Wiring Board

Abstract

The wiring substrate according to the present disclosure includes: a first insulation layer in which a first insulation filler is dispersed; and a second insulation layer positioned on the top surface of the first insulation layer. The first insulation layer contains: a protrusion filler, of the first insulation filler, positioned so as to protrude from the top surface of the first insulation layer; and a film covering a part or all of the protruding surface of the protrusion filler. The film has a structure in which a tin layer and a silane coupling agent layer are layered in this order. The second insulation layer covers the top surface of the first insulation layer including the film.

Description

[Technical field]

[0001] The present disclosure relates to a wiring board. [Background technology]

[0002] Conventionally, insulating resin layers (core layers and build-up insulating layers) included in wiring boards are filled with insulating fillers such as silica fillers for the purpose of lowering the thermal expansion coefficient and increasing density, as described in Patent Document 1, for example. In recent years, the filling rate of this insulating filler has been increasing, and as the filling rate of the insulating filler increases, more insulating filler is exposed from the surface of the insulating resin layer. As a result, the adhesion between the insulating filler and the insulating resin at the interface between the insulating resin layers becomes poor, which affects the insulation reliability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-164305 A Summary of the Invention [Means for solving the problem]

[0004] The wiring board according to the present disclosure includes a first insulating layer in which first insulating fillers are dispersed, and a second insulating layer located on the upper surface of the first insulating layer. The first insulating layer includes protruding fillers located so as to protrude from the upper surface of the first insulating layer, and a coating that covers a part or all of the protruding surface of the protruding fillers. The coating has a structure in which a tin layer and a silane coupling agent layer are laminated in this order. The second insulating layer covers the upper surface of the first insulating layer including the coating. [Brief description of the drawings]

[0005] [Figure 1] 1 is an enlarged explanatory view showing a main part of a wiring board according to an embodiment of the present disclosure; [Diagram 2]2 is an explanatory diagram showing a state in which the first insulating layer and the second insulating layer in FIG. 1 are separated. FIG. [Diagram 3] 1 is an electron microscope photograph showing a main portion of a wiring board according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] As described above, when the filling rate of the insulating filler is high, the insulating filler is exposed from the surface of the insulating resin layer in a large amount. As a result, the adhesion between the insulating filler and the insulating resin at the interface between the insulating resin layers is poor, which affects the insulation reliability. Therefore, there is a demand for a wiring board in which the insulating resin layer laminated on the surface of the insulating resin layer in which the insulating filler is dispersed has excellent adhesion and excellent insulation reliability.

[0007] According to the wiring board of the present disclosure, as described above, there is a specific coating that covers a part of the protruding surface of the protruding filler located so as to protrude from the upper surface of the first insulating layer. Due to the presence of such a specific coating, the wiring board of the present disclosure has excellent adhesion of the insulating resin layer laminated on the surface of the insulating resin layer in which the insulating filler is dispersed, and excellent insulation reliability.

[0008] A wiring board according to an embodiment of the present disclosure will be described with reference to Figs. 1 to 3. Fig. 1 is an enlarged explanatory view showing a main part of the wiring board according to an embodiment of the present disclosure. As shown in Fig. 1, the wiring board according to the embodiment includes a first insulating layer 1 and a second insulating layer 2. Although not shown, a conductor layer such as a wiring conductor layer made of a metal such as copper is present in a part between the first insulating layer 1 and the second insulating layer 2.

[0009] As shown in FIG. 1, the first insulating layer 1 has a structure in which the first insulating filler 12 is dispersed in the first insulating resin 11. The first insulating resin 11 is not limited as long as it is made of a material having insulating properties. Examples of the material having insulating properties include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, polyphenylene ether resin, and liquid crystal polymer. The first insulating resin 11 may be used alone or in combination of two or more kinds. The first insulating layer 1 may be a core substrate having insulating properties of a wiring board. The core substrate may or may not have glass fibers. The thickness of the first insulating layer 1 is not particularly limited, and is, for example, 10 μm or more and 20 mm or less in the case of a core substrate, and 2 μm or more and 100 μm or less in the case of an insulating layer for lamination.

