A forming process for a high co-planarity embedded copper core substrate

Abstract

The application relates to the field of printed circuit board manufacturing, and discloses a forming process of a high-co-planarity embedded copper core substrate, which comprises the following steps: milling an outer convex bearing step flange along the side wall of a heat-conducting copper core, performing micro-roughening and coating a silane coupling agent; processing a stepped embedding groove hole on an inner layer core plate, and cutting a reserved window for gap compensation of a prepreg punching tool volume; buckling the heat-conducting copper core into the embedding groove hole and completing symmetrical lamination; after segmented vacuum hot pressing and solidification, adopting ceramic brush roller flat grinding and acid micro-etching to modify surface height difference; and performing chemical copper deposition and pattern electroplating to form an outer layer circuit and a vertical heat dissipation pad. The application cooperates with stepped limiting and volume compensation windowing, eliminates resin filling imbalance and embedding alignment slippage, combines with composite flattening to ensure surface flatness and co-planarity, and releases thermal stress through molecular bonding to prevent interface delamination.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, and in particular to a forming process for a high coplanarity embedded copper core substrate. Background Technology

[0002] As the power consumption density of high-power semiconductor devices and integrated circuit modules continues to increase, packaging substrates are gradually evolving from traditional surface-insulated heat dissipation structures to low thermal resistance structures with internally embedded thermally conductive copper cores. Embedding the thermally conductive copper core inside the epoxy fiberglass insulating substrate can shorten the heat transfer path in the vertical direction and eliminate the thermal resistance caused by the dielectric layer, thereby meeting the junction temperature control requirements of high heat flux density chips.

[0003] In the vacuum hot pressing process of multilayer substrates, the significant differences in thermal conductivity, coefficient of thermal expansion, and elastic modulus between metallic copper and the organic insulating substrate can easily affect the flow state of the molten resin around the copper core. Due to the rapid thermal conductivity of copper, the heating rate of the copper core embedding area is usually faster than that of the surrounding insulating medium. When the molten resin in the prepreg flows through the gaps in the sidewalls of the copper core, uneven viscosity distribution and flow shear changes are likely to occur. Uneven flow pressure can drive the thermally conductive copper core to undergo planar displacement. During the subsequent cooling process, the different shrinkage rates of metallic copper and the insulating substrate can also easily lead to shear stress concentration at the bonding interface. In conventional processes, simply increasing the reserved window gap of the prepreg can provide more space for resin flow around the copper core, but it can easily cause resin loss in areas far from the copper core, resulting in insufficient resin and local depressions. It is also difficult to limit the copper core slippage caused by high-pressure resin flow. If the overflow resin film on the substrate surface is removed by strengthening mechanical grinding and cutting, further problems can be solved. Furthermore, due to the significant difference in grinding performance between metallic copper and glass fiber resin, grooves or wear tails can form at the interface between the two materials. In existing technologies, although attempts have been made to improve resin filling by modifying the sidewall configuration of the copper block or opening local glue discharge channels, it is still difficult to balance dynamic positioning and global coplanarity under the coupling effect of multiple physical fields. For example, Chinese invention patent application CN117241460A discloses an embedded copper block multilayer board and its manufacturing process. A guide groove is opened on the sidewall of the copper block, and a high-flowability prepreg melts into the guide groove to fill the gap. However, the sidewall of the copper block in this solution is still a straight wall embedded form. Under the asymmetric transverse shear force of hot-pressed high-pressure glue flow, it lacks a multi-dimensional self-locking positioning mechanism, and the copper block is prone to in-plane slippage and deflection. Moreover, its guide groove adopts a fixed size groove, which cannot achieve dynamic volume conservation and balancing according to the different thickness core boards, the solid volume of the copper block and the melt rheological characteristics of the prepreg, making it difficult to avoid local glue accumulation or underfilling.

[0004] Therefore, the technical problem to be solved by this invention is to simultaneously limit the displacement of the thermally conductive copper core during the vacuum hot pressing process of the substrate, reasonably control the filling amount of molten resin around the copper core, and finely smooth the substrate surface to reduce the coplanarity deviation caused by uneven resin flow and the misalignment of the copper core, reduce the interface stress concentration caused by the thermal shrinkage difference of different materials, and stably control the vertical height difference between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer within the micron tolerance range, while maintaining a high interface bonding strength. Summary of the Invention

[0005] To address the problems in the background art, the present invention provides the following technical solution: a forming process for a high coplanarity embedded copper core substrate, comprising the following steps:

[0006] Step S1: Mill out the outwardly protruding bearing step flange along the peripheral sidewall of the thermally conductive copper core with a thickness of 0.3mm to 0.6mm and establish the working surface. Roughen the surface of the thermally conductive copper core, and then wet and coat the surface of the thermally conductive copper core with silane coupling agent and bake and cure to form a molecular bonding transition layer.

[0007] Step S2, at the glass transition temperature A stepped insert slot is milled on the inner core plate at a temperature of not less than 170°C to fit the outer convex bearing stepped flange, and a reserved window is punched out on the prepreg. The single-sided compensation gap is set according to the volume conservation relationship between the opening volume of the stepped insert slot, the solid volume of the thermally conductive copper core and the melt flow factor of the prepreg.

[0008] Step S3: The thermally conductive copper core is snapped into the stepped mounting slot, so that the outwardly protruding bearing flange is attached to the bearing surface of the stepped mounting slot to form vertical height and planar limit. The prepreg after opening the window and the outer copper foil are symmetrically stacked on the upper and lower sides of the inner core board to form a laminate to be pressed.

[0009] Step S4: The laminate to be pressed is placed in a vacuum environment and subjected to low-temperature and low-pressure filling and degassing, high-temperature and high-pressure cross-linking and curing, and pressure holding and step-by-step cooling in sequence.

[0010] Step S5: Use a ceramic brush roller to mechanically grind and cut the surface of the hot-pressed substrate to remove the overflow resin film on the surface, and perform chemical micro-etching in an acidic micro-etching solution to adjust the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer to within the preset tolerance zone.

[0011] Step S6: Chemically deposit a copper seed layer on the surface of the trimmed substrate, attach a photoresist dry film, expose and develop it to reveal the outer layer circuitry and vertical heat dissipation pad windows, thicken the copper layer by pattern electroplating, remove the photoresist dry film and differentially etch away the exposed copper seed layer, so that the vertical heat dissipation pads are bonded to the working surface.

[0012] Preferably, step S1 includes step S11, milling shaping, step S12, micro-roughening treatment, and step S13, coupling coating, wherein: in step S11, the single-sided milling width of the convex bearing step flange is 0.25mm to 0.40mm, and the recessed step depth is 0.15mm to 0.30mm; in step S12, micro-roughening creates a roughness on the surface of the thermally conductive copper core. The surface is roughened to a micro-nano thickness of 0.35 μm to 0.45 μm; in step S13, the silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane, which is prepared as an aqueous solution with a mass fraction of 0.5% to 2.0% for wetting and coating, and then baked and cured at 100°C to 110°C to form a molecularly bonded transition layer.

[0013] Preferably, step S2 includes step S21, slot processing, and step S22, medium punching, wherein: in step S21, the inner core board adopts a high Tg epoxy fiberglass core board with a thickness of 0.15mm to 0.30mm, the stepped embedded slot includes a lower through hole and an upper supporting step hole, a gap of 0.06mm to 0.10mm is reserved between the cross-sectional size of the lower through hole and the base cross-sectional size of the thermally conductive copper core located at the lower part of the step, and a gap of 0.68mm to 0.90mm is reserved between the cross-sectional size of the upper supporting step hole and the top surface cross-sectional size of the thermally conductive copper core located at the upper part of the step; in step S22, the prepreg adopts a low flow epoxy fiberglass prepreg.

[0014] Preferably, step S4 includes step S41, a low-temperature, low-pressure filling and venting stage; step S42, a high-temperature, high-pressure crosslinking and curing stage; and step S43, a pressure-holding and stepped cooling stage, wherein: the vacuum degree of the hot-pressing cavity is evacuated to less than 50 Pa; in step S41, the temperature is increased to 110°C to 130°C at a heating rate of 1.5°C / min to 2.5°C / min, a contact pressure of 0.5 MPa to 1.0 MPa is applied and held for 15 min to 25 min to guide the molten resin. The grease fills the gap between the stepped insert slot and the reserved window and removes micropores and air bubbles; in step S42, the temperature is increased to 180°C to 200°C at a heating rate of 1.5°C / min to 2.5°C / min, the pressure is increased to 2.5MPa to 3.5MPa and held at a constant temperature and pressure for 60min to 90min; in step S43, the molding pressure is maintained at 2.5MPa to 3.5MPa and the temperature is cooled to below 60°C at a cooling rate of 1.0°C / min to 1.5°C / min to release the pressure and discharge the material.

[0015] Preferably, step S5 includes step S51, mechanical grinding and cutting, and step S52, chemical micro-etching and finishing. In step S51, the ceramic brush roller is an alumina ceramic brush roller or a silicon carbide ceramic brush roller with a particle size of 400 mesh to 1000 mesh. The working speed of the brush roller is set to 1500 rpm to 2200 rpm, and the substrate feed speed is set to 1.0 m / min to 2.0 m / min. The substrate after discharge is subjected to continuous fixed-thickness flat grinding and cutting on both sides. In step S52, the substrate after mechanical grinding and cutting is immersed in an acidic micro-etching solution for 30 s to 60 s to eliminate mechanical grinding micro-scratches.

[0016] Preferably, in step S52, the acidic micro-etching solution adopts a sulfuric acid-hydrogen peroxide system, with the sulfuric acid mass concentration controlled at 80g / L to 120g / L, the hydrogen peroxide mass concentration controlled at 30g / L to 45g / L, the bath temperature controlled at 25℃ to 35℃, and the etching rate controlled at 1.0μm / min to 1.5μm / min.

