Patent Application
20220369469
The present invention relates to a method of manufacturing a printed wiring board, and more particularly relates to a method of manufacturing a printed wiring board in which a pattern is formed by a printing process.
Conventional methods of manufacturing a printed wiring board include a method of forming a pattern by a subtractive process using a laminated board in which a metal layer is formed on a surface of a base material formed of an insulator. In this method, a printing process is used in which a pattern is printed using a screen plate and a part of the metal layer other than the pattern is removed by etching (see, for example, PTL 1).
A method of manufacturing a printed wiring board by a printing process according to the prior art will be described below with reference to the flowchart of
First, a laminated board in which a metal layer is formed on a surface of a base material formed of an insulator is prepared (step S101).
Next, after pretreatment processes such as cleaning and roughness formation, printing with an etching resist ink is performed on a pattern portion of the metal layer of the laminated board by using a screen plate (step S102).
Subsequently, the etching resist ink is cured to form an etching resist layer (step S103).
Next, the metal layer of the laminated board is etched to remove an unnecessary portion (a portion other than the pattern) (step S104).
Subsequently, the etching resist layer is stripped to remove the etching resist layer of the pattern (step S105).
Next, a solder resist layer is formed by performing, on a portion of the pattern not to be soldered, solder resist printing using a solder resist ink, and then, curing the solder resist ink (step S106).
Finally, a process for forming an outer shape and holes (step S107), and a process for finishing the surface (step S108) are performed. In the process of finishing the surface, acid is used to degrease and rust-proof the surface, with the purpose of cleaning the portion of the pattern where the solder resist layer is not formed. As a result, the printed wiring board in which the pattern is formed on the base material is manufactured.
Such a method of manufacturing a printed wiring board by a printing process in which a pattern is formed by using a screen plate is widely employed, because it is highly suitable for mass production and allows for production at low cost.
In recent years, with the progress of miniaturization and increase in density of electronic components, it is required to form a pattern of a printed wiring board with higher accuracy.
However, in a conventional printing process using a screen plate, printing with the etching resist ink is performed while pulling the screen plate, and thus a positional deviation often occurs in the etching resist layer. Therefore, there is a problem in that it is difficult to accurately form a pattern at a predetermined position. In particular, when a positional deviation in a land portion for mounting an electronic component is large, there is a problem in that a malfunction such as a short circuit may occur. Further, in addition to the printing process, examples of the subtractive process include a photographic method and the like, but this method has the problem that the productivity is generally low and the cost is high.
Therefore, a main object of the present invention is to provide, in a method of manufacturing a printed wiring board in which a pattern is formed by a printing process, a method of manufacturing a printed wiring board capable of accurately forming, at a predetermined position, a pattern of a portion requiring position accuracy.
A method of manufacturing a printed wiring board according to the present invention includes preparing a laminated board including a metal layer formed on a surface of a base material, forming a first etching resist layer by printing a pattern of a portion requiring position accuracy on the metal layer of the laminated board using a metal mask, forming a second etching resist layer by printing a pattern of a portion other than the portion requiring position accuracy on the metal layer of the laminated board using a screen plate, removing, by etching, the metal layer of the laminated board where the first etching resist layer and the second etching resist layer are not formed, and stripping the first etching resist layer and the second etching resist layer.
In the method of manufacturing a printed wiring board according to the present invention, the first etching resist layer is formed by printing a pattern of a portion requiring position accuracy using a metal mask, and thus, the pattern can be formed at a predetermined position with high accuracy, and it is possible to reduce malfunctions from a short circuit or the like. Further, the second etching resist layer is formed by printing a pattern of a portion other than the portion requiring position accuracy using a screen plate. Subsequently, portions where the first etching resist layer and the second etching resist layer are not formed are simultaneously removed by etching, and the first etching resist layer and the second etching resist layer are simultaneously stripped. Thus, it is possible to manufacture printed wiring boards in a process excellent in terms of overall mass productivity and cost reduction.
Here, the portion requiring position accuracy preferably includes a land portion for mounting an electronic component.
Further, the portion requiring position accuracy preferably includes a fiducial mark portion for positioning the printed wiring board.
High position accuracy is often required for the land portion for mounting the electronic component and the fiducial mark portion for positioning the printed wiring board, whereas other portions of the wiring pattern often do not require high position accuracy.
