An extra-long board for PCB Mini COB and its fabrication method
By creating S-shaped grooves on the PCB substrate and filling them with flexible stress-relieving strips, the warping problem caused by the difference in thermal expansion coefficients of Mini COB ultra-long boards was solved, achieving active stress release and a significant reduction in warping rate, thereby improving product reliability and yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUNAN SANLICHENG TECH CO LTD
- Filing Date
- 2026-01-26
- Publication Date
- 2026-05-29
AI Technical Summary
Existing Mini COB ultra-long boards suffer from severe warping during die bonding, wire bonding, and high-temperature operation due to the large difference in thermal expansion coefficients between the PCB substrate, chip, and colloidal materials. This leads to chip displacement, wire breakage, and reduced yield. Current technologies cannot effectively release accumulated stress.
An S-shaped groove is formed on the metal core layer of the PCB substrate and filled with a flexible stress relief strip. The flexible stress relief strip is formed by curing addition-type liquid silicone rubber and includes first and second silicone layers with different hardness and elongation, which actively absorb and release internal stress.
Significantly reduces warpage, improves reliability, avoids chip displacement, wire breakage and optical inhomogeneity caused by warpage, and ensures production yield.
Smart Images
Figure CN122121050A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of PCB board technology, and in particular to an extra-long board for PCB Mini COB and its preparation method. Background Technology
[0002] Existing Mini COB ultra-long boards (length ≥ 1.5m) are prone to warping (warping rate often > 1%) during die bonding, wire bonding, packaging, and high-temperature operation due to the large difference in thermal expansion coefficients between the PCB substrate, chip, and adhesive materials, coupled with stress accumulation caused by the ultra-long dimensions. This leads to chip displacement, wire breakage, optical non-uniformity, and even a significant drop in yield. Current technologies mostly use low CTE materials or symmetrical structures to suppress warping, which are passive rigid constraints and cannot effectively release accumulated stress, especially on ultra-long boards where the effect is limited. Summary of the Invention
[0003] To address the aforementioned technical problems, this invention provides an extra-long board for PCB Mini COB and its fabrication method, the specific technical solution of which is as follows: An extra-long board for PCB Mini COB, comprising: A PCB substrate includes a copper circuit layer, an insulating dielectric layer, and a metal core layer stacked sequentially. S-shaped trenches are formed on the metal core layer and extend along the length of the PCB substrate; A flexible stress relief strip is filled in the S-shaped groove, and the flexible stress relief strip is formed by curing addition-type liquid silicone rubber.
[0004] Preferably, the flexible stress relief band includes: A first silicone layer is disposed adjacent to the insulating dielectric layer, and the first silicone layer has a Shore hardness of 25~35A and an elongation of ≥250%. The second silicone layer is attached to the side of the first silicone layer away from the insulating dielectric layer. The second silicone layer has a Shore hardness of 8~15A and an elongation of ≥400%.
[0005] Preferably, by weight: The first silicone layer is made of the following components: 100 parts of vinyl polyorganosiloxane, 8-20 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent; The second silicone layer is made of the following components: 100 parts of vinyl polyorganosiloxane, 15-35 parts of hydrogen polyorganosiloxane, 0.1-0.3 parts of platinum addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent.
[0006] Preferably: The vinyl-containing polyorganosiloxane is selected from at least one of vinyl-terminated polydimethylsiloxane, vinyl-terminated polydimethylmethylvinylsiloxane copolymer, and side-containing vinyl polydimethylsiloxane. The platinum-based addition reaction catalyst is selected from at least one of Karstedt catalyst, Speier catalyst, and platinum-vinylsiloxane complex; The addition reaction inhibitor is selected from at least one of 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol, and diallyl maleate.
[0007] Preferably: The raw material composition of the first silicone layer also includes: 60-80 parts by weight of spherical aluminum nitride powder and 20-30 parts by weight of flake boron nitride powder; The raw material composition of the second silicone layer also includes 20-40 parts by weight of spherical alumina powder.
