Circuit board and preparation method thereof

Abstract

The present invention relates to the technical field of circuit board preparation, and in particular to a circuit board and a preparation method. A circuit board includes a core board and a composite insulation layer, wherein the composite insulation layer is laminated on the surface of the core board in the thickness direction, and the thickness t of the composite insulation layer is 120-180 μm; the composite insulation layer includes a semi-cured layer and a resin layer, and the semi-cured layer is laminated between the core board and the resin layer; the semi-cured layer is formed by curing a semi-cured sheet, and the Tg of the semi-cured sheet is greater than 230°C; the resin layer is formed by curing a layer of resin, and the Df of the resin is ≤0.003@1MHz. By complementing the material properties of the highly heat-resistant semi-cured layer and the low dielectric loss resin layer, the composite insulation layer formed by the composite of the semi-cured layer and the resin layer has low loss, high heat resistance, and high insulation performance, so that the thickness of the composite insulation layer can be controlled to t of 120-180 μm, the composite insulation layer is relatively thin, and the thermal resistance is relatively low.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board preparation, and in particular to a circuit board and a preparation method thereof. Background Art

[0002] For printed circuit boards (PCBs) integrating high-power devices, as electronic devices develop towards high frequency (>1MHz), high voltage (>1200V), and miniaturization, the insulation layer of the PCB must simultaneously withstand high-frequency alternating electric fields, high-voltage shocks, and high heat loads. This places stringent requirements on the dielectric properties, thermal management capabilities, and process compatibility of the insulation material, becoming a key bottleneck restricting the performance improvement of power modules.

[0003] The insulation layer of existing circuit boards mainly uses a single organic insulating material, and the thickness of the insulation layer is usually 100~150μm. The high-frequency dielectric loss of the single organic insulating material will cause the insulation layer to continue to heat up and rise in temperature, which may cause local melting or chemical decomposition of the material. Long-term temperature rise will accelerate material aging (such as polymer chain breakage and oxidation), causing the insulation layer breakdown voltage to drop sharply.

[0004] In order to improve the insulation performance of circuit boards under high-frequency and high-power conditions, some circuit boards increase the withstand voltage by thickening the insulation layer or stacking multiple layers. The thickness of the insulation layer reaches 170~220μm. However, the increase in the thickness of the insulation layer will lead to a significant increase in thermal resistance, causing deterioration of heat dissipation and interface air gap defects. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a circuit board and a preparation method thereof in order to address the problem that the increase in the thickness of the insulation layer of the circuit board under existing high-frequency and high-power working conditions leads to a significant increase in thermal resistance.

[0006] To solve the above problems, on the one hand, an embodiment of the present invention provides a circuit board, comprising a core board and a composite insulation layer, wherein the composite insulation layer is laminated on the surface of the core board in the thickness direction, and the thickness t of the composite insulation layer is 120~180μm; the composite insulation layer comprises a semi-cured layer and a resin layer, and the semi-cured layer is stacked between the core board and the resin layer; the semi-cured layer is formed by curing a semi-cured sheet, and the glass transition temperature Tg of the semi-cured sheet is greater than 230°C; the resin layer is formed by curing a layer of resin, and the dielectric loss factor Df of the resin at 1MHz is ≤0.003.

[0007] Preferably, the composite insulating layer further includes a pure adhesive layer, the pure adhesive layer fills the gap between the semi-cured layer and the resin layer, and the pure adhesive layer bonds the semi-cured layer and the resin layer.

[0008] Preferably, the thickness of the semi-cured layer is greater than the thickness of the resin layer, and the thickness of the resin layer is greater than the thickness of the pure glue layer.

[0009] Preferably, the prepreg is a modified prepreg;

[0010] The resin is BT resin.

[0011] Preferably, the core board includes an insulating substrate and a copper layer, the copper layer and the insulating substrate are stacked along the thickness direction of the core board, and the composite insulating layer is laminated on the surface of the copper layer facing away from the insulating substrate.

[0012] In another aspect, an embodiment of the present invention provides a method for manufacturing a circuit board, comprising:

[0013] Get the core board;

[0014] The surface of the core plate in the thickness direction is covered with a prepreg; wherein the glass transition temperature Tg of the prepreg is greater than 230°C;

[0015] Covering the surface of the prepreg with a resin film; wherein the resin film is formed by a layer of resin, and the dielectric loss factor Df of the resin at 1 MHz is ≤ 0.003;

[0016] Hot pressing, the prepreg melts and solidifies to form a prepreg layer, the resin film melts and solidifies to form a resin layer, the prepreg layer and the resin layer are cross-linked to form a composite insulating layer, and the thickness t of the composite insulating layer is 120~180μm.