The thickness of the metal mask is preferably 0.02 mm or more. When a metal mask having a thickness of 0.02 mm or more is chosen, it is possible to prevent the metal mask from being deformed due to the printing pressure of a squeegee or the like.
The metal mask is preferably a combination mask.
When a combination mask is used as the metal mask, the cost can be reduced, compared to a case where a directly attached metal mask produced by using a metal plate alone is used.
In the forming the first etching resist layer and the forming the second etching resist layer, it is preferable to print the pattern by using a UV-curable ink.
When the UV-curable ink is used to print the pattern when forming the first etching resist layer and the second etching resist layer, the first etching resist layer and the second etching resist layer can be formed at a low temperature, and it is possible to appropriately form the first etching resist layer and the second etching resist layer in a state where the base material contracts little.
When printing the pattern by using the metal mask in the forming the first etching resist layer, it is preferable to use a squeegee having a type A durometer hardness defined in JIS K6253-3 of 60 or more.
When the squeegee having a hardness of 60 or more is used in printing the pattern by using the metal mask in forming the first etching resist layer, it is possible to smoothly print the pattern.
According to the present invention, it is possible to provide a method of manufacturing a printed wiring board that allows for accurately forming, at a predetermined position, a pattern of a portion requiring position accuracy, improving overall mass productivity, and achieving cost reduction.
The above-mentioned object, other objects, features, and advantages of the present invention will become more obvious from the description of the embodiments for carrying out the invention, described below with reference to the drawings.
An embodiment of the present invention will be described below with reference to the accompanying drawings.
The printed wiring board 10 includes a base material 14. A pattern 18 is formed on a front surface 14a, being one surface of the base material 14. Note that the pattern 18 may be formed on a back surface 14b, being the other surface of the base material 14, or on both surfaces of the base material 14. If the pattern 18 is formed on both surfaces of the base material 14, a through hole penetrating the base material 14 may be formed in the base material 14 to electrically connect a pattern on the front surface 14a of the base material 14 and a pattern on the back surface 14b of the base material 14.
The base material 14 is formed of, for example, an insulating resin material having a thickness of 0.1 mm or more and 2.0 mm or less. The base material 14 is formed of, for example, a glass cloth epoxy resin laminated board, a phenolic paper substrate, an epoxy paper substrate, a glass composite substrate, a Teflon (registered trademark) substrate, an alumina substrate, a polyimide substrate, and the like.
The pattern 18 is formed of, for example, a metal such as Cu, Au, Pd, and Pt, or an alloy of these metals. The thickness of the pattern 18 is 18 μm or more and 70 μm or less. The pattern 18 is formed by etching a metal layer 16 provided on the front surface of the base material 14. The pattern 18 includes land portions 18a for mounting an electronic component 50 and wiring pattern portions 18b other than the land portions 18a.
The land portion 18a has two main surfaces and at least one side surface, and one of the two main surfaces (a first main surface) is in surface contact with the front surface 14a of the base material 14. Further, the electronic component 50 is mounted on the other main surface (a second main surface), for example. When the electronic component 50 is mounted, each of the land portions 18a and an adjacent one of the land portions 18a and a part of an external electrode of the electronic component 50 are electrically connected via a bonding material 52 such as solder. For example, when the size of the electronic component 50 in the longitudinal direction is 1.0 mm, the distance between the center of the land portion 18a and the center of the adjacent land portion 18a should be 0.5 mm or more and 1.5 mm or less. Therefore, the land portions 18a need to be accurately formed at predetermined positions. Consequently, the land portions 18a are portions requiring position accuracy.
The wiring pattern portion 18b other than the land portion has two main surfaces and at least one side surface, and one of the two main surfaces (a first main surface) is in surface contact with the front surface 14a of the base material 14. The wiring pattern portion 18b other than the land portion is mainly a portion that electrically connects the land portion 18a and the land portion 18a adjacent at a predetermined interval. Further, a part of the wiring pattern portion 18b other than the land portion is covered with a solder resist layer 40 in order to prevent solder adhesion to a portion that should not be soldered, protect the pattern, and maintain insulation reliability. Therefore, the wiring pattern portion 18b does not necessarily have to be formed at a predetermined position with high accuracy. Consequently, the wiring pattern portion 18b other than the land portion is a portion where position accuracy is not required.
