JP2000349439A - Manufacture of multilayered metal clad circuit board having internal layer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate unevenness resulting from the printed circuit of a core substrate as much as possible when formation is carried out by interposing a metallic specular plate of <=0.8 mm in thickness between laminate constitution bodies, heating and pressing them. SOLUTION: On both sides of the core substrate having printed circuits formed on both surfaces, a prepreg and metal foil are stacked from inside to the outside to obtain a laminate constitution body for forming a multilayered board having an internal layer circuit. The metallic specular plate 2 of 0.8 to 0.4 mm in thickness is interposed between laminated constitution bodies, which are integrated by being heated and pressed between press heat disks. At this time, a metallic specular plate which has >=15 N/mm2 tensile strength in a 150 deg.C atmosphere is used as the metallic specular plate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a multilayer metal foil-clad laminate having a printed circuit in an inner layer. This multilayer metal foil-clad laminate is used in the manufacture of multilayer printed circuit boards.

[0002]

2. Description of the Related Art The above-mentioned multilayer metal foil-clad laminate is prepared by laminating a prepreg and a metal foil in this order on both sides of a core substrate on which a printed circuit is formed, from the inside to the outside, and heating and pressing the laminated structure between press hot plates. It is manufactured by molding and integrating. When a plurality of core substrates are used, a prepreg is also interposed between the core substrates that have been positioned and overlapped with each other, and the heat and pressure molding is performed. In the above-mentioned heat and pressure molding, a plurality of sets of laminated structures are put in one stage of a press hot platen, and a metal mirror plate is interposed between the laminated structures. In order to reduce man-hours and manufacturing time, there is an attempt to increase the number of sets of laminated components to be put between press hot plates,
If the number of sets is simply increased, the rate of temperature rise of the laminated structure is reduced, and the time required to reach the maximum temperature is also increased. In order to solve this problem, it is necessary to reduce the thickness of the metal mirror plate interposed between the laminated components to maintain the current state of the rate of temperature rise and the time to reach the maximum temperature.

[0003] Since the metal mirror plate interposed between the laminated components is finished through a rolling process, it is difficult to finish a thin plate with a high strength material such as a stainless steel mirror plate, and the thickness is limited to 1.0 mm. It is. For example, 0.8mm
In order to finish to a very thin plate thickness below, the strength of the metal mirror plate needs to be reduced to some extent, and as a metal mirror plate that can be rolled to a thickness of 0.8 mm or less, a low strength made of aluminum, iron, etc. Mirror plates have been studied.

[0004]

SUMMARY OF THE INVENTION These aluminum,
When heat and pressure molding is performed by interposing a mirror plate made of iron or the like between the laminated components, because the strength of the mirror plate is low,
A problem arises in that unevenness due to the printed circuit of the core substrate appears on the surface of the formed multilayer metal foil-clad laminate with the inner layer circuit. The unevenness leads to poor adhesion of an etching resist film to be attached in a step of etching a metal foil on a surface of a printed circuit, mounting failure when mounting components on the printed circuit, and the like. In order to prevent the unevenness of the printed circuit on the core substrate from affecting the metal mirror plate, it is necessary to use a cushion material that absorbs the unevenness. In the conventional method, a laminated member and a metal mirror plate are alternately stacked, and a paper or rubber cushion material is arranged on the outside, but a metal mirror plate having a thickness of 0.8 mm or less has no strength. As a result, the metal mirror plate itself absorbs the unevenness due to the printed circuit of the core substrate.

[0005] As a measure for preventing the occurrence of unevenness on the surface of the multilayer metal foil-clad laminate with an inner layer circuit, one method is to set the molding pressure to a low pressure when heating and pressing the laminated structure. This method changes the prepreg characteristics in order to prevent a decrease in circuit filling property due to insufficient molding pressure (a phenomenon in which a concave portion between printed circuits of a core substrate is not sufficiently filled with a resin that melts and flows during molding and a void remains). Need to cope with low pressure molding. However, when the prepreg characteristics are changed, it becomes difficult to maintain the product performance such as the metal foil peeling strength, heat resistance, and plate thickness accuracy as before the prepreg characteristics were changed. Secondly, when heating and pressing the laminated structure,
There is a method in which heating and pressure molding is performed at a low pressure in the initial stage of heating, and then pressure is increased to perform heating and pressure molding. The low pressure is a molding pressure at a stage where the resin in the prepreg has not yet melted and the unevenness of the printed circuit of the core substrate does not affect the surface. The pressure increase is a pressure increase to a pressure necessary and sufficient for the molten resin to fill the recesses between the printed circuits of the core substrate when the resin in the prepreg is sufficiently melted. In this step, the melted resin absorbs the unevenness of the printed circuit of the core substrate and reduces the unevenness appearing on the surface.

