Method for manufacturing a stretchable circuit board and coverlay film for a stretchable circuit board

Abstract

To provide a manufacturing method of a flexibility circuit board, suppressing peeling of a coverlay film during a manufacturing step.SOLUTION: A manufacturing method of a flexibility circuit board 12, comprises: a step of preparing a core material 11 comprising a first flexibility insulation layer 5 and a conductor layer 6; a step of laminating a first separation type sheet 2, an unhardened resin layer 3 formed by a thermosetting resin composition, and a second separation type sheet in order to form a coverlay film 10; and a step of peeling the second separation type sheet from the coverlay film, and laminating at least one surface of the unhardened resin layer and the core material. A peeling strength of the unhardened resin layer of the first separation type sheet is larger than that of the second separation type sheet, and the peeling strength of a hardened material of the thermosetting resin composition is 0.015 N / mm or more and 0.035 N / mm or less, a glass transformation temperature is 300°C or larger, the glass transformation temperature of the first flexibility insulation layer and the second flexibility insulation layer is 60°C or less, and a tension elastic rat is 0.1 MPa or more and 100 MPa or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a stretchable circuit board and a coverlay film for a stretchable circuit board.

[0002] With the development of the electronics field, the requirements for miniaturization, thinning, lightening, and high density of electronic devices and the like are further increasing. Furthermore, depending on the application, there may be a requirement for a flexible device that can be freely deformed or bent for placement on curved surfaces, uneven surfaces, etc. In recent years, in response to this, stretchable circuit boards have been proposed.

[0003] On the other hand, usually, a coverlay film is often used to protect the circuit on the circuit board. The coverlay film plays a role of protecting the circuit electrically, mechanically, chemically, and thermally. Various coverlays have been reported so far. For example, in Patent Document 1, a laminate in which a stretchable resin layer is provided on a carrier film made of polyethylene terephthalate or the like and a protective film made of polyethylene terephthalate or the like is laminated thereon is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the carrier film and protective film described in Patent Document 1, as mentioned above, are not films optimized for component mounting processes using reflow soldering. Therefore, there is a possibility of problems occurring during the circuit board manufacturing process, such as peeling off or, conversely, being unable to peel off when peeling is necessary. Furthermore, even if peeling is possible, there is a risk of damage to the circuit board or detachment of electronic components. In addition, depending on the material of the carrier film and protective film, there is a risk of component mounting defects due to melting or deformation during the circuit board manufacturing process.

[0006] This invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a stretchable circuit board that can suppress the peeling of the coverlay film during the manufacturing process and allows for the mounting of electrical components by soldering, as well as a coverlay film for stretchable circuit boards that has excellent heat resistance and appropriate peeling force. [Means for solving the problem]

[0007] A method for manufacturing a stretchable circuit board according to one aspect of the present invention includes the steps of: preparing a core material comprising a first stretchable insulating layer and a conductive layer overlapping at least one surface of the stretchable insulating layer; preparing a coverlay film in which a first release sheet, an uncured resin layer containing a thermosetting resin composition, and a second release sheet are laminated in this order; peeling the second release sheet from the coverlay film and laminating the uncured resin layer and at least one surface of the core material; and curing the uncured resin layer to form a second stretchable insulating layer. The present invention is characterized in that the peel strength of the first release sheet to the uncured resin layer is greater than the peel strength of the second release sheet to the uncured resin layer, the peel strength between the cured product of the thermosetting resin composition and the first release sheet is 0.015 N / mm or more and 0.035 N / mm or less, the glass transition temperature of the first release sheet is 300°C or higher, and in both the first stretchable insulating layer and the second stretchable insulating layer, the glass transition temperature is 60°C or lower and the tensile modulus is 0.1 MPa or more and 100 MPa or less.

[0008] The manufacturing method preferably further includes a step of mounting electronic components. Furthermore, the step of mounting electronic components preferably includes a step of joining them by soldering.

[0009] Furthermore, it is preferable that the manufacturing method further includes a step of peeling off the first release sheet.

[0010] Furthermore, in the above manufacturing method, it is preferable that the tensile modulus of the first release sheet is 0.5 GPa or more and 5 GPa or less.

[0011] Furthermore, in the above manufacturing method, it is preferable that the first stretchable insulating layer and the second stretchable insulating layer are integrated.