[0017] Preferably, step S6 includes step S61, chemical deposition of a seed layer, step S62, pattern electroplating thickening, and step S63, differential micro-etching removal, wherein: in step S61, the thickness of the chemically deposited copper seed layer is 0.2 μm to 0.5 μm; in step S62, the pattern electroplating uses an acidic copper sulfate system, and the cathode current density is controlled to be 1.5 A / dm² to 2.5 A / dm², so that the thickness of the conductive copper layer and the copper layer plated on the vertical heat dissipation pad grows synchronously to 18 μm to 35 μm; in step S63, after removing the photolithographic resist dry film, the exposed substrate copper seed layer is stripped using a hydrogen peroxide-organic acid differential micro-etching solution, forming an integrated metal thermally conductive contact layer between the vertical heat dissipation pad and the working surface of the thermally conductive copper core.

[0018] Preferably, in step S3: two prepreg sheets with pre-cut windows are symmetrically stacked on the upper and lower sides of the inner core board, and a high-temperature elongated electrolytic copper foil with a nominal thickness of 18μm is disposed on the outermost layer; the convex bearing stepped flange restricts the sliding displacement of the heat-conducting copper core in the X-axis and Y-axis planes to no more than 0.025mm under pressure.

[0019] Preferably, after steps S5 and S6, the absolute value of the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is not greater than 25 μm; in the obtained embedded copper core substrate, the shear bond strength between the thermally conductive copper core and the cured resin matrix is ​​not less than 5.8 N / mm², and no interface delamination or blistering is observed after 5 reflow soldering thermal shock tests at 260℃.

[0020] The beneficial effects of this invention are:

[0021] 1. In a molding process for a high coplanarity embedded copper core substrate, the thermally conductive copper core is stably limited by the outwardly protruding bearing stepped flange and the stepped embedding slot, and the resin filling space is compensated by the reserved window of the prepreg. This makes the filling amount of molten resin during hot pressing more matched with the gap around the copper core, thereby effectively reducing resin accumulation, local missing glue and depression around the copper core. This makes the substrate surface after hot pressing smoother, and the height difference between the working surface and the surface of the adjacent insulating dielectric layer is easier to control within the required range, which is conducive to ensuring the coplanarity of subsequent device mounting.

[0022] 2. The fit between the protruding bearing flange and the stepped mounting slot can simultaneously restrict the movement of the thermally conductive copper core in both the height and planar directions. The symmetrical stacking reduces the impact of uneven force during pressing. Therefore, under the action of molten resin flow and pressing pressure, the thermally conductive copper core is not prone to planar slippage and angular deflection, and can maintain a relatively stable mounting position. This reduces the alignment deviation of the subsequent vertical heat dissipation pads and improves the consistency and reliability of the connection position between the copper core and the outer thermal conductive structure.

[0023] 3. The micro-nano roughened structure on the surface of the thermally conductive copper core can increase its bonding foundation with the resin matrix. The molecular bonding transition layer further enhances the bond between the metallic copper and the resin matrix. Combined with high-temperature and high-pressure cross-linking curing and pressure-holding stepped cooling, it can reduce the residual stress caused by the difference in thermal expansion and contraction between copper and epoxy fiberglass substrate, and reduce the risk of interface shear stress concentration. Therefore, during temperature changes and lead-free reflow soldering thermal shock, the bonding interface is less prone to microcracks, delamination and blistering, which is conducive to maintaining the bonding reliability between the embedded copper core and the substrate. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0025] Figure 1 This is a flowchart of the copper core embedding process on the substrate of the present invention.

[0026] Figure 2 This is a diagram showing the assembly relationship between the thermally conductive copper core and the laminated dielectric in this invention. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0028] A molding process for a high coplanarity embedded copper core substrate includes the following steps:

[0029] Step S1: Mill out the outwardly protruding bearing step flange along the peripheral sidewall of the thermally conductive copper core with a thickness of 0.3mm to 0.6mm and establish the working surface. Roughen the surface of the thermally conductive copper core, and then wet and coat the surface of the thermally conductive copper core with silane coupling agent and bake and cure to form a molecular bonding transition layer.

[0030] Step S2, at the glass transition temperature A stepped insert slot is milled on the inner core plate at a temperature of not less than 170°C to fit the outer convex bearing stepped flange, and a reserved window is punched out on the prepreg. The single-sided compensation gap is set according to the volume conservation relationship between the opening volume of the stepped insert slot, the solid volume of the thermally conductive copper core and the melt flow factor of the prepreg.

[0031] Step S3: The thermally conductive copper core is snapped into the stepped mounting slot, so that the outwardly protruding bearing flange is attached to the bearing surface of the stepped mounting slot to form vertical height and planar limit. The prepreg after opening the window and the outer copper foil are symmetrically stacked on the upper and lower sides of the inner core board to form a laminate to be pressed.

[0032] Step S4: The laminate to be pressed is placed in a vacuum environment and subjected to low-temperature and low-pressure filling and degassing, high-temperature and high-pressure cross-linking and curing, and pressure holding and step-by-step cooling in sequence.

[0033] Step S5: Use a ceramic brush roller to mechanically grind and cut the surface of the hot-pressed substrate to remove the overflow resin film on the surface, and perform chemical micro-etching in an acidic micro-etching solution to adjust the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer to within the preset tolerance zone.

[0034] Step S6: Chemically deposit a copper seed layer on the surface of the trimmed substrate, attach a photoresist dry film, expose and develop it to reveal the outer layer circuitry and vertical heat dissipation pad windows, thicken the copper layer by pattern electroplating, remove the photoresist dry film and differentially etch away the exposed copper seed layer, so that the vertical heat dissipation pads are bonded to the working surface.

[0035] Preferably, step S1 includes step S11, milling shaping, step S12, micro-roughening treatment, and step S13, coupling coating, wherein: in step S11, the single-sided milling width of the convex bearing step flange is 0.25mm to 0.40mm, and the recessed step depth is 0.15mm to 0.30mm; in step S12, micro-roughening creates a roughness on the surface of the thermally conductive copper core. The surface is roughened to a micro-nano thickness of 0.35 μm to 0.45 μm; in step S13, the silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane, which is prepared as an aqueous solution with a mass fraction of 0.5% to 2.0% for wetting and coating, and then baked and cured at 100°C to 110°C to form a molecularly bonded transition layer.

[0036] Preferably, step S2 includes step S21, slot processing, and step S22, medium punching, wherein: in step S21, the inner core board adopts a high Tg epoxy fiberglass core board with a thickness of 0.15mm to 0.30mm, the stepped embedded slot includes a lower through hole and an upper supporting step hole, a gap of 0.06mm to 0.10mm is reserved between the cross-sectional size of the lower through hole and the base cross-sectional size of the thermally conductive copper core located at the lower part of the step, and a gap of 0.68mm to 0.90mm is reserved between the cross-sectional size of the upper supporting step hole and the top surface cross-sectional size of the thermally conductive copper core located at the upper part of the step; in step S22, the prepreg adopts a low flow epoxy fiberglass prepreg.

[0037] Preferably, step S4 includes step S41, a low-temperature, low-pressure filling and venting stage; step S42, a high-temperature, high-pressure crosslinking and curing stage; and step S43, a pressure-holding and stepped cooling stage, wherein: the vacuum degree of the hot-pressing cavity is evacuated to less than 50 Pa; in step S41, the temperature is increased to 110°C to 130°C at a heating rate of 1.5°C / min to 2.5°C / min, a contact pressure of 0.5 MPa to 1.0 MPa is applied and held for 15 min to 25 min to guide the molten resin. The grease fills the gap between the stepped insert slot and the reserved window and removes micropores and air bubbles; in step S42, the temperature is increased to 180°C to 200°C at a heating rate of 1.5°C / min to 2.5°C / min, the pressure is increased to 2.5MPa to 3.5MPa and held at a constant temperature and pressure for 60min to 90min; in step S43, the molding pressure is maintained at 2.5MPa to 3.5MPa and the temperature is cooled to below 60°C at a cooling rate of 1.0°C / min to 1.5°C / min to release the pressure and discharge the material.

[0038] Preferably, step S5 includes step S51, mechanical grinding and cutting, and step S52, chemical micro-etching and finishing. In step S51, the ceramic brush roller is an alumina ceramic brush roller or a silicon carbide ceramic brush roller with a particle size of 400 mesh to 1000 mesh. The working speed of the brush roller is set to 1500 rpm to 2200 rpm, and the substrate feed speed is set to 1.0 m / min to 2.0 m / min. The substrate after discharge is subjected to continuous fixed-thickness flat grinding and cutting on both sides. In step S52, the substrate after mechanical grinding and cutting is immersed in an acidic micro-etching solution for 30 s to 60 s to eliminate mechanical grinding micro-scratches.

[0039] Preferably, in step S52, the acidic micro-etching solution adopts a sulfuric acid-hydrogen peroxide system, with the sulfuric acid mass concentration controlled at 80g / L to 120g / L, the hydrogen peroxide mass concentration controlled at 30g / L to 45g / L, the bath temperature controlled at 25℃ to 35℃, and the etching rate controlled at 1.0μm / min to 1.5μm / min.

[0040] Preferably, step S6 includes step S61, chemical deposition of a seed layer, step S62, pattern electroplating thickening, and step S63, differential micro-etching removal, wherein: in step S61, the thickness of the chemically deposited copper seed layer is 0.2 μm to 0.5 μm; in step S62, the pattern electroplating uses an acidic copper sulfate system, and the cathode current density is controlled to be 1.5 A / dm² to 2.5 A / dm², so that the thickness of the conductive copper layer and the copper layer plated on the vertical heat dissipation pad grows synchronously to 18 μm to 35 μm; in step S63, after removing the photolithographic resist dry film, the exposed substrate copper seed layer is stripped using a hydrogen peroxide-organic acid differential micro-etching solution, forming an integrated metal thermally conductive contact layer between the vertical heat dissipation pad and the working surface of the thermally conductive copper core.

