Circuit board manufacturing method using screen printing

Abstract

To make it possible to prevent a disconnection without making a conductive pattern layer thicker when the conductive pattern layer is stacked on an end portion of a thickened insulating layer or conductive layer.SOLUTION: An insulating layer 11 is formed on a substrate 10 by a screen printing method. The insulating layer 11 includes a main part 11a and a protruding part 11b. An inclined part 11c is formed on a side in the protruding direction of the protruding part 11b. An inclined part 11d is formed on the top surface of the protruding part 11b. The protruding part 11b shown in Fig. 1C is finer, lower in height, and has a gentler inclination of the inclined part 11c compared to the protruding portion 11b shown in Fig. 1b. When a conductive pattern layer is stacked on the insulating layer 11, even if a disconnection occurs on the protruding part 11b shown in Fig. 1B, a disconnection does not occur on the protruding part 11b shown in Fig. 1C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a circuit board by screen printing. [Background technology]

[0002] There is a technique for manufacturing circuit boards by screen printing (Patent Document 1). In the method for manufacturing circuit boards by screen printing, a screen printing mask is created on a mesh screen, with portions through which a printing paste can pass (hereinafter referred to as openings) and portions through which the printing paste cannot pass (hereinafter referred to as non-openings), and the printing paste is placed on this screen printing mask and pushed out through the openings using a squeegee to form a printing layer on the substrate.

[0003] The advantage of the screen printing method for manufacturing circuit boards is that by using a thicker screen, the insulating layer and conductive pattern layer formed as printed layers can be made thicker. By making the conductive pattern layer thicker, the pattern resistance, which is a source of loss in electronic circuits, can be reduced. Furthermore, in laminated substrates, by making the interlayer insulating layer thicker, short circuits between upper and lower conductive pattern layers due to manufacturing problems can be prevented. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-7747 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a conductive pattern is laminated on the end of a thick insulating layer, there is a problem that the conductive pattern layer may break. This will be explained with reference to Figure 8. Note that the directions (up, down, left, right) in the following explanation are directions on the drawing.

[0006] 8A and 8B are diagrams illustrating a process for manufacturing a circuit board by screen printing. Here, Fig. 8A is a plan view of a state in which an insulating layer 101 has been formed on a substrate 100, and Fig. 8B is a cross-sectional view taken along line AA in Fig. 8A. Also, Fig. 8C is a plan view of a state in which a conductive pattern layer 102 has been formed on the insulating layer 101, and Fig. 8D is a cross-sectional view taken along line AA in Fig. 8C. Here, the insulating layer 101 and the conductive pattern layer 102 are formed by screen printing.

[0007] First, as shown in Figures 8A and 8B, an insulating layer 101 is formed on the upper surface of a base material 100 of the circuit board, and then, as shown in Figures 8C and 8D, a conductive pattern layer 102 is formed from the center in the left-right direction of the insulating layer 101, over the right end portion 101a, to the upper surface of the base material 100.

[0008] However, as shown in Fig. 8D, the conductive pattern layer 102 is not formed in the step portion formed between the right end portion 101a of the insulating layer 101 and the upper surface of the substrate 100, and is separated and disconnected into a portion formed on the insulating layer 101 and a portion formed on the substrate 101. Note that, for convenience, the disconnection of the conductive pattern layer 102 is omitted in Fig. 8C.

[0009] Disconnections can be prevented by thickening the conductive pattern layer 102 in the same way as the insulating layer 101, but this may not be possible depending on the material used. The disconnections described above also occur when a conductive pattern layer is laminated on the end of a thick conductive layer. For example, in FIG. 8D , if the insulating layer 101 is a conductive layer, and the conductive pattern layer 102 shrinks during firing, causing the left end of the conductive pattern layer 102 on the substrate 100 to shift to the right from the position shown in the figure, the portion of the conductive pattern layer 102 on the conductive layer and the portion on the substrate 100 will no longer be electrically connected.

[0010] The present invention has been made to solve such problems, and its purpose is to make it possible to prevent breakage of a conductive pattern layer when the conductive pattern layer is laminated on the end of a thick insulating layer or conductive layer without making the conductive pattern layer thicker. [Means for solving the problem]

[0011] The present invention is a method for manufacturing a circuit board, which includes a first step of forming a first layer consisting of an insulating layer or a conductor layer on a substrate by screen printing, and a second step of laminating a conductive pattern layer on an end of the first layer by screen printing, wherein the first step forms a portion of the end of the first layer as a thin protrusion. [Effects of the Invention]

[0012] According to the present invention, when a conductive pattern layer is laminated on the end of a thick insulating layer or conductive layer, breakage of the conductive pattern layer can be prevented without thickening the conductive pattern layer. [Brief explanation of the drawings]

