Method for manufacturing multilayer printed wiring board and multilayer printed wiring board

Abstract

Provided are a multilayer printed wiring board manufacturing method and a multilayer printed wiring board. The multilayer printed wiring board manufacturing method includes the steps of: embedding a conductive pattern provided on a dielectric layer with a first adhesive layer having a filler content of a prescribed value or less; and laminating a laminate composed of a metal foil laminate or a metal foil on the first adhesive layer with a second adhesive layer having a filler content greater than the prescribed value.

Description

Technical Field

[0001] This invention relates to a method for manufacturing multilayer printed wiring boards and to the multilayer printed wiring board itself. Background Technology

[0002] In recent years, electronic devices such as smartphones, laptops, digital cameras, and game consoles have been continuously miniaturizing and increasing in speed. Along with this, the amount of information processed by these electronic devices is increasing rapidly. Therefore, there is a growing trend towards higher signal transmission speeds for printed circuit boards (PCBs). Multilayer PCBs are known to address this trend. These multilayer PCBs have a structure comprising conductive patterns in inner layers and conductive patterns in outer layers electrically connected by interlayer interconnect channels formed in blind vias.

[0003] Starting in 2019, smartphones and other portable communication devices began transitioning to the next-generation communication standard, 5G. 5G uses signals with frequencies ranging from several GHz to 20-30 GHz. Furthermore, around 2022, it is expected that the frequency of signals received or transmitted by communication devices will increase to approximately 50 GHz.

[0004] As the frequency increases, signal transmission loss increases. Therefore, suppressing transmission loss in signal lines becomes increasingly important.

[0005] Furthermore, in order to reduce signal transmission loss, it is desirable to use materials with excellent dielectric properties, such as dielectric constant and dielectric loss tangent (tanδ), as the insulating substrate of printed wiring boards. For example, the printed wiring board described in Japanese Patent Publication No. 2011-66293 uses liquid crystal polymer (LCP).

[0006] Multilayer printed circuit boards for high-speed transmission, such as those with stripline structures, preferably have a thick dielectric layer (insulating substrate and adhesive layer) between the inner signal lines and the outer ground layer. This reduces the capacitance between the signal lines and the ground layer. Therefore, using wide signal lines can reduce conductor resistance loss. Furthermore, adhesives with excellent dielectric properties (low dielectric constant, low dielectric loss tangent) are being developed in recent years.

[0007] Therefore, improving the transmission characteristics of multilayer printed wiring boards by increasing the thickness of the adhesive layer is being researched. For example, studies are being conducted on increasing the thickness of the adhesive layer compared to conventional adhesive layers and setting it to the same thickness as the insulating substrate. To increase the thickness of the adhesive layer, adhesives containing fillers (extenders) are required to ensure the rigidity and elasticity of the adhesive layer.

[0008] However, as the filler content increases, the adhesive's fluidity decreases. Therefore, when using adhesives with high filler content, the embedding performance of the conductive patterns in the inner layers deteriorates. Consequently, ensuring the uniformity of the thickness of the multilayer printed circuit board becomes difficult. This can lead to variations in interlayer spacing, potentially negatively impacting the signal transmission characteristics of the multilayer printed circuit board.

[0009] Furthermore, when using adhesives with high filler content, it is difficult to ensure the reliability of the interlayer connection channels (filled vias, plated vias, etc.) between the conductive patterns of the inner and outer layers. This is caused by the adhesive containing a large amount of filler remaining on the metal foil exposed on the bottom surface of the blind vias obtained by laser drilling for interlayer connections. The adhesive residue (resin residue) on the metal foil contains a large amount of filler. Therefore, even with desmearing treatment (plasma treatment or chemical treatment using a liquid), the resin residue cannot be completely removed. As a result, the conductive material of the interlayer connection channel cannot be electrically connected. Consequently, the reliability of the interlayer connection channel may not be guaranteed.

[0010] Furthermore, excessive fillers added to the adhesive can sometimes degrade dielectric properties. As a result, the transmission characteristics of multilayer printed circuit boards may deteriorate. Summary of the Invention

[0011] To solve the above-mentioned technical problems, the present invention aims to provide a multilayer printed wiring board and its manufacturing method that can ensure the uniformity of thickness of the multilayer printed wiring board even when the thickness of the adhesive layer is increased and is suitable for high-speed transmission.

[0012] Furthermore, another object of the present invention is to provide a multilayer printed wiring board and a method thereof that can ensure the reliability of interlayer connection channels and is suitable for high-speed transmission even when the thickness of the adhesive layer is increased.

[0013] The manufacturing method of the multilayer printed wiring board according to the first aspect of the present invention includes the following steps: embedding a conductive pattern on a dielectric layer using a first adhesive layer having a filler content below a specified value; and stacking a build-up layer composed of a metal foil laminate or metal foil on the first adhesive layer using a second adhesive layer having a filler content greater than the specified value.

[0014] In addition, in the manufacturing method of the multilayer printed wiring board, the first adhesive layer may not contain filler.

[0015] Furthermore, in the manufacturing method of the multilayer printed wiring board, the specified value of the filler content can be 5% by weight.

[0016] In addition, in the manufacturing method of the multilayer printed wiring board, the second adhesive layer may be thicker than the first adhesive layer.

[0017] In addition, in the manufacturing method of the multilayer printed wiring board, the filler can be an inorganic filler with flame retardant properties.

[0018] In addition, the manufacturing method of the multilayer printed wiring board may further include the following steps: using a laser to remove at least the second adhesive layer and the first adhesive layer to form blind vias and expose the conductive pattern on the bottom surface of the blind vias; forming an interlayer connection channel through the blind vias to electrically connect the conductive pattern to the metal foil.

[0019] Furthermore, in the manufacturing method of the multilayer printed wiring board, the interlayer connection channel can be formed to electrically connect the ground wiring of the conductive pattern to a ground layer, the ground layer including the patterned metal foil.

[0020] The manufacturing method of the multilayer printed wiring board according to the second aspect of the present invention includes the following steps: preparing a double-sided metal foil laminate, the double-sided metal foil laminate comprising: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; a first metal foil disposed on the first main surface; and a second metal foil disposed on the second main surface; patterning the first metal foil to form a conductive pattern; forming a first adhesive layer having a filler content below a predetermined value on the first main surface in such a way as to embed the conductive pattern; forming a second adhesive layer having a filler content greater than the predetermined value on the first adhesive layer; preparing a single-sided metal foil laminate, the single-sided metal foil laminate comprising: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; a third metal foil disposed on the third main surface; stacking the single-sided metal foil laminate on the second adhesive layer in such a way as to contact the fourth main surface with the second adhesive layer; and using a laser to remove at least the second adhesive layer and the first adhesive layer to form blind vias and expose the conductive pattern on the bottom surface of the blind vias.