[0041] Preferably, in step S3: two prepreg sheets with pre-cut windows are symmetrically stacked on the upper and lower sides of the inner core board, and a high-temperature elongated electrolytic copper foil with a nominal thickness of 18μm is disposed on the outermost layer; the convex bearing stepped flange restricts the sliding displacement of the heat-conducting copper core in the X-axis and Y-axis planes to no more than 0.025mm under pressure.

[0042] Preferably, after steps S5 and S6, the absolute value of the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is not greater than 25 μm; in the obtained embedded copper core substrate, the shear bond strength between the thermally conductive copper core and the cured resin matrix is ​​not less than 5.8 N / mm², and no interface delamination or blistering is observed after 5 reflow soldering thermal shock tests at 260℃.

[0043] Example 1: This example focuses on the manufacturing of packaging substrates for high-power RF power amplifiers and high-density power conversion modules. Addressing the limitations on vertical heat dissipation caused by increased heat flux density per unit area and the coplanarity requirements of flip-chip mounting, a 0.4mm thick C1100 thermally conductive copper plate is selected to prepare the thermally conductive copper core. A CNC machine tool is used to perform controlled-depth milling on the peripheral sidewalls of the 20mm×20mm thermally conductive copper core. A convex bearing flange with a single-sided width of 0.3mm and a recessed step depth of 0.2mm is machined along the peripheral sidewalls, forming a two-step cross-sectional profile with a lower base geometry of 19.4mm×19.4mm and an upper top surface geometry of 20mm×20mm, thus establishing the working surface of the thermally conductive copper core.

[0044] A thermally conductive copper core with a convex bearing flange was immersed in an acidic micro-etching solution containing 60 g / L sulfuric acid, 30 g / L hydrogen peroxide, and organic additives for 45 seconds. This process created a micro-nano roughened surface with micro-nano-level anchoring morphology on the sidewalls, convex bearing flange, and top and bottom surfaces of the thermally conductive copper core, resulting in a root mean square roughness of [missing value]. The thickness of the copper core is between 0.35 μm and 0.45 μm. The micro-roughened thermally conductive copper core is then immersed in a 1.2% (w / w) aqueous solution of γ-glycidyl etheroxypropyltrimethoxysilane for 3 minutes. After draining, it is placed in a hot air circulating oven at 105 °C for 15 minutes to cure. This molecularly bonded transition layer physically manifests as a continuous nanoscale chemically modified interface layer adsorbed and bonded to the micro-roughened copper surface, with a single or multiple molecular thickness ranging from 2 nm to 10 nm. Under this baking and curing process, the silanol groups generated by silane hydrolysis undergo a dehydration condensation reaction with the copper active hydroxyl groups of the micro / nano oxide layer on the micro-roughened copper surface to generate silicon-oxygen-copper covalent bonds. Unreacted silanol groups condense and crosslink to form a siloxane-silicon microstructure framework that adheres tightly to the copper substrate surface. Simultaneously, epoxy functional groups at the molecular ends extend directionally to the outer surface. During the subsequent high-temperature crosslinking stage of vacuum hot pressing, they directly undergo ring-opening covalent addition reactions with the epoxy resin matrix molecular chains of the prepreg, forming a chemical covalent crosslinking network between the copper and resin matrix. This molecular bonding transition layer enhances the bonding force between the copper core and the epoxy fiberglass substrate at room temperature and 260°C reflow soldering temperature from purely physical interlocking to chemical covalent bond locking. Tensile shear tests show that the interfacial shear bond strength stably reaches 6.2 N / mm², thus characterizing the dense integrity of the molecular bonding transition layer.

[0045] The inner core board is selected based on its glass transition temperature. FR-4 high temperature, nominal thickness 0.2mm, 175℃ The epoxy fiberglass core board is CNC milled with two-stage stepped mounting slots. The lower through-hole is 19.48mm × 19.48mm in size, with a 0.08mm gap between it and the 19.4mm × 19.4mm cross-section of the lower base of the thermally conductive copper core, corresponding to a 0.04mm side clearance for assembly. The upper supporting stepped hole is 20.68mm × 20.68mm in size, with a 0.68mm gap between it and the 20mm × 20mm cross-section of the upper surface of the thermally conductive copper core, corresponding to a 0.34mm overflow groove clearance on one side. A bearing surface is formed at the bottom of the slot. Specifically, the thermally conductive copper core is milled inwards by 0.3mm on one side from its original 20mm×20mm outline to form a 19.4mm×19.4mm lower base. The lower through-hole uses the outline of this lower base as the mating reference, with a 0.04mm tolerance assembly clearance on one side around the perimeter. A uniform overflow adhesive channel of 0.34mm on one side is formed between the upper bearing stepped hole and the 20mm×20mm top surface outline, allowing the thermally conductive copper core to fall into the bearing surface of the stepped mounting slot with uniform and symmetrical gaps around the perimeter. The dielectric layer uses the nominal unpressed thickness. For a 0.075mm thick 1080 type low-flow epoxy fiberglass prepreg, to eliminate the sharp drop in resin viscosity and excessive overflow accumulation induced by localized high-heat diffusion of the copper core during the lamination heating stage, the reserved window size of the prepreg was calculated based on the conservation relationship of melt rheological cavity volume, and a unilateral compensation gap was established. Calculate based on the following relationship: ,in, The theoretical envelope volume of the area where the heat-conducting copper core protrudes and rests on the step is taken as 4.728 mm³. The opening volume of the stepped mounting slot in the inner core board is taken as 153.25 mm³. The volume of the thermally conductive copper core embedded in the stepped mounting slot is 155.272 mm³. The perimeter of the main cross-section of the thermally conductive copper core is taken as 80mm. The initial unpressed nominal thickness of the prepreg is 0.075 mm. The melt flow factor of the prepreg within the melting temperature window of 110℃ to 130℃ is taken as 0.9. Substituting the parameters, the single-sided compensation gap is calculated. A 20.5mm × 20.5mm pre-cut window was punched into a 1080-type low-flow epoxy fiberglass prepreg using a CNC punching machine. During the calibration of the prepreg's melt flow factor, dynamic melt viscosity values ​​were continuously recorded at 1s sampling steps within a melt flow time window of 110℃ to 130℃. The discrete summation of the reciprocals of the viscosity at each sampling point was calculated as the melt flow integral value. This integral value was then normalized by comparing it with the standard integral reference value under completely unobstructed flow conditions to obtain the prepreg melt flow factor characterizing the actual lateral filling capacity of the resin at that temperature and pressure rate. When the measured viscosity was between 60 Pa·s and 120 Pa… When the viscosity is within the ·s range, the melt flow factor of the prepreg is calibrated to be 0.92, indicating that the resin can achieve 92% lateral rheological filling within the low viscosity window. In the actual lamination filling process, after the thermally conductive copper core is embedded in the stepped mounting slot, the envelope space of the outwardly protruding step flange and the edge of the stepped mounting slot constitute the preset micro-area volume to be filled. The single-sided compensation gap formed by the reserved window allows the net volume of resin flowing from the periphery to the slot gap during the prepreg softening during hot pressing to achieve equal dynamic balancing with the micro-area volume to be filled and the effective resin flow loss, thereby controlling the resin accumulation at the edge of the copper core and the lack of adhesive in the insulating dielectric layer far from the copper core area, so that the surface flatness of the substrate after hot pressing and curing is kept within the micron tolerance zone.

[0046] The surface-coupled thermally conductive copper core is snapped into the stepped mounting slot of the inner core board along the vertical height direction, so that the bottom surface of the outwardly protruding bearing flange completely abuts the bearing surface, forming a vertical height reference and planar limiting fit; two 1080 type low-flow epoxy fiberglass semi-cured sheets with pre-cut windows are symmetrically stacked on the upper and lower sides of the inner core board, and a high-temperature elongated electrolytic copper foil with a nominal thickness of 18μm is placed on the outermost layer, forming a symmetrical laminate to be pressed. The cross-sectional structure of the laminate to be pressed is based on the central axis, and the core layer is FR-4 high-strength copper foil serving as the inner core board. An epoxy fiberglass core board and its stepped mounting slots are used. The thermally conductive copper core is embedded in the stepped mounting slots, with the lower surface of the steps abutting against the support surface. The working surface and the bottom surface are exposed to the upper and lower sides, respectively. The upper and lower main surfaces of the inner core board are symmetrically covered with two prepreg sheets with pre-cut windows. A gap channel of 0.25mm on one side is left between the inner edge of the pre-cut window and the outer edge of the side wall of the thermally conductive copper core. A layer of high-temperature extended electrolytic copper foil with a thickness of 18μm is laid on the outer main surface of each set of prepreg sheets to form a symmetrical laminate to be pressed. The components of each layer maintain the preset geometric positioning and spatial assembly relationship through the above-mentioned lamination relationship. The laminate to be pressed is placed into the vacuum hot press chamber. The air in the chamber is extracted to make the vacuum level 35Pa. Then, three temperature and pressure stages are controlled in sequence. The first stage is low-temperature and low-pressure filling and venting, with a heating rate of 2℃ / min. The temperature is raised to 120℃, a contact pressure of 0.8MPa is applied and held constant for 20 minutes to allow the prepreg resin to melt and enter a low-viscosity flow state. Driven by the pressure gradient, the molten resin fills and permeates into the stepped insert slots along the reserved windows and removes micropores and bubbles. In the second stage, high-temperature and high-pressure cross-linking curing is carried out. The temperature is raised to 185℃ at a heating rate of 2℃ / min, and the pressure is increased to 3MPa and held constant for 75 minutes to allow the epoxy resin molecular chains to cross-link and build a three-dimensional network. At the same time, the epoxy groups at the ends of the silane coupling agent molecules are driven to form a covalent cross-linked network with the resin matrix. In the third stage, pressure holding and stepped cooling are carried out. The molding pressure is maintained at 3MPa and the temperature is gradually cooled to 55℃ at a cooling rate of 1.2℃ / min. Then, the pressure is released and the material is discharged. The residual thermal stress at the heterogeneous interface caused by the mismatch between the thermal expansion coefficient and elastic modulus of the multiphase material is released by controlled cooling.

