Light emitting diode package using fluid encapsulant

Abstract

A UV or DUV light emitting diode package comprising: a substrate; a first metal layer, a second metal layer, and a third metal layer formed on a top surface of the substrate, wherein the first metal layer is electrically isolated from the second metal layer by a first gap, the third metal layer surrounds the first metal layer and the second metal layer, and the third metal layer is electrically isolated from the first metal layer and the second metal layer by a second gap; a lens attached to the top surface of the substrate, wherein a cavity is formed between the substrate and the lens; an LED chip disposed in the cavity, wherein an anode of the chip is electrically connected to the first metal layer and a cathode of the chip is electrically connected to the second metal layer; and, a fluid encapsulant, wherein the cavity is completely or partially filled with the fluid encapsulant.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to light emitting diode packages using fluid encapsulants, and more particularly, to ultraviolet or deep ultraviolet light emitting diode packages using fluid encapsulants to improve reliability and light extraction. BACKGROUND

[0002] Light emitting diode (LED) packages generally include an LED chip and a package that houses the LED chip. The main function of the package is to facilitate electrical connection between the LED chip and external circuitry. Overall, the package also provides protection for the LED chip from mechanical and chemical stimuli. Fine packaging should also efficiently extract heat and light from the LED chip. This is particularly important for short wavelength LEDs such as ultraviolet (UV) or deep ultraviolet (DUV) LEDs, which generate a lot of heat and have poor light extraction.

[0003] In this specification, a DUV LED is considered to be an LED with a peak emission wavelength shorter than 350 nm, i.e., in the range of 200-350 nm, which is mainly made of AlGaN material with a high Al content. For DUV LEDs with a wavelength shorter than 280 nm, i.e., into the UV-C region, the n-AlGaN layer and the p-AlGaN layer require an Al content exceeding 60%. For AlGaN heterostructures with a high Al content, problems related to large resistivity, high contact resistivity, and strong polarization fields are inevitable. Therefore, DUV LEDs made of AlGaN heterostructures generally have additional voltage loss, and require a package with reduced thermal resistance to extract heat more efficiently. In addition, as the wavelength enters the UV-C range, the light generated in the multi-quantum well (MQW) of the DUV LED includes a large portion of transverse magnetic (TM) modes. TM mode light tends to have a large angle of incidence to the chip surface, typically greater than the critical light escape angle. This means that unless a means to expand the critical light escape angle is provided, the TM light is easily trapped inside the LED chip. In the prior art, as disclosed in US Patent Publication No. US20060138443 and US Patent No. 8,962,359, a dome-shaped lens is attached to the LED chip (or die) to improve the light extraction efficiency of the DUV LED. In addition, the lens attachment substance (or adhesive) and the chip encapsulant are the same material in the prior art, typically made of a UV transparent solidifying polymer such as polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS or silicone gel). These encapsulants / adhesives are attenuated under DUV radiation, posing a serious reliability problem for DUV LEDs.

[0004] Various embodiments of a DUV LED package with improved heat and light extraction efficiency and long-term reliability are disclosed below. SUMMARY

[0005] The present disclosure provides a light emitting diode package, comprising:

[0006] a substrate;

[0007] a first metal layer, a second metal layer, and a third metal layer formed on a top surface of the substrate, wherein the first metal layer is electrically isolated from the second metal layer by a first gap, the third metal layer surrounds the first and second metal layers and is electrically isolated from the first and second metal layers by a second gap;

[0008] a lens attached to the top surface of the substrate, wherein a cavity is formed between the substrate and the lens;

[0009] an LED chip disposed in the cavity, wherein an anode of the chip is electrically connected to the first metal layer and a cathode of the chip is electrically connected to the second metal layer; and

[0010] a fluid encapsulant, wherein the cavity is completely or partially filled with the fluid encapsulant. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application. The same reference numbers in different drawings identify the same elements, and layers can refer to a group of layers associated with the same function.

[0012] Figure 1A A top perspective view of a deep UV LED according to an aspect of the present disclosure is shown.

[0013] Figure 1B A bottom perspective view of a deep UV LED according to an embodiment of the present disclosure is shown.

[0014] Figure 1C A cross-sectional perspective view of a deep UV LED according to an embodiment of the present disclosure is shown.

[0015] Figure 1D A cross-sectional view of a lens attachment according to an embodiment of the present disclosure is shown.

[0016] Figure 1E A cross-sectional view of a deep UV LED according to an embodiment of the present disclosure is shown.

[0017] Figure 1F An exploded view of a deep UV LED according to an embodiment of the present disclosure is shown.

[0018] Figure 2A cross-sectional view of a lens attachment is shown according to embodiments of the present disclosure.

