Fine circuit printed circuit board
By introducing a silicone resin adhesive layer into the MSAP process, the bonding force between the substrate and chemical copper is improved, and the problem that existing MSAP processes are difficult to achieve refined lines is solved, and the production of refined lines is achieved equally as refined lines as SAP processes without large-scale investment and equipment re-layout.
Patent Information
- Application Number
- CN202422219626.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-10
- Publication Date
- 2025-06-27
- Estimated Expiration
- 2034-09-10
AI Technical Summary
The existing MSAP process is difficult to achieve more refined circuit production, and converting it to SAP process requires huge investment and equipment re-layout.
Based on the MSAP process, an adhesive layer made of silicone resin is introduced as an intermediate layer between the glass cloth resin substrate and traditional chemical copper, which enhances the bonding force between the substrate and chemical copper, reduces the probability of chemical copper peeling, and thus realizes the manufacturing of refined lines.
Through this method, the production of refined lines as fine as the SAP process can be achieved without large-scale investment and equipment re-layout, reducing the risk of chemical copper stripping and improving the economic and operability of production.
Smart Images
Figure CN223040272U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of printed circuit boards, and particularly to a printed circuit board with fine lines. Background Art
[0002] In the industry, there are mainly two processes for realizing the fine line process of circuit boards, namely 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 and high-adhesion dry film, a very small number of manufacturers have achieved mass production of fine lines using the MSAP process. However, the production of even finer lines still relies on the SAP process.
[0003] The main materials, equipment, and potions used in the SAP process are different from those in the MSAP process. For manufacturers that already have the MSAP process, if they change to the SAP process, the change means huge investment, re-layout of equipment, and even the need to build a new factory, which is very costly. A more realistic approach is to borrow the existing MSAP process and equipment and improve on this basis to achieve the production level of fine lines as much as possible.
[0004] Figure 1 Shows a schematic diagram comparing the process characteristics of SAP and MSAP. Figure 2 Shows a schematic diagram comparing the lines formed by the etching amounts of SAP and MSAP. The biggest difference between the SAP and MSAP processes is that the SAP process uses electroless copper as the base copper, while the MSAP process uses an extremely thin copper foil as the base copper. In the same process flow and dry film capacity, due to the bonding of electroless copper 1 and copper foil 2 in the MSAP process, the base copper thickness is large, and a relatively large etching amount is required in the later stage to form the lines. At this time, the formed lines are thinner than the expected target lines and are not suitable for forming high-density fine lines. The thickness value of the formed lines is relatively thin, that is, the problem of "thin lines" may occur.
[0005] Figure 3 Shows a schematic diagram comparing whether the electroless copper of SAP and MSAP is peeled off. To obtain finer lines, it is required to reduce the base copper thickness as much as possible. However, if the base copper thickness is infinitely reduced until the substrate is exposed, the bonding force between the traditional electroless copper 1 and the resin cannot be guaranteed, and problems such as delamination and peeling of the electroless copper 1 are likely to occur. Utility Model Content
[0006] This application is made in view of the state of the above-mentioned prior art. The object of this application is to provide a fine-line printed circuit board, comprising: a substrate made of glass cloth resin; a base copper including electroless copper and copper foil; an adhesive layer made of silicone resin, which 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 electroless copper; wherein, the thickness value range of the adhesive layer is 2um to 4um; the adhesive force between the adhesive layer and the substrate is greater than the adhesive force between the base copper and the substrate.
[0007] As a further improvement of this application, after one side of the copper foil facing away from the adhesive layer is etched, the electroless copper is deposited on the surface of the adhesive layer; the adhesive layer completely covers one side of the base copper.
[0008] As a further improvement of this application, when observed from the perspective direction perpendicular to the plane where the substrate is located, the inside of the substrate includes glass fibers that intersect perpendicularly.
[0009] As a further improvement of this application, the inside of the substrate includes glass fibers, and the extension trajectory of the glass fibers is wavy.
[0010] As a further improvement of this application, there is a plating layer on one side of the electroless copper facing away from the adhesive layer.
[0011] As a further improvement of this application, the plating layer has a non-deposited electrical copper part that forms a depression after stripping, and the bottom surface of the non-deposited electrical copper part exposes the electroless copper.
[0012] As a further improvement of this application, the plating layer has etching pits, the etching pits increase the width and depth of the non-deposited electrical copper part, and the bottom surface of the etching pits exposes the adhesive layer.
[0013] As a further improvement of this application, both the line width and line pitch of the fine-line printed circuit board are less than 20um.