[0013] [Figure 1] 5A to 5C are diagrams for explaining an insulating layer forming step in the manufacturing method for a circuit board according to the embodiment of the present invention. [Figure 2] 5A to 5C are diagrams for explaining a conductive pattern layer forming step in the manufacturing method for a circuit board according to an embodiment of the present invention. [Figure 3] 1A and 1B are diagrams showing a screen printing mask used in a method for manufacturing a circuit board according to an embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing the relationship between a change in line width of a screen printing mask and a change in printed film thickness. [Figure 5] FIG. 10 is a diagram showing the relationship between a change in line width of a screen printing mask and a change in printed film thickness relative to the line width. [Figure 6] 10A and 10B are diagrams for explaining changes in the thickness and inclination of a printing film in response to changes in the line width of a screen printing mask. [Figure 7] 10A and 10B are diagrams for explaining why the printed film thickness becomes thin and the slope becomes gentle when the line width of the screen printing mask is narrow. [Figure 8]1A to 1C are diagrams for explaining a process for manufacturing a circuit board by a screen printing method. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. <Circuit board manufacturing method> 1A and 1B are diagrams illustrating an insulating layer forming step in a method for manufacturing a circuit board according to an embodiment of the present invention, in which Fig. 1A is a plan view of the circuit board after the insulating layer forming step has been completed, and Figs. 1B, 1C, and 1D are cross-sectional views taken along lines BB, CC, and AA, respectively, of Fig. 1A.

[0015] 2A and 2B are diagrams illustrating a conductive pattern layer forming step in a method for manufacturing a circuit board according to an embodiment of the present invention, in which Fig. 2A is a plan view of the circuit board at the stage where the conductive pattern layer forming step has been completed, and Figs. 2B, 2C, and 2D are cross-sectional views taken along lines BB, CC, and AA, respectively, in Fig. 2A.

[0016] 3A and 3B are diagrams showing screen printing masks used in the method for manufacturing a circuit board according to an embodiment of the present invention. Fig. 3A is a plan view of an insulating layer screen printing mask 20 used in the insulating layer formation step, and Fig. 3B is a plan view of a conductive pattern layer screen printing mask 30 used in the conductive pattern layer formation step. The method for manufacturing a circuit board according to an embodiment of the present invention will be described with reference to these figures.

[0017] <Insulating layer formation process> 1A to 1D, an insulating layer 11 is formed on a substrate 10. The substrate 10 is made of a resin film such as PET (polyethylene terephthalate) or PI (polyimide).

[0018] The insulating layer 11 is formed by a screen printing method using an insulating layer screen printing mask 20 shown in FIG. 3A. The insulating layer screen printing mask 20 has a vertical and horizontal size of, for example, 100 mm x 100 mm in the figure, and includes openings 21 through which an insulating paste (e.g., Fujikura Kasei XB-3136) for printing passes, and non-openings 22 through which the insulating paste does not pass. Each opening 21 is composed of a main portion 21a that is rectangular in plan view, and a protruding portion 21b that protrudes from the main portion 21a. The line width of the protruding portion 21b becomes narrower (its vertical length in the figure becomes shorter) as it approaches the tip of the protruding portion 21b in the plan view. It can also be said that the protruding portion 21b becomes thinner as it approaches the tip of the protruding portion.

[0019] When forming the insulating layer 11 on the substrate 10, an insulating layer screen printing mask 20 is placed at a predetermined positional relationship (clearance) with respect to the surface of the substrate 10 (the upper surface in FIGS. 1B, 1C, and 1D), an insulating paste is placed on the surface, and a squeegee (not shown) is moved over the surface of the insulating layer screen printing mask 20 to extrude the insulating paste through openings 21 and print it on the substrate 10. The substrate 10 on which the insulating paste has been printed is then heated and baked to harden it.

[0020] The insulating layer 11 formed on the substrate 10 by this insulating layer formation process has a main portion 11a and a protruding portion 11b that, when viewed in plan, correspond to the shape of the opening 21 of the insulating layer screen printing mask 20, as shown in Figure 1A.

[0021] 1B and 1C, a sloped portion 11c is formed on the side surface of the protrusion 11b in the protruding direction, and as shown in Fig. 1D, a sloped portion 11d is formed on the top surface of the protrusion 11b. Compared to the protrusion 11b shown in Fig. 1B, the protrusion 11b shown in Fig. 1C has a narrower width (horizontal length in the figure) in response to the fact that the line width of the protrusion 21b of the insulating layer screen printing mask 20 becomes narrower as it approaches the tip in the protruding direction. Furthermore, the protrusion 11b shown in Fig. 1C is also lower in height, and the slope of the sloped portion 11c is gentler. The reasons for this and the effects will be described later.

