JP2001339158A - Method for producing multilayer metal foil clad plate having inner layer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress irregularities on the surface caused by the printed circuit on a core substrate when multilayer components are hot pressed while sandwiching metallic mirror face plates of 0.8 mm thick or less. SOLUTION: A prepreg and a metal foil are laid sequentially from the inside on the opposite sides of a core board substrate where printed circuits are formed to obtain a multilayer component 1 for forming a multilayer metal foil clad plate having an inner layer circuit. The multilayer components are hot pressed while sandwiching metallic mirror face plates 2 of 0.8-0.4 mm thick and integrated. In this regard, a metallic mirror face plate 2 having Brinell hardness 60 (HBW10/500) or above is employed.

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 the metal mirror plate with a high strength such as a stainless steel mirror plate to a thin plate thickness, and the thickness is limited to 1 mm. . For example, in order to finish the sheet with a very thin thickness of 0.8 mm or less, it is necessary to reduce the strength of the metal mirror plate to a certain extent.
As a metal mirror plate that can be rolled to 8 mm or less, a low-strength mirror plate made of aluminum, iron, or the like has 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 hardness of the metal mirror plate. That is, the method for producing a multilayer metal foil-clad laminate with an inner layer circuit according to the present invention uses a Brinell hardness of 60 (HBW) as a metal mirror plate interposed between the laminated structures.
(10/500) or more is used.

In the production of a multilayer metal-foil-clad laminate with an inner layer circuit, it is necessary to maintain the strength of the metal mirror plate so as not to absorb the unevenness of the printed circuit of the core substrate. 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. In general, the hardness of a metal decreases as the temperature increases, but by limiting the hardness of the metal mirror plate at room temperature as described above, the hardness of the metal mirror plate in a 150 ° C. atmosphere is also necessary and sufficient. By using a mirror surface plate made of
Even if the prepreg characteristics are not particularly changed, it is possible to obtain a multilayer metal foil-clad laminate with an inner layer circuit in which no irregularities appear on the surface or irregularities appearing on the surface are suppressed.

For specifying the mechanical properties of the wrought metal, numerical values such as a tensile test, a bending test, and a hardness test are used.
In the present invention, Brinell hardness by a hardness test was adopted as an index of the strength of the metal mirror plate.

In the present invention, the upper limit of the Brinell hardness of the metal mirror plate is naturally limited to a value that allows finish processing to a thickness of 0.8 mm or less by rolling. Further, unless the thickness of the metal mirror plate is set to 0.4 mm or more, even if the Brinell hardness 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 pressing is preferably controlled as follows. That is, the heating and pressurization was started, the resin contained in the prepreg was melted, the viscosity was reduced, and the heating and pressurizing was performed at 1 MPa or less until the viscosity became 5 kPa / s or less, and the viscosity became 5 kPa / s. The pressure is increased to a predetermined pressure at the stage, and the heating and pressurization is continued. According to this method, a resin in a molten state has a function as a cushion for absorbing irregularities of a printed circuit on a core substrate. Until the resin contained in the prepreg is melted, the pressure is maintained at a low level that does not cause deformation of the metal mirror plate due to the unevenness of the printed circuit.When the resin melts and its viscosity decreases, the molten resin is The pressure is increased to the pressure required to fill the recess between the printed circuits, and the heating and pressing are 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.

[0013]

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. This laminated structure 1 is formed by pressing under heat and pressure between press hot plates and integrated, but a plurality of sets of laminated structures 1 are put between the press hot plates, and 0.8 ~
A 0.4 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 stainless steel mirror plate 3
It 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 metal mirror plate 2 has a Brinell hardness of 60 (HBW 10/500) or more. Needless to say, a mirror plate having a thickness of 0.8 mm or less must be formed by rolling, and there is naturally an upper limit of the Brinell hardness at which such rolling is possible. The material that can be easily rolled and rolled to 0.8 mm or less is aluminum,
Iron and the like are not limited to these simple substances, but there are many types such as alloys containing them, 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.

