Fine circuit printed circuit board and preparation method thereof

Abstract

The invention provides a fine circuit printed circuit board and a preparation method thereof. The fine circuit printed circuit board comprises a substrate made of a glass cloth resin material; the base copper comprises chemical copper and copper foil; the bonding layer is made of an organic silicon resin material, the bonding layer is located between the substrate and the base copper, one surface of the bonding layer is bonded with the substrate, and the other surface of the bonding layer is bonded with the chemical copper; wherein the thickness value of the bonding layer ranges from 2 microns to 4 microns; the bonding force between the bonding layer and the substrate is larger than the bonding force between the base copper and the substrate. The bonding layer made of the organic silicon resin is added, and the organic silicon resin is used as a middle layer between the glass cloth resin and the traditional chemical copper, so that the bonding force between the substrate made of the glass cloth resin and the chemical copper is effectively improved, the manufacturing of a refined circuit is realized, and the transformation cost of the original MSAP process equipment is not high.

Description

Technical Field

[0001] The present application relates to the field of printed circuit boards, and in particular to a fine line printed circuit board and a preparation method thereof. Background Art

[0002] In terms of the fine circuit process of circuit boards, there are mainly two processes in the industry: MSAP and SAP. MSAP is the abbreviation of Modified Semi-Additive Process, and SAP is the abbreviation of Semi-Additive Process. In recent years, with the research and development of high-resolution LDI (laser direct imaging) equipment and high-resolution, high-density dry films, a very small number of manufacturers have achieved mass production of fine circuits using the MSAP process, but the production of more fine circuits still relies on the SAP process.

[0003] Compared with the MSAP process, the SAP process uses different main materials, equipment, and chemicals. For manufacturers that already have the MSAP process, if they change to the SAP process, the change means a huge investment, the equipment also needs to be re-arranged, and even a new factory needs to be built, which is very costly. A more realistic approach is to borrow the existing MSAP process and equipment, improve on this basis, and then try to achieve the level of refined circuit production.

[0004] Figure 1 The schematic diagram showing the comparison of the process characteristics of SAP and MSAP is shown. Figure 2 The diagram shows a comparison of the circuits formed by the etching amounts of SAP and MSAP. The biggest difference between the SAP and MSAP processes is that the SAP process uses chemical copper as the base copper, while the MSAP process uses extremely thin copper foil as the base copper. Under the same process flow and dry film capacity, MSAP has a large base copper thickness due to the mutual adhesion of chemical copper 1 and copper foil 2. A correspondingly large etching amount is required to form the circuit in the later stage. The circuit formed at this time is thinner than the expected target circuit, which is not suitable for high-density fine circuit formation. The formed circuit has a thinner thickness value, which may cause the "line thinness" problem.

[0005] Figure 3 A comparison diagram showing whether the chemical copper of SAP and MSAP is peeled off is shown. To obtain finer circuits, the base copper thickness must be reduced as much as possible. However, if the base copper thickness is infinitely reduced or even exposed to the substrate, the bonding strength between the traditional chemical copper 1 and the resin cannot be guaranteed, which can easily lead to problems such as delamination of the chemical copper 1. Summary of the invention

[0006] This application is made in view of the state of the prior art mentioned above. On the first aspect, the purpose of this application is to provide a fine line printed circuit board. It includes: a substrate, the substrate is made of glass cloth resin; base copper, the base copper includes chemical copper and copper foil; an adhesive layer, the adhesive layer is made of silicone resin, the adhesive layer is located between the substrate and the base copper, one side of the adhesive layer is bonded to the substrate, and the other side of the adhesive layer is bonded to the chemical copper; wherein the thickness of the adhesive layer ranges from 2um to 4um; the bonding force between the adhesive layer and the substrate is greater than the bonding force between the base copper and the substrate.

[0007] As a further improvement of the present application, after the side of the copper foil facing away from the bonding layer is etched, the chemical copper is deposited onto the surface of the bonding layer; the bonding layer fully covers one side of the base copper.

