Reflective composite material, in particular for surface-mounted devices (SMD), and light-emitting device with a composite material of this type

Abstract

A reflective composite material with a carrier consisting of aluminum with, on one side (A) of the carrier, an interlayer made of aluminum oxide, and with, above the interlayer, an optically active reflection-boosting multilayer system. In order to provide a high-reflectivity composite material of this kind which exhibits improved electrical connectivity when surface-mounting procedures are used, it is proposed that the thickness of the interlayer is in the range 5 nm to 200 nm, and that a layer of a metal or a metal alloy has been applied superficially on side (B) of the carrier that is opposite to the optically active reflection-boosting multilayer system, where the electrical resistivity at 25° C. of the metal or metal alloy is at most 1.2×10.sup.−1 Ωmm.sup.2/m, where the thickness of the layer applied superficially is in the range 10 nm to 5.0 μm.

Claims

1. A reflective composite material with a carrier consisting of aluminum having a thickness in the range of 0.1 mm to 1.5 mm with, located on a first side of the carrier, an interlayer made of anodically oxidized aluminum oxide having an average surface roughness Ra of less than 0.05 μm, and with, applied on the interlayer, an optically active reflection-boosting multilayer system, wherein the thickness of the interlayer consisting of the anodically oxidized aluminum oxide is in the range of 5 nm to 200 nm, and that a layer of a metal or of a metal alloy has been applied superficially on a second side of the carrier that is opposite to the optically active reflection-boosting multilayer system, where the electrical resistivity at 25° C. of the said metal or metal alloy is at most 1.2×10.sup.−1 Ωmm.sup.2/m, where the thickness of the layer applied superficially is in the range of 10 nm to 5.0 μm; wherein one or more of the layer of metal or of metal alloy superficially applied, a passivating layer located thereon, and a reflective layer of the optically active reflection-boosting multilayer system is a silver alloy layer that comprises, as alloy element(s), one or more of rare earth elements, palladium, platinum, gold, copper, indium, titanium, tin, and molybdenum; wherein at least one of the following is present: the layer of metal or of metal alloy superficially applied is a copper layer with a thickness in the range of 0.1 μm to 5.0 μm; or the layer of metal or of metal alloy superficially applied is a silver layer with a thickness in the range of 10 nm to 500 nm; or the composite material further comprises an adhesion-promoter layer made of a transition metal, the adhesion-promoter layer being arranged between the carrier consisting of aluminum and the layer of metal or of metal alloy superficially applied.

2. The composite material according to claim 1, wherein the electrical resistivity at 25° C. of the layer of a metal or of a metal alloy superficially applied on the second side of the carrier that is opposite to the optically active reflection-boosting multilayer system is at most 2.7×10.sup.−2 Ωmm.sup.2/m.

3. The composite material according to claim 1, wherein the thickness of the interlayer consisting of aluminum oxide is in the range of 10 to 100 nm.

4. The composite material according to claim 1, wherein the composite material further comprises the passivating layer deposited on the layer of a metal or of a metal alloy superficially applied, with a thickness being in the range of 10 nm to 500 nm.

5. The composite material according to claim 4, wherein the silver alloy layer comprises palladium as the alloy element along with another alloy element being present in an amount that is the same or smaller than the amount of palladium; wherein this other alloy element is aluminum, gold, platinum, copper, tantalum, chromium, titanium, nickel, cobalt, or silicon.

6. The composite material according to claim 4, wherein one or more of the layers arranged above the interlayer, the layer of a metal or of a metal alloy superficially applied, and the passivating layer, are sputter layers, CVD layers or PECVD layers, or layers produced by evaporation.

7. The composite material according to claim 1, wherein the purity of the aluminum of the carrier (1) is above 99.0%.

8. The composite material according to claim 1, wherein the thickness of the carrier is 0.1 to 1.5 mm.

9. The composite material according to claim 1, wherein a total light reflectance on a first side of the optical multilayer system is above 97%.

10. The composite material according to claim 1, wherein the composite material further comprises a configuration as lead frame for a surface-mounted device, wherein the shape of the lead frame when viewed from above is that of an H with a crossbar running obliquely between tracks configured from fingers, and where the lead frame has been produced by at least one of a die-cutting process, a bending process, and a laser cutting process.

