Method for manufacturing a multilayer printed wiring board and multilayer printed wiring board

Abstract

The problem solved by the present disclosure is to provide a method for manufacturing a multilayer printed wiring board, which helps improve the high-frequency characteristics of a multilayer printed wiring board including an insulating layer containing polyimide. The method includes the steps of providing a first laminate (21) and a second laminate (22). The first laminate (21) includes a first conductor layer (41), a first insulating layer (31) containing polyimide, and a second conductor layer (42). The second laminate (22) includes a second insulating layer (32) containing polyimide and a third conductor layer (43). The method also includes: a heating step for heating each of the first laminate (21) and the second laminate (22) under conditions including a heating temperature of at least 100°C and a heating time of at least 0.5 hours; and a laminating step for laminating the first laminate (21) and the second laminate (22) to each other with the third insulating layer (33) interposed between the second conductor layer (42) and the second insulating layer (32) after the heating step.

Description

Technical Field

[0001] The present disclosure generally relates to a method for manufacturing a multilayer printed wiring board and a multilayer printed wiring board. More particularly, the present disclosure relates to a method for manufacturing a multilayer printed wiring board including an insulating layer containing polyimide and such a multilayer printed wiring board. Background Art

[0002] Metal-clad laminates such as flexible copper-clad laminates (FCCLs) have been manufactured in the art by laminating a metal foil sheet on a film having a thermoplastic polyimide layer (see Patent Document 1).

[0003] Reference List

[0004] Patent Literature

[0005] Patent Document 1: JP 2019-210342 A Summary of the Invention

[0006] The problem solved by the present disclosure is to provide a method for manufacturing a multilayer printed wiring board, which helps to improve the RF characteristics of a multilayer printed wiring board including an insulating layer containing polyimide, and to provide a multilayer printed wiring board including an insulating layer containing polyimide and having improved RF characteristics.

[0007] A method for manufacturing a multilayer printed wiring board according to one aspect of the present disclosure includes the steps of providing a first laminate and a second laminate. The first laminate includes a first conductor layer, a first insulating layer, and a second conductor layer stacked one on top of another. The second laminate includes a second insulating layer and a third conductor layer stacked one on top of another. The first insulating layer and the second insulating layer each contain polyimide. The method also includes: a heating step, the heating step including heating each of the first laminate and the second laminate under conditions including a heating temperature equal to or higher than 100°C and a heating time equal to or greater than half an hour; and a stacking step including, after the heating step, stacking the first laminate and the second laminate with a third insulating layer interposed between the second conductor layer and the second insulating layer.

[0008] A multilayer printed wiring board according to another aspect of the present disclosure includes a first conductor layer, a first insulating layer, a second conductor layer, a third insulating layer, a second insulating layer, and a third conductor layer stacked one on top of the other. The first insulating layer and the second insulating layer each contain polyimide. A weight change measured by a dry weight measurement method is equal to or less than 3000 μg / cm 2 with the total volume of the first insulating layer, the second insulating layer, and the third insulating layer defined as a reference. 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic cross-sectional view showing a first laminate, a second laminate, and a resin sheet according to one embodiment of the present disclosure;

[0010] Figure 2 is a schematic cross-sectional view illustrating an exemplary multilayer printed wiring board according to an embodiment of the present disclosure; and

[0011] Figure 3 is a schematic cross-sectional view illustrating another exemplary multilayer printed wiring board according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0012] 1. Summary

[0013] First, we will summarize how the present inventors arrived at the concept of the present disclosure. The present inventors conducted in-depth research on the RF characteristics of printed wiring boards (PCBs) containing polyimide insulating layers and discovered that transmission loss in PCBs may not always be reduced as expected. Consequently, the present inventors conducted in-depth research into the causes of increased transmission loss and how to address such increased transmission loss, leading to the concept of the present invention.

[0014] The embodiments of the present disclosure will be described. Note that the embodiment described below is merely an exemplary embodiment of the various embodiments of the present disclosure and should not be construed as limiting. Rather, the exemplary embodiment can be easily changed in various ways according to design choices or any other factors without departing from the scope of the present disclosure.

[0015] Figure 2 and 3 Each shows an exemplary configuration of a multilayer printed wiring board 1 according to the present embodiment. Multilayer printed wiring board 1 includes a first conductor layer 41, a first insulating layer 31, a second conductor layer 42, a third insulating layer 33, a second insulating layer 32, and a third conductor layer 43 stacked one on top of the other in this order. First insulating layer 31 and second insulating layer 32 each contain polyimide.

[0016] The method for manufacturing a multilayer printed wiring board 1 according to the present disclosure includes the steps of providing a first laminate 21 and a second laminate 22 (see Figure 1). The first laminate 21 includes a first conductor layer 41, a first insulating layer 31, and a second conductor layer 42 stacked in sequence. The second laminate 22 includes a second insulating layer 32 and a third conductor layer 43 stacked in sequence. Each of the first insulating layer 31 and the second insulating layer 32 contains polyimide. The method further includes: a heating step including heating each of the first laminate 21 and the second laminate 22 under conditions including a heating temperature equal to or higher than 100°C and a heating time equal to or longer than half an hour; and a stacking step including, after the heating step, stacking the first laminate 21 and the second laminate 22 on each other with the third insulating layer 33 interposed between the second conductor layer 42 and the second insulating layer 32.