[0014] The beneficial effects of the fine-line printed circuit board of this application include: based on the structural characteristics of the printed circuit board in the existing MSAP process, by adding an adhesive layer made of silicone resin, and using silicone resin as the intermediate layer between the glass cloth resin and the traditional electroless copper, the bonding force between the substrate made of glass cloth resin and the electroless copper is effectively improved, the probability of the electroless copper peeling off from the glass cloth resin material is reduced, the manufacturing of fine lines is realized, and thus a printed circuit board with precision comparable to that produced by the SAP process can be obtained. The composite layer structure of the fine-line printed circuit board of this application has operability and is also beneficial to economy. Description of the Drawings
[0015] To more clearly illustrate the technical solutions in the embodiments, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.
[0016] Figure 1 It is a schematic comparison diagram of the process steps and characteristics of SAP and MSAP;
[0017] Figure 2 It is a schematic comparison diagram of the circuits formed by the etching amounts of SAP and MSAP;
[0018] Figure 3 It is a schematic comparison diagram of the chemical copper bonding strength of SAP and MSAP;
[0019] Figure 4 It is a schematic comparison diagram of the chemical copper bonding strength between an embodiment of the fine-line printed circuit board of the present application and SAP and MSAP;
[0020] Figure 5 It is a schematic comparison diagram of the process steps between an embodiment of the fine-line printed circuit board of the present application and SAP and MSAP;
[0021] Figure 6 It is a micrograph of an embodiment of the fine-line printed circuit board of the present application.
[0022] Description of Reference Numerals
[0023] 1 - Chemical copper; 2 - Copper foil; 3 - Adhesive layer; 4 - Substrate; 401 - Glass fiber; 5 - Masking film; 501 - Exposure tank; 6 - Plating layer; 601 - Unprecipitated part of electrical copper; 7 - Etching pit; 8 - Protective glue; L - Line width; S - Line pitch. Detailed Embodiments
[0024] The exemplary embodiments of the present application will be 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 used to exhaust all feasible ways of the present application, nor to limit the scope of the present application.
[0025] Refer to Figure 4 and Figure 5, embodiments of the present application provide a fine-line printed circuit board, which may include a substrate 4, base copper, and an adhesive layer 3. Among them, the substrate 4 may be made of glass cloth resin. The base copper includes electroless copper 1 and copper foil 2. The adhesive layer 3 is made of silicone resin. 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 electroless copper 1. Among them, the thickness value range of the adhesive layer 3 may be 2 um to 4 um; the adhesion force between the adhesive layer 3 and the substrate 4 is greater than the adhesion 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 extrusion-bonded into shape. During the processing of the fine-line printed circuit board of the present application, when the substrate 4 is not yet 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 that will be bonded to the electroless copper 1 later. Electroless copper 1, commonly known as deposited copper, is a process of depositing a copper layer on a non-conductive substrate of a PCB by chemical methods. This is a self-catalytic redox reaction that can metallize a non-conductive substrate (such as insulating materials like epoxy resin) to provide a conductive basis for subsequent circuit production. The copper foil 2 is a solid thin copper sheet made by methods such as rolling. The copper foil 2 has good electrical conductivity and processability.
[0026] The silicone resin can be Primer (primer) resin, also known as an adhesion promoter or chemical cross-linking agent. The silicone resin acts as the adhesive layer 3 of the substrate 4 to improve adhesion. The silicone resin is mainly used in surfaces that are difficult to bond or in fields with very high requirements for moisture resistance and heat resistance. Some silicone resins contain highly dispersed silicic acid (i.e., silicic acid dispersant), 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.
[0027] In one example, the silicone resin is coated on the copper foil 2. The silicone resin and the copper foil 2 are first combined into a composite layer as a whole, and this composite layer as a whole is then pressed together with the glass cloth resin serving as the substrate 4 by a press.
[0028] 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 simply referred to as the P-MSAP process.
[0029] 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 below the copper foil 2, and the electroless 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 completely covers the side of the base copper.
[0030] In another embodiment, the thickness of the copper foil 2 can be three values: 3um, 2um, and 1.5um.
[0031] In another embodiment, the substrate 4 includes glass fibers 401. When observed from a perspective direction perpendicular to the plane of the substrate 4, assuming that the glass fibers 401 can be seen, several glass fibers 40 inside the substrate 4 are in a state of perpendicular intersection. When observed from a perspective direction parallel to the plane of the substrate 4, the extension trajectory of the glass fibers 401 is wavy.
