JPH08125338A - Circuit board for inner layer, and multilayer printed circuit board using the same circuit board - Google Patents

Abstract

PURPOSE: To provide a circuit board for an inner layer in which a crack due to thermal impact scarcely occurs at the insulating layer of a multilayer printed circuit board and the multilayer printed circuit board using the circuit board. CONSTITUTION: A circuit board for an inner layer comprises an insulating board layer 2, and a conductor circuit 3 formed by etching the surface of the layer 2, wherein the upper edge 3a of the circuit 3 is chamfered to form a curved surface. A multilayer printed circuit board comprises the circuit board for the inner layer, and an insulating layer 4 covered with the circuit 3 of the circuit board for the inner layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner layer circuit board and a multilayer printed wiring board using the inner layer circuit board.

[0002]

2. Description of the Related Art In recent years, printed wiring boards used in electronic equipment and electric equipment have been required to have higher density, smaller size and thinner thickness. In response to these demands, even in an inner layer circuit board using a glass-based epoxy resin insulating substrate that is commonly used for printed wiring boards, for example, an insulating layer is formed by applying a resin such as epoxy resin to a conductor circuit. The method (hereinafter referred to as the build-up method) is adopted.

[0003]

A multilayer printed wiring board having an insulating layer formed by the above method does not use a prepreg in which a glass base material is impregnated with a resin, so that the insulating layer has a thickness of several tens of μm. Since it can be formed to a thin thickness, it is suitable for thinning, but cracks occur when moisture absorption or thermal shock such as solder is repeatedly applied, resulting in deterioration of insulation due to withstand voltage and moisture absorption. It is difficult to obtain sufficient reliability as a plate.

FIG. 2 (a) is a sectional view of the main part of the inner layer circuit board.
FIG. 2B shows a cross section of the main part of a multilayer printed wiring board using this inner layer circuit board. As shown in FIG. 2A, the cross section of the conductor circuit 13 formed on the surface of the insulating substrate layer 12 of the inner layer circuit board 11 has an arcuate constriction 15 due to overetching. Therefore, the upper edge 13a of the conductor circuit 13 is sharply sharpened. Figure 2 (b)
As shown in, when the insulating layer 14 is formed by applying a resin using the inner layer circuit board 11 in such a state,
Cracks 16 are likely to occur in the insulating layer 14 in contact with the upper edge 13a of the conductor circuit 13. This crack reaches the surface of the thin insulating layer 14 as time passes. The reason why the insulation property is deteriorated due to the withstand voltage and moisture absorption in a multilayer printed wiring board having a thin insulating layer 14 is presumed to be that migration easily occurs due to moisture absorption from the cracks.

The present invention has been made in view of the above facts, and an object of the present invention is to provide an inner-layer circuit board in which cracks due to thermal shock do not easily occur in an insulating layer of a multilayer printed wiring board, and the inner-layer circuit board. It is to provide a multilayer printed wiring board using.

[0006]

An inner layer circuit board according to claim 1 of the present invention is an inner layer circuit comprising an insulating substrate layer 2 and a conductor circuit 3 formed by etching on the surface of the insulating substrate layer 2. The plate is characterized in that the upper end edge 3a of the conductor circuit 3 is chamfered to form a curved surface.

An inner layer circuit board according to claim 2 of the present invention is
The inner layer circuit board according to claim 1, wherein the conductor circuit 3 is provided.
Is characterized in that the upper edge 3a thereof forms a curved surface having a radius of curvature of 10 μm or more.

A multilayer printed wiring board according to claim 3 of the present invention is an inner layer circuit board according to claim 1 or 2, and an insulating layer 4 covering the conductor circuit 3 of the inner layer circuit board.
It is characterized by consisting of.

The present invention will be described below with reference to the drawings.
FIG. 1A is a cross-sectional view of an essential part of an inner layer circuit board according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of an essential part of a multilayer printed wiring board according to an embodiment of the present invention. .

