Silicone resin light transmission enhancement treatment method and system for PLCC-encapsulated LEDs

Abstract

This application relates to the technical field and discloses a method and system for enhancing the light transmittance of silicone resin in PLCC-encapsulated LEDs. The method includes placing a thermocured PLCC-encapsulated LED in an atmosphere treatment chamber, introducing a mixed atmosphere of inert gas and oxygen, and controlling the oxygen concentration; irradiating the light-emitting surface of the silicone resin with near-ultraviolet light under the mixed atmosphere, causing the deactivated platinum catalyst in the under-crosslinked surface layer to transform into an active state, catalyzing the hydrosilylation reaction between residual hydrogen-containing silicon groups and vinyl silicon groups, while simultaneously using oxygen to re-deactivate some of the active platinum, thereby forming a dynamic balance between ultraviolet activation and oxygen re-deactivation; after irradiation, switching to an inert atmosphere and maintaining the chamber temperature allows the remaining active platinum to continue catalyzing the crosslinking reaction. This invention enables controllable re-crosslinking of the under-crosslinked surface layer of silicone resin, improving the light transmittance of the light-emitting surface.

Description

Technical Field

[0001] This application relates to the field of LED packaging material processing technology, specifically a method and system for enhancing the light transmittance of silicone resin in PLCC-packaged LEDs. Background Technology

[0002] Light-emitting diodes (LEDs) are characterized by their small size, fast response speed, low power consumption, and long lifespan, and are widely used in lighting, displays, automotive electronics, and other fields. PLCC-packaged LEDs typically use optical-grade silicone resin to encapsulate and protect the chip and bonding wires, leveraging the excellent light transmittance, heat resistance, and photoaging resistance of silicone resin to maintain the device's light extraction efficiency and long-term reliability. Among existing silicone resin encapsulation materials, addition-type silicone resins typically utilize a platinum catalyst to catalyze a hydrosilylation reaction between hydrogen-containing silicon groups and vinyl silicon groups, forming a cross-linked network through thermosetting.

[0003] In actual encapsulation, the curing state of silicone resin is affected by factors such as material formulation, curing temperature, curing time, and surface atmosphere. For PLCC-encapsulated LEDs that have already undergone thermosetting, the silicone resin body can usually reach the expected degree of curing, but the surface area near the free light-emitting surface may still have insufficient cross-linking and residual reactive groups. This kind of surface inhomogeneity will create a refractive index difference between the surface layer and the internal body, increasing the interface reflection loss during light propagation. At the same time, residual groups and low molecular weight components may also have an adverse effect on the optical stability during subsequent use.

[0004] Existing improvement methods mainly optimize silicone resin formulation, curing temperature, and curing time. However, extending or increasing the overall thermosetting conditions makes it difficult to selectively treat already formed under-crosslinked areas on the surface and may increase process time and the thermal load on the encapsulation structure. Therefore, there is still room for further improvement in how to effectively and controllably post-treat the light-emitting surface of the thermo-cured silicone resin without changing the existing encapsulation structure to improve the crosslinking state and light transmittance of the surface layer. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for enhancing the light transmittance of silicone resin in PLCC-encapsulated LEDs, so as to solve the problems mentioned in the background art.

[0006] According to one aspect of this application, a method for enhancing the light transmittance of silicone resin in a PLCC-encapsulated LED is provided, comprising the following steps: The PLCC-encapsulated LED that has been thermosetting is placed into an atmosphere treatment chamber, and a mixed atmosphere of inert gas and oxygen is introduced into the chamber, controlling the oxygen concentration to be within the range where the platinum catalyst can be partially activated under ultraviolet light irradiation. The silicon resin light-emitting surface is irradiated with near-ultraviolet light under the mixed atmosphere. The near-ultraviolet light reduces the deactivated platinum catalyst in the under-crosslinked surface layer to the active state. The active platinum catalyst catalyzes the hydrosilylation reaction between the residual hydrogen-containing silicon groups and vinyl silicon groups in the under-crosslinked surface layer to form crosslinking bonds. At the same time, the oxygen in the mixed atmosphere re-oxidizes part of the active platinum catalyst to the deactivated state. The activation by ultraviolet light and the re-deactivation by oxygen reach a dynamic equilibrium. After irradiation, the atmosphere of the chamber is switched to an inert gas and the chamber temperature is maintained for a period of time. At the end of irradiation, the platinum catalyst in the active state continues to catalyze the crosslinking reaction between the hydrogen-containing silicon groups and vinyl silicon groups remaining in the undercrosslinked surface layer under the inert gas atmosphere.

[0007] Preferably, the peak emission wavelength of the near-ultraviolet light is 365 to 405 nm.

[0008] Preferably, the volume fraction of oxygen in the mixed atmosphere is 800 to 2000 ppm.

[0009] Preferably, the concentrations of residual hydrogen-containing silicon groups and vinyl silicon groups in the undercrossed surface layer decrease along the direction from the light-emitting surface to the silicone resin body. The amount of crosslinking supplementation at each depth in the irradiation step is positively correlated with the concentration of the residual groups at that depth. After irradiation treatment, the crosslinking density of the undercrossed surface layer continuously increases from the surface to the body.

[0010] Preferably, the irradiance of the irradiation is 50 to 200 mW / cm². 2 The irradiation time is 60 to 180 seconds.

[0011] Preferably, the cavity temperature is maintained at 60 to 80°C during the irradiation process.

[0012] Preferably, the oxygen content in the inert gas switched after the irradiation is less than 10 ppm, and the duration of maintaining the cavity temperature for a period of time is 2 to 5 minutes.

