Method for manufacturing circuit substrate, material for circuit substrate, and inkjet printer for manufacturing circuit substrate
Patent Information
- Application Number
- PCT/JP2026/006188
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-02-20
- Filing Date
- 2026-02-19
- Publication Date
- 2026-08-27
Smart Images
Figure JP2026006188_27082026_PF_FP_ABST
Abstract
Description
Method for manufacturing a circuit board, material for a circuit board, and inkjet printing apparatus for manufacturing a circuit board
[0001] The present disclosure relates to a method for manufacturing a circuit board, a material for a circuit board, and an inkjet printing apparatus for manufacturing a circuit board.
[0002] In order to form a conductive film on the inner peripheral surface (inner wall) of a hole penetrating from the front surface to the back surface of an insulating substrate without problems by an inkjet method, when forming a conductive underlayer on the inner wall of the hole for an insulating substrate having a hole penetrating from the front surface to the back surface, with the hole blocked by a closing member from the lower side of the substrate, a filling step of filling the hole with ink by discharging conductive ink droplets into the hole by an inkjet method, a discharging step of discharging the ink filled in the hole to the outside, and a drying step of drying the inner wall ink layer remaining on the inner wall of the hole after the discharging step are known (Patent Document 1 below).
[0003] Japanese Patent Application Laid-Open No. 2023-047225
[0004] However, depending on the relationship between the hole diameter and the hole depth, the number of conductor layers to be laminated, and the rigidity and flexibility of the substrate material, poor conduction between the conductor inside the hole and the conductor outside the hole and appearance defects may occur.
[0005] Therefore, at least one aspect of the problem of the present disclosure is to provide a method for manufacturing a multilayer circuit formation substrate in which, even when the relationship between the hole diameter and the hole depth, the number of pattern formation layers, and the rigidity and flexibility of the substrate material change, the conduction between the conductor inside the hole and the conductor outside the hole and the appearance are good.
[0006] Note that, for those skilled in the art who can read from the embodiments and their descriptions characteristic of the present disclosure described in the specification, drawings, etc. of the present disclosure, problems that are obvious may also become problems to be solved by the divided invention when a divisional application is made based on the present disclosure.
[0007] To achieve the above-mentioned objectives, the method for manufacturing a circuit board according to the present disclosure includes the steps of: forming a first primer resin layer on a first surface of a first core substrate; forming a first protective layer on the first primer resin layer; forming through holes that penetrate the first core substrate; a first ink ejection step of ejecting an ink composition containing metal nanoparticles to form a first in-hole ink layer on the first protective layer and inside the through holes; a first protective layer peeling step of peeling off the first protective layer to which the first ink layer is attached; and a second ink ejection step of ejecting an ink composition to form a first conductive pattern underlayer on the first primer resin layer.
[0008] Furthermore, the circuit board material of this disclosure comprises a core substrate, a first primer resin layer formed on a first surface of the core substrate, a second primer resin layer formed on a second surface of the core substrate, a first protective layer formed on the first primer resin layer, and a second protective layer formed on the second primer resin layer.
[0009] Furthermore, the inkjet printing apparatus for manufacturing circuit boards according to the present disclosure comprises an inkjet head, a stage, and a peeler, wherein at least a first primer resin layer is formed on a first core substrate, a first protective layer is formed on the first primer resin layer, and through holes are formed penetrating the first core substrate, the inkjet head ejects an ink composition containing metal nanoparticles to form a first ink layer on the first protective layer and in the holes of the through holes, the peeler peels off the first protective layer to which the first ink layer is attached, the inkjet head ejects the ink composition to form a first conductive pattern underlayer on the first primer resin layer and a second ink layer in the holes of the through holes.
[0010] According to this disclosure, it is possible to provide a method for manufacturing a multilayer circuit board that maintains good conductivity between conductors inside and outside the holes, as well as a good appearance, even when the relationship between hole diameter and hole depth, the number of pattern formation layers, and the rigidity of the substrate material change.
[0011] This is a process study diagram of a circuit board manufacturing method. This is a flowchart showing the processing flow related to the circuit board manufacturing method of this disclosure. This is a process diagram for explaining the circuit board manufacturing method of this disclosure. This is an inkjet printing apparatus according to this disclosure. This is a process diagram for explaining the circuit board manufacturing method of this disclosure. This is a diagram showing the ink droplet ejection position in a top view of a through hole. This is a process diagram for explaining the circuit board manufacturing method of this disclosure. This is a cross-sectional view of a multilayer circuit board (4 layers). This is a cross-sectional view of a multilayer circuit board (6 layers). This is a diagram illustrating a method for manufacturing circuit board material using a primer film material. This is a diagram illustrating a method for manufacturing circuit board material using a primer film material.
[0012] The method for manufacturing circuit boards and applications of the circuit boards described herein are applicable, for example, to wiring Cu seed printing, TGV (formation of insulating layer, Cu vias and seed layer), and solder resist printing (solder resist dam) in PCBs (printed circuit boards) and package substrates. They are also applicable, for example, to the formation of various layers (including, for example, bonding material, insulating layer, passivation layer, photoresist, and release layer), flux coating, and package marking in advanced packaging.
[0013] Furthermore, it can be applied, for example, to the formation of quantum dot layers and OLED layers in flat panel displays. It can also be applied, for example, to the formation of perovskite layers, electrodes, and encapsulation layers in perovskite solar cells.
[0014] When the circuit board of this disclosure is, for example, a so-called PCB, it may include a single-sided board (one-layer board), a double-sided board (two-layer board), a four-layer board, a six-layer board, an eight-layer board, or a multilayer board with more layers.
[0015] Rigid PCBs can be multilayered, for example, having a total of 4, 6, 8, or even more layers. In general, PCBs with 4 or more layers are sometimes referred to as multilayer boards. In these multilayer boards, conventional processes such as subtractive methods require repeated steps for each layer, including wiring pattern formation, lamination pressing, through-hole formation, and copper plating.
[0016] On the other hand, flexible PCBs have thin substrates and, because patterns are formed on flexible polyimide films or similar materials, their basic structure is relatively simple and they rarely have the thickness or complexity of rigid PCBs. Therefore, the manufacturing process of rigid multilayer PCBs (printed circuit boards) using inkjet printing is sometimes considered more difficult than that of flexible PCBs (flexible circuit boards). One reason for this is ensuring conductivity between both sides through conductive layers formed in processed holes, such as through-holes.
