JP2011119567A - Method of manufacturing printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that since ultraviolet irradiated from the surface of a solder resist is absorbed and attenuated on the way as it penetrates inside because a solder resist having larger thickness than usual is exposed by ultraviolet irradiation in a printed wiring board for large current, an inside solder resist can't obtain sufficient exposure amount compared with a surface portion, undercut occurs by allowing the lower portion of the solder resist to be eroded by sodium carbonate aqueous solution, adhesion is deteriorated, and a solder dam is peeled off in the severe case. <P>SOLUTION: In one of processes of forming first and second solder resist layers, a non applied portion to which photosensitive solder resist ink is not applied is provided onto a region including a solder mounting land and its periphery at the time of application of the photosensitive solder resist ink. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a printed wiring board used in various electronic devices such as a personal computer, a mobile communication telephone, a video camera, and an in-vehicle device.

  In recent years, as electronic devices have higher functionality and higher density, electronic components are becoming increasingly smaller, highly integrated, faster, and multi-pinned. Especially for in-vehicle use, there is a growing demand for printed circuit boards for large currents of several tens to several hundreds of amps for control units such as power steering, engine control, ABS system, airbags and junction boxes connecting them. Yes.

  The printed wiring board corresponding to this large current needs to increase its cross-sectional area by increasing the width or thickness of the conductor circuit, reduce its electrical resistance, and suppress heat generation. However, if the width of the conductor circuit is too large, the area of the printed wiring board itself is increased, which is against the demand for downsizing of electronic devices. Therefore, the expansion of the width of the conductor circuit should be limited to some extent. I must. For this reason, the mainstream printed wiring boards for large currents have a conductor circuit with a large thickness. The thickness of the conductor circuit is generally about 18 to 70 μm, but in the case of a printed wiring board for high current, there are 100 to several hundred μm, and some of them may be several mm.

  As the thickness of the conductor circuit increases, it is necessary to increase the thickness of the solder resist that covers the conductor circuit. Several methods of solder resist ink coating have been put to practical use, but in any method, the thickness of solder resist ink coating is limited to about 100 μm, and a thicker conductor circuit is covered. In order to do so, various ideas have been devised.

  A conventional method for manufacturing a printed wiring board will be described below.

  After going through the through holes, metal plating, and conductor circuit formation, the parts other than the parts used for soldering and mounting parts of the conductor circuit and the parts used for contact with the outside will be covered with solder resist. . At present, this solder resist is formed by applying UV-sensitive solder resist ink to the entire surface of the printed wiring board, and after drying, selectively select the necessary parts in the exposure process of irradiating UV light through a negative pattern exposure film. The photographic method in which photopolymerization is performed, and then the unexposed portion is developed and removed with an aqueous sodium carbonate solution or the like has become the mainstream. As a method for applying the solder resist ink here, in addition to the conventional screen printing method, various methods such as a spray coating method, a roll coating method, and a curtain coating method have been put into practical use.

  In order to coat a thick conductive circuit with solder resist ink, it is necessary to increase the amount of solder resist ink applied, but each application method has the following problems.

  That is, in the screen printing method, coating is performed by extruding the solder resist ink placed on the plate by sliding the squeegee on the plate, but a certain amount of coating can be performed even if the squeegee is repeatedly slid. Once the amount is reached, no further thickness can be obtained.

  Since printing is performed in a state where the printing plate and the printed wiring board are in contact with each other, there is no gap between the printing plate and the printed wiring board when the squeegee passes even if the wet ink is repeatedly printed. Because. In the spray coat type, roll coat type, and curtain coat type, the viscosity of the solder resist ink suitable for each application method is smaller than that in the screen printing method, and when the coating thickness is increased, there is a problem due to ink drooping. appear.

  In consideration of productivity, it is common to suspend the printed wiring board vertically in the drying process after application, but in this case, the phenomenon that the ink on the upper side sag in the lower direction occurs. Also, even if the printed wiring board is held horizontally instead of being suspended, the sagging from the end surface may occur, causing ink to become icicle-shaped or fall down on the end surface. appear.