[0019] Figure 3A A top perspective view of a lens attachment grommet is shown according to embodiments of the present disclosure.

[0020] Figure 3B A bottom perspective view of a lens attachment grommet is shown according to embodiments of the present disclosure.

[0021] Figure 3C A cross-sectional view of a lens attachment is shown according to embodiments of the present disclosure.

[0022] Figure 4 Reliability data for two deep UV LED packages according to the present disclosure is plotted.

[0023] Figure 5A A top perspective view of an LED package including a bare deep UV LED chip mounted on a submount is shown according to another aspect of the present disclosure.

[0024] Figure 5B A top perspective view of an LED package including a deep UV LED covered by a lens is shown according to another aspect of the present disclosure. Figure 5A A top perspective view of a deep UV LED of the LED package shown.

[0025] Figure 5C A cross-sectional view of the deep UV LED shown in Figure 5B A perspective cross-sectional view of the deep UV LED shown in

[0026] Figure 6 A cross-sectional view of an LED package formed on a printed circuit board is shown according to another aspect of the present disclosure. DETAILED DESCRIPTION

[0027] In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these details. One skilled in the art will recognize that embodiments of the present disclosure described below can be implemented in a variety of ways and using a variety of apparatuses. One skilled in the art will also recognize that additional modifications, applications, and embodiments are within the scope of the present disclosure and that the present disclosure can provide additional opportunities for employing the principles of the present disclosure. Thus, the embodiments described below are illustrative only and are not intended to be limiting in any sense.

[0028] According to an aspect of the present disclosure, a DUV LED is provided that includes at least a DUV LED chip, a lens, a lens attachment (sealant or adhesive), and a chip encapsulant. The lens is substantially rigid (solid) and can be a flat DUV transparent window, or have a portion that is spherical or dome shaped, or any other suitable shape. The encapsulant is not rigid or solid. In some embodiments, the encapsulant can be a fluid or liquid, in other embodiments, the encapsulant can be a grease or gel. Optionally, both the lens and the encapsulant are DUV transparent, with a DUV refractive index optionally higher than 1.3. The lens attachment, which is optionally DUV transparent, reflective or absorbing, can be an elastomer when cured, and can reversibly extend more than 10%, for example, 100-1000%, when subjected to an external force or when relaxed. More specifically, the reversible extension as used herein means that the lens attachment can be compressed or stretched in one direction without degrading its material properties, such as mechanical strength, sealing, and elasticity.

[0029] One embodiment of a DUV LED 1000 package according to the present disclosure is shown in Figures 1A-1F This is a surface mount device (SMD). Figure 1A 、 Figure 1B and Figure 1Fare top and bottom perspective views, respectively, of a DUV LED 1000, and an exploded view. The base of the DUV LED 1000 is a submount 10, which can be an insulating ceramic body with high thermal conductivity. In one embodiment, the submount 10 can be an AIN ceramic body with a thickness of about 500 pm, which has a thermal conductivity higher than 100 W / m-K, for example, 130-320 W / m-K. In other embodiments, the base of the DUV LED 1000 can be a printed circuit board (PCB) or a metal core printed circuit board (MCPCB) to form a chip-on-board (COB) LED, which is described in more detail below, or can be other suitable base. DUV LED embodiments based on the ceramic submount 10 are disclosed in detail below as examples to illustrate the principles of the present disclosure. As shown, metal layers 21, 22, 23 can be formed side-by-side on the top surface of the submount 10 and are electrically isolated from each other by the gap formed between them. The metal layers 21, 22, 23 can have the same composition and thickness, for example, they can be 50-100 pm thick (such as 65 pm) metal layers made of copper, gold tin, or gold. In one embodiment, the metal layers 21, 22, 23 are formed by electroplating and are made of 65 pm copper coated with 4 pm nickel and about 100 nm gold. The gap formed between them can be 60-150 pm (such as 100 pm) wide and the same height as the thickness of the metal layers. In the DUV LED 1000, the metal layer 21 and the metal layer 23 are used as anode and cathode, respectively, to receive (contact) the anode and cathode of the DUV LED chip 50 and the electrostatic discharge (ESD) diode 52, respectively. The ESD diode 52 can be a zener diode or a pair of zener diodes that will conduct to shunt current and protect the DUV LED chip 50 if an unwanted high voltage spike occurs due to static or electrical surges. The metal layer 22 can be used to bond to the base 60.

