Method for manufacturing a medium density board for PCBs

Abstract

A preparation method of a medium density board for PCB, comprising preparation of adhesive, preparation of medium density board, preparation of phenolic resin layer, polyurethane acrylate resin layer and subsequent polishing treatment. A certain content of boron nitride powder is added in the adhesive; a double-layer resin layer is applied on the substrate of the medium density board, and hydroxyl modified nano graphene sheets are added in the resin layer; the preparation of the surface resin layer is improved; the medium density board prepared by the method can effectively reduce hole displacement deviation, hole wall roughness, burr, drilling temperature and burr when used as a backing plate during PCB drilling, improve hole position precision and drill bit wear and punching amount, and ensure the quality of drilling.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of printed circuit board, in particular to a preparation method of medium density board for PCB. BACKGROUND

[0002] The cushion plate is a kind of auxiliary plate-shaped material used for protecting the processed board and drill machine and improving the drilling quality in the process of drilling the printed circuit board. It can protect the circuit board, improve the hole position accuracy, reduce the burr of the hole, help the drill head to dissipate heat and reduce wear, and improve the drilling quality and the service life of the drill bit. The cushion plate can prevent the drill bit from colliding with the drill machine workbench, reduce the burr on the outlet surface, and require a certain hardness to prevent deflection, burr and hole wall contamination. However, the hardness cannot be too high, otherwise the drill bit will be worn out, and the cushion plate will be easily warped. It also needs to be uniform and flat in thickness. If the cushion plate material is not uniform, with irregular distribution of hard spots or soft spots, the drill bit will be easily stuck. If the drill bench is not flat, the drill bit will be easily twisted and broken when the pressure foot is pressed. If the cushion plate is not flat, it cannot match the drill machine workbench, and the drill bit will move up and down with the plate, which will cause the drill bit to break due to unbalanced force when it is retracted, and also affect the drilling accuracy and increase the burr.

[0003] With the rapid development of printed circuit boards, various cushion plate materials have also appeared. Common types of cushion plates include medium-high density wood cushion plates, melamine cushion plates and phenolic resin plates. During high-speed drilling, the drill bit will generate a horizontal centrifugal force on the cover plate, circuit board and cushion plate, which will easily cause the contact interface to deviate. In addition, the cushion plate is easy to form powdery waste which can be brought out by the drill bit and enter the drill hole, affecting the quality of the PCB board. The temperature of the drill bit increases in the high-speed friction environment, which on one hand causes the resin type cushion plate material to melt and stick to the surface of the drill bit, and then remain in the inner wall of the drill hole. SUMMARY

[0004] Based on the defects and deficiencies of the prior art, the present application provides a preparation method of medium density board for PCB. According to the method of the present application, a medium density board with good hardness, reduced PCB drilling burr, avoided drill dust remaining in the drill hole, reduced drill bit wear, and effectively improved PCB drilling quality is prepared.

[0005] In order to solve the technical problems of the present application, the following technical solutions are implemented:

[0006] A preparation method of medium density board for PCB, comprising the following steps:

[0007] (1) Preparation of the adhesive: formaldehyde and methyl phenol with a molar ratio of (1.1-1.2):1 are put into a reactor, then 7-10% of the total mass of the reactants potassium hydroxide is added and mixed uniformly, heated to 65-75°C and reacted for 30-40 min; then 0.2-0.3% of the total mass of the reactants 3-aminopropyl triethoxysilane is added when the temperature is raised to 90-100°C, and the reaction continues for 60-90 min; after the reaction is completed, the temperature is lowered to 25-35°C for vacuum dehydration, 1-2% of the total weight of the reactants boron nitride powder is added, and uniform stirring is continued to obtain the adhesive;

