Method for manufacturing printed wiring board

Abstract

According to the present invention, a low-cost and highly accurate printed wiring board is obtained.　This method for manufacturing a printed wiring board comprises a step for forming a solder resist layer 130 for selectively covering a surface of a printed board 100 having a printed wiring group 120 including a land 124 on a surface thereof, such that all or a part of the surface of at least the land 124 is exposed. The step for forming the solder resist layer 130 includes a first step for forming a first sub-solder resist layer 131 through inkjet printing, and a second step for forming a second sub-solder resist layer 132 through screen printing. In a plan view of the printed board 100, the first sub-solder resist layer 131 is formed around the land 124, and the second sub-solder resist layer 132 is formed around at least an edge part 131a of the first sub-solder resist layer 131 on the side adjacent to the periphery of the land 124.

Description

Printed wiring board manufacturing method

[0001] The present invention relates to a method for manufacturing a printed wiring board, which includes a step of forming a solder resist film.

[0002] A printed wiring board comprises a substrate and printed wiring provided on the substrate, which forms a predetermined circuit pattern and includes lands for mounting electronic components by soldering. In order to prevent short circuits and oxidation of the printed wiring, a solder resist layer made of insulating resin (solder resist) is further formed on the surface of the printed wiring board on which the printed wiring is formed, except for the areas corresponding to the lands. In other words, only the lands are exposed on the surface of the printed wiring board, and the other areas of the printed wiring and the surface of the printed board are covered with solder resist.

[0003] In recent years, the miniaturization of electronic components such as capacitors included in printed wiring boards has progressed, and accordingly, there is a demand for the size of the lands soldered to the electronic components to be reduced accordingly. Therefore, it is necessary to form the solder resist layer precisely in the desired position and shape so that the solder resist layer does not overlap the lands and interfere with soldering when mounting the components.

[0004] A known method for forming a solder resist layer with high precision so that it does not overlap the lands is to form a pattern using a photodevelopment method, but this method requires a large number of steps, such as exposure and development, which results in high costs and long working hours. Therefore, Patent Document 1 proposes a technology for forming a solder resist layer using screen printing, which is less expensive.

[0005] The technology disclosed in Patent Document 1 forms a solder resist layer by screen-printing and curing two types of resin materials (solder resist inks) with different viscosities. Specifically, the solder resist ink with a higher viscosity covers the periphery of the lands, while the solder resist ink with a lower viscosity covers the entire printed wiring board, thereby aiming to form a solder resist layer with high accuracy at low cost.

[0006] Patent No. 7014744

[0007] In the above-mentioned conventional solder resist formation method, two types of mesh are used as screen printing plates depending on the type of solder resist ink and the printing location. However, changing the plate requires a setup change and cleaning after each use. Furthermore, to maintain the plate's precision after use, it must be stored in a temperature- and humidity-controlled location. Furthermore, because the plate is flexible, its quality gradually deteriorates with use, resulting in a deterioration in the precision of the resulting solder resist layer. To maintain precision, the plate must be periodically remade, which results in high costs.

[0008] SUMMARY OF THE INVENTION Therefore, a primary object of the present invention is to provide a method for manufacturing a printed wiring board that can provide a printed wiring board at low cost and with high precision.

[0009] The method for manufacturing a printed wiring board according to the present invention comprises a step of forming a solder resist layer that selectively covers the surface of a printed circuit board having printed wiring including lands on its surface so that at least all or part of the surface of the lands is exposed, and the step of forming the solder resist layer comprises a first step of forming a first sub-solder resist layer by inkjet printing and a second step of forming a second sub-solder resist layer by screen printing, and in this method for manufacturing a printed wiring board, in a planar view of the printed circuit board, the first sub-solder resist layer is formed around the lands, and the second sub-solder resist layer is formed around at least the edge of the first sub-solder resist layer that is adjacent to the periphery of the lands.

[0010] According to the present invention, it is possible to obtain a printed wiring board at low cost and with high precision.

[0011] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

[0012] 10 is a plan view showing a printed wiring board according to a first embodiment of the present invention; FIG. 11 is a schematic cross-sectional view taken along line II-II in FIG. 1; and FIG. 12 is a flowchart illustrating a method for manufacturing a printed wiring board according to the first embodiment of the present invention. (A) to (C) are cross-sectional views illustrating a method for manufacturing a printed circuit board of a printed wiring board according to the first embodiment of the present invention. (A) to (D) are cross-sectional views illustrating a method for manufacturing a printed wiring board according to the first embodiment of the present invention. (A) to (C) are plan views illustrating a method for manufacturing a printed wiring board according to the first embodiment of the present invention. (A) to (F) are cross-sectional views showing an example of the configuration of a laminate according to the first embodiment of the present invention. (A) to (C) are cross-sectional views illustrating a method for manufacturing a printed wiring board according to a modified example of the first embodiment of the present invention. (A) to (D) are cross-sectional views illustrating a method for manufacturing a printed wiring board according to a modified example of the first embodiment of the present invention. A plan view showing a printed wiring board according to a second embodiment of the present invention. A schematic cross-sectional view taken along line XI-XI in FIG. 1A to 1D are cross-sectional views illustrating a method for manufacturing a printed wiring board according to a second embodiment of the present invention; 1A to 1C are plan views illustrating a method for manufacturing a printed wiring board according to a second embodiment of the present invention; 1A to 1C are cross-sectional views illustrating a method for manufacturing a printed wiring board according to a modified example of the second embodiment of the present invention; 1A to 1D are cross-sectional views illustrating a method for manufacturing a printed wiring board according to a modified example of the second embodiment of the present invention.

