Preparation method of solder mask layer
The method uses a UV absorber and specific wavelength light source to prevent light penetration in ultra-thin circuit boards, addressing unclean development issues and ensuring clean solder mask formation on ultra-thin circuit boards.
Patent Information
- Application Number
- CN202310738627.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-21
- Publication Date
- 2024-12-24
AI Technical Summary
The issue of unclean development of solder mask layers on ultra-thin circuit boards (≤0.2mm and substrate layer thickness ≤50μm) due to light penetration, causing interference between opposite sides during exposure.
A method involving a UV absorber, such as titanium dioxide, in the substrate layer to block light penetration, combined with a specific wavelength (370-430nm) light source and a developing solution (Na2CO3 concentration 0.8-1.5%) to prevent unclean development, and a photosensitive resin (epoxy or acrylic) for the solder mask.
Prevents unclean development of solder mask layers on ultra-thin circuit boards by blocking light penetration, ensuring clean exposure and development, thereby maintaining the integrity of the solder mask.
Smart Images
Figure CN119183260A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of printed circuit board manufacturing process, and in particular to a method for preparing a solder mask. Background Art
[0002] During the production process of printed circuit boards (PCBs), solder mask treatment is required to form a solder mask layer to protect the copper surface and circuits and ensure that the circuit board has good electrical functions. The production of solder mask layers on printed circuit boards generally includes processes such as printing solder mask, exposure, development, baking or light curing. The exposure method is generally to use a light source to illuminate the area that needs to be exposed, and the area that does not need to be exposed can be shielded from the light source by a film or other means.
[0003] With the development of science and technology, terminal electronic products are becoming lighter and lighter, and circuit boards are also developing in the direction of being thinner and shorter. For ultra-thin circuit boards (total thickness ≤ 0.2mm and substrate layer thickness ≤ 50μm), due to the thin thickness, the light source is easy to penetrate. When the solder mask on one side of the circuit board is exposed, the solder mask on the other side will absorb the exposure energy of the penetrating light source in advance, and solidify, resulting in unclean development. Summary of the invention
[0004] In view of this, the present application proposes a method for preparing a solder mask layer to solve the technical problem that the solder mask layer of an ultra-thin circuit board is easily developed uncleanly.
[0005] One embodiment of the present application provides a method for preparing a solder mask, wherein the solder mask is disposed on the surface of a printed circuit board. The printed circuit board includes a substrate layer and a conductive circuit layer disposed on the surface of the substrate layer, the thickness of the printed circuit board is ≤0.2 mm, the thickness of the substrate layer is ≤50 μm, and the substrate layer includes a UV absorber. The preparation method includes the following steps: laminating a solder mask on the surface of the printed circuit board; exposing: irradiating the solder mask with a light source, the wavelength of the light source is 370 nm to 430 nm, and the exposure amount is 150 to 450 mj / cm 2 ; using a developing solution to remove the unexposed portion of the solder mask; curing the developed solder mask to form the solder mask layer.
[0006] In one embodiment, the ultraviolet absorber includes one or more of titanium dioxide, benzotriazoles, benzophenones, triazines, salicylates or cyanoacrylates.
[0007] In one embodiment, in the exposure step, the exposure time is 28S to 40S.
[0008] In one embodiment, the developing solution includes a Na2CO3 solution.
[0009] In one embodiment, the concentration of the Na2CO3 solution is 0.8% to 1.5%.
[0010] In one embodiment, the solder mask includes a photosensitive resin, and the photosensitive resin includes an epoxy resin and / or an acrylic resin.
[0011] In one embodiment, the method for preparing the printed circuit board includes the following steps: providing a copper clad laminate, the copper clad laminate including a substrate layer and a copper foil layer disposed on the surface of the substrate layer; forming a conductive circuit layer from the copper foil layer to obtain the printed circuit board.
[0012] In one embodiment, the substrate layer includes glass fiber, epoxy resin and ultraviolet absorber, and the weight percentage of the ultraviolet absorber in the copper clad laminate is 11% to 15%.