[0017] Optionally, after the surface of the core board in the thickness direction is covered with a prepreg, the method further comprises:

[0018] A pure adhesive film is covered on the surface of the prepreg facing away from the core board; wherein the pure adhesive film is formed by a layer of evenly distributed pure adhesive;

[0019] Subsequently, the resin film is covered on the pure adhesive film. During hot pressing, the pure adhesive film flows to fill the gap between the prepreg and the resin film and adhere the prepreg and the resin film. The pure adhesive film melts and solidifies to form a pure adhesive layer.

[0020] Optionally, the thickness of the semi-cured layer is greater than the thickness of the resin layer, and the thickness of the resin layer is greater than the thickness of the pure glue layer.

[0021] Optionally, the prepreg is a modified prepreg;

[0022] The resin is BT resin.

[0023] Optionally, during the hot pressing, a gradient temperature increase process and a gradient temperature decrease process are adopted;

[0024] During the gradient temperature increase process, the first stage, the second stage and the third stage are sequentially performed. In the first stage, the temperature is increased to 70-120° C. to pre-flow the prepreg; in the second stage, the temperature is increased to 120-170° C. to cross-link the resin film and the pure adhesive layer; in the third stage, the temperature is increased to 200° C.

[0025] During the gradient cooling process, the fourth stage, the fifth stage and the sixth stage are carried out in sequence. In the fourth stage, the temperature is lowered to 170-190° C.; in the fifth stage, the temperature is lowered to 110-130° C.; in the sixth stage, the temperature is naturally cooled to room temperature.

[0026] A circuit board provided by an embodiment of the present invention has a semi-cured layer formed by curing a semi-cured sheet with a glass transition temperature Tg>230°C, which has high heat resistance, and a resin layer formed by curing a resin with a dielectric loss factor Df≤0.003 at 1MHz, which has low dielectric loss characteristics. The semi-cured layer is stacked between the core board and the resin layer, so that the insulation structure of the circuit board is composed of the semi-cured layer as the inner layer and the resin layer as the outer layer to form a main frame. The semi-cured layer with high heat resistance is in contact with the core board that generates high heat. The semi-cured layer can maintain a stable shape at high temperatures, can ensure the structural strength of the main frame, and provide dimensional stability at high temperatures for the composite insulation layer. The resin layer with low dielectric loss characteristics can effectively reduce high-frequency signal transmission loss, block high-frequency leakage current paths, and reduce dielectric thickness thermal resistance, so that the composite insulation layer provides a highly reliable insulation structure for the circuit board.

[0027] By complementing the material properties of the highly heat-resistant semi-cured layer and the low dielectric loss resin layer, the composite insulation layer formed by the combination of the semi-cured layer and the resin layer has low loss, high heat resistance and high insulation performance, and can simultaneously achieve high-frequency withstand voltage and dielectric thickness thermal resistance control, so that the thickness t of the composite insulation layer can be controlled within 120~180μm, the composite insulation layer is relatively thin, and the thermal resistance is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0029] Figure 1 is a schematic diagram of a circuit board provided in one embodiment of the present invention;

[0030] Figure 2 for Figure 1 A schematic diagram of a core board in a circuit board;

[0031] Figure 3 for Figure 1 Schematic diagram of the circuit board exploded before hot pressing.

[0032] The reference numerals in the specification are as follows:

[0033] 100, core board; 200, composite insulation layer; 300, metal foil; 1, semi-cured layer; 2, resin layer; 3, pure adhesive layer; 4, copper layer; 5, insulating substrate; 6, semi-cured sheet; 7, resin film; 8, pure adhesive film. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The insulation layer of existing circuit boards mainly uses a single organic insulating material, and the thickness of the insulation layer is usually between 100 and 150 μm. The high-frequency dielectric loss of the single organic insulating material will cause the insulation layer to continue to heat up and rise in temperature, which may cause local melting or chemical decomposition of the material. Long-term temperature rise will accelerate material aging (such as polymer chain breakage and oxidation), causing the insulation layer breakdown voltage to drop sharply.