  Therefore, in order to ensure the thickness of the solder resist ink necessary for the printed wiring board for high current, after applying and drying with a normal amount of thickness, it is possible to respond by applying and drying again from there. It is common. Thereby, in the screen printing method, the plate is further brought into contact with the solder resist layer after the drying formed at the first time, so that the solder resist layer can be formed again without damaging the solder resist layer formed at the first time. Is possible. In the spray coat type, roll coat type and curtain coat type, a new amount of solder resist ink having a normal thickness is applied on the dried solder resist layer formed at the first time. The applied solder resist ink is dry and does not affect dripping.

  Next, a conventional method for producing a printed wiring board by the above-described twice printing in the screen printing method will be described in detail with reference to the drawings. FIG. 3 is a cross-sectional view showing a conventional method for manufacturing a printed wiring board.

  FIG. 3A shows the printed wiring board before the solder resist is formed. A predetermined conductor circuit is formed on the substrate 3, and the conductor circuit is constituted by a wiring circuit 1 that performs an energization function and a mounting land 2 that is used for soldering mounting. The printed wiring board used in the description of FIG. 3 has a conductor circuit formed on only one surface for the sake of simplicity of explanation, but in most cases a conductor circuit is actually formed on both surfaces. is there.

  First, after performing a predetermined pretreatment such as derusting and washing, a first solder resist layer 7 is formed as shown in FIGS. 3B and 3C. In solder resist coating by the screen printing method, a printing plate 6 is placed on a printed wiring board as shown in FIG. 3B, and the solder resist ink 5 placed on the plate 6 is moved by moving the squeegee 4 for printing. To do. The plate 6 used here can be printed on the entire surface in principle. However, in a printed wiring board having a through hole, there may be a case where a sealing portion is partially provided (not shown) at the location, for example, when the solder resist ink 5 is prevented from entering the through hole. Thereafter, the solder resist ink 5 is dried to obtain a state in which the first solder resist layer 7 is formed as shown in FIG.

  Next, as shown in FIGS. 3D and 3E, the second solder resist layer 8 is formed on the surface of the first solder resist layer 7. Similarly to the formation of the first solder resist layer 7, as shown in FIG. 3 (d), the printing plate 6 is disposed on the printed wiring board and the solder resist ink 5 placed on the plate 6. The squeegee 4 is moved for printing. As with the formation of the first solder resist layer 7, the plate 6 used here can be printed on the entire surface except for the sealing portion that blocks the through-hole portion provided as necessary. Usually, the plate 6 used at the time of forming the first solder resist layer 7 is repeatedly used. Thereafter, the solder resist ink 5 is dried to obtain a state in which the second solder resist layer 8 is formed as shown in FIG. The solder resist ink 5 used for the first solder resist layer 7 and the second solder resist layer 8 is the same except for special cases. In FIG. 3E, for the sake of explanation, the first solder resist layer 7 and the second solder resist layer 8 are shown separately, but in an actual product, these two layers cannot be distinguished. Therefore, in FIG. 3 (f), these two layers are shown without distinction for the sake of simplicity of explanation.

  Then, after exposing by ultraviolet irradiation through an exposure film, it develops with the aqueous solution of sodium carbonate, heat-hardens, and solder resist formation is completed like FIG.3 (f). In FIG. 3 (f), the solder resist of the mounting land 2 part to be soldered and mounted is removed. Furthermore, a solder dam 9 is formed between adjacent mounting lands 2 to prevent solder bridges.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

Japanese Unexamined Patent Publication No. 63-200594

  However, in the above conventional method for manufacturing a printed wiring board, the following problems are concerned. That is, since the solder resist having a thickness larger than usual is exposed by ultraviolet irradiation, the ultraviolet light irradiated from the surface of the solder resist is absorbed and attenuated as it penetrates into the inside. Therefore, the internal solder resist may not be able to obtain a sufficient exposure amount as compared with the surface portion. In this case, at the boundary between the exposed area and the unexposed area in the development process, the lower part of the solder resist is eroded by the aqueous solution of sodium carbonate as shown in FIG.