[0010] The first insulating filler 12 dispersed in the first insulating resin 11 has the function of reducing the thermal expansion coefficient of the first insulating layer 1. The first insulating filler 12 is not limited, and examples thereof include inorganic insulating fillers such as silica, alumina, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Filler 12 may be used alone or in combination of two or more.

[0011] The average particle diameter of the first insulating filler 12 is not limited. In order to increase the filling rate of the first insulating filler 12, it is preferable that there are multiple types of average particle diameters. The first insulating filler 12 may have an average particle diameter of, for example, 0.1 μm or more and 1 μm or less. The filling rate of the first insulating filler 12 in the first insulating layer 1 is not limited. In order to sufficiently reduce the thermal expansion coefficient of the first insulating layer 1, the filling rate of the first insulating filler 12 in the first insulating layer 1 may be 50 mass % or more and 90 mass % or less. The average particle diameter may be measured, for example, by X-ray CT analysis. The filling rate may be detected by energy dispersive X-ray analysis.

[0012] The first insulating filler 12 has a first insulating layer 1The wiring board includes protruding fillers 121 positioned so as to protrude from the upper surface of the wiring board. A part of the protruding surface of the protruding fillers 121 is covered with a coating 13 as shown in Figures 2 and 3. Figure 2 is an explanatory diagram showing a state in which the first insulating layer 1 and the second insulating layer 2 are separated from each other in Figure 1. Figure 3 is an electron microscope photograph showing a main part of a wiring board according to one embodiment. The coating 13 may cover the entire protruding surface of the protruding fillers 121.

[0013] Coating 13 has a structure in which a tin layer and a silane coupling agent layer are laminated in this order from the surface of protruding filler 121. The presence of such coating 13 can improve the adhesion of second insulating layer 2 laminated on the surface of first insulating layer 1, and can improve the insulation reliability of the resulting wiring board according to one embodiment.

[0014] The tin layer has a function of stably depositing the silane coupling agent layer on the surface of the protruding filler 121, and contains tin and tin oxide. When tin is oxidized, the insulation resistance increases, and therefore, for example, the insulation reliability between adjacent wiring conductors can be improved compared to when tin is not oxidized. The thickness of the tin layer is not limited. The tin layer has a thickness of, for example, 2 nm or more and 5 nm or less. When the tin layer is present, for example, tin and tin oxide are detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) described later. The thickness of the tin layer can be measured by observation with a transmission electron microscope.

[0015] The silane coupling agent layer is positioned so as to cover the tin layer. The silane coupling agent is a compound having a functional group that reacts with an inorganic material and a functional group that reacts with an organic material in the molecule. Therefore, for example, the silane coupling agent layer has a molecular structure with a functional group that reacts with the protruding filler 121, which is an inorganic material, and the conductor layer and a functional group that reacts with the second insulating layer 2, which is an organic material, and is connected, thereby improving the adhesion (adhesion) between the first insulating filler 12 and the second insulating resin 21 contained in the second insulating layer 2. The thickness of the silane coupling agent layer is not limited. The silane coupling agent layer has a thickness of, for example, 15 nm or less, and may be thicker than the tin layer.

[0016] The presence or absence of a silane coupling agent layer can be confirmed, for example, by performing mass analysis using time-of-flight secondary ion mass spectrometry (TOF-SIMS) or analyzing the above-mentioned functional group structure using Fourier transform infrared spectroscopy (FTIR). TOF-SIMS is a surface analysis method for qualitatively analyzing elements and molecules present on the very surface. Specifically, when a focused ion beam is irradiated onto a solid sample in an ultra-high vacuum, neutral particles and secondary ions are released into the vacuum due to the sputtering phenomenon. The constituent elements of the sample surface are analyzed by precisely measuring the flight time of these secondary ions until they reach a detector. If a silane coupling agent layer is present, for example, polydimethylsiloxane is detected by TOF-SIMS.

