The present disclosure relates to a light emitting device having a light-emitting diode (LED) chip.
In the relevant art, according to industrial practices, a fluorescent material is generally disposed on LED chip by means dispensing, molding, spray coating and so on. However, these conventional methods have problems concerning process control and costs due to their processing properties. For example, dispensing tends to see precipitation of the fluorescent material that is turn brings about the yellow-halo problem, leading to inconsistent color temperature and a wide range of bins. Molding has distribution of the fluorescent material vary with distribution of pressure, and also tends to have inconsistent color temperature and a wide range of bins. Spray coating, on the other hand, is less subject to problems related to inconsistent color temperature and a wide range of bins, but the process requires repeated spray coating and tests, making it a time-consuming and low-material-utilization approach.
In addition, anisotropic conductive adhesive (ACA) is also used in the industry for binding before molding is performed to install a translucent layer. Such an approach is as illustrated in detail in
In view of the above, the present disclosure provides a novel packaging scheme for addressing the problems related to traditional application of fluorescent material. A light emitting device of the present disclosure comprises: a substrate; an LED chip, disposed on the substrate; and a fluorescent layer, the fluorescent layer being at least partially and conformally coated on the LED chip and the substrate. In a variant example of the foregoing light emitting device, the light emitting device further comprises a reflective portion, surrounding the LED chip and/or the fluorescent layer. In another variant example of the foregoing light emitting device, the light emitting device comprises a translucent layer coated on the fluorescent layer.
Particularly, the present disclosure uses semi-cured fluorescent resin to form the fluorescent layer, and this approach has at least the advantages listed below.
A. The semi-cured fluorescent resin helps to control distribution of the fluorescent material, keeping the manufacturing cost low and allowing quick processing of light emitting devices.
B. With the use of semi-cured fluorescent resin, the thickness of plastic sheet can be controlled effectively, thereby reducing the problems related to inconsistent color temperature and wide bin range.
C. The semi-cured fluorescent resin protects the LED chip and the die bonding area from external force and foreign matters that cause the chip to come off or get damaged.
D. It is applicable to a molding process using ACA. In this case the semi-cured fluorescent resin protects the chip and the electrode pads by preventing the resin of the translucent layer from passing through ACA, and in turn preventing the chip from separating from the electrode pads.
E. It is applicable to a wiring process. In this case the semi-cured fluorescent resin protects the chip and the wires, balls or welding spots from external compression.
With the aforementioned advantages, the disclosed packaging scheme is suitable for various LED devices from and processes for all types of chips, making it of great industrial applicability.
In addition, the disclosed packaging method conformally disposes the fluorescent layer on the LED chip. For preventing the problem that fluorescent material is affected by the external moisture and has the overall reliability degraded, the encapsulation resin suitable has its moisture permeability below 11 g/m2/24 Hr and has its oxygen permeability below 400 cm3/m2/24 Hr so as to reduce impact of moisture/oxygen on the fluorescent material. By using encapsulation resin with specific physical properties, reliability of the fluorescent material can be effectively improved. Particularly, tetravalent-manganese-activated red fluorescent material is subject to hydrolysis when affected by moisture and has its luminous efficacy and reliability degraded. The red fluorescent material has a chemical formula of A2[MF6]:Mn4+, wherein A is selected from Li, Na, K, Rb, Cs, NH4 and any combination thereof and M is selected from Ge, Si, Sn, Ti, Zr and any combination thereof. In addition, fluorescent materials of other color may be used for further expanding the color gamut of the resultant light emitting device. Thus, by selecting encapsulation resin that has its moisture permeability and oxygen permeability in the above-indicated ranges, the present invention can solve its potential technical issues.
It is to be noted that in the present disclosure the encapsulation resin refers to any resin covering the LED chip for packaging the chip. In a lamination process, it may solely refer to a fluorescent layer (where there is no translucent layer), or a combination of a fluorescent layer and a translucent layer (where there is a translucent layer). In a dispensing process, it may refer to dispensing resin. Such dispensing process will be described in detail later.
The present disclosure as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of illustrative examples when read in conjunction with the accompanying drawings.
The components in the disclosed device are now to be described by emphasizing their materials and features.