[0047] After hot pressing, the substrate has a cured overflow resin film on both sides. Using a 600-mesh silicon carbide ceramic brush roller at a working speed of 1800 rpm and a substrate feed speed of 1.5 m / min, the substrate is continuously mechanically ground and cut to a controlled thickness, removing the cured resin layer adhering to the working surface and surrounding area of ​​the thermally conductive copper core. Following mechanical grinding, the substrate undergoes continuous chemical micro-etching. It is then placed in an acidic micro-etching spray line and immersed in a sulfuric acid-hydrogen peroxide micro-etching system at a bath temperature of 30℃, a sulfuric acid concentration of 100 g / L, and a hydrogen peroxide concentration of 35 g / L for 40 seconds. The micro-etching rate is controlled at 1.2 μm / min, and the micro-etching depth is 0.8 μm. This process eliminates mechanical grinding micro-scratches and smooths the interface between the metallic copper surface and the epoxy fiberglass insulating substrate, making the working surface of the thermally conductive copper core smooth. The vertical height difference between the surface of the copper core and the adjacent insulating dielectric layer surface is stably converged to the +12μm to +18μm range within the preset tolerance zone. In the above-mentioned composite leveling process, mechanical flat grinding is used to perform surface cutting and thickness determination on the overflow cured resin on the surface of the insulating dielectric layer. However, at the interface between the copper core and the insulating substrate, due to the difference between the ductility of copper metal and the wear resistance of resin glass fiber, the copper surface is prone to residual micro mechanical scratches and micro edge flash. The acidic micro etching solution used in chemical micro-etching uses the oxidation of hydrogen peroxide and the complexation of sulfuric acid to selectively and uniformly chemically etch the copper surface to a depth of 0.8μm, which passivates and dissolves the sharp scratches and side metal micro burrs on the copper surface into a smooth micro-arc surface. Meanwhile, the insulating dielectric layer remains chemically inert in the acidic bath. Through the combination of mechanical macro-peeling and chemical micro-leveling, mechanical stress scratches and height abrupt changes at the metal interface are eliminated.

[0048] On the working surface of the substrate after thickness adjustment, a dense and homogeneous copper seed layer with a thickness of 0.3 μm is deposited using a full-board electroless chemical copper plating process. A photoresist dry film resistant to electroplating is then attached to the surface of the copper seed layer. Direct laser imaging and alignment exposure are performed, followed by development with a weak alkaline developer to expose the outer electrical conductive circuitry area and the vertical heat dissipation pad pattern window coaxially aligned with the working surface of the thermally conductive copper core. The substrate is then immersed in an acidic copper sulfate electroplating bath to thicken the pattern through electroplating, with the cathode current density controlled at 2A. / dm², with an electroplating thickening time of 45min, allowing the copper layer of the conductive lines and the copper layer of the vertical heat dissipation pads to grow epitaxially by 25μm simultaneously; subsequently, the photolithography resist dry film is removed using a 3.5% sodium hydroxide solution, and the exposed 0.3μm base copper seed layer is etched away in a hydrogen peroxide-organic acid weak acid differential etching solution. This integrated metal thermally conductive contact layer is not an independently assembled additional component in the structural entity, but rather consists of a micro-coarsened thermally conductive copper core at the bottom. The working surface, the 0.3μm chemically deposited copper seed layer attached thereon, and the outer 25μm electroplated copper vertical heat dissipation pad together form a pure metal homogeneous metallurgical interface. During the forming process, the nanoscale pure copper crystal nuclei catalyzed by chemically deposited copper are directly attached to and epitaxially grown on the surface of the thermally conductive copper core metal copper lattice after being micro-coarsened and activated, forming a dense continuous seed layer. Subsequently, during the pattern electroplating process of acidic copper sulfate, divalent copper ions are continuously electrodeposited and stacked along the grain boundaries of the seed layer to a thickness of 25μm under the drive of a current density of 2A / dm². The electroplated copper grains and the underlying copper matrix grains form a tight in-situ lattice interwoven and solidified structure. After the excess seed layer outside the window is removed by differential micro-etching, the polymer insulating medium interlayer and the micro-air gap at the interface are completely eliminated between the vertical heat dissipation pad and the working surface of the thermally conductive copper core, forming a direct and continuous heat-conducting integral pure copper conduction path, so that the two form a direct and continuous conductive contact without intermediate polymer medium layer and oxide physical barrier.

[0049] The high coplanarity embedded copper core substrate, after optical surface profilometer and thermomechanical reliability tests, shows that under the flow shearing action of high-pressure molten resin filling during the vacuum lamination stage, the geometric self-locking constraint of the outwardly convex bearing stepped flange and stepped embedding slot limits the embedding alignment slip of the thermally conductive copper core in the X and Y axis planes to within 0.02mm, and the vertical heat dissipation pad and the working surface of the thermally conductive copper core are coaxially aligned. The specific principle of the thermally conductive copper core's in-plane constraint is as follows: In the spatial topology and degree-of-freedom constrained structure, after the thermally conductive copper core is partially removed by CNC deep milling, the unremoved upper solid edge forms a... The protruding, 0.3mm wide stepped flange supports the inner core plate. When the thermally conductive copper core falls into the stepped mounting slot of the inner core plate, the lower surface of the protruding stepped flange directly abuts against the horizontal bearing surface inside the slot, forming a rigid elevation reference and vertical height limit in the vertical direction to restrict the downward movement of the Z-axis. In the horizontal planes of the X and Y axes, a 0.04mm assembly clearance is maintained between the lower through-hole of the stepped mounting slot and the copper core substrate, and a 0.34mm overflow groove clearance is maintained between the upper supporting stepped hole and the top outer contour. When a vertical forming pressure of 3MPa is applied during the vacuum hot pressing stage, the upper and lower parts are symmetrically stacked. The normal pressure of the layer generates strong interfacial static friction self-locking resistance at the contact point of the bearing surface. Simultaneously, during the melting and rheological process of the semi-cured sheet with symmetrically opened upper and lower sections, molten resin flows synchronously from the sides of the copper core into the annular gap with symmetrical dynamic pressure. The uniform hydrostatic pressure around the perimeter and the vertical positive pressure friction of the bearing surface form a dynamic mechanical balance, offsetting the asymmetric lateral flow shear thrust. This allows the thermally conductive copper core to achieve self-centering and locking within the clearance tolerance range, strictly limiting the horizontal slip displacement to within 0.025mm. Relying on the physical anchoring effect of the micro / nano roughened surface and the combined effect of the molecularly bonded transition layer, the thermally conductive copper core... The interfacial shear bond strength between the hot copper core and the cured resin matrix reaches 6.2 N / mm²; the sample underwent 5 consecutive cycles of 260℃ lead-free reflow soldering thermal shock test, and no microcracks, delamination, blistering, or edge debonding failure occurred at the bonding interface; the vertical heat dissipation pad and the C1100 thermally conductive copper core with a thermal conductivity of 398 W / m·K directly form an integrated metal thermally conductive contact layer, which reduces the total thermal resistance of the vertical heat transfer path to 0.21 K / W, and the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer converges within the preset tolerance zone, meeting the high reliability flip-chip coplanarity requirements of micro-pitch power semiconductor devices.

[0050] Example 2: This example investigates the effects of thermally conductive copper core structure dimensions, unilateral compensation gap, interface modification parameters, and surface leveling methods on substrate coplanarity and bonding interface. This example utilizes a CNC deep milling machine with positioning accuracy better than ±0.003mm, a CNC punching machine with repeatability better than ±0.005mm, a vacuum hot press with temperature control accuracy of ±1℃ and cavity ultimate vacuum better than 10Pa, a ceramic brush roller grinding machine with brush speed adjustment accuracy of ±10rpm, and a chemical micro-etching line test platform with spray pressure control accuracy of ±0.01MPa. The test system is equipped with a non-contact white light interferometer surface topology instrument with a measurement repeatability of 0.005μm and a minimum force resolution of 0.01N. The test equipment includes a microcomputer-controlled electronic universal testing machine, a high-precision optical image measuring instrument with an alignment measurement accuracy of 0.001mm, a high-temperature lead-free reflow soldering test furnace with a temperature control accuracy of ±1.5℃, and a semiconductor transient thermal resistance tester with a steady-state temperature measurement accuracy of 0.05℃. The values ​​of thermally conductive copper core thickness, convex bearing step flange size, single-sided compensation gap, silane coupling agent concentration, and hot-pressing temperature and pressure gradient are determined based on the difference in thermal expansion coefficient and elastic modulus between high thermal conductivity copper and epoxy fiberglass substrate, the conservation relationship of resin melt filling volume, and the requirements for cooling stress release. The test also includes the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer, the offset of the mounting plane position, shear bond strength, reflow soldering delamination rate, and total thermal resistance of the vertical heat transfer path.

[0051] The sample included 3 test sample groups and 7 control sample groups. Test sample group 1 of the present invention used a C1100 thermally conductive copper plate with a thickness of 0.4 mm. A convex bearing flange with a single-sided width of 0.3 mm and a recessed step depth of 0.2 mm was milled. The surface of the thermally conductive copper core was slightly roughened to a root mean square roughness of 0.38 μm, and then coated with a 1.2% (w / w) aqueous solution of γ-glycidyl etheroxypropyltrimethoxysilane. The inner core board used a high-Tg epoxy fiberglass core board with a glass transition temperature of 175℃ and a thickness of 0.2 mm. The core board was machined to form a lower through-hole with a size of 20.08 mm × 20.08 mm and an upper bearing step hole with a size of 20.68 mm. The device features a stepped insert slot measuring 20.68 mm. It utilizes a 1080-type low-flow epoxy fiberglass prepreg with a nominal unpressed thickness of 0.075 mm, and punches out a reserved window with a single-sided compensation gap of 0.25 mm according to volume conservation principles. The hot-pressing process employs a three-stage stepped temperature-pressure process: first, low-temperature, low-pressure filling and venting at 120℃ and 0.8 MPa; then, high-temperature, high-pressure cross-linking and curing at 185℃ and 3 MPa; followed by pressure holding and stepped cooling. After discharge, it undergoes mechanical grinding with a 600-mesh silicon carbide ceramic brush roller, and chemical micro-etching finishing using a sulfuric acid-hydrogen peroxide system. Finally, electroplating thickens the outer conductive lines and vertical heat dissipation pads.