[0022] <Conductive pattern formation process> In this step, as shown in FIGS. 2C and 2D, a conductive pattern layer 12 is formed on the insulating layer 11 formed in the insulating layer forming step.

[0023] The conductive pattern layer 12 is formed by a screen printing method using a conductive pattern layer screen printing mask 30 shown in Figure 3B. The conductive pattern layer screen printing mask 30 has the same vertical and horizontal dimensions as the insulating layer screen printing mask 20, and has openings 31 that are rectangular in plan view and allow a conductive paste (e.g., Fujikura Kasei FA-353N) to pass through, and non-openings 32 that do not allow the conductive paste to pass through. The line width of the openings 31 (the length in the vertical direction in the figure) is narrower than the main portion 21a of the insulating layer screen printing mask 20 and wider than the base end side of the protruding portions 21b.

[0024] When forming the conductive pattern layer 12 on the insulating layer 11, a conductive pattern layer screen printing mask 30 is placed at a predetermined positional relationship (clearance) with respect to the surface of the base material 10 on which the insulating layer 11 has been formed, a conductive paste is placed on the surface, and a squeegee (not shown) is moved over the surface of the conductive pattern layer screen printing mask 30 to extrude the conductive paste through the openings 31 and print it on the insulating layer 11. Then, the base material 10 on which the conductive paste has been printed is heated and baked to harden it.

[0025] 2A, the conductive pattern layer 12 formed on the insulating layer 11 by this conductive pattern layer formation step has a rectangular shape in plan view corresponding to the shape of the opening 21 of the conductive pattern layer screen printing mask 30. Also, as shown in FIG. 2D, the conductive pattern layer 12 has an inclined portion 12a that follows the inclined portion 11d of the protruding portion 11b of the insulating layer 11.

[0026] 2B, the conductive pattern layer 12 laminated on the protruding portion 11b of the insulating layer 11 shown in Fig. 1B is separated and disconnected at the inclined portion of the side surface of the protruding portion 11b, whereas as shown in Fig. 2C, the conductive pattern layer 12 laminated on the protruding portion 11b shown in Fig. 1C, which is thinner, lower, and has a gentler slope than the protruding portion 11b of the insulating layer 11 shown in Fig. 1B, is not disconnected. In other words, although the main portion 11a of the insulating layer 11 is thickened, the thin thickness of the protruding portion 11b and the gentle slope improve the adhesion of the conductive paste and prevent disconnection.

[0027] Next, the reason why the protrusion 11b shown in FIGS. 1B, 1C, and 1D is formed will be explained. <Relationship between changes in line width of screen printing mask and changes in printing film thickness> Figure 4 shows the relationship between changes in line width of a screen printing mask and changes in printed film thickness. This figure is taken from Asada Mesh Co., Ltd.'s "Screen Printing Principles and Standard Techniques, High-Quality Screen Printing, 2014 Technical Information, No. 0005." Here, in BS-400 / 23, 400 is the number of lines, 23 is the wire diameter, and 55 and 40 are the mesh thickness. CL also represents the calendering (rolling) process.

[0028] As shown in the figure, the print film thickness becomes thinner as the line width becomes narrower. Also, for fine lines (line width 120 μm or less), the print film thickness changes by roughly the same amount as the line width changes, even if the mesh thickness is different.

[0029] 3A, the line width of the protruding portion 21b of the opening 21 of the insulating layer screen printing mask 20 becomes narrower toward the tip in the protruding direction, and therefore the film thickness of the protruding portion 11b of the insulating layer 11 printed on the substrate 10 through this protruding portion 21b becomes thinner toward the tip in the protruding direction. As a result, the protruding portion 11b having the film thickness shown in FIGS. 1B, 1C, and 1D is formed.

[0030] <Relationship between the change in line width of a screen printing mask and the change in printing film thickness with respect to the line width> Figure 5 is a diagram showing the relationship between the change in line width of a screen printing mask and the change in printing film thickness with respect to the line width. The graph in this figure illustrates the values calculated based on the relationship between the change in line width and the change in printing film thickness of one of the screen printing masks ("BS-400 / 23-40CL") shown in the graph of Figure 4. However, even if calculated based on the relationship between the change in line width and the change in printing film thickness of the other screen printing mask ("BS-400 / 23-55"), a similar graph will be obtained. Also, Figure 6 is a diagram for explaining the change in thickness and slope of the printing film with respect to the change in line width of the screen printing mask, that is, a diagram for explaining Figure 5.

[0031] From Figure 5, it can be seen that as the line width becomes narrower, the value of the printing film thickness with respect to the line width (printing film thickness / line width. Hereinafter referred to as aspect ratio) becomes smaller. That is, for example, as shown in Figure 6A, assume that a protruding portion 11b with a printing film thickness D1 is formed when the insulating layer 11 is formed with a line width W1. Next, as shown in Figure 6B, assume that a protruding portion 11b with a printing film thickness D2 is formed when the insulating layer 11 is formed with a line width W2 (W2 < W1).

