
miniaturization. This additional miniaturization potential can be
utilized for the use of these components in mobile electronic
product systems, for example as a white light source. Increased
light yields through greater utilization of the lateral emission in
special installation situations with further degrees of freedom of
design or straightforward lateral light output possibilities extend
the functionality.
[0034] The plastics compression molding material, as a starting
material, may be a commercially available compression molding
material and substantially comprises, for example, an epoxy-cresol
novolak or conventional epoxy resin systems with an anhydride or a
conventional phenol curing system.
[0035] The conversion material dispersed in the plastics
compression molding material may be an inorganic luminescent
pigment powder which contains phosphors of the general formula
A.sub.3B.sub.5X.sub.12:M. In particular, particles from the group
consisting of the Ce-doped garnets may be used as luminescent
pigments, Ce-doped yttrium aluminum garnet
(Y.sub.3Al.sub.5O.sub.12Ce) being mentioned in particular. Further
possible phosphors are sulfide- and oxysulfide-based host lattices,
aluminates, borates, etc., having metal centers appropriately
excitable in the short-wave range. Organometallic phosphor systems
may also be used. The luminescent pigments may also contain a
plurality of different phosphors and the conversion material may
contain a plurality of different luminescent pigments.
[0036] The phosphor can also be formed by soluble and sparingly
soluble organic dyes and phosphor mixtures.
[0037] Furthermore, an adhesion promoter, preferably in liquid
form, can be mixed with the preferably predried conversion material
in order to improve the adhesion of the conversion material with
the plastics compression molding material. Particularly when
inorganic luminescent pigments are used,
3-glycidyloxypropyltrimethoxysilane or further derivatives based on
trialkoxysilane can be used as adhesion promoters.
[0038] Monofunctional and polyfunctional polar agents having
carboxyl, carboxylic ester, ether and alcohol groups, such as, for
example, diethylene glycol monomethyl ether, can be used for
modifying the phosphor surfaces. This improves the wettability of
the high-energy phosphor surfaces and hence the compatibility and
dispersing during the processing with the molding material.
[0039] Furthermore, a mold release agent or lubricant can be mixed
with the plastics compression molding material before the mixing
with the conversion material. Such mold release agents facilitate
the removal of the cured molding material from the mold. A solid
wax-based mold release agent or a metal soap with long-chain
carboxylic acids, in particular stearates, can be used as such a
mold release agent.
[0040] For example, inorganic fillers, by means of which the
refractive index of the molding material can be increased, may be
admixed as further fillers, with the result that the light yield of
the component can be increased. For example, TiO.sub.2, ZrO.sub.2,
.alpha.-Al.sub.2O.sub.3 or another metal oxide may be used as such
fillers.
[0041] In an advantageous embodiment of the invention, glass
particles, so-called glass fillers, are added to the molding
material as a filler. The glass transition temperature T, of the
molding material is thus increased. The glass transition
temperature of the molding material limits the temperature range
permissible for the component since exceeding the glass transition
temperature may lead to flow of the molding material and
consequently to stresses and defects in the radiation-emitting chip
and wire connections attached thereto. The addition of glass
particles to the molding material advantageously increases the
temperature range permissible for the component. Furthermore, the
component can be operated at a higher operating current and more
radiation can be produced. A further advantage is a reduction of
the coefficient of thermal expansion of the molding material, which
coefficient is therefore better adapted to the coefficient of
thermal expansion of the leadframe, so that the thermal stability
of the component is further increased.
[0042] As a result of the addition of glass particles, the
refractive index of the molding material is furthermore increased
so that the refractive index jump between the radiation-emitting
chip and the molding material is smaller and advantageously the
radiation output is greater.
[0043] Finally, the water absorption of the molding material is
reduced by the addition of glass particles. This advantageously
leads to an improved thermal load capacity of the component. In
particular, the risk of damage to or of bursting of the component
during soldering in, owing to an excessively high water content
(so-called popcorn effect), is advantageously reduced.
[0044] The mean particle size of the glass particles is preferably
less than 100 .mu.m, particularly preferably less than 50 .mu.m.
Inter alia, the risk of blockage of the often narrow feed channels
of an injection mold is thus reduced.
[0045] The proportion of glass particles in the molding material
may be 90% by weight or more and is preferably between 10% by
weight and 50% by weight. In the last-mentioned range, the molding
material is distinguished both by high transparency and by a high.
glass transition temperature.