[0008] Preferably: The PCB substrate has a length of 1.5~3m and a width of 50~200mm; The thickness of the copper layer in the circuit is 35~140μm; The thickness of the insulating dielectric layer is 50~150μm; The thickness of the metal core layer is 1.0~2.5mm.
[0009] Preferably: The width of the S-shaped groove is 0.1~0.5mm; The depth of the S-shaped trench is 40% to 60% of the thickness of the metal core layer; The distance between any two adjacent curved sections on the same side of the S-shaped groove in the length direction is 200~500mm.
[0010] This embodiment also provides a preparation method for preparing the PCB MiniCOB extra-long board as described in any of the above embodiments, the preparation method comprising the following steps: S1. Pre-treat the PCB substrate; S2. The S-shaped trench is formed on the metal core layer; S3. Preparation of addition-type liquid silicone rubber; S4. Vacuum inject the addition-type liquid silicone rubber into the S-shaped groove and cure it to form the flexible stress-relieving band.
[0011] Preferably: Step S3 specifically includes the following sub-steps: S31. By weight, 100 parts of vinyl-containing polyorganosiloxane, 8-20 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent are mixed evenly to prepare a first addition-type liquid silicone rubber composition. S32. By weight, 100 parts of vinyl-containing polyorganosiloxane, 15-35 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent are mixed evenly to prepare a second addition-type liquid silicone rubber composition. Step S4 specifically includes the following sub-steps: S41. Fix the PCB substrate with the metal core layer facing upward, and inject the first addition-cured liquid silicone rubber composition into the bottom of the S-shaped trench under vacuum conditions; S42. Pre-curing the first addition-cured liquid silicone rubber composition to obtain a first silicone layer; S43. Under vacuum conditions, the second addition-type liquid silicone rubber is injected into the remaining space in the S-shaped groove, and after curing, a second silicone layer is obtained. The first silicone layer and the second silicone layer form the flexible stress relief band.
[0012] Preferably, after step S4, the following steps are further included: S5. Apply a protective layer to the surface of the metal core layer and the exposed surface of the flexible stress relief strip. The protective layer is selected from at least one of a thin copper foil layer, a solder resist ink layer, and an aluminum foil layer. The thickness of the protective layer is 10~50μm.
[0013] The PCB Mini COB extra-long board provided by this invention has the following beneficial effects: 1. By actively absorbing and releasing accumulated internal stress through the built-in flexible stress relief strip, the warpage rate is significantly reduced.
[0014] 2. Improve reliability and effectively avoid problems such as chip displacement, wire breakage and optical inhomogeneity caused by warping. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.
[0016] Figure 1 A cross-sectional schematic diagram of an extra-long PCB Mini COB board provided for an embodiment of the present invention; Figure 2 This is a top view of an extra-long PCB Mini COB board provided for an embodiment of the present invention.
[0017] Figure Labels 1-PCB substrate; 11-Circuit copper layer; 12-Insulating dielectric layer; 13-Metal core layer; 2-S-shaped trench; 3-Flexible stress relief strip. Detailed Implementation
[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.
[0019] It should be noted that similar labels in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0020] Please see Figure 1 and Figure 2 This embodiment provides an extra-long board for PCB Mini COB, comprising: The PCB substrate 1 includes a copper circuit layer 11, an insulating dielectric layer 12, and a metal core layer 13 stacked sequentially.
[0021] S-shaped trench 2 is formed on the metal core layer 13 and extends along the length of the PCB substrate 1.
[0022] The flexible stress relief band 3 is filled in the S-shaped groove 2. The flexible stress relief band 3 is formed by curing addition-type liquid silicone rubber.
