A process for the production of an ultra-low dielectric constant circuit board

Abstract

The application discloses a preparation process of an ultra-low dielectric constant circuit board and relates to the technical field of circuit boards.The process comprises the following steps: S1: manufacturing inner-layer high-frequency signal lines: high-frequency signal lines are formed on a substrate through a dry film pasting, exposure, development and etching process; S2: manufacturing anti-soldering bridges: anti-soldering bridges are formed around the high-frequency signal lines through a silk printing, exposure and development process; S3: processing a semi-cured sheet vacuum cavity area: the semi-cured sheet on the upper layer of the high-frequency lines is removed through mechanical milling to form semi-cured sheet grooves; S4: compression molding: all layers are laminated together through a brown oxidation, plate arranging and plate pressing mode to form an outer-layer semi-finished circuit board containing a vacuum cavity; and S5: processing non-plating through holes: non-plating through holes are formed at non-signal line positions in the vacuum cavity area through mechanical drilling, so that the ultra-low dielectric constant circuit board is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit boards, and in particular to a preparation process of an ultra-low dielectric constant circuit board. Background Art

[0002] As modern electronic devices rapidly advance toward higher speeds and higher frequencies, the performance requirements for circuit board materials are becoming increasingly stringent. Dielectric constant, a key parameter affecting signal transmission rate and loss, has become a key factor limiting circuit performance in high-frequency applications. Traditional circuit board materials often suffer from high dielectric constants, leading to significant signal delays and increased energy loss, making them difficult to meet the demands of high-precision and high-efficiency transmission.

[0003] In existing technologies, the main strategies for reducing the dielectric constant include introducing low-dielectric additives or designing porous structures to reduce material density. However, these methods often come with significant performance trade-offs: for example, low-dielectric additives may weaken the mechanical strength of the material, while porous structures can easily lead to insufficient interlayer bonding, increasing the risk of delamination of the circuit board. In addition, a single material system usually has difficulty balancing the needs of rigid support and flexible buffering, resulting in a decrease in overall reliability. At the same time, the choice of solder mask material has a significant impact on circuit performance. The polar groups in traditional solder mask materials are prone to generate additional dielectric loss in high-frequency environments, further exacerbating signal degradation.

[0004] Therefore, the current technology landscape urgently requires an innovative fabrication process that can effectively reduce the dielectric constant of circuit boards without sacrificing mechanical strength and thermal stability. An ideal solution would address the performance contradictions inherent in existing technologies through collaborative material optimization and structural design innovation, thereby providing more reliable hardware support for high-frequency electronic devices. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for preparing an ultra-low dielectric constant circuit board to solve the problems raised in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A process for preparing an ultra-low dielectric constant circuit board comprises the following steps: S1: making an inner-layer high-frequency signal circuit: forming a high-frequency signal circuit 1 on an inner-layer substrate by dry film lamination, exposure, development, and etching processes;

[0008] S2: Making solder mask bridges: forming solder mask bridges 2 around the high-frequency signal line 1 through screen printing, exposure, and development processes;

[0009] S3: Processing the prepreg vacuum cavity area: Cover the prepreg on the same layer as the solder mask bridge 2, and remove the prepreg on the high-frequency circuit by mechanical gong, forming prepreg grooves 3 on both sides of the solder mask bridge 2;

[0010] S4: Pressing and forming: Pressing the inner substrate and the outer substrate together by browning, arranging and pressing to form an outer semi-finished circuit board including the vacuum cavity 4;

[0011] S5: Processing non-plated through holes: Mechanically drilling non-plated through holes 5 at non-signal line positions in the vacuum cavity 4 area to obtain an ultra-low dielectric constant circuit board.

[0012] Furthermore, in step S1 , the line width tolerance of the high-frequency signal line 1 is ±10 μm.

[0013] Furthermore, in step S2, the median thickness of the solder mask bridge 2 is equal to the thickness of the upper prepreg of the high-frequency signal circuit 1, the width of the solder mask bridge 2 is 0.1-0.4 mm, and the solder mask bridge 2 is prepared from solder resist ink.

