JP7515099B2 - Manufacturing method of laminate and manufacturing method of printed wiring board - Google Patents

Description

This disclosure relates to a method for manufacturing a laminate and a method for manufacturing a printed wiring board.

Patent Document 1 discloses a method for manufacturing a multilayer laminate. This manufacturing method includes disposing a first prepreg layer between first and second metal foils, forming a first insulating layer by thermally curing the first prepreg layer under pressure, and forming a first conductor wiring by performing a wiring formation process on the first metal foil. The above manufacturing method further includes laminating a second prepreg layer and a third metal foil in this order on the first conductor wiring, and thermally curing the second prepreg layer under pressure to form a second insulating layer to obtain a multilayer laminate.

JP 2016-129264 A

In the case of Patent Document 1, a multilayer printed wiring board (printed wiring board) can be obtained by fabricating conductor wiring from each of the second and third metal foils. However, in this case, the printed wiring board may be prone to warping.

The objective of the present disclosure is to provide a method for manufacturing a laminate that can be used to manufacture a printed wiring board and that can reduce the risk of warping in the printed wiring board, and a method for manufacturing a printed wiring board using this laminate.

A method for manufacturing a laminate according to one embodiment of the present disclosure includes a lamination step of laminating a resin sheet and a metal foil in this order on a core material having a first conductor layer, a first insulating layer, and a second conductor layer laminated in this order to produce a laminate, and a heating step of heating the laminate to produce a laminate having the core material, a second insulating layer made from the resin sheet, and a third conductor layer made from the metal foil laminated in this order. The second insulating layer has a higher resin content than the first insulating layer. The heating step is performed in a state where the laminate is curved so that the outer surface of the metal foil is convex.

A method for manufacturing a printed wiring board according to one embodiment of the present disclosure includes a wiring formation step of fabricating conductor wiring by removing a portion of at least one of the second conductor layer and the third conductor layer in the laminate.

The above-described aspects of the present disclosure have the advantage of providing a method for manufacturing a laminate that can be used to manufacture a printed wiring board and that can reduce the risk of warping in the printed wiring board, and a method for manufacturing a printed wiring board using this laminate.

FIG. 1 is a cross-sectional view of a laminate according to one embodiment of the present disclosure. FIG. 2 is an explanatory view of an example of a step of laminating a first conductor layer, a first insulating layer, and a second conductor layer in the above embodiment. 3A and 3B are cross-sectional views of a first and second example core material according to the embodiment. FIG. 4 is an explanatory diagram of an example of a step of overlaying a resin sheet and a metal foil on the first conductor layer in the above embodiment. Fig. 5A is a perspective view of the laminate according to the embodiment in a rolled up state, and Fig. 5B is a cross-sectional view of the laminate. FIG. 6 is a cross-sectional view of the printed wiring board according to the above embodiment.

First, we will provide an overview of one embodiment of the present disclosure.

The method for manufacturing the laminate 12 according to this embodiment includes a lamination step (see FIGS. 2 to 4) of manufacturing a laminate 11 by stacking a resin sheet 2B and a metal foil 33 in this order on the first conductor layer 34 of a core material 14 in which a first conductor layer 34, a first insulating layer 21, and a second conductor layer 38 are stacked in this order. This method further includes a heating step (see FIGS. 1 and 5A to 5B) of manufacturing a laminate 12 in which a core material 14, a second insulating layer 22 made of a resin sheet 2B, and a third conductor layer 39 made of a metal foil 33 are stacked in this order by heating the laminate 11. The second insulating layer 22 has a higher resin content than the first insulating layer 34. The heating step is performed in a state in which the laminate 11 is curved so that the outer surface of the metal foil 33 is convex.

By removing a portion of each of the second conductor layer 38 and the third conductor layer 39 in the laminate 12, the first conductor wiring 35 and the second conductor wiring 36 can be produced from the second conductor layer 38 and the third conductor layer 39, respectively. This allows the printed wiring board 13 to be manufactured.

According to this embodiment, warping of the printed wiring board 13 can be prevented. The reason for this is presumably as follows.

When the laminate 11 is heated to produce the laminate 12, stress is likely to occur inside the second insulating layer 22 in a direction that causes the second insulating layer 22 to shrink. This is because the second insulating layer 22 has a higher resin content than the first insulating layer 34, and therefore the second insulating layer 22 is more likely to shrink than the first insulating layer 34 when cooled after heating. Also, if the resin sheet 2B has thermosetting properties, the second insulating layer 22 is more likely to shrink due to the hardening shrinkage caused by the hardening of the resin sheet 2B. Therefore, if the heating process is performed without bending the laminate 11, if conductor wiring is produced from the second conductor layer 34 and the third conductor layer 39 by removing parts of each of the second conductor layer 38 and the third conductor layer 39, the constraint applied to the second insulating layer 22 will be loosened, and the stress in the second insulating layer 22 will be released, causing the second insulating layer 22 to shrink, and the printed wiring board will be prone to warping.