[0008] (2) Preparation of the medium density board: pine fiber powder and bamboo fiber powder are uniformly mixed in a mass ratio of (1-2):(8-9) to obtain mixed fiber powder; the adhesive prepared above and the curing agent are mixed uniformly in a mass ratio of (75-85):(15-25), and then the mixed fiber powder is immediately glued by a gluing device; the mixed fiber powder is laid and hot-pressed to form a medium density board, and then both sides are polished;

[0009] (3) 5-10 parts of hydroxyl-modified nano-graphene sheets are added to 50-70 parts of phenolic resin, then 3-5 parts of tributyl phosphate is added, and the mixture is stirred uniformly to obtain a mixture; the medium density board is soaked in the above mixture for 20-30 min; after being taken out, it is left to stand and dry, and a phenolic resin layer with a thickness of 0.2-0.3 mm is formed on the surface;

[0010] (4) The medium density board obtained in step (3) is coated with UV varnish on both sides, dried and cured to form a polyurethane acrylate resin layer with a thickness of 0.2-0.3 mm on the surface; wherein the composition of the UV varnish is 50-70 parts of polyurethane acrylate resin, 10-20 parts of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, 5-10 parts of hydroxyethyl methacrylate, 5-10 parts of hydroxyl-modified nano-graphene sheets, and 150-200 parts of isopropyl alcohol;

[0011] (5) The surface of the polyurethane acrylate resin layer is polished.

[0012] Further, the curing agent in step (2) is selected from one of ethyl sulfate, benzene sulfonyl chloride, and p-toluenesulfonyl chloride.

[0013] Further, the hot-pressing process parameters in step (2) are: pressure 3.5-4 MPa, temperature 170-180°C, and hot-pressing time 5-10 min; the thickness of the medium density board formed by hot-pressing is 2.5-3.0 mm, and the thickness of the medium density board after polishing is 2.1-2.5 mm.

[0014] Further, the thickness of the hydroxyl-modified nano-graphene sheets in steps (3) and (4) is 10-20 nm, and the diameter is 0.1-0.5 μm.

[0015] Further, the specific process steps of step (4) are as follows: the polyurethane acrylate resin is added to isopropyl alcohol and stirred to fully dissolve, then 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, hydroxyethyl methacrylate, and hydroxyl-modified nanographene sheets are added, and stirring is continued until uniformity is achieved to obtain a UV varnish; the UV varnish is brushed on the phenolic resin layer, and after leveling, it is placed in an oven at 50-60 DEG C for 5-10 min for drying; and finally, it is irradiated with a UV lamp for 1-2 min.

[0016] Further, the roughness (Ra) after polishing treatment is 0.15-0.30, which can effectively prevent the drill from slipping during drilling.

[0017] The application further discloses the medium-density board for PCB drilling prepared by the method.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] (1) The preparation process of the medium-density board substrate is improved, a certain content of boron nitride powder is added to the adhesive, the good hardness, high thermal conductivity and low thermal expansion coefficient of the boron nitride powder are utilized, the overall hardness is effectively improved, the performance of subsequent drilling is guaranteed, and good heat conduction is achieved to reduce the drilling temperature.

[0020] (2) The double-layer resin layer is applied to the substrate of the medium-density board, and the hydroxyl-modified nanographene sheets are added to the resin layer, the drilling temperature is effectively reduced, the molten resin layer is prevented from being attached to the hole wall due to temperature rise to form drill chips, and the hole wall roughness is reduced.

[0021] (3) The preparation of the surface resin layer is improved, the hardness of the resin layer formed by the surface resin layer is higher than 85, and the expansion of burrs and burrs during drilling is effectively inhibited.

[0022] (4) The medium-density board prepared by the application is used as a pad plate during PCB drilling, the hole displacement deviation, hole wall roughness, burrs, drilling temperature and burrs are effectively reduced, the hole position precision and drill wear and drilling amount are improved, and the drilling quality is guaranteed. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and effect of the application more clear and definite, the application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the application.