[0013] A. First Embodiment An example of a method for manufacturing a printed wiring board according to a first embodiment of the present invention will now be described.

[0014] 1. Printed Wiring Board A printed wiring board 10, which is an example of a printed wiring board according to a first embodiment of the present invention, will be described. Fig. 1 is a plan view showing printed wiring board 10 according to the first embodiment of the present invention. Fig. 2 is a schematic cross-sectional view taken along line II-II in Fig. 1.

[0015] The printed wiring board 10 includes a printed circuit board 100 and a solder resist layer 130 provided on the printed circuit board 100 .

[0016] (Printed Circuit Board) The printed circuit board 100 includes a base material 110 and a printed wiring group 120 provided on the base material 110. As will be described later, the base material 110 can have various configurations, but for example, a glass epoxy board can be used.

[0017] The printed wiring group 120 is a thin film layer of a conductive material that is bonded to the surface of the base material 110 and then processed by etching or other means to form a predetermined circuit pattern. The conductive material of the printed wiring group 120 may be, for example, copper foil.

[0018] A predetermined number of lands for soldering to electronic components are provided at arbitrary locations on each of the printed wirings constituting the printed wiring group 120. In this embodiment, as an example in which the configuration is simplified for the purpose of explanation, a land 124 is formed at the end of the second printed wiring 122 in the first printed wiring 121, the second printed wiring 122, and the third printed wiring 123 constituting the printed wiring group 120. Although the land 124 is shown as having a rectangular shape wider than the second printed wiring 122 in a plan view, it may have a circular or any other shape.

[0019] (Solder Resist Layer) The solder resist layer 130 is an insulating layer provided on the printed wiring board 10 so as to cover the entire surface of the printed circuit board 100 except for a portion of the printed circuit board 100 including the lands 124 and their surroundings.

[0020] The solder resist layer 130 has a first sub-solder resist layer 131 formed around the lands 124 in a plan view of the printed circuit board 100 (hereinafter simply referred to as "plan view"), and a second sub-solder resist layer 132 formed around the edge of the first sub-solder resist layer 131 on the side adjacent to the periphery of the lands 124. Details will be described below.

[0021] The first auxiliary solder resist layer 131 is an insulating layer having a rectangular frame shape in plan view, formed to seamlessly surround the lands 124, including part of the second printed wiring 122. Specifically, the first auxiliary solder resist layer 131 has a rectangular opening 131x in plan view at the center of its rectangular outline in plan view, and the lands 124 are disposed within the opening 131x. In the first auxiliary solder resist layer 131, an edge 131a of the opening 131x, which forms the inner edge adjacent to the periphery of the lands 124, is formed to be spaced apart from the edge 124a of the lands 124 by a predetermined distance G. In other words, the first auxiliary solder resist layer 131 is formed so as not to overlap or contact the lands 124. The dimension of the distance G can be any value depending on the shape and dimensions of the lands 124, but is preferably in the range of 50 μm to 200 μm, for example.

[0022] In the first auxiliary solder resist layer 131, the distance between the edge 131a and the edge 131b, i.e., the width W1 of the frame shape, can be any value depending on the circuit pattern of the printed wiring group 120, but it is preferable that it be in the range of 100 μm or more and 300 μm, for example.

[0023] The shape of the opening 131x preferably corresponds to the shape of the land 124. That is, if the land 124 is circular or has any other shape, the opening 131x preferably has a similar shape to that shape.

[0024] The thickness T1 of the first sub-solder resist layer 131 can be any value depending on the design conditions of the printed wiring board 10, but is preferably in the range of 5 μm to 20 μm, for example.

[0025] The second auxiliary solder resist layer 132 is an insulating layer formed to further surround from the outside the periphery of the exposed portion of the printed circuit board 100, including the lands 124, which is surrounded by the first auxiliary solder resist layer 131, and to cover all remaining portions of the printed circuit board 100. Specifically, the second auxiliary solder resist layer 132 has an opening 132x that is rectangular in plan view corresponding to the position of the first auxiliary solder resist layer 131, and is formed so that the opening 131x of the first auxiliary solder resist layer 131 is located within the opening 132x. An edge 132a of the opening 132x, which forms the inner edge of the second auxiliary solder resist layer 132, is formed to be located outside the opening 131x of the first auxiliary solder resist layer 131 and inside an edge 131b, which forms the outer edge of the first auxiliary solder resist layer 131.

[0026] As a result, the solder resist layer 130 has an overlapping region 130a, which is a region formed by overlapping the second solder resist sub-layer 132 on the first solder resist sub-layer 131. The dimension L of the overlapping region 130a in plan view can be any value depending on the shape and dimensions of the first solder resist sub-layer 131 and the circuit pattern of the printed wiring group 120, but is preferably in the range of 50 μm to 200 μm, for example.

[0027] The shape of the opening 132x preferably corresponds to the shape of the opening 131x. That is, if the opening 131x is circular or has any other shape, the opening 132x preferably has a similar shape to that shape.

[0028] The thickness T2 of the second auxiliary solder resist layer 132 can be any value depending on the design conditions of the printed wiring board 10, but is preferably in the range of 5 μm to 30 μm, for example. Furthermore, the thickness T2 of the second auxiliary solder resist layer 132 and the thickness T1 of the first auxiliary solder resist layer 131 preferably have a relationship of T2>T1.