However, in this embodiment, as described above, the heating process curves the laminate 11 so that the outer surface 3A of the metal foil 33 becomes convex, and therefore the laminate 11 is prone to warping in the opposite direction to the warping that occurs during the manufacture of the printed wiring board 13. Therefore, when the printed wiring board 13 is manufactured from this laminate 11, it is believed that the tendency for warping that occurs during the manufacture of the laminate 11 and the tendency for warping that occurs due to the shrinkage of the second insulating layer 22 during the manufacture of the printed wiring board 13 cancel each other out, making the printed wiring board 13 less likely to warp.

Next, this embodiment will be described in more detail with reference to Figures 1 to 6.

The laminate 12 manufactured in this embodiment has a structure in which the second conductor layer 38, the first insulating layer 21, the first conductor layer 34, the second insulating layer 22, and the third conductor layer 39 are laminated in this order, as shown in FIG. 1. The laminate 12 may be curved so that the outer surface of the third conductor layer 39 is convex. In other words, the laminate 12 may be curved so as to protrude in the direction D1 from the first insulating layer 21 toward the second insulating layer 22.

The first conductor layer 34 is a layer made of the first metal foil 31 (see FIG. 2) and is embedded between the first insulating layer 21 and the second insulating layer 22. In the example of FIG. 1, the first conductor layer 34 is wiring 37. Note that the first conductor layer 34 may not be wiring 37, but may be, for example, metal foil. When the first conductor layer 34 is wiring 37, the first conductor layer 34 is formed, for example, by removing a portion of the first metal foil 31 laminated on the first insulating layer 21 by etching or the like.

The second conductor layer 38 is a layer made from the second metal foil 32 and is formed in close contact with the first insulating layer 21.

The third conductor layer 39 is a layer made of metal foil (third metal foil) 33 and is formed in close contact with the second insulating layer 22.

The first insulating layer 21 is an electrically insulating layer, and is formed by adhering the first resin sheet 2A (see FIG. 2) to the first conductor layer 34 and the second conductor layer 38. When the first conductor layer 34 is wiring 37, the first insulating layer 21 is also in close contact with the second insulating layer 22.

Examples of the first resin sheet 2A include a liquid crystal polymer film, a polyimide film, and a prepreg.

The first resin sheet 2A contains, for example, a thermosetting resin. In this case, it is preferable that the first resin sheet 2A is a prepreg.

When the first resin sheet 2A is a prepreg, the prepreg is obtained by impregnating a reinforcing material with a thermosetting resin composition (hereinafter, sometimes referred to as composition (X)), and then heating and drying the composition (X) as necessary.

Composition (X) contains a thermosetting resin.

The thermosetting resin may contain at least one resin selected from the group consisting of, for example, epoxy resin, phenol resin, cyanate resin, melamine resin, and imide resin. Examples of the epoxy resin include multifunctional epoxy resin, bisphenol type epoxy resin, novolac type epoxy resin, and biphenyl type epoxy resin.

Composition (X) may further contain a filler.

The filler is preferably an inorganic filler. The inorganic filler may contain at least one selected from the group consisting of, for example, silica, aluminum hydroxide, magnesium hydroxide, calcium carbonate, talc, and alumina.

The proportion of the filler relative to the total amount of composition (X) is preferably 30% by mass or more and 80% by mass or less. When the proportion of the filler is 30% by mass or more, the dimensional change before and after the etching treatment and the dimensional change from the etching treatment to the aging treatment can be made smaller. Furthermore, when the proportion of the filler is 80% by mass or less, the composition (X) can be impregnated into the reinforcing material.

Composition (X) may further contain a curing agent and a curing accelerator.

Examples of hardeners include phenol-based hardeners and dicyandiamide hardeners.

Examples of curing accelerators include imidazoles, phenolic compounds, amines, and organic phosphines.

Composition (X) may further contain a solvent. This solvent is used to dilute the components in composition (X). Composition (X) containing a solvent is also called a varnish. Examples of the solvent include methyl ethyl ketone, toluene, styrene, and methoxypropanol.

As described above, the prepreg contains a reinforcing material. Examples of reinforcing materials include inorganic fibers such as glass cloth, glass paper, and glass mat, and organic fibers such as aramid cloth. When the reinforcing material is glass cloth, it may be a woven glass fabric or a nonwoven glass fabric.

The thickness of the prepreg is, for example, 0.013 mm or more and 0.500 mm or less, but is not limited to this.

The second insulating layer 22 is an electrically insulating layer, and is formed by adhering a resin sheet (second resin sheet) 2B (see FIG. 4) to the first conductor layer 34 and the third conductor layer 39. Examples of such a second resin sheet 2B include a polyimide film and a prepreg.

