JP2007165436A - Process for manufacturing circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board, equipped with an IVH structure ideal as a high density board in a very easy and stable manner in which interlayer electrical connection by conductive paste can be precisely ensured. <P>SOLUTION: The process for producing a circuit board comprises a step for forming a laminate, by laminating prepreg sheets 11 each provided previously with via holes filled with conductive paste 16 on opposite sides of a core substrate 12 equipped with two or more wiring layers 17 and then further laminating a metal foil 13, and a step for alternately laminating the laminate and a metal intermediate plate and then hardening the laminate by hot-pressing at a temperature for curing the resin of the prepreg sheet in the laminate, wherein the prepreg sheet 11 comprises a layer 14 of thermosetting resin under semi-cured state on the opposite surfaces of a reinforcing material 15 and the ratio of (thickness t<SB>r</SB>of the resin layer 14)/(thickness t<SB>c</SB>of the wiring layer 17 on the core substrate) is 1.5 or smaller. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a circuit board used in various electronic devices.

  As electronic devices have become smaller and more dense in recent years, circuit boards on which electronic components are mounted have been increasingly adopted from the conventional single-sided board to double-sided and multilayer boards, and more circuits and components can be integrated on the board. High density substrates have been developed.

  A conventional example will be described below with reference to FIG.

  A substrate material 21 shown in FIG. 3A is a so-called prepreg sheet in which a glass fiber woven fabric used for a circuit board is impregnated with a thermosetting epoxy resin or the like to be in a B-stage state by a method such as drying. A film 22 is attached to both sides of the substrate material 21 by a laminating method using a hot roll or the like.

  Next, as shown in FIG. 3B, via holes 23 are formed in the substrate material 21 by a processing method such as a laser, and then conductive particles such as copper powder and a thermosetting resin, a curing agent, a solvent, and the like are kneaded. Then, the conductive paste 24 made into paste is filled to obtain the configuration shown in FIG.

  Next, the film 22 is peeled to obtain a shape in which the conductive paste 24 protrudes as shown in FIG. 3D, and the copper foil 25 is disposed on both sides thereof.

  Next, the substrate material 21 is heat-cured as shown in FIG. 3 (e) by being sandwiched between SUS and other metal intermediate plates and heated and pressed by a hot press (not shown), and the conductive paste 24 is compressed and turned upside down. The copper foil 25 is electrically connected.

  Further, the copper foil 25 is processed into a desired pattern by a method such as photolithography etching to form a circuit wiring layer 26, thereby obtaining a double-sided circuit board as shown in FIG.

  In FIG. 3, a surface finish process such as a solder resist of the outer layer portion usually disposed on the circuit board or a plating process on the circuit wiring layer 26 is not shown, but is disposed as necessary.

  Further, when manufacturing a multilayer circuit board, as shown in FIG. 4, a substrate material 36 filled with a conductive paste 35 and a copper foil 34 are overlapped on top and bottom of a once completed core substrate 31 while being aligned. Heat press. Thereby, a laminated cured product as shown in FIG. 4C can be obtained.

  Further, the copper foil 34 is processed into a desired pattern by a method such as photolithography etching to form a circuit wiring layer 37, thereby obtaining a multilayer circuit board as shown in FIG.

  In FIG. 4, a surface finish process such as a solder resist on the outer layer portion usually disposed on the circuit board or a plating process on the circuit wiring layer 37 is not shown, but is disposed as necessary.

  In addition, by repeating the above manufacturing method, a multilayered circuit board can be obtained.

  However, when the multilayer circuit board is formed by the manufacturing method as described above, a defect may occur in the interlayer connection between the surface layer copper foil and the circuit of the core board. This will be described below with reference to FIG.

  That is, the conductive particles in the conductive paste 43 as shown in FIG. 5A are generated as outflow particles 45 flowing out of the via holes 44 along with the resin flow when the prepreg sheet is heated, or FIG. The via deformation 47 is caused by the external force 46 in the surface direction of the prepreg sheet generated during the forming process as shown in b).

  The surface direction external force 46 is generated when the thermal expansion coefficient of the metal intermediate plate (not shown) to be used is significantly different from the thermal expansion coefficient of the core substrate (not shown) in the hot press process.