[0008] As a further improvement of the present application, when observed along a viewing direction perpendicular to the plane where the substrate is located, the interior of the substrate includes glass fibers that cross each other perpendicularly.

[0009] As a further improvement of the present application, the substrate includes glass fibers inside, and the extension trajectory of the glass fibers is wavy.

[0010] As a further improvement of the present application, a side of the chemical copper facing away from the bonding layer has an electroplating layer.

[0011] As a further improvement of the present application, the electroplating layer is provided with a recessed electrical copper non-precipitated portion formed after film stripping, and the bottom surface of the electrical copper non-precipitated portion exposes the chemical copper.

[0012] As a further improvement of the present application, the electroplating layer is provided with etching pits, the etching pits increase the width and depth of the non-precipitated portion of the electrical copper, and the bottom surface of the etching pits exposes the bonding layer.

[0013] As a further improvement of the present application, the line width and line spacing of the fine line printed circuit board are both less than 20um.

[0014] In a second aspect, a method for preparing a fine circuit printed circuit board is provided, which is used to manufacture the fine circuit printed circuit board of the present application, comprising: step S1: making the adhesive layer and the copper foil adhere to each other, so that the side of the adhesive layer not adhered by the copper foil is bonded to the substrate; step S2, weak etching: etching and removing the copper foil; step S3, chemical copper: depositing the chemical copper on the side of the adhesive layer facing away from the substrate; step S4, film exposure and development: pasting a photosensitive dry film on the side of the chemical copper facing away from the substrate, and placing it under ultraviolet light, the photosensitive dry film forms a circuit pattern; step S5, electroplating: coating the surface of the chemical copper with a layer of electroplating by electroplating; step S6, film stripping: stripping off the photosensitive dry film in step S4; step S7, etching: partially etching the chemical copper and the electroplating layer, and the remaining part of the chemical copper and the part of the electroplating layer form a circuit matching the circuit pattern.

[0015] As a further improvement of the present application, the organic silicone resin of the adhesive layer contains a silicic acid dispersant, which expands on the surface of the substrate and promotes permanent bonding.

[0016] As a further improvement of the present application, the thickness of the copper foil is 3um, 2um or 1.5um.

[0017] The beneficial effects of the fine circuit printed circuit board of the present application include: based on the structural characteristics of the printed circuit board in the existing MSAP process, by adding an adhesive layer of organic silicone resin material, the organic silicone resin is used as an intermediate layer between the glass cloth resin and the traditional chemical copper, which effectively improves the bonding force between the glass cloth resin substrate and the chemical copper, reduces the probability of chemical copper peeling off from the glass cloth resin material, and realizes the manufacture of fine circuits, thereby obtaining a printed circuit board with a precision comparable to that of the SAP process. The composite layer structure of the fine circuit printed circuit board of the present application is operable and is also beneficial to economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 It is a comparative schematic diagram of the process steps and characteristics of SAP and MSAP;

[0020] Figure 2 It is a comparative schematic diagram of the circuits formed by the etching amount of SAP and MSAP;

[0021] Figure 3It is a comparative schematic diagram of the chemical copper binding force of SAP and MSAP;

[0022] Figure 4 It is a schematic diagram comparing the chemical copper bonding force of one embodiment of the fine line printed circuit board of the present application with SAP and MSAP;

[0023] Figure 5 It is a schematic diagram comparing the process steps of one embodiment of the fine line printed circuit board of the present application with SAP and MSAP;

[0024] Figure 6 It is a microscope image of one embodiment of the fine line printed circuit board of the present application.

[0025] Description of Reference Numerals

[0026] 1-chemical copper; 2-copper foil; 3-adhesive layer; 4-substrate; 401-glass fiber; 5-film; 501-exposure tank; 6-electroplating layer; 601-unprecipitated part of electrical copper; 7-etching pit; 8-protective glue; L-line width; S-line spacing. DETAILED DESCRIPTION

[0027] The exemplary embodiments of the present application are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are only used to teach those skilled in the art how to implement the present application, and are not intended to exhaust all possible methods of the present application, nor to limit the scope of the present application.

