Multilayer wiring board

Abstract

To provide a multilayer wiring board with the feature that the wiring formed in the bottom of the cavity of the multilayer wiring board protrudes higher than the insulating layer at the bottom of the board.SOLUTION: A multilayer wiring board is a multilayer wiring board with cavities in which an insulating layer with modulus α is the bottom of the cavity and an insulating layer with modulus β greater than said modulus α is the sidewall of the cavity, and the difference in modulus between the insulating layer at the bottom of the cavity and the insulating layer at the sidewall of the cavity is 2.3 GPa or greater and the wiring in the bottom of the cavity protrudes from the surface of the bottom of the cavity comprising the insulating layer with the elastic modulus α.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In a multilayer wiring board having a cavity for mounting an electronic component, the cavity for mounting a semiconductor element or the like is formed by countersinking the cavity portion from one surface side with an NC processing machine. When performing countersinking, the depth of the tip of the processing tool must be controlled with high precision so that the maximum thickness of the wiring formed at the bottom of the cavity is left. However, it was difficult to maintain a constant thickness of the wiring formed at the bottom of the cavity due to factors such as the accuracy of the NC processing machine, accumulated errors due to continuous processing in production, and variations in the thickness of the layer wiring board.

[0003] Therefore, for example, Patent Document 1 discloses a technique for electrically detecting the machining depth by contacting a pattern formed on an inner layer of a multilayer wiring board with a machining tool. In conventional processing including the technique disclosed in Patent Document 1, after the cavity is formed, the wiring surface at the bottom of the cavity and the insulating layer surface are formed to be at the same height.

[0004] However, the wiring formed on the surface of a multilayer wiring board protrudes higher than the surface insulating layer, and there is a problem in that the bonding conditions are different when mounting a semiconductor element on the wiring on the surface of this multilayer wiring board and when mounting a semiconductor element on the wiring at the bottom of the cavity. For example, the wiring on the surface of a multilayer wiring board is joined with solder covering the surface and sides of the wiring, but the wiring at the bottom of the cavity is joined with solder only on the surface of the wiring, resulting in a lower joint strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-022643 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, the present invention provides a multilayer wiring board characterized in that wiring formed at the bottom of a cavity of the multilayer wiring board protrudes higher than the insulating layer at the bottom. [Means for solving the problem]

[0007] A first aspect of the present invention is a multilayer wiring board having a cavity in which an insulating layer having an elastic modulus α serves as the bottom of the cavity and an insulating layer having an elastic modulus β greater than the elastic modulus α serves as the side wall of the cavity, wherein wiring provided at the bottom of the cavity protrudes from the surface of the insulating layer constituting the bottom of the cavity.

[0008] A second aspect of the present invention is the multilayer wiring board according to the first aspect, characterized in that the difference in elastic modulus between the elastic modulus β and the elastic modulus α is 2.3 GPa or more.

[0009] A third aspect of the present invention is the multilayer wiring board according to the first and second aspects, characterized in that the bottom and sidewall of the cavity have blasted surfaces. Effect of the Invention

[0010] According to the present invention, a multilayer wiring board can be obtained in which the wiring formed at the bottom of the cavity protrudes from the surface of the insulating layer at the bottom of the cavity, thereby achieving an industrially significant effect of increasing the reliability of the wiring and the mounted elements joined to the wiring. [Brief description of the drawings]

[0011] [Figure 1] 2 is a cross-sectional view showing a schematic view of a cavity portion of the multilayer wiring board of the present invention. [Diagram 2]FIG. 11 is a cross-sectional view that illustrates a cavity portion of a conventional multilayer wiring board. [Diagram 3] 1 is a diagram showing a flow for manufacturing a multilayer wiring board according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An embodiment of the present invention and a conventional embodiment will be described with reference to Figs. FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional embodiment. In Figures 1 and 2, A and B are multilayer wiring boards (three-layer wiring boards). Although a three-layer wiring board has been used in the description, a multi-layer wiring board having more than three layers also has a similar cavity.

