JP2004276384A - Screen printing plate and its manufacturing method - Google Patents

Abstract

Provided is a screen printing plate suitable for manufacturing a highly reliable multilayer wiring board which is highly reliable and can be made compact and the like, and a method for manufacturing the same.
A screen printing plate (10) has an elastic layer (11) forming a squeegee surface, and metal layers (12a, 12b, 12c, 12d) laminated on one surface side of the elastic layer (11), coaxial in the thickness direction of the laminate. And a paste filling hole 13 that penetrates through the screen, wherein the paste filling hole 13 has a large diameter on the squeegee surface side of the elastic layer 11 and a small diameter on the printing surface side, and the hole wall 13C has a stepped shape Is formed.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a screen printing plate suitable for manufacturing a highly reliable high-density wiring type wiring board and the like, and a manufacturing method thereof.
[0002]
[Prior art]
As electronic devices such as mobile phones and personal computers become shorter, lighter, and thinner, wiring boards that form electrical circuits are not only required to have higher density wiring and shorter, lighter and thinner, but also to improve circuit reliability and reduce Cost reduction is required. In response to such a demand, a via connection structure in which wiring patterns are arranged in a multilayered manner via an insulating layer, and the wiring patterns are connected by projecting conductive bumps penetrating the interlayer insulating layer. Multilayer wiring boards are known (see Patent Literatures 1 and 2).
[0003]
To manufacture this type of multilayer wiring board, a copper foil having a thickness of, for example, about 12 μm is prepared, and a conductive composition (for example, a silver paste) is screen-printed on one principal surface of the copper foil to obtain a bottom surface diameter. A substantially conical (projection-shaped) conductive bump having a height of about 50 to 100 μm and a height of about 50 to 150 μm is formed. Here, the conductive bumps are aligned with the bumps that have been initially printed and supported when the bumps are dried, and are screen-printed with silver paste again to build up to the required height.
[0004]
A screen printing plate having a through hole for filling and transferring a conductive paste corresponding to a predetermined pattern by screen printing of the conductive bump is used. Usually, for example, a screen printing plate is formed of a stainless steel plate having a thickness of about 0.2 mm and a hole having the same diameter of about 0.1 to 0.3 μm penetrating in a thickness direction thereof. In the means using this screen printing plate, it is difficult to ensure the flatness of the inner wall surface by drilling the through hole, so even if the conductive paste is press-fitted into the through hole from the squeegee surface, it is dense and good. It often occurs that it is difficult to form the required conductive bump with reproducibility. In particular, it is extremely difficult to form a conductive bump having a fine diameter and a high height (having a large aspect ratio), and there is a possibility that the density of wiring and the reliability of connection may be impaired.
[0005]
In order to solve such an inconvenience, screen printing plates have been proposed in which the essential parts are enlarged and shown in cross section in FIGS. 5 and 6 (see Patent Documents 3 and 4). FIG. 5 shows the squeegee surface as the metal layer 1, the printing surface as the plastic layer 2, and the diameter of the through hole 3 for press-fitting and transferring the conductive paste is enlarged (tapered) toward the printing surface. It is. In FIG. 6, the metal layer 1 is used for the printing surface side, the plastic layer 2 is used for the squeegee surface, and the diameter of the through-hole 3 for press-fitting and transferring the conductive paste is set to be the same over the entire area.
[0006]
In the case of the screen printing plate having the configuration shown in FIG. 5, since it can be in close contact with the surface to be printed, occurrence of displacement can be prevented, and the screen can be formed without damaging the shape of the filled conductive bumps. The printing plate can be removed. On the other hand, in the case of the screen printing plate having the configuration shown in FIG. 6, only the printing surface side is the auxiliary layer 1, so that the inner wall surface of the hole formed in the metal layer 1 is kept flat and smooth. In the process of removing the screen printing plate or the like, it becomes easy to control the outer shape of the conductive bump.
[0007]
[Patent Document 1]
JP-A-10-79579 (page 4, FIG. 1)
[0008]
[Patent Document 2]
JP-A-11-112149 (page 2, FIG. 1)
[0009]
[Patent Document 3]
Japanese Patent Application Laid-Open No. 11-138738 (page 4, FIG. 1)
[0010]
[Patent Document 4]
JP-A-2001-347628 (page 4, FIG. 1)
[0011]
[Problems to be solved by the invention]
In the production of a multilayer wiring board including means for printing and carrying conductive bumps for via connection using the screen printing plate, the interlayer connection between wiring patterns and the like must be inserted by pressurizing the conductive bumps. Therefore, there is an advantage that high-density wiring and simplification of a manufacturing process can be achieved. In other words, in connection between wiring pattern layers, drilling by drilling or the like for each interlayer insulator layer can be omitted, and plating processing in the drilling or filling operation of the conductive composition is not only unnecessary, but also fine. A highly reliable via connection can be achieved.