The second resin sheet 2B contains, for example, a thermosetting resin. In this case, the second resin sheet 2B is preferably a prepreg. When the second resin sheet 2B contains a thermosetting resin, curing shrinkage occurs when the second resin sheet 2B is heated. However, as described above, in this embodiment, even if the second resin sheet 2B cures and shrinks, warping is unlikely to occur in the printed wiring board 13.

When the second resin sheet 2B is a prepreg, the prepreg is formed in the same manner as when the first resin sheet 2A is a prepreg. That is, the prepreg contains a reinforcing material and a composition (X).

If composition (X) contains a polyfunctional epoxy resin as a thermosetting resin, a crosslinked structure is formed when composition (X) is cured, and therefore curing shrinkage is particularly likely to occur when the second resin sheet 2B is cured to produce the second insulating layer 22. However, in this embodiment, even if composition (X) contains a polyfunctional epoxy resin, as described above, the laminate 11 is curved in the heating process so that the outer surface 3A of the metal foil 33 is convex, making it difficult for the printed wiring board 13 to warp due to the curing shrinkage of the second resin sheet 2B.

As described above, the resin content of the second insulating layer 22 is higher than that of the first insulating layer 21. That is, the second resin sheet 2B is manufactured so that the resin content of the second insulating layer 22 is higher than that of the first insulating layer 21. In this embodiment, even if the resin content of the second insulating layer 22 is higher than that of the first insulating layer 21, the printed wiring board 13 is less likely to warp. The difference between the resin content of the second insulating layer 22 and the resin content of the first insulating layer 21 is not particularly limited, but for example, the resin content of the second insulating layer 22 is 66% by mass or more and 74% by mass or less, the resin content of the first insulating layer 21 is 64% by mass or more and 72% by mass or less, and the difference between the two is 1% by mass or more and 3% by mass or less.

The materials of the first metal foil 31, the second metal foil 32, and the third metal foil 33 may be the same or different. Each of the first metal foil 31, the second metal foil 32, and the third metal foil 33 is, for example, a copper foil, an aluminum foil, or a stainless steel foil. The thickness of each of the first metal foil 31, the second metal foil 32, and the third metal foil 33 is, for example, 2 μm or more and 70 μm or less, but is not limited to this.

The manufacturing method for the laminate 12 according to this embodiment includes a lamination process and a heating process.

In the lamination process, a resin sheet and metal foil are layered in this order on top of the first conductor layer of the core material 14, which is made up of a first conductor layer, a first insulating layer, and a second conductor layer layered in this order, to produce a laminate.

The manufacturing method of the laminate 12 may further include a step of preparing the core material 14 (hereinafter referred to as the core preparation step) before the lamination step. In the core preparation step, for example as shown in FIG. 3A, the first metal foil 31, the first resin sheet 2A, and the second metal foil 32 are first laminated in this order to prepare a first laminate 1A. The first laminate 1A is heat pressed to laminate the first metal foil 31, the first resin sheet 2A, and the second metal foil 32 together. This results in a core material 14 in which the first conductor layer 34 made from the first metal foil 31, the first insulating layer 21 made from the first resin sheet 2A, and the second conductor layer 38 made from the second metal foil 32 are laminated in this order.

When hot pressing the first laminate 1A, for example, a double belt method can be used. This double belt press method can be performed by a manufacturing device such as that shown in FIG. 2. This manufacturing device is equipped with a double belt press device 7.

The double belt press device 7 includes a pair of endless belts 4, a drum 9, and a pair of heat press devices 10. The pair of endless belts 4 are arranged vertically so as to sandwich the first laminate 1A therebetween. Of the pair of endless belts 4, one of the endless belts 4 is wound around two drums 9, and the other endless belt 4 is wound around two drums 9. The pair of heat press devices 10 are arranged so as to sandwich the endless belts 4, 4 and the first laminate 1A therebetween. The heat press devices 10 heat press the first laminate 1A through the endless belts 4. The heat press devices 10 include, for example, hydraulic plates. The hydraulic plates are configured to heat press the first laminate 1A through the endless belts 4 by hydraulic pressure of a heated liquid.

The endless belt 4 is made of, but not limited to, metal.

In addition, a pair of drums 9 facing each other vertically rotate to send out the core material 14 made from the first laminate 1A toward the winder 8A. In tandem with this rotation, a pair of endless belts 4 rotate.

When the first laminate 1A is hot-pressed, the first metal foil 31, the first resin sheet 2A, and the second metal foil 32 are continuously supplied to the double belt press device 7. The first laminate 1A, in which the first metal foil 31, the first resin sheet 2A, and the second metal foil 32 are laminated in this order, is formed immediately before being supplied to the double belt press device 7, and this first laminate 1A is hot-pressed using the double belt press method.