[0036] To improve the insulation performance of circuit boards under high-frequency, high-power conditions, either thickening the insulation layer or stacking multiple layers to increase the withstand voltage, with the thickness reaching 170-220μm, can significantly increase thermal resistance, leading to poor heat dissipation and interface air gap defects. Alternatively, ceramic materials or inorganic filler-modified resins can be used to replace single organic insulating materials to improve high-frequency insulation. However, these materials are expensive and, due to the mismatch in thermal expansion coefficients, are incompatible with existing circuit board processes, making large-scale application difficult.

[0037] In order to solve the above problems, the present invention provides a circuit board.

[0038] like Figure 1 As shown, a circuit board provided by one embodiment of the present invention includes a core board 100 and a composite insulating layer 200. The composite insulating layer 200 is laminated on the surface of the core board 100 in the thickness direction. The thickness t of the composite insulating layer 200 is 120-180 μm.

[0039] Composite insulation layer 200 includes a prepreg layer 1 and a resin layer 2. Prepreg layer 1 is laminated between core board 100 and resin layer 2. Prepreg layer 1 is formed by curing a layer of prepreg 6, which has a glass transition temperature (Tg) greater than 230°C. Resin layer 2 is formed by a layer of resin having a dielectric loss factor (Df) of 0.003 or less at 1 MHz.

[0040] The semi-cured layer 1 formed by curing the semi-cured sheet 6 with Tg>230°C has high heat resistance, and the resin layer 2 formed by curing the resin with a dielectric loss factor Df≤0.003 at 1MHz has low dielectric loss characteristics. The semi-cured layer 1 is stacked between the core board 100 and the resin layer 2, so that the insulation structure of the circuit board is composed of the semi-cured layer 1 as the inner layer and the resin layer 2 as the outer layer to form the main frame. The semi-cured layer 1 with high heat resistance is in contact with the core board 100 that generates high heat. The semi-cured layer 1 can maintain a stable shape at high temperatures, can ensure the structural strength of the main frame, and provide dimensional stability at high temperatures for the composite insulation layer 200. The resin layer 2 with low dielectric loss characteristics can effectively reduce high-frequency signal transmission loss, block high-frequency leakage current paths, and reduce dielectric thickness thermal resistance, so that the composite insulation layer 200 provides a highly reliable insulation structure for the circuit board.

[0041] By complementing the material properties of the semi-cured layer 1 with high heat resistance and the resin layer 2 with low dielectric loss characteristics, the composite insulation layer 200 formed by the composite of the semi-cured layer 1 and the resin layer 2 has low loss, high heat resistance and high insulation performance, and can simultaneously achieve high-frequency withstand voltage (breakdown voltage > 2700V) and dielectric thickness thermal resistance control, thereby achieving a comprehensive improvement in high-frequency high-power carrying capacity and long-term thermal stability.

[0042] Compared with increasing the withstand voltage by thickening the insulating layer or stacking multiple layers, which results in the insulating layer thickness reaching 170~220μm and significantly reduces the heat dissipation performance, in the present application, the composite insulating layer 200 formed by the composite of the semi-cured layer 1 and the resin layer 2 has low loss, high heat resistance and high insulation performance, so that the thickness t of the composite insulating layer 200 can be controlled at 120~180μm, the composite insulating layer 200 is relatively thin, and the thermal resistance is relatively low.

[0043] Moreover, compared with using ceramic materials or inorganic filler-modified resins to replace a single organic insulating material, the semi-cured layer 1 of the composite insulating layer 200 is formed by curing the semi-cured sheet 6, and the resin layer 2 is formed by curing the resin. Both are compatible with standard circuit board processes, avoiding the process compatibility issues of inorganic materials, and the material cost is low, which can reduce the circuit board processing cost.

[0044] In one embodiment, the composite insulating layer 200 further includes a pure adhesive layer 3 , which fills the gap between the semi-cured layer 1 and the resin layer 2 , and bonds the semi-cured layer 1 and the resin layer 2 .

[0045] Pure glue is an adhesive without fillers, which is used for interlayer bonding and air gap filling. Pure glue has the characteristics of low expansion coefficient, which can coordinate the thermal stress matching between different materials of semi-cured layer 1 and resin layer 2, reduce delamination problems, and further improve the reliability of circuit boards.

[0046] The pure adhesive layer 3 is used for interface bonding and to eliminate the air gap between the semi-cured layer 1 and the resin layer 2, so that the semi-cured layer 1 and the resin layer 2 are densely cross-linked to obtain a dense and reliable composite insulation layer 200, eliminating the interference of the air gap on the electric field distribution, and further reducing the dielectric thickness thermal resistance, thereby achieving performance optimization of the high-frequency and high-power circuit board insulation structure through a specific stacking combination.

