TWI487451B - Manufacturing method of multilayer printed wiring board - Google Patents

Description

Multilayer printed wiring board manufacturing method

The present invention relates to a method of manufacturing a multilayer printed wiring board, and more particularly to a method of manufacturing a build-up type multilayer printed wiring board.

In recent years, miniaturization and high functionality of electronic devices have been progressing, as represented by portable information terminals such as mobile phones. Therefore, there is an increasing demand for higher density of printed wiring boards used in electronic equipment.

Therefore, in order to mount an electronic component or the like at a high density on a printed wiring board, a laminated multilayer flexible printed wiring board has been researched and developed (see, for example, Patent Document 1). In the laminated multi-layer flexible printed wiring board, a double-sided flexible printed wiring board or a multilayer flexible printed wiring board is used as a core substrate, and one or two layers are formed on both sides or one side of the core substrate. Build-up layer. In the laminated multi-layer flexible printed wiring board, in order to electrically connect the build-up layer to the inner core substrate, a plating process is provided on the inner wall of the bottomed through hole (conductive hole) to obtain an interlayer. Conducted plated through holes.

However, as the bottomed through hole becomes deep, the following problems occur. First, since the constituent members of the printed wiring board thermally expand, the plated through holes are easily broken. Further, in order to obtain interlayer conduction, when a plating film is formed on the inner wall of the bottomed through hole, the plating solution easily stays at the bottom of the through hole, so that a desired plating thickness cannot be obtained. For the reason shown above, the deeper the bottomed through hole, the more difficult it is to ensure the electrical reliability of the through hole wiring.

In view of the countermeasure against this problem, it is considered that a sufficiently thick plating film is formed on the inner wall of the bottomed through hole. However, if the thickness of the plating film formed on the inner wall of the bottomed through hole is increased, it is unavoidable that the thickness of the conductor layer formed on the buildup layer is also increased. The circuit pattern of the outer layer is formed by wet etching the conductor layer on the buildup layer in a desired pattern. Therefore, as the thickness of the conductor layer increases, it becomes less likely that the conductor layer on the buildup layer is finely processed. As a result, in the circuit pattern of the outer layer, a fine pattern cannot be formed, and it becomes difficult to mount the electronic component at a high density on the build-up layer.

As described above, in the conventional laminated type multilayer flexible printed wiring board, there is a problem that it is difficult to meet the high-density mounting requirements.

However, among the laminated multi-layer flexible printed wiring boards, from the viewpoint of high density and improvement in design freedom, in particular, a laminated type multilayer having a so-called stacked via via structure can be obtained. Flexible printed wiring board. Here, the stacked via structure refers to a structure in which an interlayer connection portion formed by a plated through hole of a build-up layer is superposed on an interlayer connection portion formed by a plated through hole of a core substrate.

A method of inexpensively and stably manufacturing a multilayer printed wiring board having a stacked via structure capable of high density mounting is strongly desired.

In the past, a method has been disclosed in which a through-hole (step via) of a so-called stepped via structure is formed by laser processing (see Patent Document 2, Patent Document 3, and Patent Document 4). The stepped via structure can be efficiently formed by the techniques disclosed in these documents. However, in this method, electrolytic copper plating for coating the inner wall of the stepped through hole by the plating film is usually performed once. Therefore, there is a tendency that the plating film formed on the side wall of the hole (small diameter side) below the stepped through hole tends to be thin. Therefore, there is a case where it is difficult to sufficiently ensure the reliability of the interlayer connection.

Next, a method of manufacturing a laminated type multilayer printed wiring board having a stacked via structure by a conventional technique will be described in detail using FIG. Fig. 3 is an engineering sectional view for explaining a method of manufacturing a laminated type multilayer printed wiring board having a stacked via structure.

First, a flexible insulating base material 101 (for example, 25 μm thick) such as polyimide or a double-sided copper clad laminate 104 having copper foil 102 and copper foil 103 (both of which are, for example, 8 μm thick) is prepared. .

Next, as is clear from Fig. 3 (1), the double-sided copper-clad laminate 104 is formed with a bottomed through-hole 105 belonging to the bottomed through hole by a laser processing method. The copper foil 103 is exposed at the bottom of the bottomed through hole 105. Thereafter, electrolytic plating is performed on the copper foils 102 and 103 and the inner wall of the bottomed through hole 105 by performing electroconductive treatment on the copper foils 102 and 103 and the bottomed via 105 and subsequent electrolytic plating treatment. Membrane. The thickness of the electrolytic plating film is formed to a desired value (for example, about 15 μm) for ensuring the connection reliability of the via wiring. Through the above-described work, a plated bottomed through hole 106 belonging to the bottomed type interlayer conduction portion that electrically connects the copper foil 102 of the flexible insulating base material 101 and the copper foil 103 is formed.

Next, as is clear from Fig. 3 (1), the copper foil 102 and the copper foil 103 of the flexible insulating base material 101 are etched in a predetermined pattern by photofabrication to form a circuit pattern ( Inner layer circuit pattern). More specifically, a circuit pattern is formed on both sides of the flexible insulating base material 101 by a series of processes consisting of formation of a resist layer, exposure, development, etching of a copper foil, and peeling of a resist layer. .