However, the degree of the irregularities appearing on the surface can vary depending on the material of the metal mirror plate interposed between the laminated structures, the thickness of the conductor constituting the printed circuit of the core substrate, the material of the prepreg, and the like. Only the control of the molding pressure described above may not sufficiently suppress the unevenness formed on the surface. In particular, when the thickness of the conductor constituting the printed circuit of the core substrate is 70 μm or more, or when the viscosity of the prepreg before the resin is melted is high, the unevenness of the surface tends to increase.

The problem to be solved by the present invention is that a multi-layer metal foil-clad laminate containing an inner layer circuit is formed by heating and pressing with a metal mirror plate having a thickness of 0.8 mm or less interposed between the laminated structures. In addition, even if the prepreg characteristics are not particularly changed,
The purpose is to prevent irregularities due to the printed circuit of the core substrate from appearing on the surface as much as possible.

[0008]

SUMMARY OF THE INVENTION The present invention is intended to prevent a metal mirror plate from absorbing irregularities of a printed circuit on a core substrate even when the thickness of the metal mirror plate is reduced to 0.8 mm or less. In addition, the above problem is solved by limiting the strength of the metal mirror plate. That is, the method for producing a multilayer metal-foil-clad laminate with an inner circuit according to the present invention is characterized in that, as a metal mirror plate interposed between laminated structures, the tensile strength at 150 ° C. atmosphere is 150 N / mm ² or more. It is characterized by using a metal mirror plate.

[0009] In the production of a multilayer metal foil-clad laminate with an inner layer circuit, the process of maintaining the strength of the metal mirror plate so as not to absorb the unevenness of the printed circuit of the core substrate is performed during the initial heating and pressurizing and during the prepreg. Until the resin is melted by heating and thermally cured. The temperature at which the resin in the prepreg ends the thermosetting reaction in the production of the multilayer metal foil-clad laminate with the inner layer circuit is 150 ° C. or less. Therefore, it is necessary to limit the tensile strength at 150 ° C. of the metal mirror plate, and by using the metal mirror plate having the above tensile strength, no irregularities appear on the surface without particularly changing the prepreg characteristics. Alternatively, it is possible to obtain a multilayer metal foil-clad laminate having an inner circuit in which unevenness appearing on the surface is suppressed. Generally, the strength of a metal decreases as the temperature increases, and in the present invention, it is meaningless to specify the strength of the metal mirror plate at room temperature. Factors that specify the mechanical properties of metal wrought materials include tensile strength, proof stress, elongation, hardness, ductility, etc., but by specifying the tensile strength, the material hardness, ductility, various workability, etc. Since it can be judged to some extent, the tensile strength, which is the most basic physical property of the wrought metal, was adopted as a method of specifying the strength of the metal mirror plate.

The upper limit of the tensile strength of the metal mirror plate is as follows:
Naturally, it is limited to a value that can be finished to a thickness of 0.8 mm or less by rolling. Also, the thickness of the metal mirror plate is 0.4 mm
Otherwise, even if the tensile strength of the metal mirror plate is limited as described above, it is difficult to solve the problem of the present invention.