[0014] Furthermore, in step S3, the distance between the prepreg pit 3 and the high-frequency signal line 1 is 0.5-3 mm, the single-side width of the prepreg pit 3 exceeds the width of the solder mask bridge 2 by 0.1 mm, and the thickness of the prepreg is 1.5-2.5 mil.

[0015] Furthermore, in step S4, the platen parameters are a temperature of 180-200° C., a pressure of 300-400 psi, and a time of 90-120 min.

[0016] Furthermore, in step S5 , the diameter of the non-plated through hole 5 is 0.25-1 mm, and the number of the non-plated through holes 5 provided in each vacuum cavity 4 is ≥2.

[0017] Furthermore, the preparation method of the solder resist ink comprises the following steps:

[0018] Step 1: Add 1,5-naphthalenediol and ethyl 4-bromobutyrate to acetone, stir evenly, add potassium carbonate, heat to 70-75°C and reflux for 3-4 days, extract the reaction product with ether and hydrochloric acid, wash with deionized water, dry over anhydrous sodium sulfate, filter, collect the organic layer, and evaporate to dryness to obtain compound 1; add compound 1 to tetrahydrofuran, add 0.5 mol / L sodium hydroxide aqueous solution, react at room temperature for 12-13 hours, add 1 mol / L hydrochloric acid aqueous solution, react for 3-4 days, filter, and dry to obtain compound 2; add compound 2, glycidol, and 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride to tetrahydrofuran, add 4-dimethylaminopyridine, react at room temperature for 24-25 hours, rotary evaporate, wash, centrifuge, and dry to obtain a naphthyl epoxy monomer;

[0019] Furthermore, in the preparation process of the compound 1, the molar ratio of 1,5-naphthalenediol: ethyl 4-bromobutyrate: potassium carbonate is 9.3:23.1:54; in the preparation process of the naphthyl epoxy monomer, the molar ratio of compound 2: glycidol: 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride: 4-dimethylaminopyridine is 10:30:30:3.

[0020] Step 2: Add the naphthyl epoxy monomer to ethyl 2-2-ethoxyethoxyacetate, heat to 85-86°C, stir evenly, cool to room temperature, add cholic acid and 4-dimethylaminopyridine, heat to 115-120°C and react for 12-13 hours, cool to room temperature, add 1,2,3,6-tetrahydrophthalic anhydride and hydroquinone, heat to 95-98°C and react for 7-8 hours, add glycidyl methacrylate, heat to 110-115°C and react for 3-4 hours to obtain a naphthyl photocurable resin;

[0021] Furthermore, in the preparation process of the naphthyl photocurable resin, the mass ratio of naphthyl epoxy monomer: cholic acid: 4-dimethylaminopyridine: 1,2,3,6-tetrahydrophthalic anhydride: hydroquinone: glycidyl methacrylate is 3:5.7:0.052:8.4:0.052:4.2.

[0022] Step 3: adding isophorone diisocyanate to a reaction vessel, adding p-hydroxyanisole, dibutyl tin dilaurate, and hydroxyethyl acrylate, heating to 30-32° C. for reaction, and when the isocyanate group content in the reaction system reaches the theoretical value, a double-bond terminated polyurethane precursor is obtained; further heating to 50-52° C., adding isophorone diisocyanate, p-hydroxyanisole, and dibutyl tin dilaurate, stirring evenly, adding polyethylene glycol 100 and 2,2-dihydroxymethacrylic acid, and keeping warm for reaction, when the isocyanate group content in the reaction system reaches the theoretical value, a double-bond terminated oligomeric polyurethane is obtained; adding a light-curable epoxy resin containing a dihydroxy group carboxylic acid to a reaction vessel, adding p-hydroxybenzyl ether, dibutyl tin dilaurate, and a double-bond terminated oligomeric polyurethane, heating to 50-52° C., when the isocyanate group content in the reaction system is 0%, adding the product to a methanol aqueous solution for purification, and vacuum drying to obtain a polyurethane-modified light-curable epoxy resin;