[0023] In this design, the side of the PCB substrate 1 containing the copper layer 11 is the front side, and the side containing the metal core layer 13 is the back side. Multiple S-shaped trenches 2 can be provided along the width of the metal core layer 13, or only one can be provided. The S-shaped trenches form multiple locally flexible regions distributed along the length of the metal core layer. The addition-cured liquid silicone rubber filling these regions has low hardness and high elongation after curing, enabling controllable micro-deformation under thermal expansion and contraction or process stress. The S-shaped (serpentine) design further increases the deformation freedom of the trench path, allowing the flexible stress-relieving bands to form distributed "buffer hinges" along the length.
[0024] When the substrate experiences internal stress due to CTE mismatch, this stress accumulates in the rigid metal core region and is transmitted to the flexible stress-relieving strip. The flexible strip actively absorbs and releases the stress through its own elastic deformation, preventing the stress from continuing to be transmitted to the front-side circuit layer and chip area, thereby preventing the occurrence and development of overall warping. At the same time, since the trench is a non-through blind trench and the filling material has good thermal conductivity, it will not significantly block the heat dissipation path of the metal core layer.
[0025] The PCB Mini COB extra-long board provided in this embodiment has the following beneficial effects: 1. By actively absorbing and releasing accumulated internal stress through the built-in flexible stress relief strip, the warpage rate is significantly reduced.
[0026] 2. Improve reliability and effectively avoid problems such as chip displacement, wire breakage and optical inhomogeneity caused by warping.
[0027] Furthermore, the flexible stress relief band 3 includes: A first silicone layer is disposed adjacent to the insulating dielectric layer 12. The first silicone layer has a Shore hardness of 25~35A and an elongation of ≥250%.
[0028] The second silicone layer is attached to the side of the first silicone layer away from the insulating dielectric layer 12. The second silicone layer has a Shore hardness of 8~15A and an elongation of ≥400%.
[0029] The first silicone layer has slightly higher hardness and moderate elongation, providing necessary mechanical support for the substrate near the chip while maintaining a certain degree of elastic cushioning. The second silicone layer is ultra-soft and has high elongation, providing greater deformation space and primarily absorbing overall bending stress. This gradient design of elastic modulus—"slightly harder on the front and ultra-softer on the back"—allows stress to be gradually absorbed during transmission: chip-side stress is initially buffered by the harder first layer and then significantly released by the ultra-soft second layer, preventing stress concentration and reflection back to the front. Simultaneously, the dual-layer structure forms a continuous flexible band through interface bonding, ensuring the uniformity and stability of stress release.
[0030] Further, by weight: The first silicone layer is made of the following components: 100 parts of vinyl polyorganosiloxane, 8-20 parts of hydrogen polyorganosiloxane, 0.1-0.3 parts of platinum addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent.
[0031] The second silicone layer is made of the following components: 100 parts of vinyl polyorganosiloxane, 15-35 parts of hydrogen polyorganosiloxane, 0.1-0.3 parts of platinum addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent.
[0032] Furthermore: The vinyl-containing polyorganosiloxane is selected from at least one of vinyl-terminated polydimethylsiloxane, vinyl-terminated polydimethylmethylvinylsiloxane copolymer, and side-containing vinyl polydimethylsiloxane.
[0033] The platinum addition reaction catalyst is selected from at least one of Karstedt catalyst, Speier catalyst, and platinum-vinylsiloxane complex.
[0034] The addition reaction inhibitor is selected from at least one of 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol, and diallyl maleate.
[0035] Furthermore: The raw material composition of the first silicone layer also includes: 60-80 parts by weight of spherical aluminum nitride powder and 20-30 parts by weight of flake boron nitride powder.
[0036] The raw material composition of the second silicone layer also includes: 20-40 parts by weight of spherical alumina powder.
[0037] The first silicone layer, with its highly filled spherical AlN and sheet-like BN, forms a highly efficient thermally conductive network, rapidly transferring heat from the chip to the metal core. Simultaneously, the filler can be surface-treated without significantly sacrificing elasticity. The second silicone layer, with its low filler, provides only basic thermal conductivity, prioritizing the retention of ultra-high elongation to ensure stress release capabilities. This gradient thermal design allows heat to be rapidly dissipated from the chip side, while the flexible back layer absorbs the stress generated by thermal expansion.
