Multi-layer wiring board

Abstract

To provide a multilayer wiring board with a cavity that has a stable depth to the required depth even under conditions where electrical detection is not required and electrical detection is not possible because there is no wiring at the bottom of the cavity, in a multilayer wiring board where the cavity is formed after the board is formed to the multilayer wiring board or in an intermediate process.SOLUTION: A multilayer wiring board has cavities, and the bottom of the cavity is an insulating layer with a low modulus of elasticity α and the sidewalls of the cavity are insulating layers with a high modulus of elasticity β.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer wiring board having a cavity.

Background Art

[0002] Due to the demand for higher density, the multilayerization of wiring boards has progressed, and a multilayer wiring board provided with a "cavity" as a storage location for electronic components such as semiconductor elements has been manufactured. Methods for forming the "cavity" in the multilayer wiring board include a method of laminating the substrate so that through holes are formed in a portion where the "cavity" is to be formed in advance, and a method of forming the "cavity" in the laminated multilayer wiring board by cutting or the like later.

[0003] The method of forming the "cavity" later is obtained, for example, by drilling the cavity portion from one surface side of the multilayer wiring board with an NC machining tool. In this case, the depth of the machining tool tip must be precisely controlled so that the height indicated by the wiring formed at the bottom of the cavity is left as much as possible. However, due to the accuracy of the NC machining tool, the cumulative error due to continuous machining during production, the variation in the thickness of the multilayer wiring board, etc., it has been difficult to keep the height of the wiring formed at the bottom of the cavity constant. Therefore, Patent Document 1 discloses a technique for electrically detecting the machining depth by the contact between the wiring pattern formed at the bottom of the cavity of the multilayer wiring board and the machining tool.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of such a situation, the present invention provides a multilayer wiring board in which a cavity is formed after substrate formation or in an intermediate process on the multilayer wiring board, eliminating the need for electrical detection. Even under conditions where there is no wiring at the bottom of the cavity and electrical detection is impossible, the present invention aims to provide a multilayer wiring board having a cavity with a stable depth up to the required depth.

Means for Solving the Problems

[0006] A first aspect of the present invention is a multilayer wiring board having a cavity, wherein the bottom of the cavity is an insulating layer with a modulus of elasticity α , where the elastic modulus α is 5 GPa or less and the side wall portion of the cavity is an insulating layer having a modulus of elasticity β greater than the modulus of elasticity α. and the difference between the elastic modulus β and the elastic modulus α is 2.3 GPa or more The multilayer wiring board is characterized by this.

[0007] A second aspect of the present invention is a multilayer wiring board characterized in that the bottom and side wall portions of the cavity in the first aspect have a blasted surface.

Effects of the Invention

[0008] According to the present invention, even in a multilayer wiring board in which a cavity is formed later, a multilayer wiring board with a stable processing depth of the cavity can be obtained, and it has a remarkable industrial effect.

Brief Description of the Drawings

[0009] [Figure 1] It is a cross-sectional view schematically showing the cavity portion of the multilayer wiring board of the present invention. [Figure 2] It is a cross-sectional view schematically showing the cavity portion of a conventional multilayer wiring board. [Figure 3] It is a diagram showing the flow of manufacturing the multilayer wiring board of the present invention.

Embodiments for Carrying Out the Invention

[0010] Embodiments of the present invention and conventional embodiments will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing an embodiment according to the present invention, and FIG. 2 is a diagram showing a conventional embodiment. In FIGS. 1 and 2, 1 and 100 are multilayer wiring boards (3-layer wiring boards). Although the description is made using a 3-layer wiring board, the same cavities are provided in multilayer wiring boards having more than 3 layers.

[0011] First, a conventional multilayer wiring board having a "cavity" will be described with reference to FIG. 2. The conventional multilayer wiring board B is formed by laminating substrates that are insulating layers having the same elastic modulus. Through-hole processing and necessary processing are performed on each of the laminated substrates using an NC processing machine, and substrates having the required number of layers are laminated to form a multilayer wiring board. Then, a cavity is formed by performing counterboring using an NC processing machine at a position where a cavity is required.