As shown in FIG. 1A, in the circuit board for an inner layer of the present invention, an insulating substrate layer 2 and a conductor circuit 3 are formed on the surface of the insulating substrate layer 2. The conductor circuit 3 is used as an inner layer circuit of a multilayer printed wiring board. The insulating substrate layer 2 is a substrate obtained by curing a resin of a prepreg obtained by impregnating a base material with a resin. Examples of the resin include epoxy resins, polyimide resins, fluororesins, phenol resins, PPO resins, and the like alone, modified products, and mixtures. The base material is not particularly limited, but an inorganic material such as glass fiber is preferable because it is superior in heat resistance and moisture resistance.
Further, an organic fiber cloth base material having excellent heat resistance and a mixture thereof can also be used. The conductor circuit 3 is formed by etching a metal foil such as copper provided on the surface of the insulating substrate layer 1.

The upper edge 3a of the conductor circuit 3 formed by etching is chamfered to form a curved surface. The chamfering is performed after the conductor circuit 3 is formed by etching. Examples of methods for chamfering the upper edge 3a of the conductor circuit 3 include mechanical polishing methods such as buff polishing and scrub polishing, and chemical treatment methods such as soft etching. The radius of curvature (R) of the roundness of the curved surface formed on the upper edge 3a of the conductor circuit 3 is preferably 10 μm or more. When the radius of curvature of the curved surface (R) is 10 μm or more, cracks are less likely to occur in the insulating layer described below when used in a multilayer printed wiring board.

As shown in FIG. 1B, the multilayer printed wiring board of the present invention comprises the inner layer circuit board 1 and an insulating layer 4 covering the conductor circuit 3 of the inner layer circuit board 1. The insulating layer 4 is a resin cured layer. Examples of the resin include the resin forming the insulating substrate layer 4, and may be the same resin as the insulating substrate layer 4 or different resins, but the same resin is preferable in terms of the same dimensional behavior. Among them, when an epoxy resin is used, the effect of preventing a decrease in insulation due to withstand voltage or moisture absorption is remarkably exhibited.

The insulating layer 4 may be formed by applying a resin to the conductor circuit 3 and curing the applied resin, or may be formed by curing a resin of a prepreg in which a base material is impregnated with the resin. May be. The build-up method in which a resin is applied is preferable for thinning because the thickness of the insulating layer 4 can be formed to be as thin as several tens of μm.

In the above-mentioned multilayer printed wiring board, the outer conductor circuit 5 is formed on the insulating layer 4 by using subtocratic, additive or the like. Further, if necessary, through-hole plating is applied to form conductive paths (not shown) in the through-holes.

As described above, the multilayer printed wiring board of the present invention uses the inner layer circuit board 1 in which the upper end edge 3a of the conductor circuit 3 is chamfered to form a curved surface. The generation of cracks in the contacting insulating layer 4 is suppressed. Therefore, no migration occurs due to moisture absorption from the cracks. As a result, even if it is repeatedly subjected to thermal shock, the dielectric strength does not deteriorate due to withstand voltage and moisture absorption.

[0016]

In the inner layer circuit board according to the first or second aspect of the present invention, since the upper edge 3a of the conductor circuit 3 forms a chamfered curved surface, when used for a multilayer printed wiring board. In addition, no crack is generated in the insulating layer 4 in contact with the upper edge 3a of the conductor circuit 3.

Since the multilayer printed wiring board according to claim 3 of the present invention has the inner-layer circuit board 1 and the insulating layer 4 covering the conductor circuit 3 of the inner-layer circuit board 1, it is insulated. Cracks are unlikely to occur in the layer 4, and therefore, no migration occurs due to moisture absorption from the cracks.

[0018]

【Example】

Example 1 As a circuit board for the inner layer, a glass cloth base material epoxy resin laminated board having a thickness of 1.6 mm, in which a copper foil having a thickness of 35 μm is arranged on both sides, a land diameter of 1.0 mm, a conductor circuit width of 0.2 mm,
Lattice-shaped conductor circuits were produced by etching with a land center interval of 2.54 mm pitch. 200 lands were produced.

Next, buffing of the conductor circuit was performed using a buff having a roughness of # 600. The cross section of the obtained inner layer circuit board was observed with an optical microscope, and the radius of curvature (R) of the curved surface of the upper edge of the conductor circuit was measured. The radius of curvature (R) was 30 μm.
Met. Epoxy resin was applied to both surfaces of the inner-layer circuit board on which the conductor circuits were formed to form an insulating layer having a thickness of 80 μm to obtain a multilayer printed wiring board.