[0052] In test sample group 2 of this invention, the thickness of the thermally conductive copper core was adjusted to 0.6 mm, the single-sided width of the convex bearing step flange was set to 0.4 mm, the depth of the recessed step was set to 0.3 mm, and the mass fraction of the silane coupling agent was maintained at 1.2%. The thickness of the inner core plate was 0.3 mm, the size of the lower through hole of the stepped embedding slot was 20.10 mm × 20.10 mm, and the size of the upper bearing step hole was 20.90 mm × 20.90 mm. A 2116 type low-flow epoxy fiberglass semi-cured sheet with a nominal unpressed thickness of 0.105 mm was used, and the calculated single-sided compensation gap was 0.32 mm. This group also adopted three-stage stepped temperature and pressure, as well as mechanical flat grinding and chemical micro-etching finishing with ceramic brush rollers. The high-temperature and high-pressure cross-linking curing temperature was set to 190°C and the pressure was set to 3.2 MPa.

[0053] The thermally conductive copper core of test sample group 3 of this invention has a thickness of 0.3 mm, a single-sided width of 0.25 mm for the outwardly convex bearing step flange, a recessed step depth of 0.15 mm, and a silane coupling agent mass fraction of 1.2%. The inner core plate has a thickness of 0.15 mm, the lower through hole size of the stepped embedded slot is 20.06 mm × 20.06 mm, and the upper bearing step hole size is 20.56 mm × 20.56 mm. A 106-type low-flow epoxy fiberglass semi-cured sheet with a nominal unpressed thickness of 0.05 mm is used. The calculated single-sided compensation gap is 0.18 mm. This group adopts a three-stage stepped temperature and pressure method, as well as mechanical flat grinding and chemical micro-etching finishing with ceramic brush rollers. The high-temperature and high-pressure cross-linking curing temperature is 185℃ and the pressure is 2.8 MPa.

[0054] After the preparation of each group of samples, a white light interferometric surface morphology instrument was used to collect contour height data along the diagonal at the interface between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer, and the vertical height difference range of the entire board surface was calculated. A high-precision optical image measuring instrument was used to align the center baseline of the thermally conductive copper core with the alignment mark of the outer layer pattern and measure the positional deviation of the mounting plane. The shear bond strength between the thermally conductive copper core and the cured resin matrix was measured on an electronic universal testing machine. The samples were placed in a reflow soldering test oven and subjected to five consecutive reflow thermal shock cycles at a peak temperature of 260℃ and a constant temperature time of 30s. The bonding interface was then inspected using an ultrasonic scanning microscope and the delamination rate was calculated. The total thermal resistance of the vertical heat transfer path from the mounting end of the heating chip to the bottom surface of the substrate was measured using a semiconductor transient thermal resistance tester.

[0055] After preparing test sample group 1 of the present invention according to the above process, the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is +12μm to +18μm, the positional offset of the embedding plane is 0.016mm, the shear bond strength between the thermally conductive copper core and the cured resin matrix is ​​6.2N / mm², the delamination rate of reflow soldering at 260℃ is 0%, and the total thermal resistance of the vertical heat transfer path is 0.21K / W. After adjusting the thickness of the thermally conductive copper core, the flange size of the outwardly protruding bearing step, the single-sided compensation gap, and the high-temperature and high-pressure cross-linking curing parameters to the values ​​of test sample group 2 of the present invention, the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is +15μm to +22μm, the positional offset of the embedding plane is 0.021mm, the shear bond strength is 5.9N / mm², the delamination rate of reflow soldering at 260℃ is 0%, and the total thermal resistance of the vertical heat transfer path is 0.16K / W. When using the structure and process parameters of test sample group 3 of this invention, the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is +8μm to +15μm, the offset of the mounting plane position is 0.014mm, the shear bond strength is 6.5N / mm², the delamination rate of 260℃ reflow soldering is 0%, the total thermal resistance of the vertical heat transfer path is 0.24K / W, the thermally conductive copper core thickness of the three test samples covers 0.3mm to 0.6mm, the combined statistical results show that the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer ranges from +8μm to +22μm, the offset of the mounting plane position remains within 0.021mm, the shear bond strength is between 5.9N / mm² and 6.5N / mm², no delamination or blistering occurs after 5 260℃ reflow soldering thermal shocks, and the total thermal resistance of the vertical heat transfer path is between 0.16K / W and 0.24K / W.

[0056] Control group 1 used a flat-walled, straight-edge thermally conductive copper core with a thickness of 0.4 mm. It did not have an outwardly protruding bearing flange and a corresponding slotted step surface. Its silane coupling agent mass fraction was 1.2%, and the single-sided compensation gap was 0.25 mm. It still used three-stage stepped temperature and pressure and mechanical flat grinding and chemical micro-etching finishing with ceramic brush rollers. Under the action of high-pressure molten resin flow, the thermally conductive copper core lacked the limiting of the outwardly protruding bearing flange and bearing surface. The vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer increased to +36 μm to -28 μm. The positional deviation of the embedding plane increased to 0.095 mm. The shear bond strength decreased to 4.1 N / mm². The delamination rate of the 260℃ reflow soldering was 18%, and the total thermal resistance of the vertical heat transfer path was 0.32 K / W.

[0057] Control group 2 used a 0.4 mm thick thermally conductive copper core with a convex bearing stepped flange, a silane coupling agent mass fraction of 1.2%, and maintained a three-stage stepped temperature and pressure system, as well as mechanical grinding and chemical micro-etching finishing of the ceramic brush roller. However, instead of determining the reserved window according to the melt rheological volume conservation relationship, the experimental gap of 0.05 mm was added on one side according to the top surface contour of the thermally conductive copper core for punching. Under these conditions, the molten resin formed a large stacked bulge on the side edge of the thermally conductive copper core, the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer was +48 μm to +62 μm, the offset of the mounting plane position was 0.038 mm, the shear bond strength was 5.4 N / mm², the delamination rate of the 260℃ reflow soldering was 12%, and the total thermal resistance of the vertical heat transfer path was 0.27 K / W.

[0058] Control group 3 uses a 0.4mm thick thermally conductive copper core with a convex bearing stepped flange and a single-sided compensation gap of 0.25mm. It is finished by three-stage stepped temperature and pressure, mechanical flat grinding and chemical micro-etching of ceramic brush rollers, but without silane coupling agent coating. The corresponding silane coupling agent mass fraction is 0%. The vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is +13μm to +19μm, and the offset of the embedding plane position is 0.018mm. The thermally conductive copper core and the cured resin matrix retain only the physical anchoring effect of the micro-nano roughened surface. The shear bond strength is reduced to 3.2N / mm². After 5 reflow soldering thermal shocks at 260℃, the delamination rate reaches 42%, and the total thermal resistance of the vertical heat transfer path is 0.22K / W.

[0059] Control group 4 uses a 0.4mm thick thermally conductive copper core with a convex bearing flange, a silane coupling agent mass fraction of 1.2%, a single-sided compensation gap of 0.25mm, and the surface is still mechanically ground and chemically micro-etched using ceramic brush rollers. However, the three-stage stepped temperature and pressure is changed to a single-stage conventional pressurization, directly heating to 185℃ at 2℃ / min and applying a pressure of 2.5MPa for pressure holding and curing. Under this condition, there is no independent low-temperature and low-pressure filling and venting stage. The vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is +32μm to -22μm, the offset of the embedding plane position is 0.052mm, the shear bond strength is 4.6N / mm², the delamination rate of reflow soldering at 260℃ is 26%, and the total thermal resistance of the vertical heat transfer path is 0.29K / W.

[0060] Control group 5 used a thermally conductive copper core with a thickness of 0.4 mm and an outwardly convex bearing stepped flange. The mass fraction of silane coupling agent was 1.2%, the single-sided compensation gap was 0.25 mm, and a three-stage stepped temperature and pressure were maintained. However, after hot pressing, mechanical grinding with a sanding belt was used instead of mechanical flat grinding and chemical micro-etching finishing with ceramic brush rollers. Due to the difference between the ductility of metallic copper and the grinding resistance of epoxy glass fiber, mechanical micro-scratches and local interface grooves appeared in the interface area between copper and resin. The vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer reached +41 μm to -35 μm. The positional deviation of the embedding plane was 0.020 mm. The shear bond strength was 5.8 N / mm². The delamination rate of the 260℃ reflow soldering was 0%. The total thermal resistance of the vertical heat transfer path was 0.23 K / W.

[0061] Control group 6 used a thermally conductive copper core with a thickness of 0.4 mm and an outwardly convex bearing stepped flange. The mass fraction of the γ-glycidyl etheroxypropyltrimethoxysilane aqueous solution was adjusted to 0.2%, the single-sided compensation gap was maintained at 0.25 mm, and a three-stage stepped temperature and pressure, as well as mechanical flat grinding and chemical micro-etching finishing of ceramic brush rollers were used. At this concentration, the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer was +14 μm to +19 μm, and the offset of the embedded plane position was 0.017 mm. The silanol coverage density of the copper surface decreased, the continuity of the molecular bonding transition layer formed at the interface decreased, the shear bond strength was 4.3 N / mm², the delamination rate after 5 reflow soldering thermal shocks at 260℃ was 22%, and the total thermal resistance of the vertical heat transfer path was 0.22 K / W.

