A laminate of a printed circuit board and a method for preparing the same

Abstract

The present invention discloses a laminate of a printed circuit board and a preparation method thereof. The present invention prepares a precursor solution by a simple method, and the precursor solution forms a porous bonding layer when heated, and the porous structure enhances the bonding strength between the resin layer and the carrier foil; preferably, the carrier foil is a super-smooth carrier foil, and the super-smooth carrier foil can achieve high-frequency and high-speed transmission of circuit board signals.

Description

Technical Field

[0001] The present invention relates to the field of printed circuit boards, and particularly to a laminate of a printed circuit board and a preparation method thereof. Background Art

[0002] With the advent of the 5G era, the high-frequency and high-speed requirements of communication devices have become increasingly prominent. As the substrate material of a printed circuit board (PCB) that connects semiconductor devices, its high-frequency and high-speed development is particularly crucial. Compared with low-frequency and low-speed signals, when high-frequency and high-speed signals are transmitted, the skin effect is more serious, that is, the signals are more concentrated on the surface layer of the copper conductor. At this time, the influence of the surface roughness of the copper foil on signal loss increases exponentially. Therefore, compared with conventional electronic copper foils, electronic copper foils for high-frequency and high-speed applications need to use a low-roughness surface to reduce signal loss. However, the reduction of roughness will inevitably lead to a decrease in the interfacial bonding strength between the copper foil and the resin in the PCB substrate, making it difficult to meet the reliability specification requirements of the PCB. Therefore, how to ensure good interfacial bonding strength while reducing the surface roughness of the copper foil is one of the key problems faced by high-frequency and high-speed PCB substrates. The interfacial bonding strength between the copper foil and the resin in the PCB substrate mainly comes from two aspects: one is the mechanical anchoring effect provided by the rough profile of the copper foil surface; the other is the chemical bonding effect generated between the copper foil and the resin, and usually a silane coupling agent that can connect the inorganic / organic interface is used to achieve effective chemical bonding force. For conventional PCB substrates, the surface roughness of the copper foil is relatively large, and the interfacial bonding strength mainly comes from the mechanical anchoring effect, and the chemical bonding plays an auxiliary role. For high-frequency and high-speed PCB substrates, the roughness of the copper foil is greatly reduced, the mechanical anchoring effect is strongly reduced, and the chemical bonding effect cannot provide sufficient bonding force.

[0003] In order to meet the application of high-frequency and high-speed PCB substrates, it is very important to take measures to increase the chemical bonding effect. At present, improving the chemical bonding effect is mainly divided into two aspects. First: developing new interfacial adhesives, such as modified silane coupling agents, etc.; second: directly modifying the substrate (usually the resin) to increase its surface chemical activity. However, there are difficult-to-handle problems when using silane coupling agents, and the adhesion to the resin is also insufficient. Modifying the resin usually involves additional processing steps, the cost cannot be controlled, and the means of resin modification have limited improvement in the bonding strength. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a laminate of a printed circuit board and a preparation method thereof; the prepared porous bonding layer is beneficial to improving the bonding strength between the carrier foil and the resin layer; on the one hand, after hot-pressing the resin to form a laminate, a negative pressure will be formed in the porous layer, enhancing the mechanical anchoring effect between the resin and the substrate; on the other hand, the porous bonding layer can be tightly bonded to the carrier foil and the resin through chemical bonding.

[0005] To solve the above technical problems, the first aspect of the present invention is to provide a laminate for a printed circuit board, which specifically includes the following steps:

[0006] A carrier foil;

[0007] A porous adhesive layer disposed on the carrier foil;

[0008] A resin layer disposed on the porous adhesive layer.

[0009] Furthermore, the thickness of the porous adhesive layer is 50 - 1000 nm; for example, 50 nm, 100 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, and 1000 nm, etc., including but not limited to the listed thicknesses; preferably 200 - 500 nm.

[0010] Furthermore, the pore size of the porous adhesive layer is 50 - 500 nm; for example, 50 nm, 100 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, and 500 nm, etc., including but not limited to the listed pore sizes; preferably 200 - 400 nm.

[0011] Furthermore, the roughness of the carrier foil is 0.01 - 0.3 μm; preferably 0.1 μm.

[0012] Furthermore, the carrier foil includes but is not limited to copper foil and aluminum foil.

[0013] Furthermore, the porous adhesive layer is obtained by coating a precursor solution on the carrier foil and heating; the precursor solution contains the following components: lithium bis(trifluoromethanesulfonyl)imide, zinc nitrate, a thermal decomposition gas-generating substance, ethyl acetate, water, and ammonia water.

[0014] Furthermore, the volume ratio of ethyl acetate : water : ammonia water in the precursor solution is (1 - 2) : (1 - 2) : (1 - 2).