[0029] The solder resist layer 130 is formed on the printed wiring board 10 having one land 124 as a land, and has an opening 131x in the first sub-solder resist layer 131 that exposes the land 124, but the solder resist layer may selectively cover the entire or part of the surface of the land included in the printed wiring so as to expose it, depending on the various circuit patterns of the printed wiring on the printed wiring board.

[0030] 2. Method for Manufacturing a Printed Wiring Board A printed wiring board 10, which is an example of a printed wiring board according to a first embodiment of the present invention, will be described. Fig. 3 is a diagram showing a flowchart illustrating a method for manufacturing the printed wiring board 10 according to the first embodiment of the present invention. Figs. 4 and 5 are schematic cross-sectional views showing the state of the printed wiring board 10 in the steps shown in the flowchart of Fig. 3, and are cross-sectional views corresponding to the cross-sectional view of line II-II in Fig. 2. Fig. 6 is a plan view showing the state of the printed wiring board 10 in the steps shown in the flowchart of Fig. 3.

[0031] (Manufacturing of Printed Circuit Board) First, a laminate 200 is prepared, in which a copper foil layer 112, which serves as the base of a printed wiring group 120, is bonded to the surface of a substrate 110 (step S001). FIG. 7A shows a cross section of the laminate 200 prepared in step S001. In the laminate 200, the substrate 110 is configured by impregnating glass cloth with epoxy resin. This results in a printed circuit board 100 as a glass epoxy board. In this case, the thickness of the substrate 110 is preferably 0.1 mm or more and 2.0 mm or less, and the thickness of the copper foil layer 112 is preferably 18 μm or more and 70 μm or less.

[0032] The laminate 200 may have the following configuration. Specifically, as shown in FIG. 7B, the substrate 110 may be made of paper impregnated with phenolic resin. This results in a printed circuit board 100 as a paper-phenolic board. In this case, the thickness of the substrate 110 is preferably 0.8 mm or more and 2.0 mm or less, and the thickness of the copper foil layer 112 is preferably 35 μm or more and 70 μm or less.

[0033] 7C, the substrate 110 may be configured by bonding a glass cloth laminate 111b to both sides of a paper core 111a, and impregnating both materials with epoxy resin. This results in a composite substrate-epoxy printed circuit board 100. In this case, the thickness of the substrate 110 is preferably 0.8 mm to 1.6 mm, and the thickness of the copper foil layer 112 is preferably 35 μm.

[0034] 7(D), the substrate 110 may be configured by bonding a laminated material 111b of glass cloth to both sides of a core material 111a of glass nonwoven fabric, and impregnating both materials with epoxy resin. This results in a printed circuit board 100 as a glass composite substrate. In this case, the thickness of the substrate 110 is preferably 0.8 mm or more and 1.6 mm or less, and the thickness of the copper foil layer 112 is preferably 18 μm or more and 70 μm or less.

[0035] Similarly, as shown in FIG. 7E , the substrate 110 may be configured by bonding a laminate material 111b, an insulating layer with excellent thermal conductivity, which is a mixture of epoxy resin and filler, to the surface of an aluminum core material 111a on which the copper foil layer 112 is bonded. The filler may be a metal oxide, a metal hydroxide, or glass cloth. This results in an aluminum-based printed circuit board 100. In this case, the thickness of the core material 111a is preferably 1.0 mm to 3.0 mm, the thickness of the laminate material 111b is preferably 80 μm to 120 μm, and the thickness of the copper foil layer 112 is preferably 18 μm to 105 μm.

[0036] Similarly, as shown in Fig. 7(F), the substrate 110 may be configured by bonding a laminate material 111b, which is an insulating layer having a configuration similar to that of the insulating layer in Fig. 7(E), to the surface of a core material 111a, which is a copper plate, on the side where the copper foil layer 112 is bonded. This results in a printed circuit board 100 as a copper-based substrate. In this case, it is preferable that the thickness of the core material 111a is 1.0 mm or more and 1.5 mm or less, the thickness of the laminate material 111b is 120 μm, and the thickness of the copper foil layer 112 is 35 μm or more and 105 μm or less.

[0037] Next, a mask having a planar shape corresponding to the circuit pattern of the printed wiring group 120 is prepared (step S002). When the printed wiring group 120 is obtained by a photography method, the mask is prepared as a film having the circuit pattern as an opening. When the printed wiring group 120 is obtained by a printing method, the mask is prepared as a screen plate having the circuit pattern as an opening. When the mask is applied directly to the laminate to obtain the printed wiring group 120, the mask is prepared by software, for example, as CAD data of the printing pattern.

[0038] Next, an etching resist layer having a circuit pattern is formed on the copper foil layer 112 using a mask (step S003). When the printed wiring group 120 is obtained by a photographic method, an etching resist ink is uniformly applied to the copper foil layer 112, and a mask is laminated thereon. Unnecessary portions of the applied etching resist ink are removed through exposure and development processes. When the printed wiring group 120 is obtained by a printing method, a negative shape of the mask is formed on a screen plate on the copper foil layer 112, and the etching resist ink is formed on the copper foil layer 112 by screen printing. Alternatively, the etching resist ink is directly printed on the copper foil layer 112 using a printer. Figure 4(A) shows the state in which the etching resist layer 140 has been formed on the surface of the laminate 200 in step S003.

[0039] Next, the laminate 200 on which the etching resist layer 140 has been formed is etched to remove the copper foil layer 112 except for the portion covered by the etching resist layer 140 (step S004). As a result, the planar shape of the copper foil layer 112 forms a circuit pattern that reflects the planar shape of the etching resist layer 140. Fig. 4(B) shows the state in which the planar shape of the copper foil layer 112 forms a circuit pattern on the surface of the laminate 200 through the etching resist layer 140 in step S004.