[0023] Furthermore, in the preparation process of the double-bond terminated polyurethane precursor, the mass ratio of isophorone diisocyanate: p-hydroxyanisole: dibutyl tin dilaurate: hydroxyethyl acrylate is 117:0.17:0.52:59; in the preparation process of the double-bond terminated oligomeric polyurethane, the mass ratio of isophorone diisocyanate: p-hydroxyanisole: dibutyl tin dilaurate: polyethylene glycol 100, 2,2-dihydroxymethacrylic acid is 229:0.4:1.2:100:69 ; In the preparation process of polyurethane-modified light-curing epoxy resin, the mass ratio of light-curing epoxy resin containing dihydroxy carboxylic acid: hydroxybenzyl ether: dibutyl tin dilaurate: double-bond terminated oligomeric polyurethane is 500:0.99:2.97:50; the light-curing epoxy resin containing dihydroxy carboxylic acid is first prepared by a ring-opening reaction of epoxy resin with acrylic acid and 2,2-dihydroxymethylacrylic acid, and then an esterification reaction with 1,2,3,6-tetrahydrophthalic anhydride.

[0024] Step 4: Add naphthalene-based photocurable resin and polyurethane-modified photocurable epoxy resin to diethylene glycol ethyl ether acetate, add epoxy-functionalized silica, thermosetting agent, and barium sulfate, ball mill for 30-45 minutes, add phthalocyanine green, reactive diluent, and composite photoinitiator, and stir at room temperature for 3-4 hours to obtain solder mask ink.

[0025] Furthermore, in the preparation process of the solder resist ink, the components, calculated by mass, include 2-4 parts of naphthalene-based photocurable resin, 1-3 parts of polyurethane-modified photocurable epoxy resin, 5-7 parts of diethylene glycol ethyl ether acetate, 0.25-0.3 parts of epoxy-functionalized silica, 0.25-3 parts of thermosetting agent, 0.75-1 parts of barium sulfate, 0.1-0.15 parts of phthalocyanine green, 0.15-0.2 parts of active diluent, and 0.15-0.2 parts of composite photoinitiator.

[0026] Furthermore, the thermal curing agent is thermosetting epoxy resin NC3000;

[0027] Furthermore, the reactive diluent is pentaerythritol triacrylate;

[0028] Furthermore, the composite photoinitiator is a mixture of 907 and ITX in a mass ratio of 3:2;

[0029] Furthermore, during the preparation of the double-bond terminated polyurethane precursor, the theoretical -NCO content was 11.73%, and during the preparation of the double-bond terminated oligomeric polyurethane, the theoretical -NCO content was 2.36%;

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention achieves ultra-low dielectric constant, high thermal stability and high reliability through the rigid structure of naphthalene-based resin, flexible modification of polyurethane, low dielectric design of vacuum cavity and optimized process parameters, providing an ideal solution for high-frequency circuit boards.

[0032] 2. The rigid naphthalene ring structure of the naphthalene-based photocurable resin in the solder mask ink of the present invention forms an ordered molecular arrangement through π-π stacking, reducing the free vibration of the polar groups hydroxyl and carboxyl; the polyurethane-modified photocurable epoxy resin introduces a flexible chain segment polyethylene glycol to reduce the polar density of the molecular chain; the synergistic vacuum cavity structure reduces the volume share of the dielectric material and uses the air dielectric constant ≈1 to replace the traditional semi-cured sheet, significantly reducing the overall dielectric constant and giving the circuit board ultra-low dielectric constant performance.

[0033] 3. The present invention utilizes the rigid structure of naphthalene-based photocurable resin to inhibit the movement of molecular chains at high temperatures and cooperates with polyurethane-modified photocurable epoxy resin to form a stable three-dimensional cross-linked structure through chemical grafting, thereby greatly improving the thermal stability of solder mask ink.