<Substrate/Carrier>
In the present disclosure, a carrier forms substrates after cutting. In the present disclosure, the substrate/carrier may be a board made of any suitable material, such as a metal leadframe, a printed circuit board, a ceramic board, a glass board, a plastic board and a flexible board. Particularly, where the substrate /carrier is realized by a metal leadframe, it is preferable that the metal leadframe has its internal space filled with a space filler, so as to enhance the overall mechanical strength of the leadframe. Additionally, in some embodiments, the carrier may be removed after a later singulation step, so as to produce a light emitting device without substrate. In this case, the carrier is preferably one with release film on it, so it can be easily removed from the light emitting device when the final singulation step has been done.
<Chip>
In the present disclosure, any suitable LED chip may be used. Preferably, the LED chip may be one made of any GaN-based semiconductors, e.g. an InGaN chip. More preferably, the LED chip has a peak wavelength between 450 nm and 460 nm. The LED chip may be one of any of various designs, e.g. a horizontal chip, a vertical chip and a flip chip. It is to be specially noted that both horizontal and vertical chips require a conductive wire for connection with external electrodes. Such conductive wire and other components as well as their assembly will be detailed by means of some embodiments provided later.
<Fluorescent Material>
Any fluorescent materials that commonly used in the art can be used for the purpose of the present disclosure. Particularly, the fluorescent material may be one or more selected from the group consisting of: Sr5(PO4)3Cl:Eu2+, (Sr,Ba)MgAlO17:Eu2+, (Sr,Ba)3MgSi2O8:Eu2+, SrAl2O4:Eu2+, SrBaSiO4:Eu2+, CdS:In, CaS:Ce3+, Y3(Al,Gd)5O12:Ce2+, Ca3Sc2Si3O12:Ce3+, SrSiON:Eu2+, ZnS:Al3+,Cu+, CaS:Sn2+, CaS:Sn2+,F, CaSO4:Ce3+,Mn2+, LiAlO2:Mn2+, BaMgAl10O17: Eu2+,Mn2+, ZnS:Cu+,Cl−, Ca3WO6:U, Ca3SiO4Cl2:Eu2+, SrxBayClzAl2O4-z/2:Ce3+,Mn2+ (X:0.2, Y:0.7, Z:1.1), Ba2MgSi2O7:Eu2+, Ba2SiO4:Eu2+, Ba2Li2Si27:Eu2+, ZnO:S, ZnO:Zn, Ca2Ba3(PO4)3Cl:Eu2+, BaAl2O4:Eu2+, SrGa2S4:Eu2+, ZnS:Eu2+, Ba5(PO4)3Cl:U, Sr3WO6:U, CaGa2S4:Eu2+, SrSO4: Eu2+,Mn2+, ZnS:P, ZnS:P3−,Cl−, ZnS:Mn2+, CaS:Yb2+,Cl, Gd3Ga4O12:Cr3+, CaGa2S4:Mn2+, Na(Mg,Mn)2LiS4O10F2:Mn, ZnS:Sn2+, Y3Al5O12:Cr3+, SrB8O13:Sm2+, MgSr3Si2O8:Eu2+,Mn2+, α-SrO.3B2O3:Sm2+, ZnS—CdS, ZnSe:Cu+,Cl, ZnGa2S4:Mn2+, ZnO:Bi3+, BaS:Au,K, ZnS:Pb2+, ZnS:Sn2+,Li+, ZnS:Pb,Cu, CaTiO3:Pr3+, CaTiO3:Eu3+, Y2O3:Eu3+, (Y,Gd)2O3:Eu3+, CaS:Pb2+,Mn2+, YPO4:Eu3+, Ca2MgSi2O7:Eu2+,Mn2+, Y(P,V)O4:Eu3+, Y2O2S:Eu3+, SrAl4O7:Eu3+, CaYAlO4:Eu3+LaO2S:Eu3+, LiW2O8:Eu3+,Sm3+, (Sr,Ca,Ba,Mg)10(PO4)6Cl2: Eu2+,Mn2+, Ba3MgSi2O8: Eu2+,Mn2+, ZnS:Mn2+,Te2+, Mg2TiO4: Mn4+, K2SiF6:Mn4+, SrS:Eu2+, Na1.23K0.42Eu0.12TiSi4O11, Na1.23K0.42Eu0.12TiSi5O13:Eu3+, CdS:In,Te, CaAlSiN3:Eu2+, CaSiN3:Eu2+, (Ca,Sr)2Si5N8:Eu2+, and Eu2W2O7.