[0017] The present embodiment makes it possible to provide a kind of multilayer printed wiring board 1, it includes the first insulating layer 31 and the second insulating layer 32 as the insulating layer containing polyimide respectively, and its transmission loss (i.e. the absolute value of transmission loss) has been reduced.The reason for speculation is as follows.If the insulating layer containing polyimide contains water, the relative dielectric constant and the dielectric loss tangent of the insulating layer will increase, which causes transmission loss when the electric signal is transmitted by the multilayer printed wiring board 1 including the insulating layer containing polyimide.In contrast, according to the present embodiment, multilayer printed wiring board 1 is manufactured by above-mentioned heating step, therefore, the water content of the first insulating layer 31 and the second insulating layer 32 respectively containing polyimide can be reduced by drying the first insulating layer 31 and the second insulating layer 32.This should reduce the relative dielectric constant and the dielectric loss tangent of the first insulating layer 31 and the second insulating layer 32 respectively, thus reducing the transmission loss of multilayer printed wiring board 1.

[0018] In addition, the present embodiment also reduces the possibility of causing an increase in transmission loss over time in the multilayer printed wiring board 1. This is probably because manufacturing the multilayer printed wiring board 1 by the method according to the present embodiment makes it easier to keep the water content of each of the first insulating layer 31 and the second insulating layer 32 sufficiently low.

[0019] Next, the method for manufacturing the multilayer printed wiring board 1 according to the present disclosure will be described in more detail.

[0020] 2. First laminate and second laminate

[0021] As described above, the first laminate 21 and the second laminate 22 are provided as materials for the multilayer printed wiring board 1 .

[0022] The first laminated body 21 includes a first conductor layer 41 , a first insulating layer 31 , and a second conductor layer 42 sequentially stacked on one another.

[0023] The first conductor layer 41 can be, for example, a metal foil sheet (first metal foil sheet 61). For example, the first metal foil sheet 61 can be a copper foil sheet. The thickness of the first conductor layer 41 is preferably equal to or greater than 2 μm. This reduces the possibility of damage to the first conductor layer 41 when forming the first laminate 21. The thickness is more preferably equal to or greater than 5 μm, and even more preferably equal to or greater than 10 μm. The thickness of the first conductor layer 41 is preferably equal to or less than 40 μm. This makes it easier to increase the flexibility of the first laminate 21. The thickness is more preferably equal to or less than 30 μm, and even more preferably equal to or less than 25 μm.

[0024] As described above, the first insulating layer 31 contains polyimide. Polyimide preferably has a glass transition temperature. The first insulating layer 31 may be, for example, a polyimide film (first polyimide film 71) formed by molding polyimide into a sheet shape.

[0025] Polyimide is synthesized, for example, by synthesizing polyamic acid from aromatic carboxylic dianhydride and aromatic diamine and imidizing the polyamic acid.

[0026] The aromatic carboxylic acid dianhydride may contain, for example, at least one selected from the group consisting of: pyromellitic dianhydride; 2,3,6,7-naphthalenetetracarboxylic dianhydride; 3,3′,4,4′-biphenyltetracarboxylic dianhydride; 1,2,5,6-naphthalenetetracarboxylic dianhydride; 2,2′,3,3′-biphenyltetracarboxylic dianhydride; 3,3′,4,4′-benzophenonetetracarboxylic dianhydride; 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride; 3,4,9,10-perylenetetracarboxylic dianhydride; bis(3,4 -dicarboxyphenyl)propane dianhydride; 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride; 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride; bis(2,3-dicarboxyphenyl)methane dianhydride; bis(3,4-dicarboxyphenyl)ethane dianhydride; oxydiphthalic dianhydride; bis(3,4-dicarboxyphenyl)sulfonate dianhydride; terephthalic bis(trimellitic acid monoester anhydride); ethylene bis(trimellitic acid monoester anhydride); bisphenol A bis(trimellitic acid monoester anhydride); and their derivatives.