[0032] In this case, from Figure 5, (D2 / W2) < (D1 / W1). That is, the protruding portion 11b shown in Figure 6B has a lower height with respect to the line width (smaller aspect ratio) than the protruding portion 11b shown in Figure 6A. The dotted line 11b' in Figure 6B represents a protruding portion with the same aspect ratio as the protruding portion 11b shown in Figure 6A at a line width W2. That is, (D2' / W2) = (D1 / W1). Also, the protruding portion 11b shown in 6B has a gentler slope of the inclined portion 11b compared to the protruding portion 11b shown in Figure 6A. The reason for this will be described later with reference to Figure 7.

[0033] Here, the protrusion 11b shown in Figure 6A and the protrusion 11b shown in Figure 6B correspond to the protrusion 11b shown in Figure 1B and the protrusion 11b shown in Figure 1C, respectively, and therefore, a protrusion 11b having a film thickness and a slope as shown in Figures 1B and 1C is formed.

[0034] Next, the reason why the printing film thickness becomes thinner and the slope becomes gentler when the line width of the screen printing mask is narrow will be explained with reference to Fig. 7. Fig. 7 shows a graph showing the relationship between the change in line width of the screen printing mask and the change in printing film thickness, as well as the state of plate release when the line width is narrow and the state of plate release when the line width is medium.

[0035] The paste is placed on a screen printing mask and pushed out through the openings using a squeegee to form a printing layer on the substrate. At the moment when the screen printing mask is released from the substrate, the paste is held with an adhesion force proportional to the area of ​​contact with the substrate, and separates midway between the paste that has adhered to the mesh part and the emulsion wall surface.

[0036] In the case of a narrow, thin line, the adhesion between the paste and the substrate is very weak, so most of the paste remains in contact with the emulsion walls and mesh during stencil release, resulting in a thin print film and a gentler slope. On the other hand, when the line width is relatively wide—more than twice the total thickness of the screen printing mask ("medium" in the figure), most of the paste in the mesh openings is transferred to the substrate during stencil release, resulting in a thick print film and a steeper slope. Naturally, in the case of the "thin line" in the figure, the print film is thinner and the slope is gentler than when the line width is between "thin line" and "medium" in the figure.

[0037] As described above in detail, according to the method for manufacturing a circuit board according to an embodiment of the present invention, when a conductive pattern is laminated on the end of a thickened insulating layer, breakage of the conductive pattern can be prevented without thickening the conductive pattern.

[0038] It should be noted that the above-described embodiment relates to the case where a conductive pattern is laminated on the end of a thickened insulating layer, but the present invention can also be used to laminate a conductive pattern on the end of a thickened conductive layer, making it possible to prevent breakage of the laminated conductive pattern without thickening the conductive pattern.

[0039] In the embodiment described above, the protrusions 21b of the insulating layer screen printing mask 20 are triangular in plan view, so that their widths linearly narrow toward the tips. However, they may be configured so that their widths narrow nonlinearly toward the tips. Furthermore, they may be configured so that they have a portion whose width narrows nonlinearly toward the tips, such as a gourd shape in plan view. In short, it is sufficient to configure the width of at least a portion (part or all) of the protrusions to narrow toward the tips. [Explanation of symbols]

[0040] 10...substrate, 11...insulating layer, 11a...main portion, 11b...protruding portion, 12...conductive pattern layer, 20...insulating layer screen printing mask, 21...opening, 21a...main portion, 21b...protruding portion, 22...non-opening, 30...conductive pattern layer screen printing mask, 31...opening, 32...non-opening.

Claims

1. A method for manufacturing a circuit board, comprising: a first step of forming a first layer made of an insulating layer or a conductor layer on a substrate by a screen printing method; and a second step of laminating a conductive pattern layer on an end portion of the first layer by the screen printing method, A method for manufacturing a circuit board, wherein the first step forms a part of an end portion of the first layer as a thin protrusion.

2. 2. The method for manufacturing a circuit board according to claim 1, The method for manufacturing a circuit board, wherein at least a portion of the protruding portion is thinner as it approaches a tip in a protruding direction.

3. 3. The method for manufacturing a circuit board according to claim 2, At least a portion of the protrusion is tapered linearly.

4. 3. The method for manufacturing a circuit board according to claim 2, The method for manufacturing a circuit board, wherein at least a portion of the protrusion tapers non-linearly.

5. The method for manufacturing a circuit board according to any one of claims 1 to 4, The protrusion has a slope on the top surface and the side surface.

6. 6. The method for manufacturing a circuit board according to claim 5, In the method for manufacturing a circuit board, the thinner the protrusion, the gentler the inclination of the side surface.

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