[0013] In one embodiment, the method for preparing the printed circuit board also includes the following step: laminating a build-up circuit substrate on the side of the conductive circuit layer facing away from the base material layer, the build-up circuit substrate including a dielectric layer and a build-up circuit layer, and the dielectric layer is located between the conductive circuit layer and the build-up circuit layer.
[0014] In one embodiment, before the step of laminating the solder mask on the surface of the printed circuit board, the preparation method further includes the step of pre-treating the printed circuit board.
[0015] The preparation method of the solder mask described in the present application selects a light source with a specific wavelength (370nm~430nm) for exposure, and sets an ultraviolet absorber such as titanium dioxide in the substrate layer, so that the light source cannot penetrate the substrate layer, so that when the solder mask on one side is exposed, it will not affect the solder mask on the other side, thereby reducing the probability of unclean development of the solder mask of the ultra-thin circuit board (thickness ≤0.2mm and the thickness of the substrate layer ≤50μm). BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 A schematic cross-sectional view of a copper clad laminate provided in accordance with one embodiment of the present application.
[0017] Figure 2 For Figure 1 A cross-sectional schematic diagram of a through hole being arranged on a copper clad laminate is shown.
[0018] Figure 3 For Figure 2 Schematic diagram of the cross-section of the structure shown after electroplating.
[0019] Figure 4 For the general Figure 3 The cross-sectional view of a printed circuit board formed by forming a conductive circuit layer with a copper foil layer of the structure shown in one embodiment.
[0020] Figure 5 For Figure 4 The cross-sectional view of the printed circuit board shown is a schematic diagram of the surface of the solder mask laminated.
[0021] Figure 6 For the general Figure 5 The cross-sectional schematic diagram of the solder mask after being exposed, developed, and cured to form a solder mask layer.
[0022] Figure 7 A schematic cross-sectional view of a printed circuit board provided in another embodiment of the present application.
[0023] Figure 8 For Figure 7 The cross-sectional view of the printed circuit board shown is a schematic diagram of the surface of the solder mask laminated.
[0024] Fig. 9 For the general Figure 8 The cross-sectional schematic diagram of the solder mask after being exposed, developed, and cured to form a solder mask layer.
[0025] Main component symbols
[0026] Solder mask 100
[0027] Printed circuit board 200, 300
[0028] Solder mask 10
[0029] Copper clad laminate 20
[0030] Base material layer 21
[0031] Copper foil layers 22, 24
[0032] Conductive structure 23
[0033] Conductive circuit layer 25
[0034] Through hole 201
[0035] Build-up circuit substrate 30
[0036] Dielectric layer 31
[0037] Build-up circuit layer 32
[0038] The following specific implementation manner will further illustrate the embodiments of the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION
[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the technical field of the present application. The terms used herein are only for the purpose of describing specific implementation methods and are not intended to limit the present application embodiments.
[0040] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.
[0041] It will be understood that when a layer is referred to as being “on” another layer, it can be directly on the other layer or intervening layers may be present therebetween. In contrast, when a layer is referred to as being “directly on” another layer, there are no intervening layers present.
[0042] Here, the embodiments of the present application are described with reference to the cross-sectional views, which are schematic diagrams of the idealized embodiments (and intermediate configurations) of the present application. Thus, it is foreseeable that the shapes of the diagrams are different due to manufacturing processes and / or tolerances. Therefore, the embodiments of the present application should not be interpreted as being limited to the specific shapes of the regions illustrated here, but should include deviations in shapes such as those produced due to manufacturing. The regions shown in the figures are themselves only schematic, and their shapes are not intended to illustrate the actual shapes of the devices, and are not intended to limit the scope of the present application.
[0043] Some embodiments of the present application are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.
[0044] First embodiment
[0045] See also Figures 1 to 6 The first embodiment of the present application provides a method for preparing a solder mask 100, wherein the solder mask 100 is disposed on a surface of a printed circuit board 200. The method for preparing the solder mask 100 includes steps S10 to S40. It is understood that the numbering of the steps is intended to clearly describe the specific preparation method, and is not intended to limit the order of the steps.
[0046] See also Figures 1 to 5 In step S10, a solder mask 10 is pressed on the surface of the printed circuit board 200. The method for preparing the printed circuit board 200 may include steps S11 to S14.