[0034] 4. The present invention utilizes the flexibility of polyurethane chain segments to enhance the interfacial bonding between the resin and the substrate through hydrogen bonding and physical entanglement. Through the synergistic effect of naphthalene-based resin and polyurethane, a "rigid and flexible" composite structure is formed, balancing tensile strength and toughness, giving the solder mask ink excellent adhesion and mechanical properties; combined with the non-plated through-hole design, the interlayer bonding strength is improved through the mechanical locking effect, reducing the risk of delamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of a process for preparing an ultra-low dielectric constant circuit board according to the present invention;

[0036] 1: High-frequency signal line; 2: Solder mask bridge; 3: Prepreg pit; 4: Vacuum cavity; 5: Non-plated through hole. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] In the following examples, all raw materials are commercially available.

[0039] The preparation method of a naphthyl epoxy monomer comprises the following steps: adding 9.3 mmol of 1,5-naphthalenediol and 23.1 mmol of ethyl 4-bromobutyrate to acetone, stirring evenly, adding 1.54 mmol of potassium carbonate, heating to 70°C and reflux reaction for 3 days, extracting the reaction product with ether and hydrochloric acid, washing with deionized water, drying over anhydrous sodium sulfate, filtering, collecting the organic layer, and evaporating to dryness to obtain compound 1; adding 10 mmol of compound 1 to tetrahydrofuran, adding 0.5 mol / L sodium hydroxide aqueous solution, reacting at room temperature for 12-13 hours, adding 1 mol / L hydrochloric acid aqueous solution, reacting for 3-4 days, filtering, and drying to obtain compound 2; adding 10 mmol of compound 2, 30 mmol of glycidol, and 30 mmol of 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride to tetrahydrofuran, adding 3 mmol of 4-dimethylaminopyridine, reacting at room temperature for 24-25 hours, rotary evaporation, washing, centrifugation, and drying to obtain the naphthyl epoxy monomer;

[0040] The preparation method of a naphthyl photocurable resin comprises the following steps: adding 3 g of a naphthyl epoxy monomer to ethyl 2-2-ethoxyethoxyacetate, heating to 85° C., stirring evenly, cooling to room temperature, adding 5.7 g of cholic acid and 0.052 g of 4-dimethylaminopyridine, heating to 115° C. and reacting for 12 hours, cooling to room temperature, adding 8.4 g of 1,2,3,6-tetrahydrophthalic anhydride and 0.052 g of hydroquinone, heating to 95° C. and reacting for 7 hours, adding 4.2 g of glycidyl methacrylate, heating to 110° C. and reacting for 3 hours, to obtain a naphthyl photocurable resin;

[0041] The preparation method of polyurethane modified light-curing epoxy resin comprises the following steps: adding 117g of isophorone diisocyanate into a reaction container, adding 0.17g of p-hydroxyanisole, 0.52g of dibutyl tin dilaurate, and 59g of hydroxyethyl acrylate, heating to 30°C for reaction, and obtaining a double-bond terminated polyurethane precursor when the isocyanate group content in the reaction system reaches a theoretical value; further heating to 50°C, adding 229g of isophorone diisocyanate, 0.4g of p-hydroxyanisole, and 1.2g of dibutyl tin dilaurate, stirring evenly, and adding 100g of polyurethane. 100 g of diol and 69 g of 2,2-dihydroxymethylacrylate were reacted at a heat-insulating temperature. When the isocyanate group content in the reaction system reached the theoretical value, a double-bond terminated oligomeric polyurethane was obtained. 500 g of a light-curing epoxy resin containing a dihydroxy carboxylic acid was added to a reaction vessel. 0.99 g of p-hydroxybenzyl ether, 2.97 g of dibutyl tin dilaurate, and 50 g of a double-bond terminated oligomeric polyurethane were also added. The reaction was heated to 50° C. When the isocyanate group content in the reaction system was 0%, the product was purified by adding it to a methanol aqueous solution and vacuum-dried to obtain a polyurethane-modified light-curing epoxy resin.