[0062] Control group 7 used a 0.4 mm thick thermally conductive copper core with a convex bearing stepped flange. The mass fraction of γ-glycidyl etheroxypropyltrimethoxysilane aqueous solution was adjusted to 3%, and the single-sided compensation gap was maintained at 0.25 mm. Three-stage stepped temperature and pressure, as well as mechanical flat grinding and chemical micro-etching of ceramic brush rollers were used for finishing. The vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer was +13 μm to +18 μm, and the offset of the embedded plane position was 0.019 mm. Silane molecules underwent multi-layer self-polymerization and steric hindrance accumulation on the surface of the thermally conductive copper core. The low cross-linked oligomer interlayer formed underwent phase separation and softening at high temperature, and the shear bond strength decreased to 4.8 N / mm². After 5 reflow soldering thermal shocks at 260 °C, the delamination rate was 15%, and the total thermal resistance of the vertical heat transfer path was 0.21 K / W.

[0063] The gradient results of control groups 3, 6 and 7 show that the shear bond strength and reflow solder delamination rate change accordingly under the conditions of no coating of silane coupling agent, mass fraction of 0.2% and mass fraction of 3%; γ-glycidyl ether oxypropyltrimethoxysilane with a mass fraction of 0.5% to 2% is within the concentration range used in this process, forming a molecular bond transition layer between the micro-nano roughened surface and the epoxy resin network.

[0064] Based on the structure, process, and test results of each group of samples, the convex bearing stepped flange and stepped embedded slot were used for limiting the position. The single-sided compensation gap was determined according to the melt rheological volume conservation relationship. The samples were then subjected to low-temperature and low-pressure filling and venting, high-temperature and high-pressure cross-linking and curing, and pressure holding and stepped cooling in sequence. After mechanical grinding and chemical micro-etching by ceramic brush rollers, the vertical height difference between the working surface of the substrate and the surface of the adjacent insulating dielectric layer was controlled within ±25μm. The positional deviation of the embedded plane of the thermally conductive copper core in the X-axis and Y-axis planes was controlled within 0.025mm. The shear bond strength between the thermally conductive copper core and the cured resin matrix was maintained above 5.8N / mm². No interface delamination failure occurred after the 260℃ reflow soldering thermal shock. The total thermal resistance of the vertical heat transfer path was maintained below 0.24K / W.

[0065] Example 3: This example is used for the high-density packaging substrate molding of high-power RF power amplifiers and power conversion modules. The key control is on the prepreg melt rheological filling and balancing, the interface bonding reaction path, and the surface thickness leveling parameters. A high-purity C1100 thermally conductive copper plate with a thickness of 0.5mm is selected to prepare the thermally conductive copper core. A CNC machine tool is used to perform controlled-depth milling on the peripheral sidewalls of the thermally conductive copper core with a planar geometric dimension of 25mm×25mm. A convex bearing flange with a single-sided width of 0.35mm and a recessed step depth of 0.25mm is cut along the peripheral sidewalls, so that the thermally conductive copper core forms a two-step cross-sectional configuration with a lower base geometric dimension of 24.3mm×24.3mm and an upper top surface geometric dimension of 25mm×25mm, thereby establishing the working surface and rigid bearing bottom surface of the thermally conductive copper core.

[0066] The heat-conducting copper core, after being processed with a convex bearing step flange, was immersed in an acidic micro-etching solution containing 60 g / L sulfuric acid, 30 g / L hydrogen peroxide, and added organic additives for 45 seconds. This process created micro-nano-concave-convex anchoring morphologies on the sidewalls, convex bearing step flange, and top and bottom surfaces of the heat-conducting copper core, resulting in a root mean square roughness of 0.35 μm to 0.45 μm. Subsequently, the micro-roughened heat-conducting copper core was immersed in a solution containing 1.5% γ-glycidyl etheroxypropyltrimethylammonium chloride. Immerse in an aqueous solution of oxysilane for 3 minutes, drain, and then bake in a hot air circulating oven at 105℃ for 15 minutes to cure. The silanol groups generated by the hydrolysis of the trimethoxy group of the silane coupling agent molecule dehydrate and condense with the active copper hydroxyl groups of the micro-nano oxide layer on the surface of the thermally conductive copper core to form Si-O-Cu covalent bonds. The unreacted silanol groups condense with each other to form a microscopic silicon-oxygen network framework, so that the reactive functional groups with epoxy groups at the ends of the molecules extend to the outer layer, forming a molecular bonding transition layer with dual inorganic and organic reactivity.

[0067] The inner core board is made of FR-4 high-Tg epoxy fiberglass core board with a glass transition temperature of 175℃ and a thickness of 0.25mm. Stepped recessed slots are machined using a CNC milling machine. The lower through-hole has a size of 24.38mm × 24.38mm, forming a 0.08mm gap with the 24.3mm × 24.3mm cross-sectional dimension of the lower base of the thermally conductive copper core. The upper supporting stepped hole has a size of 25.7mm × 25.7mm, forming a 0.7mm gap with the 25mm × 25mm cross-sectional dimension of the upper top surface of the thermally conductive copper core. The opening volume of the stepped recessed slot is 156.859mm³. The dielectric layer is made of 2116 type low-flow epoxy fiberglass prepreg with a nominal unpressed thickness of 0.105mm. The prepreg's thickness is measured using a rotational rheometer. The dynamic melt viscosity was measured at a heating rate of 2℃ / min. The dynamic melt viscosity of the resin was found to be between 60 Pa·s and 120 Pa·s in the temperature range of 110℃ to 130℃. The melt flow factor of the prepreg was 0.92 after melt filling integral calibration. The envelope volume of the thermally conductive copper core step region is known to be 8.628 mm³, the solid volume of the thermally conductive copper core embedded in the groove is 159.884 mm³, and the perimeter of the thermally conductive copper core cross section is 100 mm. Substituting the above geometric parameters and the melt flow factor of the prepreg into the volume conservation relationship, the single-sided compensation gap was found to be 0.29 mm. A reserved window with a geometric dimension of 25.58 mm × 25.58 mm was punched out on the 2116 type low flow epoxy fiberglass prepreg using a CNC punching machine.

[0068] The coupled and modified thermally conductive copper core is inserted vertically into the stepped mounting slot of the inner core board, so that the bottom surface of the outwardly protruding bearing flange is in contact with the bearing surface, forming a vertical elevation reference and planar limit. Low-flow epoxy fiberglass prepreg with pre-cut windows and 18μm electrolytic copper foil are symmetrically stacked on the upper and lower sides of the inner core board to form the laminate to be pressed. The laminate is then placed in a vacuum hot press and evacuated to a 30Pa environment. The first stage involves low-temperature, low-pressure filling and venting, followed by heating to 120℃ at 2℃ / min and applying a contact pressure of 0.8MPa for 20 minutes to allow the low-viscosity melt to melt. The molten resin fills and permeates into the stepped insert slots along the reserved windows, expelling microbubbles; the second stage involves high-temperature and high-pressure cross-linking and curing, with the temperature increased to 190°C at 2°C / min, the pressure increased in stages to 3.2MPa, and the temperature and pressure held constant for 80min, so that the three-dimensional network of epoxy resin is cross-linked and cured, while driving the terminal epoxy groups of the silane coupling agent to complete covalent cross-linking with the resin matrix; the third stage involves pressure holding and stepped cooling, maintaining the molding pressure at 3.2MPa, and gradually cooling to 50°C at a cooling rate of 1.2°C / min before depressurization and discharge, releasing the heterogeneous residual thermal stress of the heterogeneous material during the cooling and shrinkage process.

[0069] The finished substrate is fed into a thickness-fixing and leveling system. Using an 800-mesh silicon carbide ceramic brush roller, both sides of the substrate are mechanically ground at 1800 rpm and a feed speed of 1.5 m / min to remove the excess cured resin adhering to the working surface of the thermally conductive copper core. The ground substrate is then immersed in an acidic micro-etching spray tank containing 100 g / L sulfuric acid, 35 g / L hydrogen peroxide, and a temperature controlled at 30°C for 45 seconds. The micro-etching rate is controlled at 1.2 μm / min, and the micro-etching depth is 0.9 μm, for chemical micro-etching finishing and removal of impurities. Mechanical grinding scratches reduce the vertical height difference between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer to the range of +10μm to +16μm. Subsequently, a 0.3μm copper seed layer is chemically deposited across the entire board, and a photolithographic resist film is attached. After exposure and development, the outer electrical conductive circuit area and the pattern window of the vertical heat dissipation pad are exposed. The pattern is then electroplated to a thickness of 25μm in an acidic copper sulfate plating bath at a current density of 2A / dm². The photolithographic resist film is removed, and differential micro-etching is used to remove the exposed thin seed layer, allowing the vertical heat dissipation pad to be directly bonded to the working surface of the thermally conductive copper core, forming an integrated metal thermally conductive contact layer.

[0070] Tests on the fabricated high coplanarity embedded copper core substrate showed that the limiting fit between the protruding bearing stepped flange and the stepped mounting slot, as well as the single-sided compensation gap formed by the reserved window, controlled the planar positional deviation of the thermally conductive copper core under hot-pressing adhesive flow within 0.018 mm. The molecular bonding transition layer enabled the interfacial shear bond strength between the thermally conductive copper core and the cured resin matrix to reach 6.3 N / mm². After five consecutive cycles of 260°C lead-free reflow soldering thermal shock, there were no delamination or microcrack defects at the bonding interface. The vertical heat dissipation pad directly formed an integrated metal thermally conductive contact layer with the working surface of the thermally conductive copper core. The total thermal resistance of the vertical heat transfer path was 0.18 K / W. The vertical height difference between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer remained within the preset tolerance zone, meeting the surface mount coplanarity requirements of fine-pitch power semiconductor devices.

