Printed circuit board

Abstract

The objective is to make the distribution of glass particles dispersed in the resin insulating layer within the spaces between wiring in areas where wiring is densely packed nearly uniform. [Solution] A printed wiring board comprising a first resin insulating layer, a conductor layer formed on the first resin insulating layer, and a second resin insulating layer covering the first resin insulating layer and the conductor layer, wherein the conductor layer forms a conductor circuit, the conductor circuit includes a first conductor circuit which is a region with dense wiring and a second conductor circuit which is a region with sparse wiring, and the second resin insulating layer is filled between the wiring of each of the first and second conductor circuits, wherein the cross-sectional shape of the wiring in the first conductor circuit is an inverted trapezoid shape, and the cross-sectional shape of the wiring in the second conductor circuit is a trapezoid shape.

Description

Technical Field

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[0001] The present invention relates to a printed wiring board, and particularly to the cross-sectional shape of the conductor circuit of the printed wiring board.

Background Art

[0002] Patent Document 1 discloses a conventional printed wiring board. This printed wiring board has a conductor layer on a first resin insulating layer, and the first resin insulating layer and the conductor layer are covered with a second resin insulating layer. The conductor layer forms a conductor circuit, and the conductor circuit includes a first conductor circuit that is a region where the wiring is dense and a second conductor circuit that is a region where the wiring is sparse. Between the wirings of the first conductor circuit and between the wirings of the second conductor circuit, the second resin insulating layer is filled. In the first conductor circuit, the cross-sectional shape of the wiring is rectangular, and in the second conductor circuit, the cross-sectional shape of the wiring is trapezoidal.

Prior Art Documents

Patent Documents

[0007] The printed circuit board of the present invention is A first resin insulating layer, a conductor layer formed on the first resin insulating layer, and a second resin insulating layer covering the first resin insulating layer and the conductor layer, Equipped with, The conductor layer forms a conductor circuit, The conductor circuit includes a first conductor circuit and a second conductor circuit which is a region with less wiring compared to the first conductor circuit. The second resin insulating layer is filled between the wiring of the first conductor circuit and between the wiring of the second conductor circuit. In the first conductor circuit, the cross-sectional shape of the wiring is an inverted trapezoid. In the second conductor circuit, the cross-sectional shape of the wiring is trapezoidal. It is characterized by the following. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the printed circuit board of the present invention. [Figure 2] (a) and (b) are schematic explanatory diagrams illustrating, in a partially enlarged cross-section, the second resin insulating layer, which is filled in the space between the wirings of the first conductor circuit, in the printed circuit board of the above embodiment and in a conventional printed circuit board, respectively, together with the wiring. [Modes for carrying out the invention]

[0009] An embodiment of the printed circuit board of the present invention will be described below with reference to the drawings. In the example shown in Figures 1, 2(a), and 2(b), the dimensions of each component, particularly the height dimension, are described using dimensions different from the actual dimensions in order to better understand the features of the present invention.

[0010] Figure 1 is a schematic cross-sectional view showing one embodiment of the printed circuit board of the present invention. Figures 2(a) and 2(b) are explanatory diagrams that schematically show, in partially enlarged cross-sections, the second resin insulating layer filled in the space between the wirings of the first conductor circuit, together with the wiring, in the printed circuit board of the above embodiment and a conventional printed circuit board, respectively.

[0011] The printed circuit board of this embodiment comprises a first resin insulating layer 1, a conductor layer 2 formed on the first resin insulating layer 1, and a second resin insulating layer 3 covering the first resin insulating layer 1 and the conductor layer 2, with the conductor layer 2 forming a conductor circuit C. The conductor circuit C includes a first conductor circuit C1, which is a region with relatively dense wiring, and a second conductor circuit C2, which is a region with sparser wiring compared to the first conductor circuit C1, and the second resin insulating layer 3 is filled between the wiring W1 of the first conductor circuit C1 and between the wiring W2 of the second conductor circuit C2.

[0012] The first resin insulating layer 1 is formed from an insulating resin such as epoxy resin containing a large number of inorganic particles, such as glass particles, and a seed layer is formed on the first resin insulating layer 1 by, for example, sputtering and electroless copper plating. A dry film resist is laminated on this seed layer. The dry film resist is exposed and developed to form a plating resist layer having openings corresponding to the circuit pattern of the conductor circuit C. Next, an electrolytic copper plating layer is formed on the portion of the seed layer exposed through the openings in the plating resist layer. After that, the plating resist layer is removed, and then the portion of the seed layer covered by the plating resist layer and on which the electrolytic copper plating layer is not formed is removed by etching, and a conductor layer 2 having a conductor circuit C is formed from the seed layer and electrolytic copper plating layer remaining on the first resin insulating layer 1. When removing this portion of the seed layer, for example, the immersion time in the etching solution, the temperature of the etching solution, and the flow of the etching solution near the upper surface of the first resin insulating layer 1 are also adjusted. This allows the angle of inclination of the sides of the wirings W1 and W2 with respect to the upper surface of the first resin insulating layer 1 to be set so that the cross-sectional shapes of the wirings W1 and W2 are rectangular, trapezoidal, or inverted trapezoidal.