[0038] Furthermore: The length of PCB substrate 1 is 1.5~3m and the width is 50~200mm.
[0039] The thickness of the copper layer 11 in the circuit is 35~140μm.
[0040] The thickness of the insulating dielectric layer 12 is 50~150μm.
[0041] The thickness of the metal core layer 13 is 1.0~2.5mm.
[0042] Furthermore: The width of the S-shaped groove 2 is 0.1~0.5mm.
[0043] The depth of the S-shaped trench 2 is 40% to 60% of the thickness of the metal core layer 13.
[0044] The distance between any two adjacent curved sections on the same side of the S-shaped groove 2 in the length direction is 200~500mm.
[0045] This embodiment also provides a preparation method for preparing an extra-long board for PCB Mini COB as described above, the preparation method comprising the following steps: S1. Pre-treat the PCB substrate 1.
[0046] S2. An S-shaped groove is formed on the metal core layer 13.
[0047] S3. Preparation of addition-type liquid silicone rubber.
[0048] S4. Vacuum inject addition-type liquid silicone rubber into the S-shaped groove 2 and cure it to form a flexible stress-relieving band 3.
[0049] The process involves several key steps: pretreatment (such as pre-baking) removes residual stress from the substrate to prevent new warping from being introduced during subsequent processing; precision machining of non-through S-shaped blind trenches from the back side ensures the integrity of the front-side circuitry; addition-cure liquid silicone rubber is cured at low temperatures (≤80℃) to avoid thermal stress introduced by high temperatures; and vacuum infusion eliminates air bubbles to ensure dense, defect-free filling and a strong bond with the metal core layer. The overall process is compatible with existing MCPCB production lines, requiring only additional trenching and infusion steps to embed a flexible buffer structure within the rigid substrate, enabling active stress release.
[0050] In specific implementation, step S1 pretreatment preferably involves baking the ultra-long metal core PCB in a 120℃ oven for 2-4 hours to remove moisture absorption and internal stress; step S2 uses UV laser or precision CNC milling to process S-shaped grooves from the back side with controlled depth, followed by ultrasonic cleaning and plasma activation to improve surface wettability; step S3 involves vacuum degassing and mixing the addition-type liquid silicone rubber composition in a planetary mixer; step S4 involves fixing the substrate with the back side facing up on a vacuum injection stage, placing it at room temperature for 30 minutes after injection to remove microbubbles, and then curing it at 80℃ for 2-4 hours; after curing, excess silicone on the back side can be lightly scraped to make it flush with or slightly concave 0.05mm from the metal core layer.
[0051] Furthermore: Step S3 specifically includes the following sub-steps: S31. By weight, 100 parts of vinyl-containing polyorganosiloxane, 8-20 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent are mixed evenly to prepare a first addition-type liquid silicone rubber composition.
[0052] S32. By weight, 100 parts of vinyl-containing polyorganosiloxane, 15-35 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent are mixed evenly to prepare a second addition-type liquid silicone rubber composition.
[0053] Step S4 specifically includes the following sub-steps: S41. Fix the PCB substrate 1 with the metal core layer 13 facing upward, and inject the first addition-type liquid silicone rubber composition into the bottom of the S-shaped trench 2 under vacuum conditions.
[0054] S42. Pre-curing the first addition-type liquid silicone rubber composition to obtain a first silicone layer.
[0055] S43. Under vacuum conditions, the second addition-type liquid silicone rubber is injected into the remaining space in the S-shaped groove 2, and after curing, a second silicone layer is obtained. The first silicone layer and the second silicone layer form a flexible stress relief band 3.