[0046] Preferably, the conversion material and optionally the
further fillers are mixed by first mixing them coarsely and then
milling the mixture in a mill, with the result that a very fine,
homogeneous powder is obtained.
[0047] The mixed molding material may therefore contain the
following constituents (in % by weight): [0048] a) plastics
compression molding material .gtoreq.60% [0049] b) conversion
material >0 and .ltoreq.40% [0050] C) adhesion promoter
.gtoreq.0 and .ltoreq.3% [0051] d) mold release agent .gtoreq.0 and
.ltoreq.2% [0052] e) surface modifier .gtoreq.2 0 and .ltoreq.5%
[0053] f) antioxidant .gtoreq.0 and .ltoreq.5% (e.g. based on
phosphite or based on sterically hindered phenols) [0054] g) UV
light stabilizer .gtoreq.0 and .ltoreq.2% [0055] h) glass particles
.gtoreq.0 and .ltoreq.80%.
[0056] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0057] Although the invention is illustrated and described herein
as embodied in a surface-mountable radiation-emitting component and
process for its production, it is nevertheless not intended to be
limited to the details shown, since various modifications and
structural changes may be made therein without departing from the
spirit of the invention and within the scope and range of
equivalents of the claims.
[0058] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
DESCRIPTION OF DRAWINGS
[0059] FIG. 1 is a schematic sectional view of a first embodiment
of a component according to the invention;
[0060] FIG. 2 is a schematic sectional view of a second embodiment
of a component according to the invention;
[0061] FIG. 3 is a schematic perspective view of a third embodiment
of a component according to the invention; and
[0062] FIG. 4 is a schematic perspective view of a fourth
embodiment of a component according to the invention.
DETAILED DESCRIPTION
[0063] Referring now to the figures of the drawing in detail and
first, particularly, to FIG. 1 thereof, there is shown an
embodiment of a component according to the invention in a cross
section that is taken along a longitudinal axis of a leadframe
10.
[0064] In an originally one-piece and cohesive leadframe 10, two
leadframe connections 11 and 12 are formed, which are initially
held together in a manner known per se by narrow connecting webs
but are isolated from one another in the course of the production
process by separation of these connecting webs.
[0065] On one leadframe connection 12, a completely processed
semiconductor LED 1 having an electrically conductive connecting
means, such as conductive silver or the like, is adhesively bonded
or soldered on the inside end section of the leadframe connection,
so that the n-side or p-side of the semiconductor LED 1 is
connected to the leadframe terminal 12. The opposite p-conducting
or n-conducting contact side is connected by a bond wire 2 to the
end section of the other leadframe connection 11.
[0066] The component is surrounded by a plastics compression
molding material 3, into which a conversion material 4 in the form
of phosphor particles can preferably be introduced. This will be
explained in more detail below.
[0067] In the illustrated component, the mounting surface is
parallel to the plane of the section. The leadframe 10 is flat
throughout and is approximately perpendicular to the mounting
surface so that the second predetermined angle is about 90.degree.
within the manufacturing tolerances.
[0068] This design permits both economical manufacture of the
leadframe, for example by punching out of a metal sheet or of a
foil without additional bends, and a very small space requirement
of the component. The emission takes place predominantly
perpendicular to the leadframe 10, so that a main emission
direction 7 is approximately parallel to the mounting surface, and
the first predetermined angle is O.degree. within the manufacturing
tolerances.
[0069] FIG. 2 shows a schematic sectional view of a further
embodiment of a component according to the invention. The plane of
the section is once again along a longitudinal axis of the
leadframe 10. and is oriented perpendicular to the plane of the
section chosen in FIG. 1.
[0070] Here, the leadframe 10 has lateral recesses 5. These
recesses 5 are filled with the surrounding plastics compression
molding material, thus forming a type of toothed system between the
leadframe 10 and the covering. This toothed system ensures
mechanically stable anchoring of the leadframe in the covering. For
this purpose, it would also be possible to form non-illustrated
passages in the leadframe 10.