[0021] The manufacturing method of the third-party multilayer printed wiring board of the present invention includes the following steps: preparing a first single-sided metal foil laminate, the first single-sided metal foil laminate comprising: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; a first metal foil disposed on the first main surface; patterning the first metal foil to form a conductive pattern; forming a first adhesive layer having a filler content below a predetermined value on the first main surface by embedding the conductive pattern; forming a second adhesive layer having a filler content above the predetermined value on the first adhesive layer; preparing a second single-sided metal foil laminate, the second single-sided metal foil laminate comprising: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; a second metal foil disposed on the first main surface. On the three main surfaces; the second single-sided metal foil laminate is stacked on the second adhesive layer in such a manner that the fourth main surface contacts the second adhesive layer; a third adhesive layer having a filler content greater than the specified value is formed on the second main surface of the first insulating substrate; a third single-sided metal foil laminate is prepared, the third single-sided metal foil laminate comprising: a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface; a third metal foil disposed on the sixth main surface; the third single-sided metal foil laminate is stacked on the third adhesive layer in such a manner that the fifth main surface contacts the third adhesive layer; and at least the second adhesive layer and the first adhesive layer are removed using a laser to form a blind hole, so that the conductive pattern is exposed on the bottom surface of the blind hole.

[0022] The manufacturing method of the multilayer printed wiring board according to the fourth aspect of the present invention includes the following steps: preparing a first single-sided metal foil laminate, the first single-sided metal foil laminate comprising: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; a first metal foil disposed on the second main surface of the first insulating substrate by a first adhesive layer having a filler content greater than a predetermined value; forming a second adhesive layer having a filler content less than the predetermined value on the first main surface of the first insulating substrate; disposing a second metal foil on the second adhesive layer; patterning the second metal foil to form a conductive pattern; and forming a conductive pattern on the second adhesive layer by embedding the conductive pattern. A third adhesive layer having a filler content below the specified value; preparing a second single-sided metal foil laminate, the second single-sided metal foil laminate comprising: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; a third metal foil disposed on the third main surface of the second insulating substrate by a fourth adhesive layer having a filler content greater than the specified value; stacking the second single-sided metal foil laminate on the third adhesive layer in such a manner that the fourth main surface contacts the third adhesive layer; and using a laser to remove at least the fourth adhesive layer, the second insulating substrate, and the third adhesive layer to form blind vias and expose the conductive pattern on the bottom surface of the blind vias.

[0023] The multilayer printed wiring board of the present invention includes: a dielectric layer having a first main surface and a second main surface opposite to the first main surface; a conductive pattern disposed on the first main surface of the dielectric layer; a first adhesive layer disposed on the dielectric layer in such a manner as to embed the conductive pattern, and having a filler content below a predetermined value; a second adhesive layer disposed on the first adhesive layer, having a filler content greater than the predetermined value; and a stack consisting of a metal foil stack or metal foil laminated on the second adhesive layer.

[0024] In addition, the multilayer printed wiring board may also include interlayer connection channels, which electrically connect the conductive pattern to the metal foil through blind holes extending from the metal foil to the first adhesive layer.

[0025] Additionally, in the multilayer printed wiring board, the interlayer connection channel can electrically connect the ground wiring of the conductive pattern to the ground layer, which includes the patterned metal foil.

[0026] In addition, the multilayer printed wiring board may also include a stack, which is composed of a metal foil stack or metal foil laminated on the second main surface of the dielectric layer by an adhesive layer.

[0027] In addition, in the multilayer printed wiring board, the filler content of the first adhesive layer can be less than 5% by weight.

[0028] According to the present invention, a multilayer printed wiring board and its manufacturing method can be provided that can ensure the uniformity of thickness of the multilayer printed wiring board even when the thickness of the adhesive layer is increased and is suitable for high-speed transmission. Attached Figure Description

[0029] Figure 1 This is a top view of the high-frequency signal transmission component used in this embodiment.

[0030] Figure 2 This is a top view showing the signal lines and grounding wiring of the inner layer in region R of the multilayer printed wiring board of this embodiment.

[0031] Figure 3A This is a process cross-sectional view used to illustrate the manufacturing method of the multilayer printed wiring board according to the first embodiment.

[0032] Figure 3B It is used to explain what follows. Figure 3A A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the first embodiment.

[0033] Figure 3C It is used to explain what follows. Figure 3B A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the first embodiment.

[0034] Figure 4A This is a process cross-sectional view used to illustrate the manufacturing method of the multilayer printed wiring board according to the second embodiment.

[0035] Figure 4B It is used to explain what follows. Figure 4A A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the second embodiment.

[0036] Figure 4C It is used to explain what follows. Figure 4B A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the second embodiment.

[0037] Figure 4D It is used to explain what follows. Figure 4C A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the second embodiment.

[0038] Figure 5A This is a process cross-sectional view used to illustrate the manufacturing method of the multilayer printed wiring board according to the third embodiment.

[0039] Figure 5B It is used to explain what follows. Figure 5AA process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the third embodiment.

[0040] Figure 5C It is used to explain what follows. Figure 5B A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the third embodiment.

[0041] Figure 5D It is used to explain what follows. Figure 5C A process cross-sectional view of the manufacturing method of a multilayer printed wiring board according to the third embodiment.

[0042] Figure 6 This is a diagram showing the composition of test pieces used for residual film and flame retardancy tests. Detailed Implementation

[0043] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, components with equivalent functions are given the same reference numerals. The drawings are schematic. The relationship between thickness and planar dimensions (aspect ratio), and the ratio of thicknesses of each layer, etc., may not necessarily match the actual components.

[0044] <High-frequency signal transmission component 100>

[0045] First, refer to Figure 1 The high-frequency signal transmission component 100 of the embodiment will be described. Figure 1 This is a top view of the high-frequency signal transmission component 100. The high-frequency signal transmission component 100 is housed within the casing of an information processing terminal such as a smartphone or tablet. The high-frequency signal transmission component 100 electrically connects an antenna for receiving or transmitting wireless signals to a main substrate including a mounted signal processing chip.