[0042] The preparation method of a light-curing epoxy resin containing a dihydroxy carboxylic acid comprises the following steps:

[0043] Under nitrogen protection, 50.0g of diethylene glycol ethyl ether acetate was added to a 1L three-necked flask equipped with a stirrer, the temperature was raised to 90°C, 88.8g of epoxy resin NPCN-704 was added, and the temperature was kept constant for one hour to fully dissolve it. The temperature was lowered to 60°C and 19.1g of acrylic acid and 38.2g of 2,2-dihydroxymethylacrylic acid dissolved in 40g of diethylene glycol ethyl ether acetate were added. The temperature was raised to 70°C and 1.5g of 4-dimethylaminopyridine dissolved in 2g of diethylene glycol ethyl ether acetate was added. The reaction was stirred at a constant temperature of 95°C for 1 hour, and then the temperature was raised to 105°C and the reaction was stirred at a constant temperature for 12 hours. The reaction system was then cooled to 80° C., 94.0 g of 1,2,3,6-tetrahydrophthalic anhydride and 0.5 g of hydroquinone dissolved in 30 g of diethylene glycol ethyl ether acetate were added, and the temperature was raised to 90° C. and stirred for reaction for 3 hours to obtain a light-curing epoxy resin containing a dihydroxy group carboxylic acid.

[0044] Example 1: A process for preparing an ultra-low dielectric constant circuit board, comprising the following steps: A method for preparing a solder resist ink, comprising the following steps: adding 2 parts of a naphthalene-based photocurable resin and 3 parts of a polyurethane-modified photocurable epoxy resin to 5 parts of diethylene glycol ethyl ether acetate, adding 0.25 parts of epoxy-functionalized silica, 0.25 parts of a thermosetting agent, and 0.75 parts of barium sulfate, ball milling for 30 minutes, adding 0.1 parts of phthalocyanine green, 0.15 parts of a reactive diluent, and 0.15 parts of a composite photoinitiator, and stirring at room temperature for 3 hours to obtain a solder resist ink;

[0045] S1: Making an inner high-frequency signal circuit: forming a high-frequency signal circuit 1 on the inner substrate through dry film lamination, exposure, development, and etching processes;

[0046] S2: Making solder mask bridges: Screen printing, exposure, and development of solder mask ink are performed around the high-frequency signal line 1 to form solder mask bridges 2; the width of the solder mask bridge is 0.2 mm;

[0047] S3: Processing the prepreg vacuum cavity area: Cover the prepreg on the same layer as the solder mask bridge 2, and remove the prepreg on the high-frequency circuit by mechanical gong, forming prepreg grooves 3 on both sides of the solder mask bridge 2; the distance between the prepreg groove 3 and the high-frequency signal circuit 1 is 2mm, and the thickness of the prepreg is 2mil;

[0048] S4: Pressing and forming: Pressing the inner substrate and the outer substrate together by browning, arranging, and pressing to form an outer semi-finished circuit board including the vacuum cavity 4; the pressing temperature is 180°C, the pressure is 300 psi, and the time is 90 minutes;

[0049] S5: Processing non-plated through holes: Mechanically drilling non-plated through holes 5 at non-signal line positions in the vacuum cavity 4 area to obtain an ultra-low dielectric constant circuit board. The diameter of the non-plated through hole 5 is 0.5 mm, and the number of the non-plated through holes 5 is 2.

[0050] Example 2: A process for preparing an ultra-low dielectric constant circuit board, comprising the following steps: A method for preparing a solder resist ink, comprising the following steps: adding 3 parts of a naphthalene-based photocurable resin and 2 parts of a polyurethane-modified photocurable epoxy resin to 5 parts of diethylene glycol ethyl ether acetate, adding 0.25 parts of epoxy-functionalized silica, 0.25 parts of a thermosetting agent, and 0.75 parts of barium sulfate, ball milling for 30 minutes, adding 0.1 parts of phthalocyanine green, 0.15 parts of a reactive diluent, and 0.15 parts of a composite photoinitiator, and stirring at room temperature for 3 hours to obtain a solder resist ink;

[0051] The remaining steps are the same as those in Example 1.

[0052] Example 3: A process for preparing an ultra-low dielectric constant circuit board, comprising the following steps: A method for preparing a solder resist ink, comprising the following steps: adding 4 parts of a naphthalene-based photocurable resin and 1 part of a polyurethane-modified photocurable epoxy resin to 5 parts of diethylene glycol ethyl ether acetate, adding 0.25 parts of epoxy-functionalized silica, 0.25 parts of a thermosetting agent, and 0.75 parts of barium sulfate, ball milling for 30 minutes, adding 0.1 parts of phthalocyanine green, 0.15 parts of a reactive diluent, and 0.15 parts of a composite photoinitiator, and stirring at room temperature for 3 hours to obtain a solder resist ink;

[0053] The remaining steps are the same as those in Example 1.

