A silicone film for CSP, its preparation method and application

Abstract

This invention relates to the field of chip packaging technology, specifically to a silicone film for CSP (Chip Surface Mount Technology) and its preparation method and application. By weight percentage, the components include: 30-50% silicone resin, 20-50% modified glass powder, and 20-50% phosphor. The raw materials for preparing the modified glass powder include a modifier and glass powder, wherein the modifier includes 20-50 wt% silane coupling agent, 30-50 wt% organic solvent, and 20-50 wt% water. The silicone film prepared in this application, when used for CSP surface mounting of Mini LEDs, exhibits a light transmittance >97%, color tolerance ≤3, and a material rejection rate <2%.

Description

Technical Field

[0001] This invention relates to the field of chip packaging technology, specifically to a silicone film for CSP, its preparation method, and its application. Background Technology

[0002] Surface Mount Technology (SMT), as an advanced electronic assembly technology, achieves high-density, high-reliability, and high-efficiency production by directly mounting electronic components onto the surface of printed circuit boards, and has become dominant in the electronics manufacturing industry in recent years. In the field of LED (Light Emitting Diode) technology, Mini LED, as a next-generation display technology, has attracted much attention due to its high brightness, high contrast, and local dimming capabilities. Chip-scale packaged (CSP) LEDs are key to miniaturization. When Mini LED CSPs are applied to SMT production lines, they can be quickly and accurately mounted onto PCBs using equipment such as pick-and-place machines, improving production efficiency and product performance, while also supporting complex multi-layer circuit board designs. Traditional SMT LED chips, due to their relatively large weight, do not exhibit significant adhesion issues after the tape-and-reel process, resulting in generally high yields. However, Mini CSPs, due to their extremely light weight, are prone to tape adhesion even with slight surface stickiness during the tape-and-reel process. This leads to inaccurate component positioning during SMT assembly, resulting in low yields, which not only increases rework costs but also affects production efficiency and product reliability. Therefore, surface adhesion has become a key bottleneck restricting the widespread application of Mini CSP in SMT.

[0003] Chinese invention patent CN116565078B discloses a white CSP suitable for high-power single-sided light emission and its packaging method. The packaging steps include attaching protective tape to the electrode side of the LED chip, filling reflective adhesive between the protective tape and double-sided adhesive tape, removing the protective tape, cutting the reflective adhesive, removing the double-sided adhesive tape and temporary carrier, and obtaining the single-sided light emission white CSP. This method effectively improves the power and reliability of the prepared CSP. However, the tape in this invention has high adhesiveness and is not suitable for CSP mounting of small-sized Mini LEDs. Summary of the Invention

[0004] The first aspect of the present invention provides a silicone film for CSP, comprising, by weight percentage: 30-50% organosilicon resin, 20-50% modified glass powder and 20-50% phosphor; the raw materials for preparing the modified glass powder include a modifier and glass powder, wherein the modifier includes 20-50 wt% silane coupling agent, 30-50 wt% organic solvent and 20-50 wt% water.

[0005] The applicant's research found that adding modified glass powder to a silicone film, with the modified glass powder added at an amount of 30-40 wt%, can improve the hardness of the silicone film while reducing its surface tackiness. This may be due to the surface properties of the modified glass powder and its interaction with the silicone resin: a specific amount of modified glass powder and silicone resin cross-link through reaction to form a uniform network, optimizing the interface structure, which strengthens the internal bonding force and blocks the adsorption of surface moisture. In particular, the modified glass powder is surface-treated with a silane coupling agent to form a hydrophobic interface, enhancing the adhesion to the silicone resin and improving the overall mechanical strength and hardness. At the same time, the hydrophobic properties of the modified glass powder reduce the adhesion between surface molecules, making the silicone film surface smoother and further reducing tackiness.

[0006] Optionally, the amount of modified glass powder added to the silicone film is 30-40 wt%.

[0007] Optionally, the amount of the silane coupling agent added to the modifier is 25-40 wt%.

[0008] The refractive index of the silicone resin is >1.48.

[0009] The refractive index of the glass powder is >1.48.

[0010] Optionally, the refractive index difference between the glass powder and the silicone resin is <0.04.

[0011] Optionally, the refractive index difference between the glass powder and the silicone resin is ≤0.03.

[0012] The glass powder has a D50 particle size of 0.5-10 μm.

[0013] Optionally, the D50 particle size of the glass powder is 0.5-8 μm.

[0014] Optionally, the D50 particle size of the glass powder is 0.5-5 μm.

[0015] The phosphor includes at least one of YAG-based phosphors, nitride-based phosphors, and silicate-based phosphors.

[0016] The viscosity of the silicone resin at 25°C is 2000-4000 mPa·s.