[0071] Example 4: This example combines Figures 1 to 2 The molding process of a high coplanarity embedded copper core substrate is described, such as... Figure 1As shown, in step S1, a convex bearing step flange is milled along the peripheral sidewall of the thermally conductive copper core with a thickness of 0.3 mm to 0.6 mm to establish the working surface. The surface of the thermally conductive copper core is then slightly roughened, and a silane coupling agent is applied to the roughened surface of the thermally conductive copper core and baked to cure, forming a molecular bonding transition layer. In step S2, a stepped insert slot that matches the convex bearing step flange is milled on the inner core plate with a glass transition temperature (Tg) of not less than 170°C. A reserved window is punched on the prepreg. The single-sided compensation gap is set according to the volume conservation relationship between the opening volume of the stepped insert slot, the solid volume of the thermally conductive copper core, and the melt flow factor of the prepreg. In step S3, the thermally conductive copper core is snapped into the stepped insert slot, so that the convex bearing step flange fits against the bearing surface of the stepped insert slot to form vertical height and planar limitation. The prepreg with windows and the outer copper foil are symmetrically stacked on the upper and lower sides of the inner core board to form a laminate to be pressed; in step S4, the laminate to be pressed is placed in a vacuum environment and subjected to low-temperature and low-pressure filling and degassing, high-temperature and high-pressure cross-linking and curing, and pressure holding and step cooling in sequence; in step S5, a ceramic brush roller is used to mechanically grind the surface of the hot-pressed substrate to remove the overflow resin film on the surface, and chemical micro-etching is performed in an acidic micro-etching solution to adjust the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer to within the preset tolerance zone; in step S6, a copper seed layer is chemically deposited on the surface of the adjusted substrate, a photolithographic resist dry film is attached, and the outer circuit and vertical heat dissipation pad window are exposed by exposure and development, the copper layer is thickened by pattern electroplating, the photolithographic resist dry film is removed, and the exposed copper seed layer is removed by differential micro-etching, so that the vertical heat dissipation pad is bonded to the working surface.

[0072] like Figure 2 As shown, the outer layer circuitry is stacked and bonded to the copper seed layer, which is then bonded to the prepreg. The prepreg has a pre-formed window inside, and the vertical heat dissipation pads are thermally connected to the integrated metal thermal contact layer. The integrated metal thermal contact layer is tightly bonded to the thermally conductive copper core, and the prepreg is also wrapped around the thermally conductive copper core. The side edge of the thermally conductive copper core has a protruding abutment step flange, and a molecular bonding transition layer is attached to the surface of the protruding abutment step flange. The thermally conductive copper core is embedded in a stepped mounting slot, which is opened in the inner core board.

[0073] Example 5: This example addresses the thickness tolerance of high-Tg epoxy fiberglass core boards used as inner core boards in different production batches, as well as the batch fluctuations in the melt rheological properties of low-flow epoxy fiberglass prepregs. Before lamination assembly, the stepped milling depth and reserved window parameters are pre-compensated and calibrated. A contact thickness gauge is used to sample the thickness of discrete measurement points of the inner core board of the current batch and calculate the average board thickness. Based on the average board thickness, the axial cutting depth of the CNC machine tool for controlled depth milling is corrected so that the depth of the recessed step of the heat-conducting copper core protruding against the stepped flange matches the thickness of the inner core board. A sample of the low-flow epoxy fiberglass prepreg of the current batch is cut and placed in a rheometer to measure the melt dynamic viscosity and filling amount in the corresponding temperature range. The melt flow factor of the prepreg of this batch is determined by integral calculation. Then, the measured geometric parameters and the melt flow factor of the prepreg are substituted into the volume conservation relationship to calculate the single-sided compensation gap, and based on this, the CNC punching machine is driven to punch and form the reserved window of the prepreg.

[0074] In the surface thickness leveling process, to compensate for the surface height difference fluctuations caused by the wear and passivation of the ceramic brush roller and the decay of the micro-etching solution concentration, a grinding power compensation and micro-etching rate closed-loop adjustment are adopted. A laser displacement sensor collects the surface contour height difference of the substrate online. When the vertical height difference between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer deviates from the preset tolerance zone, the control system increases the downward pressure of the ceramic brush roller and increases the working speed of the brush roller in 50 rpm increments to compensate for brush roller grinding wear. Simultaneously, an online photometric analyzer continuously monitors the concentrations of sulfuric acid and hydrogen peroxide in the micro-etching tank, and replenishing solution is added via a metering pump to maintain the micro-etching rate at 1.0 μm / min to 1.5 μm / min, thereby eliminating mechanical grinding scratches and smoothing the interface between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer. The process aims to bring the vertical height difference across the entire board surface within a preset tolerance zone. Specifically, a laser displacement sensor scans the height profile diagonally along the substrate at a sampling frequency of 20 points per second. When the calculated average vertical height difference exceeds the upper limit of the +10μm to +25μm range by 1μm, the control system sends a control signal to the servo pressurizing cylinder, increasing the grinding air pressure by 0.02MPa and driving the spindle motor to increase its speed by 50rpm until the height difference falls back to the target range. Simultaneously, an online photometric analyzer performs colorimetric analysis on the absorbance of the bath solution every 5 minutes. When the hydrogen peroxide concentration is detected to be below 30g / L, a micro-metering pump injects a 30% hydrogen peroxide concentrate at a flow rate of 50mL / min, stabilizing the micro-etching rate at 1.2μm / min.

[0075] Example 6: This example is used for heat dissipation of high-power integrated circuit modules under temperature alternation and high heat flow impact conditions. A C1100 thermally conductive copper plate with a thickness of 0.45mm is selected to prepare a thermally conductive copper core. A CNC milling machine is used to perform controlled depth milling on the peripheral sidewalls of the thermally conductive copper core with a planar geometric dimension of 22mm×22mm. A convex bearing flange with a single-sided width of 0.32mm and a recessed step depth of 0.22mm is cut along the peripheral sidewalls, so that the thermally conductive copper core forms a two-step cross-sectional configuration with a lower base geometric dimension of 21.36mm×21.36mm and an upper top surface geometric dimension of 22mm×22mm, thereby establishing the working surface and rigid bearing bottom surface of the thermally conductive copper core.

[0076] The thermally conductive copper core, after being processed to support the protruding step flange, was placed in a micro-etching tank and micro-etched for 45 seconds in an acidic micro-etching solution containing 60 g / L sulfuric acid, 30 g / L hydrogen peroxide, and added organic additives. This process created micro-nano-concave-convex anchoring morphologies on the sidewalls, protruding step flange, and top and bottom surfaces of the thermally conductive copper core, resulting in a root mean square roughness of 0.35 μm to 0.45 μm. Subsequently, the micro-roughened thermally conductive copper core was immersed in 1.3% γ-glycidyl etheroxypropyl... Immerse the sample in an aqueous solution of trimethoxysilane for 3 minutes, drain, and then bake in a hot air circulating oven at 105°C for 15 minutes to cure. The silanol groups generated by the hydrolysis of the trimethoxy groups of the silane coupling agent molecules dehydrate and condense with the active copper hydroxyl groups of the micro-nano oxide layer on the surface of the thermally conductive copper core to form Si-O-Cu covalent bonds. The unreacted silanol groups condense with each other to form a silicon-oxygen network framework, so that the reactive functional groups with epoxy groups at the ends of the molecules extend to the outside, forming a molecular bonding transition layer with both inorganic and organic bidirectional reactive activity.

[0077] The inner core board is made of FR-4 high-Tg epoxy fiberglass core board with a glass transition temperature of 175℃ and a thickness of 0.22mm. A two-stage stepped embedding slot is machined using a CNC milling machine. The lower through-hole has a size of 21.44mm × 21.44mm, forming a 0.08mm gap with the 21.36mm × 21.36mm cross-sectional dimension of the lower base of the thermally conductive copper core. The upper supporting stepped hole has a size of 22.72mm × 22.72mm, forming a 0.72mm gap with the 22mm × 22mm cross-sectional dimension of the upper top surface of the thermally conductive copper core. The opening volume of the stepped embedding slot is 117.842mm³. The dielectric layer is made of 1080 type low-flow epoxy fiberglass prepreg with a nominal unpressed thickness of 0.075mm. A rotational rheometer was used to measure... The dynamic melt viscosity of the prepreg was determined at a heating rate of 2℃ / min. The dynamic melt viscosity of the resin was measured to be between 50 Pa·s and 150 Pa·s in the temperature range of 110℃ to 130℃. The melt flow factor of the prepreg was 0.9 after melt filling integral calibration. The envelope volume of the thermally conductive copper core stepped region is known to be 5.702 mm³, the solid volume of the thermally conductive copper core embedded in the groove is 119.544 mm³, and the perimeter of the main cross section of the thermally conductive copper core is 88 mm. Substituting the above geometric parameters and the melt flow factor of the prepreg into the volume conservation relationship, the single-sided compensation gap was calculated to be 0.34 mm. A reserved window with a geometric dimension of 22.68 mm × 22.68 mm was punched out on the 1080 type low-flow epoxy fiberglass prepreg using a CNC punching machine.

[0078] The coupled and modified thermally conductive copper core is snapped into the stepped mounting slot of the inner core board along the vertical height direction, so that the bottom surface of the outwardly protruding bearing step flange is in contact with the bearing surface, forming a vertical height reference and plane limit. Two 1080-type low-flow epoxy fiberglass semi-cured sheets with pre-cut windows are symmetrically stacked on the upper and lower sides of the inner core board, and an 18μm electrolytic copper foil is laid on the outermost layer to form the laminate to be pressed. The laminate to be pressed is sent into a vacuum hot press and evacuated to a vacuum environment of 35Pa. The first stage is low-temperature and low-pressure filling and degassing. The temperature is increased to 120℃ at 2℃ / min and a contact pressure of 0.8MPa is applied and held for 20min to make the low viscosity The first stage involves filling and permeating the molten resin into the stepped insert slots along the reserved windows and expelling microbubbles. The second stage involves high-temperature and high-pressure cross-linking and curing, with the temperature increased to 185°C at a rate of 2°C / min, the pressure increased to 3MPa, and the temperature and pressure held constant for 75 minutes. This allows the epoxy resin molecular chains to cross-link and form a three-dimensional network, while simultaneously driving the epoxy groups at the ends of the silane coupling agent molecules to form a covalent cross-linked network with the resin matrix. The third stage involves pressure holding and stepped cooling, maintaining the 3MPa molding pressure, and then gradually cooling to 55°C at a rate of 1.2°C / min before releasing the pressure and discharging the material. This controlled cooling releases the residual thermal stress at the heterogeneous interface caused by the mismatch between the thermal expansion coefficient and elastic modulus of the multiphase material.