  In order to realize an ideal electrical connection, as shown in FIG. 5 (c), the conductive paste 43 efficiently contacts the conductive particles in the conductive paste efficiently by the vertical compression force 48 in the vertical direction. However, the surface metal foil and the inner wiring layer need to be in strong contact.

  Therefore, the generation of the outflow particles 45 and the via deformation 47 are the result of insufficient efficient compression of the conductive paste.

  In order to solve the above-mentioned problems, the present inventors set a specific temperature condition or select a specific metal intermediate plate in the hot press process to prevent via deformation and make the conductive paste efficient. The method of compression was also examined, and it was confirmed that it was effective.

As prior art document information related to the invention of this application, for example, Patent Document 1 and Patent Document 2 are known.
JP-A-6-268345 JP 2004-221236 A

  However, even when the method of the present inventors is used, a defect may occur in the interlayer connection between the surface layer copper foil and the circuit of the core substrate.

  That is, in the circuit board molding process, if the flow of the thermosetting resin of the prepreg sheet is remarkably large or the amount of the resin is large, even if the conductive paste is once vertically compressed in the vicinity of the softening temperature of the resin, it is excessive due to subsequent heating. There is a problem that the compression of the resin is eased by the resin flow, and it is difficult to ensure the electrical connection between the layers.

  Even when via deformation is suppressed by using an appropriate metal intermediate plate at the time of molding, if the resin amount of the prepreg sheet is too large, the amount of compression of the conductive paste becomes insufficient, and as a result, the electrical connection between the layers can be ensured. It can be difficult.

  The present invention first discloses an appropriate material configuration for a circuit board having an interlayer electrical connection using a conductive paste, and uses the material configuration in a manufacturing method.

  As a result, the interlayer electrical connection by the conductive paste can be ensured accurately, and a circuit board having an ideal IVH structure as a high-density board can be provided very easily and stably.

  In order to solve the above problems, the present invention has the following configuration.

  That is, a step of stacking a prepreg sheet having via holes filled with a conductive paste on both surfaces of a core substrate having two or more wiring layers and further stacking a metal foil to form a laminate, and heating the laminate The prepreg sheet includes a resin layer made of a thermosetting resin in a semi-cured state on both surfaces of the reinforcing material, and (thickness of the resin layer) / ( The circuit board manufacturing method is characterized in that the ratio of the wiring layer thickness of the core substrate is 1.5 or less, or a conductive paste is filled on both surfaces of the core substrate having two or more wiring layers A step of stacking prepreg sheets having via holes, further stacking metal foils to form a laminate, a step of alternately stacking the laminate and metal intermediate plate, and a step of heating and pressing the laminate to cure and form the laminate And The prepreg sheet has a resin layer made of a thermosetting resin in a semi-cured state on both surfaces of the reinforcing material, and (thickness of the resin layer) / (wiring layer thickness of the core substrate) A circuit board manufacturing method characterized in that the ratio is 1.5 or less.

  An example of the above configuration will be described below with reference to FIG.

In the present invention, a prepreg sheet 11 preliminarily provided with via holes filled with a conductive paste 16 is stacked on both surfaces of a core substrate 12 including two or more wiring layers 17 and a metal foil 13 is further stacked to form a laminate. A circuit board including at least a step of forming, and a step (not shown) of alternately laminating the laminate and the metal intermediate plate, and heating and pressing at a temperature at which the resin of the prepreg sheet of the laminate is cured. in the method of manufacturing prepreg sheet 11 is its use is provided with a resin layer 14 made of a thermosetting resin in a semi-cured state on both surfaces of the reinforcing member 15, and (the thickness t _r of the resin layer 14 ) / (Thickness t _c of the wiring layer 17 of the core substrate) is 1.5 or less.

  Although it is the lower limit side of the ratio, this is determined by the moldability (circuit filling), so it is not particularly limited in the present invention, and may be any value that does not cause molding defects. The thickness of the resin layer 14 of the prepreg sheet 11 may be determined from the thickness of 17 and the area ratio of the wiring layer 17 in the substrate area.

  The step of curing and molding the laminate by heating and pressurizing in the method for manufacturing a circuit board is performed at a first heating temperature for a certain period of time, and then a second heating temperature higher than the first heating temperature. After heating for a certain time, it is preferable to heat for a certain time at a third heating temperature higher than the second heating temperature.