  The influence of this undercut 10 is manifested in the solder dam 9 part provided between the mounting lands 2. The solder dam 9 originally has a small width. However, when the undercut 10 occurs, the solder dam 9 has a cross-sectional shape as shown in FIG. 3F, and the lower width becomes extremely smaller than the upper width. As a result, there is a problem that the contact area between the solder dam 9 and the substrate 3 is reduced, and the solder dam 9 is peeled off when the adhesion is severely deteriorated.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a method for manufacturing a printed wiring board that does not cause the solder dam to peel off from the printed wiring board for high current.

  In order to achieve this object, the printed wiring board manufacturing method of the present invention applies a photosensitive solder resist ink to at least one surface of a printed wiring board on which a conductor circuit having a soldering mounting land is formed. A step of forming a first solder resist layer by drying, a second step of applying a photosensitive solder resist ink again to the surface of the printed wiring board on which the first solder resist layer is formed, and drying; A step of forming a solder resist layer, an exposure step of selectively irradiating the first and second solder resist layers with ultraviolet rays, and developing an unexposed portion of the first and second solder resist layers A developing step of dissolving in a liquid, and one of the steps of forming the first or second solder resist layer includes the step of forming the photosensitive solder resist layer. When key of coating, the is that soldering lands with the photosensitive solder resist ink to provide a non-coating portion not coated to a region including the periphery. By this structure, the thickness of the solder dam is reduced without reducing the thickness of the solder resist of the conductor circuit portion that needs to be coated by making the region including the solder dam an uncoated portion where the photosensitive solder resist ink is not applied. Can do. Therefore, the amount of attenuation when ultraviolet rays irradiated from the surface of the solder resist penetrate into the inside can be reduced, and the internal solder resist can obtain a sufficient exposure amount as compared with the surface portion. As a result, the undercut of the solder dam can be reduced, the contact area between the solder dam and the base material can be secured, and the solder dam can be prevented from peeling off.

  The printed wiring board manufacturing method of the present invention is a method in which a photosensitive solder resist ink is not applied to a region including the solder mounting land and its periphery in the step of forming the first or second solder resist layer. The process performed by providing the application part is to apply the photosensitive solder resist ink by screen printing. With this configuration, the non-applied portion where the photosensitive solder resist ink is not applied can be provided by sealing the plate used for screen printing so that the photosensitive solder resist ink does not pass through.

  The printed wiring board manufacturing method of the present invention is a method in which a photosensitive solder resist ink is not applied to a region including the solder mounting land and its periphery in the step of forming the first or second solder resist layer. The step performed by providing the application part is a step of forming the first solder resist layer. With this configuration, even if a step is generated between the application portion and the non-application portion of the first solder resist layer, the photosensitive solder resist ink is formed by applying the coating over both regions in the formation of the second solder resist layer. The leveling action of the step can smoothly finish the step.

  The printed wiring board manufacturing method of the present invention is a method in which a photosensitive solder resist ink is not applied to a region including the solder mounting land and its periphery in the step of forming the first or second solder resist layer. The other step, which is not a step performed by providing an application portion, is to apply the photosensitive solder resist ink on both sides simultaneously. With this configuration, there is no need to apply and dry each side separately, and the productivity can be improved.

  Moreover, the manufacturing method of the printed wiring board of this invention is that the application | coating method which apply | coats a photosensitive soldering resist ink simultaneously on both surfaces is a spray coat type or a roll coat type. With this configuration, there is an effect that simultaneous application on both sides can be realized by a spray coating method or a roll coating method.

  Moreover, the manufacturing method of the printed wiring board of this invention makes the area | region containing the solder dam part between soldering mounting lands into the non-application part which does not apply | coat photosensitive soldering resist ink. With this configuration, the thickness of the solder dam can be reduced without reducing the thickness of the solder resist of the conductor circuit portion that needs to be covered. Therefore, the amount of attenuation when ultraviolet rays irradiated from the surface of the solder resist penetrate into the inside can be reduced, and the internal solder resist can obtain a sufficient exposure amount as compared with the surface portion. As a result, the undercut of the solder dam can be reduced, the contact area between the solder dam and the base material can be secured, and the solder dam can be prevented from peeling off.