[0027] The aromatic diamine may contain, for example, at least one selected from the group consisting of: 2,2-bis[4-(4-aminophenoxy)phenyl]propane; 4,4′-diaminodiphenyl ether; 3,4′-diaminodiphenyl ether; 1,3-bis(4-aminophenoxy)benzene; 1,4-bis(4-aminophenoxy)benzene; p-phenylenediamine; 4,4′-diaminodiphenylpropane; 4,4′-diaminodiphenylmethane; benzidine; 3,3′-dichlorobenzidine; 4,4′-diaminodiphenyl sulfide; 3,3′-diaminodiphenyl sulfone; 4,4′-diaminodiphenyl sulfone; 4,4′-diaminodiphenyl sulfone; ethers; 3,3′-diaminodiphenyl ether; 3,4′-diaminodiphenyl ether; 1,5-diaminonaphthalene; 4,4′-diaminodiphenyldiethylsilane; 4,4′-diaminodiphenylsilane; 4,4′-diaminodiphenylethylphosphine oxide; 4,4′-diaminodiphenyl-N-methylamine; 4,4′-diaminodiphenyl-N-phenylamine; 1,4-diaminobenzene (p-phenylenediamine); 1,3-diaminobenzene; 1,2-diaminobenzene; 2,2-bis[4-(4-aminophenoxy)phenyl]propane; 2,2′-bis(trifluoromethyl)benzidine; bis(4-aminophenyl)terephthalate; and derivatives thereof.

[0028] There are no particular restrictions on the polymerization method, polymerization catalyst, reaction temperature, and reaction time for obtaining polyamic acid from aromatic carboxylic dianhydride and aromatic diamine. There are no particular restrictions on the curing agent and curing conditions for imidizing the polyamic acid.

[0029] For example, the thickness of first insulating layer 31 may be equal to or greater than 25 μm and equal to or less than 500 μm. Setting the thickness to 25 μm or greater makes it easier to reduce the transmission loss of multilayer printed wiring board 1. Setting the thickness to 500 μm or less increases the likelihood that multilayer printed wiring board 1 will have sufficient flexibility. This thickness is more preferably equal to or greater than 50 μm, and even more preferably equal to or greater than 75 μm. In addition, this thickness is more preferably equal to or less than 300 μm, and even more preferably equal to or less than 200 μm.

[0030] The second conductor layer 42 may be, for example, a conductor line. The conductor line may be made of a metal such as copper. The thickness of the second conductor layer 42 is preferably equal to or greater than 2 μm. This reduces the possibility of damage to the second conductor layer 42 during formation of the first laminate 21. This thickness is more preferably equal to or greater than 5 μm, and even more preferably equal to or greater than 10 μm. The thickness of the second conductor layer 42 is preferably equal to or less than 40 μm. This increases the possibility of the first laminate 21 having increased flexibility. This thickness is more preferably equal to or less than 30 μm, and even more preferably equal to or less than 25 μm.

[0031] An exemplary method for forming the first laminate 21 will be described.

[0032] For example, a laminate is formed by sequentially stacking a metal foil sheet (first metal foil sheet 61), a polyimide film (first polyimide film 71), and another metal foil sheet (second metal foil sheet). This laminate is then heat-pressed to integrate the first metal foil sheet 61, the first polyimide film 71, and the second metal foil sheet. Examples of methods for heat-pressing the laminate include a method using a double belt press.

[0033] If the laminate is hot-pressed by double-belt pressing, for example, the heating temperature is equal to or higher than 300°C and equal to or lower than 400°C, for example, the pressing pressure is equal to or higher than 3 MPa and equal to or lower than 5 MPa, and for example, the heating time is equal to or longer than 1 minute and equal to or shorter than 5 minutes.

[0034] Next, for example, the second metal foil sheet is patterned using photolithography as needed to form conductor lines. This transforms the first metal foil sheet 61, the first polyimide film 71, and the second metal foil sheet into the first conductor layer 41, the first insulating layer 31, and the second conductor layer 42, respectively.

[0035] Meanwhile, the second laminate body 22 includes a second insulating layer 32 and a third conductor layer 43 which are sequentially stacked on each other.

[0036] The third conductor layer 43 may be, for example, a metal foil sheet (third metal foil sheet 63). The third metal foil sheet 63 may be, for example, a copper foil sheet. The thickness of the third conductor layer 43 is preferably equal to or greater than 2 μm. This reduces the possibility of damage to the third conductor layer 43 when forming the second laminate 22. This thickness is more preferably equal to or greater than 5 μm, and even more preferably equal to or greater than 10 μm. This thickness is preferably equal to or less than 40 μm. This increases the possibility of the second laminate 22 having increased flexibility. This thickness is more preferably equal to or less than 30 μm, and even more preferably equal to or less than 25 μm.

[0037] As described above, the second insulating layer 32 contains polyimide. Polyimide preferably has a glass transition temperature. The second insulating layer 32 can be, for example, a polyimide film (second polyimide film 72) formed by molding polyimide into a sheet shape. The polyimide can be the same as the polyimide of the first insulating layer 31.

[0038] For example, the thickness of second insulating layer 32 may be equal to or greater than 25 μm and equal to or less than 500 μm. Setting the thickness to 25 μm or greater makes it easier to reduce the transmission loss of multilayer printed wiring board 1. Setting the thickness to 500 μm or less increases the likelihood that multilayer printed wiring board 1 will have sufficient flexibility. This thickness is more preferably equal to or greater than 50 μm, and even more preferably equal to or greater than 75 μm. In addition, this thickness is more preferably equal to or less than 300 μm, and even more preferably equal to or less than 200 μm.

[0039] An exemplary method for forming the second laminate 22 will be described.