[0056] The first composition has a lower crosslinking density and slightly higher hardness, forming a supportive and thermally conductive layer near the front side (chip side); the second composition has an optimized crosslinking density and extremely low hardness, forming an ultra-soft buffer layer on the back side. The first composition is first poured in and pre-cured to a gel state (non-flowing but not fully crosslinked) to prevent mixing with the subsequent second composition and ensure a clear interface; defoaming is performed twice under vacuum to ensure no air gaps. This ultimately forms a flexible strip with a continuous "hard-soft" bond, achieving graded stress absorption and synergistic heat dissipation.
[0057] In practice, S31 and S32 are mixed in different containers (with optional addition of thermally conductive filler), stirred and degassed before use; when pouring the first composition in S41, the pouring volume is controlled to be 40%~60% of the trench volume, allowing the liquid level to naturally fill to the designed height; S42 pre-curing is preferably done at 80℃ for 20~40 minutes, until the surface is touch dry but the interior can still flow slightly; S43 then pour the second composition to fill the trench; S44 complete curing can be done by staged heating (e.g., first 60℃ for 1 hour, then 80℃ for 2 hours) to ensure uniform cross-linking; after curing, the back can be lightly ground or scraped to make the silicone surface flush with or slightly lower than the metal core layer by 0.05~0.1 mm, which facilitates subsequent back processing.
[0058] Furthermore, the following steps are included after step S4: S5. Apply a protective layer to the surface of the metal core layer 13 and the exposed surface of the flexible stress relief strip 3. The protective layer is selected from at least one of the following: thin copper foil layer, solder resist ink layer, and aluminum foil layer. The thickness of the protective layer is 10~50μm.
[0059] The thin protective layer covers the exposed silicone surface to prevent dust, moisture or mechanical damage, while providing an additional heat dissipation interface or EMC shielding; the thin thickness and good material flexibility impose minimal constraints on silicone deformation and do not affect the buffering function of the flexible stress release strip; the thin copper foil layer can further improve the overall heat dissipation uniformity.
[0060] In practice, step S5 can be performed after curing and smoothing the back side: if a solder resist ink layer is selected, it can be screen printed or sprayed and then UV cured; if a thin copper foil layer (18~35μm) is selected, it can be attached by hot pressing or chemical copper plating; if an aluminum foil layer is selected, it can be bonded with thermally conductive adhesive. Before application, ensure the back side is clean, and after application, light rolling can be used to ensure flatness and adhesion.
[0061] Specific embodiments are provided below. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.
[0062] Example 1 Step 1: Substrate Preparation Ten commercially available aluminum-based PCB substrates were selected, with the following specifications: length 2.0 m, width 100 mm, and total thickness 2.0 mm (70 μm copper layer, 100 μm insulating dielectric layer, and 1.83 mm aluminum core layer).
[0063] Pre-bake the substrate in a 120℃ oven for 3 hours to remove internal stress and moisture, then cool it to room temperature for later use.
[0064] Step 2: S-groove machining Eight S-shaped blind grooves were machined from the back of the substrate (aluminum core layer side) using a UV laser processing machine (wavelength 355 nm, power 30 W).
[0065] Groove parameters: width 0.32 mm, depth 0.95 mm, and the same-side bends are spaced 320 mm apart along the length direction.
[0066] After processing, the surface is cleaned with an ultrasonic cleaner (300 W, 40 kHz) for 15 min, and then treated with a plasma cleaner (500 W, oxygen atmosphere) for 5 min to improve surface wettability.
[0067] Step 3: Preparation of silicone rubber composition Add the following ingredients sequentially to a 5 L planetary mixer: 0.68 kg of vinyl-containing polyorganosiloxane, 0.20 kg of spherical alumina powder, and 6.8 g of silane coupling agent KH-560.
[0068] After dispersing at high speed (800 rpm) for 40 min, add: 102 g of hydrogen-containing polyorganosiloxane, 1.36 g of platinum addition reaction catalyst, and 0.54 g of 1-ethynyl-1-cyclohexanol.