By adopting the double belt press method, uniform pressure is applied to the entire pressurized surface of the first laminate 1A via a pair of endless belts 4. This reduces the variation in pressure applied to the first resin sheet 2A between the first metal foil 31 and the second metal foil 32.

When the first laminate 1A is heat-pressed, for example, the first laminate 1A is heated as it approaches the double belt press device 7. The first laminate 1A is then further heated as it passes through the drum 9, and is heat-pressed via the endless belt 4 while passing through the heat press device 10. The heat-pressed first laminate 1A is then cooled as it passes through the drum 9 and leaves the heat press device 10. The produced core material 14 is then wound into a roll by the winder 8A, and formed into the first roll 81.

Conditions for heat pressing the first laminate 1A include, for example, a heating temperature of 200°C to 320°C, a pressure of 1 MPa to 5 MPa, and a heating time of 2 minutes to 5 minutes. The heating time of the first laminate 1A is the time required for the first laminate 1A to pass through the heat pressing device 10. The conditions for heat pressing the first laminate 1A are not limited to the above.

When the first insulating film 1B contains a thermosetting resin, it is preferable that the first insulating layer 21 in the core material 14 before the lamination process contains a thermosetting resin that is not completely cured. For this reason, it is preferable that the conditions for heat pressing the first laminate 1A in the core production process are such that the first insulating film 2B is not completely cured. In this case, when the core material 14 is heated with the second insulating film 2B superimposed thereon, the first insulating layer 21 undergoes cure shrinkage, which makes it easier to alleviate the difference in dimensional change between the first insulating layer 21 and the second insulating layer 22, and therefore makes it particularly difficult for the printed wiring board 13 to warp.

In this embodiment, the core material 14 continuously fed from the double belt press device 7 is wound into a roll by the winding machine 8A and formed into a first roll 81.

In the core fabrication process, the first conductor layer 34 may be formed as the wiring 37. In this case, the first conductor layer 34 can be formed as the wiring 37 by removing a portion of the first conductor layer 34 (see FIG. 3B). To form the wiring 37, for example, the core material 14 is pulled out from the first roll 81 and transported, the first conductor layer 34 is etched to form the wiring 37, and then the core material 14 is wound up in a roll shape in a position opposite the first roll 81. For example, a subtractive method can be used as the etching process.

In this embodiment, the core material 14 having the first conductor layer 34 formed as the wiring 37 shown in FIG. 3B is used in the lamination process. Note that the core material 14 may be used in the lamination process without forming the first conductor layer 34 as the wiring 37, with the first conductor layer 34 remaining as a uniform metal layer as shown in FIG. 3A.

The lamination process is a process in which a resin sheet (second resin sheet) 2B and a metal foil (third metal foil) 33 are layered in this order on the first conductor layer 34 of the core material 14 to produce a laminate (second laminate) 11 (see Figure 4).

In the lamination process, it is preferable to heat press the second laminate 11. When heat pressing the second laminate 11, for example, a double belt method can be adopted. This double belt press method can be performed by a manufacturing apparatus as shown in FIG. 4. This manufacturing apparatus includes a double belt press device 7. In this manufacturing apparatus, the core material 14 wound in a roll shape is placed on a payout machine 8B.

The double belt press device 7 includes a pair of endless belts 4, a drum 9, and a pair of heat press devices 10. The pair of endless belts 4 are arranged vertically so as to sandwich the second laminate 11 therebetween. Of the pair of endless belts 4, one of the endless belts 4 is wound around two drums 9, and the other endless belt 4 is wound around two drums 9. The pair of heat press devices 10 are provided so as to sandwich the endless belts 4, 4 and the second laminate 11 therebetween. The heat press devices 10 heat press the second laminate 11 through the endless belts 4. The heat press devices 10 include, for example, hydraulic plates. The hydraulic plates are configured to heat press the second laminate 11 through the endless belts 4 by hydraulic pressure of a heated liquid.

The endless belt 4 is made of, but not limited to, metal.

In addition, a pair of drums 9 facing each other vertically rotate to send out the second laminate 11 toward the winder 8C. In conjunction with this rotation, a pair of endless belts 4 rotate.

During the lamination process, the core material 14, the second resin sheet 2B, and the third metal foil 33 are continuously supplied to the double belt press device 7. A second laminate 11 in which the core material 14, the second resin sheet 2B, and the third metal foil 33 are laminated in this order is formed between the payout machine 8B and the double belt press device 7, and this second laminate 11 is hot pressed using the double belt press method.

By using a double belt press method in the second lamination process, uniform pressure is applied to the entire pressurized surface of the second laminate 11 via a pair of endless belts 4. This reduces the variation in pressure applied to the second resin sheet 2B between the third metal foil 33 and the core material 14. By heat pressing the second laminate 11, the second resin sheet 2B and the third metal foil 33 are tightly attached to each other.