Next, as is clear from Fig. 3 (1), a cover film 109 having an adhesive layer 108 on an insulating film 107 (e.g., 12 μm thick) such as a polyimide film is prepared. The subsequent agent layer 108 is composed of an adhesive such as acrylic or epoxy. Next, a lamination process of adhering the cover film 109 to the flexible insulating base material 101 on which the circuit pattern is formed is performed using a vacuum laminator or the like. The thickness of the adhesive layer 108 is formed so that the thickness (for example, 25 μm) of the inside of the plated bottomed through hole 106 can be completely filled with an adhesive. The double-sided core substrate 110 shown in Fig. 3 (1) is obtained through the above-described processes.

Next, as is clear from Fig. 3 (2), a single-sided copper clad laminate 111 having a copper foil (for example, a thickness of 12 μm) on one surface of a flexible insulating base material (for example, a polyimide having a thickness of 25 μm) is prepared. An opening is formed in a predetermined portion of the copper foil of the single-sided copper clad laminate 111 by the above-described photolithography etching method. The copper foil having the opening is formed into a conformal mask (also referred to as a metal mask) for laser shading. The opening formed in the copper foil is used to form a through hole by removing a resin such as a flexible insulating base material exposed on the bottom surface of the opening by laser processing.

Next, as is apparent from Fig. 3 (2), the single-sided copper clad laminates 111 and 111 having the common mask are passed through the adhesive layers 112 and 112 by using the bonding material for laminating the double-sided core substrate 110. The layers are respectively laminated on the front and back surfaces of the double-sided core substrate 110.

Next, as is clear from Fig. 3 (2), the laser processing is performed using the common mask of the single-sided copper clad laminate 111, thereby forming the stepped through holes 113A and the through holes 113B and 113C.

Next, as is clear from Fig. 3 (3), the copper foil on the single-sided copper-clad laminate 111, the inner wall of the stepped through-hole 113A, and the inner walls of the through-holes 113B and 113C are subjected to a conductive treatment and subsequent The electrolytic plating treatment is performed to form an electrolytic plating film. The thickness of the electrolytic plating film is, for example, about 25 to 30 μm to ensure the reliability of interlayer connection. Thereby, plated through holes 114A, 114B, and 114C for obtaining conduction between the core substrate and the layer of the buildup layer are formed. The plated through hole 114A is plated to the inner wall of the stepped through hole 113A, and the plated through hole 114B is plated to the inner wall of the through hole 113B opposed to the stepped through hole 113A. The clad layer through hole 114C is a plating treatment for the inner wall of the through hole 113C.

Next, as is clear from Fig. 3 (3), the outer layer circuit patterns 115 and 115 are formed by etching the copper foil of the single-sided copper clad laminates 111 and 111 in a predetermined pattern by a photosensitive etching method. Thereafter, a photoresist layer (not shown) is formed as necessary, and surface treatment such as solder plating, nickel plating, or gold plating is applied to the terminals of the circuit pattern, and the outer shape processing is performed by drilling a hole or the like using a mold.

Through the above works, a laminated type multilayer printed wiring board 116 having a stacked via structure is obtained. As can be seen from Fig. 3 (3), the plated through-holes 114A are formed directly above the plated bottomed vias 106 of the inner core double-sided core substrate 110, and the plated through-holes 106 and the plated layers are plated. Hole 114A forms a stacked via configuration. In the laminated type multilayer printed wiring board 116, the interlayer connection between the front surface and the back surface of the double-sided core substrate 110 is performed by plating the bottomed through holes 106.

In addition, as shown in FIG. 3 (3), the multilayer printed wiring board 116 has a component mounting portion 116a in which a build-up portion is laminated on the double-sided core substrate 110, and flexibility extending from the component mounting portion 116b. Wire portion 116b. The flexible wire portion 116b is not provided with a part of the double-sided core substrate 110 of the build-up layer.

Through the above works, the inside of the plated bottomed through hole 106 must be completely filled with the backing material. However, the plated bottomed through hole 106 is less likely to be filled with the adhesive than the plating through hole formed by performing the plating treatment on the inner wall of the through hole of the double-sided copper clad laminate 104. This is based on the fact that the plating through-via is filled in the two directions of the front and back surfaces. On the other hand, the bottom-plated through-holes can be filled only in one direction. Therefore, compared with the case where the interlayer connection of the double-sided core substrate 110 is performed by plating through the through holes, the case where the thickness of the subsequent material layer 108 becomes thick is unavoidable. Therefore, the laminated via 113 becomes deep. As a result, as described above, the plating thickness for ensuring the reliability of the interlayer connection becomes large. For example, when the plating via holes 114A, 114B, and 114C are formed as described above, electrolytic plating for forming a plating film of about 25 to 30 μm must be performed. It is assumed that the thickness of the conductor layer (copper foil + electrolytic plating film) on the single-sided copper clad laminate 111 is performed on the copper foil (12 μm thick) of the single-sided copper clad laminate 111. The total is 37 to 42 μm. The patterning of the conductor layer is performed by wet etching, so that it is difficult to form a fine circuit pattern having a circuit pitch of about 100 μm.