Particularly, a red fluorescent material activated by tetravalent manganese may be used in the present disclosure. Such red fluorescent material has a chemical formula of A2[MF6]:Mn4+, where A is selected from Li, Na, K, Rb, Cs, NH4 and any combination thereof and M is selected from Ge, Si, Sn, Ti, Zr and any combination thereof.
In the present disclosure, the red fluorescent material has an average particle size (d50) preferably between 18 μm and 41 μm. Examples of such red fluorescent material include: K2SiF6:Mn4+, K2TiF6:Mn4+ and K2GeF6:Mn4+ in which K2SiF6:Mn4+ is preferable. These red fluorescent materials when excited by a light source having a peak in a wavelength range between 450 nm and 460 nm can emit light having a primary peak in a wavelength range between 600 nm and 650 nm. It is to be noted that the primary peak mentioned herein refers to the wavelength at which point the fluorescent materials reach the greatest luminous intensity thereof. Moreover, the present disclosure is not limited to use of a single red fluorescent material, and two or more fluorescent materials recited previously can be used together.
For further expanding the color gamut of the light emitting device, it is preferable to use an oxynitride fluorescent material as a green light source. More preferably, the green fluorescent material has a chemical formula selected from the group consisting of M(II)7Al12−x−ySix+yO25−xNx−yCy:A; M(II)7M(III)12−x−ySix+yO25−xNx−yCy:A; and M(II)7M(III)12−x−ySix+yO25−x±3δ/2Nx∓δ−yCy:A, where 0<x≦12; 0<y<x; 0<x+y≦12; 0<δ≦3; and δ<x+y; M(II) is a bivalent cation selected from the group consisting of: Be, Mg, Ca, Sr, Ba, Cu, Co, Ni, Pd, Zn, Cd and any combination thereof; M(III) is a trivalent cation selected from the group consisting of: B, Al, Ga, In, Sc, Y, La, Gd and any combination thereof; and A is an active center selected from the group consisting of: Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Mn, Bi, Sb and any combination thereof. In the present disclosure, the green fluorescent material has an average particle size (d50) preferably between 18 μm and 22 μm.
Where a red fluorescent material and a green fluorescent material are used together in the present disclosure, the red fluorescent material and the green fluorescent material have a weight ratio of 1:1˜3:1 because such ratio endows the resultant light emitting device with better color rendering.
<Fluorescent Layer>
In the present disclosure, the fluorescent layer is formed by curing and cutting semi-cured fluorescent resin. The semi-cured fluorescent resin referred to herein is a B-stage resin composition. Under this state, the resin composition has good shape-retaining ability, yet is capable of deforming under external force, and it softens when heated and swells when contacting a solvent, without being fully melted or dissolved. Further, in the present disclosure, the semi-cured fluorescent resin comprises a fluorescent material, a siloxane resin, a catalyst and a solvent. Based on the weight of the fluorescent layer, the weight of the fluorescent material is 10% to 60%; the weight of the siloxane resin is 28% to 89.3%; the weight of the catalyst is 0.1% to 2%; and the weight of the solvent is 0.1% to 2%. Moreover, in the present disclosure, the semi-cured fluorescent resin may also comprise a softening agent. Preferably, based on the weight of the fluorescent resin, the weight of the softening agent is 0.5% to 8%. Particularly, after the semi-cured fluorescent resin with the foregoing composition undergoes a curing process (e.g. pressing/baking), the solvent evaporates therefrom. At this time, based on the weight of the final fluorescent layer, the weight of the fluorescent material is 10% to 61.2%; the weight of the siloxane resin is 28% to 91.1%; and the weight of the catalyst is 0.1% to 2%. Where a softening agent is used, the weight of the softening agent is 0.5% to 8.2%.
In some embodiments, the fluorescent layer may be made of resin having its moisture permeability below 11 g/m2/24 Hr and having its oxygen permeability below 400 cm3/m2/24 Hr. Preferably, the resin us such selected that its moisture permeability is below 10.5 g/m2/24 Hr, and oxygen permeability is below 382 cm3/m2/24 Hr, so as to reduce hydrolysis or degradation of the fluorescent material and in turn improve the overall reliability of the light emitting device. Such selection of the resin improves the reliability of the tetravalent-manganese-activated red fluorescent material significantly.
