KR102186151B1 - Method of printed circuit board - Google Patents

Abstract

The present invention comprises the steps of forming a circuit pattern on a substrate to improve undercut defects due to uncured solder resist layer; Forming a first solder resist layer using a photocurable resin on the substrate on which the circuit pattern is formed; Exposing the first solder resist layer to light through a first mask to form a cured region and an uncured region; Forming a second solder resist layer on the first solder resist layer by using a photocurable resin; Curing the dam formation by exposing the second solder resist layer to light through a second mask; Increasing the height of the dam forming portion by repeating the step of forming the second solder resist layer and curing the dam forming portion at least once; And developing the substrate in which the formation of the solder resist layer and exposure are repeated to remove the uncured solder resist layer. It may include.

Description

Manufacturing method of printed circuit board {Method of printed circuit board}

The present invention relates to a method of manufacturing a printed circuit board, and more particularly, to a method of manufacturing a printed circuit board capable of preventing undercut defects in a solder resist layer.

The recent trend of semiconductor packaging technology is miniaturization, thinning, and multifunctionalization. Currently, FCCSP (Flip Chip Chip Scale Package) for package-on-package (PoP) is being mass-produced reflecting such a trend, and in the side of printed circuit board (PCB), 2-step solder resist (SR) structure Is preferred.

In general, in the 2-step solder resist structure, a thin solder resist is formed in the flip chip (FC) area, and a thick solder resist is formed in the package on package (PoP) top ball area. It is common. In the 2-step solder resist, when the chip is bonded to the flip chip area, the solder resist in the outer PoP (Package on Package) top ball area acts as an underfill barrier, or PoP (Package On). Package) Since the solder resist in the top ball area is formed at a relatively high height, the Pitch prevents bumps in the PoP (Package on Package) top ball area from being bridged to each other. ) Can be further reduced. Accordingly, in recent years, in order to further reduce the bump pitch in the package on package (PoP) top ball area, there is an increasing demand to further increase the thickness of the solder resist in the package on package (PoP) top ball area.

In order to increase the thickness of the solder resist in the package on package (PoP) top ball region, a 2-step or more solder resist process is performed. In the case of forming a solder resist thickness of 25 to 40 μm, 2- step The solder resist opening can be formed. However, in order to form the thickness of a solder resist of 40 μm or more, a 3-step or more coating of a solder resist is required. In the past, exposure was performed after the first solder resist coating, followed by the second and third solder resist coating, and then exposure was performed. . However, in this case, in the second exposure process, the solder resist layer thickened by stacking two or more layers must be exposed and cured.Because the thickness of the solder resist is too thick compared to the transmittance to UV, the lower portion of the solder resist is UV It is not cured sufficiently by Accordingly, an undercut (FIG. 1A) defect occurs because an uncured solder resist lower region is etched by an etching solution in a subsequent development process. In particular, this tendency becomes more severe as the thickness of the solder resist increases.

Korean Patent Publication No. 2011-0020542

Accordingly, the present invention was devised to solve the above problems that have been raised in conventional printed circuit boards, and a printed circuit board capable of solving an undercut defect during a developing process for forming a solder resist opening of a printed circuit board. It is an object of the present invention to provide this.

In order to effectively achieve such an object, the present invention includes the steps of forming a circuit pattern on a substrate; Forming a first solder resist layer using a photocurable resin on the substrate on which the circuit pattern is formed; Exposing the first solder resist layer to light through a first mask to form a cured region and an uncured region; Forming a second solder resist layer on the first solder resist layer by using a photocurable resin; Curing the dam formation by exposing the second solder resist layer to light through a second mask; Increasing the height of the dam formation portion by repeating the step of forming the second solder resist layer and the step of curing the dam formation portion at least once; And removing the uncured solder resist layer by developing the substrate in which the formation of the solder resist layer and exposure are repeated.

The dam forming part may be formed in a package on package (PoP) top ball region, and the first solder resist layer may be formed using a liquid photocurable resin.

The remaining solder resist layers excluding the first solder resist layer may be formed using a solid photocurable resin film, and the substrate having the outer circuit is pre-soldered before the step of forming the first solder resist layer. It may further include a step of pre-treatment.

The step of forming the cured region and the uncured region by exposure may be performed by UV Direct Imaging (UV-DI) instead of the first mask, and the dam formation portion is cured by exposing through the second mask. The step can also be performed by UV Direct Imaging (UV-DI).

In addition, after the step of developing the substrate, a post-curing process may be performed on the printed circuit board.

The method of manufacturing a printed circuit board according to the present invention can prevent undercut defects when forming a thick solder resist requiring 3-step or more solder resist coating, thereby providing a printed circuit board with improved reliability.