[0015] Furthermore, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to zinc nitrate and the thermal decomposition gas-generating substance in the precursor solution is (5 - 30) : (10 - 30) : (5 - 30).

[0016] Furthermore, the ratio range of the total mass of lithium bis(trifluoromethanesulfonyl)imide, zinc nitrate, and the thermal decomposition gas-generating substance in the precursor solution to the total volume of ethyl acetate, water, and ammonia water is (10 - 100) mg : 1 mL. The preferred ratio range is (20 - 90) mg : 1 mL

[0017] Further, the thermal decomposition gas-producing substance is selected from one or more of ammonium bicarbonate, sodium bicarbonate, sodium carbonate, ammonium carbonate, hydrogen peroxide, ammonium chloride, and ammonium nitrate.

[0018] Further, the bonding strength between the carrier foil and the resin is 0.3 - 0.6 N / mm

[0019] The second aspect of the present invention is to provide a method for preparing the laminate described in the first aspect, specifically including the following steps:

[0020] (1) Place the carrier foil on a heating table, coat the precursor solution on the carrier foil, and heat to obtain the porous bonding layer;

[0021] (2) Bond the resin semi-cured sheet to the side of the porous bonding layer away from the carrier foil; hot press to form a resin layer.

[0022] Further, the coating methods include but are not limited to drop coating, spin coating, spraying, screen printing, and vapor deposition.

[0023] Further, the heating temperature in step (1) is 150 - 250 °C.

[0024] Further, in step (2), the hot pressing temperature is 150 - 250 °C; the hot pressing pressure is 0.1 - 1 Mpa; preferably 0.1 Mpa.

[0025] Further, in step (2), the hot pressing time is 10 - 60 min; for example, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, etc., including but not limited to the times listed above. Preferably 10 - 30 min.

[0026] Advantages of the present invention:

[0027] A new interfacial bonding layer is prepared by a simple and economical method. The preparation process of the bonding layer precursor solution is simple, without additional processing steps, reducing costs and facilitating industrial production and application.

[0028] The porous bonding layer prepared by the present invention can be firmly bonded to the ultra-smooth copper. At the same time, the specific surface area of the porous structure is large, and the pores form negative pressure, thereby enhancing the bonding strength between the copper foil and the resin. The porous structure can not only produce a mechanical anchoring effect with the resin, but also provide bonding force through chemical bonding of metal ions with the functional groups of the resin and the carrier foil, thus improving the interfacial bonding strength. Description of the Drawings

[0029] Figure 1 is a planar scanning electron micrograph of the ultra-smooth copper foil used in the present invention;

[0030] Figure 2It is the plan view scanning electron micrograph of the porous coating prepared in Example 1 of the present invention;

[0031] Figure 3 It is the cross-sectional scanning electron micrograph of the porous coating prepared in Example 1 of the present invention;

[0032] Figure 4 It is the plan view scanning electron micrograph of the porous coating prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the exemplified embodiments are not intended to limit the present invention.

[0034] The ultra-smooth copper foil in the embodiments of the present invention is purchased from Sinopharm Group, with a roughness Rz = 0.1um; the thickness is 18um; the resin used is purchased from Sinopharm Group, which is divinylbenzene resin, and the thickness is 0.4mm.

[0035] Example 1

[0036] This example relates to a porous coating, and the specific preparation method is as follows:

[0037] At room temperature, 5mg of LiTFSI, 10mg of ZnNO3 and 5mg of NH4HCO3 powder raw materials are dissolved in 1mL of a mixed solvent (the volume ratio of ethyl acetate: water: ammonia water is 1:1:1), and stirred evenly. The ultra-smooth copper surface is ultrasonically cleaned with ethanol and dried for later use. The ultra-smooth copper is heated on a hot stage, the heating temperature is 150 degrees, the precursor solution is evenly sprayed on the copper surface, and the heating time is 10min, so as to form a porous coating on the ultra-smooth copper surface.

[0038] Scanning electron microscopy shows that the ultra-smooth copper surface is relatively flat and there are no hole distributions ( Figure 1 ); while the porous coating includes a large number of holes, the pore diameter is about 200nm ( Figure 2 ), and the thickness is about 200nm ( Figure 3 ). The ultra-smooth copper and the resin semi-cured sheet are placed on a hot stage, the hot stage temperature is 150 degrees, a pressure of 0.1MPa is applied, and the hot pressing time is 10min until the resin is completely cured. Without the porous coating, the bonding strength between the ultra-smooth copper and the resin is 0.11N / mm. When the porous coating is present, the bonding strength between the ultra-smooth copper and the resin is increased to 0.31N / mm.