[0017] When manufacturing rigid multilayer PCBs using an inkjet method, ensuring conductivity between the front and back surfaces, and between certain layers, through via holes such as through-holes, presents certain challenges. Figure 1 is a schematic diagram illustrating this.
[0018] In Figure 1, a primer resin layer P1 is formed on one surface (first surface) of the first core substrate F1, which is the core substrate. Furthermore, ink droplets of an ink composition containing metal nanoparticles are ejected onto the primer resin layer P1 by inkjet printing to form an ink layer SK1. This ink layer SK1 can form a desired conductive pattern by an inkjet printing device, and this conductive pattern can form an electrical circuit.
[0019] When forming the ink layer, ink droplets are sometimes introduced into the inner walls of through-holes H1 to ensure conductivity between the front and back surfaces of the substrate and between layers. These ink layers are subjected to heat treatment, including light irradiation, or reduction reactions to impart conductivity through bonding and fusion between metal nanoparticles, forming the conductive pattern underlayer HEK1. Then, electroless or electrolytic plating is performed to deposit conductors and form a conductive plating layer SPM1.
[0020] When using an inkjet method, it is common to form the through-hole conductor on the inner wall of the through-hole H1 and the conductor layer on the substrate in this manner. However, if the ink on the inner wall of the through-hole H1 is applied to the circuit pattern ink on the substrate at the same time during the manufacturing process, the thickness of the conductor layer may become too large after the conductor is deposited in the plating process, which can cause a break in the connection between the through-hole conductor and the patterned conductor.
[0021] On the other hand, if the thickness of the ink layer is reduced in order to reduce the thickness of the conductive plating layer SPM1, there is a risk that the formation of the conductor on the inner wall of the through-hole H1 will be insufficient. As will be explained in more detail later, in order to apply ink directly to the inner wall of the through-hole, it is necessary to use the inertia of the inkjet head, which moves relative to the substrate, to inject ink droplets from an oblique direction, so the thickness will be thinner than the ink layer of ink dropped onto the substrate surface.
[0022] To solve these problems, one approach is to reduce the viscosity of the ink introduced into the through-holes and to apply a wettability-enhancing treatment to the inside of the holes so that the dropped ink droplets can easily flow down the inner surface of the holes. However, this requires preparing two types of ink with different viscosities: one for the substrate surface and one for inside the holes. Performing the printing process using two types of ink in this way is not economical, and it also requires at least two types of ink tanks and inkjet heads.
[0023] Therefore, this disclosure provides a method for manufacturing a circuit-forming substrate and a circuit substrate that can reduce poor conductivity between conductors inside and outside holes, as well as appearance defects, even when the relationship between hole diameter and hole depth, the number of laminated conductive layers, and the rigidity of the substrate material change. For example, when a process used for a flexible substrate (2 layers) with conductive patterns formed on both sides is applied to a rigid multilayer printed circuit board (4 or more layers), the relationship between hole diameter and hole depth, the number of laminated conductive layers, and the rigidity of the substrate material will change. Even in such cases, poor conductivity between conductors inside and outside holes, as well as appearance defects, can be reduced.
[0024] This disclosure includes detailed descriptions of embodiments with accompanying drawings to aid in understanding the invention. In each drawing, the scale may differ from that of actual objects in order to make each component, area, etc., recognizable. The embodiments described herein are merely illustrative, and those skilled in the art will understand that the invention is implementable even if some specific details are omitted or modified. Furthermore, detailed descriptions of well-known technologies may be omitted to ensure clarity in the specification. Where numerical labels such as "1st," "2nd," etc. are used in the description, they are for identifying each element and do not define the number of elements. In general, the singular form may be understood to include the plural form, and the plural form may include the singular form.
[0025] In this specification, conductive portions and through holes provided in printed circuit boards, etc., will be referred to as "holes." However, in cases where processing steps or everyday expressions are required, such as drilling holes, the term "hole" may be used. However, these terms are merely differences in terminology and technically refer to the same opening, cavity, etc.
[0026] Embodiments of this disclosure will be described with reference to the drawings. Figure 2 is a flowchart showing the process flow of the method for manufacturing a circuit board according to this disclosure. Figures 3, 5, 6, and 7 are schematic diagrams showing the method for manufacturing a circuit board according to this disclosure. Figure 4 is a diagram showing an inkjet printing apparatus that can perform some of the processes of the method for manufacturing a circuit board according to this disclosure.
[0027] In step S100 of Figure 2, the first core substrate F1 is prepared as shown in Figure 3(a).
[0028] The core substrate will be described primarily as a composite material, such as FR-4, which is a glass fiber woven cloth (glass cloth or glass woven fabric) impregnated with epoxy resin. Other materials may include fluororesins (PTFE), glass cloth-based polyphenylene ether resin (PPE), glass, polyimide, polyester, polyethylene terephthalate, polyethylene naphthalate, and other resin substrates, alumina substrates, aluminum nitride substrates, sapphire substrates, and silicon wafer substrates. In terms of electrical conductivity, the material may generally be an insulator or semiconductor. In addition, the core substrate may be a prepreg. Prepregs are generally used as interlayer insulating layers, but they can also be used as core substrates. A prepreg is a resin-impregnated fiber intermediate material. The resin-impregnated fiber intermediate material may mean an intermediate material provided in the form of a solid layer or sheet, provided by impregnating, for example, continuous fibers (including unidirectional bundles, woven or knitted fabrics, nonwoven fabrics, etc.) with a precursor of a polymer matrix (oligomer, prepolymer, molten thermoplastic resin, resin solution, or precursor polymer that becomes ceramics through an inorganic reaction). When a thermosetting resin is used as the matrix, it may be in a so-called semi-cured (B-stage) state.
[0029] A rigid core substrate may be made of a material having a hardness of, for example, a tensile modulus of 10 GPa or more. Since the tensile modulus is expressed using the same physical quantity as Young's modulus, it may also be defined by Young's modulus. Generally, even in resins and their composite materials, which are called semi-flexible and have a relatively high tensile modulus, it is only about a few GPa, so a material with a hardness of 10 GPa or more in tensile modulus is used as a rigid substrate. For example, an insulating rigid substrate containing glass epoxy resin has a tensile modulus of about 20 GPa.