[0024] Example 1

[0025] A preparation method of a medium-density board for PCB, comprising the following steps:

[0026] (1) Preparation of the adhesive: formaldehyde and methyl phenol with a molar ratio of 1.1:1 were placed in a reactor, then 7% of potassium hydroxide based on the total mass of the reactants was added and mixed uniformly, heated to 65°C and reacted for 30 min; then 0.2% of 3-aminopropyl triethoxysilane based on the total mass of the reactants was added when the temperature was raised to 90°C, and the reaction was continued for 60 min; after the reaction was completed, the temperature was lowered to 25°C for vacuum dehydration, 1% of boron nitride powder based on the total weight of the reactants was added, and uniform stirring was continued to obtain the adhesive;

[0027] (2) Preparation of the medium density board: pine fiber powder and bamboo fiber powder were uniformly mixed in a mass ratio of 1:9 to obtain mixed fiber powder; the adhesive prepared above and the curing agent ethyl sulfate were mixed uniformly in a mass ratio of 75:25, and then the mixed fiber powder was immediately glued by a gluing device; the mixed fiber powder was laid and hot-pressed to form a medium density board, and then both sides were polished; the hot-pressing process parameters were: pressure 3.5 MPa, temperature 170°C, hot-pressing time 5 min; the thickness of the medium density board formed by hot-pressing was 3.0 mm, and the thickness of the medium density board after polishing was 2.5 mm.

[0028] (3) 5 parts of hydroxyl-modified nano-graphene sheets were added to 50 parts of phenolic resin, then 3 parts of tributyl phosphate were added, and the mixture was stirred uniformly to obtain a mixture; the medium density board was soaked in the above mixture for 20 min; after taking out, it was placed and dried, and a phenolic resin layer with a thickness of 0.2 mm was formed on the surface;

[0029] (4) 50 parts of polyurethane acrylate resin were added to 150 parts of isopropyl alcohol and stirred to dissolve completely, then 10 parts of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, 5 parts of hydroxyethyl methacrylate, and 5 parts of hydroxyl-modified nano-graphene sheets were added, and the mixture was stirred uniformly to obtain a UV varnish; the UV varnish was brushed on the phenolic resin layer, leveled, and then placed in an oven at 50°C for drying for 5 min; finally, it was irradiated with an ultraviolet lamp for 1 min; a phenolic resin layer with a thickness of 0.2 mm was formed on the surface;

[0030] (5) The surface of the polyurethane acrylate resin layer was polished.

[0031] Example 2

[0032] A method for preparing a medium density board for PCB, comprising the following steps:

[0033] (1) Preparation of the adhesive: formaldehyde and methyl phenol with a molar ratio of 1.2:1 were placed in a reactor, then 10% of the total mass of the reactants was added potassium hydroxide and mixed uniformly, heated to 75°C and reacted for 40 min; then 0.3% of the total mass of the reactants was added 3-aminopropyl triethoxysilane at 100°C, and the reaction continued for 90 min; after the reaction was completed, the temperature was lowered to 35°C for vacuum dehydration, 2% of the total weight of the reactants was added boron nitride powder, and uniform stirring was continued to obtain the adhesive;

[0034] (2) Preparation of the medium density board: pine fiber powder and bamboo fiber powder were uniformly mixed in a mass ratio of 2:8 to obtain mixed fiber powder; the adhesive prepared above was mixed with curing agent ethyl sulfate in a mass ratio of 85:15, and then the mixed fiber powder was immediately glued by a gluing device; the mixed fiber powder was laid and hot-pressed to form a medium density board, and then double-sided polishing was performed; the hot-pressing process parameters were: pressure 4 MPa, temperature 180°C, hot-pressing time 10 min; the thickness of the medium density board formed by hot-pressing was 2.5 mm, and the thickness of the medium density board after polishing was 2.1 mm.