[0046] like Figure 1 As shown, the high-frequency signal transmission component 100 includes: a multilayer printed wiring board 110 forming an elongated ribbon-shaped cable portion; and a connector 120 disposed at the end of the multilayer printed wiring board 110.

[0047] The multilayer printed wiring board 110 is a flexible printed wiring board (FPC). The multilayer printed wiring board 110 has a three-layer stripline structure including signal lines sandwiched between upper and lower ground layers through a dielectric layer.

[0048] like Figure 2As shown, signal lines 112 and ground lines 113 extend along the long side of the multilayer printed circuit board 110, forming the inner layer wiring pattern of the multilayer printed circuit board 110. Signal lines 112 and ground lines 113 are alternately disposed on the dielectric layer 111. For example, the signal lines 112 are high-frequency signal input lines ranging from several GHz to tens of GHz. The ground lines 113 are electrically connected to the outer ground layer (not shown) through interlayer connection channels 114, such as filled vias or plated vias. Furthermore, the number of signal lines 112 is not limited to the number shown.

[0049] Connector 120 is disposed at the end of multilayer printed wiring board 110. Figure 1 Connector 120 is electrically connected, for example, to a main substrate or an antenna. Connector 120 has a connection pin 121 electrically connected to signal line 112 and a connection pin 122 electrically connected to ground wiring 113.

[0050] Alternatively, the signal lines of the multilayer printed circuit board 110 can be configured as differential lines. In this case, the two signal lines are configured to run in parallel without intersecting the grounding wiring. Furthermore, multiple differential lines can be configured, separated by grounding wiring. Alternatively, single-ended transmission lines and differential lines can be configured in a mixed manner.

[0051] Furthermore, the planar shape of the signal line 112 and the grounding line 113 is not limited to... Figure 2 The shape shown is a straight line. For example, it could also be the shape described in Japanese Patent Publication No. 2019-106508.

[0052] (First Implementation)

[0053] Reference Figures 3A-3C The process cross-sectional view illustrates the manufacturing method of the printed wiring board according to the first embodiment.

[0054] First, such as Figure 3A As shown in (1), a double-sided metal foil laminate 10 is prepared. The double-sided metal foil laminate 10 includes: an insulating substrate 11; a metal foil 12 disposed on the upper surface of the insulating substrate 11; and a metal foil 13 disposed on the lower surface of the insulating substrate 11. The metal foils 12 and 13 are formed on the insulating substrate 11 by means of a seed layer (not shown) formed on the main surface of the insulating substrate 11.

[0055] The material of the insulating substrate 11 is not particularly limited. Examples include polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyetheretherketone (PEEK), liquid crystal polymer (LCP), and fluoropolymers (PFA, PTFE, etc.). From the perspective of reducing transmission loss of high-speed signals, insulating materials with low relative permittivity and dielectric loss tangent (tanδ) are preferred.

[0056] The insulating substrate 11 has a thickness of, for example, 25 μm. The metal foils 12 and 13 are, for example, copper foils with a thickness of 12 μm. Alternatively, the metal foils 12 and 13 can be foils made of metals other than copper (silver, aluminum, etc.).

[0057] Next, as Figure 3A As shown in (2), the metal foil 12 of the double-sided metal foil laminate 10 is patterned using a known photolithography method. By doing so, a conductive pattern 12a is formed. This conductive pattern 12a includes a pattern corresponding to the signal line 112 described above and a pattern corresponding to the ground wiring 113.

[0058] Next, as Figure 3A As shown in (3), an adhesive layer 14 is formed on the upper surface of the insulating substrate 11 in such a way as to embed conductive patterns 12a. The adhesive layer 14 has a thickness of, for example, 17 μm.

[0059] The adhesive layer 14 may also be formed by an adhesive applied to the insulating substrate 11. Alternatively, the adhesive layer 14 may be formed by laminating a protective film (not shown) with an adhesive layer formed on one side of a protective film (covering film) onto the insulating substrate 11, and then peeling off the protective film.

[0060] The adhesive layer 14 has a filler content of less than a specified value (e.g., less than 5% by weight). Preferably, the adhesive layer 14 is completely free of filler. Adhesives with low filler content have high fluidity. Therefore, the embedding performance of the conductive pattern 12a can be improved. As a result, the uniformity of the thickness of the multilayer printed wiring board can be improved.

[0061] Next, as Figure 3A As shown in (4), an adhesive layer 15 is formed on the adhesive layer 14. The adhesive layer 15 may be formed by an adhesive applied to the adhesive layer 14. Alternatively, the adhesive layer 15 may be formed by laminating a protective film (not shown) with an adhesive layer formed on one side of the protective film onto the adhesive layer 14 and then peeling off the protective film.

[0062] Adhesive layer 15 is an adhesive layer containing filler. Adhesive layer 15 has a filler content greater than a specified value. The filler content is determined, for example, based on the thickness of adhesive layer 15 and the degree of uniformity of thickness required for the multilayer printed wiring board. For example, adhesive layer 15 has a filler content of 25% by weight and a thickness of 20 μm.

[0063] Furthermore, there are no particular limitations on the material of the filler. To improve the heat resistance and flame retardancy of multilayer printed wiring boards, inorganic fillers with heat resistance and flame retardancy can be used. In this case, for example, fillers containing metal phosphonate salts (such as aluminum phosphonate salts) can be used.

[0064] As materials for adhesive layers 14 and 15, thermosetting materials that ensure sufficient adhesive strength are used. For example, adhesives containing polyolefins, polystyrene, or polyimide as the main component are used. Alternatively, adhesives having dielectric properties equal to or greater than those of the insulating substrate 11 may also be used.

[0065] Next, as Figure 3B As shown in (1), a laminate consisting of a single-sided metal foil laminate 20 is stacked on the adhesive layer 15. The single-sided metal foil laminate 20 includes an insulating substrate 21 and a metal foil 22 disposed on the upper surface of the insulating substrate 21. The metal foil 22 is formed on the insulating substrate 21 through a seed layer (not shown).

[0066] The material of the insulating substrate 21 is not particularly limited. The same material as the insulating substrate 11 can be used. From the perspective of reducing transmission loss of high-speed signals, an insulating material with a small relative permittivity and a positive dielectric loss tangent is preferred.

[0067] The insulating substrate 21 has a thickness of 25 μm, for example. The metal foil 22 is, for example, a 12 μm thick copper foil. Alternatively, the metal foil 22 may also be a foil made of a metal other than copper (silver, aluminum, etc.).