  Moreover, the manufacturing method of the printed wiring board of this invention is that the thickness of the conductor circuit formed in the printed wiring board is 100 micrometers or more. With this configuration, the solder dam can be prevented from being peeled off from a printed wiring board that requires a conductor circuit having a thickness of 100 μm or more.

  According to the method for producing a printed wiring board of the present invention, even in a printed wiring board for a large current having a large conductor circuit thickness, the solder dam underlayer can be obtained without reducing the thickness of the solder resist of the conductor circuit portion that needs to be coated. It is possible to provide a method for manufacturing a printed wiring board that reduces cutting and does not have to worry about peeling of the solder dam.

Sectional drawing which shows the manufacturing method of the printed wiring board in Embodiment 1 of this invention Sectional drawing which shows the manufacturing method of the printed wiring board in Embodiment 2 of this invention Sectional drawing which shows the manufacturing method of the conventional printed wiring board

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a method for manufacturing a printed wiring board according to Embodiment 1 of the present invention. The present invention relates to a solder resist forming process for a printed wiring board for large current having a conductor circuit thickness of 100 μm or more, and FIG. 1A shows the printed wiring board before the solder resist is formed. The printed wiring board used in the present invention has a conductor circuit on at least one surface of the surface layer. In the first embodiment, the thickness of the conductor circuit is 150 μm, and a printed wiring board having the conductor circuit only on one side is used for the convenience of explanation. In FIG. 1A, a predetermined conductor circuit is formed on a substrate 13 of a printed wiring board, and the conductor circuit is composed of a wiring circuit 11 that performs an energization function and a mounting land 12 that is used for solder mounting. Yes. The wiring circuit 11 has a minimum width and gap of 0.2 mm, and the mounting land 12 has a width of 1.0 mm and a gap of 0.4 mm. In addition, the thickness of the base material 13 was 1.0 mm.

  First, as a pretreatment, after performing a soft etching treatment with sulfuric acid and hydrogen peroxide solution, a first solder resist layer 17 is formed as shown in FIGS. 1B and 1C. FIG. 1B shows solder resist coating by a screen printing method. In the screen printing method, as shown in FIG. 1B, a printing plate 16 is arranged on a printed wiring board, and printing is performed by moving the solder resist ink 15 placed on the plate 16 by moving the squeegee 14. As the plate 16 here, as shown as the sealing portion 18 in FIG. 1B, a plate in which a portion corresponding to a region including the mounting land 12 and its periphery is marked is used. This is to make the area including the mounting land 12 and the periphery thereof a non-coating portion where the solder resist ink is not applied. In principle, the entire area other than the non-application area is printed. Although not shown in FIG. 1, the printed wiring board may have a through-hole. In this case, in order to prevent the solder resist ink 15 from entering the through-hole, a part of the through-hole portion is also visible. A stop can be provided. Thereafter, the solder resist ink 15 is dried at 80 ° C. for 20 minutes to obtain a state in which the first solder resist layer 17 is formed as shown in FIG.

  Next, as shown in FIGS. 1D and 1E, a second solder resist layer 19 is formed on the surface of the first solder resist layer 17. Similarly to the formation of the first solder resist layer 17, as shown in FIG. 1 (d), the printing plate 16 is disposed on the printed wiring board, and the solder resist ink 15 placed on the plate 16. The squeegee 14 is moved for printing. Unlike the plate 16 used in forming the first solder resist layer 17, the region including the mounting land 12 and its periphery is not an uncoated portion, and includes the region in principle. Full-surface printing is performed. Thereafter, the solder resist ink 15 is dried at 80 ° C. for 20 minutes to obtain a state in which the second solder resist layer 19 is formed as shown in FIG. In the present embodiment, the same solder resist ink 15 is used for the first and second solder resist layers. Therefore, in FIG. 1 (e), the first solder resist layer 17 and the second solder resist layer 19 are shown separately for the sake of explanation, but in the actual product, these two layers cannot be distinguished. . Therefore, in FIG. 1 (f), the two layers are illustrated without distinction for the convenience of explanation. Note that the solder resist ink 15 of the first and second solder resist layers may be different inks for special purposes. Even in that case, if the method of the first embodiment is followed, the effect of the present invention is not affected.

