JP7014744B2 - Manufacturing method of printed wiring board - Google Patents

Description

The present invention relates to a method for manufacturing a printed wiring board.

The printed wiring board is provided with a circuit pattern and a pad (electrode pad) for mounting an electronic component by using a conductive material such as copper foil. From the viewpoint of protecting the circuit pattern, preventing short circuits of the circuit pattern, preventing oxidation of the copper foil, and the like, the surface of the printed wiring board on the circuit pattern side is covered with a solder resist made of an insulating resin. Since the electronic components are soldered to the pad, the pad is not covered by the solder resist and is exposed.

When accuracy is required, the solder resist pattern is often formed by a photo development method. Specifically, for example, as shown in Patent Document 1 below, after forming a circuit pattern on an insulating substrate, a photocurable resin is applied to the entire surface of the substrate, exposed through a mask film, and further. After the procedure of applying the development process, the procedure of forming the pattern of the solder resist is performed.

Japanese Unexamined Patent Publication No. 63-200594

Forming a solder resist pattern by a photographic development method as described in Patent Document 1 requires a large number of man-hours and has a problem of high cost. On the other hand, if the solder resist is formed by screen printing, exposure processing and development processing are not required, so that the cost of the printed wiring board can be reduced.

On the other hand, chip components (for example, multilayer ceramic capacitors) have been miniaturized in recent years, and are shifting from the 1005 size, which has been widely used until now, to the 0603 size. Along with this, the area of the pad tends to be smaller. When the pad area is reduced in this way, when the solder resist is screen-printed, the solder resist may squeeze out onto the pad due to misalignment due to deterioration of the screen mesh or ink bleeding. If electronic components are soldered to a printed wiring board with this protrusion left unattended, the amount of solder on the pad will fluctuate, so the chip components will stand up when passed through a reflow furnace due to differences in surface tension, the so-called Manhattan phenomenon. May occur. Therefore, it is necessary to avoid ink spilling onto the pad as much as possible so that the surface of the pad has a predetermined shape and area.

In order to prevent ink from squeezing out, it is conceivable to increase the distance between the pad and the solder resist (resist clearance), but this results in a result contrary to the demand for high-density mounting, which has been emphasized in recent years. In addition, it is conceivable to replace the ink with a high-viscosity type, but this makes it difficult to put abundant ink on the corners of the circuit pattern, and the insulation performance of the solder resist deteriorates.

Therefore, an object of the present invention is to provide an inexpensive printed wiring board capable of accurately controlling the shape and area of the pad.

In order to solve the above problems, the method for manufacturing a printed wiring board according to the present invention includes a base material made of an insulating material, a pad, a circuit pattern, and a solder resist that covers the circuit pattern. A printed wiring board in which a part or all of the surface is arranged in an uncoated region without a solder resist, and a first layer in contact with the base material and the first layer at the edge of the solder resist on the uncoated region side. A second layer is provided on the layer, and the first layer and the second layer are formed by screen printing and curing , including the end portion of each layer on the uncovered region side . The first layer is formed by curing the first resin material, and the second layer is formed by curing a second resin material different from the first resin material, and the uncoated layer of the second layer is formed. The first in manufacturing a printed wiring board in which the entire thickness direction of the second layer at the end on the region side is retracted in a direction away from the pad from the end on the uncovered region side of the first layer . The viscosity of the first resin material is made higher than the viscosity of the second resin material, and the end portion of the second layer on the non-covered region side is inclined so as to project toward the pad side toward the base material side. The end portion of the first layer on the uncovered region side is characterized by having a shape closer to a vertical plane than the end portion of the second layer.

By making the viscosity of the first resin material higher than the viscosity of the second resin material in this way, the first layer of the solder resist can be formed with high accuracy . Further, since the end portion of the second layer on the uncovered region side is recessed from the end portion of the first layer on the uncovered region side, even if the second layer is roughly formed, the second layer is placed on the pad. The two layers are less likely to stick out. Therefore, it is possible to accurately manage the shape and area of the pad. Moreover, since it is sufficient to select an appropriate resin material, the manufacturing cost of the printed wiring board can be reduced.