[0013] Preferably, before introducing the mixed atmosphere, the cavity is first purged with an inert gas containing less than 10 ppm of oxygen to reduce the residual oxygen concentration in the cavity to below 50 ppm.

[0014] Preferably, before the irradiation step, the PLCC-encapsulated LED is heated to 120 to 150°C in an inert atmosphere and held for 10 to 30 minutes to promote the volatilization and removal of low molecular weight cyclic siloxanes in the surface layer of the silicon resin light-emitting surface. After completion, the temperature is lowered to 60 to 80°C before proceeding with subsequent steps.

[0015] In another aspect, this application also provides a silicone resin light transmission enhancement treatment system for PLCC-encapsulated LEDs, comprising: The mixed atmosphere establishment module is used to place the thermo-cured PLCC packaged LED into the atmosphere treatment chamber, introduce a mixed atmosphere of inert gas and oxygen into the chamber, and control the oxygen concentration to be within the range where the platinum catalyst can be partially activated under ultraviolet light irradiation. The ultraviolet irradiation crosslinking module is used to irradiate the light-emitting surface of the silicone resin with near-ultraviolet light in the mixed atmosphere. The near-ultraviolet light reduces the deactivated platinum catalyst in the under-crosslinked surface layer to an active state. The active platinum catalyst catalyzes the hydrosilylation reaction between the hydrogen-containing silicon groups and vinyl silicon groups in the under-crosslinked surface layer to form crosslinking bonds. At the same time, the oxygen in the mixed atmosphere re-oxidizes part of the active platinum catalyst back to the deactivated state, so that the ultraviolet light activation and oxygen re-deactivation reach a dynamic balance. The atmosphere switching and heat preservation module is used to switch the cavity atmosphere to an inert gas after irradiation and maintain the cavity temperature for a period of time, so that the platinum catalyst, which is in an active state at the end of irradiation, can continue to catalyze the hydrogen-containing silicon groups and vinyl silicon groups remaining in the undercrosslinked surface layer to complete the crosslinking reaction under the inert gas atmosphere.

[0016] In another aspect, this application also provides an electronic device comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the silicon resin light transmission enhancement treatment method for PLCC packaged LEDs as described above.

[0017] In another aspect, this application provides a storage medium storing computer program instructions that can be executed by a processor to implement the silicon resin light transmission enhancement treatment method for PLCC packaged LEDs as described above.

[0018] Another aspect of this application provides a computer program product, including a computer program that, when executed by a processor, implements the silicon resin light transmission enhancement treatment method for PLCC-packaged LEDs as described above.

[0019] This application addresses the problem of insufficient local crosslinking on the light-emitting surface of silicone resin after thermosetting PLCC-encapsulated LEDs. Under a controlled micro-oxygen atmosphere, near-ultraviolet light is used to selectively activate a deactivated platinum catalyst. A controllable dynamic equilibrium of catalytic activity is established through oxygen re-deactivation, allowing residual hydrogen-containing silicon groups and vinyl silicon groups in the under-crosslinked surface layer to continue hydrosilylation reactions at an appropriate rate, thus achieving in-situ re-crosslinking of the surface layer. Because the content of residual reactive groups varies at different depths, the crosslinking density distribution remains continuously varying from the surface to the bulk after re-crosslinking, further forming a smooth refractive index transition and reducing internal reflection losses caused by abrupt refractive index changes between the original under-crosslinked layer and the silicone resin bulk. Based on this, after irradiation, switching to an inert atmosphere allows the still-active platinum catalyst to continue limited subsequent crosslinking, further ensuring a more complete surface reaction. Therefore, this invention achieves a synergistic improvement in the light transmittance and long-term stability of the silicone resin light-emitting surface without altering the existing encapsulation structure or introducing additional heterogeneous materials. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a method for enhancing the light transmittance of a PLCC-encapsulated LED with silicone resin, provided as an embodiment of this application.

[0022] Figure 2 This is a schematic diagram of the ultraviolet activation and oxygen re-deactivation crosslinking mechanism provided in the embodiments of this application.

[0023] Figure 3 This is a schematic diagram of the cross-linking and refractive index gradient of the under-crosslinked silicone resin surface layer provided in the embodiments of this application.

[0024] Figure 4 This is a schematic diagram of a silicone resin light transmission enhancement treatment system for a PLCC-encapsulated LED, provided as an embodiment of this application.

[0025] Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] This embodiment provides a method for enhancing the light transmittance of silicone resin in PLCC (Plastic Leaded Chip Carrier) packaged LEDs, applicable to PLCC packaged LED products using platinum-catalyzed addition-cure silicone resin as the potting material. Platinum-catalyzed addition-cure silicone resin refers to an organosilicon encapsulant that uses platinum complexes as catalysts to achieve cross-linking and curing through a hydrosilylation reaction between hydrogen-containing silicon groups (Si-H) and vinyl silicon groups (Si-CH=CH2). It is the most widely used optical-grade potting system in the LED packaging industry. The object of treatment is a semi-finished PLCC packaged LED that has completed silicone resin thermosetting; at this point, the degree of cross-linking of the silicone resin body meets the design requirements, with only the surface layer of the light-emitting surface exhibiting insufficient cross-linking due to the continuous oxidation of the platinum catalyst by trace amounts of atmospheric oxygen during the thermosetting process. The equipment required for implementing this method includes a sealed atmosphere treatment chamber, an ultraviolet LED light source module with a peak wavelength of 365 to 405 nm, a mass flow control supply system for inert gas and trace oxygen, and a chamber temperature regulation device. All processing steps are completed under normal pressure.