[0068] In the lamination process, the single-sided metal foil laminate 20 is laminated onto the adhesive layer 15 with the insulating substrate 21 facing the adhesive layer 15. Subsequently, heat and pressure are applied using a vacuum pressing device or a vacuum laminating device. Through this heat treatment process, the adhesive layers 14 and 15 are cured, resulting in… Figure 3B The stack shown in (1).

[0069] Next, as Figure 3BAs shown in (2), the metal foil 22 is irradiated with a laser. This removes the metal foil 22, the insulating substrate 21, the adhesive layer 15, and the adhesive layer 14, forming a blind via (BVH) H1. At this time, the conductive pattern 12a (ground wiring) is exposed on the bottom surface of the blind via (BVH) H1. Alternatively, the metal foil 22 can be pre-patterned to form a conformal mask with an opening at the location where the blind via is formed. This conformal mask can be used to form the blind via H1.

[0070] More specifically, firstly, a CO2 laser processing machine is used to irradiate designated locations on the laminate with laser pulses to create holes. The diameter of the blind hole H1 is, for example, φ150μm to 200μm. Subsequently, resin residue (residual film) of the conductive pattern 12a is removed through a desmearing process. As previously mentioned, the adhesive layer 14 on which the conductive pattern 12a is embedded has a filler content below a specified value. Therefore, the residual film can be removed through the desmearing process.

[0071] Similarly, as Figure 3B As shown in (2), the metal foil 13 is irradiated with a laser. This removes the metal foil 13 and the insulating substrate 11, forming a blind via H2. At this point, the conductive pattern 12a (grounding wiring) is exposed on the bottom surface of the blind via H2. The diameter of the blind via H2 is, for example, φ150μm~200μm. In the desmearing process of the blind via H2, the back-side treatment film (Ni / Cr film, etc.) of the conductive pattern 12a is removed.

[0072] Next, as Figure 3C As shown in (1), the blind hole H1 is filled with conductive paste 31 by printing methods such as screen printing. The blind hole H2 is filled with conductive paste 32. The conductive pastes 31 and 32 contain metal particles dispersed in a resin binder of a thermosetting resin in the form of a paste.

[0073] After filling conductive pastes 31 and 32, they are subjected to heat treatment. This causes the metal particles contained in conductive pastes 31 and 32 to bond metallically with each other. Simultaneously, the thermosetting reaction of the adhesive resin in conductive pastes 31 and 32 is completed. By doing so, as... Figure 3C As shown in (2), filled vias 31c and 32c are formed as interlayer connection channels.

[0074] Next, as Figure 3C As shown in (2), metal foils 13 and 22 are patterned using a known photolithography method to form conductive patterns 13a and 22a. Conductive patterns 13a and 22a include a ground layer electrically connected to the filled vias 31c and 32c.

[0075] Subsequently, as needed, surface treatment of the exposed wiring layer, formation of a surface protective film, and shaping are carried out.

[0076] After the above-mentioned processes, such as Figure 3C As shown in (2), the multilayer printed wiring board 1 of the first embodiment is obtained.

[0077] Furthermore, in the manufacturing method described above, after forming the adhesive layer 15 on the adhesive layer 14, the single-sided metal foil laminate 20 is stacked. However, this embodiment is not limited to this. For example, the adhesive layer 15 may be pre-formed on the lower surface of the insulating substrate 21 of the single-sided metal foil laminate 20. In this case, the single-sided metal foil laminate 20 is stacked on the adhesive layer 14.

[0078] Furthermore, the thickness of the insulating substrate 11 can be the sum of the thickness of the insulating substrate 21 and the thickness of the adhesive layer 15. Thus, a multilayer printed wiring board 1 having a structure substantially symmetrical in the thickness direction with the conductive pattern 12a as its center is obtained.

[0079] In addition, the double-sided metal foil laminate 10 used Figure 3A (1) may have metal foils 12 and 13 formed on the insulating substrate 11 by an adhesive layer (not shown). Similarly, the single-sided metal foil laminate 20 may also have metal foil 22 formed on the insulating substrate 21 by an adhesive layer (not shown).

[0080] Furthermore, in the manufacturing method described above, a single-sided metal foil laminate 20 is used as the laminate. However, it is not limited to this; metal foil can also be used as the laminate. In this case, the metal foil is directly laminated onto the adhesive layer 15.

[0081] Furthermore, in the manufacturing method described above, filled vias filled with cured conductive paste are formed as interlayer connection channels. However, this is not a limitation; plated vias can also be formed. In this case, a metal plating layer (e.g., a copper plating layer) is formed on the inner wall of the blind vias H1 and H2. Thus, plated vias are formed that electrically connect the conductive pattern 12a to the metal foils 13 and 22.

[0082] As described above, in the first embodiment, the conductive pattern 12a formed on the insulating substrate 11 is covered by an adhesive layer 14 having a filler content below a predetermined value. Furthermore, a laminate (metal foil laminate or metal foil) is laminated on the adhesive layer 14 by an adhesive layer 15 having a filler content greater than a predetermined value.

[0083] Therefore, according to the first embodiment, even when the thickness of the adhesive layer 15 is increased to increase the thickness of the dielectric layer between the conductive pattern 12a and the conductive pattern 22a, the uniformity of the thickness of the multilayer printed wiring board 1 can be ensured. As a result, a multilayer printed wiring board suitable for high-speed signal transmission can be provided.

[0084] Furthermore, the conductive pattern 12a is embedded through the adhesive layer 14. Therefore, when forming the blind via H1, the formation of residual film on the conductive pattern 12a can be suppressed. That is, the residual film on the conductive pattern 12a can be removed by the conventional desmearing process after perforation. Therefore, according to this embodiment, even when forming an adhesive layer with a high filler content, the reliability of the interlayer connection channel can be ensured.

[0085] In addition, the adhesive layer 15 contains flame-retardant fillers at a specified level or higher. Therefore, a multilayer printed wiring board with excellent heat resistance and flame retardancy can be provided.

[0086] Furthermore, the adhesive layer 14, in which the conductive pattern 12a is embedded, has a low filler content. Therefore, sufficient adhesion strength between the adhesive layer 14 and the insulating substrate 11 can be ensured. As a result, a multilayer flexible printed wiring board with strong bending capability can be provided.

[0087] Furthermore, in the first embodiment, the signal lines of the conductive pattern 12a are embedded in an adhesive layer having a low filler content (i.e., a low dielectric constant). Therefore, it is possible to improve the transmission characteristics of high-speed signals.