Since the first resin material having a high viscosity does not easily exude after coating, it is possible to form a solder resist opening shape with high accuracy. Even if a second resin material having a low viscosity is applied after the first layer is formed, the end portion of the second layer on the uncovered region side is retracted from the end portion of the first layer on the uncoated region side. Therefore, even if the applied second resin material has some misalignment or exudation, the second resin material does not reach the pad. Therefore, it is possible to prevent the solder resist from protruding onto the pad, and it is possible to accurately manage the shape and area of the pad. Since most of the circuit pattern is covered with a second layer using a low-viscosity resin, the solder resist can be reliably formed at the corners of the circuit pattern. Therefore, it is possible to avoid deterioration of the insulating property of the circuit pattern.

In general screen printing, elongation due to deterioration of the screen plate over time is unavoidable, so there is a limit to preventing the solder resist from sticking out. However, by adopting the above configuration, the solder resist does not stick out and the pad is used. The shape and area of the screen can be managed with high accuracy. Therefore, screen printing, which has a large cost advantage, can be adopted without any problem.

Further, the first layer can be provided only around the uncovered area.

The first layer may be provided at a distance from the pad or may be provided on the edge of the pad.

According to the present invention, it is possible to provide an inexpensive printed wiring board capable of accurately controlling the shape and area of the pad. This makes it possible to reduce the size of electronic components mounted on the printed wiring board.

It is a top view which shows the 1st Embodiment of a printed wiring board. It is sectional drawing which was looked at by the arrow A line of FIG. It is sectional drawing which was looked at by the arrow BB of FIG. It is a top view which shows the 2nd Embodiment of a printed wiring board. It is sectional drawing which took the arrow | view by the line CC of FIG. It is a top view which shows the 3rd Embodiment of a printed wiring board. It is sectional drawing which saw the arrow with the DD line of FIG. It is a top view which shows the modification of the 3rd Embodiment of a printed wiring board. It is sectional drawing which saw the arrow in the D'-D'line of FIG. It is a top view which shows the 4th Embodiment of a printed wiring board. It is sectional drawing which was looked at by the EE line of FIG.

Hereinafter, embodiments of the printed wiring board will be described with reference to FIGS. 1 to 9.

1 to 3 show the first embodiment of the printed wiring board according to the present invention. Of these, FIG. 1 is a plan view showing the first embodiment. FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1, and FIG. 3 is a cross-sectional view taken along the line BB of FIG. In FIG. 1, the region where the first layer 5a of the solder resist 5 described later is formed is provided with a scattered dot pattern, and the region where the second layer 5b is formed is hatched.

As shown in FIGS. 1 to 3, the printed wiring board 1 has a base material 2 made of an insulating material, a pad 3 formed of a conductive material (for example, copper foil) on the surface of the base material 2, and a circuit pattern 4. And a solder resist 5 that covers the circuit pattern 4. Although the pad 3 having a rectangular contour is illustrated in FIG. 1, the shape of the pad 3 is arbitrary, and the pad 3 may have another form of contour (for example, a circular contour).

The pad 3 is a portion that serves as an electrode when soldering an electronic component, and is usually in a state of being electrically connected to the circuit pattern 4.

The solder resist 5 is formed by curing an insulating resin material. The solder resist 5 has a function of protecting the circuit pattern 4, preventing a short circuit of the circuit pattern 4, and further preventing oxidation of the copper foil by covering the surface of the circuit pattern 4. The solder resist 5 is formed over the entire surface of the printed wiring board 1, but since the electronic components are soldered to the pad 3, the pad 3 is not covered with the solder resist 5 and is in an exposed state. That is, the surface of the pad 3 faces the uncoated region M without the solder resist 5. When a through hole (not shown) is formed in the printed wiring board 1, the solder resist 5 is not formed in this through hole either.

In the present embodiment, the edge portion of the solder resist 5 on the uncoated region M side is formed so as to be in contact with the base material 2 and above the first layer 5a (direction separated from the base material 2). It has a two-layer structure including a second layer 5b that overlaps with the above. The first layer 5a is formed continuously in an endless manner so as to be separated from the pad 3 and surround the entire circumference of the pad 3, and is formed only around the uncovered region M. The second layer 5b is formed by retracting the end portion 5b1 on the uncovered region side from the end portion 5a1 on the uncovered region side of the first layer 5a in a direction in which the uncovered region M expands. Therefore, as shown in FIG. 2, the resist clearance α between the first layer 5a and the pad 3 is smaller than the resist clearance β between the second layer 5b and the pad 3 (α <β). The end portion 5b1 of the second layer 5b is located approximately at the intermediate portion in the width direction of the first layer 5a.