[0040] Next, the etching resist layer 140 is removed from the laminate 200 by peeling it off with an ink remover (step S005), thereby obtaining the printed circuit board 100. Figures 4(C) and 6(A) show the state in which the printed circuit board 100 is obtained by removing the etching resist layer 140 from the laminate 200 in step S005.

[0041] (Formation of Solder Resist Layer) Next, the solder resist layer 130 is formed on the printed circuit board 100 .

[0042] First, in a first step, the first auxiliary solder resist layer 131 is formed by inkjet printing around a part of the second printed wiring 122 of the printed wiring group 120 and the lands 124 (step S006).

[0043] 6B, the first auxiliary solder resist layer 131 has a rectangular outer shape in plan view, has a rectangular opening 131x formed in the center in plan view, and the land 124 is arranged within the opening 131x. Specifically, using an inkjet printer to which the shape of the first auxiliary solder resist layer 131 has been input as CAD data, solder resist ink 301 is applied by inkjet printing as shown in FIG. 5A, and then the solder resist ink 301 is UV-cured and thermally cured in that order, thereby forming the first auxiliary solder resist layer 131.

[0044] In the above description, the first step is to form one first sub-solder resist layer 131 around the land 124 for the printed wiring board 10 having one land 124 as a land, but the first step may be any step that selectively forms each of a plurality of first sub-solder resist layers corresponding to all or part of a plurality of lands depending on the design of the printed wiring board.

[0045] The thickness T1 of the first sub-solder resist layer 131 can be any value depending on the design conditions of the printed wiring board 10, but is preferably in the range of 5 μm to 20 μm, for example. Inkjet printing is preferably performed in an environment with a temperature of 20° C. to 25° C. and a humidity of 30% to 70%.

[0046] By using inkjet printing to print the solder resist ink 301, the edge 131a of the opening 131x of the first sub-solder resist layer 131 can be formed with high precision while being separated from the edge 124a of the land 124 by a predetermined distance G without contacting or overlapping the surface of the land 124.

[0047] Furthermore, by using inkjet printing to print the solder resist ink 301, the coordinates of the printing position can be optically obtained using a CCD camera or the like for each production of the printed wiring board 10, and the position on the X-axis and Y-axis on the surface of the printed circuit board 100 can be corrected successively. Specifically, the recognition marks, lands 124, and other corners of specific locations on the printed wiring group 120 that have been created in advance when the printed wiring group 120 is formed are read, and the printing position is set based on the read positions.

[0048] This makes it possible to eliminate the cost of replacing the printing plate, which is required in other printing methods, and to maintain uniform precision of the first auxiliary solder resist layer 131 even when the printed wiring board 10 is repeatedly manufactured.

[0049] The solder resist ink 301 used for the first sub-solder resist layer 131 is a resin that is primarily made of acrylate resin and is capable of both UV curing and heat curing, and preferably has a viscosity in the range of 10 mPa·s to 45 mPa·s. The solder resist ink 301 is preferably stored in a cool, dark place at a temperature of 0°C to 30°C.

[0050] The curing conditions for the solder resist ink 301 are preferably as follows for both UV curing and thermal curing. That is, for UV curing, the layering light intensity is preferably in the range of 100 mJ / cm2 to 500 mJ / cm2. For thermal curing, the curing temperature is preferably 150°C and the exposure time is preferably in the range of 20 minutes to 70 minutes. Figure 6(B) shows the state after the first sub-solder resist layer 131 has been formed on the printed circuit board 100 in step S006.

[0051] Next, in a second step, a second auxiliary solder resist layer 132 is formed on the printed circuit board 100 by screen printing (step S007).

[0052] The second auxiliary solder resist layer 132 is formed to surround from the outside the periphery of the exposed portion of the printed circuit board 100, including the lands 124, which is surrounded by the first auxiliary solder resist layer 131, and to cover all remaining portions of the printed circuit board 100. Specifically, as shown in Fig. 5(B) , a screen plate 300 is placed on the first auxiliary solder resist layer 131, and as shown in Fig. 5(C) , a squeegee (not shown) is pressed against the screen plate 300 parallel to the printed circuit board 100, and solder resist ink 302 is printed so as to fill the screen openings 300x on the screen plate 300. Thereafter, as shown in Fig. 5(D) , the screen plate 300 is removed from the printed circuit board 100, and the solder resist ink 302 is cured to form the second auxiliary solder resist layer 132.

[0053] In the above description, the second step is to form one second sub-solder resist layer 132 around the exposed portion of the printed circuit board 100, including the land 124, for the printed wiring board 10 having one land 124. However, the second step may be any step that forms each of the multiple first sub-solder resist layers and a second sub-solder resist layer that spans the surface of the printed circuit board, depending on the design of the printed wiring board.

[0054] The thickness of the second auxiliary solder resist layer 132 can be any value depending on the design conditions of the printed wiring board 10, but is preferably in the range of 5 μm to 20 μm, for example. Furthermore, the thickness of the second auxiliary solder resist layer 132 is preferably greater than the thickness of the first auxiliary solder resist layer 131 formed previously. This allows the first auxiliary solder resist layer 131 and the second auxiliary solder resist layer 132 to be formed by taking advantage of the advantages of their respective printing methods. Furthermore, screen printing is preferably performed in an environment with a temperature of 20° C. to 25° C. and a humidity of 30% to 70%.