[0012]
However, there are concerns about the following problems in terms of mass productivity and reliability. In particular, in a structure forming a via connection with a fine (small) diameter of about 50 μm desired for high-density wiring, it is necessary to densely and uniformly fill the conductive composition in the through hole 3 having a small diameter. Problems, such as difficulties in the operation. That is, in the conventional conductive bump print forming means using a screen printing plate, for example, drying and printing are performed when forming a conductive bump having a maximum diameter (bottom diameter) of about 150 μm and a height of about 130 to 160 μm. Must be repeated multiple times.
[0013]
In the repetition process of the screen printing and the drying process, positioning and arrangement of the screen printing plate and press-fitting of the conductive paste through the screen printing plate are performed each time. However, the printing plate illustrated in FIG. 5 has a squeegee surface 1 of a metal layer and a plastic layer 2 on the printing side. Since the side diameter 3a is small, there are many cases where the press-fitting is limited and a dense and uniform filling of the paste cannot be achieved. Further, since the diameter 3b of the through-hole 3 on the printing surface side is enlarged, it is difficult to deaerate even if the conductive paste is press-fitted. As a result, the conductive bump containing bubbles is formed by printing. There is fear. In the case of the printing plate shown in FIG. 6, only the printing surface side is made of the metal layer 1 and the inner wall surface 3c of the through hole 3 is smoothed. Although the possibility of damaging the outer peripheral surface is eliminated, the problem that air bubbles easily remain in the through-holes still remains because the press-in diameter 3a is as small as the printing-surface-side diameter 3b.
[0014]
As described above, in the case of the conventionally used screen printing plate, it is difficult to form a fine and uniform shaped fine-diameter conductive bump by printing in any case. This may adversely affect the reliability or quality of the product, resulting in a decrease in the yield of the final product and an increase in cost. In other words, the formation of the conductive bumps in the insufficiently defoamed state, or the formation of the conductive bumps containing bubbles leads to a decrease in the function and reliability of the via connection portion, and thus a final product is not manufactured. There is concern that reliability will decrease. In particular, when the final product is used in an environment with a temperature change, the connection may be peeled off due to expansion of residual bubbles in the conductive bump area that constitutes the via connection. This raises a problem.
[0015]
The present invention has been made in view of the above circumstances, and has as its object to provide a screen printing plate suitable for manufacturing a highly reliable multilayer wiring board which is highly reliable and can be made compact, and a method for manufacturing the same. And
[0016]
[Means for Solving the Problems]
The screen printing plate according to the present invention includes an elastic layer forming a squeegee surface of a paste to be printed, and a metal layer joined to a surface of the elastic layer facing the squeegee surface to form a laminate with the elastic body. A screen printing plate having a paste filling hole penetrating the laminate in the thickness direction thereof,
The paste filling hole has a large diameter on the squeegee surface side and a small diameter on the printing surface side, and the hole wall of the paste filling hole has a stepped cross section in the thickness direction.
[0017]
Further, the manufacturing method of the present invention is characterized in that a first metal layer having an opening with a fine diameter in the thickness direction and at least one layer having an opening with a large diameter with respect to the opening of the first metal layer. A step of laminating the second metal layer through an adhesive film while aligning the openings with each other, and increasing the diameter of the second metal layer with respect to the opening of the second metal layer through the adhesive film on the top surface of the laminate A step of coaxially positioning and laminating an elastic body layer in which the opening is formed and coaxially positioning the opening with respect to the opening of the second metal layer;
Forming a through-hole having a stepped hole wall by removing the adhesive film remaining over the openings.
[0018]
That is, the screen printing plate of the present invention eliminates the dependence of the hole wall shape of the printed bump by positively leaving the conductive ink paste on the hole wall at the time of printing, and smoothly performs the spiral press-fitting that occurs at the time of filling the paste. It can be carried out. The paste remaining on the hole wall by press-fitting plays a role of lubrication for the subsequent paste to be further press-fitted, and ensures smooth press-fitting. When the screen is removed after printing, an appropriate amount of paste is transferred to the printing surface and becomes a bump due to the viscoelasticity of the paste in the hole, so that the shape of the stepped hole wall does not hinder the bump shape.