[0030] Metallic contacts 31-33 are formed on the bottom surface of the submount 10. The metallic contacts 31, 33 are electrically connected to the metallic layers 21, 23, respectively, through metallic vias 12 formed in the submount 10. The metallic contacts 31-33 can have the same thickness and metal as the metallic layers 21-23. The metallic contact 32 is not biased and serves as a heat conducting pad, conducting heat together with the bond pad 42 formed thereon. The metallic contacts 31-33 are electrically isolated from each other by gaps of 100-200 μιη (such as 170 μιη) in width. Bond pads 41-43 are formed on the metallic contacts 31-33, respectively. Thus, the bond pads 41, 43 are electrically connected to the anode and cathode of the DUV LED chip 50 and the ESD diode 52, respectively. The bond pads 41-43 are used for soldering to a circuit board and can be made of copper, gold tin, gold, or tin with a thickness of 150-250 μιη (such as 200 μιη). In one embodiment, the bond pads 41-43 are formed by electroplating and are made of 200 μιη copper coated with 4 μιη nickel and about 100 nm gold. The bond pads 41-43 are electrically isolated from each other by gaps of 100-300 μιη (such as 270 μιη) in width.

[0031] A pedestal 60 is formed on the metallic layer 22, which can be a metallic (such as aluminum plated copper) ring with a central opening surrounding the DUV LED chip 50 and the ESD diode 52. The pedestal 60 can be bonded or electroplated on the metallic layer 22. The pedestal 60 can have a height (vertical dimension) of 200-500 μιη, such as 360 μιη, and a width (circumferential width of the ring or lateral dimension) of 400-600 μιη, such as 450 μιη. The inner sidewall of the central opening of the pedestal 60 surrounding the DUV LED chip 50 can be DUV reflective and has a tilt angle with respect to the top surface of the submount 10 so that light emitted from the edge of the DUV LED chip 50 can be reflected upward. There can be a notch 601 on the top surface of the pedestal 60 with a depth of 40-60 μιη (such as 50 μιη) and a width of 80-120 μιη (such as 100 μιη). A number (e.g., 4) of supports 90 are formed on the top surface of the pedestal 60 to help position the lens 100 on top of the pedestal 60 between the supports 90. The supports 90 can be made of copper and coated with a DUV reflective metal, such as aluminum, with a height of 100-500 μιη, such as 200-400 μιη. The lens 100 is substantially rigid (solid) and can be a flat DUV transparent window, or a portion with a spherical or dome shape (like a lens) as shown in FIG. 1. The lens 100 can be made of a DUV transparent material, such as a glass or a plastic, with a thickness of 100-500 μιη, such as 200-400 μιη. The lens 100 can be bonded or electroplated on the pedestal 60. The lens 100 can be electrically isolated from the metallic contacts 31-33 by gaps of 100-300 μιη (such as 270 μιη) in width. Figures 1A-1F(As shown). Lens 100 may be made of DUV transparent materials (such as fused silica, quartz, sapphire, AlN, CYTOP (CYTOP is a registered trademark of AGC Inc. (AGC Corporation) (formerly Asahi Glass Co., Ltd.)) and polytetrafluoroethylene amorphous fluoropolymer (AF), etc.).

[0032] According to another aspect of this disclosure, the encapsulation 80, such as Figure 1A , Figure 1C as well as Figure 1E As shown, the encapsulant 80 is in a liquid, grease, or gel state, completely immersing the DUV LED chip 50 and ESD diode 52, and completely filling the cavity defined by the abutment 10, base 60, and lens 100. The encapsulant 80 preferably has a high viscosity (optionally in the range of 100-2000 cSt at 20°C), suitable surface tension (optionally in the range of 10-100 dyne / cm at 20°C), and low vapor pressure (optionally in the range of 10 at 100°C). -4 -10 -8 (Within the scope of the material). According to this disclosure, the main component of the encapsulant 80 is perfluoropolyether (PFPE) oil, with the chemical formula: F-(CF(CF3)-CF2-O). nCF2CF3, where the degree of polymerization n is typically in the range of 10-60. These compounds are collectively known by a variety of names, including PFPE, perfluoroalkyl ether (PFAE), and perfluoropolyalkylether (PFPAE). PFPE oils are commonly used as lubricants and are commercially available under the trademarks Fomblin and Krytox (such as Fomblin Y LVAC and HVAC grade oils, Krytox oil GPL 107, and XP1A7, among others). Krytox is a registered trademark of Chemours Corporation, while Fomblin is a brand of fluoropolymer produced by Solvay Specialty Polymers S.P.A. Some Fomblin oils and Krytox oil GPL 107 and XP1A7 are DUV transparent and have chemical and thermal stability with a DUV refractive index greater than 1.3. Thus, Fomblin oils and Krytox oil GPL 107 and XP1A7 are suitable materials for the encapsulant 80. The encapsulant 80 can also be a PFPE oil doped with nanoparticles (50-200 nm) of Si02, AI2O3, MgF2, CaF2, Teflon amorphous fluoropolymer, polytetrafluoroethylene (PTFE), amorphous fluoropolymer CYTOP, etc. at a particle volume concentration of 3-20 vol.%. As the volume concentration of the nanoparticles increases, the encapsulant 80 changes from a liquid oil to a transparent grease. These doped nanoparticles are DUV transparent and have a higher DUV refractive index than the PFPE oil, which can improve the light extraction efficiency of the encapsulant 80.