[0028] The following detailed description, in conjunction with specific embodiments, illustrates the implementation process of the silicone resin light transmission enhancement treatment method for PLCC-encapsulated LEDs described in this application. It should be noted that these embodiments are merely illustrative of this application and not intended to limit its scope of protection. Any conventional adjustments or substitutions made by those skilled in the art to the steps without departing from the concept of this application should be included within the scope of protection of this application.

[0029] like Figure 1 As shown in the figure, this application discloses a schematic diagram of a method for enhancing the light transmittance of silicone resin in PLCC-encapsulated LEDs, including the following method steps: Step S1: Introduce a mixture of inert gas and oxygen into the cavity and control the oxygen concentration. Step S2: Irradiate the light-emitting surface of the silicone resin with near-ultraviolet light in a mixed atmosphere; Step S3: After irradiation, switch the cavity atmosphere to an inert gas and maintain the cavity temperature.

[0030] In some embodiments, for step S1, before the processing begins, the PLCC-packaged LED to be processed is placed flat on a carrier inside the atmosphere treatment chamber, with the light-emitting surface of the silicone resin facing the light source. Optionally, before introducing the subsequent mixed atmosphere, the chamber is first purged with high-purity nitrogen gas with an oxygen content of less than 10 ppm. The purging flow rate is set according to the chamber volume; for example, a 50L chamber is purged at a flow rate of 20L / min for about 40 seconds to reduce the residual oxygen concentration in the chamber to below 50 ppm. The purging simultaneously removes trace amounts of moisture and volatile organic compounds adsorbed on the surface of the silicone resin. Subsequently, the chamber heating is started, raising the temperature to a set value within the range of 60 to 80°C, for example, 70°C. The lower limit of 60°C is chosen because the kinetic rate of the hydrosilylation reaction is insufficient to meet industrial cycle time below this temperature; the upper limit of 80°C balances the long-term thermal stability of the PLCC substrate material (PPA or PCT) and the bonding reliability of the gold wire bonding points.

[0031] In one embodiment, after the chamber temperature stabilizes, a trace amount of oxygen is precisely introduced into the pure nitrogen carrier gas using a mass flow controller to stabilize the oxygen volume fraction in the chamber atmosphere at a set value. Optionally, the oxygen volume fraction is set in the range of 800 to 2000 ppm, for example, 1200 ppm.

[0032] The purpose and function of introducing controlled trace amounts of oxygen include the fact that polydimethylsiloxane has high oxygen permeability, with a diffusion coefficient of approximately 5 × 10⁻⁶ at around 70°C. -5 cm 2 Oxygen molecules can reach dissolution equilibrium with the atmosphere within seconds within a depth of several micrometers on the surface of the silicone resin. Therefore, the controlled oxygen partial pressure does not create a concentration spatial gradient within the silicone resin, but rather establishes a uniform dissolved oxygen concentration across the entire depth of the target treatment layer. This uniformly distributed dissolved oxygen plays a rate-regulating role in the catalytic activity of the platinum catalyst during the subsequent ultraviolet irradiation step; the specific mechanism will be explained in later steps.

[0033] According to Fick's second law, the diffusion characteristic time τ L 2 / D, where L is the target diffusion depth and D is the diffusion coefficient of oxygen in polydimethylsiloxane. At 70°C, the diffusion coefficient D of oxygen in polydimethylsiloxane... 5×10 -5 cm 2 / s. For 3μm (i.e., 3×10⁻⁶), -4 Target depth (cm), τ (3×10 -4 ) 2 / (5×10 -5 ) 1.8×10 -3s, meaning on the order of milliseconds; even under the most conservative estimates (considering the effect of phenyl substituents on free volume in silicone resin, the diffusion coefficient is reduced to approximately 1 × 10⁻⁶). -5 cm 2 / s), τ 9×10 -3 The time s is still much shorter than the irradiation time of more than 60 seconds in step S2. Therefore, before irradiation begins (after waiting for about 30 seconds after the atmosphere stabilizes in the aforementioned steps), dissolved oxygen has been sufficiently homogenized within the depth range of the target treatment layer.

[0034] In one embodiment, when the oxygen volume fraction is below 500 ppm, the reactivation effect of dissolved oxygen on the platinum catalyst is weak. After UV activation, the platinum catalyst is almost entirely converted to the active state, and the crosslinking reaction is largely completed within seconds. This results in a very narrow processing time window, making precise control difficult in industrial production. When the oxygen volume fraction exceeds 3000 ppm, the reactivation rate of dissolved oxygen is much higher than the activation rate of UV light. Under irradiation conditions, the platinum catalyst remains almost entirely in an inactive state, and the crosslinking reaction cannot be effectively advanced. Within the range of 800 to 2000 ppm, the two rates are on the same order of magnitude. The steady-state activity ratio of the platinum catalyst can be flexibly adjusted by the oxygen partial pressure, and the corresponding reaction rate allows the target crosslinking degree to be increased within 60 to 180 seconds, matching the process cycle of the LED packaging production line.

[0035] For a specific batch of products, the optimal oxygen volume fraction setting can be determined through the following calibration process: Take several samples of PLCC-packaged LEDs from the same batch and treat them under different oxygen volume fractions (500, 800, 1000, 1200, 1500, 1800, 2000, and 2500 ppm) with the same irradiation parameters. Measure the rate of change of forward luminous flux at the main emission wavelength before and after treatment for each sample. Select the oxygen volume fraction corresponding to the largest rate of change as the process setting value for that batch. Since the platinum catalyst content and the Si-H to vinyl silicon ratio differ among manufacturers' silicone resin formulations, the optimal oxygen partial pressure will slightly deviate depending on the formulation. The above calibration method is applicable to various mainstream encapsulation silicone resin brands.