[0040] For example, a laminate is formed by sequentially laminating a metal foil sheet (third metal foil sheet 63) and a polyimide film (second polyimide film 72). If necessary, a suitable plastic film may be laminated as a release film on the other surface of the second polyimide film 72 opposite to the third metal foil sheet 63. This laminate is then heat-pressed to integrate the third metal foil sheet 63 and the second polyimide film 72. Examples of methods for heat-pressing the laminate include a method using a double belt press.

[0041] If the laminate is hot-pressed by double-belt pressing, for example, the heating temperature is equal to or higher than 300°C and equal to or lower than 400°C, for example, the pressing pressure is equal to or higher than 3 MPa and equal to or lower than 5 MPa, and for example, the heating time is equal to or longer than 1 minute and equal to or shorter than 5 minutes.

[0042] Subsequently, if necessary, the release film is peeled off from the second polyimide film 72. This converts the third metal foil sheet 63 and the second polyimide film 72 into the third conductor layer 43 and the second insulating layer 32, respectively.

[0043] 3. Heating step

[0044] As described above, the first laminate 21 and the second laminate 22, which are materials for the multilayer printed wiring board 1, are heated to a heating temperature equal to or higher than 100°C, and the heating time is equal to or longer than half an hour. This can reduce the water content in the first laminate 21 (particularly, in the first insulating layer 31 thereof), and can also reduce the water content in the second laminate 22 (particularly, in the second insulating layer 32 thereof). The heating temperature and the heating time are preferably set so that the heat history Th (°C·h) calculated by the following formula (A) using the value of the heating temperature Tp (°C) and the value of the heating time Tm (h) is equal to or higher than 150 (°C·h):

[0045] Tp×Tm=Th (A)

[0046] That is, if the heating temperature is 100° C., the heating time is preferably set to a value equal to or greater than 1.5 hours. If the heating time is one hour, the heating temperature is preferably set to a value equal to or greater than 150° C.

[0047] The heating temperature is preferably 100° C. or higher, more preferably 115° C. or higher, and even more preferably 130° C. or higher. In addition, the heating temperature is preferably 200° C. or lower, more preferably 180° C. or lower, even more preferably 150° C. or lower, and particularly preferably 135° C. or lower.

[0048] The heating time is preferably equal to or longer than half an hour, more preferably equal to or longer than one hour, and even more preferably equal to or longer than two hours. In addition, the heating time is preferably equal to or shorter than ten hours, more preferably equal to or shorter than five hours, and even more preferably equal to or shorter than three hours.

[0049] The heating step may be performed under a suitable atmosphere such as an air atmosphere or a nitrogen atmosphere.

[0050] This heating step can be performed by, for example, heating the first laminate 21 and the second laminate 22 using an appropriate dryer.

[0051] 4. Standby steps

[0052] The method for manufacturing a multilayer printed wiring board 1 according to this embodiment preferably includes a standby step. The standby step includes placing the first laminate 21 and the second laminate 22 in an atmosphere having a temperature of 18°C ​​or higher and 28°C or lower and a relative humidity of 45% RH or higher and 65% RH or lower for up to one hour between the end of the heating step and the start of the lamination step. That is, the interval from the end of the heating step to the start of the lamination step is preferably equal to or shorter than one hour. In addition, during the interval from the end of the heating step to the start of the lamination step, the first laminate 21 and the second laminate 22 are preferably placed in an atmosphere having a temperature of 18°C ​​or higher and 28°C or lower and a relative humidity of 45% RH or higher and 65% RH or lower. This makes it easier to reduce the transmission loss of the multilayer printed wiring board 1. This is probably because the first insulating layer 31 and the second insulating layer 32 are less likely to absorb water during the interval from the end of the heating step to the start of the lamination step.

[0053] The first laminated body 21 and the second laminated body 22 can be placed in the above-mentioned atmosphere by, for example, placing the first laminated body 21 and the second laminated body 22 that have just undergone the heating step in a constant temperature and humidity chamber whose internal space is adjusted to the above-mentioned atmosphere.

[0054] The atmosphere in which the first laminate 21 and the second laminate 22 are placed during the standby step does not necessarily need to be the atmosphere described above. Alternatively, the first laminate 21 and the second laminate 22 may be placed in any other suitable atmosphere that makes it less likely that the first insulating layer 31 and the second insulating layer 32 absorb water. Optionally, the method for manufacturing the multilayer printed wiring board 1 according to this embodiment may not include the standby step, and the lamination step may be started directly after the heating step is completed.

[0055] 5.Layering steps

[0056] The lamination step includes laminating the first laminate 21 and the second laminate 22 with the third insulating layer 33 interposed between the second conductor layer 42 and the second insulating layer 32 after the heating step. That is, the first laminate 21, the third insulating layer 33, and the second laminate 22 are laminated so that the second conductor layer 42 and the third insulating layer 33 are laminated, and the third insulating layer 33 and the second insulating layer 32 are laminated. In this way, a multilayer printed wiring board 1 is obtained.