[0033] The cavity defined by the submount 10, the pedestal 60, and the lens 100 holds the encapsulant 80, which is preferably sealed, i.e., hermetic. This is achievable because the pedestal 60 is bonded or plated on the metal layer 22, and the lens 100 is attached to the pedestal 60 by using the sealing lens attachment 70. As shown in FIG. 1, the lens 100 is attached to the pedestal 60 by the sealing lens attachment 70. The sealing lens attachment 70 is applied on the top surface of the pedestal 60, particularly in the notch 601. When a force is applied to the lens 100 towards the pedestal 60, the sealing lens attachment 70 will be compressed and evenly spread out. Upon curing (thermal or UV), the sealing lens attachment 70 hermetically secures the lens 100 on the pedestal 60. The notch 601 helps the sealing lens attachment 70 to spread out more evenly and improves the mechanical strength and hermeticity because the portion of the sealing lens attachment 70 in the notch 601 is thicker and more stretchable. Figure 1C Figure 1D As shown in FIG. 1, the lens 100 is attached to the pedestal 60 by the sealing lens attachment 70. The sealing lens attachment 70 is applied on the top surface of the pedestal 60, particularly in the notch 601. When a force is applied to the lens 100 towards the pedestal 60, the sealing lens attachment 70 will be compressed and evenly spread out. Upon curing (thermal or UV), the sealing lens attachment 70 hermetically secures the lens 100 on the pedestal 60. The notch 601 helps the sealing lens attachment 70 to spread out more evenly and improves the mechanical strength and hermeticity because the portion of the sealing lens attachment 70 in the notch 601 is thicker and more stretchable.

[0034] Since the encapsulant 80 is non-solid, its coefficient of thermal expansion tends to be larger than that of the solid pedestal 60 and lens 100, etc. For example, the coefficient of thermal expansion of the encapsulant PFPE oil can be about 100-400 x 10 -6 ​ / ℃, which is more than 10 times that of most solids. To accommodate the difference in thermal expansion between the encapsulation 80, the base 60, and the lens 100, according to another aspect of this disclosure, the lens attachment 70, after curing, is an elastomer that can reversibly stretch more than 10%, for example, 100-1000%, under external force or relaxation. The lens attachment 70 can be made of polydimethylsiloxane (PDMS or silicone). Cured silicone is a very durable elastomer. The lens attachment 70 can be transparent, reflective, or absorbent of DUV. To have DUV reflectivity or absorptive properties, the lens attachment 70 made of silicone can be doped with DUV reflective nanoparticles, such as polytetrafluoroethylene, CYTOP, Al, or DUV absorptive nanoparticles, such as carbon. Having DUV absorptive or reflective properties can reduce the aging effect of the lens attachment 70 under DUV radiation. Alternatively, as Figure 1D As shown, a DUV reflective coating 101, such as an aluminum film, can be applied to the lens attachment area of ​​the lens 100 to protect the lens attachment 70 from exposure to DUV light.

[0035] In addition, such as Figure 1E As shown, since the encapsulant 80 is a fluid, it can fill all possible air gaps or voids between the DUV LED chip 50 and the substrate 10. This gives the DUV LED 1000 superior light and heat extraction capabilities. In addition to direct conduction from the DUV LED chip 50 to the substrate 10, heat can also be easily transferred from the DUV LED chip 50 to the base 60 (the large metal component), resulting in lower thermal resistance for the DUV LED 1000.

[0036] Figure 2 The DUV LED 2000 shown is similar to the DUV LED 1000, except for the base. The base 60' of the DUV LED 2000 has no notch and is spaced from the lens 100 by a gasket 62, the top surface of which has a notch 621. The notch 621 may have similar dimensions to the notch 601. In some embodiments, the notch 621 does not penetrate the gasket 62. In other embodiments, the notch 621 may partially penetrate or completely penetrate the gasket 62 to divide the gasket 62 into two separate parts. During assembly, the gasket 62 is formed on the base 60', and the lens attachment 70 is applied to the gasket 62 and the notch 621.