In the present disclosure, the term “moisture permeability” refers to measured values obtained using TSY-TH1 Water Vapor Permeability Tester, and the term “oxygen permeability” refers to measured values obtained using i-Oxtra 7600 Oxygen Permeation Analyzer.
<Reflective Portion>
The present disclosure may further comprise a reflective portion. The reflective portion is formed by curing and cutting reflective resin. Particularly, the reflective resin is a resin composition containing reflective particles. The reflective particles contribute to high light convergence and may be selected form TiO2, SiO2, ZrO, MgO, BaSO4 and any combination thereof, in which TiO2 is preferable. The resin may be epoxide-based resin or siloxane-based resin, in which siloxane-based resin is preferable.
<Translucent Layer>
In the present disclosure, the translucent layer is made by curing and cutting translucent resin and may comprise light-diffusing particles for further enhanced uniformity of light. The light-diffusing particles may be selected from BN, SiO2 and the combination thereof. Additionally, in some embodiments of the present disclosure, the translucent layer and the semi-cured fluorescent resin have the same basic resin and are formed into translucent layers through similar processes, with the only difference relying on addition of the fluorescent material. In this case, the translucent layer is also conformal, and the cured translucent layer serves to protect the fluorescent layer by preventing moisture from entering the fluorescent layer, so as to improve endurance of the light emitting device. However, in some embodiments, the translucent layer has its moisture permeability and oxygen permeability preferably lower than those of the fluorescent layer, making it more protective. Particularly, in some embodiments, the translucent layer is made of resin having its moisture permeability below 11 g/m2/24 Hr and having its oxygen permeability below 400 cm3/m2/24 Hr. Preferably, the resin has its moisture permeability below 10.5 g/m2/24 Hr, and has its oxygen permeability below 382 cm3/m2/24 Hr.
A first embodiment is herein described in detail to illustrate the fluorescent layer of the present disclosure in regards of process and characteristic.
The method of the present disclosure and characteristics and other parameters of the semi-cured fluorescent resin are herein described in detail with reference to
The mixture such made is then applied to a plane to form a thin layer. Again, the present disclosure has no limitation to the method of applying, and the method may be rotary coating, spin coating, knife coating, and dipping coating. In addition, for controlling the thickness of the final semi-cured fluorescent resin within a preferable range between 45 μm and 230 μm, the thin layer is such made that its thickness is 50 μm to 250 μm, more preferably 70 μm to 185 μm. In the examples mentioned below, knife coating is used for forming the thin layer as an example. When the thickness is below 45 μm, the fluorescent resin tends to have weakened strength, and the fluorescent material tends to have uneven distribution and in turn poor color uniformity. On the other hand, a thickness greater than 250 μm is too thick and thus leads to unnecessary high material costs. Besides, the excessive thickness thickens the final light emitting device, and is against to the prevailing trend toward microminiaturization.
After formed, the thin layer is processed into a semi-cured state. In the present disclosure, the method for making the thin layer a semi-cured one may be any suitable technologies without limitation, and preferably baking. Particularly, the baking temperature is preferably performed for 1 to 4 hours at 65° C. to 75° C. so as to endow the fluorescent layer with acceptable shape-retaining ability and ability to deform under external force.
Optionally, before baked, the thin layer may be put aside for a while or performs centrifugal treatment to let the fluorescent material deposit at the bottom of the thin layer. Alternatively, thin layers each having different concentrations of the fluorescent material or having different types of fluorescent materials may be stacked and baked together, so as to form a laminated semi-cured fluorescent layer.
After formed, the semi-cured thin layer is cut into pieces of semi-cured fluorescent resin. The cutting may be performed in any manner without limitation. In addition, the present disclosure may include measuring color temperature of the cut pieces of semi-cured fluorescent resin, so as to sort the cut pieces by color temperature.
One specific example of the semi-cured fluorescent resin according to the present disclosure will be discussed below.