When the second laminate 11 is heat-pressed, for example, the second laminate 11 is heated as it approaches the double belt press device 7. The second laminate 11 is then further heated as it passes through the drum 9, and is heat-pressed via the endless belt 4 while passing through the heat press device 10. The heat-pressed second laminate 11 is then cooled as it passes through the drum 9 and leaves the heat press device 10. The second laminate 11 is then wound into a roll by the winder 8C, and formed into a second roll 82.

Conditions for heat pressing the second laminate 11 include, for example, a heating temperature of 200°C to 320°C, a pressure of 1 MPa to 5 MPa, and a heating time of 2 minutes to 5 minutes. The heating time of the second laminate 11 is the time required for the second laminate 11 to pass through the heat pressing device 10. The conditions for heat pressing the second laminate 11 are not limited to the above.

In this embodiment, the second laminate 11 continuously fed from the double belt press device 7 is wound into a roll by the winding machine 8C and formed into a second roll 82 (see Figures 4 and 5A). Such a second laminate 11 is curved so that the outer surface 3A of the third metal foil 33 is convex (see Figure 5B). In other words, the second laminate 11 is curved so as to protrude from the first insulating layer 21 in the direction D1 toward the second resin sheet 2B. The curvature of the second laminate 11 is achieved by winding the second laminate 11 by the winding machine 8C so that the outer surface (the surface not in contact with the second resin sheet 2B) 3A of the third metal foil 33 faces outward when the second roll 82 is formed.

The second winding body 82 as shown in FIG. 5A has an inner peripheral surface 83 and an outer peripheral surface 84. The inner peripheral surface 83 is the inner peripheral surface of a cylinder formed by the second winding body 82, and the outer peripheral surface 84 is the outer peripheral surface of the cylinder.

When the second resin sheet 2B has thermosetting properties, it is preferable that the second resin sheet 2B is not completely cured in the second laminate 11 obtained by the lamination process. Specifically, it is preferable that the second resin sheet 2B contains a thermosetting resin that is not completely cured.

In addition, when the first resin sheet 1A contains a thermosetting resin, the first insulating layer 21 made from the first resin sheet 1A may be completely cured or may not be completely cured in the second laminate 11 after the heat pressing in the lamination process. It is more preferable that the first insulating layer 21 is not completely cured. Specifically, it is preferable that the second insulating layer 22 contains a thermosetting resin that is not completely cured. In other words, it is preferable that in the lamination process, the second laminate 11 is heat pressed under conditions in which the first insulating layer 21 is not completely cured.

When the first insulating layer 21 in the second laminate 11 is not completely cured, for example, when the glass transition temperature of the first insulating layer 21 becomes 280°C or higher and 320°C or lower when the first insulating layer 21 is completely cured, it is preferable that the glass transition temperature of the first insulating layer 21 in the second laminate 11 is 190°C or higher and 220°C or lower. In addition, the glass transition temperature of the second resin sheet 2B when the second resin sheet 2B is not completely cured may be the same as above.

In the lamination process, when the second laminate 11 is heat-pressed under conditions in which the first insulating layer 21 is not completely cured, the printed wiring board 13 is further prevented from warping. The reason for this is presumably as follows. When the second laminate 11 is curved so that the outer surface 3A of the third metal foil 33 is convex during heating in the heating process, the first insulating layer 21 and the second resin sheet 2B are completely cured in the state in which they are curved, causing cure shrinkage in the first insulating layer 21, which makes it easier to alleviate stress caused by cure shrinkage in the second resin sheet 2B. Therefore, it is believed that the tendency for warping caused by shrinkage of the second insulating layer 22 during the manufacture of the printed wiring board 13 is reduced, making the printed wiring board 13 less likely to warp.

In this embodiment, the heating process is carried out after the lamination process.

The heating step is a step of manufacturing a laminate 12 by heating the second laminate 11 in a curved state so that the outer surface 3A of the third conductor layer 39 is convex. In this laminate 12, the second conductor layer 38, the first insulating layer 21, the first conductor layer 34, the second insulating layer 22 made from the second resin sheet 2B, and the third conductor layer 39 made from the third metal foil 33 are laminated in this order.

During the heating process, the thermosetting resin in the second laminate 11 can be cured. Therefore, the heating process in this embodiment also serves as an after-cure process.

The radius of curvature of the curved second laminate 11 in the heating step is preferably 2.5 mm or more and 500 mm or less. The radius of curvature of the second laminate 11 is the radius of curvature of the outer surface 3A of the third metal foil 33 in the cross section of the second laminate 11 in the thickness direction. This radius of curvature is a preferred condition for the degree of curvature of the second laminate 11 when the second laminate 11 is heated in the heating step. When the radius of curvature of the second laminate 11 is within the above range, a laminate 12 having a curved shape such that the outer surface 3A of the third conductor layer 39 is convex can be easily obtained, and warping is less likely to occur in the printed wiring board 13 produced using this laminate 12.