11. The composite material according to claim 10, wherein the composite material further comprises a configuration as frame device in the form of a circuit board in strip form in which a large number of lead frames have been combined in fields in the form of line elements and of column elements, by way of connectors.

12. The composite material according to claim 1, wherein the composite material further comprises a configuration as a coil with width up to 1600 mm.

13. A light-emitting device comprising a composite material according to claim 1, which forms a lead frame for an electronic component, where the electronic component lies on and is secured to the upper side on the lead frame and is electrically contacted to the lead frame by means of a separate wire, and where a composite comprising the electronic component and the lead frame is cohesively bonded on the underside in an electrically conductive manner to a printed circuit board.

14. The light-emitting device according to claim 13, wherein the lead frame has been connected to the printed circuit board by way of a tin-containing solder layer.

15. The light-emitting device according to claim 13, wherein the electronic component is a light-emitting diode configured as chip.

16. The composite material according to claim 2, wherein the electrical resistivity at 25° C. of the layer of a metal or of a metal alloy superficially applied on the second side of the carrier that is opposite to the optically active reflection-boosting multilayer system is at most 1.8×10.sup.−2 Ωmm.sup.2/m.

17. The composite material according to claim 1, wherein the transition metal is titanium, chromium or nickel.

18. The composite material according to claim 1, wherein the thickness of the copper layer is in the range of 0.5 μm to 1.5 μm.

19. The composite material according to claim 1, wherein the thickness of the silver layer is in the range of 50 nm to 250 nm.

20. The composite material according to claim 4, wherein the thickness of the passivating layer is in the range of 50 nm to 250 nm.

21. The composite material according to claim 4, wherein the passivating layer consists of Ag, Ni, Pd, Au, or a combination thereof.

22. The composite material according to claim 8, wherein the thickness of the carrier is 0.2 to 0.8 mm.

23. The composite material according to claim 9, wherein the total light reflectance on the first side of the optical multilayer system is at least 98%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIG. 1 is an enlarged diagram of a section through an embodiment of a composite material of the invention, where the layer thicknesses are depicted purely diagrammatically and are not to scale,

(3) FIG. 2 is a plan view of a subregion of an embodiment of a light-emitting device of the invention,

(4) FIG. 3 is a plan view of an embodiment of a lead frame composed of a composite material of the invention for a light-emitting device of the invention, and

(5) FIG. 4 is a cross section through an embodiment of a light-emitting device of the invention.

(6) The drawings are provided herewith for purely illustrative purposes and are not intended to limit the scope of the present invention.

DETAILED DESCRIPTION

(7) The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description, corresponding reference numerals indicate like or corresponding parts and features.

(8) In relation to the description that follows, it is expressly emphasized that the invention is neither restricted to the embodiment nor restricted to all of, or a plurality of, features of feature combinations described. Instead, inventive importance can be attached to each individual subfeature of the embodiment, either per se independently of all of the other subfeatures described in connection therewith or in combination with any desired suitable other features.

(9) The same parts also always have the same reference signs in the various figures of the drawing, and the said parts are respectively therefore also generally described only once.

(10) As firstly is apparent from FIG. 1, a reflective composite material V of the invention with a carrier 1 consisting of aluminum has, located on one side A of the carrier 1, an interlayer 2 made of aluminum oxide, and applied on the interlayer 2, an optically active reflection-boosting multilayer system 3. The carrier 1 can be configured as coil with width up to 1600 mm, preferably with width 1250 mm, and with thickness D.sub.1 about 0.1 to 1.5 mm, preferably about 0.2 to 0.8 mm. Because all of the thin layers located on the carrier, in particular the interlayer 2 and the layers of the optically active multilayer system 3, are negligibly small in comparison with the carrier, the thickness D.sub.1 of the carrier is also the main factor determining the total thickness DG of the composite material V of the invention.