[0013] First, a conventional multilayer wiring board having a "cavity" will be described with reference to FIG. Conventional multilayer wiring board B is made by stacking substrates with insulating layers having the same elastic modulus. An NC machining machine is used to perform through-hole drilling and other necessary processing on each of the substrates to be stacked. After the required number of substrates are stacked to form a multilayer wiring board, cavities are formed by using an NC machining machine to perform countersinking processing in the positions where cavities are required.

[0014] 2, a cavity 100 including a sidewall 210, a bottom 110, and, if necessary, wiring 300 is formed by spot boring. The surface of the bottom 110 of the cavity 100 has the same height as the insulating layer 430, which is the insulating layer 420 constituting the sidewall 210, and the wiring 300 formed on the substrate of the insulating layer 410. Furthermore, as mentioned above, it is difficult to maintain a constant height for the wiring 300 formed on the bottom 110 of the cavity due to factors such as the accuracy of the NC machining machine, accumulated errors due to continuous processing during production, and variations in the thickness of the multilayer wiring board.

[0015] In contrast to such conventional multilayer wiring boards with cavities and their manufacturing methods, the inventors developed the idea for the present invention by finding the key to solving the problem in the relationship between the elastic modulus of the insulating layer and the processing depth by blasting, since the processing time for blasting differs depending on the type of board. Through extensive research and investigation, they arrived at the present invention.

[0016] Therefore, the present inventors prepared five types of insulating layers with different elastic moduli as test materials (in this application, the "flexural modulus" in the manufacturer's catalog is referred to as "elastic modulus"). Next, a resist mask with an opening of the same size was formed on one side of each of the five types of test materials, and the blast processing was carried out under the same conditions to measure the processing depth. The blasting process was carried out using one set of conditions (abrasive grains, discharge amount, feed speed, etc.) and the same part was processed one to four times, and the processing depth was measured with a microscope (Hirox: RH-2000). The results are shown in Table 1.

[0017] [Table 1]

[0018] From Table 1, it can be seen that even if the same blasting process is performed, the processing depth differs depending on the elastic modulus. Furthermore, even in a multilayer wiring board in which insulating layer 2 is laminated on insulating layer 1, the rate at which insulating layer 1 is polished by blasting is slow. Therefore, if the difference in elastic modulus is 2.3 GPa or more, a cavity with the insulating layer with a low elastic modulus at its bottom can be created by blasting. Furthermore, since insulating layers 1 and 2, which have an elastic modulus of 5 GPa or less, have an average depth of 10 μm or less per cycle, it is believed that a multilayer wiring board with a cavity of stable depth can be obtained by using an insulating layer of 5 GPa or less as the bottom of the cavity and laminating a substrate with an insulating layer having a higher elastic modulus to fabricate a cavity with the insulating layer of higher elasticity as the sidewall.

[0019] Next, based on the above findings, we applied this to a multilayer wiring board. An embodiment of the present invention will be described with reference to FIG. 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 explanation. It has an insulating layer 10 with an elastic modulus α (hereinafter also referred to as "insulating layer 10 with low elastic modulus α") and an insulating layer 20 with an elastic modulus β greater than the elastic modulus α (hereinafter also referred to as "insulating layer 20 with high elastic modulus β"). As shown in FIG. 1, the bottom 11 of the cavity 1 is formed of the insulating layer 10 with the low elastic modulus α, and the side wall 21 of the cavity 1 is formed of the insulating layer 20 with the high elastic modulus β.

[0020] The insulating layer 10 having a low elastic modulus α constituting the bottom of the cavity may have an insulating layer having an elastic modulus that is not important laminated thereunder. Also, the insulating layer 20 having a high elastic modulus β constituting the cavity sidewall 21 may be an insulating layer having a plurality of laminated substrates.

[0021] Next, the manufacturing flow of the multilayer wiring board of the present invention is shown in FIG. 3, taking a three-layer wiring board as an example. FIG. 3(1) shows a substrate a on which necessary wiring 30 and the like are formed on an insulating layer 10 having a low elastic modulus α, which forms the bottom of a cavity. Next, as shown in FIG. 3(2), an insulating layer 20 having a high elastic modulus β and copper foil are laminated on the substrate a, and necessary wiring 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 etc. and the insulating layer 20 having a high elastic modulus β. Then, blasting is performed as shown in Fig. 3(4). This blasting forms a cavity 1 with the insulating layer 10 having a low elastic modulus α as the bottom and the insulating layer 20 having a high elastic modulus β as the sidewall as shown in Fig. 3(5). Then, as shown in FIG. 3(6), the blast resist mask 40 is removed to obtain the multilayer wiring board A having the cavity 1.