In the heating step, it is preferable to heat the second laminate 11 while it is in the state of the second roll 82. That is, when heating the second laminate 11 in a state where it is curved so that the outer surface 3A of the metal foil 33 is convex, it is preferable to curve the second laminate 11 by rolling it into a roll. In this case, the second roll 82 can be heated at once, and the laminate 12 can easily be curved in such a way that the laminate 12 is warped in the opposite direction to the warping that occurs during the manufacture of the printed wiring board 13. The second roll 82 can be heated in a heating furnace in which the temperature inside the furnace is set to a predetermined temperature suitable for hardening the second laminate 11.

When the second laminate 11 is heated while still in the state of the second roll 82, the radius of curvature of the outer peripheral surface 84 of the second roll 82 is preferably 2.5 mm or more and 500 mm or less, and the radius of curvature of the inner peripheral surface 83 is preferably 2.5 mm or more and 500 mm or less.

The above "state of the second roll 82" means that when the second laminate 11 is heated, the second laminate 11 is rolled and curved. However, the second laminate 11 may be heated in a state other than the state of the second roll 82, so long as the second laminate 11 is heated in a curved state such that the outer surface 3A of the third metal foil 33 is convex.

It is preferable that the thermosetting resin in the second laminate 11 is completely cured by the heating process. Specifically, it is preferable that the first insulating layer 21 and the second resin sheet 2B are completely cured by the heating process. As described above, the second insulating layer 22 is produced from the second resin sheet 2B by the heating process, and the third conductor layer 39 is produced from the third metal foil 33. The heating time of the heating process is, for example, 0.5 hours or more and 5.0 hours or less, but is not limited to this. The heating temperature of the heating process is, for example, 200°C or more and 300°C or less, but is not limited to this.

The thickness of the first insulating layer 21 is, for example, 15 μm or more and 50 μm or less, but is not limited to this. The thickness of the second insulating layer 22 is, for example, 15 μm or more and 50 μm or less, but is not limited to this.

The printed wiring board 13 of this embodiment includes fabricating conductor wiring by removing a portion of at least one of the second conductor layer 38 and the third conductor layer 39 in the laminate 12.

In the wiring formation process, for example, a portion of each of the second conductor layer 38 and the third conductor layer 39 in the laminate 12 is removed to produce the first conductor wiring 35 and the second conductor wiring 36 from the second conductor layer 38 and the third conductor layer 39, respectively. In the wiring formation process, an etching process can be used to produce the first conductor wiring 35 and the second conductor wiring 36.

The printed wiring board 13 is manufactured by removing a portion of each of the second conductor layer 38 and the third conductor layer 39 in the wiring formation process. As described above, this printed wiring board 13 is less likely to warp.

In this embodiment, the cutting process is performed after the heating process. This cutting process may be performed between the heating process and the wiring formation process, or after the wiring formation process. When the cutting process is performed between the heating process and the wiring formation process, the laminate 12 is cut to a size suitable for manufacturing the printed wiring board 13. When the cutting process is performed after the wiring formation process, the product of the wiring formation process is cut to a size suitable for the printed wiring board 13. Since the printed wiring board 13 is less likely to warp, even if the printed wiring board 13 is temporarily stored in the magazine rack, it is less likely to fall from the magazine rack. This makes it easier to transport the printed wiring board 13 while it is stored in the magazine rack.

As shown in FIG. 6, the printed wiring board 13 has a structure in which a first conductor wiring 35, a first insulating layer 21, a first conductor layer 34, a second insulating layer 22, and a second conductor wiring 36 are laminated in this order. The first conductor layer 34 is embedded between the first insulating layer 21 and the second insulating layer 22. The first conductor wiring 35 is in close contact with the surface of the first insulating layer 21. The second conductor wiring 36 is in close contact with the surface of the second insulating layer 22.

When the first conductor layer 34 is wiring 37, the first insulating layer 21 and the second insulating layer 22 are in close contact with each other in areas other than the wiring 37.

In the above embodiment, a double belt method is used to produce the second laminate 11 in the lamination process, but instead of the double belt method, a vacuum press method, a linear pressure roll method, or a vacuum laminator method may be used.

In the above embodiment, the second laminate 11 is heated in the heating step while remaining as the second roll 82, but the second laminate 11 may be heated by, for example, preparing two heating plates each having a curved surface and sandwiching the second laminate 11 between the curved surfaces of the two heating plates. In this case, the second laminate 11 can be heated while being curved by the curved surfaces.

The present disclosure will be explained in more detail below with reference to examples.