[0030] Flexible core substrates include, for example, polyamide synthetic resins such as polyimide, polyamide, polyester such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), nylon (registered trademark) as specified by nylon 6, 10, nylon 4, 6, etc., polyether ether ketone, resins such as acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polyvinyl chloride, epoxy resins, polystyrene, and polyphenylene sulfide (PPS).
[0031] Other flexible core substrates may include, for example, polyvinylidene chloride, polyvinyl alcohol, styrene-acrylonitrile copolymer, polyethylene, styrene-vinyl acetate copolymer, polyacetal, cellulose acetate, polycarbonate, thermoplastic polyurethane, and polytetrafluoroethylene.
[0032] In step S101 of Figure 2, a first primer resin layer P1 is formed on the first core substrate F1, as shown in Figure 3(b). The primer resin layer can also be formed by applying a liquid primer to a support film, curing it to form a primer film material, and then pressing the core substrate between the film from both sides. This method will be described later.
[0033] Thus, a primer resin layer may be formed on the core substrate and the interlayer insulating layer described later for various purposes, such as improving the applicability of the ink composition, modifying the surface of the substrate, or controlling the behavior of inkjet droplets upon impact.
[0034] The material of the primer resin layer includes, for example, an epoxy resin and is adjusted to have a predetermined elastic modulus, as described later.
[0035] The primer resin layer can be formed, for example, by coating a diluted primer resin layer material onto a core substrate and curing it by raising the temperature. The diluting solvent may be, for example, ethylene glycol monomethyl ether diluted to prepare a 50% dilution. Other diluting solvents can also be used. When using the ratio of curable resin to the total value of diluting solvent and curable resin as one of the dilution ratios, it is preferably 1 to 90%, more preferably 10 to 70%, and even more preferably 20 to 60%. If the dilution ratio is high, the viscosity of the liquid may increase, and it tends to result in poor uniform coating properties.
[0036] The coating film thickness may be, for example, 1 to 100 μm relative to the core substrate. More preferably, it is 5 to 70 μm, and even more preferably, 10 to 50 μm. If the coating film thickness is too low, it may not reach the specified film thickness, making it difficult to achieve the desired physical properties described above. If the coating film thickness is too high, the material cost tends to be high, and the ratio of the primer resin layer thickness to the core substrate thickness becomes high, which may result in the substrate properties not being met.
[0037] For curing after coating, the material may be heated to a temperature suitable for curing and held for 1 to 120 minutes. While the curing temperature cannot be precisely determined, it is believed that a suitable curing temperature for the primer resin layer material can be determined by a reasonable number of trials and experiments for those skilled in the art. As an example of a suitable curing temperature, it is preferable to obtain the exothermic peak using TGDTA measurement and set the temperature within ±30°C of that exothermic peak. The primer curing time is preferably 1 to 120 minutes, more preferably 10 to 60 minutes, and even more preferably 30 to 60 minutes. If the curing time is too short, the primer may not cure properly, and if the curing time is too long, productivity may decrease.
[0038] The thickness of the primer resin layer after curing may be 0.5 to 50 μm. More preferably, it is 0.5 μm to 30 μm, and even more preferably, 1 μm to 20 μm. If the thickness is too low, it may be difficult to achieve the desired physical properties described above. If the thickness is too high, the material cost tends to be high, and the ratio of primer to substrate thickness becomes high, which may result in the substrate properties not being met.
[0039] In step S102 of Figure 2, a protective layer S1 is formed on the first primer resin layer P1, as shown in Figure 3(c).
[0040] The protective layer S1 is provided for the purpose of protecting the surface of the primer resin layer, and its thickness can be appropriate, ranging from a thin film or film to a plate. The material may be a metal such as aluminum, and from the viewpoint of ease of drilling, for example, aluminum metal foil or metal film is used. Other materials may be used for antistatic purposes, polypropylene or polyethylene terephthalate may be used for high heat resistance protection, and polyvinyl chloride or polyethylene may be used for general purposes. It should be noted that since a lithography process is not used for the protective layer S1, it is clear that photosensitive materials such as photosensitive dry film resists are not used.
[0041] Considering the ease of peeling the protective layer S1 from the primer resin layer, it is desirable to form it by externally adding a material that has a homogeneous, integrated structure from the outset, such as a film or plate. For example, if it is formed by applying and curing a resin liquid, subsequent removal may be difficult.
[0042] Here, we will explain that the intermediate product with the protective layer formed may be used as the material for the circuit board of this disclosure, or may be traded independently. The circuit board material of this disclosure may be a circuit board material comprising a core substrate, a first primer resin layer formed on the first surface of the core substrate, a second primer resin layer formed on the second surface of the core substrate, a first protective layer formed on the first primer resin layer, and a second protective layer formed on the second primer resin layer. Such a circuit board material can be used as a material specifically for the method of manufacturing the circuit board of this disclosure. It should also be noted that the intermediate product with the protective layer formed may be traded with through holes formed by a drill or the like.
[0043] In such a case, an intermediate product is formed into a primer film material having a support film layer and a primer resin layer through the steps of applying a primer liquid onto one plane of the support film and curing the primer liquid. The primer film material is arranged such that the primer resin layers of the primer film material face the front side and the back side, respectively, of a core substrate having front and back planes. Then, one of the support film layers of each primer film material is pressed to crimp each of the core substrate and the primer resin layer. Through these steps, a first primer resin layer can be formed on the first surface of the core substrate and a second primer resin layer can be formed on the second surface of the core substrate, so that it can be manufactured as a material for a circuit board. This will be described later.
[0044] In addition, although the present disclosure is applicable to various primers, for example, the storage elastic modulus of the primer resin layer at 25°C is ８ 4.0711×10 ７ or less, and the loss elastic modulus may be 6.4825×10
[0045] or less. In this case, the primer resin layer can further control the landing position of the inkjet droplets and draw an appropriate pattern.
[0046] In step S103 of FIG. 2, as shown in FIG. 3(d), drilling is performed to form a through hole H1. The drilling can form a through hole by, for example, mechanical drilling, laser processing, or a combination thereof.