[0028] See also Figure 4 and Figure 5, the embodiment of the present application provides a fine line printed circuit board, which may include a substrate 4, a base copper and an adhesive layer 3. Wherein, the substrate 4 may be made of glass cloth resin. The base copper includes chemical copper 1 and copper foil 2. The adhesive layer 3 is made of silicone resin, and the adhesive layer 3 is located between the substrate 4 and the base copper, one side of the adhesive layer 3 is bonded to the substrate 4, and the other side of the adhesive layer 3 is bonded to the chemical copper 1. Wherein, the thickness value of the adhesive layer 3 may range from 2um to 4um; the bonding force between the adhesive layer 3 and the substrate 4 is greater than the bonding force between the base copper and the substrate 4. When the adhesive layer 3 is bonded to the copper foil 2, the adhesive layer 3 and the copper foil 2 are extruded and bonded to form. During the processing of the fine line printed circuit board of the present application, when the substrate 4 has not yet been bonded to the adhesive layer 3, the adhesive layer 3 is temporarily bonded to the copper foil 2, and the side of the adhesive layer 3 bonded to the copper foil 2 is also the side bonded to the chemical copper 1 later. Chemical copper 1 is commonly known as copper deposition, which is a process of depositing a copper layer on a non-conductive substrate of a PCB by a chemical method. This is a self-catalytic redox reaction that can achieve metallization on a non-conductive substrate (such as insulating materials such as epoxy resin), thereby providing a conductive basis for subsequent circuit production. The copper foil 2 is a solid thin copper sheet made by calendering and other methods. The copper foil 2 has good conductivity and processability.

[0029] The silicone resin can be a Primer resin, which can also be called an adhesion promoter or a chemical crosslinking agent. The silicone resin acts as an adhesive layer 3 of the substrate 4 to improve adhesion. The silicone resin is mainly used for surfaces that are difficult to bond or in areas where moisture resistance and heat resistance are very high. Some silicone resins contain highly dispersed silicic acid (i.e., silicic acid dispersants), which can expand on the surface and promote permanent bonding. Therefore, it can be coated on the bonding surface of the copper foil 2 or on one side of the substrate 4. The silicone resin compatible with a specific adhesive can achieve the best adhesion of the substrate 4.

[0030] In one example, the silicone resin is coated onto the copper foil 2 , and the silicone resin and the copper foil 2 are first combined into a composite layer as a whole, and the composite layer as a whole is then pressed together with the glass cloth resin as the substrate 4 by a press.

[0031] The manufacturing process of the fine line printed circuit board of the present application is improved by using silicone resin on the basis of the MSAP process, which can be referred to as the P-MSAP process.

[0032] In another embodiment, when the adhesive layer 3 is bonded to the copper foil 2, and the side of the copper foil 2 facing away from the adhesive layer 3 undergoes weak etching, the thickness of the copper foil 2 becomes thinner until the copper foil 2 completely disappears, thereby exposing the adhesive layer 3 under the copper foil 2, and the chemical copper 1 is newly deposited on the surface of the adhesive layer 3. The side of the adhesive layer 3 facing away from the substrate 4 always fully covers the side of the base copper.

[0033] In another embodiment, the thickness of the copper foil 2 can be 3um, 2um, and 1.5um.

[0034] In another embodiment, the substrate 4 has glass fibers 401. When observing along a viewing direction perpendicular to the plane where the substrate 4 is located, it is assumed that the glass fibers 401 can be seen, and the plurality of glass fibers 40 inside the substrate 4 are mutually perpendicularly crossed. When observing along a viewing direction parallel to the plane where the substrate 4 is located, the extension trajectory of the glass fibers 401 is wavy.