  In particular, the first heating temperature is preferably once heated for a certain period of time at a temperature near the resin softening point of the prepreg sheet 11 before the laminate is cured and formed.

  The thermal expansion coefficient of the metal intermediate plate is preferably in the vicinity of the thermal expansion coefficient of the core substrate 12. Of course, they may be included in the circuit board manufacturing method. When the insulating layer of the core substrate 12 is made of a general glass epoxy, the thermal expansion of SUS304 or SUS301 as the metal intermediate plate approximates the core substrate, and is most preferable.

  Next, although it is the detail of the prepreg sheet 11 used for the manufacturing method of the said circuit board, it is preferable that the resin softening temperature of the prepreg sheet 11 is lower than the reaction start temperature of the electrically conductive paste 16 used in that case.

  The conductive paste 16 is a mixture including at least conductive particles and a thermosetting resin, and the conductive particles are preferably a metal such as gold, copper, silver, indium, solder, Particles in which the metal is covered on the surface of the spherical substance may be used. On the other hand, it is preferable that the thermosetting resin of the conductive paste 16 is mainly composed of a liquid epoxy resin.

  In addition, the reinforcing material 15 of the prepreg sheet 11 is preferably one or more of a glass fiber woven fabric and a glass fiber non-woven fabric when an inorganic reinforcing material is mainly used. Furthermore, it is more preferable that the resin of the prepreg sheet 11 using them as the reinforcing material 15 contains an inorganic filler in the range of 30 to 80 phr.

  The specific inorganic filler is not particularly limited as long as it is non-conductive such as silica, aluminum hydroxide, aluminum nitride, and alumina. However, the filler size is preferably 10 μm or less in diameter. On the other hand, when the organic reinforcing material is mainly used, it is preferably at least one of organic films such as polyimide and aramid, aramid woven fabric, and aramid nonwoven fabric.

  Furthermore, the resin of the prepreg sheet 11 described so far is most preferably an epoxy resin as a main component, but may be a polyimide resin, a polyester resin, a cyanate ester resin, or the like.

  Further, the details of the other constituent materials in the present invention are as follows. The core substrate 12 may be a circuit substrate having two or more layers, and the via hole 18 for electrically connecting the layers is not limited to a conductive paste. In particular, it may be secured by through holes, bumps, filled plating or the like, and is not particularly limited. However, the surface of the wiring layer 17 of the core substrate 12 is preferably roughened. Specifically, the surface of the double-side roughened foil is used, or chemical polishing such as CZ treatment or physical polishing such as sandblasting is performed. It may be formed by processing.

  Further, in the case of a core substrate (not shown) provided with a through hole, it is preferable to fill the cavity with resin or to perform lid plating.

  Furthermore, the metal foil 13 of the present invention is preferably a copper foil that is generally used for circuit board applications.

When manufacturing a high layer of the circuit board by repeating the method of manufacturing a circuit board of the present invention, the ratio of (the thickness t _r of the resin layer 14 of prepreg sheet 11) / (the thickness t _m of the metal foil 13) If it is 1.5 or less, the effect of the present invention is naturally obtained.

  A step of stacking a prepreg sheet preliminarily provided with via holes filled with a conductive paste on both surfaces of a core substrate including two or more wiring layers, and further stacking a metal foil to form a laminate; In the method of manufacturing a circuit board, which includes at least a step of alternately stacking metal intermediate plates and heating and pressing at a temperature at which the resin of the prepreg sheet of the laminate is cured, the prepreg sheet used is reinforced A resin layer made of a thermosetting resin in a semi-cured state on both surfaces of the material, and a ratio of (thickness of the resin layer) / (wiring layer thickness of the core substrate) is 1.5 or less; By satisfying the requirements, it is possible to easily compress the via conductive paste to ensure electrical connection between layers, and to form IVH which is an ideal interlayer connection method for increasing the density of circuit boards. .

  Also, in the above circuit board manufacturing method, the laminate is heated once at a temperature near the resin softening point of the prepreg sheet before being cured, or the thermal expansion coefficient of the metal intermediate plate is the thermal expansion coefficient of the core board. By adding at least one of the proximity, the conductive paste of the via can be compressed extremely efficiently, so that high quality IVH can be provided to the circuit board.