[0088] (Second Implementation)

[0089] Next, refer to Figures 4A to 4D The process cross-sectional views illustrate the manufacturing method of the printed wiring board according to the second embodiment. In each figure, the same reference numerals are given to the same constituent elements as in the first embodiment. One difference from the first embodiment is that in the second embodiment, the original raw material is a single-sided metal foil laminate, and the laminate is laminated not only on its upper surface side but also on its lower surface side.

[0090] First, such as Figure 4A As shown in (1), a single-sided metal foil laminate 10A is prepared. The single-sided metal foil laminate 10A includes an insulating substrate 11 and a metal foil 12 disposed on the upper surface of the insulating substrate 11. The metal foil 12 is formed on the insulating substrate 11 by means of a seed layer (not shown) formed on the main surface of the insulating substrate 11.

[0091] Next, as Figure 4A As shown in (2), the metal foil 12 of the single-sided metal foil laminate 10A is patterned using a known photolithography method to form a conductive pattern 12a.

[0092] Next, as Figure 4A As shown in (3), an adhesive layer 14 is formed on the upper surface of the insulating substrate 11 by embedding conductive pattern 12a.

[0093] Next, as Figure 4AAs shown in (4), an adhesive layer 15 is formed on the adhesive layer 14.

[0094] Next, as Figure 4B As shown in (1), a laminate consisting of a single-sided metal foil laminate 20 is stacked on the adhesive layer 15. In this embodiment, no heating and pressurization treatment is performed in this process.

[0095] Next, as Figure 4B As shown in (2), an adhesive layer 15A is formed on the lower surface of the insulating substrate 11. The adhesive layer 15A may be formed by an adhesive applied to the lower surface of the insulating substrate 11. Alternatively, the adhesive layer 15A may be formed by laminating a protective film (not shown) having an adhesive layer formed on one side of the protective film on the lower surface of the insulating substrate 11, and then peeling off the protective film.

[0096] Adhesive layer 15A is an adhesive layer containing filler. Adhesive layer 15A has a filler content greater than a specified value. For example, the filler content is determined based on the thickness of adhesive layer 15A and the required uniformity of thickness for the multilayer printed wiring board. For example, adhesive layer 15A has a filler content of 25% by weight and a thickness of 20 μm. Furthermore, the material of the filler in adhesive layer 15A is the same as the material of the filler included in adhesive layer 15 as described in the first embodiment. Adhesives containing flame-retardant fillers may also be used.

[0097] Next, as Figure 4C As shown in (1), a laminate consisting of a single-sided metal foil laminate 20A is stacked on an adhesive layer 15A. The single-sided metal foil laminate 20A includes an insulating substrate 23 and a metal foil 24 disposed on the upper surface of the insulating substrate 23. The metal foil 24 is formed on the insulating substrate 23 through a seed layer (not shown).

[0098] The material of the insulating substrate 23 is not particularly limited. The same material as the insulating substrates 11 and 21 can be used. The material of the metal foil 24 is the same as that of the metal foil 22 described in the first embodiment.

[0099] In the lamination process, a single-sided metal foil laminate 20A is laminated on the adhesive layer 15A with the insulating substrate 23 facing the adhesive layer 15A. Subsequently, heat and pressure are applied using a vacuum pressing device or a vacuum laminating device. Through this heat treatment process, the adhesive layers 14, 15, and 15A are cured, resulting in… Figure 4C The laminate shown in (1). In addition, here, after stacking the upper and lower layers (single-sided metal foil laminate 20 and single-sided metal foil laminate 20A), the heat and pressure treatment is performed all at once. However, it is not limited to this, and the heat and pressure treatment can also be performed separately after each layer is stacked.

[0100] Next, as Figure 4C As shown in (2), by irradiating the metal foil 22 with a laser, the metal foil 22, insulating substrate 21, adhesive layer 15, and adhesive layer 14 are removed, forming a blind via H1A with the conductive pattern 12a (ground wiring) exposed on the bottom surface. Since the details of this process are the same as in the first embodiment, detailed descriptions are omitted. Alternatively, the metal foil 22 can be pre-patterned, and a conformal mask with an opening can be formed at the location where the blind via is formed. This conformal mask can be used to form the blind via H1A.

[0101] Similarly, as Figure 4C As shown in (2), the metal foil 24 is irradiated with a laser. This removes the metal foil 24, the insulating substrate 23, the adhesive layer 15A, and the insulating substrate 11, forming a blind via H2A. At this time, a conductive pattern 12a (grounding wiring) is exposed on the bottom surface of the blind via H2A. Alternatively, the metal foil 24 can be pre-patterned to form a conformal mask with an opening at the location where the blind via is formed. This conformal mask can be used to form the blind via H2A.

[0102] Next, as Figure 4D As shown in (1), the blind hole H1A is filled with conductive paste 31A using a printing method such as screen printing. The blind hole H2A is then filled with conductive paste 32A. The conductive pastes 31A and 32A are the same conductive pastes as those 31 and 32 described in the first embodiment.

[0103] After filling with conductive pastes 31A and 32A, the conductive pastes 31A and 32A are subjected to heat treatment. Thus, as... Figure 4D As shown in (2), filled vias 31Ac and 32Ac are formed as interlayer connection channels.

[0104] Next, as Figure 4D As shown in (2), the metal foils 22 and 24 are patterned using a known photolithography method. By doing so, conductive patterns 22a and 24a are formed, which include a ground layer electrically connected to the filled vias 31Ac and 32Ac.

[0105] Subsequently, as needed, surface treatment of the exposed wiring layer, formation of a surface protective film, and shaping are carried out.

[0106] After the above-mentioned processes, such as Figure 4D As shown in (2), the multilayer printed wiring board 1A of the second embodiment is obtained.

[0107] According to the second embodiment, similarly to the first embodiment, the uniformity of the thickness of the multilayer printed wiring board 1 can be ensured, and the reliability of the interlayer connection channels can be ensured.

[0108] Furthermore, according to the second embodiment, even if the single-sided metal foil laminates 10A, 20, and 20A used are the same (i.e., the insulating substrates 11, 21, and 23 have the same thickness), a multilayer printed wiring board with a structure that is substantially symmetrical in the thickness direction with the conductive pattern 12a (signal line) as the center can be obtained. Thus, a multilayer printed wiring board with excellent bending characteristics can be provided.

[0109] In addition, adhesive layers 15 and 15A contain flame-retardant fillers at a specified content or higher. Therefore, a multilayer printed wiring board with excellent heat resistance and flame retardancy can be provided.