[0036] In some embodiments, for step S2, the light-emitting surface of the silicone resin is irradiated with near-ultraviolet light in the mixed atmosphere. The near-ultraviolet light reduces the deactivated platinum catalyst in the undercrosslinked surface layer to the active state. The active platinum catalyst catalyzes the hydrosilylation reaction between the residual hydrogen-containing silicon groups and vinyl silicon groups in the undercrosslinked surface layer to form crosslinking bonds. At the same time, the oxygen in the mixed atmosphere re-oxidizes part of the active platinum catalyst to the deactivated state, and the ultraviolet light activation and oxygen re-deactivation reach a dynamic equilibrium.

[0037] Specifically, after the atmosphere stabilizes, the ultraviolet LED light source module is turned on, applying near-ultraviolet light irradiation to the silicon resin light-emitting surface from directly above the PLCC package. The peak emission wavelength of the light source can be selected as 365nm, 385nm, or 405nm, with a spectral half-width of, for example, not exceeding 15nm; the irradiance is set between 50 and 200mW / cm². 2 Within this range, the irradiation time is set to 60 to 180 seconds, for example, an irradiance of 100 mW / cm². 2 Irradiation time: 120 seconds.

[0038] The selection of this wavelength range is based on the photochemical properties of platinum catalysts. The most commonly used platinum catalyst in LED silicon resins is the Karstedt type, whose active state is Pt. 0 The complex formed by coordination with divinyltetramethyldisiloxane exhibits light absorption in the 350 to 410 nm wavelength range; when platinum is in the Pt state due to oxygen poisoning... 2+ In the oxidized state, the photon energy in the above-mentioned band can reduce Pt 2+ Restore to Pt 0 Active state. The wavelength range of 365 to 405 nm is near ultraviolet, with photon energies of 3.06 to 3.40 eV, which is lower than the Si-C bond dissociation energy (approximately 3.7 eV) and the Si-O bond dissociation energy (approximately 4.7 eV), and will not cause photo-splitting of the silicone resin backbone.

[0039] In one embodiment, near-ultraviolet photons penetrate the silicone resin to reach the interior of the undercrosslinked surface layer. The penetration depth of near-ultraviolet light in the transparent silicone resin is much greater than the thickness of the undercrosslinked surface layer, and it is absorbed by the oxidized and deactivated platinum species distributed within the layer. The light energy then converts Pt... 2+ Restore to Pt 0 Pt after restoring catalytic activity 0 It then catalyzes the hydrosilylation reaction between the surrounding residual hydrogen-containing silicon groups and vinyl silicon groups, forming a Si-CH2-CH2-Si crosslinking bond with each catalytic cycle.

[0040] Meanwhile, the dissolved oxygen established in the aforementioned steps continues to generate activated Pt 0 Re-oxidized to Pt 2+ Deactivated state. A single platinum atom remains active for only a few milliseconds to hundreds of milliseconds after each photoactivation, before being reactivated by oxygen oxidation, awaiting activation by the next ultraviolet photon. This cycle repeats, and the two processes of ultraviolet photoactivation and oxygen reactivation reach a dynamic equilibrium at the platinum catalyst population level, with the proportion of active platinum catalyst tending to a stable steady-state value.

[0041] Figure 2 This is a schematic diagram of the UV activation and oxygen reactivation crosslinking mechanism provided in the embodiments of this application, as shown below. Figure 2As shown, in the undercrosslinked silicone resin surface layer, near-ultraviolet light photochemically activates the oxidized and deactivated platinum catalyst, enabling Pt to... 2+ Reduced to catalytically active Pt 0 Active Pt 0 The residual hydrogen-containing silicon groups in the catalytic reaction undergo hydrosilylation with the vinyl silicon groups to form Si-CH2-CH2-Si crosslinks, thus achieving supplementary crosslinking of the undercrosslinked surface layer. Simultaneously, dissolved oxygen in the surface layer continuously carries away some of the active Pt. 0 Re-oxidized to deactivated Pt 2+ This allows for a dynamic equilibrium between UV activation and oxygen deactivation at the platinum catalyst population level. By controlling the proportion of active platinum catalyst through this dynamic equilibrium, the crosslinking reaction can proceed at a controllable rate, avoiding excessively rapid or excessively inhibited crosslinking processes.

[0042] The steady-state activity ratio of platinum catalysts is determined by the competition between the UV activation rate and the oxygen reactivation rate, and the following relationship describes this balance:

[0043] In the formula This represents the mole fraction of platinum catalysts in the active state. The ultraviolet light activation rate constant is expressed in cm⁻¹. 2 ·mW -1 ·s -1 The rate at which platinum species are reduced from the oxidized state to the active state under a unit irradiance; Ultraviolet irradiance reaching the surface of silicone resin, in mW / cm² 2 ; The oxygen reactivation rate constant is expressed in L·mol⁻¹. -1 ·s -1 The rate at which dissolved oxygen re-oxidizes active platinum is characterized. This represents the dissolved oxygen concentration within the silicone resin surface layer, expressed in mol / L, calculated from the oxygen partial pressure in the atmosphere using Henry's Law.