1A is a cross-sectional view in which an undercut defect occurs according to a conventional solder resist forming method.
1B is a cross-sectional view of a printed circuit board according to a method of forming a solder resist layer according to an embodiment of the present invention.
2A is a cross-sectional view showing a state in which a circuit pattern is formed on a substrate during a process of forming a solder resist layer according to an embodiment of the present invention.
2B is a cross-sectional view after a first solder resist layer is formed during a process of forming a solder resist layer according to an embodiment of the present invention.
2C is a cross-sectional view of a process of developing a first solder resist layer during a process of forming a solder resist layer according to an embodiment of the present invention.
2D is a cross-sectional view after a second solder resist layer is formed during a process of forming a solder resist layer according to an embodiment of the present invention.
2E is a cross-sectional view of a process of developing a second solder resist layer during a process of forming a solder resist layer according to an embodiment of the present invention.
2F is a cross-sectional view after a third solder resist layer is formed during a process of forming a solder resist layer according to an embodiment of the present invention.
2G is a cross-sectional view of a process of developing a third solder resist layer during a process of forming a solder resist layer according to an embodiment of the present invention.
2H is a cross-sectional view after a fourth solder resist layer is formed during a process of forming a solder resist layer according to an embodiment of the present invention.
2I is a cross-sectional view of a process of developing a fourth solder resist layer during a process of forming a solder resist layer according to an embodiment of the present invention.
2J is a cross-sectional view of a printed circuit board on which development is completed during a process of forming a solder resist layer according to an embodiment of the present invention.

The terms used herein are used to describe specific embodiments, and are not intended to limit the present invention. As used herein, the singular form may include the plural form unless the context clearly indicates another case. In addition, when used herein, "comprise" and/or:comprising" excludes the presence or addition of the mentioned shapes, numbers, steps, actions, members, elements and/or groups. Not to do.

Objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments associated with the accompanying drawings. In adding reference numerals to elements of each drawing in the present specification, it should be noted that, even though they are indicated on different drawings, only the same elements are to have the same number as possible. In addition, in describing the present invention, when it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In this specification, terms such as first and second are used to distinguish one component from other components, and the component is not limited by the terms.

Hereinafter, the present invention invented to improve undercut defects, which is a problem of the conventional solder resist layer forming method, will be described in detail with reference to the accompanying drawings.

2A to 2J are cross-sectional views showing a process of manufacturing a printed circuit board according to an embodiment of the present invention.

In order to manufacture the printed circuit board 100 of this embodiment, first, a circuit pattern 20 is formed on the substrate using a conductive material (FIG. 2A). In this case, the circuit pattern 20 formed on the substrate may be formed of metal. In addition, the substrate may have a flip chip area 80 on which a flip chip is mounted and a package on package (PoP) top ball area 70 for mounting a package on package. have.

At this time, in the case of the flip chip region 80, since the solder resist layer is not thick, even if the process of forming the openings 50 of the solder resist is performed by the conventional method mentioned above, Undercut defects due to hardening may not occur. However, in the case of the PoP (Package on Package) top ball region 70 having a relatively thick solder resist thickness, when the solder resist must be formed in three or more layers, when using the conventional method, the solder resist layer Since the lower region is uncured, the uncured solder resist layer may be etched in a subsequent development process, resulting in an undercut defect (FIG. 1A). In order to prevent the above defects, according to an exemplary embodiment of the present invention, an exposure process is performed every time each solder resist layer is formed, thereby preventing defects due to uncured solder resist (FIG.

Thereafter, a first solder resist layer 31 may be formed using a photocurable resin on the substrate on which the circuit pattern 20 is formed of a conductive material (FIG. 2B).

At this time, the solder resist layer may be formed by a screen printing method, a roller coating method, a curtain coating method, a spray coating method, and a solder resist film lamination method. It is not limited.

In the case of the screen printing method, a solder resist pattern is directly printed using a plate making method. In this case, exposure and development are not necessary, and curing can be performed immediately. In the case of the roller coating method, a photocurable resin having a lower viscosity than that used in the screen printing method can be applied thinly on a roller made of a material such as rubber to coat the substrate. However, in this method, it may be difficult to control the thickness of the solder resist layer coated according to the substrate, and it may be difficult to form a uniform coating layer. In the case of the curtain coating method, a photocurable resin having a lower viscosity than that used for roller coating is used, and the photocurable resin is passed through a slit (not shown) while passing the substrate under the slit to form a solder resist layer. This is how to coat. This method can obtain very uniform coating quality and can be applied without limitation on the size of the substrate. The spray coating method is a method of coating by spraying photocurable resin ink, and may have an advantage in that it is easy to control the thickness of the solder resist layer.