As described above, in the related art, there has been a problem that a laminated type multilayer printed wiring board that satisfies high-density mounting requirements cannot be manufactured. Of course, this problem is the same even in the multilayer printed wiring board which does not have the flexible wire 116b.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2004-200260

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2008-235801

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2008-288434

[Patent Document 4] Japanese Laid-Open Patent Publication No. 2009-026912

The present invention is to solve the above problems in that a multilayer printed wiring board capable of high density mounting cannot be obtained because it is difficult to form a fine outer layer circuit pattern, and an object of the present invention is to provide a laminated type multilayer printed wiring having a stacked via structure capable of high density mounting. The manufacturing method of the board.

According to an aspect of the invention, there is provided a method of manufacturing a multilayer printed wiring board, characterized in that a double-sided conductive film laminated plate having a first conductive film and a second conductive film on each of a front surface and a back surface is formed The first conductive film and the second conductive film are electrically connected to the through hole and the plated through hole, and the first conductive film and the second conductive film are etched in a predetermined pattern. A double-sided flexible substrate having an inner layer circuit pattern, comprising: an insulating film; and a cover film formed on an adhesive layer on one surface of the insulating film, after being melted by the adhesive layer of the cover film a subsequent agent that completely fills the inside of the through hole, and allows the cover film to be adhered under the condition that the air void not filled by the adhesive is allowed to be generated inside the plated bottomed through hole. a double-sided core substrate is formed on the double-sided laminated substrate of the double-sided flexible substrate, and at least the side of the open surface of the double-sided core substrate on which the bottom via hole is plated is laminated Forming a third conductive film on one side; removing the above-mentioned adhesive inside the plated through-hole by laser processing to eliminate the air void, thereby exposing the plating bottom at the bottom a through hole forming a stepped through hole in which the plated through hole is a lower hole, and plating the inner wall of the third conductive film and the stepped through hole to form the third conductive film and the inner portion The layer circuit pattern is electrically connected to the plating via hole, and the third conductive film subjected to the plating treatment is etched in a predetermined pattern to form an outer layer circuit pattern.

With these features, the present invention achieves the effects as described below.

In a laminated type multilayer printed wiring board having a stacked via structure according to an embodiment of the present invention, the stacked via structure is a plated through-hole through which the surface and the back surface of the double-sided flexible substrate are electrically connected a hole; and a plated through hole disposed on the plated bottomed through hole. The plated through hole is formed by electrically connecting the outer layer circuit pattern and the inner layer circuit pattern, and forms an inner wall of the stepped through hole formed in the bottomed through hole formed in the double-sided flexible substrate as a small diameter hole. Those who have a plating film. Thereby, a stepped via structure composed of a plated bottomed through hole and a plated through hole formed thereon is formed.

According to the feature as described above, according to an embodiment of the present invention, it is not necessary to completely fill the backing material in the inside of the plated through-hole formed in the double-sided flexible substrate when the cover film is laminated. This is based on the fact that the adhesive in the plated bottomed via is removed when the stepped via is formed. Therefore, the thickness of the adhesive layer can be made as small as possible within a range in which the adhesive can be filled in the through-holes of the double-sided flexible substrate.

As a result, the stepped via holes can be made shallower than in the prior art. Thereby, when the electrolytic plating treatment is performed in order to form the plated through-hole, the electrodeposition easiness is improved, and the influence on the plated through-holes due to the thermal expansion of the constituent members is alleviated.

Therefore, with the present invention, the yield can be improved, and the plating thickness required for ensuring the connection reliability of the via wiring can be reduced as much as possible. Therefore, with the present invention, the outer layer circuit pattern formed in the buildup layer can be made finer.

Further, according to the present invention, when the plating via hole is formed, an electrolytic plating film is formed on the plated bottom via hole of the double-sided flexible substrate. Thereby, due to the asymmetrical shape, the plated through-holes which are more easily concentrated in thermal stress than the through-holes are reinforced, and the connection reliability can be improved.

Further, since the plated through-holes are reinforced as described above, the plating of the plated bottom vias can be made thick to the extent that the connection reliability of the plating through-vias can be ensured. As a result, the time required for the plating process can be shortened, and the cost can be reduced. Further, the inner layer circuit pattern formed on the double-sided flexible substrate can be made fine.

As described above, according to the present invention, there is provided a method of inexpensively and stably manufacturing a laminated type multilayer printed wiring board having a stacked via structure capable of high density mounting.

Hereinafter, a method of manufacturing a laminated type multilayer printed wiring board having a stacked via structure according to an embodiment of the present invention will be described with reference to the drawings.

Here, constituent elements having the same functions are denoted by the same reference numerals, and detailed description thereof will be omitted. In addition, the mode is shown as a model, and the display is centered on the characteristic portion of the embodiment, and the relationship between the thickness and the plane size, the thickness ratio of each layer, and the like are different from those of the actual person.

First, a method of manufacturing the laminated type multilayer printed wiring board 32 having a stacked via structure according to an embodiment of the present invention will be described with reference to FIGS. 1A to 1C and 2 .

1A to 1C are structural cross-sectional views for explaining a method of manufacturing the laminated type multilayer printed wiring board 32. Fig. 2 is a cross-sectional view showing a multilayer printed wiring board 32 of the present embodiment.

First, it is understood from the first FIG. 1 (1) that the copper foil 2 and the copper foil 3 (the first conductive film and the second) are provided on both sides of the flexible insulating base material 1 (for example, a polyimide having a thickness of 25 μm). A double-sided copper clad laminate 4 of a conductive film). The thickness of the copper foil 2 and the copper foil 3 is, for example, 5 μm.