[0047] In step S104 of FIG. 2, as shown in FIG. 5(e), a desmear treatment may be performed on the smear generated during the drilling process for hole opening, or other residues or debris, using the desmear treatment apparatus 400. Depending on the type of hole opening process, the name of the by-product may be different. For example, in laser processing, it may be called char. In the present disclosure, these post-treatments are collectively and simply referred to as desmear treatment. The desmear treatment may be a dry desmear process from the viewpoints of low environmental impact without using chemical solutions and high processing efficiency even when the hole diameter is small. The dry desmear process may be any one of a plasma treatment method, an ion milling method, a method using ultraviolet rays and ozone, a corona discharge treatment method, and a reactive ion etching method.
[0048] In step S105 of FIG. 2, as shown in FIGS. 5(f) to 5(g), an inkjet printing apparatus is used to discharge and apply an ink composition containing metal nanoparticles from an inkjet head toward the through hole H1.
[0049] FIG. 4 shows a configuration example of an inkjet printing apparatus for discharging an ink composition. The inkjet printing apparatus 300 may include a system control unit 310 and a plurality of module groups controlled by the system control unit 310. The plurality of module groups may include, for example, a handling module 320, a printing module 330, and a stage module 340.
[0050] The handling module 320 may include a handler 32I for handling a workpiece such as a core substrate, a handler control system (not shown), a peeler 322 for peeling a protective layer, and a peeler control system 323 for controlling the peeler 322. <PAGEREF _Ref403847401 \h>104The peeler 322 may be built in as a part of the configuration of the inkjet printing apparatus 300 or may be arranged adjacent thereto.
[0052] The printing module 330 may include an inkjet head 331 that ejects ink, an ink supply system 332 that includes an ink tank for supplying ink, and a head control system 333 that controls the operation of the inkjet head 331.
[0053] The stage module 340 may include a stage 341 for placing and transporting workpieces, and a stage control system 342 for controlling the operation of the stage 341.
[0054] Such an inkjet printing apparatus can also be used as a dedicated apparatus for the method of manufacturing a circuit board of the present disclosure, or for the method of manufacturing a circuit board of the present disclosure. As will be described later, for example, an intermediate circuit board having at least a first primer resin layer formed on a first core substrate, a first protective layer formed on the first primer resin layer, and through holes formed through the first core substrate can be processed by an inkjet head discharging an ink composition containing metal nanoparticles to form a first ink layer on the first protective layer and in the holes of the through holes, a peeler peeling off the first protective layer to which the first ink layer is attached, and the inkjet head discharging an ink composition to form a first conductive pattern underlayer on the first primer resin layer and a second ink layer in the holes of the through holes.
[0055] The ink composition is applied by the deposition of inkjet droplets of the ink composition containing metal nanoparticles, ejected from the inkjet head 331. The metal nanoparticles can be various, such as gold, silver, platinum, copper, or alloys thereof, and are not technically limited to a single metal. However, considering conductivity, availability, cost, and global supply, copper nanoparticles may be a suitable example. Therefore, metal nanoparticles and copper nanoparticles may be described together in the following. A copper nano-ink composition containing copper nanoparticles, a coating material, a dispersant, and a solvent is described below as an example, but copper nano-inks with other compositions may also be used.
[0056] The copper nanoparticles preferably have an average particle size of 1 nm to 200 nm, and more preferably 10 nm to 100 nm. If the particle size is too small, the reactivity of the particles may increase, potentially reducing the storage and stability of the ink. If the particle size is too large, the uniformity of the thin film may decrease, and precipitation of ink particles may occur more easily.
[0057] Ink compositions capable of forming the conductive pattern underlayer SEK2 can be broadly classified into two types: particle-dispersed and reduction-type. Either type of ink composition can be used. Particle-dispersed inks have properties similar to pigment inks, while reduction-type inks have properties similar to dye inks. These classifications are merely for convenience. Furthermore, there are thermal decomposition-type inks that use metal salts or complexes as precursors, generating metals through thermal decomposition; some consider these to be reduction-type inks.
[0058] Particle-dispersed ink compositions improve conductivity by sintering the printed pattern using light, heat, plasma, or a combination thereof, fusing the metal nanoparticles together to create conductivity. Therefore, they may also be called physically sintered inks. For example, photosintering using a flash lamp can be applied. Furthermore, chemical reduction treatment can also improve the conductivity of particle-dispersed ink compositions. For instance, by reducing the oxide film on the surface of copper nanoparticles using a chemical reduction reagent such as formaldehyde, the reduction reaction from copper oxide to copper proceeds, producing active, zero-valent copper. As a result, it is possible to induce a fusion phenomenon between metal nanoparticles similar to that of the physically sintered type described above. The copper nanoparticles are dispersed in an organic solvent and coated with a coating material. The coating material prevents the copper nanoparticles from easily oxidizing and may be, for example, a carboxylic acid, more preferably a monocarboxylic acid with an integer number of carbon atoms from 6 to 10, such as hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, or decanoic acid. The dispersant is used to disperse copper nanoparticles coated with a coating material to form an ink. Its purpose is to uniformly disperse the copper nanoparticles, which are the dispersed phase, in the solvent, which is the dispersion medium, and to maintain a stable dispersed state without aggregation. The dispersant may be a carboxylic acid-based, thiol-based, phenol-based, phosphoric acid-based, or amine-based compound. Preferably, it may be a carboxylic acid-based compound that can coordinate with copper.
[0059] Reducing ink compositions can form bulk metal by generating fine metal nanoparticles in situ using chemical reduction. They can be processed at relatively low temperatures. For example, copper formate nanoink, an example of a reducing ink composition, contains copper formate, an alkanolamine, and a solvent having two or more functional groups capable of coordinating with the copper formate within its molecular structure. In the copper formate ink composition, the copper formate is dissolved in the solvent in an ionic state and is reduced to zero-valent copper by heat treatment. This differs from the sintering mechanism, where heating removes the solvent and other substances, causing the particles to bond together.
[0060] Therefore, although the treatment for conductivity enhancement differs depending on the type of ink, their purpose is the same, and in this disclosure, these will be collectively referred to as the conductivity enhancement treatment.
[0061] The solvent used in the ink composition may be an aqueous solvent or an organic solvent. The organic solvent may be an alcohol-based solvent or a derivative thereof, and more specifically, glycol ethers such as ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, or mixtures thereof can be used, and solvents described later may also be used.
[0062] In addition, stabilizers and other additives may be used.