[0044] in and The two parameters can be obtained through the following experiment: prepare a thin film sample with the same formulation as the silicone resin used in production, with a thickness of, for example, 100 μm, and track the Si-H absorption peak (2160 cm⁻¹) in situ using Fourier transform infrared spectroscopy (FTIR) under ultraviolet irradiation conditions. -1 The intensity of the nearby oxygen decreases over time. A set of decay curves were measured under pure nitrogen and several different oxygen partial pressures. By fitting the above relationship, the specific values ​​of the two constants can be obtained.

[0045] Specifically, the input data consists of thin film samples (thickness) prepared with the same formulation as the silicone resin used in production. ,size (placed on a quartz slide), under ultraviolet irradiation conditions (irradiance) Set to multiple levels: The following is an in-situ tracking method using Fourier transform infrared spectroscopy (FTIR). absorption peak ( The intensity of the nearby area decreases over time. The FTIR spectral resolution is... The spectrum was scanned 32 times, with a spectral line recorded at 10-second intervals. The scans were performed in pure nitrogen (oxygen content...) ) and multiple oxygen partial pressure conditions (oxygen volume fraction: Each set of attenuation curves was measured. The absorption peak area was then calculated using the Lambert-Beer law. Converted to relative concentration of functional groups ,in This represents the area of ​​the initial absorption peak before irradiation begins.

[0046] Under pure nitrogen conditions ( (The oxygen reactivation term is negligible). Concentration decay follows first-order kinetics: , fitting get Get Then, under different oxygen partial pressures, Concentration decay satisfies ,in The apparent rate constant for the hydrosilylation reaction is given (determined independently at the corresponding temperatures by differential scanning calorimetry (DSC)). The obtained... Substitute the values ​​and fit them using the least squares method under each oxygen partial pressure. The decay curve is optimized by minimizing the mean square error between the predicted and measured values. .

[0047] and With mean Output in standard deviation form, typical values ​​are as follows: Under the conditions, for Karstedt-type platinum catalysts, the content is methylphenyl silicone resin system, (coefficient of variation) ), (coefficient of variation) The obtained parameters serve as fixed input values ​​for the silicone resin formulation in subsequent process settings.

[0048] In one embodiment, the irradiance is 50 to 200 mW / cm². 2 The range was determined based on a lower limit of 50 mW / cm.2 To maintain under the target oxygen partial pressure conditions The minimum required irradiation level, not less than 0.1, is given by the above formula in the known... , , Calculations under the given conditions yielded an upper limit of 200 mW / cm². 2 Due to the limited effect of the thermal effect of the light source on the temperature rise of the silicone resin surface, the irradiation time can be determined by confirming that the measured surface temperature during the irradiation process does not exceed the set upper limit. The determination of the irradiation time includes treating a series of samples for 30, 60, 90, 120, 150, 180, and 240 seconds respectively under the set irradiance and oxygen partial pressure, measuring the transmittance of the light-emitting surface of each sample, and the transmittance increases with time and tends to saturate. The time corresponding to reaching 95% of the saturation value is taken as the process time.

[0049] In one embodiment, during the initial thermosetting stage, the formation of the under-crosslinked surface layer on the light-emitting surface stems from the continuous supply of atmospheric oxygen from the free surface inwards, which inhibits the activity of the platinum catalyst at the surface. The intensity of this inhibition decreases from the surface inwards: the oxygen concentration is highest immediately adjacent to the surface, the platinum is most severely inhibited, and there are the most residual unreacted groups; towards the bulk direction, the platinum activity gradually recovers, and the crosslinking tends to be complete. Therefore, after thermosetting, the residual concentrations of hydrogen-containing silicon groups and vinyl silicon groups decrease from the light-emitting surface towards the bulk direction, while the corresponding crosslinking density increases, eventually connecting with the bulk at a depth of approximately 0.5 to 3 μm.

[0050] In ultraviolet irradiation treatment, because dissolved oxygen is sufficiently homogenized at all depths of the surface layer, the steady-state activity ratio of the platinum catalyst is [high / low]. The conversion rate of residual groups consumed by the crosslinking reaction at each depth is approximately the same. Values ​​and the same irradiation time are controlled. After the crosslinking is completed, the crosslinking density distribution at each depth satisfies:

[0051] In the formula For post-processing depth Crosslinking density at the location, in mol / m 3 ; The maximum crosslinking density is the density required for all functional groups in the silicone resin formulation to fully react, determined by the formulation feed ratio, in mol / m³. 3 ; For processing depth Crosslinking density at the location, in mol / m 3 ; The apparent rate constant for platinum-catalyzed hydrosilylation reaction is given in seconds. -1 It depends on the processing temperature; Irradiation time, in seconds.

[0052] in, The method for determining the temperature was differential scanning calorimetry (DSC). Non-isothermal DSC scans were performed on uncured silicone resin formulation samples at four heating rates of 5, 10, 15, and 20 °C / min, and the exothermic peak temperature of the hydrosilylation reaction was recorded. According to the Kissinger equation:

[0053] Where β is the heating rate (K / min). The temperature at which heat is released is K. R is the activation energy of the reaction (J / mol), and R is the universal gas constant (8.314 J·mol). -1 ·K -1 C is a constant. Let ln(β / ) for 1 / Perform a linear fit and obtain the activation energy from the slope. Under isothermal conditions, =A·exp(- / RT), where the pre-exponential factor A is obtained by fitting the DSC curve. Within the temperature range of 60-80℃, typical... The value is approximately 0.02~0.08s. -1 The specific value depends on the platinum catalyst content and the molar ratio of Si-H to vinyl silicon in the silicone resin formulation.