[0035] (3) 20 parts of hydroxyl-modified nano-graphene sheets were added to 70 parts of phenolic resin, then 5 parts of tributyl phosphate was added, and the mixture was stirred uniformly to obtain a mixture; the medium density board was soaked in the above mixture for 30 min; after taking out, it was placed and dried, and a phenolic resin layer with a thickness of 0.3 mm was formed on the surface;

[0036] (4) 70 parts of polyurethane acrylate resin was added to 200 parts of isopropyl alcohol and stirred to dissolve completely, then 20 parts of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, 10 parts of hydroxyethyl methacrylate, and 10 parts of hydroxyl-modified nano-graphene sheets were added, and the mixture was stirred uniformly to obtain a UV varnish; the UV varnish was brushed on the phenolic resin layer, and after leveling, it was placed in an oven at 60°C for drying for 10 min; finally, it was irradiated with ultraviolet lamp for 2 min; a phenolic resin layer with a thickness of 0.5 mm was formed on the surface;

[0037] (5) The surface of the polyurethane acrylate resin layer was polished.

[0038] Example 3

[0039] A method for preparing a medium density board for PCB, comprising the following steps:

[0040] (1) Preparation of adhesive: Formaldehyde and methylphenol with a molar ratio of 1.15:1 were placed in a reactor, and then 8% potassium hydroxide (total mass of reactants) was added and mixed evenly. The mixture was heated to 70°C and reacted for 35 min. Then, when the temperature was raised to 95°C, 0.25% 3-aminopropyltriethoxysilane (total mass of reactants) was added and the reaction was continued for 80 min. After the reaction was completed, the temperature was lowered to 30°C for vacuum dehydration. Boron nitride powder (total weight of reactants) was added and stirred evenly to obtain the adhesive.

[0041] (2) Preparation of medium density board: Pine fiber powder and bamboo fiber powder are mixed evenly at a mass ratio of 1.5:8.5 to obtain mixed fiber powder; the adhesive prepared above is mixed evenly with curing agent ethyl sulfate at a mass ratio of 80:20 and then applied to the mixed fiber powder through an adhesive applicator; the mixed fiber powder is laid out and hot-pressed to form medium density board, and then double-sided sanding is performed; the hot-pressing process parameters are: pressure 3.7MPa, temperature 175℃, hot-pressing time 7min; the thickness of the medium density board formed by hot pressing is 2.7mm, and the thickness of the medium density board after sanding is 2.4mm.

[0042] (3) Add 5 parts of hydroxyl-modified nano-graphene sheets to 60 parts of phenolic resin, then add 4 parts of tributyl phosphate, stir thoroughly to obtain a mixture; immerse medium density board in the above mixture for 25 minutes; remove and let stand and dry to form a phenolic resin layer with a thickness of 0.25 mm on the surface.

[0043] (4) Add 60 parts of polyurethane acrylate resin to 180 parts of isopropanol and stir until fully dissolved. Then add 15 parts of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 7 parts of hydroxyethyl methacrylate, and 8 parts of hydroxyl-modified nanographene sheets. Continue stirring until uniform to obtain UV varnish. Brush the UV varnish onto the phenolic resin layer, level it, and place it in an oven at 55°C to dry for 8 minutes. Finally, irradiate with a UV lamp for 1.5 minutes to form a phenolic resin layer with a thickness of 0.24 mm on the surface.

[0044] (5) Polish the surface of the polyurethane acrylate resin layer.

[0045] To facilitate a better comparison, the applicant conducted a comparative experiment on the technical solution.

[0046] Comparative Example 1

[0047] Comparative Example 1 follows the same steps as Example 1, except that boron nitride powder is not added in step (1).

[0048] Comparative Example 2

[0049] Comparative Example 2 follows the same steps as Example 1, except that hydroxyl-modified nanographene sheets are not added in step (3).

[0050] Comparative Example 3

[0051] Comparative Example 3 and Example 1 are the same in steps, the only difference is that no hydroxyl modified nanographene sheet is added in step (4).