[0063] The content of copper nanoparticles in the ink composition may be 5% to 60% by weight, or 10% to 30% by weight, by mass ratio. The reason for selecting these ranges is that if the content is too low, there may be insufficient nanoparticles to form a conductive layer made of copper nanoparticles, potentially causing pores such as pinholes. If the content is too high, the particles may aggregate easily within the ink, potentially impairing the stability of the ink.
[0064] The viscosity of the ink composition is preferably 1 to 100 mPa·s at a measurement temperature of 25°C, as measured by an E-type viscometer or rheometer. More preferably, the viscosity is 1 to 100 mPa·s and 1 to 50 mPa·s when the shear rate is 100 (1 / S) or higher. This is because the conditions are suitable for the environment in which the ink is ejected by the inkjet head, and if the viscosity is too high, ejection from the inkjet head becomes difficult.
[0065] Figure 6 shows the process of ejecting ink droplets around a through-hole. In this figure, for example, ink droplets D10 are ejected onto the hole portion DH1 of the pattern design PD, which includes a through-hole indicated by a dotted line. The application of the ink composition includes a filling step in which ink is filled into the through-hole H1 by ejecting ink droplets D10, which are droplets of the ink composition, onto the through-hole H1 using an inkjet method, while the lower side of the through-hole H1 is blocked by a closure member (not shown) on the lower side of the core substrate F1. This is achieved by using a material such as a porous sheet that absorbs excess droplets as the closure member, so that the ink is initially filled into the through-hole whose lower end is blocked by the closure member. This fills the hole with ink so that the ink completely adheres to the entire inner wall of the through-hole. At that time, because the ink composition has the appropriate viscosity as described above, it falls down the inner wall due to gravity. It is also conceivable that hydroxyl groups are formed on the inner surface of the hole by dry desmearing after drilling, making it hydrophilic and allowing the ink composition to drip smoothly. Therefore, it is possible to apply ink by allowing it to flow along the inner wall without completely filling the through-hole H1 with ink.
[0066] Furthermore, ink droplet ejection is not limited to single droplets; multiple droplets can also be ejected. Ink ejection is possible not only when the relative relationship between the workpiece and the inkjet head is stationary, but also when the relative relationship shifts in the Y direction or in the X direction due to the stage.
[0067] In step S106 of Figure 2, the protective layer S1 is peeled off using the peeler 322, as shown in Figure 5(h). The specific configuration and procedure for peeling are not particularly limited, but methods such as fixing the lower side of the workpiece with a vacuum suction pad on the stage and gripping the upper side with a vacuum suction pad to lift the protective layer, using a roller to roll it up, or using an ionizer to blow ionized air while peeling can be used as appropriate.
[0068] In step S107 of Figure 2, as shown in Figure 7(i), ink droplets D20 land from the inkjet head 331 on the primer resin layer P1 from which the protective layer S1 has been peeled off, forming the shape of the conductive pattern underlayer SEK2, thereby printing the designed pattern using the ink composition. It is preferable that the ink ejection rate (or ink ejection duty cycle) of ink droplet D20 per unit time be lower than the ink ejection rate of ink droplet D10 per unit time when introducing ink into the holes. This is because using the same ink ejection rate per unit time may result in an inappropriate balance between the thickness of the ink on the primer layer and the ink in the holes.
[0069] In this disclosure, the pattern is pre-formed by inkjet printing, eliminating the need for etching to form the desired shape of the pattern. In other words, the basic wiring pattern is already formed on the circuit-forming substrate when the inkjet droplets land on it. This method of additionally forming circuits is superior in terms of reducing environmental impact. Furthermore, although the protective layer to which the ink droplets are attached is peeled off and removed when introducing ink droplets into the holes, the position where the ink is dropped can be precisely determined according to the design position of the holes, thus reducing the amount of ink used. This is different from methods that only use processes such as sputtering, vapor deposition, and plating to form the metal layer.
[0070] In step S108 of Figure 2, as shown in Figure 7(j), the pattern of dropped ink droplets is subjected to a conductive treatment to form a conductive pattern underlayer SEK2. Then, after undergoing drying processes such as heat treatment and hot air treatment using nitrogen or airflow, the above conductive treatment is performed.
[0071] In the conductive treatment process, in addition to removing components other than metal nanoparticles from the ink composition, it is necessary to induce bonding, melting, and contact between the metal nanoparticles. The state in which metal nanoparticles are bonded together while maintaining their shape is called necking, and the phenomenon in which the nanoparticles melt from the necking state and become one with a change in shape is called fusion. Sometimes, interparticle bonding is simply called necking. Through this sintering, the nanoparticles melt and become bulk, improving conductivity and allowing them to adhere closely to the primer layer on the core substrate.
[0072] In step S109 of Figure 2, as shown in Figure 7(k), a plating process is performed on the conductive pattern underlayer SEK2 to form a conductive pattern plating layer SPM2 and a pore plating layer HPM1. If the metal nanoparticles are copper, copper may be plated. The plating method is the same as known plating processes using known plating solutions, and specifically may include electroless copper plating, electrolytic copper plating, etc. Although omitted in the drawings, it can be confirmed in cross-section using various microscopes that the plating layer is laminated on the sintered layer of metal nanoparticles. This laminates the plating metal and further improves conductivity.
[0073] The circuit board manufactured as described above comprises at least a first primer resin layer formed on a first core substrate, through holes penetrating the first core substrate and the first primer resin layer, a first in-hole conductor layer formed on the inner surface of the through holes, and a first conductive pattern base layer formed on the first primer resin layer and the first in-hole conductor layer, wherein the first in-hole conductor layer and the first conductive pattern base layer may be electrically connected.
[0074] This makes it possible to provide a method for manufacturing a multilayer circuit board that ensures good conductivity between conductors inside and outside the holes, as well as a good appearance, even when the relationship between hole diameter and hole depth, the number of pattern-forming layers, and the rigidity of the substrate material change. While such effects are brought about by the entire process, it is important to note that proper ink application is possible by applying the ink in two stages: by introducing a sufficient amount of ink into the holes to ensure the conductor layer inside the holes, and by removing the protective layer, followed by dispensing the ink composition in a pattern onto the primer resin layer.