[0035] like Figure 5 As shown, in another embodiment, the side of the chemical copper 1 facing away from the bonding layer 3 has an electroplating layer 6. The electroplating layer 6 is provided with an undeposited portion 601 of electrical copper after film stripping, wherein the undeposited portion 601 of electrical copper is called the undeposited portion 601 of electrical copper because, from a process perspective, it is produced by electroplating compared to the generation process of the chemical copper 1. From the perspective of the final shape, the undeposited portion 601 of electrical copper can also be called an electroplating pit. The bottom surface of the undeposited portion 601 of electrical copper exposes the chemical copper 1. Further, the electroplating layer 6 is provided with an etching pit 7, which increases the width and depth of the undeposited portion 601 of electrical copper, and the bottom surface of the etching pit 7 exposes the bonding layer 3. Before forming the electroplating layer 6, a film 5 is first provided on the surface of the chemical copper 1, and a developing tank 501 is formed in the film 5, and the electroplating layer 6 fills these developing tanks 501.

[0036] like Figure 5 As shown, in another embodiment, the width of the etching pit 7 is the line distance S, that is, the distance between two adjacent "lines", and the distance between two adjacent etching pits 7 is the line width L. The line width L and the line distance S can both be less than 20um. The "line" in the line distance S and the line width L corresponds to Figure 6 The electroplating layer 6 and chemical copper 1 in the highlighted part. The P-MSAP process can achieve a precise processing effect with a line width L and a line spacing S less than 20um by adding an additional adhesive layer 3 of silicone resin and a weak etching step. Figure 5A comparative schematic diagram of the process steps of SAP, MSAP, and P-MSAP is shown. P-MSAP sequentially undergoes a starting step, a weak etching step, a chemical copper step, a film exposure and development step, an electroplating step, a film stripping step, and an etching step. The starting step in the method for preparing a fine-circuit printed circuit board of the present application refers to bonding the side of the adhesive layer 3 that is not bonded by the copper foil 2 to the substrate 4 when the adhesive layer 3 and the copper foil 2 are bonded to each other; the weak etching step refers to etching away the copper foil 2; the chemical copper 1 step refers to the deposition of chemical copper 1 on the side of the adhesive layer 3 that is away from the substrate 4, that is, the side on which the copper foil 2 originally contacted the adhesive layer 3; the film exposure and development step refers to applying a photosensitive dry film to the side of the chemical copper 1 that is away from the substrate 4. Exposure is exposure, which is to place the PCB board with the photosensitive dry film under ultraviolet light to make the surface of the photosensitive dry film The photosensitive material undergoes a chemical reaction to form the desired circuit pattern; the electroplating step refers to covering the surface of the chemical copper 1 with a layer of electroplating layer 6 by electroplating; the stripping step refers to removing the unnecessary part of the photosensitive dry film on the PCB board after the photosensitive dry film is exposed and developed. The purpose of stripping is to expose the copper layer that needs to be etched for subsequent etching processes; the etching step is to remove the unnecessary part of the copper layer on the PCB board, partially etch the chemical copper 1 and the electroplating layer 6, and the remaining part of the chemical copper 1 and the electroplating layer 6 form a circuit that matches the circuit pattern. P-MSAP has one more weak etching step than MSAP. Finally, the process characteristics of SAP, MSAP, and P-MSAP are shown in the following table:

[0037]

[0038] In a non-limiting example, see Figure 6 , we can see the effect of chemical copper 1 being between electroplating layer 6 and bonding layer 3. Figure 6 The substrate 4 shown in the example does not contain glass fiber 401. Figure 6 This is a photo of the fine circuit printed circuit board of the present application after slicing, so one side of the electroplating layer 6 is covered with protective glue 8. Figure 6 Also corresponds to Figure 5 The state after etching in P-MSAP is completed.

[0039] Factories with MSAP process capabilities can adopt the P-MSAP process. The P-MSAP process can achieve the same level of refined circuits as the industry's SAP process capabilities, and does not require the introduction of specialized equipment or changes to the factory layout, so the factory does not need to be significantly modified, and the additional equipment costs are small. In addition, there is no need to introduce special chemicals, which is more environmentally friendly, has no restrictions on the choice of interlayer materials, and has high flexibility in matching, which can meet the product needs of various printed circuit boards.