[0047] like Figure 1As shown, step S11, a copper clad laminate 20 is provided. The copper clad laminate 20 includes a substrate layer 21 and a copper foil layer 22 disposed on the surface of the substrate layer 21, and the thickness of the substrate layer 21 is ≤50μm. In this embodiment, the copper clad laminate 20 is a plate-like material made by impregnating glass fiber or other reinforcing materials with epoxy resin and ultraviolet absorber, and then covering one or both sides with copper foil and hot pressing. That is, the substrate layer of the copper clad laminate 20 includes glass fiber, epoxy resin and ultraviolet absorber. The ultraviolet absorber is used to absorb ultraviolet rays and prevent ultraviolet rays from passing through the substrate layer 21. The weight percentage of the ultraviolet absorber in the copper clad laminate 20 is 11% to 15%, so that it can effectively prevent ultraviolet rays from passing through without affecting the performance of the copper clad laminate 20. In this embodiment, the copper foil layer 22 is disposed on two opposite surfaces of the substrate layer 21. In other embodiments, the copper foil layer 22 can be disposed only on one surface of the substrate layer 21.
[0048] Further, the ultraviolet absorber may be, but is not limited to, one or more of titanium dioxide (TiO2, titanium dioxide), benzotriazoles, benzophenones, triazines, salicylates or cyanoacrylates. In this embodiment, the ultraviolet absorber is titanium dioxide. Titanium dioxide has strong anti-ultraviolet ability because of its high refractive index and high photosensitivity. The anti-ultraviolet ability of titanium dioxide is related to its particle size: when the particle size is large, the blocking of ultraviolet rays is mainly based on reflection and scattering, and it is effective for both medium-wave (280-320nm) and long-wave ultraviolet rays (320-400nm); when the particle size is small, the reflection and scattering of ultraviolet rays in the long-wave region are not obvious, and the absorption of ultraviolet rays in the medium-wave region is significantly enhanced.
[0049] like Figure 2 As shown, in step S12, a through hole 201 may be formed on the copper clad laminate 20 by, but not limited to, mechanical drilling, laser, etc. The through hole 201 penetrates the substrate layer 21 and the copper foil layer 22 along the thickness direction. The number of the through hole 201 may be one or more, and the present application does not limit it.
[0050] like Figure 3 As shown, in step S13, metal may be filled in the through hole 201 by, but not limited to, electroplating. The through hole 201 and the metal in the through hole 201 form a conductive structure 23. In this embodiment, the metal is copper. It is understood that when copper is electroplated in the through hole 201, a copper foil layer 24 will also be formed on the surface of the copper foil layer 22 away from the substrate layer 21.
[0051] like Figure 4As shown, in step S14, the copper foil layers 22 and 24 on the surface of the substrate layer 21 are made into a conductive circuit layer 25 to obtain a printed circuit board 200. The conductive structure 23 electrically connects the conductive circuit layers 25 on the upper and lower sides of the substrate layer 21. In this embodiment, the printed circuit board 200 is a thin product, the thickness of the printed circuit board 200 is ≤0.2 mm, and the thickness of the substrate layer 21 is ≤50 μm.
[0052] Specifically, a resist film (not shown) may be laminated on the outer side of the copper foil layer 24, and then exposure, development, etching, removal of the resist film and other steps may be performed to form the conductive circuit layer 25. The lamination, exposure, development, etching, removal and other steps are commonly used technical means in the art and will not be described in detail herein.
[0053] In some embodiments, the printed circuit board 200 may be pretreated before laminating the solder mask 10. The pretreatment may include steps such as brushing, pickling and micro-etching, water washing, and roughening treatment. The printed circuit board 200 may be roughened by ultrasound. The vibration frequency of the ultrasound may be 25 Hz (Hertz) to control the surface roughness Ra of the conductive circuit layer 25 to be greater than 0.3, thereby improving the bonding force between the printed circuit board 200 and the solder mask 10. After the roughening treatment, the printed circuit board 200 may also be dried. The above pretreatment steps are not necessary steps. In some embodiments, the pretreatment steps may also be omitted.