Then, the double-sided copper clad laminate 4 is formed by a laser processing method, a resin etching method, or the like, and a through hole 5 penetrating through the double-sided copper clad laminate 4 and a bottomed through hole 6 are formed. As shown in Fig. 1A (1), the bottomed through hole 6 is a bottomed through hole in which the copper foil 3 is exposed on the bottom surface. The processing diameters of the through holes 5 and the bottomed through holes 6 are each, for example, 70 μm in diameter.

When using the laser processing method in this project, the following two methods can be selected. The first method is called a method of the co-type laser processing method. In this method, openings of the same diameter as the diameter of the through holes are provided in the copper foils 2, 3 to form a common type of mask. Thereafter, the common mask is irradiated with the laser light to remove the insulating resin exposed at the opening. The second method is called a method of direct laser processing. In this method, a common mask is not formed, and the copper foil is directly irradiated with laser light to remove the copper foil and the insulating resin therebelow. In the present embodiment, it is not necessary to perform a co-type laser processing method for etching a copper foil by a photolithography process, but a direct laser by a carbon dioxide laser is selected in consideration of productivity. Processing method.

Before the direct laser processing method is performed, the copper foils 2, 3 of the double-sided copper clad laminate 4 are subjected to surface treatment. That is, the copper foil surface on which the laser light is irradiated is formed into a roughening treatment of a low thickness. Thereby, when laser processing is performed using a carbon dioxide laser (wavelength: about 9.8 μm), the absorption of the laser light of the copper foils 2, 3 can be stably improved. In the present embodiment, Multi-bond 150 of Japan MacDermid Co., Ltd. is used for the roughening treatment. Thereby, the adhesion to the electrolytic copper plating film 7 formed in the subsequent work can be ensured, and the absorption of the carbon dioxide laser light in the surface of the copper foil can be improved. It was confirmed that the absorption rate of carbon dioxide laser light was actually increased from about 20% to about 30% before and after the surface treatment.

In the present embodiment, the through hole 5 and the bottomed through hole 6 are simultaneously processed. Therefore, the copper foil 2 can be easily processed on the surface of the copper foil 2 by performing the above-described roughening treatment. At the same time, the copper foil surface is formed to have a low thickness so as not to penetrate the copper foil 3 when the bottomed through hole 6 is formed, and the back surface of the copper foil 3 is treated so that the absorption of the laser light is reduced to good. However, when the through hole 5 is to be formed efficiently, it is preferable to perform the roughening treatment as the back surface treatment of the copper foil 3.

The thinner the copper foils 2, 3 of the double-sided copper clad laminate 4, the easier it is to penetrate the copper foils 2, 3 during laser processing. Therefore, when the thickness of the copper foil is as small as 10 μm or less as described in the present embodiment, since the bottomed through hole 6 is easily formed, a low-thickness copper foil which is treated as a back surface with almost no roughening treatment is used. 3 is better.

Here, the laser processing method will be described in detail. First, the case where the bottomed through hole 6 is processed will be described. When the copper foil 2 is processed, an average of 1 shot of laser light energy is set (set to power P). Next, it is preferable to finish the processing of the copper foil 2 by one emission. After that, when the resin of the flexible insulating base material 1 is processed until the copper foil 3 is exposed, the energy of the laser light emitted by the average one is reduced to (1/2) P to (1/3) P, and 2 to 2 3 launch complete resin processing. Next, the case of penetrating the through hole 5 will be described. At this time, the double-sided copper foil and the resin are processed using laser light having an average light emission of laser light energy of the above-described power P. Continuous irradiation of 3 to 4 is performed to complete the processing of the through hole 5.

When a thinner copper foil is used, in order to easily form the bottomed through hole 6, the back surface (the surface in contact with the base material) of the copper foil 3 which becomes the bottom of the bottomed through hole 6 is formed to have a low thickness. Along with this, the back surface of the copper foil 2 (the surface in contact with the base material) is roughened. Next, the through via 5 is formed by processing the surface of the copper foil 3. According to this method, the through-holes 6 can be easily formed while forming the through-holes efficiently. Further, in another method, the through hole 5 may be formed by performing laser processing from the surface of the copper foil 2 and the surface of the copper foil 3 in two directions. At this time, since the surfaces of the copper foils 2 and 3 are subjected to the roughening treatment, they are easy to process from any direction, and there is no need to consider the back surface treatment state (the thickness of the copper foil) of the copper foil.

Next, in order to remove the stain (resin residue) generated when the through hole 5 and the bottomed through hole 6 are formed, plasma treatment and wet etching (desmut treatment) are performed. The optimum conditions for the plasma treatment of the through-hole 5 and the bottomed through-hole 6 are substantially the same. On the other hand, regarding wet etching using sodium persulfate or the like, the optimum conditions are different between the two. That is, the wet etching is almost unnecessary for the through via 5. It is not preferable to perform etching so that the copper foils 2 and 3 are retracted, which may adversely affect the subsequent conductive treatment. On the other hand, in order to remove the dissimilar metal such as nickel or chromium on the back surface of the copper foil 3 caused by the back surface treatment, the bottomed via hole 6 is required to be etched by 1 to 2 μm. In view of the influence on the through-hole 5, it is preferable to complete the treatment with as little etching amount as possible. In the present embodiment, etching is performed at 1 μm.