First, based on the weight of the final fluorescent resin, 19.12 g of siloxane resin, 0.455 g of toluene, 9.8 g of yttrium aluminium garnet fluorescent material and 0.6 g of a catalyst were put into a vacuum deaearation mixer for two-stage mixing so as to form a mixture. The first stage was performed for 3 minutes under 1 atm and at the room temperature with a rotation rate of 800 rpm. The second stage lasted 30 seconds in a vacuum at the room temperature, with a rotation rate of 1200 rpm. The mixture such formed was then applied to a platform by means of knife coating so as to form a thin layer with a thickness of 75 μm. Afterward, the thin layer was baked for 2 hours in an oven of 70° C., so that the resin was partially cured and became B-stage/semi-cured fluorescent resin. The semi-cured fluorescent resin was at last cut into a predetermined size. A blue light emitting diode having a wavelength of 460 nm was used for measuring color temperature so as to sort the cut pieces of the semi-cured fluorescent resin by color temperature.
The following description is directed to the second through fourth embodiments of the present disclosure and stresses the manufacturing process and features of the disclosed light emitting device.
After finalized as described above, the semi-cured fluorescent resin can be used to make the disclosed light emitting device. The process for making the light emitting device of the present disclosure is herein explained with reference to the accompanying drawings.
First, as shown in
Then, semi-cured fluorescent resin 504 as made in the first embodiment is deposited to the carrier 500 having the LED chip 502, as shown in
After provision of the providing semi-cured fluorescent resin 504, laminating operation is performed, as shown in
Referring to
In the present disclosure, the laminating operation depicted in
First, the carrier 500 carrying the chip 502 and the semi-cured fluorescent resin 504 are placed on a hot-compressing cushion 600 (made of PTFE or PET) and fed into the laminating chambers 602a, 602b (Step 1;
In some variant examples, the light emitting device comprises a reflective portion, and the fluorescent layer is coated on the reflective portion, as shown in
In particular, after the LED chip 502 is deposited in the step of
In some variant examples, the light emitting device comprises a translucent layer 810. The translucent layer 810 is conformally coated on the fluorescent layer 514, as shown in
Particularly, after the semi-cured fluorescent resin 504 is laminated in
In some variant examples not shown, multiple layers of semi-cured fluorescent resin are stacked to form multilayer fluorescent resin, and finally form stacked fluorescent layers. In this example, different layers of the semi-cured fluorescent resin may be arranged according to the concentrations of the fluorescent material therein so as to provide desired light emission pattern and color uniformity. For example, the layers with higher fluorescent material concentrations are arranged lower (closer to the LED chip after laminated), while those with lower fluorescent material concentrations are stacked thereon, so that the fluorescent material concentrations are reduced upward as the fluorescent resin/fluorescent resin layers are stacked. On the contrary, the layers of the semi-cured fluorescent resin having lower fluorescent material concentrations may be arranged lower, and those with higher fluorescent material concentrations may be put thereon in order, so that the material concentrations are increased upward as the layers are stacked. Additionally, In light of light conversion rate, the fluorescent resins with different fluorescent materials may be orderly stacked. For instance, the layers are such arranged that yellow/green fluorescent materials are close to the LED chip, and red fluorescent materials are arranged on the yellow/green fluorescent materials.
In the present disclosure, the translucent layer and the fluorescent layer are made of materials with different characteristics. Since the fluorescent layer directly covers the chip, the conductive wire and the substrate, it serves to not only keep the relative position of the three components, but also to some extent buffer the pressure generated when the translucent layer is applied. The translucent layer is subject to its optical and protective purposes, and may thus have its shape designed for better light diffusion. In particular, the translucent layer is usually made of a material having relatively high mechanical strength and relatively low moisture permeability and oxygen permeability. However, for the sake of tight combination and easy application, it may be made of the same basic resin as the fluorescent layer. In this case the translucent layer and the fluorescent layer are substantially the same.