[0019]
The paste filling hole in the stepped hole wall can be easily obtained by laminating an elastic body having openings having different diameters and a plurality of metal layers with the openings aligned. By arranging the elastic layer on the squeegee surface side and arranging the metal layer having the smallest diameter opening on the printing surface side, a conical filling hole can be obtained. The cross-sectional shape and diameter of the printed bump are substantially determined by this minimum diameter opening.
[0020]
The hole diameter difference at each step of the step-like hole wall of the paste filling hole according to the present invention depends on the diameter and aspect ratio of the conductive bumps to be printed, but is generally about 10 to 50 μm, preferably about 20 μm. ４０40 μm. Drilling of each opening in the thickness direction is performed by, for example, laser beam processing, etching processing, or the like.
[0021]
In addition, if the stepped hole wall is preliminarily subjected to a water-repellent treatment using, for example, a fluorine-based resin, the conductive bump can be easily removed after printing. Furthermore, each metal layer may be a thin plate of, for example, stainless steel or nickel, and its thickness is preferably selected in consideration of, but not limited to, the aspect ratio of a conductive bump to be printed, Generally, it is 40 to 60 μm. The thickness of the plurality of metal layers may be constant throughout, but it does not matter if the thickness of the metal layer on the elastic body side is set to be thicker than the metal layer on the printing surface side.
[0022]
As described above, the elasticity of the elastic layer due to the squeezing operation, and the effective press-in filling by enlarging the diameter of the conductive paste press-in side, the ease of defoaming to the press-in side, and the printing plate By removing the conductive bumps by the openings having the minimum diameter during the removing process, it is possible to easily form high-quality conductive bumps that are dense and have a fixed shape.
[0023]
Further, the manufacturing method according to the present invention can provide a highly practical screen printing plate capable of printing and forming high-quality conductive bumps with good reproducibility as described above with high yield.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. The screen printing plate according to the present invention has a structure as shown in FIG. That is, the screen printing plate according to the present invention includes the elastic layer 11 forming the squeegee surface and the metal layer 12 bonded to the back surface of the elastic layer 11 facing the squeegee surface. This is a printing plate in which a paste filling hole 13 penetrating coaxially in the thickness direction is formed.
[0025]
The paste filling hole 13 is a conical hole having a maximum diameter of the opening 13A on the squeegee surface side and a minimum diameter of the opening 13B on the printing surface, and has a wall surface extending from the squeegee surface side opening 13A to the printing surface side opening 13B. Has a stepped wall 13C which is reduced in diameter stepwise.
[0026]
The metal layer 12 has a laminated structure of a plurality of metal layers. Each of the metal layers 12a, 12b, 12c, and 12d has an opening 13a (13B), 13b, 13c, and 13d having a different opening diameter. A metal layer 12a having an opening 13a having an opening diameter is disposed, and metal layers 12b, 12c, and 12d having a larger opening diameter are sequentially disposed on the elastic body layer 11 side so that the openings are coaxial, thereby forming a laminated structure. Thus, the opening of the elastic layer 11 forming the squeegee surface has a maximum diameter, and the laminated body 10 of the elastic layer 11 and the metal layer 12 has the stepped wall surface, the large diameter side is set to the squeegee surface side, and the small diameter side is set. Is provided on the printing surface side to form a screen printing plate having a paste filling hole.
[0027]
Here, the elastic layer 11 is, for example, a silicone rubber layer having a thickness of about 200 μm, the metal layer 12 is a stainless steel thin plate, the metal layer 12a is about 50 μm in thickness, the metal layer 12b is about 50 μm in thickness, and the metal layer 12c is The thickness is about 50 μm. The elastic layer 11 and the metal layers 12a, 12b, 12c, and 12d form a laminated body joined and integrated with an epoxy resin-based adhesive (not shown).
[0028]
The opening diameter 13A of the elastic layer 4 is 150 μm, the diameter of the opening 12d of the metal layer 12d is 110 μm, the diameter of the opening 12c of the metal layer 12c is 90 μm, the opening 12b of the metal layer 12b is 70 μm, and the opening 13a of the metal layer 12a. The diameter 13B is 50 μm, and is set so that a conductive bump having a maximum diameter of 50 μm and a height of 145 ± 15 μm can be formed by performing screen printing four times. In the configuration of the screen printing plate, a thin elastic layer having a through-hole having the same opening diameter as the opening diameter 13B of the metal layer 12a is laminated and integrated on the printing surface side of the lower surface of the metal layer 12a, and covered. A structure that improves the adhesion to the printing surface may be used.