[0057] The third insulating layer 33 contains, for example, a cured product of a thermosetting resin composition. In this case, the third insulating layer 33 is formed of the resin sheet 23 containing a dried product or a semi-cured product of the thermosetting resin composition.

[0058] The thermosetting resin composition contains a thermosetting resin. The thermosetting resin composition preferably contains a polyolefin-based elastomer and a thermosetting resin. This makes it easier to increase the flexibility of third insulating layer 33, thereby making multilayer printed wiring board 1 more flexible. The ratio of the polyolefin-based elastomer to the entire thermosetting resin composition is preferably equal to or greater than 50% by mass and equal to or less than 95% by mass. This makes it even easier to increase the flexibility of third insulating layer 33.

[0059] The polyolefin-based elastomer preferably contains at least one selected from the group consisting of: polystyrene-poly(ethylene / propylene) block-polystyrene copolymer; polystyrene-poly(ethylene-ethylene / propylene) block-polystyrene copolymer; polystyrene-poly(ethylene / butylene) block-polystyrene copolymer; polystyrene-polyisoprene block copolymer; hydrogenated polystyrene-polyisoprene-polybutadiene block copolymer; polystyrene-poly(butadiene / butylene) block-polystyrene copolymer; ethylene-glycidyl methacrylate copolymer; ethylene-glycidyl methacrylate-methyl acrylate copolymer; and ethylene-glycidyl methacrylate-vinyl acetate copolymer.

[0060] In this case, the thermosetting resin preferably contains at least one selected from the group consisting of epoxy resins, phenol resins, bismaleimide resins, cyanate resins, melamine resins, imide resins, and polyphenylene ether oligomers having vinyl groups at both ends thereof.

[0061] If the thermosetting resin contains an epoxy resin, the epoxy resin contains at least one resin selected from the group consisting of, for example, a multifunctional epoxy resin, a bisphenol epoxy resin, a novolac epoxy resin, and a biphenyl epoxy resin.

[0062] The thermosetting resin composition may further contain at least one of a curing agent or a curing accelerator. The curing agent may contain, for example, at least one of a phenolic curing agent or a dicyandiamide curing agent. The curing accelerator may contain, for example, at least one selected from the group consisting of an imidazole, a phenolic compound, an amine, and an organic phosphine.

[0063] The thermosetting resin composition may further contain a filler. The filler contains, for example, at least one selected from the group consisting of silicon dioxide, aluminum hydroxide, magnesium hydroxide, calcium carbonate, talc, and aluminum oxide.

[0064] The resin sheet 23 can be formed by, for example, shaping a thermosetting resin composition into a sheet shape and then heating the thermosetting resin composition under appropriate conditions.

[0065] In the lamination step, for example, first, the first laminate 21, the resin sheet 23, and the second laminate 22 are laminated so that the second conductor layer 42 and the resin sheet 23 are laminated to each other, and the resin sheet 23 and the second insulating layer 32 are laminated to each other, thereby forming the multilayer laminate 5 (see Figure 1 ).

[0066] This multilayer laminate 5 is heat-pressed by an appropriate method. Examples of the method for heat-pressing the multilayer laminate 5 include a method using vacuum pressing, a hot roll lamination method using at least a pair of metal rolls, and a method using double belt pressing.

[0067] The multilayer laminate 5 is hot-pressed to soften and melt the resin sheet 23, thereby causing it to flow. Subsequently, a thermosetting reaction of the resin sheet 23 is allowed to proceed. In this way, the third insulating layer 33 is formed from the resin sheet 23, and the first laminate 21 and the second laminate 22 are bonded together via the third insulating layer 33. In this way, the multilayer printed wiring board 1 (see Figure 2 ).

[0068] Third insulating layer 33 preferably has a relative dielectric constant of 2.9 or less and a dielectric loss tangent of 0.003 or less. This makes it even easier to reduce the transmission loss of multilayer printed wiring board 1. Third insulating layer 33 has such values ​​of relative dielectric constant and dielectric loss tangent by appropriately setting the composition of the thermosetting resin composition used to make third insulating layer 33.

[0069] Optionally, the thickness of the first conductor layer 41 can be increased to a value greater than the thickness of the first metal foil sheet 61 by plating the first conductor layer 41 after the lamination step. In addition, the thickness of the third conductor layer 43 can be increased to a value greater than the thickness of the third metal foil sheet 63 by plating the third conductor layer 43.

[0070] The first conductor layer 41 can be transformed into a conductor line by patterning the first conductor layer 41 using a suitable method such as a subtractive method after the lamination step. Similarly, the third conductor layer 43 can be transformed into a conductor line by patterning the third conductor layer 43 using a suitable method such as a subtractive method (see Figure 3 ).

[0071] Furthermore, through holes (plated through holes) can also be formed by, for example, providing through holes through the multilayer printed wiring board 1 by an appropriate method such as laser processing or drilling and forming conductors on the inner surfaces of the through holes by plating.