[0054] like Figure 5 As shown, in step S15, a solder mask 10 is pressed on the surface of the printed circuit board 200. In this embodiment, the solder mask 10 is pressed on the surface of the conductive circuit layer 25 away from the substrate layer 21, and the solder mask 10 covers the conductive circuit layer 25 and the surface of the substrate layer 21 exposed from the conductive circuit layer 25.
[0055] In some implementations, the main material of the solder mask 10 is a photosensitive resin, which may be, but is not limited to, epoxy resin, acrylic resin, or a mixture of epoxy resin and acrylic resin.
[0056] Step S20, exposure: use a light source to illuminate the area of the solder mask 10 that needs to be exposed, and the area that does not need to be exposed can be shielded from the light source by a film or other means. The wavelength of the light source is 370nm to 430nm, and the exposure amount is 150 to 450mj / cm 2 For example, the exposure wavelength can be set to 370nm-390nm, or 400nm-430nm. Selecting a light source with a wavelength of 370nm-430nm can ensure the exposure effect of the solder mask 10 and prevent the light source from penetrating the substrate layer 21.
[0057] In some embodiments, the exposure time is 28S to 40S. For example, the exposure time of the upper solder mask 10 may be 35S to 40S, and the exposure time of the lower solder mask 10 may be 28S to 32S.
[0058] Step S30 , removing the unexposed portion of the solder mask 10 with a developing solution.
[0059] In some embodiments, the developer solution is a Na2CO3 solution. The Na2CO3 solution can dissolve the unexposed area of the solder mask 10. Furthermore, the concentration (mass percentage, i.e., the mass of the solute as a percentage of the mass of the solution) of the Na2CO3 solution can be 0.8% to 1.5%.
[0060] See also Figure 6 , step S40, curing the developed solder mask 10 to form the solder mask 100. The developed solder mask 10 can be cured by, but not limited to, baking, UV curing, etc., and the curing time can be adjusted according to actual needs. The curing operation can increase the strength and reliability of the printed circuit board 200. It is understandable that the solder mask 10 on one side can be exposed, developed, and cured first, and then the solder mask 10 on the other side can be exposed, developed, and cured.
[0061] The printed circuit board 200 formed with the solder mask 100 is subjected to AVI (Audio Video Interleaved) inspection to detect whether there is a defect of unclean development. After AVI inspection, the printed circuit board 200 prepared in this embodiment has no abnormal appearance inspection, and the solder mask 100 is not observed to have a defect of unclean development.
[0062] Second embodiment
[0063] See also Figures 1 to 4 as well as Figures 7 to 9 The second embodiment of the present application provides a method for preparing a solder mask 100, wherein the solder mask 100 is disposed on the surface of a printed circuit board 300. The difference between this embodiment and the first embodiment is that the printed circuit board 300 of this embodiment is different, and the printed circuit board 300 of this embodiment is formed by further adding layers on the basis of the printed circuit board 200 of the first embodiment.
[0064] See also Figures 1 to 4 After preparing a circuit board including a substrate layer 21 and two conductive circuit layers 25, refer to Figure 7, a build-up circuit substrate 30 can also be laminated on the outer side of the conductive circuit layer 25 (i.e., the side of the conductive circuit layer 25 away from the base layer 21) to obtain a printed circuit board 300. The build-up circuit substrate 30 includes a dielectric layer 31 and a build-up circuit layer 32, and the dielectric layer 31 is located between the conductive circuit layer 25 and the build-up circuit layer 32. The material of the dielectric layer 31 can be, but is not limited to, polyimide (PI), polyester resin (PET), polyethylene naphthalate diformicacid glycol ester (PEN), liquid crystal polymer (LCP), and modified polyimide (MPI). The material of the dielectric layer 31 can also be the same as that of the base layer 21, including glass fiber, epoxy resin, and ultraviolet absorber (titanium dioxide). The build-up circuit layer 32 and the conductive circuit layer 25 may be electrically connected via a conductive structure 23 . Figure 7 FIG. 3 shows a printed circuit board 300 including two conductive circuit layers 25 and two build-up circuit layers 32 (ie, including four circuit layers). In other embodiments, Figure 7 The printed circuit board 300 shown in the figure is multiplied to obtain a printed circuit board with more circuit layers. The printed circuit board of the present application is a thin product, and its thickness is less than or equal to 0.2 mm regardless of the number of circuit layers.