[0029]
Further, by forming the water-repellent coating on the stepped wall surface, it is possible to smoothly remove the paste remaining in the holes by printing.
[0030]
Further, the printing plate manufacturing method according to the present invention is performed by means schematically showing a part of the embodiment in FIG. That is, an opening 13a (13B) having an opening diameter of 50 μm in the thickness direction is formed by laser beam processing, and an opening 13b having an opening diameter of 70 μm is coaxially formed with the opening 13a of the first metal layer 12a. The second metal layer 12b formed by laser beam processing, the third metal layer 12c formed by laser beam processing with an opening 13c having a diameter of 90 μm coaxially with the opening 13b of the second metal layer 12b, The fourth metal layer 12d in which an opening 13d having a diameter of 110 μm is formed by laser beam processing coaxially with the opening 13c of the third metal layer 12c, and coaxially with the opening 13d of the fourth metal layer 12d. A silicone rubber thin plate 11 having an opening 13A having a diameter of 150 μm formed by laser beam processing is prepared.
[0031]
Then, the metal layers 12a, 12b, 12c, 12d and the silicone rubber thin plate 11 are sequentially positioned and laminated via an epoxy resin adhesive film 14, as shown in FIG. Next, the laminate is heated and pressed, and the respective layers 11, 12a, 12b, 12c, and 12d are joined and integrated by the joining action of the adhesive film 14. Thereafter, the adhesive film 14 interposed between the joined and integrated layers and remaining in the through hole 13 is removed to make it penetrate. Here, the removal of the adhesive film 14 is performed by, for example, incineration by laser beam irradiation. The obtained paste filling hole 13 forms a concentric stepped wall 13C as shown in FIG.
[0032]
The shape of the paste filling hole does not necessarily have to be a conical shape, and can be deformed according to the ease of squeegee or the shape of the bump formed on the printing surface. FIG. 4B shows a structure in which the opening on the squeegee surface side and the stepped wall are made elliptical, the small-diameter opening 13B on the printing surface side is made circular, and the opening shapes on the squeegee surface side and the printing surface side are changed. FIG. 4C shows an example in which the opening 13A on the side surface of the squeegee, the opening 13B on the printing surface side, and the stepped wall 13C are rectangular. The size of an ellipse or a square can be converted to the diameter of a circle by area conversion.
[0033]
Next, an example of using the screen printing plate having the above configuration will be described with reference to FIG. First, as shown in (a), an electric field copper foil 15 having a thickness of about 12 μm is prepared, and a screen printing plate 10 is positioned and arranged with one principal surface side of the copper foil as a printing surface 15a. A conductive paste (for example, silver paste) 16 is placed on the plate to have a substantially uniform thickness, and squeegee 17 is used for squeezing. That is, the silver paste 16 is press-fitted into the through-hole 13 of the screen printing plate, and the copper foil surface 15a is formed by printing a protruding (substantially conical) conductive bump. In the printing plate of this embodiment, since the opening of the paste filling hole is larger in diameter than the printing surface side, a conductive paste having a high viscosity can be easily pressed into the filling hole.
[0034]
The conductive paste 16 is pushed by the squeegee 17 toward the lower printing surface while rotating in a spiral as shown by an arrow in FIG. The fluid velocity of the paste near the stepped wall 13C decreases, and when the printing plate is removed due to a difference in viscous flow from the paste at the center of the hole, a part of the printing plate is pulled out from the printing surface side opening, but close to the wall. The side paste remains. The bump 15a formed by the first printing has a spindle-shaped raised shape as shown in FIG.
[0035]
Thereafter, the screen printing plate was removed and subjected to a drying treatment at 100 ° C. for about 3 minutes. Then, the screen printing plate was positioned and arranged on the conductive bump printing surface again, and the paste 16 was screen-printed and temporarily dried. The conductive bump 18b is printed on the bump 18a. That is, the second squeegee is performed at a stage where the conductive paste is not dried in the holes, and the paste 18 is pressed through the same paste as in the first squeegee, as shown in FIG. The additional paste 18b is overlaid on top of the above. Further, by the third squeegee, the paste 18c is overlapped and the height of the bump is further extended as shown in FIG.