First, a laminated board 12 in which the metal layer 16 is formed on the front surface of the base material 14 is prepared (step S001).
Next, a metal mask 32 is used to print a pattern of the land portions 18a, being portions requiring position accuracy (step S002).
As illustrated in
Next, the etching resist ink 36 printed on the surface of the laminated board 12 is cured to form the first etching resist layer 20a (step S003).
Here, the metal mask 32 is, for example, a metal plate made of stainless steel. Unlike a screen plate, the metal mask 32 is placed on the surface of the laminated board 12 when performing printing, and thus highly accurate printing can be performed.
Further, the thickness of the metal plate forming the metal mask 32 is preferably 0.02 mm or more. If a metal plate having a thickness of 0.02 mm or more is chosen, it is possible to prevent the metal mask 32 from being deformed due to the printing pressure of the squeegee or the like.
Further, portions of the metal mask 32 corresponding to the land portions 18a are formed so as to penetrate the metal plate. Based on the pattern 18, through holes 32a are formed at the portions corresponding to the land portions 18a, by, for example, laser processing, etching processing, or additive processing. Laser processing is a method of producing the through holes 32a by a laser processing machine. Therefore, the through holes 32a can be formed with high accuracy. Further, the etching processing is a method of forming the through holes 32a by chemical etching. Therefore, a number of holes can be formed simultaneously. The additive processing is a method of forming the through holes 32a by electroforming using nickel (Ni). Therefore, it is possible to produce the fine through holes 32a.
Moreover, in addition to the above-mentioned types of processing, electrolytic polishing, fluorine coating, half-etching and the like may be employed. In electrolytic polishing, the unevenness of an inner wall of the through holes 32a can be smoothed by passing a direct current between the metal mask 32 serving as an anode and a cathode serving as a counter electrode, via an electrolytic solution. Further, in the fluorine coating, the unevenness of the inner wall of the through holes 32a can be smoothed by applying a fluororesin to the inner wall of the through holes 32a. Moreover, in the half-etching, when it is desired to adjust the amount of ink in a specific one of the through holes 32a, the through holes 32a can be formed with a different plate thickness in one metal mask. The through holes 32a formed by using laser processing, etching processing, additive processing, or the like are further subjected to processing such as electrolytic polishing, fluorine coating, and half-etching to make the through holes 32a smoother. In particular, it is preferable to perform the electrolytic polishing and/or fluorine coating after the laser processing. If the electrolytic polishing and/or fluorine coating are performed in addition to the laser processing, it is possible to further smoothen the unevenness of the inner wall of the through holes 32a. Consequently, the first etching resist layer 20a can be formed with higher accuracy.
Further, for example, it is possible to use, as the metal mask 32, a directly attached metal mask in which a metal plate is directly bonded to a frame, or a combination mask fabricated by bonding a mesh made of such as polyester or stainless steel to a frame and bonding a metal plate within the mesh. In particular, if the combination mask is used, the metal mask 32 can be produced at a lower cost than the directly attached metal mask.
Further, when performing printing with the etching resist ink 36 to form the first etching resist layer 20a, it is preferable to use the squeegee 30 having a type A durometer hardness defined in JIS K6253-3 of 60 or more. If the squeegee 30 described above is used, the etching resist ink 36 can be applied to the surface of the metal mask 32 with an appropriate pressure, and printing with the etching resist ink 36 can be performed smoothly. Various materials such as metal, plastic, and urethane can be used as the material of the squeegee 30. Further, it is desirable that the printing pressure of the squeegee 30 is as low as possible.
Next, a screen plate 34 is used to print the wiring pattern portion 18b, being a portion other than the portion requiring position accuracy (step S004).
As illustrated in
Next, the etching resist ink 36 printed on the surface of the laminated board 12 is cured to form the second etching resist layer 20b (step S005).
Here, the screen plate 34 is, for example, a mesh made of stainless steel, polyester, or polyarylate, and the like, and only the wiring pattern portion 18b other than the land portion is opened. When printing with the screen plate 34 is performed, a gap (clearance) is provided between the screen plate 34 and the laminated board 12, and printing is performed on the laminated board 12 while pulling the screen plate 34.