Next, it can be seen from FIG. 1A (2) that the copper foils 2 and 3, the inner wall of the through-hole 5 and the inner wall of the bottomed through-hole 6 are subjected to a conductive treatment and an electrolytic copper plating treatment. This forms an electrolytic copper plating film 7 (about 8 μm thick). Thereby, the copper plating layer 8 on the copper foils 2, 3, the plating through-hole 9, and the plated through-hole 10 are formed. The plating penetrates through-holes 9 through the interlayer conduction circuit, and the plated through-holes 10 are provided with a bottom-type interlayer conduction circuit. Each of the plated through holes electrically connects the copper foil 2 on the surface of the flexible insulating base material 1 to the copper foil 3 on the back surface.

Among them, the liquid renewability of the treatment liquid in the above-described conductive treatment process and electrolytic copper plating project is not the same as that of the through hole 5 and the bottomed through hole 6. That is, the liquid renewability of the bottomed through hole 6 is inferior to that of the through hole 5. Therefore, the engineering flow under the condition that the bottomed through hole 6 can be processed is basically performed. Regarding the electrolytic copper plating process, the adhesion of the side wall near the bottom of the bottomed through hole 6 is likely to be deteriorated. Therefore, the electrolytic copper plating treatment is preferably carried out using a plating bath containing a high concentration of copper sulfate.

Next, as shown in Fig. 1(A), the resist layers 11 and 11 are formed on the copper plating layers 8 and 8. A dry film resist is used in forming the resist layer 11. The dry film resist is preferably a thickness (for example, 20 μm) which can be used for tenting through the through hole 9 and the plated bottomed through hole 10. Thereby, the resist is prevented from entering the plating through-hole 9 and the plated bottomed through hole 10, and the peeling of the resist layer 11 which is performed later can be easily performed. Among them, a liquid resist or an electrodeposition resist may be used instead of the dry film resist.

Next, as is understood from FIG. 1A (4), the resist layer 11 is etched in a predetermined pattern by exposure and development of the resist layer 11 by a photolithography process, and then the patterned resist is patterned. The layer 11 is formed as a mask, and the copper plating layer 8 and the copper foils 2, 3 are etched. Thereafter, the resist layer 11 is peeled off. Thereby, the inner layer circuit patterns 12A and 12B are formed on the front and back surfaces of the flexible insulating base material 1, respectively.

The double-sided flexible substrate 13 shown in Fig. 1A (4) is obtained by the above-described process.

Next, it is understood from FIG. 1B (5) that the cover film 16 having the insulating film 14 (for example, 12 μm thick) such as a polyimide film and the adhesive layer 15 formed on one surface of the insulating film 14 is prepared. The subsequent agent layer 15 is composed of an adhesive such as acrylic or epoxy. Next, a lamination process of the double-sided adhesive cover film 16 on the double-sided flexible substrate 13 is performed using a vacuum laminator or the like. Thereby, the inner layer circuit patterns 12A and 12B and the plating through via 9 are filled by the adhesive layer 15.

In the present laminating process, it is not necessary to completely fill the inside of the plated bottomed through hole 10 with an adhesive. In other words, in the lamination process, the inside of the plating through-hole 9 is completely filled by the adhesive which is melted by the adhesive layer 15 of the cover film 16, and the inside of the plated bottomed through hole 10 is allowed to occur. The air void 15a filled by the adhesive after the adhesive layer 15 is melted is carried out under the condition of the air void 15a filled. As described above, the thickness of the adhesive layer 15 in the present embodiment can be completely filled in the plating through-hole 9, and it is not necessary to consider the filling state inside the plated through-hole 10 . Therefore, the adhesive layer 15 is as thin as possible within a range in which the plating through-hole 9 can be completely filled. In the present embodiment, the thickness of the adhesive layer 15 is 15 μm. As shown in Fig. 1B (5), the air gap 15a may be generated inside the plated bottomed through hole 10. However, in the post-engineering, all of the adhesive in the plated through-hole 10 is completely removed by laser processing, so that the air void 15a does not become a problem.

In the above-mentioned work, the double-sided core substrate 17 which becomes the core substrate of the multilayer printed wiring board shown in FIG. 1B (5) is obtained.

Next, as shown in FIG. 1B (6), a single copper foil 18 (third conductive film) having a thickness of, for example, 12 μm is provided on one surface of the flexible insulating base material 19 (for example, a polyimide having a thickness of 25 μm). The copper clad laminate 20 is covered. Next, the opening 18a is formed in the copper foil 18 of the single-sided copper-clad laminate 20 by the photosensitive etching processing method. More specifically, a resist layer (not shown) is formed on the copper foil 18, and the resist layer is patterned by exposure and development. Next, the patterned resist layer is formed into a mask, and the copper foil 18 is etched. Thereby, the common type mask 21 is formed. The opening portion 18a is used to form a through hole by removing the resin of the base material by laser processing in a post-engineering process.