[0110] Furthermore, in the manufacturing method described above, after forming an adhesive layer 15A on the lower surface of the insulating substrate 11, a single-sided metal foil laminate 20A is stacked. However, this embodiment is not limited to this. For example, the adhesive layer 15A may be pre-formed on the insulating substrate 23 of the single-sided metal foil laminate 20A. In this case, the single-sided metal foil laminate 20A is stacked on the insulating substrate 11.

[0111] Furthermore, in the manufacturing method described above, single-sided metal foil laminates 20 and 20A are used as the laminates. However, this is not a limitation; metal foil can also be used as the laminate. In this case, the metal foil is directly laminated on the adhesive layers 15 and 15A.

[0112] Furthermore, in the manufacturing method described above, filled vias filled with cured conductive paste are formed as interlayer connection channels. However, this is not a limitation; plated vias can also be formed. In this case, a metal plating layer (e.g., a copper plating layer) is formed on the inner wall of the blind vias H1A and H2A. Thus, plated vias are formed that electrically connect the conductive pattern 12a to the metal foils 22 and 24.

[0113] Alternatively, the single-sided metal foil laminate 10A may also include a metal foil 12 formed on the insulating substrate 11 by an adhesive layer (not shown). Similarly, the single-sided metal foil laminate 20 may also include a metal foil 22 formed on the insulating substrate 21 by an adhesive layer (not shown). The single-sided metal foil laminate 20A may also include a metal foil 22 formed on the insulating substrate 23 by an adhesive layer (not shown).

[0114] (Third Implementation)

[0115] Next, refer to Figures 5A to 5D The process cross-sectional views illustrate the manufacturing method of the printed wiring board according to the third embodiment. In each figure, the same reference numerals are used for the same constituent elements as in the first embodiment. One difference from the first embodiment is that, in the third embodiment, conductive patterns 12a are formed on the adhesive layer.

[0116] First, such as Figure 5A As shown in (1), a single-sided metal foil laminate 10B is prepared. The single-sided metal foil laminate 10B includes an insulating substrate 11 and a metal foil 13, the metal foil 13 being disposed on the lower surface of the insulating substrate 11 by an adhesive layer 11a. The adhesive layer 11a has a filler content greater than a specified value (e.g., 25% by weight). In addition, the filler material of the adhesive layer 11a is the same as the filler material of the adhesive layer 15 described in the first embodiment. The adhesive layer 11a may also contain flame-retardant filler.

[0117] Next, as Figure 5A As shown in (2), an adhesive layer 16 with a filler content of less than a specified value (e.g., 5% by weight) is formed on the upper surface of the insulating substrate 11 of the single-sided metal foil laminate 10B. The adhesive layer 16 may also be formed by an adhesive applied to the upper surface of the insulating substrate 11. Alternatively, the adhesive layer 16 may be formed by peeling off a protective film (not shown) having an adhesive layer formed on one side of a protective film on the upper surface of the insulating substrate 11. The adhesive layer 16 may also not contain filler.

[0118] Next, as Figure 5A As shown in (3), a metal foil 17 is disposed on the adhesive layer 16. This metal foil 17 is, for example, a copper foil. Preferably, the metal foil 17 is a low-roughness copper foil. Furthermore, the material of the metal foil 17 is not limited to copper. In this process, more specifically, after the metal foil 17 is placed on the adhesive layer 16, a heat-pressurization process is performed using a vacuum pressing device or a vacuum coating device. By doing so, the adhesive layer 16 is cured, causing the metal foil 17 to adhere to the adhesive layer 16.

[0119] Next, as Figure 5A As shown in (4), the metal foil 17 is patterned to form a conductive pattern 17a. The conductive pattern 17a includes a pattern corresponding to the signal line 112 mentioned above and a pattern corresponding to the ground wiring 113.

[0120] Next, as Figure 5B As shown in (1), an adhesive layer 18 with a filler content of a specified value (e.g., 5% by weight) or less is formed on the adhesive layer 16 by embedding conductive patterns 17a. The adhesive layer 18 may also be formed by an adhesive applied to the adhesive layer 16. Alternatively, the adhesive layer 18 may be formed by peeling off a protective film (not shown) having an adhesive layer formed on one side of a protective film after the adhesive layer 16 is laminated. In addition, the adhesive layer 18 may not contain filler.

[0121] Next, as Figure 5BAs shown in (2), a laminate composed of a single-sided metal foil laminate 20B is stacked on the adhesive layer 18. The single-sided metal foil laminate 20B includes an insulating substrate 21 and a metal foil 22, the metal foil 22 being disposed on the upper surface of the insulating substrate 21 via an adhesive layer 21a. The adhesive layer 21a has a filler content greater than a specified value (e.g., 25% by weight). Furthermore, the filler material of the adhesive layer 21a is the same as the filler material of the adhesive layer 15 described in the first embodiment. The adhesive layer 21a may also contain flame-retardant filler.

[0122] In the lamination process, a single-sided metal foil laminate 20B is laminated on the adhesive layer 18 with the insulating substrate 21 facing the adhesive layer 18. Subsequently, heat and pressure are applied using a vacuum pressing device or a vacuum laminating device. Through this heat treatment, the adhesive layer 18 is cured, resulting in… Figure 5B The stacked body shown in (2).

[0123] Next, as Figure 5C As shown in (1), metal foil 22 is irradiated with a laser. This removes metal foil 22, adhesive layer 21a, insulating substrate 21, and adhesive layer 18, forming a blind via H1B. The conductive pattern 17a (grounding wiring) is exposed on the bottom surface of blind via H1B. Similarly, metal foil 13 is irradiated with a laser. This removes metal foil 13, adhesive layer 11a, insulating substrate 11, and adhesive layer 16, forming a blind via H2B. The conductive pattern 17a is exposed on the bottom surface of blind via H2B. Alternatively, metal foils 22 and 13 can be pre-patterned, forming a conformal mask with openings at the locations where blind vias are formed. Using this conformal mask, blind vias H1B and H2B are formed.

[0124] The specific methods for forming blind holes H1B and H2B are the same as in the first and second embodiments. The conductive pattern 17a is embedded in an adhesive layer 18 having a filler content below a specified value. Therefore, residual film on the surface of the conductive pattern 17a can be removed by descaling after laser perforation. Similarly, the conductive pattern 17a is formed on an adhesive layer 16 having a filler content below a specified value. Therefore, residual film on the back side of the conductive pattern 17a can be removed by descaling after laser perforation.