Note that the etching resist ink 36 used when forming the first etching resist layer 20a and the second etching resist layer 20b is preferably a UV-curable ink. When the UV-curable ink is used as the etching resist ink 36, the etching resist ink 36 is cured by irradiation with ultraviolet rays. If the UV-curable ink is used, the heat for curing the etching resist ink is low, and thus, it is possible to form the first etching resist layer 20a and the second etching resist layer 20b in a state where the base material 14 contracts little.
Further, it is desirable that the etching resist ink 36 has a viscosity at which printing by the metal mask 32 and the screen plate 34 is possible.
Next, the metal layer 16 of the laminated board 12 is etched to remove a portion other than the pattern 18 (step S006).
Subsequently, the first etching resist layer 20a and the second etching resist layer 20b are stripped by an ink stripping agent, to remove the first etching resist layer 20a and the second etching resist layer 20b (step S007).
Next, the solder resist layer 40 is formed by performing, on a portion of the pattern not to be soldered, solder resist printing using a solder resist ink, and then, curing the solder resist ink (step S008).
Finally, a process for forming an outer shape and holes (step S009), and a process for finishing the surface (step S010) are performed. In the process of finishing the surface, acid is used to degrease and rust-proof the surface, with the purpose of cleaning the surface of the portion of the pattern where the solder resist layer is not formed. As a result, the printed wiring board 10 in which the pattern 18 is formed on the base material 14 is manufactured.
The following experiment was conducted to compare a positional deviation in a case where the metal mask 32 is used for printing and in a case where the screen plate 34 is used for printing.
In the experiment, a printed wiring board fabricated according to the manufacturing process of the present invention illustrated in
As illustrated in
In the above embodiment, a case where the portion requiring position accuracy is the land portion for mounting the electronic component has been described, but the present invention is not limited thereto.
For example, when an electronic component is automatically inserted to and/or automatically mounted on the printed wiring board 10, a fiducial mark may be provided on the surface of the printed wiring board 10, as a mark for aligning the printed wiring board 10 with an inserting machine or a mounter. In this case, the fiducial mark is a portion requiring position accuracy, as with the land portion. Therefore, a pattern of the fiducial mark may be printed in step (S002) in which the metal mask 32 is used to print the pattern of the portion requiring position accuracy.
Further, in the embodiment described above, a case where the etching resist ink 36 is a UV-curable ink has been described, but the present invention is not limited thereto. For example, a thermosetting ink may be used as the etching resist ink 36.
As described above, in a printing process using a conventional screen plate, printing with the etching resist ink is performed on the metal layer of the laminated board while pulling the screen plate 34, and thus, a positional deviation often occurs in the etching resist layer. However, in the present invention, the metal mask 32 is used to print a pattern of the portion 18a where position accuracy is required (for example, a land portion or a fiducial mark portion), to form the first etching resist layer 20a, and thus, the portion 18a where position accuracy is required can be accurately formed at a predetermined position. Further, in the present invention, the screen plate 34 is used to print a pattern of the portion 18b other than the portion requiring position accuracy (for example, a wiring pattern portion other than the land portion, or a portion other than the fiducial mark portion), to form the second etching resist layer 20b. Subsequently, portions of the metal layer 16 other than the first etching resist layer 20a and the second etching resist layer 20b are simultaneously removed by etching, and the first etching resist layer 20a and the second etching resist layer 20b are simultaneously stripped. Thus, it is possible to realize a method of manufacturing a printed wiring board that allows for improving overall mass productivity and achieving cost reduction.
Note that, in order to print the pattern 18 with high accuracy, a method in which all the patterns are printed by using the metal mask 32 may also be considered. However, when the patterns 18 are close to each other, the strength of the metal mask 32 decreases and the metal mask 32 may deform during printing. Therefore, it is preferable to use the metal mask 32 and the screen plate 34 together, as in the present invention.
As described above, embodiments of the present invention are disclosed in the above description, but the present invention is not limited thereto.
That is, various modifications can be made to the above-described embodiments with respect to the mechanism, shape, material, number of components, positions, arrangement, and the like, without departing from the technical idea and purpose of the present invention, and these modifications are included in the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-019375 | Feb 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/001885 | 1/21/2020 | WO |