[0047] In one embodiment, the thickness of the prepreg layer 1 is greater than that of the resin layer 2 , and the thickness of the resin layer 2 is greater than that of the adhesive layer 3 .

[0048] The insulation structure of the circuit board is composed of a semi-cured layer 1 as an inner layer and a resin layer 2 as an outer layer to form a main frame. The semi-cured layer 1 with high heat resistance can maintain a stable shape at high temperatures, can ensure the structural strength of the main frame, and provide dimensional stability at high temperatures for the composite insulation layer 200. Therefore, compared with the resin layer 2 with low dielectric loss, the thickness of the semi-cured layer 1 with high heat resistance is designed to be relatively larger, which can improve the stability of the insulation structure of the circuit board.

[0049] In one embodiment, the prepreg 6 is a modified prepreg;

[0050] The resin is BT resin.

[0051] Modified prepregs primarily consist of a reinforcing material and a modified resin system. The reinforcing material is typically glass fiber cloth (such as E-glass fiber), which provides mechanical strength and dimensional stability. Other fibers (such as polyarylate fiber and carbon fiber) can also be used to tailor the material to specific performance requirements. The modified resin system is based on epoxy resin and is modified by adding other resins (such as bismaleimide triazine resin (BT resin), cyanate ester resin, polyphenylene ether (PPE), silicone resin, etc.) or functional fillers (such as ceramic fillers and flame retardants) to optimize the material's heat resistance, dielectric properties, mechanical strength, flame retardancy, moisture absorption, and other indicators.

[0052] BT resin has high frequency low loss (dielectric loss factor Df≤0.003 at 1MHz) and high insulation (5x10 12 ~14Ω･cm), the modified prepreg combines high heat resistance (Tg>230℃) with structural strength.

[0053] Based on the synergistic effect of modified prepreg, BT resin and pure adhesive, through a specific lamination technology (modified prepreg-pure adhesive-BT resin), an insulation enhancement structure for high-frequency and high-power circuit boards is constructed to achieve reduced dielectric loss, increased breakdown voltage and controlled dielectric thickness and thermal resistance at high frequencies.

[0054] Moreover, BT resin, modified semi-cured sheet and pure glue are fixed material models adapted to the standard circuit board lamination process. They are fully compatible with the standard circuit board process and avoid the process compatibility issues of inorganic materials. The material cost of the composite insulation layer 200 is 1 / 3 of the ceramic core board solution, greatly reducing costs.

[0055] In one embodiment, if Figure 1 As shown, the core board 100 includes an insulating substrate 5 and a copper layer 4. The copper layer 4 and the insulating substrate 5 are stacked along the thickness direction of the core board 100. The composite insulating layer 200 is laminated on the surface of the copper layer 4 facing away from the insulating substrate 5.

[0056] Specifically, the core board 100 is a copper clad board, and circuits are formed on the surface of the copper clad board by exposure, development, and etching.

[0057] In other embodiments, the resin may be ABF resin or a modified cyanate resin.

[0058] In one embodiment, the circuit board further includes a metal foil 300 , which is laminated on the composite insulating layer 200 .

[0059] The conductive lines may be formed by patterning the metal foil 300 using an etching process. The metal foil 300 may be a copper foil.

[0060] It should be noted that Figure 1 The following is just an example of a circuit board structure. Figure 1 Only the composite insulating layer 200 on one side of the circuit board is shown in FIG. In other embodiments, the composite insulating layer 200 may be formed on one side of the circuit board. Figure 1 Layers are added to the circuit board shown in the figure to form a multi-layer circuit board.

[0061] In addition, an embodiment of the present invention provides a method for preparing a circuit board, comprising:

[0062] S1: If Figure 2 As shown, a core plate 100 is obtained.

[0063] Specifically, the core board 100 includes an insulating substrate 5 and a copper layer 4. The copper layer 4 and the insulating substrate 5 are stacked along the thickness direction of the core board 100, and the copper layer 4 forms a circuit. The core board 100 can be a copper clad laminate, and the surface of the copper clad laminate is formed with circuits by exposure, development, and etching.

[0064] S2: If Figure 3 As shown, the surface of the core board 100 in the thickness direction is covered with a prepreg 6 ; wherein the glass transition temperature Tg of the prepreg 6 is greater than 230°C.