[0054] As can be seen from the above formula, The cross-linking increases from the surface to the bulk (the less cross-linked the surface, the more severe the problem). The cross-linking density decreases from the surface to the bulk; after treatment, the cross-linking density increases at all depths, but the increase is greatest at the surface and smallest at deeper depths. The refractive index of the silicone resin is maintained in a continuously increasing manner from the surface to the bulk. The refractive index of the silicone resin is positively correlated with the crosslinking density. Increased crosslinking density leads to tighter molecular packing and increased polarizability per unit volume. Therefore, the treated light-emitting surface exhibits a gradual transition in refractive index from the surface to the bulk, eliminating the abrupt refractive index change at the original interface between the under-crosslinked layer and the bulk. When light travels from the silicone resin bulk to the outside, it passes through this continuously increasing refractive index transition layer. Fresnel internal reflections that occurred at the original abrupt change are suppressed, resulting in a corresponding increase in the transmittance of the light-emitting surface.

[0055] Figure 3 This is a schematic diagram illustrating the cross-linking process and refractive index gradient of the under-crosslinked silicone resin surface layer provided in an embodiment of this application. Figure 3As shown, after the PLCC-encapsulated LED completes thermosetting, an under-crosslinked surface layer with a thickness of approximately 0.5–3 μm is formed near the light-emitting surface of the silicone resin. Before treatment, the concentrations of residual hydrogen-containing silicon groups and vinyl silicon groups gradually decrease from the light-emitting surface towards the silicone resin bulk, while the crosslinking density correspondingly increases. After near-ultraviolet irradiation treatment under a controlled oxygen atmosphere, a supplementary crosslinking reaction occurs at all depths. The surface region has a larger amount of supplementary crosslinking due to the greater number of residual groups, while the amount of supplementary crosslinking gradually decreases towards the bulk, ensuring that the crosslinking density after treatment still maintains a continuous increase from the surface to the bulk. Since the refractive index of silicone resin is positively correlated with the crosslinking density, a continuous refractive index gradient transition layer is formed on the light-emitting surface after treatment, thereby reducing Fresnel internal reflection caused by the abrupt change in refractive index between the original under-crosslinked layer and the bulk, and improving the transmission performance of the light-emitting surface.

[0056] Meanwhile, the crosslinking reaction consumes a large amount of residual hydrogen-containing silicon groups and vinyl silicon groups, which are the starting sites for photo-oxidation of the surface layer during LED operation; after the residual amount is reduced, the initiation rate of yellowing of the surface layer under the synergistic effect of blue light and heat is reduced.

[0057] In one embodiment, when its value approaches zero, the amount of crosslinking is weak, and surface layer defects are hardly repaired; when its value is much greater than 1, all residual groups at each depth are consumed, and the crosslinking density reaches a high level everywhere. The gradual transition structure disappears, becoming a uniform layer. In actual processes, [the following is taken]: Within the range of 0.7 to 1.6, the undercrosslinked surface layer achieves a significant increase in crosslinking degree while retaining the gradual transition from the surface to the bulk.

[0058] In some embodiments, for step S3, after irradiation, the chamber atmosphere is switched to an inert gas and the chamber temperature is maintained for a period of time. At the end of irradiation, the platinum catalyst in the active state continues to catalyze the hydrogen-containing silicon groups and vinyl silicon groups remaining in the undercrosslinked surface layer to complete the crosslinking reaction under the inert gas atmosphere.

[0059] Specifically, after the irradiation reaches the set time, the ultraviolet light source is turned off, and the cavity atmosphere is immediately switched to an inert gas, optionally with an oxygen content of less than 10 ppm. The current cavity temperature is maintained for a period of time, such as 2 to 5 minutes.

[0060] After the atmosphere was switched to an inert gas, the dissolved oxygen in the chamber rapidly dropped to an extremely low level, eliminating the reactivation effect on the platinum catalyst. The portion of the platinum catalyst that remained in an active state at the end of irradiation—that is, the platinum activated by ultraviolet photons in the last few milliseconds but not yet reactivated by oxygen—was no longer oxidized under the inert gas atmosphere, maintaining its active state and continuing to catalyze the crosslinking reaction between the residual hydrogen-containing silicon groups and vinyl silicon groups in the undercrosslinked surface layer. During this stage, no new platinum was photoactivated (the light source was turned off), only the existing stock of active platinum at the end of irradiation was consumed; the reaction scale was limited and naturally decayed. Maintaining the temperature favored the reaction rate, allowing this batch of active platinum to convert all available residual groups within minutes.

[0061] After the holding time ends, allow the product to cool naturally to room temperature before removing it for subsequent packaging.

[0062] Optionally, in some embodiments, a low molecular weight siloxane pre-removal step is added before step S1: the chamber temperature is raised to 120 to 150°C under an inert atmosphere and maintained for 10 to 30 minutes to accelerate the volatilization and removal of low molecular weight cyclic siloxanes (D4 to D8 components, boiling point 175 to 290°C) in the silicone resin surface layer using high temperature; after completion, the temperature is lowered to 60 to 80°C before proceeding to subsequent steps. During thermosetting, low molecular weight components migrate and aggregate to the free surface, forming a liquid-like surface film and occupying some space. Pre-removal frees up reaction sites for the crosslinking reaction and reduces the possibility of micropores left due to the slow volatilization of low molecular weight substances during subsequent LED operation. The pre-removal temperature is lower than the original curing temperature of the silicone resin and does not affect the already completed crosslinking structure of the substrate.