[0017] Optionally, the viscosity of the silicone resin at 25°C is 2000-3000 mPa·s.

[0018] The silane coupling agent may be selected from at least one of the following grades: KH-560, KH-570, KH-550, KH-792.

[0019] The second aspect of the present invention provides a method for preparing a silicone film for CSP, comprising the following steps: mixing organosilicon resin, modified glass powder and phosphor evenly, and coating the mixture to obtain a silicone film.

[0020] The mixing temperature is 40-80℃, and the time is 1-3 hours.

[0021] A third aspect of the present invention provides an application of a silicone film for CSP, which is used in the CSP surface mounting of Mini LEDs.

[0022] The specific steps of the application are as follows: Mini LED chips are arranged in an array on a substrate, the Mini LED chips, the substrate, and the silicone film are placed in a high-temperature vacuum press to make the silicone film completely adhere to the LED chips, and the silicone film is cut.

[0023] Optional, can be applied to a five-sided emitting Mini CSP ( Figure 1 ) or single-sided luminous Mini CSP ( Figure 2 and Figure 3 ).

[0024] Beneficial effects

[0025] 1. This invention improves the hardness of a silicone film and reduces its surface stickiness (reducing the scrap rate) by adding modified glass powder to the silicone film, with the amount of modified glass powder added to the silicone film being 30-40 wt%.

[0026] 2. This invention limits the amount of modified glass powder added to the silicone film to 30-40wt%, and applies it to the CSP surface mount of Mini LEDs, with a color tolerance ≤3 and a material rejection rate <2%.

[0027] 3. By limiting the amount of silane coupling agent added to the modifier to 25-40wt%, this invention can be applied to the CSP surface mount of Mini LEDs to further reduce color tolerance and rejection rate, with color tolerance ≤2.5 and rejection rate <1.5%.

[0028] 4. By limiting the refractive index of the silicone resin and glass powder, this invention can effectively improve the light transmittance of the silicone film while maintaining its low viscosity.

[0029] 5. By limiting the refractive index difference between the glass powder and the silicone resin to <0.04, the light transmittance of the film can be further improved to 98%. Attached Figure Description

[0030] Figure 1 This is a structural diagram of a silicone film used in a five-sided light-emitting Mini CSP.

[0031] Figure 2This is a structural diagram of a silicone film used in a single-sided light-emitting Mini CSP.

[0032] Figure 3 This is a structural diagram of a silicone film used in a single-sided light-emitting Mini CSP.

[0033] The components include: 1. Flip-chip Mini LED; 2. Silicone film; 3. Substrate; 4. White reflective film. Detailed Implementation

[0034] Example 1

[0035] A silicone film for CSP, comprising, by weight percentage: 30% silicone resin, 35% modified glass powder, and 35% phosphor.

[0036] The raw materials for preparing the modified glass powder are a modifier and glass powder. The modifier is: 30wt% silane coupling agent (brand name: KH-560, purchased from Shandong Baiqian Chemical Co., Ltd.), 40wt% organic solvent (anhydrous ethanol), and 30wt% water.

[0037] The silicone resin is Dow Corning OE-6630, with a viscosity of 2500 mPa·s at 25°C and a refractive index of 1.53 (>1.48), and was purchased from Coposi Electronic Materials Zhangjiagang Co., Ltd.

[0038] The glass powder is grade T802, with a particle size D50 of 2.6 μm and a refractive index of 1.50, and was purchased from Zhongcheng Engineering Construction (Guangdong) Group Co., Ltd.

[0039] The phosphor is brand name YAG05 and was purchased from Shenzhen Gelang Optoelectronics Co., Ltd.

[0040] The modified glass powder is prepared by mixing a silane coupling agent, water, and an organic solvent evenly to obtain a modifier; adding the glass powder to a high-speed mixer, adding the modifier during the mixing process, and modifying it (60℃, 2h); and then drying and sieving to obtain the modified glass powder.

[0041] A method for preparing a silicone film for CSP: a silicone film is prepared by uniformly mixing organosilicon resin, modified glass powder, and phosphor and then coating it.

[0042] Example 2

[0043] The specific implementation method is the same as in Example 1; the difference is that, by weight percentage, the silicone film components include: 42% organosilicon resin, 20% modified glass powder, and 38% phosphor.

[0044] Example 3

[0045] The specific implementation method is the same as in Example 1; the difference is that, by weight percentage, the silicone film component includes: 18% organosilicon resin, 50% modified glass powder, and 32% phosphor.

[0046] Comparative Example 1

[0047] The specific implementation method is the same as in Example 1; the difference is that, by weight percentage, the silicone film component includes: 58% silicone resin and 42% phosphor; no modified glass powder is added.