[0017] Coating 13 may not only cover a portion of the protruding surface of protruding filler 121, but may also be located on a portion of the top surface of first insulating layer 1 other than protruding filler 121, as shown in Fig. 2. In this way, coating 13 is located on a portion other than protruding filler 121, thereby making it possible to further improve the adhesion of second insulating layer 2 laminated on the surface of first insulating layer 1.

[0018] There are no limitations on the proportion of the upper surface of the first insulating layer 1 that is occupied by the coating 13. When viewed from above, the proportion of the upper surface of the first insulating layer 1 that is occupied by the coating 13 may be, for example, 40% or more and 80% or less. If the proportion of the coating 13 is 40% or more and 80% or less, excellent adhesion can be exhibited while maintaining excellent insulation reliability.

[0019] The second insulating layer 2 is located on the upper surface of the first insulating layer 1. As shown in FIG. 1, the second insulating layer 2 has a structure in which the second insulating filler 22 is dispersed in the second insulating resin 21. The second insulating resin 21 is not particularly limited as long as it is made of a material having insulating properties, similar to the first insulating resin 11. Examples of the material having insulating properties include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, polyphenylene ether resin, and liquid crystal polymer. The second insulating resin 21 may be the same resin as the first insulating resin 11, or may be a different resin. The second insulating resin 21 may be used alone or in combination of two or more kinds. The thickness of the second insulating layer 2 is not particularly limited, and is, for example, 2 μm or more and 100 μm or less.

[0020] The second insulating filler 22 dispersed in the second insulating resin 21 has a function of reducing the thermal expansion coefficient of the second insulating layer 2. The second insulating filler 22 is not limited, and like the first insulating filler 12, examples of the second insulating filler include inorganic insulating fillers such as silica, alumina, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. The second insulating filler 22 may be the same insulating filler as the first insulating filler 12, or may be a different insulating filler. The second insulating filler 22 may be used alone or in combination of two or more types.

[0021] The average particle diameter of the second insulating filler 22 is not limited. In order to increase the filling rate of the second insulating filler 22, it is preferable that there are multiple types of average particle diameters. The second insulating filler 22 may have an average particle diameter of, for example, 0.1 μm or more and 1 μm or less. The filling rate of the second insulating filler 22 in the second insulating layer 2 is not limited. In order to sufficiently reduce the thermal expansion coefficient of the second insulating layer 2, the filling rate of the second insulating filler 22 in the second insulating layer 2 may be 50 mass % or more and 90 mass % or less. The method of calculating the average particle diameter and the filling rate is as described above.

[0022] In the wiring board according to one embodiment, the method for forming the coating 13 on the surface of the first insulating layer 1 is not limited, and for example, the coating 13 can be formed by the following procedure. First, a resin film made of a first insulating resin 11 having a first insulating filler 12 dispersed therein is prepared. This resin film (resin plate) becomes the precursor of the first insulating layer 1. Below, a case where the first insulating layer 1 is a core layer will be described.

[0023] Next, a through hole is formed in the resin film as necessary. The through hole is formed, for example, by drilling, blasting or laser processing. When the first insulating layer 1 is a build-up insulating layer, a via hole is formed instead of a through hole. Next, a desmear process is performed, and a seed layer is formed of a metal such as copper by electroless plating on the surface of the resin film and the inner wall surface of the through hole. Next, a resist is formed on the surface of the resin film, and exposure and development are performed. Next, a metal such as copper is formed on the surface of the resin film of the through hole and the inner wall surface of the through hole by electrolytic plating. After that, the resist is peeled off, and the seed layer is also removed.

[0024] Next, metal oxide films such as copper oxide films are removed by acid washing, and then tin is deposited by tin plating to a thickness of about 100 nm on the surfaces of the protruding fillers 121 protruding from the upper surface of the resin film and on the portions other than the protruding fillers 121.

[0025] Next, the excessively precipitated tin is removed by etching using, for example, nitric acid. By performing etching in this manner, the thickness of the tin is adjusted to about 2 nm to 5 nm. Since the amount of tin precipitated on the copper is greater than that on the protruding filler 121, the thickness is adjusted to about 10 nm to 20 nm by etching with nitric acid. In order to adjust 100 nm of tin to about 2 nm to 5 nm, it is sufficient to immerse the substrate in nitric acid for about 2 seconds to 90 seconds. The thickness of the tin layer can be adjusted by the time of immersion in nitric acid.