[0065] See also Figure 8 , a solder mask 10 is pressed onto the surface of the printed circuit board 300. In this embodiment, the solder mask 10 is pressed onto the surface of the build-up circuit layer 32 away from the dielectric layer 31, and the solder mask 10 covers the build-up circuit layer 32 and the surface of the dielectric layer 31 exposed from the build-up circuit layer 32.
[0066] See also Fig. 9 After the steps of exposure, development and curing, the solder mask 100 is formed.
[0067] The preparation method of the solder mask 100 described in the present application selects a light source with a specific wavelength (370nm~430nm) for exposure, and sets an ultraviolet absorber such as titanium dioxide in the substrate layer 21, so that the light source cannot penetrate the substrate layer 21, so that when the solder mask 10 on one side is exposed, it will not affect the solder mask 10 on the other side, thereby reducing the probability of unclean development of the solder mask 100 of the ultra-thin circuit board (thickness ≤0.2㎜ and the thickness of the substrate layer 21 ≤50μm).
[0068] The above descriptions are some specific implementations of the present application, but they are not limited to these implementations in actual application. For ordinary technicians in this field, other variations and changes made according to the technical concept of the present application should all fall within the protection scope of the present application.
Claims
1. A method for preparing a solder mask, wherein the solder mask is disposed on a surface of a printed circuit board, characterized in that: The printed circuit board comprises a substrate layer and a conductive circuit layer arranged on the surface of the substrate layer, the thickness of the printed circuit board is ≤0.2 mm, the thickness of the substrate layer is ≤50 μm, the substrate layer comprises an ultraviolet absorber, and the preparation method comprises the following steps: Laminating a solder mask on the surface of the printed circuit board; Exposure: Irradiate the solder mask with a light source having a wavelength of 370nm to 430nm and an exposure amount of 150 to 450mj / cm 2 ; Using a developing solution to remove the unexposed portion of the solder mask; The developed solder mask is cured to form the solder mask layer.
2. The method for preparing a solder mask according to claim 1, wherein: The ultraviolet absorber includes one or more of titanium dioxide, benzotriazoles, benzophenones, triazines, salicylates or cyanoacrylates.
3. The method for preparing a solder mask according to claim 1, wherein: In the exposure step, the exposure time is 28S to 40S.
4. The method for preparing a solder mask according to claim 1, wherein: The developing solution includes a Na2CO3 solution.
5. The method for preparing a solder mask according to claim 4, wherein: The concentration of the Na2CO3 solution is 0.8% to 1.5%.
6. The method for preparing a solder mask according to claim 1, wherein: The solder mask includes a photosensitive resin, and the photosensitive resin includes an epoxy resin and / or an acrylic resin.
7. The method for preparing a solder mask according to claim 1, wherein: The method for preparing the printed circuit board comprises the following steps: A copper-clad laminate is provided, wherein the copper-clad laminate comprises a substrate layer and a copper foil layer disposed on a surface of the substrate layer; The copper foil layer is made into a conductive circuit layer to obtain the printed circuit board.
8. The method for preparing a solder mask according to claim 7, wherein: The substrate layer comprises glass fiber, epoxy resin and ultraviolet absorber, and the weight percentage of the ultraviolet absorber in the copper clad laminate is 11% to 15%.
9. The method for preparing a solder mask according to claim 7, wherein: The method for preparing the printed circuit board also includes the following steps: laminating a build-up circuit substrate on the side of the conductive circuit layer away from the base material layer, the build-up circuit substrate including a dielectric layer and a build-up circuit layer, and the dielectric layer is located between the conductive circuit layer and the build-up circuit layer.
10. The method for preparing a solder mask according to claim 1, wherein: Before the step of laminating the solder mask on the surface of the printed circuit board, the preparation method further comprises the step of pre-treating the printed circuit board.