[0012] As shown in FIG. 2, a cavity 100 having a side wall portion 210, a bottom portion 110, and wiring 300 as required is formed by counterboring. The surface of the bottom portion 110 of the cavity 100 has the same height as the insulating layer 430, which is the insulating layer 420 constituting the side wall portion 210, and the wiring 300 formed on the substrate of the insulating layer 410. And, as described above, it is difficult to keep the height of the wiring 300 formed on the bottom portion 110 of the cavity constant due to the accuracy of the NC processing machine, the cumulative error due to continuous processing during production, the variation in the thickness of the multilayer wiring board, and the like.

[0013] Regarding such a conventional multilayer wiring board having a cavity and its manufacturing method, the inventors of the present invention found the key to solving the problem in the relationship between the elastic modulus of the insulating layer and the processing depth by blasting, because the processing time of blasting varies depending on the type of substrate, and conducted intensive research and investigation, thus arriving at the present invention.

[0014] Therefore, the inventors of the present invention prepared 5 types of insulating layers having different elastic moduli as test materials (in the present application, the "flexural elastic modulus" in the manufacturer's catalog is described as the "elastic modulus"). Next, a resist mask having openings of the same size was formed on one side of those five types of test materials, and they were subjected to blasting under the same conditions to measure the processing depth. In the blasting process, the same portion was processed from one time to four times using one type of condition (abrasive grains, discharge amount, feed rate, etc.), and the processing depth was measured with a microscope (manufactured by HYLUX: RH-2000). The results are shown in Table 1.

[0015]

Table 1

[0016] It can be seen from Table 1 that even when the same blasting process is performed, the processing depth varies due to the difference in elastic modulus. Also, in a multilayer wiring board in which the insulating layer 2 is laminated on the insulating layer 1, since the insulating layer 1 is polished at a slow rate by the blasting process, if there is a difference in elastic modulus of 2.3 GPa or more, a cavity having a low-elasticity insulating layer at the bottom can be formed by the blasting process. Furthermore, since the insulating layer 1 and the insulating layer 2 having an elastic modulus of 5 GPa or less have an average depth of 10 μm or less per time, when a cavity having an insulating layer of 5 GPa or less at the bottom and a substrate having an insulating layer with a higher elastic modulus laminated thereon with the higher-elastic modulus insulating layer as the side wall portion is manufactured, it is considered that a multilayer wiring board having a cavity with a stable depth can be obtained.

[0017] Next, based on the above findings, an application to a multilayer wiring board was carried out. An embodiment of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, a three-layer wiring board A according to an embodiment of the multilayer wiring board of the present invention will be used for the description. It has an insulating layer 10 with an elastic modulus α (hereinafter also referred to as "insulating layer 10 with a low elastic modulus α") and an insulating layer 20 with an elastic modulus β larger than the elastic modulus α (hereinafter also referred to as "insulating layer 20 with a high elastic modulus β"). As shown in FIG. 1, the bottom 11 of the cavity 1 is formed of the insulating layer 10 with a low elastic modulus α, and the side wall portion 21 of the cavity 1 is formed of the insulating layer 20 with a high elastic modulus β.

[0018] The substrate of the insulating layer 10 with a low elastic modulus α that constitutes the bottom of this cavity may have a configuration in which a substrate of an insulating layer with any elastic modulus is laminated thereunder. Further, the insulating layer 20 with a high elastic modulus β that constitutes the cavity side wall portion 21 may be an insulating layer in which a plurality of substrates are laminated.