Next, it is understood from Fig. 1B (6) that the single-sided copper clad laminates 20 and 20 on which the common mask 21 is formed are laminated through the adhesive layers 22 and 22 by using an adhesive for laminating. On both sides of the double-sided core substrate 17. In the case of the backing material used herein, it is preferred that the low flow type (pre-dip type) or the bonding sheet or the like has a small outflow. Alternatively, the single-sided copper-clad laminate 20 having the unprocessed copper foil 18 may be passed through the subsequent material layer 22, and then the copper foil 18 may be etched in a predetermined pattern after the double-sided core substrate 17 is formed. Common type mask 21.

Next, as is clear from the first FIG. 1 (7), the laser beam processing is performed using the common type mask 21 to form the stepped through holes 23 and the through holes 24A and 24B. The stepped through hole 23 penetrates through the flexible insulating base material 19, the adhesive layer 22, the insulating film 14, and the adhesive layer 15, and the plated bottomed through hole 10 is exposed at the bottom. In this laser processing project, the resin inside the plated through-hole 10 is completely removed, and the air void 15a is destroyed. The through holes 24A and 24B penetrate the flexible insulating base material 19, the adhesive layer 22, the insulating film 14, and the adhesive layer 15, and the inner layer circuit patterns 12A and 12B are exposed at the bottom.

Among them, in order to form the stepped through hole 23, it is necessary to remove the resin which is inside the plated bottomed through hole 10. Therefore, the amount of the resin material to be removed is more than that of the through holes 23A, 24B. Therefore, in forming the stepped through hole 23, it is preferable to increase the number of shots of the laser processing or to increase the pulse width of the laser light. For the laser used in the laser processing, a UV-YAG laser, a carbonic acid laser, a pseudo-molecular laser, or the like can be selected.

Next, as is understood from FIG. 1C (8), the inner wall of the stepped through hole 23 and the inner walls of the through holes 24A and 24B are subjected to a conductive treatment and an electrolytic plating treatment to form an electrolysis. The coating film 25 is applied. Thereby, the copper plating layer 26 on the copper foil 18 and the plating via holes 27, 28, 29 are formed. The plated through holes are electrically connected to the inner layer circuit patterns 12A and 12B and the copper foil 18 and the copper plating layer 26 (the outer layer circuit pattern 30 thereafter). The plated through hole 27 is formed by forming a plating layer on the inner wall of the stepped through hole 23. The plated through hole 28 is formed with a plating layer on the inner wall of the through hole 24A opposed to the stepped through hole 23. The plated through hole 29 is formed by forming a plating layer on the inner wall of the through hole 24B.

The thickness of the electrolytic plating film 25 is formed to a value required for ensuring connection reliability. In the present embodiment, the thickness of the adhesive layer 15 is further reduced as compared with the prior art, whereby the thickness of the electrolytic plating film 25 is also thinner than the conventional technique (for example, about 25 to 30 μm). To the extent of, for example, 15 μm to 20 μm.

As is apparent from Fig. 1C (8), the stacked via structure in which the plated through-holes 27 are formed in the plated bottomed via 10 is completed by the above-described process.

Next, as is apparent from Fig. 2, the outer layer circuit pattern 30 is formed by etching the copper foil 18 and the electrolytic plating film 25 in a predetermined pattern by a photosensitive etching method. After that, a photoresist layer (not shown) is formed as necessary, and a surface treatment such as solder plating, nickel plating, or gold plating is applied to the terminals of the circuit pattern, and the outer shape processing is performed by drilling using a mold or the like. .

Through the above process, the laminated type multilayer printed wiring board 32 having the stacked via structure of the present embodiment shown in Fig. 2 can be obtained.

The multilayer printed wiring board 32 of the present embodiment is a single-sided copper-clad laminate 20 or 20 which is formed on the front and back surfaces of the double-sided core substrate 17 which is an inner layer and which is formed by laminating the outer layers 22 and 22 . The present embodiment is not limited thereto, and the outer layer may be laminated on the surface of the double-sided core substrate 17, that is, the open surface side of the plated through-hole 10 of the double-sided core substrate 17, through the adhesive layer 22. Single-sided copper clad laminate 20. Thereby, it is possible to obtain a multilayer printed wiring board having a buildup layer on only one side.

The inner layer circuit patterns 12A, 12B are electrically connected to the outer layer circuit pattern 30 by plating the via holes 27, 28, 29.

In the multilayer printed wiring board 32 obtained by the manufacturing method of the present embodiment, the component mounting portion 32a in which the buildup layer 31 is laminated on the double-sided core substrate 17 belonging to the flexible printed wiring board; The layered core substrate 17 is not laminated with the layered flexible wire portion 32b. That is, the flexible wire portion 32b is configured to extend from the component mounting portion 32a. This embodiment is not limited thereto, and a multilayer printed wiring board in which the double-sided core substrate 17 does not constitute the flexible wire member 32b can be manufactured.

Further, in the present embodiment, a method of manufacturing the flexible multilayer printed wiring board will be described, but the present invention is not limited thereto.

Further, in the laser processing method, in addition to the aforementioned common-type laser processing method or direct laser processing method, there is also a case where the copper foil 18 is formed with an opening having a larger diameter than the upper hole of the stepped through hole 23. A large window method of irradiating laser light having the same beam diameter as that of the upper hole of the stepped through hole 23 is irradiated. The optional laser processing method is not limited to the user in the description of the above embodiment, and the common method, the direct laser method, and the large window method can be arbitrarily selected for each project. However, if the direct laser method is used, the thickness of the copper foil as shown in the present embodiment is preferably 15 μm or less.