[0075] Furthermore, after the processing of the first surface (tentatively referred to as the front surface) of the core substrate is completed, the core substrate can be turned over and the same processing can be performed on the second surface (tentatively referred to as the back surface). Briefly, the process includes the steps of: forming a second primer resin layer on the second surface of the first core substrate; forming a second protective layer on the second primer resin layer; a third ink ejection step of ejecting an ink composition containing metal nanoparticles to form a third in-hole ink layer on the second protective layer and in the holes of the through-holes; a second protective layer peeling step of peeling off the second protective layer to which the third ink layer is attached; and a fourth ink ejection step of ejecting an ink composition to form a second conductive pattern underlayer on the second primer resin layer.
[0076] To elaborate, in this case, a circuit board with a second protective layer formed on the first core substrate is prepared in advance prior to drilling. After drilling, the first ink ejection process, the second ink ejection process, the third ink ejection process, and the fourth ink ejection process are performed. In this way, a circuit board with conductive patterns formed on both sides of the substrate can be manufactured.
[0077] Figure 8 also shows an example of a four-layer circuit board as an example of a multilayer circuit board manufactured using the circuit board manufacturing method of this disclosure. This four-layer circuit board 104 comprises a first core substrate F1, interlayer insulating layers R1 and R2 on its first and second surfaces, and conductive layers C1 to C4. The conductive layers C1 to C4 are conductive patterns formed by conductive treatment of the ink composition and plating treatment as described above.
[0078] The interlayer insulating layers R1 and R2 may be, for example, prepregs. Prepregs can be formed, for example, by a hot melt method.
[0079] Figure 9 also shows an example of a 6-layer circuit board as another example of a multilayer circuit board. This 4-layer circuit board 104 has a first core substrate F1, interlayer insulating layers R1 and R2 on its first and second surfaces, and conductive layers C1 to C4. The conductive layers C1 to C4 are conductive patterns formed by conductive treatment of the ink composition and plating treatment as described above.
[0080] Furthermore, although not shown in the figures, when the manufacturing method of this disclosure is used, it can be confirmed by cross-sectional observation with various electron microscopes that in multilayer circuit boards with four or more layers, a layer like a resin is formed at the connection point between the inner conductor layers (conductor layers C1 and C2 in Figure 8, conductor layers C1, C2, C4, and C5 in Figure 9, and as appropriate for multilayers with more than four layers) and the conductor layer HC inside the hole. This is thought to represent an interfacial adhesion state formed by the direct contact between the layer laminated by the plating of the inner conductor layers and the metal layer formed by the ink composition introduced into the inner wall of the through hole, because no primer resin layer is formed on the inner wall of the through hole.
[0081] Furthermore, although not shown in the diagram, it is also possible to manufacture 8-layer circuit boards and even-numbered circuit boards with more than 8 layers.
[0082] In this disclosure, the type of through-hole suitable for forming a conductor within is a so-called through-hole, but it can also be applied to via holes such as blind vias and buried vias.
[0083] Furthermore, the process of forming a first primer resin layer on the first surface of the core substrate will also be explained, which involves the steps of applying a liquid primer to one plane of a support film, curing the liquid primer to form a primer film material having a support film layer and a primer resin layer, arranging the primer resin layer of the primer film material on the front and back sides of the core substrate, which has a front and back plane, with the primer resin layer facing the first core substrate, and pressing the support film layer side of either of the primer film materials to press the first core substrate and the primer resin layer together.
[0084] Figures 10 and 11 illustrate a method for manufacturing circuit board materials using primer film materials. As shown in Figure 10, a layered structure of primer film material 2F is formed, having a support film layer CF (CF1T) and a primer film layer P (P1T). First, a support film material for forming the support film layer is prepared. The support film layer CF1T is made of materials such as polyimide (PI), polyethylene terephthalate (PET), aluminum, polypropylene (PP), or polyphenylene sulfide (PPS). These metal foils or resin films can be used as the support film layer. The thickness of the support film is, for example, 20 to 60 μm, preferably 25 to 50 μm. The material of the support film preferably has heat resistance of 150°C or higher, which is sufficient to withstand prepreg lamination. The support film can also be used as the protective layer (applicable to protective layers including a first protective layer and a second protective layer). The support film layer CF1T also serves as the protective layer, and when the support film layer is also a protective layer, it has the effect of both protecting the primer layer and supporting the primer layer. In this case, the support film layer will be peeled off after the ink composition described later is ejected.
[0085] Next, a primer liquid PS is applied onto the support film layer CF1T. The primer liquid is, for example, a material containing an epoxy resin material that forms the primer resin layer, diluted in a diluting solvent. The coating film thickness may be, for example, 1 to 100 μm. More preferably, it may be 5 to 70 μm, and even more preferably 10 to 50 μm. If the coating film thickness is too low, it may not be possible to reach the specified film thickness, making it difficult to achieve the desired physical properties described above. If the coating film thickness is too high, the material cost tends to be high, and the ratio of the thickness of the primer resin layer to the thickness of the substrate becomes high, which may result in the substrate properties not being met.
[0086] Next, the layer formed by the applied liquid primer PS is dried. Drying is basically a process of removing any remaining organic solvent from the layer formed by the liquid primer PS, by increasing the temperature or changing the pressure to evaporate the organic solvent. Next, the dried layer is fully cured. Full curing is a process of curing the epoxy resin contained in the primer liquid to ensure rigidity that can withstand the removal of the support film. If this step is omitted, the primer resin layer may not be sufficiently cured, and the result of removing the support film may be undesirable. Furthermore, the fully cured state can also be described as a state in which the reactive functional groups in the epoxy resin have formed covalent bonds through crosslinking or polymerization reactions. In particular, it is acceptable for almost all (80-95%) of the reactive functional groups in the epoxy resin to have formed covalent bonds through crosslinking or polymerization reactions. Note that drying and curing may be performed consecutively without a time interval. For example, the drying process may be a treatment at 80°C for 30 minutes using a heating device such as a heater, and the full curing process may be a treatment at 180°C for 60 minutes. Once the curing is complete, a primer film material is formed comprising a primer resin layer and a support film layer.