  Then, after selectively exposing by ultraviolet irradiation through an exposure film by a well-known method, it develops with sodium carbonate aqueous solution, heat-hardens, and solder resist formation is completed like FIG.1 (f). In FIG. 1 (f), the solder resist of the mounting lands 12 to be soldered and mounted is removed, and solder dams 20 are formed between the adjacent mounting lands 12 to prevent solder bridges.

  As can be seen from the above description, only the second solder resist layer 19 is formed in the region including the mounting land 12 and its periphery set as the non-application portion in FIG. 1B at the stage of FIG. In other regions, the first and second solder resist layers are formed. As a result, the wiring circuit 11 that needs to be covered with the solder resist layer can secure the thickness as before, and the solder resist thickness in the region including the mounting land 12 and its periphery is larger than that in the other regions. Can be small. As a result, the thickness of the solder resist at the location where the solder dam 20 between the adjacent mounting lands 12 is formed can be reduced, and the undercut of the solder dam 20 that occurs due to the large thickness of the solder resist, which has been a conventional problem. Can be prevented. When the solder resist thickness is small, the amount of UV light irradiated from the surface is absorbed and attenuated when penetrating into the interior, and the internal solder resist can obtain a sufficient exposure amount. . Therefore, the problem that the solder dam 20 is peeled off due to the undercut can be prevented.

  In addition, among the area | region including the mounting land 12 demonstrated as an area | region set as a non-application | coating part in FIG.1 (b) and its periphery, suppose that the periphery shows the following area | region. That is, it includes a space between adjacent mounting lands 12 forming the solder dam 20 as described above, and further includes a boundary between an unexposed portion and an exposed portion for exposing the mounting lands 12 in the development process, and further needs to be covered. There is no wiring circuit 11 with. By doing so, it is possible to prevent the undercut at the boundary between the solder dam 20 and other unexposed portions and exposed portions. Here, it is considered that the above-described undercut can be prevented by including the periphery of the mounting land as a non-application portion, even if the mounting land 12 portion is not included. However, if the mounting land 12 part is used as an application part and the mounting land 12 part is used as a non-application part, there will be a difference in level between them, which is not preferable in view of the adhesion to the negative film in the exposure process. However, if there is a design limitation, at least the solder dam 20 may be a non-application portion.

  In the description of the above embodiment, the printed wiring board is used in which a conductor circuit is formed on only one side, but even if the conductor circuit is formed on both sides, the solder resist is applied and dried. What is necessary is just to repeat the method similar to the method in a process on both surfaces. In this case, two layers of solder resist may be formed on one side and then two layers of solder resist may be formed on the other side, or one layer of solder resist may be formed on both sides. Then, one layer of solder resist may be formed on both sides again. In addition, it goes without saying that the same method may be used for a multilayer printed wiring board in which a circuit is formed on the inner layer.

  In addition, it is also effective to adopt a method in which the entire surface application process without providing the non-application part in FIG. By doing so, the number of times of coating can be reduced by one compared with the case of separately coating on both sides. Examples of a method that can be applied on both sides simultaneously include a spray coating method and a roll coating method.

(Embodiment 2)
Next, another embodiment of the present invention will be described. FIG. 2 is a cross-sectional view showing a method for manufacturing a printed wiring board according to Embodiment 2 of the present invention. The second embodiment is different in that the plate 16 used in the coating process of the first solder resist layer 17 in the first embodiment and the plate 16 used in the coating process of the second solder resist layer 19 are replaced, The other contents are the same as those in the first embodiment. In the first embodiment, the plate 16 in which the portion corresponding to the area including the mounting land 12 and its periphery is used as the sealing portion 18 is used when forming the first solder resist layer 17 as shown in FIG. However, in the second embodiment, the plate 16 having the sealing portion 18 is used when forming the second solder resist layer 19 as shown in FIG. As a result, similarly to FIG. 1 (e), even in the stage of FIG. 2 (e), only one solder resist layer is formed in the region including the mounting land 12 set as the non-application portion and its periphery. In other regions, two solder resist layers are formed. As a result, the thickness of the solder resist at the location where the solder dam 20 between the adjacent mounting lands 12 is formed can be reduced, and the undercut of the solder dam 20 generated due to the large thickness of the solder resist, which is a conventional problem, and The effect that the problem that the solder dam 20 is peeled off due to the undercut can be prevented is obtained similarly.