  Furthermore, if the resin softening temperature of the prepreg sheet used in the method for manufacturing a circuit board of the present invention is lower than the reaction start temperature of the conductive paste used at that time, the conductive paste of the via is firstly removed in the softened state of the prepreg sheet. After sufficient compression, the conductive paste begins to harden, so that the electrical connection between the layers can be more easily ensured.

  Moreover, the circuit board provided with highly rigid IVH can be provided by selecting either a glass fiber woven fabric or a glass fiber nonwoven fabric as the reinforcing material of the prepreg sheet.

  Further, by including an inorganic filler in the range of 30 to 80 phr in the resin of these prepreg sheets, the structure is such that a prepreg sheet having a structure in which resin flow is relatively likely to occur, for example, a glass fiber woven fabric impregnated with a thermosetting resin. However, since the resin flow can be controlled, sufficient electrical connection between the layers can be easily ensured.

  In addition, by selecting any one of an organic film, an aramid woven fabric, and an aramid nonwoven fabric as a reinforcing material for the prepreg sheet, a circuit board having a lightweight and low dielectric IVH can be provided.

  Furthermore, the present invention not only provides a circuit board having an IVH made of a high-quality conductive paste, but also facilitates the material design of a prepreg sheet suitable for the circuit board, and consequently the structural specifications of the desired circuit board. On the other hand, all combinations of the required wiring layer material and prepreg sheet can be determined simultaneously with the design. That is, since verification for finding out the structural specification that is normally performed is unnecessary, a circuit board having a high-quality IVH structure can be provided stably and in various specifications in a short period of time.

  A method for manufacturing a circuit board in the embodiment of the present invention will be described below.

(Embodiment)
The materials used in the circuit board manufacturing method of the present invention and the formation of the characteristic laminated cured product of the present invention will be described in detail below with reference to FIG. 1 and FIG. A part of the description of the same steps is omitted.

Example 1
The prepreg sheet 11 was impregnated with 50 wt% of a thermosetting epoxy resin containing 50 phr of aluminum hydroxide having a softening point of 70 ° C. and a particle size of 2 to 8 μm on a glass fiber woven fabric of 250 mm square and a thickness of about 80 μm and semi-cured. A composite material was used. As a schematic configuration, the resin layer 14 in FIG. 1 is a thermosetting epoxy resin and has a thickness of 7.4 μm, and the reinforcing material 15 is a glass woven cloth and has a thickness of 80 μm.

  The conductive paste 16 to be filled is mainly composed of copper powder and a thermosetting epoxy resin (solvent-free type), and contains an acid anhydride-based curing agent, which is 85% by weight and 12.5% by weight, respectively. And kneaded sufficiently with three rolls so as to be 2.5% by weight. Note that the reaction start temperature of the conductive paste 16 is 120 ° C.

  Further, as the core substrate 12, the thickness of the prepreg sheet 11 and the conductive paste 16 manufactured by the same manufacturing method as in FIG. 3 and electrically connected between the layers through the via holes 18 made of the conductive paste 16. A double-sided substrate of about 100 μm was used.

A prepreg sheet 11 is laminated on both surfaces of the core substrate 12 and a copper foil 13 having a thickness of 14 μm (mass thickness 128 g / m ² ) is further laminated to prepare a laminated body. The laminated body is SUS304 having a thickness of about 1 mm. Ten sets were placed on the plate via the plate.

  Next, the laminated set is put into a vacuum hot press, and once heated and held at 70 ° C., which is the resin softening temperature of the prepreg sheet, as shown in FIG. -The temperature increase rate in the curing region was set to 5 ° C / min. In addition, it shape | molded by heating and pressurizing with a pressure of 5 MPa.

  Next, a circuit wiring layer was formed on the cured laminate by a photolithography etching method to obtain a four-layer circuit board. The four-layer circuit board is a test board in which the outermost wiring layer and the inner core board wiring layer are interconnected by vias having a hole diameter of 150 μm, and vias having a total of 600 holes are connected in series. Six test boards per set were assigned.

(Example 2)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a glass fiber woven fabric having a thickness of about 80 μm is impregnated with 54 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 12.4 μm.

(Example 3)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a glass fiber woven fabric having a thickness of about 80 μm is impregnated with 58 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 18.2 μm.