In the method according to the present invention, the hot press molding is preferably controlled as follows. That is, the molten resin contained in the start and the prepreg heating and pressing its viscosity is decreased, until 5 × 10 ⁴ POISE following performs heating and pressurization by 1N / mm ² or less, 5 × 10 ⁴ POISE Then, the pressure is raised to a predetermined pressure and heating and pressurization are continued. This method
The resin in the molten state is provided with a function as a cushion for absorbing irregularities of the printed circuit of the core substrate.
Until the resin contained in the prepreg is melted, the pressure is maintained at a low pressure that does not cause deformation of the metal mirror plate due to the unevenness of the printed circuit, and when the resin melts and the viscosity decreases, the molten resin is printed. The pressure is increased to the pressure necessary to fill the recess between the circuits, and the heating and pressurization is continued. It is possible to form a multilayer metal foil-clad laminate with an inner layer circuit having a small surface unevenness more stably without being affected by the shape and thickness of the printed circuit of the core substrate.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method according to the present invention, heat and pressure molding is performed in a configuration as shown in FIG. A prepreg and a metal foil are stacked in this order on both sides of a core substrate having a printed circuit formed on both sides from the inside to the outside, thereby forming a laminated structure 1 for forming a multilayer metal foil-clad laminate with an inner layer circuit. The laminated structure 1 is formed by pressing under pressure between hot press plates and integrated, but a plurality of sets of the laminated structures are put between the press hot plates, and a thickness of 0 is set between the laminated hot plates. 0.8-0.
A 4 mm metal mirror plate 2 is interposed. On the outermost side of the plurality of laminated components, a 1.2 mm-thick stainless steel mirror plate 3 and a cushion material 4 made of a kraft paper layer are laminated in this order from inside to outside. The mirror surface plate 3 made of stainless steel is arranged to prevent the surface properties of the cushion material 4 from being transferred to the metal foil surface of the laminated structure located closest to the cushion material 4. In the above description, the number of core substrates constituting one set of laminated components is one, but a plurality of core substrates may be used in one set of laminated components. In this case, a prepreg is also interposed between the core substrates.

In the present invention, the tensile strength of the metal mirror plate 2 at 150 ° C. in an atmosphere is 150 N / mm ^2.
Above. Needless to say, since a mirror-finished plate having a thickness of 0.8 mm or less needs to be formed by rolling, there is naturally an upper limit of the tensile strength at which such rolling is possible. Materials that can be easily rolled and can be rolled to 0.8 mm or less are aluminum, iron, and the like, but there are many types such as not only a single substance but also alloys containing these, and the strengths are greatly different from one another. Depending on the method of rolling, the strength may be different even for the same material, and there are many options for selecting the material of the metal mirror plate 2.

[0014] The resin contained in the prepreg is melted and its viscosity is reduced to 1 N / N until it becomes 5 × 10 ⁴ POISE or less.
The embodiment of the invention in which heating and pressurization is performed at a pressure of not more than mm ² and the pressure is increased to a predetermined pressure when the pressure becomes 5 × 10 ⁴ POISE is preferable. Since it is difficult to measure the viscosity of the resin in the actual heating and pressing molding process, a temperature-resin melt viscosity curve at each heating rate for the prepreg to be used is determined in advance, and the laminated structure is heated and heated. When pressing,
The viscosity of the resin is estimated based on the curve while measuring the temperature of the laminated structure and the rate of temperature rise. Figure 2 shows a glass woven base epoxy resin prepreg (ANSI grade FR-
Regarding 4), the temperature rise rate is 1 ° C / min, 2 ° C / min, 3
It shows the relationship between the temperature of the prepreg and the viscosity of the resin in each case of ° C./min. As the temperature rise measurement speed increases, the resin viscosity reaches 5 × 10 ⁴ POISE at a lower temperature, and the minimum melt viscosity also decreases.

[0015]

EXAMPLES Examples 1 to 8 and Comparative Examples 1 to 4 A 0.2 mm thick glass woven base epoxy resin double-sided copper-clad laminate (ANSI grade FR-4) was etched.
Printed circuits were formed on both sides to form a core substrate. The printed circuit was formed by repeatedly arranging a line having a width of 1 mm and a length of 100 mm. In each example, the thickness of the copper foil forming the printed circuit is as shown in Table 1. Also,
0.1 mm thick glass woven base epoxy resin prepreg (A
NSI grade FR-4) was prepared. The prepreg and the 18 μm thick copper foil were laminated on both sides of the core substrate in this order from the inside to the outside. A laminate was obtained. The arrangement of the laminated structure between the press hot plates,
As already described with reference to FIG. 1, the heating rate of heating was set to 2 ° C./min. A 0.4 mm thick aluminum mirror plate was used as the metal mirror plate 2 interposed between the laminated components. This aluminum mirror plate is an aluminum-magnesium alloy,
Three types (tensile strengths 140, 160 and 210 N / mm ² in an atmosphere of 150 ° C.) having different chemical components and qualities were selected. Table 1 shows the tensile strength of the aluminum mirror plate used in each example, and the initial set pressure of the heat and pressure molding and the set pressure after the pressure was raised when the resin viscosity reached 5 × 10 ⁴ POISE. showed that. In addition, Examples 2, 4, 6, 8
In Comparative Examples 2 and 4, the pressure was not increased during the molding, and the heat and pressure molding was performed at a constant pressure of ^2.5 N / mm ² from the beginning. Table 1 also shows the surface roughness Ra of the four-layer copper-clad laminate containing the inner circuit formed in each example.