[0063] Optionally, in some embodiments, the ultraviolet irradiation in step S2 is performed in a pulsed mode instead of continuous irradiation. The ratio of the duration of the bright period to the dark period in the pulse cycle can be selected from 1.5 to 3, for example, 100ms of bright time plus 50ms of dark time. During the dark period, the silicone resin surface is not irradiated, and the micro-area temperature drops slightly, avoiding the accumulation of local temperature rise that may be caused by continuous irradiation under high irradiance settings. The time-averaged irradiance in the pulsed mode should be between 50 and 200 mW / cm². 2 Within the range, the total irradiation time, after being converted according to the average hourly irradiance, is equivalent to the continuous irradiation mode.

[0064] Optionally, in some embodiments, an in-situ optical monitoring device is set up during the irradiation process in step S2 to detect the irradiation of the silicone resin light-emitting surface by the optical fiber in the visible light band and collect the reflection signal. As the crosslinking reaction progresses, the refractive index of the surface layer gradually approaches the bulk value, and the surface reflectivity shows a decreasing trend; when the change in surface reflectivity within a continuously set time period is less than a set threshold, it is determined that the reaction is approaching saturation and irradiation is terminated. The above threshold is, for example, taking the change in reflectivity within 10 consecutive seconds as less than 0.5% of the initial reflectivity. Its specific value can be determined by comparing the normal treatment time and the overtreatment time of 3 times the duration on the same formulation sample: when the difference in the final transmittance of the two groups of samples is less than the resolution of the photometer, the rate of change in reflectivity corresponding to the endpoint of the normal treatment is the reasonable threshold.

[0065] In some embodiments, 365nm or 385nm ultraviolet LEDs are mature commercial devices with a single LED power of several watts; the mass flow controller has an accuracy of ±1% of full scale, and the oxygen flow rate corresponding to 1200ppm oxygen at a nitrogen carrier gas flow rate of 20L / min is approximately 0.024L / min, which is within the controllable range of conventional equipment. The processing chamber can be modified based on the existing thermosetting oven of the packaging production line, adding an ultraviolet light source window and a gas mixing inlet. The overall processing time from entering the chamber to cooling out of the chamber is less than 5 minutes.

[0066] As an example, a 3030-type PLCC white LED encapsulated in methylphenyl silicone resin with a refractive index of 1.50 was processed as follows: cavity temperature 70℃, oxygen volume fraction 1200ppm, ultraviolet light source peak wavelength 365nm, and irradiance 100mW / cm². 2 The sample was continuously irradiated for 120 seconds, and then switched to pure nitrogen and maintained at 70°C for 3 minutes. Under these conditions, the positive luminous flux increased by about 2 to 4% before and after treatment, and the surface water contact angle increased from 105° to 112° as an indirect indicator of increased crosslinking density. After 1000 hours of accelerated aging at 85°C / 85% relative humidity, the luminous flux retention rate was 3 to 5 percentage points higher than that of the untreated control group.

[0067] The above method selectively reactivates the deactivated platinum catalyst in the undercrosslinked surface layer of silicone resin using ultraviolet light, and completes in-situ crosslinking of the surface layer at a controllable rate under controlled oxygen partial pressure. It also utilizes the spatial distribution characteristics of the residual group concentration to naturally form a refractive index gradient transition structure. This method achieves the repair of the light transmission performance of the light-emitting surface and the improvement of long-term reliability without introducing any foreign substances or generating new heterogeneous interfaces.

[0068] It should be noted that although the operations of the method of this application are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. On the contrary, the steps depicted in the flowchart can be performed in a different order. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0069] Please see Figure 4 , Figure 4 This application provides a silicone resin light transmission enhancement treatment system for PLCC-encapsulated LEDs. The system embodiments are similar to... Figure 1 Corresponding to the illustrated method embodiments, this system can be specifically applied to various electronic devices. The system specifically includes: The mixed atmosphere establishment module 401 is used to place the thermo-cured PLCC packaged LED into the atmosphere treatment chamber, introduce a mixed atmosphere of inert gas and oxygen into the chamber, and control the oxygen concentration to be within the range where the platinum catalyst can be partially activated under ultraviolet light irradiation. The ultraviolet irradiation crosslinking module 402 is used to irradiate the light-emitting surface of the silicone resin with near-ultraviolet light in the mixed atmosphere, so that the near-ultraviolet light reduces the deactivated platinum catalyst in the under-crosslinked surface layer to the active state. The active platinum catalyst catalyzes the hydrosilylation reaction between the hydrogen-containing silicon groups and vinyl silicon groups in the under-crosslinked surface layer to form crosslinking bonds. At the same time, the oxygen in the mixed atmosphere re-oxidizes part of the active platinum catalyst to the deactivated state, so that the ultraviolet light activation and oxygen re-deactivation reach a dynamic balance. The atmosphere switching and heat preservation module 403 is used to switch the cavity atmosphere to an inert gas after irradiation and maintain the cavity temperature for a period of time, so that the platinum catalyst, which is in an active state at the end of irradiation, can continue to catalyze the hydrogen-containing silicon groups and vinyl silicon groups remaining in the undercrosslinked surface layer to complete the crosslinking reaction under the inert gas atmosphere.

[0070] Each processing unit and / or module in the embodiments of this application can be implemented by an analog circuit that implements the functions described in the embodiments of this application, or by software that executes the functions described in the embodiments of this application.