The time until cracks due to thermal shock were generated in the obtained multilayer printed wiring board was evaluated. This evaluation test was performed according to the thermal shock of JIS-C-5012. 10 seconds for oil at a temperature of 260 ° C, 1 for water at a temperature of 20
A thermal shock test was conducted by immersing the solution in an organic solvent having a temperature of 20 ° C. for 0 second in the order of 10 seconds, and setting this as one cycle. The cycle until a crack was generated in the insulating layer of this multilayer printed wiring board was measured. In the crack measurement, the refractive index changed at the location of the crack so that it looked white. Therefore, it was judged whether there was a location where the whitening phenomenon occurred in the insulating layer. As shown in Table 1, the results required 70 cycles until crack initiation.

Example 2 A multilayer printed wiring board was produced in the same manner as in Example 1 except that buffing was performed using a buff having a roughness of # 1000. Curvature radius (R) of the upper edge of the conductor circuit of the inner layer circuit board
Was 10 μm. Next, in the same manner as in Example 1, the time until the occurrence of cracks was measured. As the result is shown in Table 1, it took 65 cycles until a crack was generated.

Example 3 Instead of the buffing in Example 1, a scrubbing machine (CIB) was used.
A multilayer printed wiring board was prepared in the same manner as in Example 1 except that scrubbing was performed for 1 minute using A-GEIGY Co .: producer-120). The radius of curvature (R) of the upper edge of the conductor circuit of the inner layer circuit board was 25 μm. Next, in the same manner as in Example 1, the time until the occurrence of cracks was measured. As shown in Table 1, 66 cycles were required until cracks were generated.

Example 4 A multilayer printed wiring board was prepared in the same manner as in Example 3 except that the scrubbing time in Example 3 was 3 minutes. The radius of curvature (R) of the upper edge of the conductor circuit of the inner layer circuit board is 40.
μm. Next, in the same manner as in Example 1, the time until the occurrence of cracks was measured. As shown in Table 1, it took 75 cycles until cracks occurred.

Example 5 Example 1 was repeated except that the buffing in Example 1 was replaced by soft etching using a soft etching solution for 2 minutes.
A multilayer printed wiring board was produced in the same manner as in. The above soft etching solution contains 30 parts of cupric chloride (CuCl ₂ ).
A liquid having a liquid temperature of 40 ° C. was used in which g / l and hydrochloric acid (HCl) were mixed at a ratio of 3.0 mol / l. The radius of curvature (R) of the upper edge of the conductor circuit of the inner layer circuit board is 50 μm
Met. Next, in the same manner as in Example 1, the time until the occurrence of cracks was measured. As the result is shown in Table 1, 79 cycles were required until crack initiation.

Example 6 A multilayer printed wiring board was produced in the same manner as in Example 5 except that the soft etching time in Example 5 was 4 minutes. Curvature radius (R) of the upper edge of the conductor circuit of the inner layer circuit board
Was 35 μm. Next, in the same manner as in Example 5, the time until the occurrence of cracks was measured. As shown in Table 1, the results required 71 cycles until crack initiation.

Comparative Example 1 In the same manner as in Example 1, a conductor circuit of an inner layer circuit board was produced by etching. When the cross section of the obtained inner layer circuit board was observed with an optical microscope, the upper edge of the conductor circuit was sharply pointed. Using this inner layer circuit board, as in Example 1,
An insulating layer having a thickness of 80 μm was formed to produce a multilayer printed wiring board. Next, in the same manner as in Example 1, the time until the occurrence of cracks was measured. As shown in Table 1, the results showed that cracks occurred in 55 cycles.

[0027]

[Table 1]

Example 7 In the same manner as in Example 1, a conductor circuit of the inner layer circuit board was produced by etching. Then, buffing was performed using a buff having a roughness of # 600. The radius of curvature (R) of the upper edge of the conductor circuit of the obtained inner layer circuit board was 30 μm.