In this embodiment, the translucent layer is formed by laminated layers of semi-cured resin. However, in some variant examples, the translucent layer may be formed by means of molding, rotary coating, or knife coating so as to have an even upper surface, and its material may be resin of relative high rigidity, e.g. epoxy resin. Reference is now made to
In some variant examples, the fluorescent layer and the translucent layer may have their lateral surface provided with reflective portions, as shown in
After the structure as shown in
In the light emitting device as shown in
In the variant example shown in
The present disclosure has no limitation to the method that prevents the fluorescent layer from extending to the edges of the substrate. For example, the fluorescent layer may be precut after laminated in the step of
In the present disclosure, while the fluorescent layer is conformally coated on the LED chip and the substrate, its thickness is unnecessarily uniform. In some variant examples, the fluorescent layer has a variable thickness, as shown in
In the light emitting device as shown in
In the present disclosure, for minimizing degradation of the fluorescent material, it is preferable to use a resin composition having its moisture permeability below 11 g/m2/24 Hr and having its oxygen permeability below 400 cm3/m2/24 Hr as the encapsulation resin (referred to the fluorescent layer and/or the translucent layer with the conformal process). Particularly, in the present disclosure, such encapsulation resin provides excellent protection to tetravalent-manganese-activated fluorescent materials. The following experiment is discussed for explaining the benefits of the encapsulation resin.
In addition, in some variant examples, an oxynitride fluorescent material may be further added, as shown in
In the present disclosure, the dispensing resin may be a phenyl siloxane resin composition or a methyl siloxane resin composition. The dispensing resin has its refractive index above for example 1.5, and preferably between 1.5 and 1.6. The dispensing resin may contain the foregoing fluorescent material, and may additionally contain a staining agent, a light diffusion agent, a filler and/or other additives.
A few experiments are discussed herein for demonstrating the benefits of resin compositions that have the characteristics defined in the present disclosure. However, the scope of the present disclosure shall not be limited thereto.
A 450 nm-light beam was selected to identify the emission spectrum of a red fluorescent material of CaAlSiN3:Eu2+ (acquired from NEMOTO Company, Japan), and the result is shown in
A 450 nm-light beam was selected to identify the emission spectrum of a red fluorescent material K2Si0.95F6:Mn4+0.05 of the present disclosure, and the result is shown in
As can be seen in
(Si,Al)6(O,N)8:Eu2+ (acquired from DENKA Company Limited, Japan) and K2Si0.95F6:Mn4+0.05 were mixed at a weight ratio of 1.5:1 and then such added into Encapsulation Resin A (with moisture permeability of 10.5 g/m2/24 Hr; oxygen permeability of 382 cm3/m2/24 Hr) that a ratio between the weight of the resin and the total weight of the powder came to 1:1.2. The encapsulation resin contained the fluorescent material was then used to encapsulate an InGaN chip.
Sr7(Si,Al)12(O,N,C)25: Eu2+ and K2Si0.95F6:Mn4+0.05 were mixed at a weight ratio of 1:1 and then such added into Encapsulation Resin A (phenyl-based silicone, moisture permeability of 10.5 g/m2/24 Hr; oxygen permeability of 382 cm3/m2/24 Hr) that a ratio between the weight of the resin and the total weight of the powder came to 1:0.8. The encapsulation resin contained the fluorescent material was then used to encapsulate an InGaN chip.
Light-on tests (with a lighting current of 20 mA) were performed on the light emitting devices made in Experimental Example 2 and Experimental Example 3, respectively, and the results are shown in Table 1 below, while the spectrums thereof are shown in
From Table 1 it is clear that with the same CIE-x and CIE-y, Experimental Example 2 exhibited 100% efficiency, yet Experimental Example 3 provided even higher efficiency that is 34% more as compared to Experimental Example 2. The increase of efficiency might be attributed to difference of chemical elements between the Sr7(Si,Al)12(O,N,C)25: Eu2+ fluorescent material (containing (Sr,Ca,Ba) Al, Si, O, N, C, Eu) in Experimental Example 3 and Experimental Example 2.
Sr7(Si,Al)12(O,N,C)25: Eu2+ and K2Si0.95F6:Mn4+0.05 were mixed at a weight ratio of 1:1 and then added into Encapsulation Resin B (phenyl-based silicone, having moisture permeability of 15 g/m2/24 Hr and oxygen permeability of 726 cm3/m2/24 Hr) so the weight of the resin and the total weight of the powder came to a ratio at 1:0.8. The encapsulation resin contained the fluorescent material was then used to encapsulate an InGaN chip.
The light emitting devices obtained in Experimental Example 3 and in Comparative Example 2 were lit up at various conditions for performed endurance test, and the result are shown in Table 2 below.
Term #1: driving current of 150 mA, temperature of 60° C., relative humidity of 90%.