[0072] 6. Multilayer printed circuit boards

[0073] As described above, multilayer printed wiring board 1 according to this embodiment includes first conductor layer 41, first insulating layer 31, second conductor layer 42, third insulating layer 33, second insulating layer 32, and third conductor layer 43 stacked one on top of the other. First insulating layer 31 and second insulating layer 32 each contain polyimide. This multilayer printed wiring board 1 can be manufactured by, for example, the above-described method.

[0074] The weight change measured by the dry weight measurement method is preferably equal to or less than 3000 μg / cm 2 with the total volume of the first insulating layer 31 , the second insulating layer 32 , and the third insulating layer 33 being defined as a basis. 3 This makes it easier to particularly significantly reduce the transmission loss of the multilayer printed wiring board 1. Such a low weight variation can be achieved, for example, by manufacturing the multilayer printed wiring board 1 using the above-described method. The weight variation is more preferably equal to or less than 2000 μg / cm 3 , and even more preferably equal to or less than 500 μg / cm 3 The ideal weight change is 0 μg / cm 3 Hereinafter, a method for measuring weight change by dry weight measurement will be described in detail with reference to specific examples.

[0075] The ratio of the total thickness of first insulating layer 31 and second insulating layer 32 to the total thickness of first insulating layer 31, second insulating layer 32, and third insulating layer 33 is preferably equal to or greater than 67%. This makes it easier to significantly reduce the transmission loss of multilayer printed wiring board 1. This ratio is more preferably equal to or greater than 70%, and even more preferably equal to or greater than 80%. In addition, this ratio is equal to or less than 98%, for example, preferably equal to or less than 95%, and even more preferably equal to or less than 85%.

[0076] In this embodiment, if the insulating layer thickness X, which is the sum of the thicknesses of the first insulating layer 31, the second insulating layer 32, and the third insulating layer 33, is equal to or greater than 75 μm and equal to or less than 125 μm, or equal to or greater than 75 μm and less than 125 μm, the transmission loss Y of the multilayer printed wiring board 1 can satisfy the following inequality (1):

[0077] 0>Y≥0.6175X-126.26 (1)

[0078] And can be equal to or greater than -80.

[0079] In addition, if the insulating layer thickness X is equal to or greater than 125 μm and equal to or less than 200 μm, or equal to or greater than 125 μm and less than 200 μm, the transmission loss Y of the multilayer printed wiring board may satisfy the following inequality (2):

[0080] 0>Y≥0.1532X-68.221 (2)

[0081] And can be equal to or greater than -49.

[0082] Furthermore, if the insulating layer thickness X is equal to or greater than 200 μm and equal to or less than 325 μm, or equal to or greater than 200 μm and less than 325 μm, the transmission loss Y of the multilayer printed wiring board may satisfy the following inequality (3):

[0083] 0>Y≥0.1028X-58.135 (3)

[0084] And can be equal to or greater than -38.

[0085] Furthermore, if the insulating layer thickness X is equal to or greater than 325 μm and equal to or less than 1025 μm, the transmission loss Y of the multilayer printed wiring board may satisfy the following inequality (4):

[0086] 0>Y≥0.0113X-28.397 (4)

[0087] And it can be equal to or greater than -25. Note that the unit of transmission loss Y is dB / m.

[0088] In the present embodiment, the first insulating layer 31 and the second insulating layer 32 each contain polyimide, and the weight change measured by the dry weight measurement method is equal to or less than 3000 μg / cm 3 , thereby achieving a transmission loss Y within any of these ranges.

[0089] Example

[0090] Next, specific examples of the exemplary embodiment will be described. Note that the specific examples described below are merely examples of the exemplary embodiment and should not be construed as limiting.

[0091] 1. Manufacturing the first laminate

[0092] Polyimide films having thicknesses of 25 μm, 38 μm, 50 μm, 75 μm, 137.5 μm, and 500 μm (product name: UPILEX VT, manufactured by Ube Industries, Ltd.; specific gravity 1.2) and a copper foil sheet having a thickness of 12 μm (product number: GHY5-93F-HA-V2, manufactured by JX Nippon Mining & Metals Corporation) were provided.

[0093] A polyimide film having a thickness corresponding to the thickness of the first insulating layer in each specific example (see Tables 3 and 4) was used. A multilayer laminate was heat-pressed by a double belt method under conditions including a heating temperature of 330°C, a pressing pressure of 4 MPa, and a heating time of 5 minutes, wherein a copper foil sheet, a polyimide film, and another copper foil sheet were sequentially laminated on each other so that the matte surface of each copper foil sheet was superimposed on the polyimide film.

[0094] The semi-finished product thus obtained was cut to have a planar size of 250 mm×250 mm.

[0095] Subsequently, the semi-finished copper foil sheet is patterned by a subtractive method using a photosensitive dry film as a photoresist and a copper (II) chloride solution as an etchant, thereby forming a conductor line. In this way, a first laminate is formed.