[0055] When printing the solder resist ink 302 by screen printing, the screen plate 300 can be aligned as follows: A work guide is installed on the printing machine to which the screen plate 300 is attached, and the printed circuit board 100 is brought into contact with the work guide during printing, thereby aligning the screen plate 300 based on the assembly accuracy of the screen plate 300 and the work guide.

[0056] The alignment may be performed by providing alignment through-holes in the printed circuit board 100 and inserting pins, the positions of which are predetermined for combination with the screen plate 300, into the through-holes. Furthermore, the alignment may be performed by visually comparing the pattern of the screen plate 300 with the printed wiring group 120 of the printed circuit board 100.

[0057] The screen plate 300 is, for example, a gauze made of stainless steel, polyester, polyarylate, or the like, and has screen openings 300x open in the areas other than the masking portions 300a that shield the first sub-solder resist layer 131. When printing using the screen plate 300, a gap is provided between the screen plate 300 and the printed circuit board 100, and printing is performed on the printed circuit board 100 while the screen plate 300 is pulled.

[0058] Screen printing of the second sub-solder resist layer 132 has the advantage that it can be printed in a shorter time than inkjet printing when the printing area or coating thickness is large, and also has the advantage that when the printing area is large, the coating thickness will have less variation than inkjet printing.

[0059] The solder resist ink 302 used for the second auxiliary solder resist layer 132 can be either a UV curable resin containing acrylate resin as the main material or a thermosetting resin containing epoxy resin as the main material.

[0060] When a UV curable resin is used as the solder resist ink 302, the viscosity of the resin should be in the range of 70 dPa·s to 250 dPa·s. The curing condition of the solder resist ink 302 is preferably an integrated light amount in the range of 300 mJ / cm to 2500 mJ / cm.

[0061] When a thermosetting resin is used as the solder resist ink 302, a bisphenol A type epoxy resin or a novolac type epoxy resin with a viscosity in the range of 150 dPa·s to 350 dPa·s is used. The curing conditions for the solder resist ink 302 are preferably a temporary curing at a curing temperature in the range of 70°C to 90°C for 8 minutes, followed by a main curing at a curing temperature of 150°C for 20 to 70 minutes. The solder resist ink 302 is preferably stored in a cool, dark place at a temperature in the range of 0°C to 30°C.

[0062] 6C shows the state in step S007 in which the second auxiliary solder resist layer 132 has been formed on the printed circuit board 100. As shown in FIG. 1 , the edge 132a of the opening 132x, which becomes the inner edge of the second auxiliary solder resist layer 132, is formed so as to be located outside the opening 131x of the first auxiliary solder resist layer 131 and inside the edge 131b, which becomes the outer edge of the first auxiliary solder resist layer 131.

[0063] As a result, the completed solder resist layer 130 has an overlapping region 130 a formed by the second solder resist sub-layer 132 overlapping the first solder resist sub-layer 131 from above.

[0064] Finally, the outer shape and holes are processed and the surface is finished to complete the printed wiring board 10 (step S008). In order to clean the lands 124 and the surrounding surface on which the solder resist layer 130 is not formed, degreasing and rust removal are performed using, for example, acid.

[0065] The method for manufacturing the printed wiring board 10 according to the first embodiment of the present invention forms the solder resist layer 130 from two layers: a first sub-solder resist layer 131 formed around the land 124 through the opening 131x, and a second sub-solder resist layer 132 formed around the edge 131a of the first sub-solder resist layer 131, which is adjacent to the periphery of the land 124, through the opening 132x; and by forming the first sub-solder resist layer 131 by inkjet printing and the second sub-solder resist layer 132 by screen printing, the following effects are achieved.

[0066] That is, the first auxiliary solder resist layer 131 can be formed with high precision by using inkjet printing, while the second auxiliary solder resist layer 132, which does not require as high precision as the first auxiliary solder resist layer 131 and has a larger surface area and layer thickness, can be formed by screen printing and obtained in a shorter time and at lower cost than the first auxiliary solder resist layer 131. Furthermore, by forming the first auxiliary solder resist layer 131 by inkjet printing, there is no need to replace the plate as with other printing methods, so uniform precision can be maintained at low cost even when the printed wiring board 10 is repeatedly manufactured.

[0067] Therefore, the solder resist layer 130 can be obtained with high precision and at low cost.

[0068] In the method for manufacturing printed wiring board 10 according to the first embodiment of the present invention, screen printing is performed after inkjet printing by forming overlapping region 130a of solder resist layer 130 so that second sub-solder resist layer 132 overlaps first sub-solder resist layer 131. This allows the periphery of land 124 to be exposed more accurately in advance, thereby compensating for variations in accuracy due to screen printing and enabling solder resist layer 130 to be formed efficiently.

[0069] 3. Modification of the First Embodiment In the method for manufacturing printed wiring board 10 according to the first embodiment, overlapping region 130a of solder resist layer 130 may be formed so that first auxiliary solder resist layer 131 overlaps second auxiliary solder resist layer 132. In this case, in the flowchart for explaining the method for manufacturing a printed wiring board shown in FIG. 3, the order of the step of forming first auxiliary solder resist layer 131 by inkjet printing (step S006) and the step of forming second auxiliary solder resist layer 132 by screen printing (step S007) is reversed.