Thereafter, a first exposure process (FIG. 2C) may be performed on the first solder resist layer 31 through the first mask 60.

At this time, the region to be removed in the subsequent development process is left as an uncured solder resist layer (Figs. 2C and 31) by blocking light so that UV is not irradiated using the non-transmissive region 61 of the first mask 60. After the development process proceeds, the areas (Figs. 2c, 41, and 46) that should not be removed and remain to serve as the protective layer of the printed circuit pattern are cured by UV irradiation through the transmissive area 62 of the first mask 60. You can do it. The solder resist layer (FIGS. 2C, 41, and 46) cured through the first exposure process is not removed in a subsequent development process and remains on the printed circuit board, thereby serving as a protective layer for the printed circuit pattern. Such a first exposure process may be performed by UV-DI (UV-Direct Imaging) method without using a first mask, and a specific area is cured by irradiating UV directly to a desired area of the solder resist layer without using a mask. You can also proceed with the method.

After the first exposure process is performed, a second solder resist layer 32 may be formed on the first solder resist layer using a photocurable resin (FIG. 2D). As previously discussed, the second solder resist layer 32 is also a screen printing method, roller coating method, curtain coating method, spray coating method, and solder resist film lamination method, etc. Can be used, but is not limited thereto.

Thereafter, a second exposure process (FIG. 2E) may be performed on the second solder resist layer 32 through the second mask 65. At this time, the area (FIGS. 2E and 42) in which the dam (FIGS. 2J, 40) of the PoP (Package on Package) top ball area is formed is exposed to UV light through the transmission areas (FIGS. 2E and 67) of the second mask. It can be cured by exposure to, and the area to be removed in the subsequent development process (Fig. 2e, 32) is not irradiated with UV using the opaque area (Fig. 2e, 66) of the second mask (Fig. 2e, 65). By blocking light, the uncured solder resist layer (FIGS. 2E and 32) may remain.

In this way, the solder resist layer (FIGS. 2E, 42) cured through the secondary exposure process is not removed in the subsequent development process, but remains on the printed circuit board, and thus dam (dam) in the package on package (PoP) top ball area. 2j, 40). This secondary exposure process can also be performed by UV-DI (UV-Direct Imaging) method without using a second mask, but by irradiating UV directly onto a desired area of the solder resist layer without using a mask to cure a specific area. You can also proceed with the method.

After proceeding to the second exposure process, a third solder resist layer may be formed on the second solder resist layer using a photocurable resin (FIGS. 2F and 33). As described above, a screen printing method, a roller coating method, a curtain coating method, and a spray coating method may be used as well, but the third solder resist layer is not limited thereto.

Thereafter, a third exposure process (FIG. 2G) may be performed on the third solder resist layer (FIGS. 2F, 33) through the second mask 65 as used in the second exposure process. ) The top ball area dam (FIGS. 2J, 40) formed regions (FIGS. 2G, 43) can be cured by exposing them to UV through the transmission regions (FIGS. 2G, 67) of the second mask , The region to be removed in the subsequent development process is an uncured solder resist layer (Fig. 2G) by blocking light so that UV is not irradiated using the non-transmissive region (Fig. 2G, 66) of the second mask (Fig. , 33). The solder resist layer (FIGS. 2G and 43) cured through the third exposure process is not removed in a subsequent development process and remains on the printed circuit board, thereby serving as a protective layer for the printed circuit pattern. Such a third exposure process may be performed by UV-DI (UV-Direct Imaging) method without using a second mask, and a specific area is cured by irradiating UV directly to a desired area of the solder resist layer without using a mask. You can also proceed with the method.

The reason for forming the second solder resist layer and the third solder resist layer is to increase the thickness of the solder resist in the package on package (PoP) top ball region 70. As in this embodiment, each solder resist By performing an exposure process every time a layer is formed, an undercut defect due to uncured under the solder resist layer can be prevented. In addition, a dam is formed high around the pad exposed portion 50 of the package on package top ball area 80 by a thickly formed solder resist layer, so that the bumps are energized to each other. ), it is possible to manufacture a fine-pitch printed circuit board.

If a solder resist layer thicker than the thickness of the solder resist layer by the third solder resist layer is required, the fourth solder resist layer is formed in the same manner as the formation and exposure process of the second solder resist layer and the third solder resist layer ( 2H and 34) may be formed and exposed (FIG. 2I), and if necessary, a further solder resist layer may be formed and exposed.