[0096] 2. Manufacturing the Second Laminate

[0097] Polyimide films (product name: UPILEX VT, manufactured by Ube Industries, Ltd.) having thicknesses of 25 μm, 38 μm, 50 μm, 75 μm, 137.5 μm, and 500 μm and a copper foil sheet having a thickness of 12 μm were provided.

[0098] A polyimide film having a thickness corresponding to the thickness of the second insulating layer in each specific example (see Tables 3 and 4) was used. A multilayer laminate, in which a copper foil sheet, a polyimide film, and a release film (product name: UPILEX S, manufactured by Ube Industries, Ltd.; thickness: 25 μm) were sequentially laminated using a double belt method under conditions including a heating temperature of 330°C, a pressing pressure of 4 MPa, and a heating time of 5 minutes, was heat-pressed so that the matte surface of the copper foil sheet was superimposed on the polyimide film. The release film was then peeled from the polyimide film.

[0099] In this way, a second laminate was formed.Then, the second laminate was cut to have a plane size of 250 mm×250 mm.

[0100] 3. Heating step

[0101] The first laminate and the second laminate were loaded into a dryer and heated in an air atmosphere. At this time, the heating temperature and the heating time were as described in "Heating step conditions" in Table 1.

[0102] 4. Standby steps

[0103] In the first to twelfth embodiments, the first and second laminated bodies were placed in a thermo-hygrostat immediately after the heating step. The temperature and humidity in the thermo-hygrostat and the duration of time the first and second laminated bodies were placed in the thermo-hygrostat are as described in the "Standby Step Conditions" in Tables 3 and 4.

[0104] 5.Layering steps

[0105] Once the standby step is complete, the first laminate, the resin sheet (a sheet-like low-transmission-loss flexible multilayer board material, product number: R-BM17, available from Panasonic Corporation, with a thickness of 25 μm), and the second laminate are sequentially stacked on top of each other so that the conductor lines of the first laminate are stacked on the resin sheet, and the resin sheet is stacked on the polyimide film of the second laminate, thereby forming a multilayer laminate. The multilayer laminate is then heat-pressed using a daylight press machine in a reduced-pressure atmosphere of 50 torr (=50×(101325 / 760) Pa) or less under conditions including a maximum heating temperature of 180°C, a pressing pressure of 2 MPa, and a heating time of one hour. In this way, a multilayer printed wiring board is obtained.

[0106] 6. Forming conductor lines and other components

[0107] Each of the two copper foil sheets of the multilayer printed wiring board is plated to increase the thickness of the copper foil sheet to 27 μm. In addition, the multilayer printed wiring board is drilled to make a through hole with a diameter of 300 μm. In addition, by a subtractive method, a photosensitive dry film is used as a photoresist and copper chloride (II) solution is used as an etchant with each copper foil sheet and through hole patterning to form a conductor circuit with a thickness of 27 μm, and a through hole (plated through hole) is formed, wherein the inner surface of the through hole is plated with a copper film. The residual copper rate of the conductor circuit corresponding to the first conductor layer and the conductor circuit corresponding to the third conductor layer is shown in Tables 3 and 4. Subsequently, the etching photoresist is removed by polishing with a piece of sandpaper.

[0108] 7. Relative dielectric constant and dielectric loss tangent of the third insulation layer

[0109] The eight resin sheets (product number: R-BM17) used in the above-mentioned "5. Lamination Step" section were stacked on each other and heat-pressed in a reduced pressure atmosphere of 50 Torr (=50×(101325 / 760) Pa) or less under conditions including a maximum heating temperature of 180°C, a pressing pressure of 2 MPa, and a heating time of one hour, thereby curing. In this way, a sample was formed. The dielectric properties (including relative dielectric constant and dielectric loss tangent) of the sample were measured at a frequency of 10 GHz using a network analyzer (product number: E5071C, manufactured by Keysight Technologies) by a cavity resonator method. As a result, the relative dielectric constant was 2.2 and the dielectric loss tangent was 0.0012.

[0110] 8. Weight change measured by dry weight measurement

[0111] The weight of the multilayer printed circuit board was measured using a precision electronic balance.

[0112] The multilayer printed wiring board was heated to 135° C. for two hours in air to be dried. The weight of the dried multilayer printed wiring board was measured using a precision electronic balance.

[0113] Based on the results of this measurement, the weight change (unit: μg / cm) was calculated by the following formula: 3 ). Note that the value of weight change is defined by rounding the calculated value to one decimal place.

[0114] (AB) / {(CD)×E×0.1}×1000000

[0115] The parameters in this formula are defined as follows:

[0116] A: weight of the multilayer printed wiring board before drying (g);

[0117] B: weight of the newly dried multilayer printed circuit board (g);

[0118] C: Plane area of ​​multilayer printed circuit board (cm 2 ), which in this test is 625cm 2 ;

[0119] D: Planar area of ​​each plated through hole of a multilayer printed circuit board (cm 2 ), which in this test is 6.25 cm 2 ;as well as

[0120] E: the total thickness of the first insulating layer, the second insulating layer, and the third insulating layer (mm).