[0071] The leadframe connections 11, 12 project, in a main
extension direction of the mounting plane 13 determined by the
mounting surface 6, out of the covering of the component and
extend, a distance away from the covering, in the direction of the
mounting plane 13. A small gap which is bridged during contacting,
for example by solder contacts, is formed between the mounting
plane 13 and the leadframe connections 11, 12. Advantageously, the
positioning of the component is thus determined solely by the
mounting surface 6, with the result that mechanical stresses
between leadframe 10 and covering are avoided. Furthermore, the
slight distance of the leadframe connections 11, 12 from the
mounting plane 13 reduces the risk that the leadframe connections
11, 12, which project beyond the mounting plane 13, for example
owing to manufacturing tolerances in the encapsulation with molding
material, lead to bending of the leadframe connections 11, 12 or
tilting of the component during mounting.
[0072] FIG. 3 shows a perspective view of a further embodiment of a
component according to the invention on a support 8, for example a
circuit board. The emission takes place substantially parallel to
the main surface of the support, on which the component rests with
the mounting surface 6. On either side of the leadframe
connections, the component is bounded by inclined surfaces 9a, 9b
which are tilted relative to one another and, as so-called
demolding bevels, facilitate the separation of a mold from the
component body during product ion.
[0073] In the emission direction 7, the component is bounded by a
curved surface which is partly cylindrical in the case shown, the
cylinder axis being oriented approximately parallel to the
longitudinal axis of the leadframe. The curved surface may also be
formed spherically as part of a sphere surface or aspherically.
Furthermore, both a convex surface and a concave surface are
possible.
[0074] As a result of this shape, a lens effect and hence focusing
of the emitted radiation are achieved.
[0075] In the embodiment, the semiconductor LED 1 has an emission
spectrum which is in the ultraviolet or blue spectral range. For
the production of mixed-color or white light, an emission of the
semiconductor LED in the ultraviolet or blue spectral range is
particularly advantageous since conversion to longer wavelengths is
as a rule substantially more efficient than a conversion from
longer to shorter wavelengths. Since the ultraviolet or blue
spectral range is at the short wave end of the optically visible
range, efficient conversion to a majority of the visible
wavelengths is possible from there by means of suitable conversion
materials.
[0076] The semiconductor LED 1 is preferably based on GaN, InGaN,
AlGaN or AlInGaN. However, it may alternatively also be based on
the material system ZnS/ZnSe or on another material system suitable
for this spectral range.
[0077] In contrast to the embodiments described so far, the
embodiment of a component according to the invention, shown in FIG.
4, is provided with a main emission direction 7 arranged
perpendicular to the mounting plane 6. The first predetermined
angle here is about 90.degree.. The leadframe 10 has two S-shaped
bends, the leadframe connections projecting laterally from the
molding material 3, and the connection surfaces of the leadframe
connections being in the mounting plane 13 determined by the
mounting surface 6. The second predetermined angle here is thus
O.degree..
[0078] A radiation-emitting chip 1 in the form of a semiconductor
LED is fastened, for example soldered or adhesively bonded by an
electrically conductive bond, on one part of the two-part leadframe
10. A wire connection 2 is led to the other part of the leadframe.
As in the other embodiments, leadframe 10 and semiconductor LED are
surrounded by a radiation-permeable molding material comprising
conversion material.
[0079] In an embodiment of the production method according to the
invention, after mounting and contacting of the semiconductor LED
1, a transparent plastics compression molding material 3 is
injection-molded onto the leadframe connections 11 and 12 in a
suitable injection-molding apparatus.
[0080] Preferably, the leadframe with the semiconductor LED is
surrounded with the plastics compression molding material by
molding by means of an injection molding or injection compression
molding process. For this purpose, a subregion of the leadframe 10
with premounted semiconductor LED 1 is introduced into an injection
mold, and the plastics injection molding material 3 is liquefied
and is injected into the injection mold. It is advantageous to
preheat the leadframe (10) prior to the injection molding.
[0081] In a variant of this process, a multiplicity of leadframes,
each having radiation-emitting chips mounted thereon, can also be
encapsulated in a cohesive covering and subsequently divided into
individual components, for example by breaking, sawing or a laser
cutting method by means of a water jet.
[0082] Phosphor particles which consist of a phosphor by means of
which at least partial wavelength conversion of the light radiation
emitted by the semiconductor LED 1 is brought about are embedded as
conversion material 4 in this plastics compression molding material
3. This wavelength conversion produces an emission spectrum which
gives the optical impression of multi-colored light or white
light.