(11) The purity of the aluminum of the carrier 1 can in particular be above 99.0%, thus favourably influencing its thermal conductivity. This enables avoidance of thermal peaks. However, by way of example, it is also possible that the carrier 1 is an Al 98.3 aluminum sheet in strip form, i.e. with purity 98.3 percent. It is also possible to use aluminum alloys as carrier 1, an example being an AlMg alloy, in so far as the interlayer 2 can be formed therefrom by anodic oxidation.

(12) The optically active multilayer system 3 can by way of example—as depicted—consist of at least three layers, where two upper layers 4, 5 thereof are dielectric and/or oxidic layers and the undermost layer 6 situated thereunder is a metallic layer forming a reflective layer 6 and consisting by way of example of aluminum or silver.

(13) In the case depicted, an optionally present protective non-metallic outer layer 7 is additionally depicted, consisting of a low-absorption material, for example silicon dioxide. This type of layer structure is known from the German Utility Model DE 2 98 12 559 U1, the entire content of which is incorporated herein by way of reference in this connection. The respective thickness D.sub.4, D.sub.5 of the dielectric and/or oxidic layers 4, 5 of the optical multilayer system 3 can by way of example be in the range 30 nm to 200 nm, where this thickness D.sub.4, D.sub.5 is respectively preferably a quarter of the average wavelength of the spectral range of the electromagnetic radiation to be reflected, in order that the layers 4, 5 can act as reflection-increasing interference layers. The thickness D.sub.7 of the protective layer 7 can be in the range 0.5 nm to 20 nm, preferably in the range 0.5 nm to 10 nm. There can also be a protective layer comprising silicon nitride applied as outer layer 7 to the optical multilayer system 3.

(14) The optical multilayer system 3—inclusive of the outer layer 7—and advantageously also the layer 9, described below, of a metal or of a metal alloy, in particular configured as copper layer, can be applied in technologically advantageous manner by use of a continuous vacuum coating process. In particular, the layers 4, 5, 6, 7, 9 here can be sputter layers, in particular layers produced by reactive sputtering, CVD layers or PECVD layers, or layers produced by evaporation, in particular by electron bombardment or from thermal sources.

(15) The reflective layer 6 can optionally be attached to the interlayer 2 by way of an adhesion-promoter layer not depicted, for example consisting of aluminum oxide, titanium oxide and/or chromium oxide. The reflective layer 6 can moreover optionally have been embedded, on the upper side and underside, between barrier layers not depicted, e.g. made of nickel, nickel alloys or palladium, in order to increase resistance to temperature change.

(16) The upper dielectric and/or oxidic layer 4 of the optical multilayer system 3 is a layer with higher refractive index than the lower dielectric and/or oxidic layer 5 of the optical multilayer system 3; the upper layer 4 here can preferably consist of TiO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, MoO.sub.3 and/or ZrO.sub.2, and the lower layer 5 here can preferably consist of Al.sub.2O.sub.3 and/or SiO.sub.2.

(17) The invention provides that the thickness D.sub.2 of the interlayer 2 consisting of aluminum oxide, in particular composed of anodically oxidized aluminum, is in the range 5 nm to 200 nm, preferably in the range 10 to 100 nm. As already stated, in the context of what is known as wire bonding this advantageously permits according to the invention—as depicted in FIG. 2—firstly welding of a wire D, in particular ultrasound welding of a gold wire, on the front or upper side A of the composite material V of the invention, thus permitting problem-free electrical connection (weld point SP) between the surface A of the composite material V and an electronic component SMD applied by a surface-mounting procedure on the composite material V.

(18) It is preferable here that the arithmetic average roughness value R.sub.a of the surface of the interlayer 2 is below 0.05 μm, in particular below 0.01 μm, particularly preferably below 0.005 μm. This serves, together with the abovementioned high total light reflectance, to establish minimal diffuse light reflectance determined in accordance with DIN 5036. If higher diffuse light reflectance is required, the roughness can be increased accordingly.