[0039] Example 2

[0040] This example relates to a porous coating, and the specific preparation method is as follows:

[0041] Dissolve 10 mg of the powder raw material LiTFSI, 20 mg of ZnNO3, and 10 mg of NH4HCO3 in 1 mL of a mixed solvent (ethyl acetate, water, and ammonia water, with a volume ratio of 1:1:1) at room temperature and stir evenly. Ultrasonically clean the surface of the ultra-smooth copper with ethanol and dry it. Heat the ultra-smooth copper on a hot stage at a heating temperature of 200 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min to form a porous coating on the ultra-smooth copper surface. Scanning electron microscopy shows that the surface of the ultra-smooth copper is relatively flat without hole distribution, while the porous coating includes a large number of holes with a pore diameter of about 300 nm and a thickness of about 400 nm. Place the ultra-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. This porous coating increases the bonding strength between the ultra-smooth copper and the resin to 0.43 N / mm.

[0042] Example 3

[0043] This example relates to a porous coating, and the specific preparation method is as follows:

[0044] Dissolve 30 mg of the powder raw material LiTFSI, 30 mg of ZnNO3, and 30 mg of NH4HCO3 in 1 mL of a mixed solvent (ethyl acetate, water, and ammonia water, with a volume ratio of 1:1:1) at room temperature and stir evenly. Ultrasonically clean the surface of the ultra-smooth copper with ethanol and dry it. Heat the ultra-smooth copper on a hot stage at a heating temperature of 250 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min to form a porous coating on the ultra-smooth copper surface. Scanning electron microscopy shows that the surface of the ultra-smooth copper is relatively flat without hole distribution, while the porous coating includes a large number of holes with a pore diameter of about 300 nm and a thickness of about 400 nm. Place the ultra-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. This porous coating increases the bonding strength between the ultra-smooth copper and the resin to 0.55 N / mm.

[0045] Example 4

[0046] This example relates to a porous coating, and the specific preparation method is as follows:

[0047] Dissolve 10 mg of the powder raw material LiTFSI, 20 mg of ZnNO3, and 10 mg of NH4HCO3 in 1 mL of a mixed solvent (ethyl acetate, water, and ammonia water, with a volume ratio of 1:2:1) at room temperature and stir evenly. Ultrasonically clean the surface of the super-smooth copper with ethanol and then dry it. Heat the super-smooth copper on a hot stage at a heating temperature of 200 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min to form a porous coating on the surface of the super-smooth copper. Scanning electron microscopy shows that the surface of the super-smooth copper is relatively flat without pore distribution, while the porous coating includes a large number of pores with a pore diameter of about 350 nm and a thickness of about 500 nm. Place the super-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. This porous coating increases the bonding strength between the super-smooth copper and the resin to 0.47 N / mm.

[0048] Example 5

[0049] This example relates to a porous coating, and the specific preparation method is as follows:

[0050] Dissolve 10 mg of the powder raw material LiTFSI, 20 mg of ZnNO3, and 10 mg of NH4HCO3 in 1 mL of a mixed solvent (ethyl acetate, water, and ammonia water, with a volume ratio of 1:1:2) at room temperature and stir evenly. Ultrasonically clean the surface of the super-smooth copper with ethanol and then dry it. Heat the super-smooth copper on a hot stage at a heating temperature of 200 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min to form a porous coating on the surface of the super-smooth copper. Scanning electron microscopy shows that the surface of the super-smooth copper is relatively flat without pore distribution, while the porous coating includes a large number of pores with a pore diameter of about 400 nm and a thickness of about 500 nm. Place the super-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. This porous coating increases the bonding strength between the super-smooth copper and the resin to 0.51 N / mm.

[0051] Example 6

[0052] This example relates to a porous coating, and the specific preparation method is as follows:

[0053] Dissolve 10 mg of the powder raw material LiTFSI, 20 mg of ZnNO3, and 10 mg of NH4HCO3 in 1 mL of a mixed solvent (ethyl acetate, water, and ammonia water, with a volume ratio of 2:1:1) at room temperature and stir evenly. Ultrasonically clean the surface of the ultra-smooth copper with ethanol and dry it. Heat the ultra-smooth copper on a hot stage at a heating temperature of 200 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min to form a porous coating on the ultra-smooth copper surface. Scanning electron microscopy shows that the surface of the ultra-smooth copper is relatively flat without hole distribution, while the porous coating includes a large number of holes with a pore diameter of about 250 nm and a thickness of about 400 nm. Place the ultra-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. This porous coating increases the bonding strength between the ultra-smooth copper and the resin to 0.54 N / mm.