[0036]
The operation of temporary drying and screen printing of each printed bump is repeated four times, and then the main drying is performed at 180 ° C. for 30 minutes to maintain a constant shaping of a maximum diameter of 50 μm and a height of 145 ± 15 μm. : 3 conductive bumps were formed.
[0037]
Next, on the conductive bump forming surface 15a side of the copper foil 15, a thermoplastic insulator (for example, a liquid crystal polymer) is laminated and arranged as an interlayer insulator, and further, a laminate is formed by laminating an electrolytic copper foil on the interlayer insulator surface. Pressure is applied in the stacking direction to integrate. That is, the tip of the conductive bump penetrates the interlayer insulator and crushes and opposes the opposing copper foil surface to form a double-sided copper foil-clad board in which both copper foils are electrically connected. Both copper foils of this double-sided copper foil-clad board were subjected to photoetching treatment to form a wiring pattern, and a double-sided wiring board connected between layers was prepared. This double-sided wiring board had a reliable interlayer connection and functioned as a highly reliable wiring board.
[0038]
The present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention. For example, the number of metal layers, the thickness of each metal layer, the material of the metal, the difference in the opening diameter of each layer, etc. are determined by the material of the conductive paste to be printed or the aspect ratio of the conductive bump to be printed (width to height). Ratio) and the like can be selected as appropriate.
[0039]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the elasticity of the elastic body layer accompanying a squeezing operation, and the effective press-fitting accompanying the enlargement of the conductive paste press-in side diameter, and the ease of defoaming to the printing surface side opening. Further, the conductive bump is shaped by the opening having the smallest diameter in the process of removing the printing plate, so that a dense bump having an aspect ratio exceeding 1: 1 can be formed. A high quality conductive bump exhibiting the following can be easily formed. In other words, while achieving a reduction in length and size, it greatly contributes to mass productivity and improvement in yield of a high-density wiring or a highly functional and highly reliable mounting multilayer wiring board.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view illustrating a main configuration of a screen printing plate according to an embodiment.
FIG. 2 is an enlarged cross-sectional view showing one embodiment of a manufacturing process of the screen printing plate according to the embodiment.
FIGS. 3A, 3B, 3C, and 3D are schematic diagrams illustrating the operation of the embodiment.
4A is a plan view of a paste filling hole of the embodiment shown in FIG. 1, and FIGS. 4B and 4C are plan views of modifications of the paste filling hole.
FIG. 5 is an enlarged cross-sectional view showing a configuration of a main part of a conventional screen printing plate.
FIG. 6 is an enlarged cross-sectional view showing a main part configuration of a different conventional screen printing plate.
[Explanation of symbols]
10: Laminate (screen printing plate)
11: Elastic layer 12: Metal layer 12a, 12b, 12c, 12d: Metal layer 13: Paste filling hole 13a, 13b, 13c, 13d: Opening 13A of each metal layer: Opening 13B on squeegee surface side: Printing surface side Opening 13C: Stepped wall 14: Adhesive film 16: Paste

Claims (6)

An elastic layer forming a squeegee surface of the paste to be printed, and a metal layer forming a laminate with the elastic body joined to a surface side of the elastic layer facing the squeegee surface. A screen printing plate provided with a paste filling hole penetrating in its thickness direction,
A screen printing plate, wherein the paste filling hole has a large diameter on the squeegee surface side and a small diameter on the printing surface side, and a hole wall of the paste filling hole has a stepwise cross section in a thickness direction. The metal layer is a laminate of a plurality of metal layers having openings having different opening diameters, and forms a paste filling hole in which the opening diameter is reduced coaxially and sequentially from the squeegee surface side to the printing side surface. The screen printing plate according to claim 1. 2. The screen printing plate according to claim 1, wherein a difference in hole diameter between the step portions of the hole wall is 20 to 40 [mu] m. 2. The screen printing plate according to claim 1, wherein the wall surfaces of the holes are water-repellent. 3. The screen printing plate according to claim 2, wherein the thickness of each metal layer is 40 to 60 [mu] m. A first metal layer having an opening with a fine diameter in the thickness direction, and at least one second metal layer having an opening with a large diameter with respect to the opening of the first metal layer, Aligning and laminating via an adhesive film,
An elastic layer having an opening with a diameter larger than the opening of the second metal layer is formed on the uppermost surface of the laminate through an adhesive film, and the opening is formed with respect to the opening of the second metal layer. A step of coaxially positioning and laminating and joining and integrating each layer;
Forming a through-hole having a stepped hole wall by removing the adhesive film remaining over each of said openings.

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