[0037] Washer 62 can also have other designs. For example, washer 62 can be replaced by washer 62', which has a structured notch 621', such as... Figures 3A-3C As shown. See the top and bottom perspective views of washer 62' (respectively). Figure 3A and Figure 3BAs shown, the notch 621' on the bottom surface of washer 62' (the side that engages with base 60') is a groove that continuously surrounds the central opening of washer 62', and within the groove, only segmented regions (four segments as shown) with a width narrower than the width of the groove open to or penetrate the top surface of washer 62' (the side of receiving lens 100). Refer to the schematic cross-sectional view – Figure 3C The width W1 of the opening segment region of the top side notch 621' can be approximately one-quarter to three-quarters of the groove width W2 of the bottom side notch 621'. For example, the width of the washer 62' can be 400-500 μm, such as 450 μm, and the height can be approximately 50-150 μm (e.g., 100 μm). Furthermore, the height of the notch 621' can be 50-150 μm (e.g., 100 μm), its top opening width W1 is approximately 25-50 μm, and its bottom notch width W2 is approximately 50-100 μm. (Comparison) Figure 3C and Figure 1D Compared to DUV LED1000 and DUV LED2000, it can be expected that the DUV LED with the structured notch 621' can accommodate a more stretchable lens attachment 70.

[0038] Using experimental methods, a DUV LED with a peak wavelength of 272 nm was packaged according to the disclosure given above. A square AlN ceramic body with dimensions of 3.9 mm × 3.9 mm × 0.5 mm was used as the substrate 10 (therefore, the package is referred to as SMD3939). Metal layers 21, 22, and 23 are 65 μm thick copper layers coated with 4 μm of nickel and 100 nm of gold. Metal contacts 31-33 are 65 μm thick copper layers. Metal contacts 31 and 33 are electrically connected to metal layers 21 and 23 through three copper vias 12 with a diameter of 90 μm, respectively. Bonding pads 41-43 are 200 μm thick copper layers coated with 4 μm of nickel and 100 nm of gold. The base 60 is a 360 μm thick and 450 μm wide copper layer. The notch 601 has a depth of approximately 50 μm and a width of approximately 100 μm. The support 90 formed on the top surface of the base 60 is made of 400 μm thick copper. Most of the metal layers (except for the seed layer) or structures are formed by photolithography and electroplating. The 272nm LED chip 50 is a flip chip, bonded to the AlN ceramic substrate 10, such that the chip anode and cathode are bonded to metal layers 21 and 23, respectively. Krytox GPL 107 oil is used as the encapsulant (80), a 3.5 mm diameter hemispherical quartz lens is used as the lens 100, and SYLGARD... TM184(Sylgard is a Dow Corning brand) silicone gel (two-part) was used as the elastomeric lens attachment (70). The lens attachment silicone gel was heat cured at 150 °C for about 10 minutes. These LEDs were then placed under 350 mA DC stress to check the reliability of the package, especially the Krytox GPL 107 oil and SYLGARD TM 184 Silicone lens attachment elastomer reliability under strong DUV radiation. The encapsulated DUV intensity is estimated to be very strong, with the strongest intensity near the surface of the DUV LED chip, up to 10 4 mW / cm 2 .

[0039] The encapsulation (80) made of Krytox GPL 107 oil and a dome-shaped quartz lens 100 helps extract light from the DUV LED chip 50. The ratio of the light output power of the packaged LED to its un- packaged LED chip is defined as the light output gain, and the gain is typically greater than 1. As shown in Figure 4 the initial light output gain of this package was measured to be between 1.46-1.54 times. After 1008 hours of continuous 350 mA stress, the light output gain of the package was still in the range of 1.44-1.50 times. These numbers (1.46 vs. 1.44, 1.54 vs. 1.50) are within our measurement error. If the difference is considered as the attenuation caused by the package aging under strong DUV radiation (up to 3.63 x 1010 10 mJ / cm 2 ), these numbers imply that the light output gain of the package only dropped by 1.4%-2.6% after 1008 hours. Therefore, the present disclosure realizes a durable, long-life DUV LED packaging technology.

[0040] Figures 5A-5C A detailed structure of a DUV LED 3000 according to another aspect of the present disclosure is shown. As shown, the DUV LED 3000 does not have a metal base 60 and a support 90. However, the lens 100’ has a recessed portion 1003’ that encloses the DUV LED chip 50 and the ESD diode 52, and provides transparency and sealing for the LED.