(19) Located on that side B of the carrier 1 that is opposite to the optically active reflection-boosting multilayer system 3 there is optionally a further layer 8 which consists of aluminum oxide and which by way of example can be produced simultaneously by the production process during the electrolytic oxidation of the upper side A. However, formation thereof can be avoided if necessary by covering of the side B. There are also known processes for optional removal of such layers. If the further layer 8 which consists of aluminum oxide is present, its thickness D8 should be in the same region as the thickness D.sub.2 of the interlayer 2, i.e. in the range 5 nm to 200 nm, preferably in the range 10 to 100 nm.

(20) Another feature essential to the invention is that a layer 9 of a metal or of a metal alloy has been applied superficially on that side B of the carrier 1 that is opposite to the optically active reflection-boosting multilayer system 3, where the electrical resistivity at 25° C. of the said metal or metal alloy is at most 1.2×10.sup.−1 Ωmm.sup.2/m, where the thickness D.sub.9 of the layer 9 applied superficially is in the range 10 nm to 5.0 μm.

(21) The said layer can in particular be a copper layer applied with thickness D.sub.9 in the range 0.1 μm to 5.0 μm, preferably in the range 0.2 μm to 3.0 μm, particularly preferably in the range 0.5 μm to 1.5 μm.

(22) Another preferred embodiment of the invention provides that the layer 9 superficially applied is a silver layer with thickness D.sub.9 in the range 10 nm to 500 nm, in particular with thickness D.sub.9 in the range 50 nm to 250 nm.

(23) The maximal value of the electrical resistivity at 25° C. of the layer 9 of a metal or of a metal alloy superficially applied can preferably be 2.7×10.sup.−2 Ωmm.sup.2/m, particularly preferably 1.8×10.sup.−2 Ωmm.sup.2/m.

(24) In respect of the values of electrical resistivity underlying various materials here, reference is made to Table 1 below, which has been collated on the basis of values mentioned at various points in the literature.

(25) TABLE-US-00001 TABLE 1 Values of electrical resistivity ρ at 25° C. MATERIAL ρ in 10.sup.−2 Ω mm.sup.2/m ρ ≤ 1.8 × 10.sup.−2 Ω mm.sup.2/m particularly preferred according to the invention Ag 1.59 Cu 1.69-1.72 ρ ≤ 2.7 × 10.sup.−2 Ω mm.sup.2/m preferred according to the invention Al 2.65 Au 2.21 ρ ≤ 1.2 × 10.sup.−1 Ω mm.sup.2/m according to the invention W 5.3 Ni 6.9-7.1 Pt 10.5 Pd 10.7 Sn 10.9

(26) An overview of electrical resistivity p of ten different binary alloys (Al/Cu, Al/Mg, Cu/Au, Cu/Ni, Cu/Pd, Cu/Zn, Au/Pd, Au/Ag, Fe/Ni, Ag/Pd) with respectively different compositions can be found by way of example in the scientific paper “Electrical resistivity of ten selected binary alloys systems”, Author: Ho, C. Y. et al., in J. Phys. Chem. Ref. Data, Vol. 12, No. 2, 1983, pp. 183 to 322. Reference can be made to these values when establishing a particular chemical composition in the layer 9 provided according to the invention.

(27) However, another possibility is direct measurement in accordance with ASTM F390-11 “Standard Test Method for Sheet Resistance of Thin Metallic Films With a Collinear Four-Probe Array”. This standard also contains instructions for conversion of a sheet resistance determined in the unit Ω or “Ω square” to an electrical resistivity by taking into account the geometry of the layer, i.e. its length, width and thickness.

(28) Between the carrier 1 consisting of aluminum, or the further optionally present layer 8 consisting of aluminum oxide, and the copper layer 9, in a preferred configuration there can be an adhesion-promoter layer 10 which consists by way of example of a transition metal, in particular of titanium, chromium or nickel, with thickness D.sub.10 that can preferably be in the range 5 nm to 25 nm, particularly preferably in the range 10 nm to 20 nm.

(29) As likewise already mentioned, this advantageously has the result that the electrical contact resistance on the reverse side or underside B of the composite material V of the invention is negligibly small. This side B can therefore be soldered onto a printed circuit board PCB, or applied thereto by means of a similar coherent bonding process. The reference sign L is used in each of FIGS. 1 and 4 to indicate the coherent bonding layer. Soldering can advantageously be achieved by way of example by using tin-containing standard electrical solders, e.g. Sn.sub.96.5Ag.sub.3Cu.sub.0.5.