[0065] S3: If Figure 3 As shown, the surface of the prepreg 6 is covered with a resin film 7; wherein the resin film 7 is a film formed by a layer of resin, and the dielectric loss factor Df of the resin at 1 MHz is ≤ 0.003;

[0066] S4: As Figure 3 As shown, hot pressing is performed, the semi-cured sheet 6 is melted and solidified to form a semi-cured layer 1, the resin film 7 is melted and solidified to form a resin layer 2, and the semi-cured layer 1 and the resin layer 2 are cross-linked to form a composite insulating layer 200, and the thickness t of the composite insulating layer 200 is 120~180μm.

[0067] In step S4, the semi-cured sheet 6 with Tg>230°C is cured to form a semi-cured layer 1, which has high heat resistance, and the resin with a dielectric loss factor Df≤0.003 at 1 MHz is cured to form a resin layer 2, which has low dielectric loss characteristics.

[0068] As can be seen from steps S2 and S3, the semi-cured layer 1 is stacked between the core board 100 and the resin layer 2. The insulation structure of the circuit board is composed of the semi-cured layer 1 as the inner layer and the resin layer 2 as the outer layer to form the main frame. The semi-cured layer 1 with high heat resistance is in contact with the core board 100 that generates high heat. The semi-cured layer 1 can maintain a stable shape at high temperatures, which can ensure the structural strength of the main frame and provide dimensional stability at high temperatures for the composite insulation layer 200. The resin layer 2 with low dielectric loss characteristics can effectively reduce high-frequency signal transmission loss, block high-frequency leakage current paths, and reduce dielectric thickness thermal resistance, so that the composite insulation layer 200 provides a highly reliable insulation structure for the circuit board.

[0069] By complementing the material properties of the semi-cured layer 1 with high heat resistance and the resin layer 2 with low dielectric loss characteristics, the composite insulation layer 200 formed by the composite of the semi-cured layer 1 and the resin layer 2 has low loss, high heat resistance and high insulation performance, and can simultaneously achieve high-frequency withstand voltage and dielectric thickness thermal resistance control, thereby achieving a comprehensive improvement in high-frequency high-power carrying capacity and long-term thermal stability.

[0070] Compared with increasing the withstand voltage by thickening the insulating layer or stacking multiple layers, which results in the insulating layer thickness reaching 170~220μm and significantly reduces the heat dissipation performance, in the present application, the composite insulating layer 200 formed by the composite of the semi-cured layer 1 and the resin layer 2 has low loss, high heat resistance and high insulation performance, so that the thickness t of the composite insulating layer 200 can be controlled at 120~180μm, the composite insulating layer 200 is relatively thin, and the thermal resistance is relatively low.

[0071] Moreover, compared with using ceramic materials or inorganic filler-modified resins to replace a single organic insulating material, the semi-cured layer 1 of the composite insulating layer 200 is composed of a semi-cured sheet 6, and the resin layer 2 is composed of resin, both of which are compatible with standard circuit board processes, avoiding the process compatibility issues of inorganic materials, and the material cost is low, which can reduce the circuit board processing cost.

[0072] In one embodiment, if Figure 3 As shown, after step S2, it also includes:

[0073] S5: Covering the surface of the prepreg 6 on the side facing away from the core board 100 with a pure adhesive film 8; wherein the pure adhesive film 8 is a film formed by a layer of evenly distributed pure adhesive;

[0074] In the subsequent step S3, the resin film 7 is covered on the pure adhesive film 8. In the step S4, during hot pressing, the pure adhesive film 8 flows to fill the gap between the prepreg 6 and the resin film 7 and adheres the prepreg 6 and the resin film 7. The pure adhesive film 8 melts and solidifies to form a pure adhesive layer 3.

[0075] Pure glue is an adhesive without fillers, which is used for interlayer bonding and air gap filling. Pure glue has low expansion coefficient and high fluidity, which can better fill the interface air gap between the semi-cured layer 1 and the resin layer 2, and can coordinate the thermal stress matching between the different materials of the semi-cured layer 1 and the resin layer 2, reduce delamination problems, and further improve the reliability of the circuit board.