[0069] After stirring for another 10 minutes, the mixture was degassed under vacuum (-0.095 MPa) for 25 minutes to obtain a uniform single addition-type liquid silicone rubber composition with a viscosity of approximately 12000 mPa·s.
[0070] Step 4: Vacuum infusion and curing Fix the substrate with the back side facing up on the vacuum injection stage.
[0071] The prepared silicone rubber composition was poured into the trench under a vacuum of -0.098 MPa.
[0072] After letting it stand at room temperature for 40 minutes to remove tiny air bubbles, transfer it to an 80℃ oven to cure for 3.5 hours.
[0073] After curing, gently scrape off any excess silicone on the back with a scraper to make the silicone surface flush with the aluminum core layer.
[0074] Step 5: Mini COB Process Drilling, electroplating, printing black ink, die bonding of Mini LEDs, wire bonding, spraying fluorescent adhesive and curing are performed to obtain 10 MiniCOB ultra-long board modules.
[0075] Step Six: Performance Testing 1. Room temperature warpage test A warpage tester was used. The test subjects were 5 bare boards (with stress relief zones only, but no die bonding) and 5 complete Mini COB modules.
[0076] Environment: 25℃, 50%RH.
[0077] Method: Measure the maximum warping height of the board's diagonal. Warping rate (%) = maximum warping height / diagonal length × 100.
[0078] 2. Warpage Change Test After Thermal Shock The instrument uses a double-chamber thermal shock test chamber.
[0079] Conditions: -40℃ (15 min) to 85℃ (15 min) cycle, 1000 cycles.
[0080] Method: Warpage was measured at 25°C after initial, 500, and 1000 cycles, and the change was calculated.
[0081] Auxiliary observation: Microscopic examination of chip displacement and wire bonding status.
[0082] The test data is shown in Table 1 below: Example 2 Step 1: Substrate Preparation Ten commercially available aluminum-based PCB substrates were selected, with the following specifications: length 2.0 m, width 100 mm, and total thickness 2.0 mm (70 μm copper layer, 100 μm insulating dielectric layer, and 1.83 mm aluminum core layer).
[0083] Pre-bake the substrate in a 120℃ oven for 3 hours to remove internal stress and moisture, then cool it to room temperature for later use.
[0084] Step 2: S-groove machining Eight S-shaped blind grooves were machined from the back of the substrate (aluminum core layer side) using a UV laser processing machine (wavelength 355 nm, power 30 W).
[0085] Groove parameters: width 0.32 mm, depth 0.95 mm, and the same-side bends are spaced 320 mm apart along the length direction.
[0086] After processing, the surface is cleaned with an ultrasonic cleaner (300 W, 40 kHz) for 15 min, and then treated with a plasma cleaner (500 W, oxygen atmosphere) for 5 min to improve surface wettability.
[0087] Step 3: Preparation of silicone rubber composition Add the following ingredients sequentially to a 5 L planetary mixer: 0.25 kg of vinyl-containing polyorganosiloxane, 0.175 kg of spherical aluminum nitride powder, 0.0625 kg of flake boron nitride powder, and 2.5 g of silane coupling agent KH-560.
[0088] After dispersion at high speed (800 rpm) for 45 min, the following were added: 30 g of hydrogen-containing polyorganosiloxane, 0.5 g of platinum-based addition catalyst, and 0.2 g of 1-ethynyl-1-cyclohexanol. After stirring for another 10 min, the mixture was degassed under vacuum (-0.095 MPa) for 25 min to obtain the first addition-type liquid silicone rubber composition with a viscosity of approximately 28,000 mPa·s.
[0089] In another 5 L planetary mixer, add in sequence: 0.30 kg of vinyl polyorganosiloxane, 0.15 kg of spherical alumina powder, and 3.0 g of silane coupling agent KH-550.