[0026] Next, a silane coupling agent is applied so as to cover the formed tin layer. Examples of the silane coupling agent include FC-9100Z (manufactured by MEC Co., Ltd.), KBM-303 (manufactured by Shin-Etsu Chemical Co., Ltd.), and DOWSIL TM Commercially available products such as Z-6040 Silane (manufactured by Dow Toray Co., Ltd.) can be used. After applying the silane coupling agent, a silane coupling agent layer is formed on the surface of the tin layer by treating at a temperature of 70°C to 100°C for 1 minute to 10 minutes. As described above, the silane coupling agent layer has a thickness of 15 nm or less and may be thicker than the tin layer. The thickness of the silane coupling agent layer can be adjusted by the heating temperature or heating time.

[0027] In this way, a wiring board having excellent adhesion between insulating layers can be manufactured. The bonding between insulating layers may be between a core layer and a build-up insulating layer, or between build-up insulating layers. In this specification, the terms "first insulating layer" and "second insulating layer" are used for convenience, and are not limited to the case where the "first insulating layer" is a core layer. For example, both the "first insulating layer" and the "second insulating layer" may be a build-up insulating layer.

[0028] 1 is an enlarged explanatory view showing a main part of the wiring board 1 according to one embodiment, and therefore only two insulating layers are shown. However, the wiring board of the present disclosure may have a structure in which three or more insulating layers are stacked. In the case where the wiring board has a structure in which three or more insulating layers are stacked, the insulating layer located at the bottom of two adjacent insulating layers may be regarded as the "first insulating layer" and the insulating layer located at the top may be regarded as the "second insulating layer."

[0029] In the wiring board 1 according to the embodiment described above, the second insulating layer 2 has the second insulating filler 22 dispersed therein. However, in the wiring board according to the present disclosure, 2 The insulating filler may be absent.

[0030] Furthermore, in the wiring board 1 according to the embodiment described above, the coating 13 is located also on a part of the upper surface of the first insulating layer 1 other than the protruding filler 121. However, in the wiring board according to the present disclosure, the coating may only cover a part of the protruding surface of the protruding filler 121. [Explanation of symbols]

[0031] 1 First insulating layer 11 First insulating resin 12 First insulating filler 121 Protruding Filler 13 Coating 2 Second insulating layer 21 Second insulating resin 22 Second insulating filler

Claims

1. a first insulating layer having a first insulating filler dispersed therein; a second insulating layer located on an upper surface of the first insulating layer; Including, the first insulating layer includes protruding fillers among the first insulating fillers, the protruding fillers being positioned so as to protrude from an upper surface of the first insulating layer, and a coating that covers a part or all of the protruding surface of the protruding fillers, the coating has a structure in which a tin layer and a silane coupling agent layer are laminated in this order from the surface of the protruding filler, The second insulating layer covers an upper surface of the first insulating layer including the coating. Wiring board.

2. The wiring board according to claim 1 , wherein the coating is located on a part of the upper surface of the first insulating layer other than the protruding filler.

3. The wiring board according to claim 1 , wherein a second insulating filler is dispersed in the second insulating layer.

4. 3 . The wiring board according to claim 1 , wherein, in a plan view, a proportion of the top surface of the first insulating layer that is occupied by the coating is not less than 40% and not more than 80%.

5. The wiring board according to claim 1 , wherein the first insulating filler has an average particle size of 0.1 μm or more and 1 μm or less.

6. 3 . The wiring board according to claim 1 , wherein a filling rate of the first insulating filler in the first insulating layer is 50% by mass or more and 90% by mass or less.

7. The wiring board according to claim 1 , wherein the tin layer has a thickness of 2 nm or more and 5 nm or less.

8. The wiring board according to claim 1 , wherein the tin layer is oxidized.

9. The wiring board according to claim 1 , wherein the silane coupling agent layer has a thickness of 15 nm or less and is thicker than the tin layer.

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