Next, one prepreg in which a glass cloth having a thickness of 0.1 mm is impregnated with an epoxy resin is arranged on both surfaces of the inner-layer circuit board on which the conductor circuit is formed, and heated and pressed to have a thickness of 110 μm. An insulating layer was formed to obtain a multilayer printed wiring board. Next, in the same manner as in Example 1, the time until the occurrence of cracks was measured. As shown in Table 2, the results required 80 cycles until cracks occurred.

Example 8 Instead of the buffing of Example 7, a scrubbing machine (CIB) was used.
A multilayer printed wiring board was produced in the same manner as in Example 7 except that scrubbing was performed for 1 minute using A-GEIGY Co .: producer-120). The radius of curvature (R) of the upper edge of the conductor circuit of the inner layer circuit board was 25 μm. Next, in the same manner as in Example 7, the time until the occurrence of cracks was measured. As shown in Table 2, 77 cycles were required until cracks occurred.

Example 9 A multilayer printed wiring board was prepared in the same manner as in Example 7, except that the soft etching solution of Example 5 was used for soft etching for 2 minutes instead of the buffing of Example 7. did. Curvature radius (R) of the upper edge of the conductor circuit of the inner layer circuit board
Was 50 μm. Next, in the same manner as in Example 7, the time until the occurrence of cracks was measured. As shown in Table 2, it took 90 cycles for cracks to occur.

Comparative Example 2 In the same manner as in Example 7, a conductor circuit of the inner layer circuit board was produced by etching. When the cross section of the obtained inner layer circuit board was observed with an optical microscope, the upper edge of the conductor circuit was sharply pointed. Using this inner layer circuit board, as in Example 7,
An insulating layer having a thickness of 110 μm was formed to obtain a multilayer printed wiring board. Next, in the same manner as in Example 7, the time until the occurrence of cracks was measured. As shown in Table 2, the results showed that cracks occurred in 65 cycles.

[0033]

[Table 2]

[0034]

The inner layer circuit board according to claim 1 or 2 of the present invention is used for a multilayer printed wiring board because the upper edge 3a of the conductor circuit 3 forms a chamfered curved surface. In this case, the insulating layer 4 in contact with the upper edge 3a of the conductor circuit 3 is not cracked. As a result, even if it is repeatedly subjected to thermal shock, the dielectric strength does not deteriorate due to withstand voltage and moisture absorption.

Since the multilayer printed wiring board according to claim 3 of the present invention has the inner-layer circuit board 1 and the insulating layer 4 covering the conductor circuit 3 of the inner-layer circuit board 1, it is insulated. The layer 4 is unlikely to be cracked, and even if it is repeatedly subjected to moisture absorption or thermal shock such as soldering, the withstand voltage and the insulation property are less likely to be deteriorated due to moisture absorption. As a result, high reliability can be obtained as a multilayer printed wiring board. Above all, it is particularly effective for a multilayer printed wiring board having a thin insulating layer 4.

[Brief description of drawings]

FIG. 1A is a cross-sectional view of an essential part of an inner layer circuit board according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of an essential part of a multilayer printed wiring board according to an embodiment of the present invention. Is.

FIG. 2A is a cross-sectional view of a main part of a conventional circuit board for inner layer, and FIG. 2B is a cross-sectional view of a main part of a conventional multilayer printed wiring board.

[Explanation of symbols]

 1 inner layer circuit board 2 insulating substrate layer 3 conductor circuit 3a upper edge 4 insulating layer

Front page continuation (72) Inventor Masayuki Ishihara 1048 Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.

Claims (3)

[Claims] 1. An inner-layer circuit board comprising an insulating substrate layer (2) and a conductor circuit (3) formed by etching on the surface of the insulating substrate layer (2), said conductor circuit (3) comprising: An inner-layer circuit board, wherein the upper edge (3a) is chamfered to form a curved surface. 2. The inner-layer circuit board according to claim 1, wherein the upper edge (3a) of the conductor circuit (3) forms a curved surface with a radius of curvature of 10 μm or more. 3. A multi-layered print comprising an inner layer circuit board according to claim 1 or 2, and an insulating layer (4) covering a conductor circuit (3) of the inner layer circuit board. Wiring board.