After all the solder resist layers are formed and exposed, the uncured solder resist can be removed through a developing process.The developed printed circuit board (Fig. 2j) is a PoP (Package on Package) having a relatively high solder resist layer. It may have a dam (Figs. 2J, 40) in the top ball area. The developing process may be performed by spraying an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous sodium hydroxide solution, or an aqueous potassium hydroxide solution, but is not limited to the above aqueous solution, and may be performed in various ways other than the application method. .

If necessary, a post-cure process can be performed on the printed circuit board on which the development process has been completed. The post-cure process is a photocuring process using energy of 1,000 to 3,000 mJ/cm ² and at a temperature of 150 to 180°C. It may be made of a thermal curing process that proceeds for about 1 to 3 hours.

Another embodiment according to the present invention will be described in detail with reference to FIGS. 2A to 2J. However, content overlapping with the previously described content may be omitted for clear description of the invention.

First, a circuit pattern 20 is formed of a conductive material on a substrate (FIG. 2A). The circuit pattern 20 formed on the substrate may be formed of metal. The substrate may have a flip chip area 80 in which a flip chip is mounted and a package on package (PoP) top ball area 70 for mounting a package on package.

Thereafter, a first solder resist layer 31 may be formed on the substrate on which the circuit pattern 20 is formed of a conductive material using a liquid photocurable resin. By using a liquid photocurable resin, a screen printing method, a roller coating method, a curtain coating method, and a spray coating method may be applied, but the present invention is not limited thereto.

At this time, the reason for forming the first solder resist layer using a liquid photocurable resin is that the lower region and the wetting property of the lower region are considered that the lower region coated with the solder resist layer is a prepreg or an ABF film. It is to use a good liquid photocurable resin. In addition, since the circuit pattern 20 is formed on the substrate 10 and has a step, there may be an advantage in that the step difference can be easily filled by a liquid solder resist.

Thereafter, a first exposure process (FIG. 2C) may be performed on the first solder resist layer 31 through the first mask 60.

At this time, the region to be removed in the subsequent development process is left as an uncured solder resist layer (Figs. 2C and 31) by blocking light so that UV is not irradiated using the non-transmissive region 61 of the first mask 60. After the development process proceeds, the areas (Figs. 2c, 41, and 46) that are not removed and remain to play the role of the protective film of the printed circuit pattern are cured by irradiation with UV through the transmissive area 62 of the first mask 60. You can do it. The solder resist layer (FIGS. 2C, 41, and 46) cured through the first exposure process is not removed in a subsequent development process, but remains on the printed circuit board to serve as a protective layer for the printed circuit pattern. Such a first exposure process may be performed by UV-DI (UV-Direct Imaging) method without using a first mask, and a specific area is cured by irradiating UV directly to a desired area of the solder resist layer without using a mask. You can also proceed with the method.

After performing the first exposure process, a second solder resist layer 32 may be formed on the first solder resist layer 31 by using a solid photocurable resin film (FIG. 2D). In this case, it is preferable to use a solder resist film lamination method or the like due to the characteristics of the solid photocurable resin film, but is not limited thereto.

At this time, the reason for using a solid photocurable resin film is that in the case of a substrate on which the liquid first solder resist layer is formed, the step difference of the circuit pattern layer is flattened by the first solder resist layer formed by the liquid photocurable resin. This is because the use of a solid photocurable resin film in the form of a film may have an advantageous aspect in the manufacturing process.

Thereafter, a second exposure process (FIG. 2E) may be performed on the second solder resist layer 32 through the second mask 65. At this time, the area in which the dam (dam, FIGS. 2J, 40) of the package on package (PoP) top ball area is formed may be cured through the transmission area (FIGS. 2E and 67) of the second mask, and a subsequent phenomenon The area to be removed in the process is an uncured solder resist layer (Fig. 2e, 32) by blocking light so that UV is not irradiated using the non-transmissive area (Fig. 2e, 66) of the second mask (Fig. 2e, 65) Can be left with.

The solder resist layer (FIGS. 2E, 42) cured through the secondary exposure process is not removed in the subsequent development process, but remains on the printed circuit board, and thus dam (dam, FIG. 2J) in the package on package (PoP) top ball area. , 40) can be. This secondary exposure process can also be performed by UV-DI (UV-Direct Imaging) method without using a second mask, but by irradiating UV directly onto a desired area of the solder resist layer without using a mask to cure a specific area. You can also proceed with the method.

Thereafter, the formation of the third solder resist layer and the exposure process can be repeated in the same manner as the formation of the second solder resist layer and the exposure process, and if necessary, the formation and exposure of a further solder resist layer are repeated. can do.