Example 4
A prepreg sheet 11 obtained by impregnating 60 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. into a glass fiber woven fabric having a thickness of about 80 μm and a wiring layer thickness of 18 μm (mass thickness 165 g / m ² ) are used. Example 1 is the same as Example 1 except that a core substrate is used. That is, as a schematic configuration of FIG. 1, the thickness of the wiring layer 17 of the core substrate 12 of Example 1 is 18 μm, and the thickness of the resin layer 14 of the prepreg sheet 11 is 21.6 μm.

(Example 5)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a glass fiber woven fabric having a thickness of about 100 μm is impregnated with 50 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 9.6 μm.

(Example 6)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a glass fiber woven fabric having a thickness of about 100 μm is impregnated with 56 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 19.6 μm.

(Example 7)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a thermosetting epoxy resin having a softening point of 70 ° C. is impregnated in a glass fiber woven fabric having a thickness of about 30 μm is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 11.7 μm.

(Example 8)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a glass fiber woven fabric having a thickness of about 30 μm is impregnated with 76 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 20.5 μm.

(Comparative Example 1)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which 60 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is impregnated into a glass fiber woven fabric having a thickness of about 80 μm is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 21.6 μm.

(Comparative Example 2)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a glass fiber woven fabric having a thickness of about 100 μm is impregnated with 58 wt% of a thermosetting epoxy resin having a softening point of 70 ° C. is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 23.6 μm.

(Comparative Example 3)
Example 1 is the same as Example 1 except that a prepreg sheet 11 in which a thermosetting epoxy resin having a softening point of 70 ° C. is impregnated in a glass fiber woven fabric having a thickness of about 30 μm is used. That is, as a schematic configuration of FIG. 1, the thickness of the resin layer 14 of Example 1 is 23.8 μm.

  The wiring resistance of the test substrates obtained in Examples 1 to 8 and Comparative Examples 1 to 3 was measured, and the via connection was evaluated. In conducting the connection evaluation, the resistance value of the copper foil wiring layer was subtracted from the wiring resistance, and the connection resistance of the via alone was estimated and verified.

  First, Examples 1 to 4 and Comparative Example 1 are summarized in (Table 1).

  From Table 1, as the ratio of the resin layer thickness to the wiring layer thickness increases, the connection resistance value increases, and when it exceeds 1.5, the connection resistance value increases remarkably. Here, the increase in the connection resistance value in Examples 1 to 3 is proportional to the increase in the resin layer thickness and does not show any abnormality, and is quite normal.

  However, in Comparative Example 1, the increase in the resistance value far exceeded the amount of increase in the resin layer thickness, and when this was analyzed, the outflow of the paste particles described in FIG. 5 was detected.

  On the other hand, Example 4 was obtained by using the same prepreg sheet as in Comparative Example 1 and increasing the wiring layer thickness of the core substrate. As seen from this result, in Comparative Example 3, the connection was extremely difficult. However, the connection resistance can be secured by increasing the wiring layer thickness of the core substrate so that the ratio is 1.5 or less, which is a feature of the present invention. Has been demonstrated.

  Therefore, it can be said that the relative relationship between the thickness of the resin layer of the prepreg sheet and the thickness of the wiring layer of the core substrate greatly contributes to the connection by the conductive paste.

  Furthermore, it was proved that this relationship was established even when the thickness of the reinforcing material was changed. The results are summarized in (Table 2) and (Table 3).

  In any reinforcing material thickness (100 μm and 30 μm), when the ratio exceeded 1.5, it was extremely difficult to ensure connection resistance. That is, it can be said that the electrical connection of the conductive paste is dominated by the thickness of the resin layer formed on the surface layer regardless of the thickness of the reinforcing material.

  By the way, the amount of resin generally used as the specification of the prepreg sheet (weight ratio of the resin in the prepreg sheet) is determined from the moldability of the circuit board. That is, the determination condition is only to sufficiently fill the wiring layer of the core substrate. However, it is very unlikely that the core substrate can be used for the circuit substrate connected with the conductive paste.

  Therefore, by adding the conditions of the present invention to these conditions, it is possible to easily manufacture a circuit board connected with a conductive paste using a prepreg sheet made of any reinforcing material thickness and material. From this, it is possible to determine all combinations of the required wiring layer material and prepreg sheet at the same time as the design with respect to the structural specifications of the desired circuit board.