The width dimension W of the first layer 5a can be set to, for example, 0.5 mm. In this case, considering the error in forming the second layer 5b, the receding distance γ of the end portion 5b1 of the second layer 5b with respect to the end portion 5a1 of the first layer 5a is generally in the range of 0.05 mm to 0.45 mm. It becomes.

In the present embodiment, the first layer 5a and the second layer 5b are both formed by screen printing after forming the pad 3 and the circuit pattern 4 on the surface of the base material 2 by a known method. In order to secure a highly accurate resist clearance α, it is preferable to use a screen mesh made of stainless steel when forming the first layer 5a. On the other hand, when forming the second layer 5b, it is preferable to use a screen mesh formed of a resin such as polyester in order to increase the amount of ink supplied and secure a sufficient film thickness. If less precision is required, a resin screen mesh can also be used during the formation of the first layer 5a.

In screen printing, the first resin material is used as ink when the first layer 5a is formed, and the second resin material different from the first resin material is used as ink when the second layer 5b is formed. In the present embodiment, a material having a higher viscosity than the second resin material is used as the first resin material. The difference in viscosity between the first resin material and the second resin material is that the base resin and filler of both resin materials are common, and the mixing ratio is changed, and either the base resin or filler of both resin materials is used. It can also be obtained by changing the material of one or both.

Further, as the first resin material and the second resin material, either an ultraviolet curable type or a thermosetting type can be used. In this embodiment, the ultraviolet curable type is used as the first resin material and the second resin material. A printed wiring board having the first layer 5a and the second layer 5b as the solder resist 5 by screen-printing and curing the first resin material on the substrate and then screen-printing and curing the second resin material. 1 is completed.

The viscosity of the first resin material having a high viscosity is preferably in the range of 250 to 500 [dPa · s]. On the other hand, the viscosity of the second resin material having a low viscosity is preferably in the range of 100 to 300 [dPa · s]. As the second resin material, it is preferable to use a material having a viscosity similar to that of the ink used for forming a single-layer solder resist in screen printing as in the conventional case.

From the above difference in viscosity, as conceptually shown in FIG. 2, the end portion 5b1 of the second layer 5b formed by curing the low-viscosity resin material is on the lower side (base) due to the leveling of the resin material immediately after printing. The material 2 side) has an inclined surface shape that overhangs the pad 3 side. On the other hand, the end portion 5a1 of the first layer 5a formed by curing the high-viscosity resin material is closer to the vertical surface than the end portion 5b1 of the second layer 5b because the leveling immediately after printing is small.

In this way, by making the first resin material different from the second resin material, as the first resin material for forming the first layer 5a, a material capable of forming a solder resist around the pad 3 with high accuracy is selected. Can be done. Further, since the end portion 5b1 of the second layer 5b is retracted from the end portion of the first layer 5a, even if the second layer 5b is roughly formed on the first layer 5a, the second layer 5b Is hard to stick out on the pad 3. Therefore, the resist clearance, particularly the resist clearance α between the first layer 5a and the pad 3, can be narrowed, and even in screen printing where accuracy is difficult to obtain, the resist clearance α is 0.1 mm or smaller. Can be realized. Even with such a narrow resist clearance, the solder resist 5 does not protrude onto the pad, and the shape and area of the pad 3 can be accurately controlled.

In particular, when the viscosity of the first resin material is higher than the viscosity of the second resin material as in the present embodiment, the first resin material having a high viscosity does not easily exude after coating, so that the first layer 5a is highly accurate. Can be formed into. After that, even if a second resin material having a low viscosity is used when forming the second layer 5b, the uncovered region M of the end portion 5b1 of the second layer 5b is larger than that of the end portion 5a1 of the first layer 5a. Since it is retracted in the expanding direction, the exuded second resin material does not reach the pad 3. Therefore, it is possible to prevent the solder resist 5 from protruding onto the pad 3. Since most of the circuit pattern 4 is covered with the second layer 5b using the low-viscosity resin material, the corners of the circuit pattern 4 can be surely covered with the solder resist 5. Therefore, it is possible to avoid a decrease in the insulating property of the solder resist 5.

Next, a second embodiment will be described with reference to FIGS. 4 and 5.