[0032] As Figure 5 shown, in another embodiment, there is a plating layer 6 on the side of the electroless copper 1 facing away from the adhesive layer 3. The plating layer 6 has an unplated copper portion 601 after stripping the film. Here, the unplated copper portion 601 is called so because, from a process perspective, it is produced by electroplating compared to the formation process of the electroless copper 1. From the perspective of the final shape, the unplated copper portion 601 can also be called an electroplating pit. The bottom surface of the unplated copper portion 601 exposes the electroless copper 1. Further, the plating layer 6 has etching pits 7, and the etching pits 7 increase the width and depth of the unplated copper portion 601. The bottom surface of the etching pits 7 exposes the adhesive layer 3. Before forming the plating layer 6, a film 5 is first provided on the surface of the electroless copper 1, and a developing groove 501 is formed in the film 5, and the plating layer 6 fills these developing grooves 501.
[0033] As Figure 5 shown, in another embodiment, the width of the etching pit 7 is the line pitch S, that is, the distance between two adjacent "lines", and the distance between two adjacent etching pits 7 is the line width L. Both the line width L and the line pitch S can be less than 20um. The "lines" in the line pitch S and the line width L correspond to Figure 6 the highlighted plating layer 6 and electroless copper 1 in Figure 5Shows a schematic diagram comparing the process steps of SAP, MSAP, and P-MSAP. P-MSAP sequentially undergoes a start step, a weak etching step, a chemical copper step, a film laminating, exposure, and development step, an electroplating step, a film stripping step, and an etching step. The start step in the method for preparing a fine-line printed circuit board of the present application refers to bonding the side of the adhesive layer 3 that is not adhered to the copper foil 2 to the substrate 4 when the adhesive layer 3 and the copper foil 2 are mutually adhered; the weak etching step refers to etching and removing the copper foil 2; the chemical copper 1 step refers to depositing chemical copper 1 on the side of the adhesive layer 3 facing away from the substrate 4, that is, the side where the copper foil 2 originally contacted the adhesive layer 3; the film laminating, exposure, and development step refers to pasting a photosensitive dry film on the side of the chemical copper 1 facing away from the substrate 4. Exposure means exposing to ultraviolet light. The PCB board with the photosensitive dry film pasted on it is placed under ultraviolet light irradiation, causing a chemical reaction in the photosensitive material on the photosensitive dry film, thereby forming the required circuit pattern; the electroplating step refers to covering a layer of electroplating layer 6 on the surface of the chemical copper 1 by electroplating; the film stripping step refers to removing the unnecessary part of the photosensitive dry film on the PCB board after exposure and development. The purpose of film stripping is to expose the part of the copper layer that needs to be etched for subsequent etching process; 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 part of 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:
[0034]
[0035] In a non-limiting example, referring to Figure 6 , it can be seen the effect of chemical copper 1 being between the electroplating layer 6 and the adhesive layer 3. At the same time Figure 6 the substrate 4 in the example of Figure 6 does not contain fiberglass 401. Since Figure 6 is a photo of the sliced fine-line printed circuit board of the present application, a protective glue 8 is covered on one side of the electroplating layer 6. Figure 6 Also corresponds to Figure 5 the state after etching in P-MSAP in
[0036] Factories with MSAP process capabilities can adopt the P-MSAP process. The fine-line level of the P-MSAP process can be equivalent to the SAP process capabilities in the industry, and there is no need to introduce special equipment, nor does the factory layout need to be changed. Therefore, the factory does not need major modifications, and the increased equipment cost is not large. In addition, there is no need to introduce special chemicals, which is more environmentally friendly. There are no restrictions on the selection of interlayer materials, and the matching flexibility is high, which can meet the product requirements of various printed circuit boards.
[0037] The above embodiments are only for illustrating the technical concept and features of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it. It should not be used to limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit of the present application should be covered within the protection scope of the present application.
Claims
1. A fine line printed circuit board, characterized in that: include: A substrate, wherein 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 organic 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; The thickness of the adhesive layer ranges from 2um to 4um; and the bonding force between the adhesive layer and the substrate is greater than the bonding force between the base copper and the substrate.
2. The fine line printed circuit board according to claim 1, characterized in that: After the side of the copper foil facing away from the bonding layer is etched, the chemical copper is deposited on the surface of the bonding layer; the bonding layer 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 is located, the interior of the substrate includes glass fibers that cross each other perpendicularly.
4. The fine line printed circuit board according to claim 1, characterized in that: The substrate includes glass fibers inside, and the extension track of the glass fibers is wavy.
5. The fine line printed circuit board according to claim 1, characterized in that: The side of the chemical copper facing away from the bonding layer has an electroplating layer.
6. The fine line printed circuit board according to claim 5, characterized in that: The electroplating layer is provided with an electrical copper non-precipitated portion which is concave after film stripping, and the bottom surface of the electrical copper non-precipitated portion exposes the chemical copper.
7. The fine line printed circuit board according to claim 6, characterized in that: 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.
8. The fine line printed circuit board according to claim 1, characterized in that: The line width and line spacing of the fine line printed circuit board are both less than 20um.