[0019] Next, the manufacturing flow of the multilayer wiring board of the present invention is shown in FIG. 3 using a three-layer wiring board as an example. FIG. 3(1) shows a substrate a in which necessary wirings 30 and the like are formed on the insulating layer 10 with a low elastic modulus α that becomes the bottom of the cavity. Next, as shown in FIG. 3(2), an insulating layer 20 with a high elastic modulus β and a copper foil are laminated on this substrate a, and necessary wirings 30 and the like are formed. Then, as shown in FIG. 3(3), a resist mask 40 for blasting is formed on the surface of the formed wiring 30 and the like and the insulating layer 20 with a high elastic modulus β. Thereafter, as shown in FIG. 3(4), blasting is performed. By this blasting, as shown in FIG. 3(5), a cavity is formed in which the insulating layer 10 with a low elastic modulus α becomes the bottom and the insulating layer 20 with a high elastic modulus β becomes the side wall portion. Then, as shown in FIG. 3(6), by removing the resist mask 40 for blasting, a multilayer wiring board A provided with a cavity 1 can be obtained.

[0020] In this way, a multilayer wiring board provided with a cavity having a stable dimension in the depth direction can be obtained. Although FIG. 3 shows the features of the present invention in a three-layer wiring board, a cavity having a stable dimension in the depth direction can similarly be provided in a more multilayered wiring board.

Example

[0021] Hereinafter, the present invention will be described in detail with reference to examples.

Example

[0022] A six-layer wiring board, which is a multilayer wiring board according to an embodiment of the present invention, was fabricated and evaluated by the following process flow.

[0023] First, a core board was fabricated by performing through-hole processing, hole filling processing, wiring processing, etc. on a substrate material having copper layers on both sides of an insulating layer made of glass epoxy. Next, on both the front and back surfaces of the core board, an epoxy-based thermosetting resin with an elastic modulus of 2.7 GPa and a copper foil were combined as an insulating layer with a low elastic modulus α, and heat pressure bonding was performed to fabricate a laminated substrate. Via processing, hole filling processing, wiring processing, etc. were performed on the laminated substrate to fabricate a four-layer board.

[0024] Next, on both the front and back surfaces of the four-layer board, a thermosetting resin with an elastic modulus of 35 GPa and a copper foil were combined as an insulating layer 20 with an elastic modulus β higher than the elastic modulus α of the insulating layer 10, and heat pressure bonding was performed for lamination. Then, through-hole processing, copper plating processing in the holes, wiring processing, etc. were performed to fabricate a six-layer board. Next, a resist mask for blasting with an opening in the cavity portion was formed on the surface side of the six-layer board. As a result of performing blasting from the surface side of the six-layer board, a cavity with an insulating layer having a low elastic modulus α at the bottom and an insulating layer 20 having a high elastic modulus β at the side wall portion was formed.

[0025] In this way, a multilayer wiring board was fabricated by using a substrate with an insulating layer having a low elastic modulus for the substrate that becomes the bottom of the cavity, and using a substrate with an insulating layer having a high elastic modulus for the substrate laminated thereon. A resist mask having a predetermined opening was formed on the surface of the multilayer wiring board, and blasting was performed under predetermined conditions to form a cavity portion. As a result, it was confirmed that a cavity with a certain depth having an insulating layer with a low elastic modulus at the bottom was formed in the fabricated multilayer wiring board.

Explanation of Reference Numerals

[0026] 1, 100 Cavity 10 Insulating layer with elastic modulus α 11 Cavity bottom 20 Insulating layer with elastic modulus β (β > α) 21, 210 Cavity side wall portion 30 and 300 wirings 40 resist masks for blasting Bottom of the cavity of the conventional process 110 410 and 420 insulating layers (regardless of elastic modulus) Insulating layer at the bottom of the cavity 430 A Multilayer wiring board (3-layer wiring board) of the example of the present invention B Multilayer wiring board (3-layer wiring board) of the conventional example a Substrate

Claims

1. A multilayer wiring board having a cavity, wherein a bottom portion of the cavity is an insulating layer having a modulus of elasticity α, and the modulus of elasticity α is 5 GPa or less, a side wall portion of the cavity is an insulating layer having a modulus of elasticity β greater than the modulus of elasticity α, and a difference between the modulus of elasticity β and the modulus of elasticity α is 2.3 GPa or more. A multilayer wiring board characterized by this.

2. The multilayer wiring board according to claim 1, wherein a bottom portion and a side wall portion of the cavity are provided with a blasted surface.

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