Term #2: driving current of 150 mA, temperature of 25° C., in atmosphere.
Term #3: driving current of 150 mA, temperature of 25° C., in atmosphere.
Term #4: driving current of 45 mA, temperature of 85° C., in atmosphere.
ΔIV: reduction in brightness as compared to initial brightness, expressed in percentage.
ΔX: CIE X coordinate deviation from initial brightness.
ΔY: CIE Y coordinate deviation from initial brightness.
In the endurance tests recorded in Table 2, the only difference between Experimental Example 3 and Comparative Example 2 relies on their moisture permeability and oxygen permeability. According to the results shown in Table 2, the light emitting device obtained in Experimental Example 3 under all the test terms exhibited less IV reduction and less CIE coordinate deviation as compared to the light emitting device obtained in Comparative Example 2. This demonstrates that the combination of the fluorescent materials of the present disclosure when working with resin having its moisture permeability below 10.5 g/m2/24 Hr and having its oxygen permeability below 382 cm3/m2/24 Hr can resist hydrolysis and degradation better.
To sum up, by using the red fluorescent material that has a chemical formula of A2[MF6]:Mn4+ with encapsulation resin possessing specific physical properties, the present disclosure can not only expand the color gamut of a TV backlight source, but also prevent the red fluorescent material from hydrolysis and degradation, thereby improving overall reliability of the disclosed light emitting device. In addition, according to the present disclosure, fluorescent materials of other colors may be used additionally to further expand the color gamut of a backlight source.
The following description is directed to a case where the chip of the light emitting device requires wiring, namely the case where a horizontal chip or a vertical chip is used in the disclosed light emitting device. When a horizontal chip or vertical chip is used as the chip of the present disclosure, a conductive wire has to be provided to connect the upper surface of the chip with the circuit pattern of the substrate. In this case, a conventional approach of applying rigid resin onto the conductive wire is likely to break the wire. The present disclosure differently uses the semi-cured fluorescent resin as the precursor of the fluorescent layer, so the semi-cured fluorescent resin conforms its own shape to the conductive wire. Alternatively, the conductive wire may run through, so as to not break due to application of the resin. The cured fluorescent layer then serves as a buffer between the subsequently applied translucent layer or other external material and the conductive wire for absorbing stress so as to protect the conductive wire, or protect the connection between the chip and the electrodes.
In this embodiment, the fluorescent layer is conformally coated on the conductive wire. A void portion may be formed below the conductive wire. The fluorescent layer flanks the conductive wire from two sides of the void portion. In another embodiment, no void portion is formed below the conductive wire, and thus the fluorescent layer can fully embrace conductive wire. Alternatively, the conductive wire has its highest point, or its apogee, passing through the fluorescent layer. In this case the ends of the conductive wire that are connected to the chip are embraced by the fluorescent layer.
First, after the LED chip 1302 is deposited on the carrier 1300, wire bonding is performed to connect one end of at least one conductive wire 1304 with the upper surface of the LED chip 1302, and connect an opposite end of the conductive wire 1304 with a conductive pattern (not shown) of the carrier 1300, as shown in
Then, a semi-cured fluorescent resin 1306 is provided and laminating operation is performed. After lamination, the semi-cured fluorescent resin 1306 conformally covers the conductive wire 1304, meaning that in a top view of the assembly the semi-cured fluorescent resin 1306 flasks the conductive wire 1304 from two sides thereof. In some embodiments, a void portion may be formed below the conductive wire, as shown in
Then, as an optional step, a translucent resin 1309 is applied onto the semi-cured fluorescent resin 1306 and cured, as shown in
In some variant examples, the conductive wire may pass through the fluorescent layer. Particularly, the conductive wire has its highest point, or its apogee, passing through the fluorescent layer, and the two ends of the conductive wire that are connected to the LED chip and the light emitting device, respectively, may be embraced by the fluorescent layer, as shown in
After the wire bonding step as shown in
In some other variant examples not shown, a wired chip may be used in the embodiment as shown in
A light emitting device made using anisotropic conductive adhesive (ACA) and a molding process according to the present disclosure is now discussed. Reference is first made to