[0041] The DUV LED 3000 includes three main components: a base 10, a DUV LED chip 50, and a lens 100'. On the top surface of the base 10 are formed metal layers 21, 22, 22', 23, with the metal layer 21 and the metal layer 23 separated and electrically isolated from each other by a gap formed therebetween. The metal layer 21' and the metal layer 23' are formed on the metal layer 21 and the metal layer 23, respectively. A notch 221' is formed between the metal layer 22 and the metal layer 22', which can be deep enough to electrically isolate the metal layer 22 and the metal layer 22', e.g., the notch 221' exposes the top surface of the base 10 and completely separates the metal layer 22 and the metal layer 22' (as shown in Figure 5A The notch 221' can also allow a metal connection between the metal layer 22 and the metal layer 22', i.e., at least a portion of the notch 221' does not expose the top surface of the base 10. In the embodiment as shown in Figures 5A-5C The metal layer 22' surrounds the metal layer 21 and the metal layer 23, and the metal layer 22 surrounds the metal layer 22', which is in the form of a ring. The metal layers 21, 22, 22', 23 can have the same composition and thickness, e.g., they can be 50-100 μιη thick (such as 65 μιη) metal layers made of copper, gold tin, or gold. In one embodiment, the metal layers 21, 22, 22', and 23 are formed by electroplating and are made of 65 μιη copper coated with 4 μιη nickel and about 100 nm gold. The gap formed between them can be 60-150 μιη wide, such as 100 μιη, and the height is the same as the thickness of the metal layers. In addition, a metal platform 21' and a metal platform 23' are formed on the metal layer 21 and the metal layer 23, respectively. The height of the metal platform 21' and the metal platform 23' can be 70-150 μιη, and the size is large enough to completely accommodate and receive the anode and the cathode of the DUV LED chip 50, respectively. The metal layers 21 and 23, and the metal platforms 21' and 23' are used as anodes and cathodes, respectively, to receive (contact) the ESD diode 52 and the anode and the cathode of the DUV LED chip 50. Since the DUV LED chip 50 is located on the metal platforms 21' and 23', and the ESD diode 52 is located on the metal layers 21 and 23, the light emitted from the chip level can be avoided from being absorbed by the ESD diode 52, which is typically about 70-150 μιη thick. To this end, the metal platforms 21' and 23' are made to have a thickness equal to or greater than the thickness of the ESD diode 52.

[0042] The metal layer 22, 22' and the notch 221' can be used to engage the lens 100' using the lens attachment 70. The lens attachment 70 can be applied on top of the metal layer 22, 22', especially in the notch 221'. When a force is applied to the lens 100' towards the submount 10, the lens attachment 70 will be compressed and spread evenly within the notch 221', thus providing adhesion and sealing for the LED package. After curing, the lens attachment 70 will seal the lens 100' on the metal layer 22 and the metal layer 22', and thus, on the submount 10. The notch 221' helps to spread the lens attachment 70 more evenly and improves mechanical strength and sealing, as the portion of the lens attachment 70 in the notch 221' is thicker and more stretchable.

[0043] Metal contacts 31-33 are formed on the opposite surface (bottom surface) of the submount 10, and bonding pads 41-43 are formed on the metal contacts 31-33. The metal pads 41 and 43 are electrically connected to the metal layer 21 and 23, respectively, through the metal contacts 31 and 33 and metal vias (see FIG. 2) formed in the submount 10. The metal pads 41-43 are used for soldering to a circuit board and can be made of copper, gold-tin, gold, or tin, with a thickness of 150-350 μιη, such as 260 μιη. In one embodiment, the metal pads 41-43 are formed by electroplating and are made of 265 μιη of copper coated with 4 μιη of nickel and about 100 nm of gold (top surface uses gold as protection). The metal pads 41-43 are electrically isolated from each other by gaps with a width of 100-300 μιη, such as 270 μιη. The metal pad 42 is not biased and is used as a heat conduction pad to conduct heat. Figure 1F ) electrically connected to the metal layer 21 and 23. The metal pads 41-43 are used for soldering to a circuit board and can be made of copper, gold-tin, gold, or tin, with a thickness of 150-350 μιη, such as 260 μιη. In one embodiment, the metal pads 41-43 are formed by electroplating and are made of 265 μιη of copper coated with 4 μιη of nickel and about 100 nm of gold (top surface uses gold as protection). The metal pads 41-43 are electrically isolated from each other by gaps with a width of 100-300 μιη, such as 270 μιη. The metal pad 42 is not biased and is used as a heat conduction pad to conduct heat.

[0044] The lens 100' is substantially rigid (solid) and has a spherical portion and a recessed portion 1003' at its base. The recessed portion 1003' is formed by removing lens material in the base of the lens, and is optionally large enough to receive and surround the DUV LED chip 50 and the ESD diode 52. For example, when the DUV LED chip 50 has dimensions of 1.2 mm x 1.2 mm x 0.4 mm, the lens 100' can be a half-sphere with a diameter of 3.5 mm, and the recessed portion 1003' can have dimensions of 2.0 mm x 2.0 mm x 0.5 mm. In experience, the diameter of the lens half-spherical portion needs to be at least twice, and optionally 2.5-4 times, the lateral dimension of the DUV LED chip. The lens 100' can be made of a DUV transparent material, such as fused silica, quartz, sapphire, AIN, Cytop, and polytetrafluoroethylene amorphous fluoropolymer, etc.