[0090] After dispersing at high speed (800 rpm) for 35 min, add: 75 g of hydrogen-containing polyorganosiloxane, 0.6 g of platinum addition reaction catalyst, and 0.24 g of 1-ethynyl-1-cyclohexanol.
[0091] After stirring for another 10 minutes, the mixture was degassed under vacuum (-0.095 MPa) for 25 minutes to obtain a second addition-type liquid silicone rubber composition with a viscosity of approximately 8500 mPa·s.
[0092] Step 4: Vacuum step-by-step pouring and curing Fix the substrate with the back side facing up on the vacuum injection stage.
[0093] Under a vacuum of -0.098 MPa, the first addition-cured liquid silicone rubber composition is first poured into the bottom of the trench (the amount poured into each plate accounts for about 50% of the trench volume).
[0094] After being left at room temperature for 30 minutes, it is transferred to an 80℃ oven for pre-curing for 35 minutes to reach a gel state.
[0095] Then, inject the second addition-cured liquid silicone rubber composition into the groove under a vacuum of -0.098 MPa until it is full.
[0096] After leaving the container at room temperature for 40 minutes to allow tiny air bubbles to dissipate, it is then fully cured at 80°C for 4 hours.
[0097] After curing, gently scrape off any excess silicone on the back with a scraper to make the silicone surface flush with or slightly concave (0.05 mm) with the aluminum core layer.
[0098] Step 5: Mini COB Process Drilling, electroplating, printing black ink, die bonding of Mini LEDs, wire bonding, spraying fluorescent adhesive and curing are performed to obtain 10 MiniCOB ultra-long board modules.
[0099] Step Six: Performance Testing The test items and methods are the same as in Example 1, and the test data are shown in Table 2 below: Comparative Example 1 Ten commercially available aluminum-based PCB substrates were selected, with the following specifications: length 2.0 m, width 100 mm, and total thickness 2.0 mm (70 μm copper layer, 100 μm insulating dielectric layer, and 1.83 mm aluminum core layer).
[0100] The substrate was pre-baked in a 120℃ oven for 3 hours to remove internal stress and moisture, and then processed directly according to the Mini COB process: drilling, electroplating, printing black ink, Mini LED die bonding, wire bonding, spraying fluorescent glue and curing, to obtain 10 conventional Mini COB extra-long board modules.
[0101] The test items and methods are the same as in Example 1, and the test data are shown in Table 3 below: As can be seen from the above data, this embodiment successfully reduces the warpage of the ultra-long Mini COB board to below 0.3% by embedding an S-shaped groove in the metal core layer and filling it with a flexible stress-relieving band formed by addition-curved liquid silicone rubber. The change after thermal shock is controlled within 0.1%, which completely solves the problems of chip displacement and wire breakage caused by warpage of ultra-long boards in the prior art.
[0102] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be within the scope of protection of the present invention.
Claims
1. An extra-long board for PCB Mini COB, characterized in that, include: The PCB substrate (1) includes a copper circuit layer (11), an insulating dielectric layer (12) and a metal core layer (13) stacked sequentially. S-shaped trenches (2) are formed on the metal core layer (13) and extend along the length direction of the PCB substrate (1); A flexible stress relief strip (3) is filled in the S-shaped groove (2), and the flexible stress relief strip (3) is formed by curing addition-type liquid silicone rubber.
2. The PCB Mini COB extra-long board according to claim 1, characterized in that, The flexible stress relief band (3) includes: A first silicone layer is disposed adjacent to the insulating dielectric layer (12), the first silicone layer having a Shore hardness of 25~35A and an elongation of ≥250%; The second silicone layer is attached to the side of the first silicone layer away from the insulating medium layer (12). The second silicone layer has a Shore hardness of 8~15A and an elongation of ≥400%.