[0054] Example 4: A process for preparing an ultra-low dielectric constant circuit board, comprising the following steps: A method for preparing a solder resist ink, comprising the following steps: adding 4 parts of a naphthalene-based photocurable resin and 3 parts of a polyurethane-modified photocurable epoxy resin to 7 parts of diethylene glycol ethyl ether acetate, adding 0.25 parts of epoxy-functionalized silica, 0.25 parts of a thermosetting agent, and 0.75 parts of barium sulfate, ball milling for 30 minutes, adding 0.1 parts of phthalocyanine green, 0.15 parts of a reactive diluent, and 0.15 parts of a composite photoinitiator, and stirring at room temperature for 3 hours to obtain a solder resist ink;

[0055] The remaining steps are the same as those in Example 1.

[0056] Comparative Example 1: A process for preparing an ultra-low dielectric constant circuit board, comprising the following steps: A method for preparing a solder resist ink, comprising the following steps: adding 5 parts of a naphthyl photocurable resin to 5 parts of diethylene glycol ethyl ether acetate, adding 0.25 parts of epoxy-functionalized silica, 0.25 parts of a thermosetting agent, and 0.75 parts of barium sulfate, ball milling for 30 minutes, adding 0.1 parts of phthalocyanine green, 0.15 parts of a reactive diluent, and 0.15 parts of a composite photoinitiator, and stirring at room temperature for 3 hours to obtain a solder resist ink;

[0057] The remaining steps are the same as those in Example 1.

[0058] Comparative Example 2: A process for preparing an ultra-low dielectric constant circuit board, comprising the following steps: A method for preparing a solder resist ink, comprising the following steps: adding 5 parts of a polyurethane-modified light-curing epoxy resin to 5 parts of diethylene glycol ethyl ether acetate, adding 0.25 parts of epoxy-functionalized silica, 0.25 parts of a thermosetting agent, and 0.75 parts of barium sulfate, ball milling for 30 minutes, adding 0.1 parts of phthalocyanine green, 0.15 parts of a reactive diluent, and 0.15 parts of a composite photoinitiator, and stirring at room temperature for 3 hours to obtain a solder resist ink;

[0059] The remaining steps are the same as those in Example 1.

[0060] Experiment: Dielectric constant test: According to GB / T1409-2006, the dielectric properties of the circuit boards prepared in the examples and comparative examples were tested using an impedance analyzer at room temperature and a frequency of 10 GHz.

[0061] The experimental results are shown in Table 1 below.

[0062] Table 1 Ultra-low dielectric constant circuit board performance test data table

[0063]

[0064] Conclusion: The circuit board prepared by the present invention has the performance advantage of ultra-low dielectric constant, which is achieved by comprehensively realizing the ultra-low dielectric constant thanks to the rigid structure of naphthalene-based resin, flexible modification of polyurethane, design of vacuum cavity and optimization of process parameters.

[0065] In Comparative Example 1 and Comparative Example 2, only single components of naphthalene-based photocurable resin and polyurethane-modified photocurable epoxy resin were added, respectively, and the synergistic effect between the two components could not be exerted, resulting in a slight decrease in the dielectric constant.

[0066] The solder resist ink prepared in the examples and comparative examples was coated on the surface of release paper, dried at 75°C for 30 min, irradiated with UV light for 60 s, and finally thermally cured at 150°C for 45 min to obtain a test dry film, which was then tested for mechanical properties and thermal stability.

[0067] The mechanical properties and thermal stability glass transition temperature of the dry film were tested, where the mechanical properties range was 2N-18N at a rate of 2N / min, and the thermal stability heating rate was 5°C / min, with a test range up to 270°C.

[0068] The experimental results are shown in Table 2 below.