[0013] The second resin insulating layer 3 is formed by laminating an insulating resin, such as a film or paste, onto the first resin insulating layer 1 and the conductor layer 2, then applying pressure to cover the first resin insulating layer 1 and the conductor layer 2, and pushing it into the space S1 between the wiring W1 of the first conductor circuit C1 and the space S2 between the wiring W2 of the second conductor circuit C2. In the figure, the reference numerals L1 and L2 indicate the width of the lower end of the wiring. In addition, the reference numerals S1 and S2 may indicate the width of the lower end of the space between the wiring.

[0014] Here, when the insulating resin constituting the second resin insulating layer 3 is made of a resin R such as epoxy resin containing a large number of glass particles G, in the first conductor circuit C1 of a conventional printed circuit board, as shown in Figure 2(b), the wiring W1 with a rectangular cross-section rises vertically from the first resin insulating layer 1 and is densely packed. For this reason, the space S1 between the wiring W1 is also small and has a rectangular cross-section, making it difficult to fill the space S1 with the second resin insulating layer 3.

[0015] In addition, the glass particles G contained in the second resin insulating layer 3 in the resin R have lower fluidity than the resin R. Therefore, in a conventional printed wiring board, as shown in FIG. 2(b), at the corner of the lower end portion (the end portion on the side of the first resin insulating layer 1) of the space S1 having a rectangular cross section between the wirings W1 of the first conductor circuit C1, the content of the glass particles G of the second resin insulating layer 3 is likely to be less than other portions.

[0016] On the other hand, in the first conductor circuit C1 of the printed wiring board of this embodiment, as shown in FIGS. 1 and 2(a), the wiring W1 having an inverted trapezoidal cross section rises with an inverted inclination from the first resin insulating layer 1 toward the space S1 side and exists densely. As a result, although the space S1 between the wirings W1 is small, it has a trapezoidal cross section, and the resin R of the second resin insulating layer 3 pushed into the space S1 reaches the first resin insulating layer 1 and spreads horizontally along the upper surface of the first resin insulating layer 1, or applies a horizontal force to reach the glass particles G to the corner of the lower end portion (the end portion on the side of the first resin insulating layer 1) in the space S1.

[0017] Table 1 below shows preferred examples of the cross-sectional shapes of the wiring W1 of the first conductor circuit C1, which is a region where the wiring is relatively dense, and the wiring W2 of the second conductor circuit C2, which is a region where the wiring is sparse compared to the first conductor circuit C1, in the printed wiring board of this embodiment, as well as the widths L1 and L2 of the lower end portions (the end portions on the side of the first resin insulating layer 1) of the wirings, and the widths S1 and S2 of the lower end portions (the end portions on the side of the first resin insulating layer 1) of the spaces between the wirings. The plating resist for forming the first conductor circuit C1 and the plating resist for forming the second conductor circuit C2 may be exposed separately. In that case, the exposure amounts of both are different. Both have different cross-sectional shapes.

[0018]

Table 1

[0019] Therefore, according to the printed wiring board of this embodiment, unlike the conventional printed wiring board, there is a space S1 with a trapezoidal cross-section between the wirings W1 of the first conductor circuit C1. Thus, glass particles G can reach the corner portions on the side of the first resin insulating layer 1 within the space S1 and be dispersed almost uniformly, making the physical properties (such as thermal expansion coefficient, strength, etc.) of the second resin insulating layer 3 within the space S1 almost homogeneous.

[0020] In addition, according to the printed wiring board of this embodiment, similar to the conventional printed wiring board, there is a space S2 with an inverted trapezoidal cross-section between the wirings W2 of the second conductor circuit C2. Therefore, glass particles G can reach the corner portions on the side of the first resin insulating layer 1 within the space S2 and be dispersed almost uniformly, also making the physical properties (such as thermal expansion coefficient, strength, etc.) of the second resin insulating layer 3 within the space S2 almost homogeneous.

Explanation of Reference Numerals

[0021] 1 First resin insulating layer 2 Conductor layer 3 Second resin insulating layer C Conductor circuit C1 First conductor circuit (dense region) C2 Second conductor circuit (sparse region) L1, L2 Width of wiring S1, S2 Space (width between spaces) W1, W2 Wiring G Glass particles R Resin

Claims

1. A first resin insulating layer, a conductor layer formed on the first resin insulating layer, and a second resin insulating layer covering the first resin insulating layer and the conductor layer, Equipped with, The conductor layer forms a conductor circuit, The conductor circuit includes a first conductor circuit and a second conductor circuit which is a region with less wiring compared to the first conductor circuit. The second resin insulating layer is filled between the wiring of the first conductor circuit and between the wiring of the second conductor circuit. In the first conductor circuit, the cross-sectional shape of the wiring is an inverted trapezoid. In the second conductor circuit, the cross-sectional shape of the wiring is trapezoidal. A printed circuit board characterized by the following.

2. The printed circuit board according to claim 1, wherein in the first conductor circuit, the width of the end of the wiring on the first resin insulating layer side is 1.5 μm or more and 5.5 μm or less, and the width of the end of the space between the wirings on the first resin insulating layer side is 1.5 μm or more and 5.5 μm or less.

3. The printed circuit board according to claim 2, wherein in the first conductor circuit, the width of the end of the wiring on the first resin insulating layer side is 3.5 μm or less, and the width of the end of the space between the wirings on the first resin insulating layer side is 3.5 μm or less.

4. The printed circuit board according to claim 2 or 3, wherein in the second conductor circuit, the width of the end of the wiring on the first resin insulating layer side is 10 μm or more and 20 μm or less, and the width of the end of the space between the wirings on the first resin insulating layer side is 10 μm or more and 20 μm or less.

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