In Step 1, a metal leadframe 1500 is provided on the release film, wherein the laterals of the metal leadframe 1500 may partially or fully embedded in the release film (
In Step 2, ACA 1502 is deposited on the metal leadframe 1500 (
In Step 3, the ACA 1502 fixes the LED chip 1504 to the metal leadframe 1500 (
In Step 4, semi-cured fluorescent resin 1506 that can be placed on the surface of the LED chip 1504 is provided as a conformal pattern. The semi-cured fluorescent resin 1506 may extend to cover the lateral surface of the ACA 1502 and the lateral surface of the metal leadframe 1500 if necessary (
In Step 5, translucent resin 1508 is provided on the semi-cured fluorescent resin 1506 (
In Step 6, singulation is performed to form a plurality of light emitting devices (
Through the steps given above, a light emitting device as shown in
In some variant examples, as shown in
In some variant examples, different form the light emitting device of
In some variant examples, the lateral surface 1600a, 1602a of the electrode pads 1600, 1602 are level with the lateral surface 1616a of the fluorescent layer 1616 and the lateral 1618a of the translucent layer 1618, respectively, as shown in
Since the fluorescent layer 1616 contains the fluorescent material, if the translucent layer 1618 and the fluorescent layer 1616 have their lateral surfaces level with each other, some converted light would be directly emitted from the lateral surface of the fluorescent layer 1616, leading to inconsistent light color. For addressing this problem, in some variant examples, the translucent layer 1618 extends to cover the lateral surface 1616a of the fluorescent layer 1616 and is not level with the bottoms of the electrode pads 1600, 1602, as shown in
In some variant examples, for maintaining proper mechanical strength between the LED chip and the electrodes, especially in a case where the electrode pads 1600, 1602 are thinner than the chip 1064, the fluorescent layer 1616 may extend into the space 1608 between the P-type electrode pad 1600 and the N-type electrode pad 1602, as shown in
As an approach to improving the mechanical strength of the carrier /substrate in addition to the foregoing variant examples, a space filler 1620 may be provided at the lateral surface 1600a, 1602a of the electrode pads 1600, 1602 and filled into the space 1608. Referring to
In some variant examples, it is possible to use anisotropic conductive film (ACF) instead of ACA, thereby further improving mechanical strength of the light emitting device and preventing the LED chip from coming off the electrode pads. In particular, the ACF 1622 may be formed in various ways, such as printing or coating. The ACF 1622 may comprise the reflective particles named above for better reflectivity. Where the applied area of the ACF 1622 is greater than the combined area of the LED chip 1604 and the electrode pads 1600, 1602, light extraction efficiency is further enhanced. In addition, it is poosible to apply ACF onto a wafer directly, so that the ACF 1622 is directly formed on the electrode 1614 of the chip 1604. Thereby, the process of applying ACF to the electrically conductive leadframe during packaging operation can be omitted. The area of the ACF 1622 mat be of the same size as the area of the electrode 1614 of the chip 1604, as shown in
It is to be noted that while the light emitting device as shown in
Further, a method for manufacturing a light emitting device using ACF comprises the following steps:
Step 1: providing metal sheet;
Step 2: bonding LED chip to the metal sheet using ACF;
Step 3: providing a cover sheet to be placed on a surface of the LED chip as a conformal pattern;
Step 4: providing a resin for transfer moulding on the cover sheet; and
Step 5: performing singulation, so as to form a plurality of light emitting devices.
While the exemplary process described previously relates to use of a chip already having ACF (Step 2), it is apparent to people with ordinary skill in the art that the present disclosure is not limited thereto. Optionally, the ACF may be applied to the electrode pad/support before die bonding is performed thereon for the LED chip.
The present disclosure has been described with reference to the preferred embodiments and it is understood that the embodiments are not intended to limit the scope of the present disclosure. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present disclosure should be encompassed by the appended claims.
Number | Date | Country | Kind |
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104120755 | Jun 2015 | TW | national |
The present disclosure claims the priority benefit of Taiwan Patent Application No. 104120755, filed on Jun. 26, 2015, 2015, U.S. Patent Application No. 62/211,002, filed on Aug. 28, 2015, and U.S. Patent Application No. 62/248,313, filed on Oct. 30, 2015, which are incorporated by reference in their entirety.
Number | Date | Country | |
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62211002 | Aug 2015 | US | |
62248313 | Oct 2015 | US |