In the first embodiment described above, a plurality of adjacent pads (two in the present embodiment) are arranged in one uncovered region M. On the other hand, in the second embodiment, the first layer 5a is formed between two adjacent pads 3, and the periphery of each pad 3 is surrounded by the continuous first layer 5a in an endless manner. It forms an uncovered region M. The second layer 5b is not formed between the two pads 3. One pad 3 is arranged in each uncovered region M. Since the other configurations and actions and effects are based on the first embodiment, duplicate description will be omitted.

Next, a third embodiment will be described with reference to FIGS. 6 and 7.

In each of the embodiments shown in FIGS. 1 to 5, the first layer 5a of the solder resist 5 is provided so as to be separated from the pad 3. On the other hand, the third embodiment has a configuration in which the first layer 5a is also provided on the edge portion 3'of the pad 3 in the second embodiment. The surface of the pad 3 not covered by the first layer 5a is arranged in the uncovered region M without the solder resist 5.

In this case, the solder resist 5 protrudes from the surface of the pad 3, but the protrusion is limited to the narrow region of the edge 3'of the pad 3, and the protrusion is the high-viscosity first resin. Since the first layer 5a is made of a material, the protrusion width on the pad 3 can be accurately controlled. Therefore, even in this embodiment, it is possible to accurately manage the shape and area of the pad 3. Since the other configurations and actions and effects are based on the first embodiment, duplicate description will be omitted.

In the third embodiment, the size of the pad 3 in a plan view is slightly larger than the uncovered region M, and the region of the pad 3 other than the uncovered region M is covered with the first layer 5a. ing. However, in the present invention, for example, as in the pad 3 on the right side of FIG. 8, the size of the pad 3 in a plan view may be made much larger than that of the uncovered region M, other than the uncovered region M. In the region of the pad 3 of the above, there may be a portion not covered with the first layer 5a.

Next, a fourth embodiment will be described with reference to FIGS. 10 and 11.

In each of the embodiments shown in FIGS. 1 to 7, the first layer 5a is formed only around the uncovered region M. On the other hand, the fourth embodiment is different from each embodiment in that the first layer 5a is formed on the entire surface of the printed wiring board 1. Since the other configurations and actions and effects are the same as those in the first to third embodiments, duplicate description will be omitted.

In each of the above-described embodiments, the second layer 5b overlaps the first layer 5a at the edge of the solder resist 5 on the uncoated region M side, but the end of the second layer 5b on the uncovered region side. The first layer 5a may be overlapped on the second layer 5b as long as the portion 5b1 is retracted from the end portion 5a1 on the uncovered region side of the first layer 5a. In this case, the first layer 5a is formed after the second layer 5b is formed.

Further, each embodiment can be applied not only to a rigid substrate but also to a bendable flexible substrate. Further, in the above embodiment, the single-sided printed wiring board is exemplified, but the configuration of the present embodiment can be applied to the double-sided printed wiring board and the multi-layer printed wiring board.

1 Printed wiring board 2 Base material 3 Pad 3'Edge 4 Circuit pattern 5 Solder resist 5a First layer 5a1 End 5b Second layer 5b1 End α, β Resist clearance M Uncovered area

Claims (4)

Printed wiring having a base material made of an insulating material, a pad, a circuit pattern, and a solder resist that covers the circuit pattern, and a part or all of the surface of the pad is arranged in an uncovered area without the solder resist. It ’s a board,
A first layer in contact with the base material and a second layer superimposed on the first layer are provided on the edge of the solder resist on the uncovered region side, and the first layer and the second layer are the same. Each layer is formed by screen printing and curing, including the end portion on the uncovered region side, the first layer is formed by curing the first resin material, and the second layer is formed by curing the first resin material. Formed by curing a second resin material that is different from the first resin material,
A printed wiring board in which the entire thickness direction of the second layer at the end of the second layer on the uncovered region side is recessed from the end of the first layer on the uncovered region side in a direction away from the pad. When manufacturing
The viscosity of the first resin material is made higher than the viscosity of the second resin material, and the end portion of the second layer on the uncovered region side is inclined so as to project toward the pad side toward the base material side. A method for manufacturing a printed wiring board, wherein the end portion of the first layer on the uncovered region side is shaped to be closer to a vertical surface than the end portion of the second layer. The method for manufacturing a printed wiring board according to claim 1 , wherein the first layer is provided only around the uncovered region. The method for manufacturing a printed wiring board according to claim 1 or 2 , wherein the first layer is provided so as to be separated from a pad. The method for manufacturing a printed wiring board according to claim 1 or 2 , wherein the first layer is provided on the edge of the pad.

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