[0083] The prefabrication of the leadframe 10 and the surrounding
by injection molding with the molding material consisting of the
plastics compression molding material 3, the phosphor particles 4
and optionally further fillers are effected in such a way that the
leadframe sections 11 and 12 are led horizontally out of the
molding material.
[0084] The finished component can be soldered to a circuit board at
the connection surfaces of the leadframe connections 11 and 12,
which connection surfaces are perpendicular to the mounting
surface. A component suitable for SMT (surface mounting technology)
is thus produced.
[0085] The preparation of the molding material formed by the
plastics compression molding material 3, the phosphor particles 4
and 10 optionally further fillers is described in more detail
below.
[0086] Prereacted, storage-stable and radiation-stable transparent
compression molding materials which comprise commercial
epoxy-cresol novolaks with phenolic curing agents and whose total
chlorine content is below 1500 ppm can be used as starting
materials for the plastics compression molding material.
Preferably, these compression molding materials contain an internal
mold release agent or lubricant, which facilitates the removal of
the cured molding material from the injection mold. The presence of
such an internal mold release agent is, however, not absolutely
essential. For example, the following commercially available
compression molding materials from Nitto and Sumitomo may therefore
be used:
[0087] Nitto NT-600 (without internal mold release agent)
[0088] Nitto NT-300H-10.000 (with internal mold release agent)
[0089] Nitto NT.300S-10.000 (with internal mold release agent)
[0090] Nitto NT 360-10.000 (with internal mold release agent)
[0091] Sumitomo EME 700L (without internal mold release agent)
[0092] These compression molding materials are supplied as standard
in rod or tablet form.
[0093] The use of compression molding materials in rod or tablet
form facilitates the metering and increases the accuracy thereof
compared with a compression molding material present in powder
form. However, a compression molding material present in the form
of a powder or in another modification can of course also be used
in the invention. Furthermore, a compression molding material
present in the form of a powder could also first be brought into
rod or tablet form for more exact metering and then be further
processed.
[0094] All phosphors which are described in the above-mentioned
international publications WO 97/50132 and WO 98/12757 may be
present as conversion materials. In particular, an inorganic
luminescent pigment powder comprising phosphors having the general
formula A.sub.3B.sub.5X.sub.12:M can be used. These are, for
example, garnets doped with rare earths, in particular Ce.
[0095] Compounds that satisfy the formula
A'.sub.3B'.sub.5O.sub.12:M' have proven to be efficient phosphors
(provided that they are not unstable under the customary production
and operating conditions). Therein, A' is at least one element from
the group consisting of Y, Lu, Sc, La, Gd, Tb and Sm; B' is at
least one element from the group consisting of Al, Ga and In; and
M' is at least one element from the group consisting of Ce and Pr,
preferably Ce. The compounds YAG:Ce (Y.sub.3Al.sub.5O.sub.12:Ce),
TAG:Ce (Tb.sub.3Al.sub.5O.sub.12:Ce), TbYAG:Ce
((Tb.sub.xY.sub.1-x).sub.3 Al.sub.5O.sub.12:Ce,
0.ltoreq.x.ltoreq.1), GdYAG:Ce
((Gd.sub.xY.sub.1-x).sub.3Al.sub.5O.sub.12:Ce.sup.3+,
0.ltoreq.x.ltoreq.1) and GdTbYAG:Ce
((Gd.sub.xTb.sub.yY.sub.1-x-y).sub.3Al.sub.5O.sub.12:Ce.sub.3+,
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1) and mixtures based
thereon have proven to be particularly efficient phosphors. Al can
be at least partly replaced by Ga or In. Said phosphors are to be
understood by way of example and not as restricting the general
formula A.sub.3B.sub.5X.sub.12:M.
[0096] The compounds SrS:Ce.sup.3+, Na, SrS:ce.sup.3+, Cl,
SrS:CeCl.sub.3, CaS:Ce.sup.3+ and SrS:Ce.sup.3+ are furthermore
suitable as a phosphor. Moreover, sulfide- and oxysulfide-based
host lattices and aluminates, borates, alkaline earth metal
sulfides, thiogallates or orthosilicates, etc. having metal centers
appropriately excitable in the short-wave range or organometallic
phosphor systems can also be used. Furthermore, soluble or
sparingly soluble organic dyes and phosphor mixtures can be
used.