  The first embodiment and the second embodiment each have advantages, and it is only necessary to appropriately determine which one is selected. In the first embodiment, since the solder resist layer formed on the mounting land 12 is the second solder resist layer 19, the drying process passes only once, and the solder resist layer is developed by heating excessively. The possibility of generating residues is very low. In addition, even if a step is generated between the application portion and the non-application portion of the first solder resist layer 17, the photosensitive solder resist ink is formed by applying over both regions in the formation of the second solder resist layer 19. The leveling action can smoothly finish the level difference. On the other hand, in Embodiment 2, since the solder resist layer formed on the mounting land 12 is the first solder resist layer 17, the mounting land 12 can be protected at an early stage. Adhesion can be prevented.

  As described above, the printed wiring board manufacturing method of the present invention is a solder dam without reducing the thickness of the solder resist of the conductor circuit portion that needs to be coated, even in the printed wiring board for large current where the thickness of the conductor circuit is large. Can be provided and a printed wiring board manufacturing method can be provided without worrying about peeling of solder dams. For various electronic devices such as mobile communication telephones, video cameras, and in-vehicle devices. It is useful as a method for producing a printed wiring board to be used.

11 Wiring Circuit 12 Mounting Land 13 Base Material 14 Squeegee 15 Solder Resist Ink 16 Plate 17 First Solder Resist Layer 18 Sealing Portion 19 Second Solder Resist Layer 20 Solder Dam

Claims (7)

A step of forming a first solder resist layer by applying and drying a photosensitive solder resist ink on at least one surface of a printed wiring board on which a conductor circuit having a solder mounting land is formed on the surface; and A step of forming a second solder resist layer by applying a photosensitive solder resist ink again to the surface of the printed wiring board on which the first solder resist layer is formed and drying, and the first and second solders. An exposure step of selectively irradiating the resist layer with ultraviolet light; and a development step of dissolving the unexposed portions of the first and second solder resist layers in a developer, the first or second solder resist Any one of the steps of forming a layer is a region including the solder mounting land and its periphery when the photosensitive solder resist ink is applied. Method for manufacturing a printed wiring board and providing a non-application portion not coated with the photosensitive solder resist ink for. Of the steps of forming the first or second solder resist layer, the step of providing a non-applied portion that does not apply the photosensitive solder resist ink to the area including the solder mounting land and its periphery is performed by screen printing. The method for producing a printed wiring board according to claim 1, wherein a photosensitive solder resist ink is applied. Of the steps of forming the first or second solder resist layer, the step of providing a non-applied portion where the photosensitive solder resist ink is not applied to the area including the soldering mounting land and the periphery thereof is the first step. The method for producing a printed wiring board according to claim 1, wherein the method is a step of forming a solder resist layer. Of the steps of forming the first or second solder resist layer, the other step which is not a step of providing a non-applied portion where the photosensitive solder resist ink is not applied to the area including the solder mounting land and its periphery. The method for producing a printed wiring board according to claim 1, wherein the photosensitive solder resist ink is applied simultaneously on both sides. The method for producing a printed wiring board according to claim 4, wherein the coating method for applying the photosensitive solder resist ink on both sides simultaneously is a spray coating method or a roll coating method. 2. The method for manufacturing a printed wiring board according to claim 1, wherein a region including the solder dam portion between the solder mounting lands is a non-coated portion where the photosensitive solder resist ink is not applied. The method for producing a printed wiring board according to claim 1, wherein the thickness of the conductor circuit formed on the printed wiring board is 100 µm or more.

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