[0076] Pure glue is used for interface bonding and to eliminate the air gap between the semi-cured layer 1 and the resin layer 2, so that the semi-cured layer 1 and the resin layer 2 are densely cross-linked to obtain a dense and reliable composite insulation layer 200, eliminating the interference of the air gap on the electric field distribution, and further reducing the dielectric thickness thermal resistance, thereby achieving performance optimization of the high-frequency and high-power circuit board insulation structure through a specific stacking combination.

[0077] In one embodiment, the prepreg 6 is a modified prepreg;

[0078] The resin is BT resin.

[0079] Modified prepregs primarily consist of a reinforcing material and a modified resin system. The reinforcing material is typically glass fiber cloth (such as E-glass fiber), which provides mechanical strength and dimensional stability. Other fibers (such as polyarylate fiber and carbon fiber) can also be used to tailor the material to specific performance requirements. The modified resin system is based on epoxy resin and is modified by adding other resins (such as bismaleimide triazine resin (BT resin), cyanate ester resin, polyphenylene ether (PPE), silicone resin, etc.) or functional fillers (such as ceramic fillers and flame retardants) to optimize the material's heat resistance, dielectric properties, mechanical strength, flame retardancy, moisture absorption, and other indicators.

[0080] BT resin has high frequency low loss (dielectric loss factor Df≤0.003 at 1MHz), high insulation (5x10 12 ~14 Ω･cm) and heat resistance (Tg=200℃), the modified prepreg combines high heat resistance (Tg>230℃) with structural strength.

[0081] Based on the synergistic effect of modified prepreg, BT resin and pure adhesive, through a specific lamination technology (modified prepreg-pure adhesive-BT resin), an insulation enhancement structure for high-frequency and high-power circuit boards is constructed to achieve reduced dielectric loss, increased breakdown voltage and controlled dielectric thickness and thermal resistance at high frequencies.

[0082] Moreover, BT resin, modified semi-cured sheet, and pure glue are fixed material models adapted to the standard circuit board lamination process. They are fully compatible with the standard circuit board process, avoiding the process compatibility issues of inorganic materials and have low costs. The material cost of the composite insulation layer 200 is 1 / 3 of the ceramic core board 100 solution, greatly reducing costs.

[0083] In one embodiment, in step S2, the prepreg 6 is a modified prepreg film with a thickness of 60 μm, in step S3, the resin film 7 is a BT resin film 7 with a thickness of 50 μm, and in step S5, the pure adhesive film 8 is a polyimide adhesive film with a thickness of 30 μm.

[0084] BT resin film 7 is a film made of bismaleimide triazine (qin) resin, which has high frequency low loss (dielectric loss factor Df≤0.003 at 1MHz) and high insulation (5x10 12~14 Ω･cm), modified prepreg film is made of chemically modified prepreg 6-shaped material, taking into account high heat resistance (Tg>230℃) and structural strength.

[0085] In other embodiments, the resin material of the resin film 7 may be ABF resin or a modified cyanate resin.

[0086] In one embodiment, in step S4, during hot pressing, a gradient heating process and a gradient cooling process are used to form a dense cross-linked structure between the semi-cured layer 1, the resin layer 2 and the pure adhesive layer 3, and eliminate thermal stress to obtain a composite insulating layer 200.

[0087] The first, second, and third stages are performed sequentially during the gradient temperature increase process. In the first stage, the temperature is raised to 70-120°C to pre-flow the prepreg 6. In the second stage, the temperature is raised to 120-170°C to cross-link the resin film 7 and the adhesive layer 3. In the third stage, the temperature is raised to 200°C to ensure densification.

[0088] During the gradient cooling process, the fourth, fifth and sixth stages are carried out in sequence. In the fourth stage, the temperature is lowered to 170~190℃ to eliminate local stress; in the fifth stage, the temperature is lowered to 110~130℃ to maintain structural stability; in the sixth stage, it is naturally cooled to room temperature to avoid delamination or warping caused by sudden cooling.

[0089] Specifically, in the first stage, the temperature is raised to 70~120℃ at a rate of 5℃ / min and maintained for 30 minutes; in the second stage, the temperature is raised to 120~170℃ at a rate of 3℃ / min and maintained at a constant temperature for 60 minutes to promote the cross-linking of pure glue / BT resin; in the third stage, the temperature is raised to 200℃ at a rate of 5℃ / min and maintained at a constant temperature for 40 minutes to ensure densification.

[0090] In the fourth stage, the temperature was lowered to 180°C at a rate of 2°C / min; in the fifth stage, the temperature was lowered to 120°C at a rate of 10°C / min; in the sixth stage, the temperature was naturally cooled to room temperature.