  Therefore, verification for finding out the structural specification that is normally performed is unnecessary, and a circuit board having a high-quality IVH structure can be provided stably and with various specifications in a short period of time.

  In the present embodiment, the multilayer circuit board having four layers is described as the multilayer circuit board. However, the same effect can be obtained with a multilayer circuit board having four or more layers. In addition, the present invention is not limited to the materials and conditions shown in each embodiment, and similar effects can be obtained if the ratio of the resin layer thickness of the prepreg sheet to the wiring layer thickness of the core substrate is 1.5 or less. Is obtained.

  As described above, according to the configuration of the present invention, it is possible to facilitate electrical connection using the interlayer connection means of the conductive paste, and to provide a high-quality circuit board with high quality and quick delivery. The above applicability is great.

Sectional drawing which shows the manufacturing method of the circuit board in embodiment of this invention The figure which shows the temperature profile which shape | molds the lamination | stacking hardened | cured material in embodiment of this invention Process cross-sectional schematic diagram showing a method for manufacturing a double-sided circuit board in a conventional example Process cross-sectional schematic diagram showing a method of manufacturing a multilayer circuit board in a conventional example Schematic diagram showing cross section and external force direction showing via shape of circuit board in conventional example

Explanation of symbols

11, 21, 36 Substrate material (prepreg sheet)
12, 31 Core substrate 13, 25, 34 Metal foil (copper foil)
DESCRIPTION OF SYMBOLS 14 Resin layer 15 Reinforcement material 16, 24, 35, 43 Conductive paste 17, 26 Circuit wiring layer 18, 23, 44 Via hole 22 Film 45 Outflow particle 46 Surface direction external force 47 Via deformation 48 Vertical compression force

Claims (9)

A step of stacking a prepreg sheet having via holes filled with a conductive paste on both surfaces of a core substrate having two or more wiring layers, and further stacking a metal foil to form a laminate, and heating and pressurizing the laminate And a step of curing and molding,
The prepreg sheet includes a resin layer made of a thermosetting resin in a semi-cured state on both surfaces of the reinforcing material, and a ratio of (thickness of the resin layer) / (wiring layer thickness of the core substrate) is A method for producing a circuit board, which is 1.5 or less. The step of curing and molding the laminate by heating and pressing includes heating for a certain time at a first heating temperature, then heating for a certain time at a second heating temperature higher than the first heating temperature, 2. The circuit board manufacturing method according to claim 1, further comprising a temperature condition in which heating is performed for a predetermined time at a third heating temperature that is higher than the heating temperature of 2. The method for manufacturing a circuit board according to claim 2, wherein the first heating temperature is a temperature in the vicinity of the resin softening temperature in the prepreg sheet. The method for producing a circuit board according to claim 3, wherein a resin softening temperature of the prepreg sheet is lower than a reaction start temperature of the conductive paste containing at least conductive particles and a thermosetting resin. 2. The circuit board according to claim 1, wherein the prepreg sheet is obtained by impregnating a reinforcing material with a resin, and the reinforcing material is selected from at least one kind of glass fiber woven fabric or glass fiber nonwoven fabric. Production method. 6. The method of manufacturing a circuit board according to claim 5, wherein the resin of the prepreg sheet contains an inorganic filler in the range of 30 to 80 phr. The prepreg sheet is obtained by impregnating a reinforcing material with a resin,
The method for producing a circuit board according to claim 1, wherein the reinforcing material of the prepreg sheet is selected from at least one selected from an organic film, an aramid woven fabric, and an aramid nonwoven fabric. A step of stacking a prepreg sheet having via holes filled with a conductive paste on both surfaces of a core substrate having two or more wiring layers and further stacking a metal foil to form a laminate, and the laminate and the metal intermediate plate And a step in which the laminate is heated and pressurized to be cured and molded, and the prepreg sheet has a resin layer made of a thermosetting resin in a semi-cured state on both surfaces of the reinforcing material And the ratio of (thickness of the resin layer) / (wiring layer thickness of the core substrate) is 1.5 or less. 9. The method of manufacturing a circuit board according to claim 8, wherein a thermal expansion coefficient of the metal intermediate plate is close to a thermal expansion coefficient of the core board.

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