[0022] In this manner, a multilayer wiring board having a cavity with a stable depth dimension can be obtained, and the wiring exposed at the bottom of the cavity has a higher, i.e., protruding, characteristic than the surface of the insulating layer 10 at the bottom. FIG. 3 shows the features of the present invention in a three-layer wiring board, but wiring boards with more layers can also be provided with a cavity with a stable dimension in the depth direction. EXAMPLES

[0023] The present invention will now be described in detail with reference to examples. EXAMPLES

[0024] A six-layer wiring board, which is a multilayer wiring board according to an embodiment of the present invention, was fabricated and evaluated according to the following process flow.

[0025] First, a core board was prepared by subjecting a board material having copper layers on both sides of a glass epoxy insulating layer to through-hole processing, hole filling processing, wiring processing, and the like. Next, an epoxy thermosetting resin with an elastic modulus of 2.7 GPa and copper foil were combined as insulating layers 10 with a low elastic modulus α on both sides of the core substrate, and a laminated substrate was fabricated by thermocompression bonding. The laminated substrate was subjected to via processing, hole filling processing, wiring processing, etc. to fabricate a four-layer substrate.

[0026] Next, a thermosetting resin with an elastic modulus of 35 GPa and copper foil were combined and laminated by thermocompression bonding on both sides of the four-layer substrate to form insulating layer 20 with an elastic modulus β higher than the elastic modulus α of insulating layer 10. Then, through-hole processing, copper plating into the holes, wiring processing, etc. were performed to produce a six-layer substrate. Next, a resist mask for blasting with openings for cavities was formed on the front side of the six-layer substrate. Then, blasting was performed from the front surface side of the six-layer substrate, resulting in the formation of a cavity with insulating layer 10 with low elastic modulus α as the bottom and insulating layer 20 with higher elastic modulus β than elastic modulus α as the sidewall. It was confirmed that the wiring formed on the bottom of the cavity exposed by the blasting process was higher than the surface of the insulating layer on the bottom and protruded.

[0027] In this way, a multilayer wiring board was manufactured using a board in which the elastic modulus of insulating layer 10 of the board that forms the bottom of the cavity is lower than the elastic modulus of insulating layer 20 of the board that forms the side wall of the cavity, and a resist mask with a predetermined opening was formed on the surface of the multilayer wiring board. A blasting process was then performed under predetermined conditions to form a cavity portion. It was confirmed that the multilayer wiring board thus formed has a cavity of a constant depth, with the insulating layer at the bottom having a lower elastic modulus than the side wall of the cavity. [Explanation of symbols]

[0028] 1, 100 cavities 10 Insulating layer with elastic modulus α 11 Bottom of the cavity 20 Insulating layer with elastic modulus β (β>α) 21, 210 Cavity side wall 30, 300 Wiring 40 Blasting resist mask 110 Bottom of conventionally processed cavity 410, 420 Insulation layer (any modulus of elasticity) 430 Insulation layer at bottom of cavity A Multilayer wiring board (three-layer wiring board) according to the present invention B. Conventional multilayer wiring board (three-layer wiring board) A. Substrate

Claims

1. A multilayer wiring board having a cavity, the bottom of the cavity being an insulating layer having an elastic modulus α, and the side wall of the cavity being an insulating layer having an elastic modulus β larger than the elastic modulus α, A multilayer wiring board, characterized in that the wiring provided at the bottom of the cavity protrudes from the surface of the insulating layer constituting the bottom of the cavity.

2. 2. The multilayer wiring board according to claim 1, wherein a difference between the elastic modulus β and the elastic modulus α is 2.3 GPa or more.

3. 3. The multilayer wiring board according to claim 1, wherein a bottom portion and a side wall portion of the cavity are blast-processed surfaces.

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