3. The PCB Mini COB extra-long board according to claim 2, characterized in that, By weight: The first silicone layer is made of the following components: 100 parts of vinyl polyorganosiloxane, 8-20 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent; The second silicone layer is made of the following components: 100 parts of vinyl polyorganosiloxane, 15-35 parts of hydrogen polyorganosiloxane, 0.1-0.3 parts of platinum addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent.
4. The PCB Mini COB extra-long board according to claim 3, characterized in that: The vinyl-containing polyorganosiloxane is selected from at least one of vinyl-terminated polydimethylsiloxane, vinyl-terminated polydimethylmethylvinylsiloxane copolymer, and side-containing vinyl polydimethylsiloxane. The platinum-based addition reaction catalyst is selected from at least one of Karstedt catalyst, Speier catalyst, and platinum-vinylsiloxane complex; The addition reaction inhibitor is selected from at least one of 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol, and diallyl maleate.
5. The PCB Mini COB extra-long board according to claim 3, characterized in that: The raw material composition of the first silicone layer also includes: 60-80 parts by weight of spherical aluminum nitride powder and 20-30 parts by weight of flake boron nitride powder; The raw material composition of the second silicone layer also includes 20-40 parts by weight of spherical alumina powder.
6. The PCB Mini COB extra-long board according to any one of claims 1 to 5, characterized in that: The PCB substrate (1) has a length of 1.5~3m and a width of 50~200mm; The thickness of the copper layer (11) of the line is 35~140μm; The thickness of the insulating dielectric layer (12) is 50~150μm; The thickness of the metal core layer (13) is 1.0~2.5mm.
7. The PCB Mini COB extra-long board according to any one of claims 1 to 5, characterized in that: The width of the S-shaped groove (2) is 0.1~0.5mm; The depth of the S-shaped trench (2) is 40% to 60% of the thickness of the metal core layer (13); The distance between any two adjacent curved sections on the same side of the S-shaped groove (2) in the length direction is 200~500mm. A preparation method, characterized in that it is used to prepare the PCB MiniCOB extra-long board as described in any one of claims 1 to 7, the preparation method comprising the following steps: S1. Pre-process the PCB substrate (1); S2. The S-shaped groove is formed on the metal core layer (13); S3. Preparation of addition-type liquid silicone rubber; S4. Vacuum inject the addition-type liquid silicone rubber into the S-shaped groove (2) and cure it to form the flexible stress-relieving band (3).
8. The preparation method according to claim 8, characterized in that: Step S3 specifically includes the following sub-steps: S31. By weight, 100 parts of vinyl-containing polyorganosiloxane, 8-20 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent are mixed evenly to prepare a first addition-type liquid silicone rubber composition. S32. By weight, 100 parts of vinyl-containing polyorganosiloxane, 15-35 parts of hydrogen-containing polyorganosiloxane, 0.1-0.3 parts of platinum-based addition reaction catalyst, 0.05-0.1 parts of addition reaction inhibitor, and 0.5-2 parts of silane coupling agent are mixed evenly to prepare a second addition-type liquid silicone rubber composition. Step S4 specifically includes the following sub-steps: S41. Fix the PCB substrate (1) with the metal core layer (13) facing upward, and inject the first addition-type liquid silicone rubber composition into the bottom of the S-shaped trench (2) under vacuum conditions; S42. Pre-curing the first addition-cured liquid silicone rubber composition to obtain a first silicone layer; S43. Under vacuum conditions, the second addition-type liquid silicone rubber is injected into the remaining space in the S-shaped groove (2), and after curing, a second silicone layer is obtained. The first silicone layer and the second silicone layer form the flexible stress relief band (3).
9. The preparation method according to claim 8 or 9, characterized in that, Step S4 is followed by the following steps: S5. Apply a protective layer to the surface of the metal core layer (13) and the exposed surface of the flexible stress relief strip (3), wherein the protective layer is selected from at least one of thin copper foil layer, solder resist ink layer, and aluminum foil layer, and the thickness of the protective layer is 10~50μm.