(30) Despite a relatively thin surface layer 9 of the metal or of the metal alloy, in particular of a copper layer, there has been found to be no formation, between the composite material V of the invention and the solder, of intermetallic phases which are relatively thick in relation to the layer thickness D.sub.9, and brittle, and could lead to mechanical—and consequently also electrical—failure of the soldered joint due to thermal stresses: storage under hot conditions for up to 1000 h leads only to formation of an intermetallic phase with thickness of a few 100 nm. It was also found that the soldered bond of the bonding layer L advantageously passed typical tests, in that a peel force or shear force required to separate the connected components LF and COB decreased only by a factor of less than 2 after storage under hot conditions, e.g. at 120° C. for 1000 h.

(31) There can optionally be a passivating layer, not depicted, on the layer 9 of a metal or of a metal alloy superficially applied, and in particular on the copper layer. This can preferably consist of Ag, Ni, Pd and/or Au (Ag/Ni/Pd/Au), its typical thickness possibly being in the range 10 nm to 500 nm, preferably in the range 50 nm to 250 nm. A layer of this type moreover improves the solderability of the finished SMD component on the PCB, because the solder can achieve better wetting of the noble-metal surface.

(32) A light-emitting device LV of the invention—see in this connection FIGS. 2 and 4—comprises the reflective composite material V of the invention, which can form a lead frame LF for the electronic SMD component, for example a light-emitting diode configured as bare-chip DIE. FIG. 3 depicts this type of lead frame LF. In the form depicted, it has the shape of an H in plan view, where the crossbar Q thereof between the tracks termed fingers F does not run at right angles but instead—as depicted—frequently runs obliquely. This type of lead frame LF can be produced in technologically advantageous manner by way of example by a die-cutting process or by laser cutting. Another possible configuration, if required, is as product of a bending process, because problem-free bending of the composite material V is possible without loss of quality.

(33) It is possible here to begin by combining a large number of lead frames LF in a frame device in the form of a circuit board in strip form in which the lead frames LF are incorporated in fields, i.e. in the form of line elements and of column elements, by way of connectors. The lead frames LF can easily be removed from the frame device, for example broken away or die-cut, thus permitting advantageously easy automated mass production in particular of light-emitting devices LV of the invention. There can be electronic chips SMD provided here to the upper sides of the lead frames LF.

(34) The electronic SMD/DIE component lies on the upper side in the light-emitting device LV of the invention, i.e. on the side A of the lead frame LF, and has been electrically contacted with the lead frame LF by means of at least one separate wire D. FIG. 2 additionally depicts, alongside the LED-die (reference symbol: DIE), a Zener diode Z as further surface-mounted electronic SMD component at the bottom right-hand side. The composite made of the electronic SMD component—or in the case depicted of the two electronic SMD (DIE and Z) components depicted—and of the lead frame LF has been coherently bonded in electrically conductive manner on the underside (side B) to a printed circuit board PCB.

(35) On the carrier 1 there can also be—in a modification of the embodiment depicted—other reflection-boosting systems 3 with other layers. In this connection, particular mention may be made of the system of DE 10 2015 114 095 A1 with the reflection-boosting silver layer, in so far as it is designed according to the invention. In contrast, the system described in WO 2017/032809 A1 necessarily provides, in the interlayer 2, the presence of an organic layer-forming lacquer with thickness up to 5 μm; this situation should be avoided according to the invention. The wording “interlayer 2 made of aluminum oxide” should preferably be regarded according to the application as having the narrow meaning “exclusively consisting of”, but according to the application the optional existence of sublayers in the interlayer 2 cannot be entirely excluded. However, in every case the thickness D.sub.2 of the entire interlayer 2 should then be in the range 5 nm to 200 nm.

(36) Although the optical multilayer system 3 can have more than the layers 4, 5, 6 described above, it is not permissible according to the invention to apply thereon, as outer layer 7, an organic or organosilicon lacquer layer, e.g. based on a sol-gel layer of the type likewise described in the prior art.