[0069] Table 2 Solder mask ink dry film performance test data

[0070]

[0071] Conclusion: The solder resist ink prepared by the present invention has excellent mechanical properties and thermal stability.

[0072] In Comparative Example 1 and Comparative Example 2, only single components of naphthalene-based photocurable resin and polyurethane-modified photocurable epoxy resin were added, respectively, and the synergistic effect between the two components could not be exerted, resulting in reduced mechanical properties and thermal stability.

[0073] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A process for preparing an ultra-low dielectric constant circuit board, characterized by: The following steps are involved: S1: Making the inner high-frequency signal circuit: forming the high-frequency signal circuit on the inner substrate through dry film lamination, exposure, development, and etching processes (1); S2: Making solder mask bridges: forming solder mask bridges (2) around the high-frequency signal line (1) through screen printing, exposure, and development processes; S3: Processing the prepreg vacuum cavity area: Covering the prepreg on the same layer as the solder mask bridge (2), removing the prepreg on the upper layer of the high-frequency circuit by mechanical gong plate, forming prepreg grooves (3) on both sides of the solder mask bridge (2); S4: Pressing and forming: pressing the inner substrate and the outer substrate together by browning, arranging and pressing to form an outer semi-finished circuit board including a vacuum cavity (4); S5: Processing non-plated through holes: mechanically drilling non-plated through holes (5) at non-signal line positions in the vacuum cavity (4) area to obtain an ultra-low dielectric constant circuit board; The solder resist bridge (2) is prepared from solder resist ink; The preparation method of the solder resist ink comprises the following steps: Adding naphthalene-based photocurable resin and polyurethane-modified photocurable epoxy resin to diethylene glycol ethyl ether acetate, adding epoxy-functionalized silica, a thermal curing agent, and barium sulfate, ball milling for 30-45 minutes, adding phthalocyanine green, a reactive diluent, and a composite photoinitiator, and stirring at room temperature for 3-4 hours to obtain a solder resist ink; In the preparation process of solder resist ink, the components are calculated by mass, including 2-4 parts of naphthalene-based photocurable resin, 1-3 parts of polyurethane-modified photocurable epoxy resin, 5-7 parts of diethylene glycol ethyl ether acetate, 0.25-0.3 parts of epoxy functionalized silica, 0.25-3 parts of thermosetting agent, 0.75-1 parts of barium sulfate, 0.1-0.15 parts of phthalocyanine green, 0.15-0.2 parts of active diluent, and 0.15-0.2 parts of composite photoinitiator.

2. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: In step S1, the line width tolerance of the high-frequency signal line (1) is ±10 μm.

3. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: In step S2, the median thickness of the solder mask bridge (2) is equal to the thickness of the upper prepreg of the high-frequency signal circuit (1), and the width of the solder mask bridge (2) is 0.1-0.4 mm.

4. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: In step S3, the distance between the prepreg pit (3) and the high-frequency signal line (1) is 0.5-3 mm, the single-side width of the prepreg pit (3) exceeds the width of the solder mask bridge (2) by 0.1 mm, and the thickness of the prepreg is 1.5-2.5 mil.

5. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: In step S4, the platen parameters are temperature of 180-200° C., pressure of 300-400 psi, and time of 90-120 min.

6. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: In step S5, the diameter of the non-plated through hole (5) is 0.25-1 mm, and the number of the non-plated through holes (5) provided in the vacuum cavity (4) is ≥2.

7. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: The preparation method of the naphthalene-based photocurable resin comprises the following steps: Add a naphthyl epoxy monomer to ethyl 2-(2-ethoxyethoxy)acetate, heat to 85-86°C, stir evenly, cool to room temperature, add cholic acid and 4-dimethylaminopyridine, heat to 115-120°C and react for 12-13 hours, cool to room temperature, add 1,2,3,6-tetrahydrophthalic anhydride and hydroquinone, heat to 95-98°C and react for 7-8 hours, add glycidyl methacrylate, heat to 110-115°C and react for 3-4 hours to obtain a naphthyl light-curing resin; In the preparation process of the naphthyl photocurable resin, the mass ratio of naphthyl epoxy monomer: cholic acid: 4-dimethylaminopyridine: 1,2,3,6-tetrahydrophthalic anhydride: hydroquinone: glycidyl methacrylate is 3:5.7:0.052:8.4:0.052:4.