[0054] Example 7

[0055] This example relates to a porous coating, and the specific preparation method is as follows:

[0056] Dissolve 30 mg of the powder raw material LiTFSI, 30 mg of ZnNO3, and 30 mg of NaHCO3 in 1 mL of a mixed solvent (ethyl acetate, water, and ammonia water, with a volume ratio of 1:1:1) at room temperature and stir evenly. Ultrasonically clean the surface of the ultra-smooth copper with ethanol and dry it. Heat the ultra-smooth copper on a hot stage at a heating temperature of 250 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min to form a porous coating on the ultra-smooth copper surface. Scanning electron microscopy shows that the surface of the ultra-smooth copper is relatively flat without hole distribution, while the coating includes a certain number of holes with a pore diameter of about 150 nm and a thickness of about 400 nm. Place the ultra-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. This coating increases the bonding strength between the ultra-smooth copper and the resin to 0.35 N / mm.

[0057] Comparative Example 1

[0058] Dissolve 30 mg of the powder raw materials LiTFSI, 30 mg of ZnNO3, and 30 mg of NH4HCO3 in 1 mL of a mixed solvent (water and ammonia water, volume ratio 2:1) at room temperature and stir evenly. Ultrasonically clean the surface of the super-smooth copper with ethanol and dry it. Heat the super-smooth copper on a hot stage at a heating temperature of 250 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min. Scanning electron microscopy shows that the surface of the super-smooth copper is relatively flat without pore distribution, while the pores in the coating decrease, the pore diameter is about 100 nm, and the thickness is about 400 nm. Place the super-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured.

[0059] The bonding strength between the super-smooth copper and the resin with this coating is 0.15 N / mm, and the bonding strength is lower than that of the sample prepared when ethyl acetate is contained in the solvent. The results show that ethyl acetate in the mixed solvent is beneficial to the formation of a porous structure. As Figure 4 shown, the pore diameter of the porous layer in the scanning electron microscopy becomes smaller because ethyl acetate is volatile and easily forms a porous structure.

[0060] Comparative Example 2

[0061] Dissolve 30 mg of the powder raw materials LiTFSI, 30 mg of ZnNO3, and 30 mg of NH4HCO3 in 1 mL of a mixed solvent (ethyl acetate and water, volume ratio 1:2) at room temperature and stir evenly. Ultrasonically clean the surface of the super-smooth copper with ethanol and dry it. Heat the super-smooth copper on a hot stage at a heating temperature of 250 °C, evenly spray the precursor solution on the copper surface, and heat for 20 min. Scanning electron microscopy shows that the surface of the super-smooth copper is relatively flat without pore distribution, while the pores in the coating decrease, the pore diameter is about 100 nm, and the thickness is about 400 nm. Place the super-smooth copper and the resin semi-cured sheet on the hot stage at a hot stage temperature of 150 °C, apply a pressure of 0.1 MPa, and hot press for 10 min until the resin is completely cured. The bonding strength between the super-smooth copper and the resin with this coating is 0.17 N / mm, and the bonding strength is lower than that of the sample prepared when ammonia water is contained in the solvent. The results show that ammonia water in the mixed solvent is beneficial to the formation of a porous structure.

[0062] The above-described embodiments are merely preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A laminate of a printed circuit board, characterized in that: include: carrier foil; A porous adhesive layer disposed on the carrier foil; A resin layer disposed on the porous bonding layer; The porous bonding layer is obtained by coating a precursor solution on the carrier foil and heating the precursor solution; the precursor solution comprises the following components: lithium bis(trifluoromethylsulfonyl)imide, zinc nitrate, thermal decomposition gas-generating substances, ethyl acetate, water and ammonia water.

2. The laminate according to claim 1, wherein The thickness of the porous bonding layer is 50-1000 nm.

3. The laminate according to claim 1, wherein The pore size of the porous bonding layer is 50-500 nm.

4. The laminate according to claim 1, wherein The roughness of the carrier foil is 0.01-0.3 um.

5. The laminate according to claim 1, wherein The volume ratio of ethyl acetate: water: aqueous ammonia in the precursor solution is (1-2): (1-2): (1-2).

6. The laminate according to claim 1, wherein The mass ratio of lithium bis(trifluoromethylsulfonyl)imide to zinc nitrate and thermal decomposition gas-generating substances in the precursor solution is (5-30):(10-30):(5-30).

7. The laminate according to claim 1 or 6, wherein The thermal decomposition gas-generating substance is selected from one or more of ammonium bicarbonate, sodium bicarbonate, sodium carbonate, ammonium carbonate, hydrogen peroxide, ammonium chloride and ammonium nitrate.

8. A method for preparing a laminate according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) placing a carrier foil on a heating platform, coating a precursor solution on the carrier foil, and heating to obtain the porous bonding layer; (2) Laying a resin prepreg on the side of the porous adhesive layer away from the carrier foil; and hot pressing to form a resin layer.

9. The method according to claim 8, characterized in that The heating temperature in step (1) is 150-250°C.

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