[0125] Next, as Figure 5C As shown in (2), blind holes H1B are filled with conductive paste 31B using a printing method such as screen printing. Blind holes H2B are filled with conductive paste 32B. Conductive pastes 31B and 32B contain metal particles dispersed in a paste-like thermosetting resin, i.e., a resin binder. Conductive pastes 31B and 32B are the same conductive pastes as those in the first embodiment.

[0126] After filling conductive pastes 31B and 32B, the conductive pastes 31B and 32B are subjected to heat treatment. This causes the metal particles contained in the conductive pastes 31B and 32B to bond metallically with each other. Simultaneously, the thermosetting reaction of the adhesive resin in the conductive pastes 31B and 32B is completed. By doing so, as... Figure 5D As shown, filled vias 31Bc and 32Bc are formed as interlayer connection channels.

[0127] Next, as Figure 5D As shown, metal foils 13 and 22 are patterned using a known photolithography method to form conductive patterns 13a and 22a. The conductive patterns 13a and 22a include a ground layer electrically connected to the filled vias 31Bc and 32Bc.

[0128] Subsequently, as needed, surface treatment, surface protective film formation, and shape processing are performed on the exposed wiring layers.

[0129] After the above-mentioned processes, such as Figure 5D As shown, the multilayer printed wiring board 1B of the third embodiment is obtained.

[0130] According to the third embodiment, similarly to the first embodiment, the uniformity of the thickness of the multilayer printed wiring board 1B can be ensured, and the reliability of the interlayer connection channels can be ensured.

[0131] Furthermore, according to the third embodiment, even if the single-sided metal foil laminates 10B and 20B used are the same (i.e., the insulating substrates 11 and 21 have the same thickness), a multilayer printed wiring board with a structure that is substantially symmetrical in the thickness direction with the conductive pattern 17a (signal line) as the center can be obtained. As a result, a multilayer printed wiring board with excellent bending characteristics can be provided.

[0132] Furthermore, according to the third embodiment, a signal line with a conductive pattern 17a is sandwiched between two layers using an adhesive layer 16 and an adhesive layer 18 having a low filler content (i.e., a low dielectric constant). Therefore, improved high-speed signal transmission characteristics can be achieved.

[0133] Furthermore, according to the third embodiment, the conductive pattern 17a is made of low-roughness copper foil. Therefore, signal loss of high-speed signals can be reduced.

[0134] Furthermore, in the manufacturing method described above, filled vias containing cured conductive paste are formed as interlayer connection channels. However, this is not a limitation; plated vias can also be formed. In this case, a metal plating layer (e.g., a copper plating layer) is formed on the inner walls of the blind vias H1B and H2B. Thus, plated vias are formed that electrically connect the conductive pattern 17a to the metal foils 13 and 22.

[0135] <Tests on residual film and flame retardancy>

[0136] Figure 6 (1) is a cross-sectional view showing the structure of a test piece used to test whether residual film is generated during blind hole formation. The test piece includes an insulating substrate, a copper foil disposed on the insulating substrate, and a first adhesive layer and a second adhesive layer formed on the copper foil. A 25 μm thick polyimide film was used as the insulating substrate. The copper foil was 12 μm thick. The first adhesive layer and the second adhesive layer were formed using an adhesive mainly composed of a polyolefin-based heat-resistant resin. A filler containing aluminum phosphonate was used as the filler. In the test, the second adhesive layer was irradiated with laser pulses from a CO2 laser processing machine. After perforation, a resin residue removal process was performed. It was confirmed whether there was resin residue on the copper foil exposed at the bottom of the blind hole.

[0137] Figure 6 (2) is a cross-sectional view showing the structure of the test piece used to test the flame retardancy of printed wiring boards. According to the structure of the test piece, a first adhesive layer, a second adhesive layer, and a second insulating substrate are sequentially laminated on a first insulating substrate. Furthermore, a cover film (25 μm thick) is used to cover and protect the outer surfaces of the first and second insulating substrates. A 25 μm thick liquid crystal polymer film is used as both the first and second insulating substrates. The first adhesive layer and the second adhesive layer have a... Figure 6 (1) has the same composition. As a test, a 20mm flame vertical burning test (V test) based on the UL94 standard was conducted. Specifically, the residual flame time at one end of the test piece was measured after 10 seconds of contact with the flame.

[0138] Table 1 shows the results of tests on residual film and flame retardancy for Examples 1, 2, and Comparative Examples 1-4. The sum of the thickness of the first adhesive layer and the thickness of the second adhesive layer in any of Examples 1, 2, and Comparative Examples 1-4 is 25 μm.

[0139] Table 1

[0140]

[0141] According to the residual film test results, in Comparative Example 1, which used a test piece without a first adhesive layer, and Comparative Example 2, which used a first adhesive layer with a high filler content, residual film was observed on the copper foil even after desmearing treatment. On the other hand, in Examples 1 and 2, and Comparative Examples 3 and 4, which used low amounts (0 or 5% by weight) of flame retardant, no resin residue was observed. Based on these test results, it can be considered that when the filler content of the first adhesive layer is 5% by weight or less, resin residue formation on the bottom surface of blind holes can be suppressed.

[0142] Based on the flame retardancy test results, in Examples 1 and 2 and Comparative Examples 1 and 2, which used a second adhesive layer with a high filler content and a thickness of 20 μm or more, the residual flame time was less than 10 seconds. That is, the flame retardancy rating of V-0 was met. On the other hand, in Comparative Example 3, which used a second adhesive layer with a thickness of 15 μm, the residual flame time was about 10 seconds. In Comparative Example 4, which used a test piece without a second adhesive layer, the residual flame time was longer than 10 seconds. Based on these test results, it can be concluded that by providing a second adhesive layer with a filler content of 25% by weight or more and a thickness of 20 μm or more, the specified flame retardancy (V-0 rating) can be ensured even when a first adhesive layer with a low filler content is provided.

[0143] Based on the foregoing description, those skilled in the art will be able to conceive of additional effects or various modifications of the present invention. However, the present invention is not limited to the various embodiments described above. Constituent elements employed in different embodiments can be appropriately combined. Various additions, modifications, and partial deletions of constituent elements can be made without departing from the conceptual idea and spirit of the invention derived from the claims and their equivalents.