2.

8. The process for preparing an ultra-low dielectric constant circuit board according to claim 7, wherein: The preparation method of naphthyl epoxy monomer comprises the following steps: 1,5-naphthalenediol and ethyl 4-bromobutyrate were added to acetone, stirred evenly, potassium carbonate was added, and the mixture was heated to 70-75°C and refluxed for 3-4 days. The reaction product was extracted with ether and hydrochloric acid, washed with deionized water, dried over anhydrous sodium sulfate, filtered, and the organic layer was collected and evaporated to dryness to obtain compound 1; compound 1 was added to tetrahydrofuran, 0.5 mol / L sodium hydroxide aqueous solution was added, and the mixture was reacted at room temperature for 12-13 hours. 1 mol / L hydrochloric acid aqueous solution was added, and the mixture was reacted for 3-4 days. The mixture was filtered and dried to obtain compound 2; compound 2, glycidol, and 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride were added to tetrahydrofuran, 4-dimethylaminopyridine was added, the mixture was reacted at room temperature for 24-25 hours, rotary evaporated, washed, centrifuged, and dried to obtain a naphthyl epoxy monomer; During the preparation of compound 1, the molar ratio of 1,5-naphthalenediol: ethyl 4-bromobutyrate: potassium carbonate was 9.3:23.1:54; during the preparation of the naphthyl epoxy monomer, the molar ratio of compound 2: glycidol: 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride: 4-dimethylaminopyridine was 10:30:30:

3.

9. The process for preparing an ultra-low dielectric constant circuit board according to claim 1, wherein: The preparation method of polyurethane modified light-curing epoxy resin comprises the following steps: isophorone diisocyanate is added to a reaction vessel, followed by p-hydroxyanisole, dibutyl tin dilaurate, and hydroxyethyl acrylate, and the mixture is heated to 30-32° C. for reaction. When the isocyanate group content in the reaction system reaches the theoretical value, a double-bond terminated polyurethane precursor is obtained; the mixture is further heated to 50-52° C., isophorone diisocyanate, p-hydroxyanisole, and dibutyl tin dilaurate are added, stirred evenly, polyethylene glycol 100 and 2,2-dihydroxymethacrylic acid are added, and the mixture is kept warm for reaction. When the isocyanate group content in the reaction system reaches the theoretical value, a double-bond terminated oligomeric polyurethane is obtained; a light-curable epoxy resin containing a dihydroxy carboxylic acid is added to a reaction vessel, followed by p-hydroxybenzyl ether, dibutyl tin dilaurate, and a double-bond terminated oligomeric polyurethane. The mixture is heated to 50-52° C., and when the isocyanate group content in the reaction system is 0%, the product is purified by adding a methanol aqueous solution and vacuum drying to obtain a polyurethane-modified light-curable epoxy resin; In the preparation process of double-bond terminated polyurethane precursor, the mass ratio of isophorone diisocyanate: p-hydroxyanisole: dibutyl tin dilaurate: hydroxyethyl acrylate is 117:0.17:0.52:59; in the preparation process of double-bond terminated oligomeric polyurethane, the mass ratio of isophorone diisocyanate: p-hydroxyanisole: dibutyl tin dilaurate: polyethylene glycol 100, 2,2-dihydroxymethyl acrylate is 229:0.4:1.2:100:69; In the preparation process of the modified light-curing epoxy resin, the mass ratio of the light-curing epoxy resin containing dihydroxy carboxylic acid: hydroxybenzyl ether: dibutyl tin dilaurate: and double-bond-terminated oligomeric polyurethane is 500:0.99:2.97:

50. The light-curing epoxy resin containing dihydroxy carboxylic acid is prepared by firstly subjecting an epoxy resin to a ring-opening reaction with acrylic acid and 2,2-dihydroxymethylacrylic acid, and then subjecting the epoxy resin to an esterification reaction with 1,2,3,6-tetrahydrophthalic anhydride.

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