[0070] Specifically, the completed printed circuit board 100 shown in Fig. 9A is prepared. Next, as shown in Fig. 9B, a second auxiliary solder resist layer 132 is formed by screen printing so as to cover all remaining portions of the prepared printed circuit board 100, leaving openings 132x. The openings 132x are openings that expose the surface of the printed circuit board 100, including the lands 124, which will be inside openings 131x of the first auxiliary solder resist layer 131 to be formed later.

[0071] 8A to 8C, the specific steps of screen printing are performed by printing and curing solder resist ink 302 using a screen plate 300. Note that the details of the steps shown in each figure, the material of the solder resist ink 302, the curing conditions, etc. are the same as those in the embodiment described above with reference to FIG. 5, and therefore detailed description thereof will be omitted.

[0072] 9C, the first auxiliary solder resist layer 131 is formed on the printed circuit board 100 on which the second auxiliary solder resist layer 132 has been formed by inkjet printing a solder resist ink 302. The first auxiliary solder resist layer 131 has a rectangular outer shape in plan view and a central rectangular opening 131x in plan view, and the opening 131x is formed so that its edge 131a does not overlap the surface of the land 124 but is spaced a predetermined distance from the edge 124a of the land 124. Note that the specific details of the inkjet printing process, the material of the solder resist ink 302, the curing conditions, etc. are the same as those in the embodiment described above with reference to FIG. 5, and therefore detailed description thereof will be omitted.

[0073] By forming the overlapping region 130a of the solder resist layer 130 so that the first sub-solder resist layer 131 overlaps the second sub-solder resist layer 132, inkjet printing can be performed after screen printing, thereby precisely compensating for variations in accuracy due to screen printing and exposing the periphery of the land 124 with greater precision.

[0074] B. Second Embodiment Next, an example of a method for manufacturing a printed wiring board according to a second embodiment of the present invention will be described.

[0075] 1. Printed Wiring Board A printed wiring board 10A, which is an example of a printed wiring board according to a second embodiment of the present invention, will be described. Fig. 10 is a plan view showing the printed wiring board 10A according to the second embodiment of the present invention. Fig. 11 is a schematic cross-sectional view taken along line XI-XI in Fig. 10. However, components that are the same as or equivalent to those in Figs. 1 to 9 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0076] The printed wiring board 10A according to the second embodiment differs from the printed wiring board 10 according to the first embodiment in that the first auxiliary solder resist layer 131 is formed to cover a portion of the surface of the second printed wiring 122.

[0077] (Printed Circuit Board) The printed circuit board 100 includes a substrate 110 and a printed wiring group 120 provided on the substrate 110. The printed wiring group 120 is a thin film layer of a conductive material that is bonded to the surface of the substrate 110 and then processed by etching or other means to form a predetermined circuit pattern.

[0078] A predetermined number of lands for soldering to electronic components are provided at arbitrary locations on each of the printed wirings constituting the printed wiring group 120. In this embodiment, as an example in which the configuration is simplified for the purpose of explanation, a land 124 is formed at the end of the second printed wiring 122 in the first printed wiring 121, the second printed wiring 122, and the third printed wiring 123 constituting the printed wiring group 120. Although the land 124 is shown as having a rectangular shape wider than the second printed wiring 122 in a plan view, it may have a circular or any other shape.

[0079] (Solder Resist Layer) The solder resist layer 130 is an insulating layer provided in the printed wiring board 10A so as to cover the entire surface of the printed circuit board 100 except for a portion of the lands 124 and their surfaces.

[0080] The solder resist layer 130 has a first sub-solder resist layer 131 formed so as to expose a portion of the land 124 in a plan view of the printed circuit board 100 (hereinafter simply referred to as "plan view"), and a second sub-solder resist layer 132 formed around the edge of the first sub-solder resist layer 131 on the side opposite to the exposed area of ​​the land 124. Details will be explained below.

[0081] The first auxiliary solder resist layer 131 is an insulating layer having a rectangular frame shape in plan view, which is formed so as to expose part of the surface of the land 124, including part of the second printed wiring 122. Specifically, the first auxiliary solder resist layer 131 has an opening 131x which is rectangular in plan view at the center of its rectangular outer shape in plan view, and is formed so that the surface of the land 124 is exposed through the opening 131x.

[0082] In the first auxiliary solder resist layer 131, the distance between the edge 131a and the edge 131b, i.e., the width W1 of the frame shape, can be any value depending on the circuit pattern of the printed wiring group 120, but it is preferable that it be in the range of 100 μm or more and 300 μm, for example.

[0083] The shape of the opening 131x preferably corresponds to the shape of the land 124. That is, if the land 124 is circular or has any other shape, the opening 131x preferably has a similar shape to that shape.

[0084] The thickness T3 of the first sub-solder resist layer 131 can be any value depending on the design conditions of the printed wiring board 10, but is preferably in the range of 5 μm to 20 μm, for example.

[0085] The second auxiliary solder resist layer 132 is an insulating layer formed to further surround from the outside the periphery of the exposed portion of the printed circuit board 100, including the lands 124, which is surrounded by the first auxiliary solder resist layer 131, and to cover all remaining portions of the printed circuit board 100. Specifically, the second auxiliary solder resist layer 132 has an opening 132x that is rectangular in plan view corresponding to the position of the first auxiliary solder resist layer 131, and is formed so that the opening 131x of the first auxiliary solder resist layer 131 is located within the opening 132x. An edge 132a of the opening 132x, which forms the inner edge of the second auxiliary solder resist layer 132, is formed to be located outside the opening 131x of the first auxiliary solder resist layer 131 and inside an edge 131b, which forms the outer edge of the first auxiliary solder resist layer 131.