[0048] Comparative Example 2

[0049] The specific implementation method is the same as in Example 1; the difference is that, by weight percentage, the silicone film component includes: 50% silicone resin, 10% modified glass powder, and 40% phosphor.

[0050] Comparative Example 3

[0051] The specific implementation method is the same as in Example 1; the difference is that, by weight percentage, the silicone film component includes: 10% silicone resin, 60% modified glass powder, and 30% phosphor.

[0052] Comparative Example 4

[0053] The specific implementation method is the same as in Example 1; the difference is that, by weight percentage, the silicone film component includes: 35% silicone resin, 35% glass powder, and 30% phosphor.

[0054] Comparative Example 5

[0055] The specific implementation method is the same as in Example 1; the difference is that the refractive index of the glass powder is 1.49.

[0056] Comparative Example 6

[0057] The specific implementation method is the same as in Example 1; the difference is that the refractive index of the glass powder is 1.57.

[0058] Performance testing methods

[0059] I. The silicone films of Examples 1-3 and Comparative Examples 1-4 were applied to the CSP surface mounting of Mini LEDs. The Mini LED samples prepared were subjected to the following performance tests, wherein the sample preparation method was as follows: Figure 1 As shown, Mini LED chips 1 are arranged in an array on substrate 2. Mini LED chips 1, substrate 2, and silicone film 3 are placed in a high-temperature vacuum press to completely attach the silicone film to the LED chips. The silicone film is then cut.

[0060] 1. Discarding rate test: Three groups of samples were prepared for Examples 1-3 and Comparative Examples 1-4, with 6000 samples in each group. The average value of the measured values ​​was recorded in Table 1.

[0061] Test method: Make the CSP into a taped (group) and use SMT equipment for component placement. Component placement parameters: The position where the component placement nozzle picks up the CSP is the contact surface - 20 μm (±10 μm).

[0062] Rejection rate = (number of non-placed components / 6000) × 100%. If the rejection rate of all three groups is < 2%, it is qualified; otherwise, it is unqualified.

[0063] 2. CIE test: Prepare 3 groups of specimens for Examples 1 - 3 and Comparative Examples 1 - 4 respectively, with 20 specimens in each group. The average value of the measured values is recorded in Table 2.

[0064] Test method: Weld the CSP on a hexagonal plate and place it in the integrating sphere HAAS - 2000 of Yuanfang to test the CIE. In the CIE - 1931 coordinate system, with the target CIE as the center, if the color tolerance (SDCM) ≤ 3, it is qualified; otherwise, it is unqualified.

[0065] Second, after baking the silicone films prepared in Example 1 and Comparative Examples 5 - 6 (150 °C, 4 h), perform light transmittance tests: Test 3 pieces, with 3 points on each piece. The average value of the measured values is recorded in Table 3.

[0066] Test method: Place the silicone film (150 μm) in a light transmittance tester, fix the emission wavelength band at 450 nm for blue light, and test the light transmittance. If the light transmittance > 97%, it is qualified; otherwise, it is unqualified.

[0067] Performance test data

[0068] Table 1

[0069]

[0070] Table 2

[0071]

[0072] Table 3

[0073]

[0074] It can be seen from Table 1 and Table 2 that by adding specific modified glass powder in this application, the adhesion problem of the silicone film can be effectively solved, thereby reducing the rejection rate and color tolerance at the same time. It can be seen from Table 3 that by selecting specific refractive index silicone resins and glass powder, the light transmittance can be further improved to meet the application of CSP surface mounting for Mini LED.

Claims

1. A silicone film for CSP, characterized in that, By weight percentage, the components include: 30-50% silicone resin, 30-40% modified glass powder, and 20-50% phosphor; the raw materials for preparing the modified glass powder include a modifier and glass powder, wherein the modifier includes 25-40 wt% silane coupling agent, 30-50 wt% organic solvent, and 20-50 wt% water; The refractive index of the silicone resin is >1.48, the refractive index of the glass powder is >1.48, and the difference in refractive index between the glass powder and the silicone resin is <0.

04.

2. The silicone film for CSP according to claim 1, characterized in that, The glass powder has a D50 particle size of 0.5-10 μm.

3. The silicone film for CSP according to claim 2, characterized in that, The glass powder has a D50 particle size of 0.5-8 μm.

4. A method for preparing a silicone film for CSP according to any one of claims 1-3, characterized in that, The process includes the following steps: mixing silicone resin, modified glass powder, and fluorescent powder evenly, and then coating the mixture to obtain a silicone film.

5. An application of the silicone film for CSP according to any one of claims 1-3, characterized in that, CSP surface mount technology for MiniLEDs.

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