1MPa until the viscosity of the resin contained in the prepreg melts and decreases to a viscosity of 5 kPa / s or less.
The embodiment of the invention in which heating and pressurizing is performed below and the pressure is increased to a predetermined pressure when the viscosity becomes 5 kPa / s 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. During the pressing, the viscosity of the resin is estimated on the basis of 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-4)
The temperature rise rate is 1 ° C / min, 2 ° C / min, 3 ° C / min.
The relation between the temperature of the prepreg and the viscosity of the resin in each case of min is shown. As the heating rate increases, the resin viscosity reaches 5 kPa / s at a lower temperature, and the minimum melt viscosity also decreases.

[0016]

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 and the mirror plate between the press hot plates is as described above with reference to FIG. 1, and the heating rate of heating was set at 2 ° C./min. Further, as the metal mirror plate 2 interposed between the laminated structures,
A 0.4 mm thick aluminum mirror plate was used. This aluminum mirror plate was an aluminum-magnesium alloy, and three types (Brinell hardness of 40, 60 and 80 (HBW10 / 500)) having different chemical components and qualities were selected. Table 1 shows the Brinell hardness of the aluminum mirror plate used in each example, and also shows 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 kPa / s. . In Examples 2, 4, 6, and 8 and Comparative Examples 2 and 4, the pressure was not increased during the molding, and the heating and press molding was performed at a constant pressure of 2.5 MPa from the beginning. Surface roughness R of four-layer copper-clad laminate with inner layer circuit formed in each example
a is also shown in Table 1.

[0017]

[Table 1]

Based on the data shown in Table 1, the relationship between the Brinell hardness of the aluminum mirror plate and the surface roughness of the four-layer copper-clad laminate containing the inner layer circuit is shown in FIG.
(B). FIG. 3 (a) shows a case where the molding pressure is increased and the heating and pressing molding is performed when the viscosity of the resin contained in the prepreg reaches 5 kPa / s, and FIG. 3 (b) shows a case where the pressure is increased during molding. In this case, the heating and pressing was performed at a constant pressure of 2.5 MPa from the beginning. From FIG. 3, the Brinell hardness of the aluminum mirror plate is increased in both cases where the thickness of the copper foil of the core substrate is large and small, when the molding pressure is increased during molding, and when molding is performed at a predetermined pressure from the beginning. It can be understood that setting the surface roughness to 60 (HBW 10/500) or more leads to a reduction in surface roughness. FIG.
From the comparison between (a) and (b), it can also be understood that lowering the pressure in the initial stage and increasing the pressure in the middle of the molding leads to a further reduction in the surface roughness.

In the above-described 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.

[0020]

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 Brinell hardness 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. Furthermore, when the viscosity of the resin contained in the prepreg is reduced in the heating and pressing step and the operation of increasing the molding pressure from an initial low pressure to a predetermined pressure at a stage when the resin pressure reaches 5 kPa / s is performed, irregularities appearing on the surface are further reduced. can do.

[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 Brinell hardness 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

Continued on front page F-term (reference) 4F100 AB01C AB17 AB33C AG00 AK53 AT00A BA10A BA10C DG12 DH01B EJ202 EJ422 GB43 JK15 5E346 AA06 AA12 AA15 BB01 CC02 CC08 EE02 EE06 EE09 EE13 EE14 GG01 GG28 HH11

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 components, and the metal mirror plate has a thickness of 0.8 mm.
And a Brinell hardness of 60 (HBW1
0/500) or more. 2. The resin contained in the prepreg is melted to lower its viscosity, and is heated and pressurized at a pressure of 1 MPa or less until the viscosity becomes 5 kPa / s, and when the viscosity becomes 5 kPa / s. 2. The method for producing a multilayer metal-foil-clad laminate with an inner circuit according to claim 1, wherein the pressure is increased to a predetermined pressure and the heating and press-forming is performed.