[0086] As a result, the solder resist layer 130 has an overlapping region 130a, which is a region formed by overlapping the second solder resist sub-layer 132 on the first solder resist sub-layer 131. The dimension L of the overlapping region 130a in plan view can be any value depending on the shape and dimensions of the first solder resist sub-layer 131 and the circuit pattern of the printed wiring group 120, but is preferably in the range of 50 μm to 200 μm, for example.

[0087] The shape of the opening 132x preferably corresponds to the shape of the opening 131x. That is, if the opening 131x is circular or has any other shape, the opening 132x preferably has a similar shape to that shape.

[0088] The thickness T2 of the second solder resist sub-layer 132 can be any value depending on the design conditions of the printed wiring board 10A, but is preferably in the range of 5 μm to 30 μm, for example. Furthermore, the thickness T2 of the second solder resist sub-layer 132 and the thickness T3 of the first solder resist sub-layer 131 preferably have a relationship of T2>T3.

[0089] 2. Method for Manufacturing a Printed Wiring Board A printed wiring board 10, which is an example of a printed wiring board according to a second embodiment of the present invention, will be described. Figures 12 and 13 are schematic cross-sectional views showing the state of the printed wiring board 10 in the process shown in the flowchart of Figure 3, and are cross-sectional views corresponding to the cross-sectional view of line XI-XI in Figure 12. Figure 13 is a plan view showing the state of the printed wiring board 10 in the process shown in the flowchart of Figure 3. Note that although Figure 3 is a flowchart of the method for manufacturing a printed wiring board according to the first embodiment, it is common to the flowchart of the method for manufacturing a printed wiring board according to the second embodiment.

[0090] (Manufacturing of Printed Circuit Board) First, a printed circuit board 100 having a printed wiring group 120 arranged on the surface of a substrate 110 is prepared.

[0091] (Formation of Solder Resist Layer) Next, the solder resist layer 130 is formed on the printed circuit board 100 .

[0092] First, in the first step, the first auxiliary solder resist layer 131 is formed on the surface of the lands 124 of the printed wiring group 120 by inkjet printing (step S006).

[0093] As shown in Figure 13 (B), the first auxiliary solder resist layer 131 has a rectangular outer shape when viewed from above, and has a rectangular opening 131x formed in the center when viewed from above, with a portion of the surface of the land 124 exposed so that the opening 131x is located therein.

[0094] The thickness T3 of the first sub-solder resist layer 131 can be any value depending on the design conditions of the printed wiring board 10A, but is preferably in the range of 5 μm to 20 μm, for example. In addition, it is preferable that the inkjet printing be performed in an environment where the temperature is 20° C. to 25° C. and the humidity is 30% to 70%.

[0095] By using inkjet printing to print the solder resist ink 301, the openings 131x of the first sub-solder resist layer 131 can be formed accurately in predetermined areas on the surface of the lands 124.

[0096] The solder resist ink 301 used for the first sub-solder resist layer 131 is the same as that used for the printed wiring board 10 according to the first embodiment.

[0097] Next, in a second step, a second auxiliary solder resist layer 132 is formed on the printed circuit board 100 by screen printing (step S007).

[0098] The second auxiliary solder resist layer 132 is formed to surround from the outside the periphery of the exposed portion of the land 124, including part of the surface of the first auxiliary solder resist layer 131 formed on the surface of the land 124, and to cover all remaining portions of the printed circuit board 100. Specifically, as shown in Fig. 12(B), a screen plate 300 is placed on the first auxiliary solder resist layer 131, and as shown in Fig. 12(C), a squeegee (not shown) is pressed against the screen plate 300 parallel to the printed circuit board 100, and solder resist ink 302 is printed so as to fill the screen openings 300x in the screen plate 300. Thereafter, as shown in Fig. 12(D), the screen plate 300 is removed from the printed circuit board 100, and the solder resist ink 302 is cured to form the second auxiliary solder resist layer 132.

[0099] In the above description, the second step is to form one second sub-solder resist layer 132 around the exposed portion of the printed circuit board 100, including the land 124, for the printed wiring board 10A having one land 124 as a land. However, the second step may be any step that forms each of the multiple first sub-solder resist layers and a second sub-solder resist layer that spans the surface of the printed circuit board, depending on the design of the printed wiring board.

[0100] The thickness of the second solder resist sub-layer 132 can be any value depending on the design conditions of the printed wiring board 10A, but is preferably in the range of 5 μm to 20 μm, for example. Furthermore, the thickness of the second solder resist sub-layer 132 is preferably greater than the thickness of the first solder resist sub-layer 131 formed earlier. This allows the first solder resist sub-layer 131 and the second solder resist sub-layer 132 to be formed by taking advantage of the advantages of their respective printing methods. Furthermore, screen printing is preferably performed in an environment with a temperature of 20° C. to 25° C. and a humidity of 30% to 70%.

[0101] When printing the solder resist ink 302 by screen printing, the screen plate 300 can be aligned as follows: A work guide is installed on the printing machine to which the screen plate 300 is attached, and the printed circuit board 100 is brought into contact with the work guide during printing, thereby aligning the screen plate 300 based on the assembly accuracy of the screen plate 300 and the work guide.

[0102] The solder resist ink 302 used in the second auxiliary solder resist layer 132 is the same as that used in the printed wiring board 10 according to the first embodiment.