[0016]

[Table 1]

Based on the data in Table 1, the relationship between the tensile strength of the aluminum mirror plate and the surface roughness of the four-layer copper-clad laminate containing the inner layer circuit is shown for each copper foil thickness of the core substrate in FIG.
(B). FIG. 3A shows the case where the molding pressure is increased and the heating and press molding is performed when the viscosity of the resin contained in the prepreg reaches 5 × 10 ⁴ POISE, and FIG. 3B shows the pressure increase during molding. In this case, the heating and press-forming was carried out at a constant pressure of ^2.5 N / mm ² from the beginning. From FIG.
Regardless of whether the thickness of the copper foil of the core substrate is thick or thin, the molding pressure is increased during molding, or the molding is performed at a predetermined pressure from the initial stage, the aluminum mirror surface plate is pulled in a 150 ° C atmosphere. It can be understood that setting the strength to 150 N / mm ² or more leads to a reduction in surface roughness. Further, from a comparison between FIGS. 3A and 3B, it can be understood that a low pressure in the initial stage and a high pressure in the middle of molding leads to a further reduction in surface roughness.

In the above embodiment, the case where the thinnest mirror plate having a thickness of 0.8 mm to 0.4 mm of the metal mirror plate 2 is used has been described. In the embodiment in which the metal mirror plate 2 is made thicker, it goes without saying that better results can be obtained.

[0019]

As described above, when a multi-layered metal foil-clad laminate with an inner layer circuit is formed by heating and pressing with a thin metal mirror plate interposed between the laminated structures, as in the case of the present invention, By specifying the tensile strength at 150 ° C. of the mirror-finished plate, it is possible to suppress the influence of the unevenness of the printed circuit on the core substrate from appearing on the surface. Further, when the viscosity of the resin contained in the prepreg is reduced in the above-mentioned heating and pressing molding step and the molding pressure is increased from an initial low pressure to a predetermined pressure at a stage when the resin becomes 5 × 10 ⁴ POISE, irregularities appearing on the surface are reduced. It can be even smaller.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing how a multilayer metal foil-clad laminate containing an inner layer circuit is formed in a method according to the present invention.

Fig. 2 Measurement rate of 1 ° C / min, 2 ° C / min, 3 ° C / min
FIG. 4 is a curve diagram showing the relationship between the temperature of the glass woven fabric base epoxy resin prepreg and the resin viscosity in each case.

FIG. 3 is a curve diagram showing the relationship between the tensile strength of an aluminum mirror plate and the surface roughness of a manufactured four-layer copper-clad laminate with an inner layer circuit. (A) shows the case where the pressure is increased during the molding, and (b) shows the case where the molding is performed at a constant pressure throughout the entire process from the beginning.

[Explanation of symbols]

 1 is a laminated structure 2 is 0.8 to 0.4 mm thick metal mirror plate 3 is stainless steel mirror plate 4 is cushion material

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Claims (2)

[Claims] 1. A prepreg and a metal foil are laminated in this order from the inside to the outside on a core substrate on which a printed circuit is formed, and a plurality of sets of the laminated structure are put between press hot plates to perform heating and pressing. A metal mirror plate is interposed between the laminated structures,
The metal mirror plate has a thickness of 0.4 mm or less of 0.8 mm or less.
As described above, the tensile strength at 150 ° C.
A method for producing a multilayer metal-clad laminate having an inner layer circuit, wherein the laminate thickness is 0 N / mm ² or more. 2. The resin contained in the prepreg is melted and its viscosity is reduced to 1 N / mm ² until it becomes 5 × 10 ⁴ POISE.
2. The multi-layer metal foil cladding with an inner layer circuit according to claim 1, wherein the heating and pressurizing is performed at the following pressure, and when the pressure becomes 5 × 10 ⁴ POISE, the pressure is increased to a predetermined pressure and the heat and press forming is performed. Manufacturing method of laminated board.