[0121] The parameter values ​​in each embodiment are shown in Tables 1 and 2 below:

[0122] [Table 1]

[0123] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 A 39.7241 21.8152 17.2513 30.9429 26.3790 37.4710 102.8094 B 39.7222 21.8146 17.2510 30.9416 26.3781 37.4693 102.8031 C 625 625 625 625 625 625 625 D 6.25 6.25 6.25 6.25 6.25 6.25 6.25 E 0.325 0.125 0.075 0.225 0.175 0.3 1.025

[0124] [Table 2]

[0125] Example 8 Example 9 Example 10 Example 11 Example 12 Comparative Example 1 Comparative Example 2 A 19.6245 39.7899 21.8676 39.8024 21.8781 39.7899 21.8676 B 19.6241 39.7241 21.8152 39.7241 21.8152 39.7241 21.8152 C 625 625 625 625 625 625 625 D 6.25 6.25 6.25 6.25 6.25 6.25 6.25 E 0.101 0.325 0.125 0.075 0.225 0.325 0.125

[0126] 9. Transmission loss (initial)

[0127] A network analyzer (Product No.: E5071C, manufactured by Keysight Technologies) was used to measure the transmission loss caused when an electrical signal applied at a frequency of 20 GHz was transmitted through a test wiring (A) having a length of 1000 mm and a test wiring (B) having a length of 750 mm in a conductor line corresponding to the second conductor layer of the multilayer printed wiring board. The difference (A)-(B) between the thus measured transmission losses was calculated and multiplied by four to obtain the transmission loss (dB / m). Note that a wiring having an impedance of 50 Ω was used as each test wiring.

[0128] 10. Transmission loss (after 24 hours at 23°C and 50%)

[0129] The multilayer printed wiring board was placed in a constant temperature and humidity chamber whose internal atmosphere was adjusted to 23° C. and 50% RH, kept for 24 hours, and then the transmission loss was measured in the same manner as in the above “Transmission loss (initial)” section.

[0130] 11. Transmission loss (after 96 hours at 40°C and 90%)

[0131] The multilayer printed wiring board was placed in a constant temperature and humidity chamber whose internal atmosphere was adjusted to 40° C. and 90% RH, maintained for 96 hours, and then the transmission loss was measured in the same manner as in the above “Transmission loss (initial)” section.

[0132] 12. Test Results

[0133] The results of these tests are summarized in Tables 3 and 4 below:

[0134] [Table 3]

[0135]

[0136] [Table 4]

[0137]

[0138] These results show that, when the results obtained in the first and ninth embodiments, in which the insulating layers had the same total thickness, were compared with the results obtained in the first comparative example, the transmission loss values ​​were improved in the first and ninth embodiments, in which the manufacturing method included a heating step, compared to the first comparative example, in which the manufacturing method did not include a heating step. Similarly, when the results obtained in the second, tenth, and twelfth embodiments were compared with the results obtained in the second comparative example, the transmission loss values ​​in the second, tenth, and twelfth embodiments were improved compared to the second comparative example.

[0139] Among the first to twelfth embodiments, in the first to eighth embodiments, the weight change is particularly low (i.e., the water content of the insulating layer containing polyimide is particularly low), and the transmission loss value is within the range defined by inequality (1), (2), (3) or (4).

[0140] Furthermore, comparing the results obtained in the first embodiment with those obtained in the eleventh embodiment, the transmission loss in the first embodiment, which had a higher residual copper ratio, was less likely to deteriorate even when a heating and humidification process was performed, compared to the eleventh embodiment. Similarly, comparing the results obtained in the second embodiment with those obtained in the twelfth embodiment, the transmission loss in the second embodiment, which had a higher residual copper ratio, was less likely to deteriorate even when a heating and humidification process was performed, compared to the twelfth embodiment. This confirms that the higher the residual copper ratios of the first and third conductor layers, the less likely the transmission loss is to deteriorate over time. Note that the residual copper ratios of each of the first and third conductor layers are preferably equal to or greater than 40%, and more preferably equal to or greater than 60%.

Claims

1. A method for manufacturing a multilayer printed wiring board, the method comprising: providing a first laminate including a first conductor layer, a first insulating layer containing polyimide, and a second conductor layer sequentially stacked on each other, and a second laminate including a second insulating layer containing polyimide and a third conductor layer sequentially stacked on each other; a heating step comprising, after the step of providing the first laminate and the second laminate, heating each of the first laminate and the second laminate under conditions including a heating temperature equal to or higher than 100° C. and a heating time equal to or longer than half an hour to reduce a water content in the first insulating layer and the second insulating layer; a laminating step comprising, after the heating step, laminating the first laminate and the second laminate on each other with a third insulating layer interposed between the second conductor layer and the second insulating layer; and A standby step comprising placing the first laminate and the second laminate in an atmosphere having a temperature of 18° C. or higher and 28° C. or lower and a relative humidity of 65% RH or lower for up to one hour during an interval from the end of the heating step to the start of the laminating step.

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