[0103] 13C shows the state in step S007 in which the second auxiliary solder resist layer 132 has been formed on the printed circuit board 100. As shown in Fig. 10, the edge 132a of the opening 132x, which becomes the inner edge of the second auxiliary solder resist layer 132, is formed so as to be located outside the opening 131x of the first auxiliary solder resist layer 131 and inside the edge 131b, which becomes the outer edge of the first auxiliary solder resist layer 131.

[0104] As a result, the completed solder resist layer 130 has an overlapping region 130 a formed by the second solder resist sub-layer 132 overlapping the first solder resist sub-layer 131 from above.

[0105] Finally, the outer shape and holes are processed and the surface is finished to complete the printed wiring board 10 (step S008). In order to clean the lands 124 and the surrounding surface on which the solder resist layer 130 is not formed, degreasing and rust removal are performed using, for example, acid.

[0106] The method for manufacturing printed wiring board 10A according to the second embodiment of the present invention has the same effects as the method for manufacturing printed wiring board 10 according to the first embodiment.

[0107] 3. Modification of the Second Embodiment In the method for manufacturing the printed wiring board 10A according to the second embodiment, the overlapping region 130a of the solder resist layer 130 may be formed so that the first auxiliary solder resist layer 131 overlaps the second auxiliary solder resist layer 132. In this case, in the flowchart for explaining the method for manufacturing the printed wiring board shown in FIG. 3, the order of the step of forming the first auxiliary solder resist layer 131 by inkjet printing (step S006) and the step of forming the second auxiliary solder resist layer 132 by screen printing (step S007) is reversed.

[0108] Specifically, the completed printed circuit board 100 shown in Fig. 15(A) is prepared. Next, as shown in Fig. 15(B), a second auxiliary solder resist layer 132 is formed by screen printing so as to expose a portion of the lands 124 of the prepared printed circuit board 100 and cover the entire remaining portion, leaving openings 132x. The openings 132x are openings that expose the surface of the printed circuit board 100, including the lands 124, and that will be inside openings 131x of the first auxiliary solder resist layer 131 to be formed later.

[0109] 14(A) to 14(C), the specific steps of screen printing are performed by printing and curing solder resist ink 302 using a screen plate 300. Note that the details of the steps shown in each figure, the material of the solder resist ink 302, the curing conditions, etc. are the same as those in the embodiment described above with reference to FIG. 5, and therefore detailed description thereof will be omitted.

[0110] 15C, the first auxiliary solder resist layer 131 is formed on the printed circuit board 100 on which the second auxiliary solder resist layer 132 has been formed by inkjet printing a solder resist ink 302. The first auxiliary solder resist layer 131 has a rectangular outer shape in a plan view and a central rectangular opening 131x in a plan view, the opening 131x being positioned so as to expose part of the second auxiliary solder resist layer 132 and part of the surface of the land 124. Note that the specific details of the inkjet printing process, the material of the solder resist ink 302, the curing conditions, etc. are the same as those in the embodiment described above with reference to FIG. 5, and therefore detailed description thereof will be omitted.

[0111] By forming the overlapping region 130a of the solder resist layer 130 so that the first sub-solder resist layer 131 overlaps the second sub-solder resist layer 132, inkjet printing is performed after screen printing, and variations in accuracy due to screen printing can be precisely compensated for, allowing the exposed range of the land 124 to be determined with precision.

[0112] As described above, the embodiment of the present invention has been disclosed in the above description, but the present invention is not limited to this.

[0113] In other words, various modifications can be made to the above-described embodiments and variants in terms of mechanism, shape, material, quantity, position, arrangement, etc., without departing from the scope of the technical idea and purpose of this invention, and such modifications are included in this invention.

[0114] 10, 10A Printed wiring board 100 Printed circuit board 110 Base material 111a Core material 111b Laminate material 112 Copper foil layer 120 Printed wiring group 121 First printed wiring 122 Second printed wiring 123 Third printed wiring 124 Land 124a, 131a, 131b, 132a Edge portion 130 Solder resist layer 130a Overlapping area 131x, 132x Opening 131 First auxiliary solder resist layer 132 Second auxiliary solder resist layer 140 Etching resist layer 200 Laminated plate 300 Screen plate 300a Masking portion 300x Screen opening 301, 302 Solder resist ink

Claims

1. A method for manufacturing a printed wiring board, comprising a step of forming a solder resist layer that selectively covers a surface of a printed circuit board having printed wiring including lands on a surface thereof so that at least all or a portion of the surface of the lands is exposed, wherein the step of forming the solder resist layer comprises a first step of forming a first sub-solder resist layer by inkjet printing and a second step of forming a second sub-solder resist layer by screen printing, wherein, in a planar view of the printed circuit board, the first sub-solder resist layer is formed around the lands, and the second sub-solder resist layer is formed around at least an edge portion of the first sub-solder resist layer that is adjacent to the periphery of the lands.

2. The method for manufacturing a printed wiring board according to claim 1, further comprising forming an area around the land where the second solder resist sub-layer overlaps the first solder resist sub-layer.

3. The method for manufacturing a printed wiring board according to claim 1, further comprising forming an area around the land where the first solder resist sub-layer overlaps the second solder resist sub-layer.

4. A method for manufacturing a printed wiring board as described in claim 1, wherein the first step is a step of selectively forming each of the multiple first sub-solder resist layers corresponding to all or a portion of each of the multiple lands, and the second step is a step of forming each of the multiple first sub-solder resist layers and the second sub-solder resist layer spanning the surface of the printed circuit board.

5. The method for manufacturing a printed wiring board according to claim 1, wherein the thickness of the first sub-solder resist layer is smaller than the thickness of the second sub-solder resist layer.

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