[0091] In other embodiments, the pure glue layer 3 can be eliminated, and the time and pressure for melting and cross-linking of the semi-cured sheet 6 and the resin film 7 can be increased by increasing the temperature or pressurizing during hot pressing in step S4, so that the semi-cured layer 1 and the resin layer 2 can be better cross-linked to eliminate the air gap between the semi-cured layer 1 and the resin layer 2, thereby obtaining a densely cross-linked composite insulation layer 200.

[0092] In one embodiment, if Figure 3 As shown, after step S3, the following steps are also included:

[0093] S6: Laminating the metal foil 300 on the resin film 7;

[0094] During the subsequent hot pressing step S4 , the metal foil 300 , the prepreg 6 , the resin film 7 and the core board 100 are laminated together.

[0095] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A circuit board, characterized in that: The invention comprises a core board and a composite insulation layer, wherein the composite insulation layer is laminated on the surface of the core board in the thickness direction, and the thickness t of the composite insulation layer is 120~180μm; the composite insulation layer comprises a semi-cured layer and a resin layer, and the semi-cured layer is stacked between the core board and the resin layer; the semi-cured layer is formed by curing a semi-cured sheet, and the glass transition temperature Tg of the semi-cured sheet is greater than 230°C; the resin layer is formed by curing a layer of resin, and the dielectric loss factor Df of the resin at 1MHz is ≤0.

003.

2. The circuit board according to claim 1, wherein: The composite insulating layer further includes a pure adhesive layer, which fills the gap between the semi-cured layer and the resin layer and bonds the semi-cured layer and the resin layer.

3. The circuit board according to claim 2, wherein: The thickness of the semi-cured layer is greater than that of the resin layer, and the thickness of the resin layer is greater than that of the pure glue layer.

4. The circuit board according to claim 2, wherein: The prepreg is a modified prepreg; The resin is BT resin.

5. The circuit board according to claim 1, wherein: The core board includes an insulating substrate and a copper layer. The copper layer and the insulating substrate are stacked along the thickness direction of the core board. The composite insulating layer is laminated on the surface of the copper layer facing away from the insulating substrate.

6. A method for preparing a circuit board, characterized in that: include: Get the core board; The surface of the core plate in the thickness direction is covered with a prepreg; wherein the glass transition temperature Tg of the prepreg is greater than 230°C; Covering the surface of the prepreg with a resin film; wherein the resin film is formed by a layer of resin, and the dielectric loss factor Df of the resin at 1 MHz is ≤ 0.003; Hot pressing, the prepreg melts and solidifies to form a prepreg layer, the resin film melts and solidifies to form a resin layer, the prepreg layer and the resin layer are cross-linked to form a composite insulating layer, and the thickness t of the composite insulating layer is 120~180μm.

7. The method for preparing a circuit board according to claim 6, wherein: After the surface of the core plate in the thickness direction is covered with a prepreg, the method further comprises: A pure adhesive film is covered on the surface of the prepreg facing away from the core board; wherein the pure adhesive film is formed by a layer of evenly distributed pure adhesive; Subsequently, the resin film is covered on the pure adhesive film. During hot pressing, the pure adhesive film flows to fill the gap between the prepreg and the resin film and adhere the prepreg and the resin film. The pure adhesive film melts and solidifies to form a pure adhesive layer.

8. The method for preparing a circuit board according to claim 7, wherein: The thickness of the semi-cured layer is greater than that of the resin layer, and the thickness of the resin layer is greater than that of the pure glue layer.

9. The method for preparing a circuit board according to claim 7, wherein: The prepreg is a modified prepreg; The resin is BT resin.

10. The method for preparing a circuit board according to claim 9, wherein: During the hot pressing, a gradient heating process and a gradient cooling process are adopted; During the gradient temperature increase process, the first stage, the second stage and the third stage are sequentially performed. In the first stage, the temperature is increased to 70-120° C., and the prepreg is pre-flowed. In the second stage, the temperature is increased to 120-170° C., and the resin film and the pure adhesive layer are cross-linked. In the third stage, the temperature is raised to 200° C. During the gradient cooling process, the fourth stage, the fifth stage and the sixth stage are carried out in sequence. In the fourth stage, the temperature is lowered to 170-190° C.; in the fifth stage, the temperature is lowered to 110-130° C.; in the sixth stage, the temperature is naturally cooled to room temperature.

Images