(37) The person skilled in the art can, within the scope of the claims, provide other advantageous embodiments of the invention without departing from the scope of the invention. By way of example, in FIG. 4 the surface of the light-emitting device LV of the invention has been potted with a transparent composition M, e.g. with an epoxy resin. Alternatively or additionally, there could also be optical lens systems provided above the electronic SMD component configured as LED chip DIE.

(38) In so far as a silver layer is mentioned above, in particular as reflective layer 6, this includes the possibility that the said layer comprises alloy elements in the range 0.001 percent by mass to 5.0 percent by mass, in particular in the range 0.5 percent by mass to 3.0 percent by mass. The alloy elements can by way of example be a rare earth element such as neodymium. Elements of this type can by way of example migrate to the silver grain boundaries and/or accumulate at the surface of the silver layer, thus becoming oxidized there more readily than the nobler silver and forming a microscopically thin protective layer on the silver grains. The effectiveness of these alloy elements can be further increased by use of palladium, platinum, gold and/or copper for additional alloying. This also inhibits diffusion, and counters coalescence of silver crystallites, in particular at the relatively high temperatures that may arise under operating conditions. This advantageously results in retarded ageing of the reflective layer, i.e. delayed decrease of reflectivity due to passage of time and/or to temperature-related effects.

(39) Palladium can also be alloyed as main alloy element with the silver, the proportion by mass of palladium preferably being in the range 0.5 percent by mass to 3.0 percent by mass of the alloy, and additionally a smaller proportion or at most the same proportion of one of the elements aluminum, gold, platinum, copper, tantalum, chromium, titanium, nickel, cobalt or silicon can be present here as third alloy component.

(40) Silver layers can also be alloyed with molybdenum, and in contrast to the above in comparatively high proportions—in particular up to 70 percent by mass, preferably 5 percent by mass to 30 percent by mass. This likewise results in inhibition of diffusion, and moreover in improved adhesion properties of the silver.

(41) Indium, titanium and/or tin can also be provided as alloy elements for the silver. By way of example, an alloy that appears to be suitable in this connection preferably comprises indium and/or tin and/or also antimony and/or bismuth in the range 0.5 percent by mass to 3.0 percent by mass, where the remainder consists of silver.

(42) A suitable target for producing silver-alloy layers in a sputtering process is also described in EP 3 196 334 A1.

(43) Within this specification, embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.

(44) The invention is not restricted to the feature combinations described in the independent claims, but can also be defined via any desired other combination of particular features from the entirety of all of the individual features disclosed. In principle, therefore, practically any individual feature of independent claims 1 and 16 can be omitted or replaced by at least one individual feature disclosed at another point in the application. Claims 1 and 16 are therefore to be understood merely as an example to formulate an invention. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

LIST OF REFERENCE SIGNS

(45) 1 Carrier of V 2 Interlayer of V on 1 (side A) 3 Optically active multilayer system of V on 2 (side A) 4, 5 Upper layers of 3 (side A) 6 Undermost layer of 3, reflective layer (side A) 7 Outer layer of V at top of 3 (side A) 8 Al.sub.2O.sub.3 layer of V on 1 (side B) 9 Layer of a metal or of a metal alloy (side B) A Upper side of 1 B Underside of 1 D Wire D.sub.1 Thickness of 1 D.sub.2 Thickness of 2 D.sub.3 Thickness of 3 D.sub.4 Thickness of 4 D.sub.5 Thickness of 5 D.sub.6 Thickness of 6 D.sub.7 Thickness of 7 D.sub.8 Thickness of 8 D.sub.9 Thickness of 9 DG Total thickness of V DIE Light-emitting diode, bare-chip embodiment of SMD (FIGS. 2, 4) F H finger of LF (FIGS. 2, 3) L Bonding layer between V and PCB LF Lead frame LV Light-emitting device with V M Transparent composition of LV (FIG. 4) PCB Printed circuit board Q H crossbar of LF (FIG. 3) SMD Electronic component (surface-mounted device) SP Weld point (FIG. 2) V Composite material Z Zener diode, embodiment of SMD (FIG. 2)