Further, in the present embodiment, after the cover film 16 is laminated on both surfaces of the double-sided flexible substrate 13 to form the double-sided core substrate 17, the double-sided core substrate 17 is laminated, but the present invention is not limited thereto. Alternatively, a single-sided copper-clad laminate with an adhesive may be used instead of the cover film 16, and a build-up layer may be directly provided on the double-sided flexible substrate 13. At this time, a multilayer printed wiring board was produced as follows. First, as described above, the double-sided flexible substrate 13 on which the plating through-holes 9, the plated bottom vias 10, and the inner layer circuit patterns 12A and 12B are formed is formed. After that, a single-sided conductive film having an insulating base material, a conductive film (third conductive film) formed on the surface of the insulating base material, and an adhesive layer formed on the adhesive layer on the back surface of the insulating base material is prepared. Laminated board. Next, a lamination process in which the single-sided conductive film laminate of the adhesive layer is adhered to both surfaces of the double-sided flexible substrate 13 is performed. In the lamination process, the inside of the plating through-hole 9 is completely filled by an adhesive which is melted by the adhesive layer of the single-sided conductive film laminated plate of the adhesive layer, and the plating is provided. The inside of the hole 10 is allowed to occur under the condition that an air gap which is not filled by the adhesive after the adhesive layer is melted occurs. The multilayer printed wiring board obtained as described above is subjected to laser processing to remove the adhesive inside the plated through-hole 10 to eliminate the air void, thereby exposing the plated bottomed via 10 at the bottom to form The plated through hole 10 is formed as a stepped through hole of the lower hole. Thereafter, by plating the inner walls of the third conductive film and the stepped via holes, a plated via hole for electrically connecting the third conductive film and the inner layer circuit pattern 12A is formed. Then, the third conductive film which has been subjected to the plating treatment is etched in a predetermined pattern to form an outer layer circuit pattern, thereby obtaining a laminated type multilayer printed wiring board.

As described above, the double-sided core substrate 17 has a plating through-hole 9 and a plated bottomed through hole 10 for electrically connecting the inner layer circuit pattern 12A and the inner layer circuit pattern 12B. The stacked via structure is composed of a plated bottomed through hole 10 and a plated through hole 27 disposed on the plated bottomed through hole 10. The plated through-hole 27 is formed by forming an electrolytic plating film on the inner wall of the stepped through hole 23 formed in the plated through-hole 10 formed in the double-sided core substrate 17 as a small-diameter hole. Further, the plating through-via 10 is configured to conduct only the interlayer between the front surface and the back surface of the double-sided core substrate 17, and the interlayer conduction between the outer layer circuit pattern 30 and the inner layer circuit patterns 12A and 12B is not performed.

According to the above feature, the following effects can be obtained by the present embodiment.

When the cover film 16 is laminated, it becomes unnecessary to completely fill the inside of the plated bottomed through hole 10 with the adhesive material. That is, the inside of the plated bottomed through hole 10 may be in an incompletely filled state by means of an adhesive, and there is no air void 15a. Therefore, the thickness of the adhesive layer 15 of the cover film 16 is minimized within a range in which the inside of the plating through-hole 9 can be completely filled with the adhesive. As a result, the stepped through holes 23 can be made shallower (for example, about 10 μm) as much as possible, so that the electrodeposition ease at the time of performing the electrolytic plating treatment on the inner walls of the stepped through holes 23 and the through holes 24A, 24B is improved. Further, the plated through-holes 27, 28, and 29 are formed to be advantageous in that they are not easily affected by thermal expansion of the constituent members of the printed wiring board. Among the constituent members, the adhesive agent constituting the adhesive layer 15 in particular has a large thermal expansion coefficient, and therefore the effect of the adhesive layer 15 being thinned is large. Therefore, the yield can be improved and the thickness of the electrolytic plating film 25 required for ensuring the connection reliability can be reduced. As a result, according to the present embodiment, the fine outer layer circuit pattern 30 can be formed.

Further, according to the present embodiment, when the plating via hole 27 is formed, the electrolytic plating film 26 is formed on the plated bottom via hole 10. As a result, the plated through-holes 10 which are more easily concentrated in thermal stress than the through-holes 9 are reinforced by the asymmetric shape, and the connection reliability can be improved.

Further, according to the present embodiment, since the plated bottomed through hole 10 is reinforced, the plating thickness of the plated through hole 10 (the thickness of the electrolytic copper plating film 7) can be made thin to ensure the penetration of the plating. The degree of connection reliability of the holes 9. As a result, the time required for the plating process can be shortened, and the cost can be reduced. Further, since the copper plating layer 8 is also made thinner by the plating thickness of the plated bottomed via 10, the inner layer circuit pattern 12 of the double-sided core substrate 17 can be made fine.

In the description of the embodiment, the wiring pattern and the plating film are made of copper. However, the present invention is not limited thereto, and may be other metals such as aluminum or silver.