After forming all the solder resist layers and exposing them to light, the uncured solder resist can be removed through a developing process. The printed circuit board (Fig. 2j), which has been developed, is a package on package (PoP) having a relatively high solder resist layer. ) It may have a dam (Figs. 2J, 40) in the top ball area. The developing process may be performed by spraying an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous sodium hydroxide solution, or an aqueous potassium hydroxide solution, but is not limited to the above aqueous solution, and may be performed in various ways other than the application method. .

If necessary, a post-cure process can be performed on the printed circuit board on which the development process has been completed. The post-cure process is a photocuring process using energy of 1,000 to 3,000 mJ/cm ² and at a temperature of 150 to 180°C. It may be made of a thermal curing process that proceeds for about 1 to 3 hours.

Comparative example (Existing method)

After preparing the copper clad laminate, a 23 µm solder resist layer was coated three times to form a total 69 µm solder resist layer, and then developed after one exposure process. Thereafter, the depth of the wall of the solder resist eroded by undercut (Fig. 1A, A) is measured through the VSEM photograph.

Example

After preparing the copper clad laminate, the exposure process is performed after coating a 23㎛ solder resist layer. The above process is repeated two more times to form a total 69㎛ solder resist layer, and then the development process is performed with 1% sodium carbonate aqueous solution for 60 seconds. Proceed. Thereafter, the depth of the wall of the solder resist eroded by undercut (Fig. 1A, A) is measured through the VSEM photograph.

Comparative example Example Undercut (A) 22.16 μm 5.71 μm

As shown in Table 1 above, in the case of the solder resist layer according to the embodiment of the present invention, it can be seen that the amount of erosion on the wall of the solder resist due to undercut is significantly reduced compared to the case of the solder resist layer according to the conventional method.

10: substrate
20: circuit pattern layer
31: first solder resist layer
32: second solder resist layer
33: third solder resist layer
34: fourth solder resist layer
40: Solder resist dam in PoP top ball area
41: first cured solder resist layer
42: second cured solder resist layer
43: third cured solder resist layer
44: fourth hardened solder resist layer
46: Cured solder resist layer in a flip chip region
50: solder resist opening
60: first mask
61: first mask opaque area
62: first mask transmission region
65: second mask
66: second mask opaque area
67: second mask transmission area
70: PoP (Package on Package) top ball area
80: flip chip area
100: printed circuit board

Claims (9)

Forming a plurality of circuit patterns on a substrate;
Forming a first solder resist layer using a photocurable resin on the substrate on which the plurality of circuit patterns are formed;
Exposing the first solder resist layer to light through a first mask to form a cured region and an uncured region;
Forming a second solder resist layer on the first solder resist layer by using a photocurable resin;
Curing the dam formation by exposing the second solder resist layer to light through a second mask;
Increasing the height of the dam forming portion by repeating the step of forming the second solder resist layer and curing the dam forming portion at least once; And
Including; developing the substrate in which the formation of the solder resist layer and exposure are repeated to remove the uncured solder resist layer,
The solder resist layer has a step difference in regions other than the dam formation portion and the dam formation portion,
A first opening is formed in the dam forming part to continuously penetrate the first solder resist layer and the second solder resist layer to expose each of some of the plurality of circuit patterns,
A method of manufacturing a printed circuit board, in which a second opening is formed in a region other than the dam forming part, penetrating the first solder resist layer to expose each of some other circuit patterns among the plurality of circuit patterns. The method of claim 1,
A method of manufacturing a printed circuit board, wherein the dam forming part is formed in a package on package (PoP) top ball area. The method of claim 1,
A method of manufacturing a printed circuit board, wherein the solder resist layers other than the first solder resist layer and the first solder resist layer are formed using photocurable resins of different materials. The method of claim 1,
The first solder resist layer is a method of manufacturing a printed circuit board formed using a liquid photocurable resin. The method of claim 1,
A method of manufacturing a printed circuit board, wherein the remaining solder resist layers except for the first solder resist layer are formed using a solid photocurable resin film. The method of claim 1,
Before the step of forming the first solder resist layer, the method of manufacturing a printed circuit board further comprising: performing solder resist pre-treatment on the substrate having the circuit pattern. The method of claim 1,
The step of forming the cured region and the uncured region by exposure is performed by UV Direct Imaging (UV-DI) instead of the first mask. The method of claim 1,
A method of manufacturing a printed circuit board in which the step of curing the dam formation by exposing is performed by UV Direct Imaging (UV-DI) instead of the second mask. The method of claim 1,
A method of manufacturing a printed circuit board in which a post-curing process is performed on the printed circuit board after the step of developing the board.

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