[0045] A thin encapsulation layer 80', such as 1-100 μm thick, can be formed on the top surface of the DUV LED chip 50. In one embodiment, the encapsulation layer 80' is air-gap-free and bubble-free, and fills the entire space between the top surface of the UVC LED chip 50 and the lens 100'. The remaining space between the DUV LED chip 50 and the recess 1003' can be completely or partially filled with the encapsulation layer 80', or completely or partially filled with a filler other than the encapsulation layer 80', such as air, nitrogen, or argon. As previously described regarding the DUV LED 1000, the encapsulation layer 80' can be made of the same material as the encapsulation layer 80. For example, it can be a perfluoropolyether (PFPE) oil or grease, such as Fomblin Y LVAC and HVAC grade oils / greases, Krytox oils GPL107 and XP1A7, etc. Encapsulant 80' preferably has a high viscosity (optionally in the range of 100-2000 cSt at 20°C), a suitable surface tension (optionally in the range of 10-100 dyne / cm at 20°C), and a low vapor pressure (optionally in the range of 10 at 10°C). -4 -10 -8 (within the range of the tube). These properties ensure the long-term stability and uniform formation of the encapsulant in the narrow capillary gap (1-100 μm) between the top surface of the UVC LED chip 50 and the top inner surface of the recess 1003' of the lens 100'. The encapsulant 80' may also be a PFPE oil doped with nanoparticles (50-200 nm) such as SiO2, Al2O3, MgF2, CaF2, Teflon AF, and amorphous fluoropolymer CYTOP at a particle volume concentration of 3-20 vol.%.

[0046] Figures 5A-5C The DUV LED 3000 shown provides a simple solution that delivers superior transparency, sealing, durability, optical and thermal efficiency.

[0047] In addition, such as Figures 5A-5C As shown, variations of the DUV LED 3000 can be achieved by modifying the shape of the lens 100'. In one embodiment, the lens 100' may have a cylindrical base, and a recess 1003' is formed within the cylindrical base. In another embodiment, the hemispherical portion may be replaced by a portion of a sphere or ellipsoid.

[0048] The above embodiments are based on SMD LEDs. The same teachings and principles can be applied to on-board chip (COB) LEDs. Figure 6 Another embodiment of this disclosure illustrates flip-chip bonding of an LED package to a printed circuit board (PCB). As shown Figure 6As shown, the DUV LED 4000 is similar to the DUV LED 3000, with the only difference being the PCB and the surface mount lead frame. Thus, the description made above in relation to the DUV LED 3000 and other embodiments can apply to the DUV LED 4000 to a large extent. The PCB used can be any type of PCB, and here, for good thermal conductivity, a metal core printed circuit board (MCPCB) 10’ is employed, which has three main components: a metal trace (comprising metal layers 21-23, 21’-23’), an insulating layer 11, and a metal body 10”. The metal trace is formed on top of the insulating layer 11, which electrically isolates the metal trace from the metal body 10”. The insulating layer 11 can be made of insulating epoxy or fiberglass, such as FR4, a flame retardant insulator. It is briefly reiterated here that the DUV LED chip 50 and the ESD diode 52 are flip-chip bonded to the respective metal traces (anode and cathode) on the MCPCB 10’, and the lens 100’ is hermetically bonded to the MCPCB 10’ (on the metal layer 22, 22’ and the notch 221’) by the lens attachment 70 to enclose the DUV LED chip 50 and the ESD diode 52. A thin layer of encapsulant 80’ can be formed on the top surface of the DUV LED chip 50, such as 1-100 pm thick. The encapsulant 80’ is optionally air gap-free, bubble-free, and fills the entire space between the top surface of the UVC LED chip 50 and the lens 100’. The remaining space between the DUV LED chip 50 and the recess 1003’ can be completely or partially filled with the encapsulant 80’, or completely or partially filled with a filler other than the encapsulant 80’, such as air, nitrogen, argon. Figure 6 The DUV LED 4000 as shown provides a simple solution that enables excellent transparency, hermeticity, durability, optical and thermal efficiency.

[0049] The application has been described using exemplary embodiments. It is to be understood, however, that the scope of the present application is not limited to the disclosed embodiments. Rather, it is intended to cover various modifications and similar arrangements or equivalents as would be apparent to one skilled in the art. Accordingly, the scope of the claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and equivalents.