[0052] Comparative Example 4

[0053] Comparative Example 1 and Example 1 are the same in steps, the only difference is that no boron nitride powder is added in step (1), and no hydroxyl modified nanographene sheet is added in steps (3) and (4).

[0054] II. The basic parameters of the medium density board are detected, and the detection results are recorded in Table 1.

[0055] Table 1

[0056]

[0057] Boron nitride has good hardness, high thermal conductivity and low thermal expansion coefficient. The application of boron nitride in the medium density board substrate can effectively improve the overall hardness of the substrate and effectively avoid the warping of the substrate. The high thermal conductivity can effectively transfer the temperature of the surface resin layer during drilling, thereby avoiding the temperature rise of the drill needle.

[0058] The hydroxyl modified nanographene sheet also has excellent thermal conductivity and good lubricity. The use of the hydroxyl modified nanographene sheet in the resin layer can accelerate heat conduction on the one hand, and can improve the surface hardness on the other hand. The appropriate lubricity can avoid the breakage of the drill needle during high-speed drilling. If the surface layer also uses boron nitride, the high hardness of boron nitride can easily lead to the breakage of the drill needle. Therefore, the application tries to use a small amount of boron nitride in the substrate, and add a large amount of hydroxyl modified nanographene sheet in the resin layer.

[0059] II. According to the industry standard, the drilling test is carried out, and the test conditions are: hole diameter 0.25mm, rotation speed 150kr / min, feed speed 25mm / s, and retreat speed 300mm / s. The specific result indexes are recorded in Table 2 below.

[0060] Table 2

[0061]

[0062] Drill bit wear is an important factor affecting drilling efficiency, and the service life of the drill bit is closely related. The service life of the drill bit is generally about 2500 holes. Through the improvement of the medium density board in the application, the addition of hydroxyl modified nanographene sheets in the resin layer effectively reduces the drilling temperature, so that the temperature rise of the drill bit is not too intense, effectively reduces the drilling wear, and improves the service life of the drill bit. On the other hand, due to the decrease of the drilling temperature, the resin layer is not easy to melt, so it will not be left on the surface of the drill bit, and the drilling drill residue will also be significantly reduced. Without adding hydroxyl modified nanographene sheets, due to the relatively high temperature, part of the resin layer melts and remains on the surface of the drill bit, the roughness of the inner wall of the drilling hole also increases, and a small amount of adhesion also occurs.

[0063] From the data of Example 1 and Comparative Example 1, it can be seen that in the case of not adding boron nitride powder, the indicators are basically similar to those of adding boron nitride powder, and the difference is not large; the only big difference is the drilling temperature; the difference is caused by the relatively poor thermal conductivity of the medium density board substrate, which causes the drilling heat transfer to be less uniform than that of Example 1. Therefore, it can also be seen that boron nitride powder is also beneficial to improving the drilling quality.

[0064] From the data of Example 1 and Comparative Examples 2-3, it can be seen that in the case of not adding hydroxyl modified nanographene sheets in the single resin layer, the indicators are quite different from those of adding hydroxyl modified nanographene sheets, and the reason is that hydroxyl modified nanographene sheets are beneficial to heat dissipation of the resin layer, thereby reducing the drilling temperature and avoiding the melting of the resin layer to cause blockage and residue of the hole wall.

[0065] From the data of Example 1 and Comparative Example 4, it can be seen that in the case of not adding hydroxyl modified nanographene sheets in the two resin layers, the performance indicators are far worse than those of the application. Therefore, it can be seen that the addition of hydroxyl modified nanographene sheets can significantly improve the drilling performance of the medium density board.

[0066] When the medium density board prepared by the method of the application is used as a drilling pad, the hole displacement deviation, the hole wall roughness, the burr, the drilling temperature and the burr are effectively reduced, the hole position precision and the drill bit wear are improved, and the drilling quality is ensured.