[0040] The above embodiments are only for illustrating the technical concept and features of the present application, and their purpose is to enable people familiar with this technology to understand the content of the present application and implement it. They cannot be used to limit the scope of protection of the present application. All equivalent changes or modifications made according to the spirit of the present application should be included in the scope of protection of the present application.

Claims

1. A fine line printed circuit board, characterized in that: include: A substrate (4), wherein the substrate (4) is made of glass cloth resin; Base copper, the base copper comprising chemical copper (1) and copper foil (2); An adhesive layer (3), the adhesive layer (3) is made of an organic silicone resin material, the adhesive layer (3) is located between the substrate (4) and the base copper, one side of the adhesive layer (3) is bonded to the substrate (4), and the other side of the adhesive layer (3) is bonded to the chemical copper (1); The thickness of the adhesive layer (3) ranges from 2 um to 4 um; and the bonding force between the adhesive layer (3) and the substrate (4) is greater than the bonding force between the base copper and the substrate (4).

2. The fine line printed circuit board according to claim 1, characterized in that: After the side of the copper foil (2) facing away from the bonding layer (3) is etched, the chemical copper (1) is deposited onto the surface of the bonding layer (3); the bonding layer (3) fully covers one side of the base copper.

3. The fine line printed circuit board according to claim 1, characterized in that: When observed along a viewing angle direction perpendicular to the plane where the substrate (4) is located, the interior of the substrate (4) comprises glass fibers (401) that cross each other perpendicularly.

4. The fine line printed circuit board according to claim 1, characterized in that: The substrate (4) comprises glass fibers (401) inside, and the extension trajectory of the glass fibers (401) is wavy.

5. The fine line printed circuit board according to claim 1, characterized in that: The side of the chemical copper (1) facing away from the bonding layer (3) has an electroplating layer (6).

6. The fine line printed circuit board according to claim 5, characterized in that: The electroplating layer (6) is provided with an electrical copper non-precipitated portion (601) which is concave after film stripping, and the bottom surface of the electrical copper non-precipitated portion (601) exposes the chemical copper (1).

7. The fine line printed circuit board according to claim 6, characterized in that: The electroplating layer (6) is provided with an etching pit (7), the etching pit (7) increases the width and depth of the electrical copper non-precipitated portion (601), and the bottom surface of the etching pit (7) exposes the bonding layer (3).

8. The fine line printed circuit board according to claim 1, characterized in that: The line width (L) and line spacing (S) of the fine line printed circuit board are both less than 20um.

9. A method for preparing a fine line printed circuit board, used for manufacturing the fine line printed circuit board according to any one of claims 1 to 8, characterized in that: include: Step S1: bonding the adhesive layer (3) and the copper foil (2) to each other, so that the side of the adhesive layer (3) not bonded by the copper foil (2) is bonded to the substrate (4); Step S2, weak etching: etching and removing the copper foil (2); Step S3, chemical copper (1): depositing the chemical copper (1) onto a side of the adhesive layer (3) facing away from the substrate (4); Step S4, film pasting, exposure and development: a photosensitive dry film is pasted on the side of the chemical copper (1) facing away from the substrate (4), and the film is exposed to ultraviolet light, so that the photosensitive dry film forms a circuit pattern; Step S5, electroplating: coating the surface of the chemical copper (1) with an electroplating layer (6) by electroplating; Step S6, film stripping: stripping off the photosensitive dry film in step S4; Step S7, etching: partially etching the chemical copper (1) and the electroplating layer (6), and the remaining part of the chemical copper (1) and the electroplating layer (6) form a circuit matching the circuit pattern.

10. The method for preparing a fine line printed circuit board according to claim 9, characterized in that: The organic silicone resin of the adhesive layer (3) contains a silicic acid dispersant, which expands on the surface of the substrate (4) and promotes permanent bonding.

11. The method for preparing a fine line printed circuit board according to claim 9, characterized in that: The thickness of the copper foil (2) is 3 um, 2 um or 1.5 um.

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