[0087] Then, as shown in Figure 11, a laminate is formed using this primer film material 2F (2F1T, 2F1B). The primer layer side of the primer film material is placed on the substrate side of the substrate 1, which has a flat surface on the front and back sides, respectively. Then, the support film layer side of either the primer film material placed on the front or back side is pressed to press the substrate and the primer layer together, and by peeling off only the support film layers on the front and back sides, it becomes possible to form a primer resin layer on both sides of the substrate simultaneously. When using a primer film material, the support film to which the liquid primer is applied also serves as a protective layer after the filmized primer and support film are pressed together on the core substrate, so the timing of its peeling may be at the timing when the protective layer should be peeled off, for example, after the ink composition is ejected.
[0088] The implementations described herein are merely illustrative, and various modifications and alterations by means and structures are possible to achieve some or all of the functions, results, and benefits. All such variations and modifications are considered to fall within the scope of the implementations described herein. Furthermore, the parameters, dimensions, materials, and configurations described herein are merely illustrative and may be changed depending on the actual application. Those skilled in the art can recognize and confirm many equivalents to the specific implementations described herein through routine experimentation. Therefore, the aforementioned implementations are merely examples, and practices including aspects not explicitly expressed herein are possible within the scope of the claims of this application and their equivalents. This disclosure includes all aspects of each feature, system, article, material, kit, method described herein, and combinations thereof to the extent that they are not contradictory.
[0089] Even if multiple entities perform only a portion of the process described herein, if their actions are deemed to substantially contribute to the overall execution, they may be treated as having participated in the completion of each step of the process, in accordance with the laws of the jurisdiction. Whether an act constitutes partial implementation or indirect participation of the invention is left to the laws of each country and region. Furthermore, even if intermediate products (including data, signals, settings, semi-finished products, etc.) are transferred by export, import, or other means, and some or all of the steps are performed in different countries, substantial participation in partial implementation may be determined depending on the nature of the actions within each country.
[0090] For example, in some embodiments, a method for manufacturing a circuit board includes: [1] forming a first primer resin layer on a first surface of a first core substrate; forming a first protective layer on the first primer resin layer; forming through holes that penetrate the first core substrate; a first ink dispensing step of dispensing an ink composition containing metal nanoparticles to form a first in-hole ink layer on the first protective layer and in the holes of the through holes; a first protective layer peeling step of peeling off the first protective layer to which the ink composition has adhered; and a second ink dispensing step of dispensing the ink composition to form a first conductive pattern underlayer on the first primer resin layer. [2] A method for manufacturing a circuit board according to [1], wherein the step of forming the first primer resin layer on the first surface of the first core substrate comprises: applying a liquid primer to one plane of a support film; curing the liquid primer to form a primer film material having a support film layer and a primer resin layer; arranging the primer resin layer of the primer film material facing the first core substrate on the front side and the back side of a core substrate having a front and back plane, respectively; and pressing the support film layer side of either of the respective primer film materials to press the first core substrate and the primer resin layer together. [3] A method for manufacturing a circuit board according to [1] or [2], wherein the amount of ink ejected per unit time in the second ink ejection step is lower than the amount of ink ejected per unit time in the first ink ejection step. [4] The method for manufacturing a circuit board according to [1] or [2], wherein in the first ink ejection step, the first ink layer is ejected only around the opening of the through hole. [5] The method for manufacturing a circuit board according to [1] or [2], further comprising a first dry desmear step between the step of forming the through hole and the step of peeling off the first protective layer. [6] The method for manufacturing a circuit board according to [3], wherein the viscosity of the ink composition in the first ink ejection step is the same as the viscosity of the second ink ejection step.[7] The method for manufacturing a circuit board according to [2], wherein the support film layer is also the first protective layer, and the support film layer is peeled off as the first protective layer in a first protective layer peeling step after the first ink ejection step. [8] The method for manufacturing a circuit board according to [1], comprising: forming a second primer resin layer on the second surface of the first core substrate; forming a second protective layer on the second primer resin layer; a third ink ejection step of ejecting the ink composition to form a third in-hole ink layer on the second protective layer and in the holes of the through holes; a second protective layer peeling step of peeling off the second protective layer to which the ink composition is attached; and a fourth ink ejection step of ejecting the ink composition to form a second conductive pattern underlayer on the second primer resin layer. [9] A method for manufacturing a circuit board according to [2], comprising: a step of pressing the support film layer side of either of the respective primer film materials to press the first core substrate and the respective primer resin layers together, thereby forming a second primer resin layer on the second surface of the first core substrate; a step of forming a second protective layer on the second primer resin layer; a third ink dispensing step of dispensing the ink composition to form a third in-hole ink layer on the second protective layer and in the holes of the through holes; a second protective layer peeling step of peeling off the second protective layer to which the ink composition has adhered; and a fourth ink dispensing step of dispensing the ink composition to form a second conductive pattern underlayer on the second primer resin layer.
[10] A circuit board material comprising: a core substrate; a first primer resin layer formed on a first surface of the core substrate; a second primer resin layer formed on a second surface of the core substrate; a first protective layer formed on the first primer resin layer; and a second protective layer formed on the second primer resin layer.
[11] A circuit board material according to
[10] , comprising the steps of: applying a liquid primer to one plane of a support film; curing the liquid primer to form a primer film material having a support film layer and a primer resin layer; arranging the primer resin layer of the primer film material facing the front side and the back side of the core substrate, which has a surface and a back side, respectively; and pressing the support film layer side of either one of the primer film materials to press the core substrate and the primer resin layer, respectively, to form the first primer resin layer on the first surface of the core substrate and the second primer resin layer on the second surface of the core substrate.
[12] A circuit board material according to
[11] , wherein the support film layer is also the first protective layer and the second protective layer.
[13] A circuit board material according to any one of
[10] to
[12] , wherein the first protective layer and the second protective layer are metal.
[14] An inkjet printing apparatus for manufacturing circuit boards, comprising an inkjet head, a stage, and a peeler, wherein the inkjet head ejects an ink composition containing metal nanoparticles onto a circuit board manufacturing intermediate having at least a first primer resin layer formed on a first core substrate, a first protective layer formed on the first primer resin layer, and through holes formed through the first core substrate, thereby forming a first ink layer on the first protective layer and in the holes of the through holes, the peeler peels off the first protective layer to which the ink composition has adhered, and the inkjet head ejects the ink composition to form a first conductive pattern underlayer on the first primer resin layer and a second ink layer in the holes of the through holes.