<Examples and Comparative Examples>
Each of the examples and comparative examples was carried out using the following materials.
Thermosetting resin (multifunctional epoxy resin): EPPN-502H, manufactured by Nippon Kayaku Co., Ltd.
Hardener (phenol-based hardener): TD-209060M, manufactured by DIC Corporation.
Silica: SC-2050MTX, manufactured by Admatechs Co., Ltd.
Talc: D-800 manufactured by Nippon Talc Co., Ltd.
Aluminum hydroxide: CL-303, manufactured by Sumitomo Chemical Co., Ltd.
Reinforcement material: 1017 cloth manufactured by Asahi Kasei Corporation.
First metal foil: 3EC-M3-VLP (copper foil; thickness 9 μm, linear expansion coefficient 16 ppm/K), manufactured by Mitsui Mining & Smelting Co., Ltd.
Second metal foil: MT18Ex (copper foil; thickness 3 μm, linear expansion coefficient 16 ppm/K), manufactured by Mitsui Mining & Smelting Co., Ltd.
Third metal foil: MT18Ex (copper foil; thickness 3 μm, linear expansion coefficient 16 ppm/K), manufactured by Mitsui Mining & Smelting Co., Ltd.

[Example 1]
(1) Core Preparation Step The components shown in the "First Resin Composition" column in Table 1 were blended in a container and mixed to prepare a first resin composition as a varnish.

Next, the first resin composition was impregnated into the reinforcing material so that the resin content after curing was 68% by mass, and then the reinforcing material was dried to produce a prepreg, which is a first resin sheet. The prepreg was sandwiched between the first metal foil and the second metal foil to produce a first laminate. The first laminate was then heat-pressed using a double belt method. This double belt method was performed using the manufacturing device shown in Figure 2. When the first laminate was heat-pressed, the pressure was 4.0 MPa, the maximum heating temperature was 300°C, and the heating time was 4 minutes. Here, the maximum heating temperature was the set temperature of the heat press device, and the heating time was the time the first laminate passed through the heat press device. This resulted in a core material having a first conductor layer made from the first metal foil, a first insulating layer made from the first resin sheet (prepreg), and a second conductor made from the second metal foil.

Next, the core material was wound into a roll to form a first winding, and then only the first conductor layer of this core material was etched using an etching solution mainly containing cupric chloride, etc., to form the first conductor layer as wiring. This core material was then wound into a roll.

(2) Lamination Step The components shown in the "Second resin composition" column in Table 1 were blended in a container and mixed to prepare a second resin composition as a varnish.

Next, the reinforcing material was impregnated with the second resin composition so that the resin content after curing was 70% by mass, and then dried to produce a prepreg, which is a second resin sheet.

Next, a second resin sheet and a third metal foil were laminated in this order on the wiring of the core material to produce a second laminate, and the second laminate was hot-pressed by a double-belt method using the manufacturing device shown in Figure 4. When the second laminate was hot-pressed, the pressure was 4.5 MPa, the maximum heating temperature was 300°C, and the heating time was 3 minutes. The conditions for this hot pressing were set so that the second insulating layer made from the second resin sheet (prepreg) would not be completely cured. Here, the maximum heating temperature was the set temperature of the hot pressing device, and the heating time was the time the second laminate passed through the hot pressing device.

(3) Heating step Next, the hot-pressed second laminate was wound into a roll to produce a second roll. The second roll was heated for 2 hours in a heating furnace with an internal temperature set to 200° C., whereby the second laminate was heated in a curved state so that the outer surface of the metal foil (third metal foil) was convex. The conditions for this hot pressing were set so that the second insulating layer produced from the second resin sheet was completely cured.

This resulted in the production of a laminate having a structure in which a second conductor layer, a first insulating layer, wiring which is the first conductor layer, a second insulating layer made from a second resin sheet, and a third conductor layer made from a third metal foil were laminated in this order.

(4) Wiring Formation Step Next, the second conductor layer and the third conductor layer in the laminate were etched using an etching solution mainly composed of cupric chloride or the like to form a first conductor wiring and a second conductor wiring. This resulted in a printed wiring board having the first conductor wiring and the second conductor wiring. In this printed wiring board, the thickness of the first insulating layer, which is the cured product of the first resin sheet, was 23 μm, and the thickness of the second insulating layer, which is the cured product of the second resin sheet, was 25 μm. In addition, the linear expansion coefficient of the first insulating layer was 15 ppm/K, and the linear expansion coefficient of the second insulating layer was 15 ppm/K.

[Example 2]
The maximum heating temperature during the heat pressing in the core material preparation process was 270° C., and the heating time was 3 minutes. The heat pressing conditions were set so that the first insulating layer made of the first resin sheet (prepreg) would not be completely cured. Otherwise, a laminate and a printed wiring board were obtained in the same manner as in Example 1.

[Comparative Example 1]
In the heating step, the second laminate was heated in a flat plate state without being wound into a roll, but in the same manner as in Example 1, a laminate and a printed wiring board were obtained.

[Comparative Example 2]
In the heating step, the second laminate was heated in a flat plate state without being wound into a roll, but in the same manner as in Example 2 to obtain a laminate and a printed wiring board.