Claims

1. A method of manufacturing a multilayer printed wiring board, characterized by, The process includes the following steps: A conductive pattern is embedded in a dielectric layer using a first adhesive layer having a filler content below a specified value; and A second adhesive layer having a filler content greater than the specified value is used to laminate a layer of metal foil laminates or metal foils onto the first adhesive layer. The first adhesive layer and the second adhesive layer are thermosetting, and are cured by heat treatment. Using a laser, at least the second adhesive layer and the first adhesive layer are removed to form a blind hole exposing the conductive pattern on the bottom surface. The blind vias form interlayer connection channels that electrically connect the conductive pattern to the metal foil.

2. The method for manufacturing a multilayer printed wiring board according to claim 1, characterized in that, The first adhesive layer does not contain fillers.

3. The method for manufacturing a multilayer printed wiring board according to claim 1, characterized in that, The specified value for the filler content is 5% by weight.

4. The method for manufacturing a multilayer printed wiring board according to any one of claims 1 to 3, characterized in that, The second adhesive layer is thicker than the first adhesive layer.

5. The method for manufacturing a multilayer printed wiring board according to any one of claims 1 to 3, characterized in that, The filler is an inorganic filler with flame retardant properties.

6. The method for manufacturing a multilayer printed wiring board according to claim 1, characterized in that, The formation of the interlayer connection channel includes the following steps: Fill the blind holes with conductive paste; and The filled conductive paste is cured by heating, thereby forming a filled via that electrically connects the conductive pattern to the metal foil.

7. The method for manufacturing a multilayer printed wiring board according to claim 1, characterized in that, The formation of the interlayer connection channel includes the following steps: By forming a metal plating layer on the inner wall of the blind hole, a plated via is formed that electrically connects the conductive pattern to the metal foil.

8. The method for manufacturing a multilayer printed wiring board according to any one of claims 1 to 3, characterized in that, The formation of the interlayer connection channel further includes the following steps: electrically connecting the grounding wiring with the conductive pattern to the grounding layer, wherein the grounding layer is composed of the patterned metal foil.

9. A method for manufacturing a multilayer printed wiring board, characterized in that, The process includes the following steps: A double-sided metal foil laminate is prepared, the double-sided metal foil laminate comprising: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; a first metal foil disposed on the first main surface; and a second metal foil disposed on the second main surface; The first metal foil is patterned to form a conductive pattern; A first adhesive layer with a filler content below a specified value is formed on the first main surface by embedding the conductive pattern. A second adhesive layer having a filler content greater than the specified value is formed on the first adhesive layer; Prepare a single-sided metal foil laminate, the single-sided metal foil laminate comprising: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; and a third metal foil disposed on the third main surface; The single-sided metal foil laminate is stacked on the second adhesive layer in such a manner that the fourth main surface contacts the second adhesive layer; The first adhesive layer and the second adhesive layer are thermosetting, and are cured by heat treatment; Using a laser, at least the second adhesive layer and the first adhesive layer are removed to form a blind via, exposing the conductive pattern on the bottom surface of the blind via; and The blind vias form interlayer connection channels that electrically connect the conductive pattern to the metal foil.

10. A method for manufacturing a multilayer printed wiring board, characterized in that, The process includes the following steps: Prepare a first single-sided metal foil laminate, the first single-sided metal foil laminate comprising: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; and a first metal foil disposed on the first main surface. The first metal foil is patterned to form a conductive pattern; A first adhesive layer with a filler content below a specified value is formed on the first main surface by embedding the conductive pattern. A second adhesive layer having a filler content greater than the specified value is formed on the first adhesive layer; Prepare a second single-sided metal foil laminate, the second single-sided metal foil laminate comprising: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; and a second metal foil disposed on the third main surface; The second single-sided metal foil laminate is stacked on the second adhesive layer in such a manner that the fourth main surface contacts the second adhesive layer; A third adhesive layer having a filler content greater than the specified value is formed on the second main surface of the first insulating substrate; Prepare a third single-sided metal foil laminate, the third single-sided metal foil laminate comprising: a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface; and a third metal foil disposed on the sixth main surface; The third single-sided metal foil laminate is stacked on the third adhesive layer in such a manner that the fifth main surface contacts the third adhesive layer; and At least the second adhesive layer and the first adhesive layer are removed using a laser to form a blind hole, exposing the conductive pattern on the bottom surface of the blind hole.

11. A method for manufacturing a multilayer printed wiring board, characterized in that, The process includes the following steps: Prepare a first single-sided metal foil laminate, the first single-sided metal foil laminate comprising: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; and a first metal foil disposed on the second main surface of the first insulating substrate by a first adhesive layer having a filler content greater than a predetermined value. A second adhesive layer having a filler content below the specified value is formed on the first main surface of the first insulating substrate; A second metal foil is disposed on the second adhesive layer; The second metal foil is patterned to form a conductive pattern; A third adhesive layer with a filler content below the specified value is formed on the second adhesive layer by embedding the conductive pattern. Prepare a second single-sided metal foil laminate, the second single-sided metal foil laminate comprising: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; and a third metal foil disposed on the third main surface of the second insulating substrate by a fourth adhesive layer having a filler content greater than the specified value. The second single-sided metal foil laminate is stacked on the third adhesive layer in such a manner that the fourth main surface contacts the third adhesive layer; and At least the fourth adhesive layer, the second insulating substrate, and the third adhesive layer are removed using a laser to form a blind hole, exposing the conductive pattern on the bottom surface of the blind hole.

12. A multilayer printed wiring board, characterized in that, include: A dielectric layer having a first main surface and a second main surface opposite to the first main surface; A conductive pattern is disposed on the first main surface of the dielectric layer; A thermosetting first adhesive layer is disposed on the dielectric layer in such a way as to embed the conductive pattern, and has a filler content below a specified value; A thermosetting second adhesive layer, disposed on the first adhesive layer, has a filler content greater than the specified value; The laminate is composed of a metal foil laminate or metal foil stacked on the second adhesive layer; and Interlayer connection channels electrically connect the conductive pattern and the metal foil through blind holes extending from the metal foil to the first adhesive layer.

13. The multilayer printed wiring board according to claim 12, characterized in that, The interlayer connection channel electrically connects the grounding wiring with the conductive pattern to the grounding layer, which is composed of the patterned metal foil.

14. The multilayer printed wiring board according to claim 12 or 13, characterized in that, The multilayer printed wiring board further includes a stack, which is composed of a metal foil stack or metal foil laminated on the second main surface of the dielectric layer by an adhesive layer.

15. The multilayer printed wiring board according to claim 12 or 13, characterized in that, The first adhesive layer has a filler content of less than 5% by weight.

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