[0091] The embodiments shown in [1] to
[14] above can be combined in any way. For example, one may combine all or some of the embodiments shown in [1] with at least some of the embodiments of at least one invention from [2] onwards. In particular, it is preferable to combine the inventions shown in [1],
[10] , and
[14] with at least some of the embodiments of at least one invention from [2] onwards. Alternatively, one may extract any configuration from the embodiments shown in [1] to
[14] and combine the extracted configurations. The applicant of this application intends to obtain rights to inventions that include these configurations. Furthermore, even if there are descriptions such as "in the case of..." or "when...", these are not meant to indicate that the configuration is limited to that case or time. These are merely examples of better configurations, and the applicant intends to obtain rights to configurations that do not fall under these cases or times. Also, even if there is a sequence of descriptions, it is not limited to that order. Configurations with some parts deleted or the order rearranged are also disclosed, and the applicant intends to obtain rights to them as well.
[0092] F1, F2 Core substrate P1, P2, P3, P4, P5, P6 Primer resin layer H1 Through hole HK1 Ink layer inside hole SK1 Ink layer HEK1 Conductor layer inside hole S1 Protective layer D10 First ink droplet D20 Second ink droplet DH1 Filling ink inside hole PD Pattern design line SPM1 Conductive pattern plating layer HPM1 Ink plating layer inside hole R1, R2 Interlayer insulating layer C1, C2, C3, C4, C5, C6 Conductor layer 104 Circuit board 106 Circuit board 300 Inkjet printing device 310 System control unit 311 Human-machine interface 312 Data management system 313 Main controller 320 Handling module 321 Handler 322 Peeler 323 Peeler control system 330 Printing module 331 Inkjet head 332 Ink supply system 333 Head control system 340 Stage module 341 Stage 342 Stage control system 400 Desmear processing device
Claims
1. A method for manufacturing a circuit board, comprising:
1. A step of forming a first primer resin layer on a first surface of a first core substrate; 2. A step of forming a first protective layer on the first primer resin layer; 3. A step of forming through holes that penetrate the first core substrate; 4. A first ink ejection step of ejecting an ink composition containing metal nanoparticles to form a first in-hole ink layer on the first protective layer and in the holes of the through holes; 5. A first protective layer peeling step of peeling off the first protective layer to which the ink composition has adhered; and 6. A second ink ejection step of ejecting the ink composition to form a first conductive pattern underlayer on the first primer resin layer.
2. A method for manufacturing a circuit board according to claim 1, wherein the step of forming the first primer resin layer on the first surface of the first core substrate comprises: applying a liquid primer to one plane of a support film; curing the liquid primer to form a primer film material having a support film layer and a primer resin layer; arranging the primer resin layer of the primer film material facing the first core substrate on the front side and the back side of a core substrate having a front and back plane, respectively; and pressing the support film layer side of either of the respective primer film materials to press the first core substrate and the primer resin layer together.
3. The method for manufacturing a circuit board according to claim 1 or 2, wherein the amount of ink ejected per unit time in the second ink ejection step is lower than the amount of ink ejected per unit time in the first ink ejection step.
4. The method for manufacturing a circuit board according to claim 1 or 2, wherein in the first ink ejection step, the first ink layer is ejected only around the opening of the through hole.
5. A method for manufacturing a circuit board according to claim 1 or 2, comprising a first dry desmear step between the step of forming the through hole and the step of peeling off the first protective layer.
6. The method for manufacturing a circuit board according to claim 3, wherein the viscosity of the ink composition in the first ink ejection step is the same as the viscosity of the ink composition in the second ink ejection step.
7. The method for manufacturing a circuit board according to claim 2, wherein the support film layer is also the first protective layer, and the support film layer is peeled off as the first protective layer in the first protective layer peeling step after the first ink ejection step.
8. A method for manufacturing a circuit board according to claim 1, comprising: a step of forming a second primer resin layer on a second surface of the first core substrate; a step of forming a second protective layer on the second primer resin layer; a third ink ejection step of ejecting the ink composition to form a third in-hole ink layer on the second protective layer and in the holes of the through holes; a second protective layer peeling step of peeling off the second protective layer to which the ink composition has adhered; and a fourth ink ejection step of ejecting the ink composition to form a second conductive pattern underlayer on the second primer resin layer.
9. A method for manufacturing a circuit board according to claim 2, comprising: a step of pressing the support film layer side of either of the respective primer film materials to press the first core substrate and the respective primer resin layers together, thereby forming a second primer resin layer on the second surface of the first core substrate; a step of forming a second protective layer on the second primer resin layer; a third ink dispensing step of dispensing the ink composition to form a third in-hole ink layer on the second protective layer and in the holes of the through holes; a second protective layer peeling step of peeling off the second protective layer to which the ink composition has adhered; and a fourth ink dispensing step of dispensing the ink composition to form a second conductive pattern underlayer on the second primer resin layer.
10. A circuit board material comprising: a core substrate; a first primer resin layer formed on a first surface of the core substrate; a second primer resin layer formed on a second surface of the core substrate; a first protective layer formed on the first primer resin layer; and a second protective layer formed on the second primer resin layer.
11. A material for a circuit board according to claim 10, comprising the steps of: applying a liquid primer to one plane of a support film; curing the liquid primer to form a primer film material having a support film layer and a primer resin layer; arranging the primer resin layer of the primer film material facing the front side and the back side of the core substrate, which has a surface and a back side, respectively; and pressing the support film layer side of either one of the primer film materials to press the core substrate and the primer resin layer, respectively, to form the first primer resin layer on the first surface of the core substrate and the second primer resin layer on the second surface of the core substrate.
12. The circuit board material according to claim 11, wherein the support film layer is also the first protective layer and the second protective layer.
13. The circuit board material according to any one of claims 10 to 11, wherein the first protective layer and the second protective layer are made of metal.
14. An inkjet printing apparatus for manufacturing circuit boards, comprising an inkjet head, a stage, and a peeler, wherein, for a circuit board manufacturing intermediate having at least a first primer resin layer formed on a first core substrate, a first protective layer formed on the first primer resin layer, and through holes formed through the first core substrate, the inkjet head ejects an ink composition containing metal nanoparticles to form a first ink layer on the first protective layer and in the holes of the through holes, the peeler peels off the first protective layer to which the ink composition has adhered, and the inkjet head ejects the ink composition to form a first conductive pattern underlayer on the first primer resin layer and a second ink layer in the holes of the through holes.