<Evaluation>
[Glass transition temperature of the first insulating layer in the second laminate]
In each of the Examples and Comparative Examples, the glass transition temperature (Tg) of the first insulating layer in the second laminate after the heat pressing in the lamination process was measured by dynamic viscoelasticity measurement. When measuring this glass transition temperature (Tg), a viscoelasticity spectrometer "DMS100" manufactured by Seiko Instruments Inc. was used. In this measurement, tan δ was measured with a bending module under conditions of a frequency of 10 Hz, a heating rate of 5°C/min, and a temperature range of room temperature to 340°C, and the temperature at which tan δ was maximum was taken as the glass transition temperature (Tg). The results are shown in Table 1.

Based on these results, it can be determined that the first insulating layer in the second laminate after the heat pressing in the lamination process, i.e., the second laminate before the heating process, is completely cured in Example 1 and Comparative Example 1, but is not completely cured in the second laminate in Example 2 and Comparative Example 2.

[Evaluation of the amount of warping of printed wiring boards]
In each of the Examples and Comparative Examples, a sample having a planar dimension of 24 cm x 8 cm was cut out from the laminate obtained in the heating step. The second conductor layer and the third conductor layer of this sample were completely removed by etching using the above etching solution, and then this sample was heated at 200°C for 1 hour.

Next, the sample was placed on the measurement table so that the second insulating layer was positioned above the first insulating layer. In this state, the amount of warping of the sample was measured. The amount of warping is the maximum vertical dimension between the measurement table and the surface of the sample facing the measurement table, and is specified as a positive value when the sample has an upward convex warp, and a negative value when the sample has a downward convex warp. The results are shown in Table 1.

According to the above results, it was confirmed that by making the resin content of the second insulating layer higher than that of the first insulating layer, and by curving the second laminate so that the outer surface of the third metal foil is convex in the heating process, the second resin sheet is stretched more than the first insulating layer, and heating in that state, it is possible to make the sample less likely to warp when the second conductor layer and the third conductor layer are removed from the sample. In contrast, when the heating process was performed in a flat state of the second laminate as in the comparative example, the warping was large. As a result, it can be determined that when the second conductor layer and the third conductor layer are removed from the sample, the second insulating layer shrinks more than the first insulating layer, and the warping caused by this difference in shrinkage was mitigated in Examples 1 and 2 by heating the second laminate in a curved state in the heating process. In addition, when the heating process was performed in a state in which the first insulating layer in the second laminate was not completely cured as in Example 2, the warping was suppressed more than in Example 1. Therefore, it was confirmed that the effect of suppressing warping is high when not only the second insulating sheet but also the first insulating layer in the second laminate obtained in the lamination process contain a thermosetting resin that is not completely cured.

Reference Signs List 11 Laminate 12 Laminated plate 14 Core material 2B Resin sheet 21 First insulating layer 22 Second insulating layer 2B Resin sheet 33 Metal foil 34 First conductor layer 38 Second conductor layer 39 Third conductor layer 3A Outer surface

Claims (7)

a lamination step of laminating a resin sheet containing a thermosetting resin and a metal foil, in this order, on the first conductor layer of a core material having a first conductor layer, a first insulating layer, and a second conductor layer laminated in this order, to produce a laminate;
a heating step of heating the laminate to produce a laminate in which the core material, the second insulating layer made of the resin sheet, and the third conductor layer made of the metal foil are laminated in this order;
the second insulating layer has a higher resin content than the first insulating layer;
The heating step is performed in a state where the laminate is curved so that the outer surface of the metal foil is convex.
A method for manufacturing a laminate. The resin sheet is a prepreg.
A method for producing the laminate according to claim 1. The first insulating layer of the core material before the lamination step is performed contains a thermosetting resin that is not completely cured.
A method for producing the laminate according to claim 1 or 2. In the lamination step, the laminate is heat-pressed under conditions in which the first insulating layer is not completely cured.
A method for producing the laminate according to claim 3. a lamination step of laminating a resin sheet and a metal foil in this order on the first conductor layer of a core material having a first conductor layer, a first insulating layer, and a second conductor layer laminated in this order to produce a laminate;
a heating step of heating the laminate to produce a laminate in which the core material, the second insulating layer made of the resin sheet, and the third conductor layer made of the metal foil are laminated in this order;
the second insulating layer has a higher resin content than the first insulating layer;
The heating step is performed in a state where the laminate is wound into a roll so that the outer surface of the metal foil is curved into a convex shape.
A method for manufacturing a laminate. In the heating step, the laminate is curved by winding it into a roll.
A method for producing the laminate according to any one of claims 1 to 4 . A wiring forming step of forming a conductor wiring by removing a part of at least one of the second conductor layer and the third conductor layer in the laminate produced by the method for producing a laminate according to any one of claims 1 to 6,
A method for manufacturing a printed wiring board.

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