[0071] Based on the same inventive concept, this application also provides an electronic device, such as... Figure 5 As shown, Figure 5This is a schematic diagram of an electronic device structure according to an embodiment of the present disclosure. The method corresponding to the electronic device can be the method in the foregoing embodiments, and its problem-solving principle is similar to that method. The electronic device provided in this application includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the methods and / or technical solutions of the foregoing embodiments of the present application.

[0072] In particular, the methods and / or embodiments in this application can be implemented as computer software programs. For example, the embodiments disclosed in this application include a computer program product comprising a computer program carried on a storage medium, the computer program containing program code for performing the methods shown in the flowchart. When the computer program is executed by a central processing unit (CPU), it performs the functions defined in the methods of this application.

[0073] Another embodiment of this application provides a computer-readable storage medium having computer program instructions stored thereon, which can be executed by a processor to implement the methods and / or technical solutions of any one or more embodiments of this application described above.

[0074] The flowcharts or block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of electronic devices, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-specific system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0075] The above description represents the preferred embodiments of the present invention. It should be noted that, for those skilled in the art, various improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for enhancing the light transmittance of silicone resin in a PLCC-encapsulated LED, characterized in that, Includes the following steps: The PLCC-encapsulated LED that has been thermosetting is placed into an atmosphere treatment chamber, and a mixed atmosphere of inert gas and oxygen is introduced into the chamber, controlling the oxygen concentration to be within the range where the platinum catalyst can be partially activated under ultraviolet light irradiation. The silicon resin light-emitting surface is irradiated with near-ultraviolet light under the mixed atmosphere. The near-ultraviolet light reduces the deactivated platinum catalyst in the under-crosslinked surface layer to the active state. The active platinum catalyst catalyzes the hydrosilylation reaction between the residual hydrogen-containing silicon groups and vinyl silicon groups in the under-crosslinked surface layer to form crosslinking bonds. At the same time, the oxygen in the mixed atmosphere re-oxidizes part of the active platinum catalyst to the deactivated state. The activation by ultraviolet light and the re-deactivation by oxygen reach a dynamic equilibrium. After irradiation, the atmosphere of the chamber is switched to an inert gas and the chamber temperature is maintained for a period of time. At the end of irradiation, the platinum catalyst in the active state continues to catalyze the crosslinking reaction between the hydrogen-containing silicon groups and vinyl silicon groups remaining in the undercrosslinked surface layer under the inert gas atmosphere.

2. The method according to claim 1, characterized in that, The peak emission wavelength of the near-ultraviolet light is 365 to 405 nm.

3. The method according to claim 1, characterized in that, The volume fraction of oxygen in the mixed atmosphere is 800 to 2000 ppm.

4. The method according to claim 1, characterized in that, The concentrations of residual hydrogen-containing silicon groups and vinyl silicon groups in the undercrossed surface layer decrease along the direction from the light-emitting surface to the silicone resin body. The amount of crosslinking supplementation at each depth in the irradiation step is positively correlated with the concentration of the residual groups at that depth. After irradiation treatment, the crosslinking density of the undercrossed surface layer increases continuously from the surface to the body.

5. The method according to claim 1, characterized in that, The irradiance is 50 to 200 mW / cm². 2 The irradiation time is 60 to 180 seconds.

6. The method according to claim 1, characterized in that, The cavity temperature is maintained at 60 to 80°C during the irradiation process.

7. The method according to claim 1, characterized in that, The oxygen content in the inert gas switched after the irradiation is less than 10 ppm, and the duration of maintaining the chamber temperature for a period of time is 2 to 5 minutes.

8. The method according to claim 1, characterized in that, Before introducing the mixed atmosphere, the cavity is first purged with an inert gas containing less than 10 ppm oxygen to reduce the residual oxygen concentration in the cavity to below 50 ppm.

9. The method according to claim 1, characterized in that, Before the irradiation step, the PLCC-encapsulated LED is heated to 120 to 150°C in an inert atmosphere and held for 10 to 30 minutes to cause the low molecular weight cyclic siloxanes in the surface layer of the silicon resin light-emitting surface to volatilize and be removed. After completion, the temperature is lowered to 60 to 80°C before proceeding with the subsequent steps.

10. A silicone resin light transmission enhancement treatment system for PLCC-encapsulated LEDs, characterized in that, include: The mixed atmosphere establishment module is used to place the thermo-cured PLCC packaged LED into the atmosphere treatment chamber, introduce a mixed atmosphere of inert gas and oxygen into the chamber, and control the oxygen concentration to be within the range where the platinum catalyst can be partially activated under ultraviolet light irradiation. The ultraviolet irradiation crosslinking module is used to irradiate the light-emitting surface of the silicone resin with near-ultraviolet light in the mixed atmosphere. The near-ultraviolet light reduces the deactivated platinum catalyst in the under-crosslinked surface layer to an active state. The active platinum catalyst catalyzes the hydrosilylation reaction between the hydrogen-containing silicon groups and vinyl silicon groups in the under-crosslinked surface layer to form crosslinking bonds. At the same time, the oxygen in the mixed atmosphere re-oxidizes part of the active platinum catalyst back to the deactivated state, so that the ultraviolet light activation and oxygen re-deactivation reach a dynamic balance. The atmosphere switching and heat preservation module is used to switch the cavity atmosphere to an inert gas after irradiation and maintain the cavity temperature for a period of time, so that the platinum catalyst, which is in an active state at the end of irradiation, can continue to catalyze the hydrogen-containing silicon groups and vinyl silicon groups remaining in the undercrosslinked surface layer to complete the crosslinking reaction under the inert gas atmosphere.

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