Claims

1. A light emitting diode package comprising: a substrate; a first metal layer, a second metal layer, and a third metal layer formed on a top surface of the substrate, wherein the first metal layer is electrically isolated from the second metal layer by a first gap, the third metal layer surrounds the first and second metal layers and is electrically isolated from the first and second metal layers by a second gap; a lens attached to the top surface of the substrate, wherein a cavity is formed between the substrate and the lens; an LED chip disposed in the cavity, wherein an anode of the chip is electrically connected to the first metal layer and a cathode of the chip is electrically connected to the second metal layer; A fluid encapsulate, wherein the cavity is completely or partially filled with the fluid encapsulate, the encapsulate having a viscosity in the range of 100-2000 cSt at 20°C, a surface tension in the range of 10-100 dyne / cm at 20°C, and a vapor pressure in the range of 10 -4 -10 -8 torr at 100°C, and is UV transparent; and a lens attachment for attaching the lens to the substrate, the lens attachment being an elastomer after curing, capable of reversibly extending more than 10% when under external force or relaxed.

2. The light emitting diode package of claim 1, wherein, The encapsulant comprises a perfluoropolyether (PFPE) oil having a chemical formula of: F-(CF(CF3)-CF2-O) n -CF2CF3 wherein the degree of polymerization n is in the range of 10-60; or The PFPE oil is doped with nanoparticles selected from the group consisting of Si02, AI2O3, MgF2, CaF2, Teflon amorphous fluoropolymer, polytetrafluoroethylene (PTFE), amorphous fluoropolymer CYTOP, at a volume concentration of 3-20%.

3. The light emitting diode package of claim 1, wherein, The cavity is sealed.

4. The light emitting diode package of claim 1, further comprising a base having a central opening, wherein a bottom surface of the base is attached to the third metal layer and a top surface of the base is attached to the lens, whereby the substrate, the lens, and the base together define the cavity by enclosing the chip.

5. The light emitting diode package of claim 4, wherein, An inner sidewall of the central opening of the base is inclined at an angle to reflect light emitted from an edge of the chip in a predetermined direction, and a notch is formed on the top surface of the base.

6. The light emitting diode package of claim 4, wherein, The top surface of the base is attached to the lens using the lens attachment, the lens attachment in a fluid state is applied on the top surface of the base.

7. The light emitting diode package of claim 6, wherein, The lens attachment comprises polydimethylsiloxane.

8. The light emitting diode package of claim 4, further comprising a grommet having a central opening, wherein, A notch is formed on a top surface of the gasket, the top surface of the gasket is attached to the lens, and a bottom surface of the gasket is attached to the top surface of the base, the central opening of the gasket is aligned with the central opening of the base.

9. The light emitting diode package of claim 4, further comprising a grommet having a central opening, wherein, A groove is formed on a bottom surface of the gasket, the groove continuously surrounds the central opening, and within the groove, a segmented area having a width narrower than the groove width is open to a top surface of the gasket, the top surface of the gasket is attached to the lens, and the bottom surface of the gasket is attached to the top surface of the base, the central opening of the gasket is aligned with the central opening of the base.

10. The light emitting diode package of claim 1, wherein, The lens is attached to the third metal layer using a lens attachment.

11. The light emitting diode package of claim 10, wherein, A notch is formed on a top surface of the third metal layer, the notch does not penetrate the third metal layer in a thickness direction, or completely penetrates the third metal layer and divides the third metal layer into two metal layers electrically isolated from each other.

12. The light emitting diode package of claim 10, wherein, The lens attachment in a fluid state is applied on a top surface of the third metal layer, and after solidification becomes an elastomer, which can reversibly extend more than 10% when an external force is applied or relaxed.

13. The light emitting diode package of claim 10, wherein, The lens includes a recess in which the chip is accommodated, and a space between a top surface of the chip and an inner top surface of the recess is completely filled with the fluid encapsulant.

14. The light emitting diode package of claim 10, further comprising first and second metal platforms formed on the first and second metal layers, respectively, and electrically isolated from each other, the chip being disposed on the first and second metal platforms, and an anode of the chip being connected to the first metal platform and a cathode of the chip being connected to the second metal platform.

15. The light emitting diode package of claim 14, further comprising an electrostatic discharge diode disposed on the first metal layer and the second metal layer, wherein, An anode of the electrostatic discharge diode is connected to the first metal layer, and a cathode of the electrostatic discharge diode is connected to the second metal layer.

16. The light emitting diode package of claim 1, wherein, The chip is an ultraviolet (UV) light emitting diode chip or a deep ultraviolet (DUV) light emitting diode chip.

17. The light emitting diode package of claim 1, wherein, The substrate is a submount or a printed circuit board.

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