[0067] It should be understood that the application of the application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the application.

Claims

1. A method of producing a medium density board for PCBs, characterized by, It comprises the following steps: (1) Preparation of adhesive: formaldehyde and methyl phenol with a molar ratio of (1.1-1.2):1 are put into a reactor, then 7-10% of potassium hydroxide of the total mass of the reactants is added and uniformly mixed, heated to 65-75 DEG C and reacted for 30-40 min; then 0.2-0.3% of 3-aminopropyl triethoxysilane of the total mass of the reactants is added when the temperature is raised to 90-100 DEG C, and the reaction is continued for 60-90 min; after the reaction is completed, the temperature is lowered to 25-35 DEG C for vacuum dehydration, 1-2% of boron nitride powder of the total weight of the reactants is added, and uniform stirring is continued to obtain the adhesive; (2) Preparation of medium density board: pine fiber powder and bamboo fiber powder are uniformly mixed according to a mass ratio of (1-2):(8-9) to obtain mixed fiber powder; the adhesive prepared above and a curing agent are uniformly mixed according to a mass ratio of (75-85):(15-25), and then the mixed fiber powder is immediately glued by a gluing device; the mixed fiber powder is laid and hot-pressed to form a medium density board, and then the board is double-sided polished; (3) 5-10 parts of hydroxyl-modified nano-graphene sheets are added to 50-70 parts of phenolic resin, then 3-5 parts of tributyl phosphate is added, and the mixture is uniformly stirred to obtain a mixture; the medium density board is soaked in the mixture for 20-30 min; after being taken out, it is left to stand and dry, and a phenolic resin layer with a thickness of 0.2-0.3 mm is formed on the surface; (4) The medium density board obtained in step (3) is coated with UV varnish on both sides, dried and cured to form a polyurethane acrylate resin layer with a thickness of 0.2-0.3 mm on the surface; wherein the composition of the UV varnish comprises 50-70 parts of polyurethane acrylate resin, 10-20 parts of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, 5-10 parts of hydroxyethyl methacrylate, 5-10 parts of hydroxyl-modified nano-graphene sheets, and 150-200 parts of isopropyl alcohol; (5) The surface of the polyurethane acrylate resin layer is polished.

2. The method of producing a medium density board for a PCB according to claim 1, wherein, The curing agent in step (2) is selected from one of ethyl sulfate, benzene sulfonyl chloride, and p-toluenesulfonyl chloride.

3. The method of claim 1, wherein the medium density board for a PCB is prepared by the steps of: The hot-pressing process parameters in step (2) are: pressure 3.5-4 MPa, temperature 170-180 DEG C, and hot-pressing time 5-10 min; the thickness of the medium density board formed by hot-pressing is 2.5-3.0 mm, and the thickness of the medium density board after polishing is 2.1-2.5 mm.

4. The method of producing a medium density board for a PCB according to claim 1, wherein The thickness of the hydroxyl-modified nano-graphene sheets in steps (3) and (4) is 10-20 nm, and the diameter is 0.1-0.5 μm.

5. The method of producing a medium density board for a PCB according to claim 1, wherein The specific process steps of step (4) are as follows: polyurethane acrylate resin is added to isopropyl alcohol and stirred to dissolve completely, then 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, hydroxyethyl methacrylate, and hydroxyl-modified nano-graphene sheets are added, and the mixture is uniformly stirred to obtain UV varnish; the UV varnish is brushed on the phenolic resin layer, leveled, and then placed in an oven at 50-60 DEG C for drying for 5-10 min; finally, it is irradiated with a UV lamp for 1-2 min.

6. The method of producing a medium density board for a PCB according to claim 1, wherein The roughness Ra after polishing is 0.15-0.

30.

7. A medium density board for PCBs, prepared according to the process of any one of claims 1 to 6, characterized in that: It is used for PCB drilling pads.

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