[0079] The finished substrate is fed into a thickness leveling system. Using a 600-mesh silicon carbide ceramic brush roller, continuous mechanical grinding is performed on both sides of the substrate at a speed of 1800 rpm and a feed speed of 1.5 m / min to remove the overflow layer of cured resin adhering to the working surface of the thermally conductive copper core and the surrounding area. The ground substrate is then continuously fed into an acidic micro-etching spray line. It is immersed in a sulfuric acid-hydrogen peroxide micro-etching system with a bath temperature of 30℃, a sulfuric acid mass concentration of 100 g / L, and a hydrogen peroxide mass concentration of 35 g / L for 40 seconds. The micro-etching rate is controlled at 1.2 μm / min, and the micro-etching cutting depth is 0.8 μm. Chemical micro-etching is performed to remove mechanical grinding micro-scratches and level the interface between the metal copper surface and the epoxy fiberglass insulating dielectric layer. This brings the vertical height difference between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer to the range of +11 μm to +17 μm.

[0080] A homogeneous copper seed layer with a thickness of 0.3 μm is chemically deposited on the entire working surface of the substrate after the thickness has been fixed and leveled. A photoresist dry film is then attached, and the outer layer electrical conductive circuit area and the vertical heat dissipation pad pattern window are exposed after exposure and development. Pattern electroplating is then performed in an acidic copper sulfate plating bath at a current density of 2 A / dm² to increase the thickness by 25 μm. The photoresist dry film is then removed, and differential micro-etching is used to remove the exposed 0.3 μm base copper seed layer, so that the vertical heat dissipation pad is directly bonded to the working surface of the thermally conductive copper core, forming an integrated metal thermally conductive contact layer.

[0081] The fabricated high coplanarity embedded copper core substrate was tested and found that the limiting fit between the convex bearing stepped flange and the stepped mounting slot limited the planar positional offset of the thermally conductive copper core under the shearing action of hot-pressing adhesive to within 0.017 mm, ensuring coaxial alignment between the vertical heat dissipation pad and the working surface of the thermally conductive copper core. Relying on the combined effect of the micro-nano roughened physical anchoring morphology and the molecular bonding transition layer, the interfacial shear bond strength between the thermally conductive copper core and the cured resin matrix reached 6.4 N / mm². The sample was subjected to 260℃ without... Five consecutive cycles of lead reflow soldering thermal shock testing were performed, and no microcracks, delamination, blistering, or edge debonding failures were observed at the interface. The vertical heat dissipation pads and the C1100 thermally conductive copper core with a thermal conductivity of 398 W / m·K directly form an integrated metal thermally conductive contact layer. The total thermal resistance of the vertical heat transfer path is 0.19 K / W, and the vertical height difference between the working surface of the thermally conductive copper core and the surface of the adjacent insulating dielectric layer is kept within the preset tolerance zone, meeting the high reliability flip-chip coplanarity requirements of micro-pitch power semiconductor devices.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A molding process for a high coplanarity embedded copper core substrate, characterized in that, Includes the following steps: Step S1: Mill out the outwardly protruding bearing step flange along the peripheral sidewall of the thermally conductive copper core with a thickness of 0.3mm to 0.6mm and establish the working surface. Roughen the surface of the thermally conductive copper core, and then wet and coat the surface of the thermally conductive copper core with silane coupling agent and bake and cure to form a molecular bonding transition layer. Step S2, at the glass transition temperature A stepped insert slot is milled on the inner core plate at a temperature of not less than 170°C to fit the outer convex bearing stepped flange, and a reserved window is punched out on the prepreg. The single-sided compensation gap is set according to the volume conservation relationship between the opening volume of the stepped insert slot, the solid volume of the thermally conductive copper core and the melt flow factor of the prepreg. Step S3: The thermally conductive copper core is snapped into the stepped mounting slot, so that the outwardly protruding bearing flange is attached to the bearing surface of the stepped mounting slot to form vertical height and planar limit. The prepreg after opening the window and the outer copper foil are symmetrically stacked on the upper and lower sides of the inner core board to form a laminate to be pressed. Step S4: The laminate to be pressed is placed in a vacuum environment and subjected to low-temperature and low-pressure filling and degassing, high-temperature and high-pressure cross-linking and curing, and pressure holding and step-by-step cooling in sequence. Step S5: Use a ceramic brush roller to mechanically grind and cut the surface of the hot-pressed substrate to remove the overflow resin film on the surface, and perform chemical micro-etching in an acidic micro-etching solution to adjust the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer to within the preset tolerance zone. Step S6: Chemically deposit a copper seed layer on the surface of the trimmed substrate, attach a photoresist dry film, expose and develop it to reveal the outer layer circuitry and vertical heat dissipation pad windows, thicken the copper layer by pattern electroplating, remove the photoresist dry film and differentially etch away the exposed copper seed layer, so that the vertical heat dissipation pads are bonded to the working surface.

2. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, Step S1 includes step S11, milling shaping; step S12, micro-roughening treatment; and step S13, coupling coating. Specifically: in step S11, the single-sided milling width of the convex bearing flange abutting the step is 0.25 mm to 0.40 mm, and the depth of the recessed step is 0.15 mm to 0.30 mm; in step S12, micro-roughening creates a roughness on the surface of the thermally conductive copper core. The surface is roughened to a micro-nano thickness of 0.35 μm to 0.45 μm; in step S13, the silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane, which is prepared as an aqueous solution with a mass fraction of 0.5% to 2.0% for wetting and coating, and then baked and cured at 100°C to 110°C to form a molecularly bonded transition layer.

3. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, Step S2 includes step S21, slot processing, and step S22, medium punching. In step S21, the inner core board is a high Tg epoxy fiberglass core board with a thickness of 0.15mm to 0.30mm. The stepped slot includes a lower through hole and an upper supporting step hole. A gap of 0.06mm to 0.10mm is reserved between the cross-sectional size of the lower through hole and the cross-sectional size of the base of the thermally conductive copper core located at the bottom of the step. A gap of 0.68mm to 0.90mm is reserved between the cross-sectional size of the upper supporting step hole and the cross-sectional size of the top surface of the thermally conductive copper core located at the top of the step. In step S22, the prepreg is a low flow epoxy fiberglass prepreg.

4. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, Step S4 includes step S41, a low-temperature, low-pressure filling and venting stage; step S42, a high-temperature, high-pressure crosslinking and curing stage; and step S43, a pressure-holding and stepped cooling stage. Specifically, the vacuum level of the hot-pressing chamber is evacuated to less than 50 Pa. In step S41, the temperature is increased to 110°C to 130°C at a rate of 1.5°C / min to 2.5°C / min, a contact pressure of 0.5 MPa to 1.0 MPa is applied and maintained for 15 min to 25 min, guiding the molten resin to fill... Fill the gap between the stepped insert slot and the reserved window and remove micropore bubbles; in step S42, heat to 180°C to 200°C at a heating rate of 1.5°C / min to 2.5°C / min, pressurize to 2.5MPa to 3.5MPa and hold at constant temperature and pressure for 60min to 90min; in step S43, maintain molding pressure of 2.5MPa to 3.5MPa and cool to below 60°C at a cooling rate of 1.0°C / min to 1.5°C / min to release pressure and discharge material.

5. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, Step S5 includes step S51, mechanical grinding and cutting, and step S52, chemical micro-etching and finishing. In step S51, the ceramic brush roller is an alumina ceramic brush roller or a silicon carbide ceramic brush roller with a particle size of 400 to 1000 mesh. The working speed of the brush roller is set to 1500 rpm to 2200 rpm, and the substrate feed speed is set to 1.0 m / min to 2.0 m / min. The substrate after discharge is subjected to continuous fixed-thickness flat grinding and cutting on both sides. In step S52, the substrate after mechanical grinding and cutting is immersed in an acidic micro-etching solution for 30 to 60 seconds to remove mechanical grinding micro-scratches.

6. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, In step S52, the acidic micro-etching solution adopts a sulfuric acid-hydrogen peroxide system, with the sulfuric acid mass concentration controlled at 80g / L to 120g / L, the hydrogen peroxide mass concentration controlled at 30g / L to 45g / L, the bath temperature controlled at 25℃ to 35℃, and the etching rate controlled at 1.0μm / min to 1.5μm / min.

7. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, Step S6 includes step S61, chemical deposition of a seed layer, step S62, pattern electroplating thickening, and step S63, differential micro-etching removal. Specifically: in step S61, the thickness of the chemically deposited copper seed layer is 0.2 μm to 0.5 μm; in step S62, pattern electroplating uses an acidic copper sulfate system, with the cathode current density controlled at 1.5 A / dm² to 2.5 A / dm², allowing the copper layer of the conductive lines and the copper layer of the vertical heat dissipation pads to grow synchronously to 18 μm to 35 μm; in step S63, after removing the photolithographic resist dry film, a hydrogen peroxide-organic acid differential micro-etching solution is used to remove the exposed base copper seed layer, forming an integrated metal thermally conductive contact layer between the vertical heat dissipation pads and the working surface of the thermally conductive copper core.

8. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, In step S3: On the upper and lower sides of the inner core board, two prepreg sheets with pre-cut windows are symmetrically stacked, and a high-temperature extended electrolytic copper foil with a nominal thickness of 18μm is placed on the outermost layer; the outwardly convex bearing stepped flange restricts the sliding displacement of the heat-conducting copper core in the X-axis and Y-axis planes to no more than 0.025mm under pressure.

9. The forming process of a high coplanarity embedded copper core substrate according to claim 1, characterized in that, After steps S5 and S6, the absolute value of the vertical height difference between the working surface and the surface of the adjacent insulating dielectric layer is not greater than 25μm; in the prepared embedded copper core substrate, the shear bond strength between the thermally conductive copper core and the cured resin matrix is ​​not less than 5.8N / mm², and no interface delamination or blistering is observed after 5 reflow soldering thermal shock tests at 260℃.

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