[0097] Regarding the particle size of the phosphor particles, a
mean particle diameter between 2 .mu.m and 20 .mu.m, preferably
approximately between 4 .mu.m and 10 .mu.m, particularly preferably
between 5 .mu.m and 6 .mu.m, is advantageous. The conversion
properties can be further improved by removing the dust fraction,
i.e. for example particles having a particle diameter of less than
2 .mu.m, preferably less than 1 .mu.m, from the phosphor powder.
With decreasing particle diameter, the scatter of the radiation at
the particles increases and the conversion efficiency decreases, so
that it is advantageous to separate off the phosphor particles
having a comparatively small particle diameter.
[0098] Thus, for example, experiments have shown that milling the
phosphor, which produces a particle size d.sub.50 of substantially
less than 5 .mu.m, results in a volume fraction of up to 30% of
particles having a particle size less than 1 .mu.m. Regardless of
the difference in refractive index compared with the surrounding
matrix, for example a plastics matrix, particles having a size of
less than 1 .mu.m lead to strong light scattering and thus
adversely affect the transmission and the transparency of the
matrix.
[0099] According to simulation calculations, the pure transmission
at a wavelength of 500 nm in the case of a typical plastics matrix
having a thickness of 400 .mu.m and a phosphor concentration of
3.5% by weight with a mean phosphor particle size of 2 .mu.m is an
order of magnitude of 1,000 greater than for a particle size of 1
.mu.m and further increases sharply with increasing particle size.
For shorter wavelengths, particle sizes of 1 .mu.m or less have a
greater effect.
[0100] In particular, particles of the luminescent pigment YAG:Ce
are distinguished by particular conversion efficiency. A conversion
material based thereon is known by the product designation L175
from Osram of Germany. An experiment on mixing with a compression
molding material was carried out with this conversion material, a
compression molding material of the type Nitto NT-300 H1O.OOO with
an internal mold release agent being used. As preparation for the
experiment, the conversion material L175 was predried at
200.degree. C. for about 8 h. Thereafter, a surface modifier having
the designation diethylene glycol monomethyl ether was mixed in
liquid form with the predried converter (0.1% by weight, based on
weight of compression molding material). This mixture was sealed
airtight in a glass vessel and left to stand overnight. Directly
before processing, the conversion material was mixed with the
compression molding material of the abovementioned type. The
compression molding material had been milled beforehand in a mill
(for example a ball mill) in powder form. The mixing ratio was 20%
by weight of conversion material/DEGME mixture and 80% by weight of
Nitto NT 300H-10.000. After the coarse mixing of the mixture by
stirring, the mixture was thoroughly mixed and milled again in a
mill (for example a ball mill) and very fine powder was thus
produced.
[0101] An injection molding experiment was then carried out with
this molding material on the apparatus of the type FICO Brilliant
100. The already appropriately prefabricated leadframes 10 were
preheated at 150.degree. C. prior to the injection molding, and the
following machine parameters were set for the injection molding:
[0102] mold temp: 150.degree. C. [0103] injection time: 22.4 s
[0104] injection pressure: 73-82 bar (depending, inter alia, on the
amount of material set) [0105] curing time: 120 s
[0106] As a result, it was possible to achieve a very homogeneous,
cured molding material which was distinguished by excellent freedom
from bubbles and shrink holes. In general, it was found that
milling of the compression molding material to very fine powder
prior to mixing gave better results with regard to freedom from
bubbles and shrink holes than with the use of a coarser-particled
residual material powder.
[0107] In addition, an adhesion promoter, such as
3-glycidyloxy-propyltrimethoxysilane, for example having the
product designation A-187 from Huls AG, can also be used. This
adhesion promoter can be added to the phosphor in concentrations of
up to 3% by weight directly after the drying process and can be
mixed therewith overnight at room temperature.
[0108] According to an embodiment, the method according to the
invention has been described on the basis of an SMD (surfacemounted
design), but it can also be realized in the case of a so-called
radial diode.
[0109] The explanation of the invention with reference to the
embodiments described does not of course represent any restriction
of the invention to these embodiments. In particular, individual
features of the embodiments can also be combined in a form other
than the form described. Likewise, production processes described
are not restricted to surfacemountable components, laterally
emitting components or components which contain a conversion
material.
* * * * *