According to the above description, those skilled in the art may appreciate the additional effects or various modifications of the present invention, but the aspects of the present invention are not limited to the above embodiments. Various additions, modifications, and partial deletions may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

1, 19, 101. . . Flexible insulating substrate

2, 3, 18, 102, 103. . . Copper foil

4, 104. . . Double-sided copper laminate

5. . . Through hole

6,105. . . Bottom through hole

7. . . Electrolytic copper plating film

8, 26. . . Copper plating

9. . . Plating through the through hole

10, 106. . . Plated bottom via

11. . . Resistive layer

12A, 12B. . . Inner circuit pattern

13. . . Double-sided flexible substrate

14,107. . . Insulating film

15, 22, 108, 112. . . Subsequent layer

15a. . . Air gap

16,109. . . Cover film

17, 110. . . Double-sided core substrate

18. . . Copper foil

18a. . . Opening

20, 111. . . Single-sided copper laminate

twenty one. . . Common mask

23, 113A. . . Stepped through hole

24A, 24B, 113B, 113C. . . Through hole

25. . . Electrolytic plating film

27, 28, 29, 114A, 114B, 114C. . . Plated through hole

30, 115. . . Outer circuit pattern

31. . . Laminated through hole

32, 116. . . Multilayer printed wiring board

32a, 116a. . . Parts mounting department

32b, 116b. . . Flexible wire section

Fig. 1A is a cross-sectional view showing the construction of a method of manufacturing a multilayer printed wiring board according to an embodiment of the present invention.

Fig. 1B is a cross-sectional view of the first embodiment of the present invention for explaining a method of manufacturing a multilayer printed wiring board according to an embodiment of the present invention.

1C is a cross-sectional view of the first embodiment of the present invention for explaining a method of manufacturing a multilayer printed wiring board according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view showing a laminated type multilayer printed wiring board according to an embodiment of the present invention.

Fig. 3 is an engineering sectional view showing a method of manufacturing a laminated type multilayer printed wiring board having a stacked via structure obtained by a conventional technique.

1, 19. . . Flexible insulating substrate

9. . . Plating through the through hole

10. . . Plated bottom via

14. . . Insulating film

15, 22. . . Subsequent layer

15a. . . Air gap

16. . . Cover film

17. . . Double-sided core substrate

18. . . Copper foil

18a. . . Opening

20. . . Single-sided copper laminate

twenty one. . . Common mask

Claims (3)

A method for producing a multilayer printed wiring board, comprising: a double-sided conductive film laminated plate having a first conductive film and a second conductive film on a front surface and a back surface, wherein the first conductive film and the second conductive layer are formed The plating is electrically connected to the through hole and the plated through hole, and the first conductive film and the second conductive film are etched in a predetermined pattern to form a double layer having an inner layer circuit pattern. The flexible substrate is provided with a cover film having an insulating film and an adhesive layer formed on one surface of the insulating film, and the plating is passed through an adhesive which is melted by the adhesive layer of the cover film. The inside of the hole is completely filled, and the cover film is adhered to the double-sided flexible substrate under the condition that the inside of the plated bottomed through hole is allowed to occur in an air gap which is not filled by the above-mentioned adhesive agent. In the double-sided lamination process, a double-sided core substrate is produced, and at least the side of the open surface of the double-sided core substrate on which the bottom via hole is plated is laminated, and then the third conductive film formed on one side is laminated. a layer; the air gap is removed by laser processing to remove the adhesive in the bottom of the plated through hole, thereby exposing the plated bottomed through hole at the bottom portion to form the plated bottomed through hole a stepped via hole that is a lower hole, and a plating layer that electrically connects the third conductive film and the inner layer circuit pattern by plating the inner wall of the third conductive film and the stepped via hole The through hole is formed by etching the third conductive film subjected to the plating treatment in a predetermined pattern to form an outer layer circuit pattern. A method for producing a multilayer printed wiring board, comprising: a double-sided conductive film laminated plate having a first conductive film and a second conductive film on a front surface and a back surface, wherein the first conductive film and the second conductive layer are formed The plating is electrically connected to the through hole and the plated through hole, and the first conductive film and the second conductive film are etched in a predetermined pattern to form a double layer having an inner layer circuit pattern. The flexible substrate is provided with a single-sided conductive film laminate having an insulating base material, a third conductive film formed on the surface of the insulating base material, and an adhesive layer formed on the adhesive layer on the back surface of the insulating base material. The inside of the through-hole is completely filled by the adhesive which is melted by the adhesive layer, and air which is not filled by the adhesive is allowed to be generated inside the plated bottomed through hole. Under the condition of voids, a single-sided conductive film laminate having the adhesive layer is adhered to the both sides of the double-sided flexible substrate, and the plating is removed by laser processing. Inside the hole The air gap is eliminated by the adhesive of the portion, whereby the plated bottomed through hole is exposed at the bottom portion, and the stepped through hole having the bottom hole through which the plated through hole is formed is formed, and the third conductive film is formed And plating the inner wall of the stepped through hole to form a plated through hole for electrically connecting the third conductive film and the inner layer circuit pattern, and the third conductive film subjected to the plating treatment is The predetermined pattern is etched, thereby forming an outer layer circuit pattern. The method of manufacturing a multilayer printed wiring board according to the first or second aspect of the invention, wherein the laser processing is performed by using a common mask formed by etching the third conductive film. a conformal laser processing method performed by (conformal mask); a direct laser processing method in which the third conductive film is directly irradiated with laser light; or an opening larger than a diameter of an upper hole of the stepped through hole is formed in the foregoing 3 A conductive film that illuminates a large window of laser light having the same beam diameter as the above-mentioned upper hole diameter.