[0012] A coverlay film for a stretchable circuit board according to another aspect of the present invention is characterized in that a first release sheet, an uncured resin layer containing a thermosetting resin composition, and a second release sheet are laminated in this order, the peel strength of the first release sheet to the uncured resin layer is greater than the peel strength of the second release sheet to the uncured resin layer, the peel strength between the cured product of the thermosetting resin composition and the first release sheet is 0.015 N / mm or more and 0.035 N / mm or less, and the glass transition temperature of the first release sheet is 300°C or higher. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for manufacturing a stretchable circuit board that can suppress the peeling of the coverlay film during the manufacturing process and allows for the mounting of electrical components by soldering, as well as a coverlay film for stretchable circuit boards that has excellent heat resistance and appropriate peeling force. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic cross-sectional view showing a coverlay film for a stretchable circuit board according to one embodiment of the present invention. [Figure 2]Figure 2 is a schematic diagram showing the main steps in a method for manufacturing a stretchable circuit board according to one embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram showing an additional step in the manufacturing method of a stretchable circuit board according to one embodiment of the present invention. [Modes for carrying out the invention]

[0015] The following describes specific embodiments of the present invention, but the present invention is not limited thereto.

[0016] The method for manufacturing a stretchable circuit board in this embodiment, as shown in Figure 2, includes at least the steps of: preparing a core material comprising a first stretchable insulating layer and a conductive layer overlapping at least one side of the stretchable insulating layer (A); preparing a coverlay film in which a first release sheet, an uncured resin layer containing a thermosetting resin composition, and a second release sheet are laminated in this order (B); peeling the second release sheet from the coverlay film and laminating the uncured resin layer and at least one side of the core material (C); and curing the uncured resin layer to form a second stretchable insulating layer (D).

[0017] In the manufacturing method of this embodiment, the peel strength of the first release sheet to the uncured resin layer is greater than the peel strength of the second release sheet to the uncured resin layer, and the peel strength between the cured product of the thermosetting resin composition and the first release sheet is 0.015 N / mm or more and 0.035 N / mm or less. Furthermore, the glass transition temperature of the first release sheet is 300°C or higher, and in both the first stretchable insulating layer and the second stretchable insulating layer, the glass transition temperature is 60°C or lower, and the tensile modulus is 0.1 MPa or more and 100 MPa or less.

[0018] This configuration prevents the coverlay film from peeling off during the manufacturing process of the stretchable circuit board. Furthermore, because the release sheet is heat-resistant, it becomes possible to join electrical components to the stretchable circuit board using solder.

[0019] Hereinafter, each step will be described in more detail.

[0020] (Core material preparation step) The core material 11 used in this embodiment is not particularly limited as long as it is used as a stretchable substrate. As shown in Fig. 2(A), it includes a first stretchable insulating layer 5 and a conductor layer 6 overlapping at least one surface of the insulating layer.

[0021] The first stretchable insulating layer 5 has stretchability. Here, "having stretchability" means being elastically deformable. The stretchable insulating layer of this embodiment has a tensile elastic modulus of 0.1 MPa or more and 100 MPa or less, and a glass transition temperature (Tg) of 60 °C or less. A more preferable tensile elastic modulus is 1.0 MPa or more and 5 MPa or less, and even more preferably 1.5 MPa or more and 30 MPa or less. Also, a more preferable glass transition temperature is 50 °C or less, and the lower limit value of the glass transition temperature is not particularly limited, but it is preferably 30 °C or more from the viewpoint of surface tackiness at room temperature.

[0022] For a circuit board provided with a stretchable insulating layer having a tensile elastic modulus and a glass transition temperature within the above-mentioned ranges, since the followability during deformation into an arbitrary shape is high, for example, it is considered that a circuit board with excellent followability to clothes, etc., and being difficult to be broken and having excellent stretchability can be obtained.

[0023] In this embodiment, the tensile elastic modulus refers to the tensile elastic modulus at 20 °C and is a value measured by the following method: First, a cured product of the resin constituting the stretchable insulating layer is cut into a size of 90 mm × 5.5 mm and attached to a universal testing machine (AGS-X manufactured by Shimadzu Corporation). Then, at room temperature (25 °C), a test is performed at a tensile speed of 500 mm / min, and the slope (initial tensile elastic modulus) of r-σ is obtained by using the least squares method from all stress (σ) data corresponding to a strain (r) of 1.0% to 5.0%. Strain (r) = x / x0 (x is the moving distance of the grip, x0 is the initial distance between grips) Stress (σ) = F / (d·l) (where F is the test force, d is the film thickness, and l is the width of the test specimen)

[0024] Furthermore, the glass transition temperature was measured by cutting the cured resin material constituting the stretchable insulating layer into a 10 mm x 30 mm piece, attaching it to a dynamic viscoelasticity measuring device (DMS6100 manufactured by Seiko Instruments Inc.), and conducting a test with a strain amplitude of 10 μm, a frequency of 10 Hz (sine wave), and a heating rate of 5 °C / min, and calculating the peak temperature of tanδ.

[0025] Furthermore, the elongation at break of the stretchable insulating layer according to this embodiment is preferably 50% or more. In this embodiment, the elongation at break refers to the elongation rate until breakage and, together with the tensile modulus mentioned above, is an indicator of the flexibility of the insulating layer. A more preferable elongation at break is 100% or more and 500% or less. In this embodiment, the higher the upper limit of the elongation at break, the better, but 1000% is sufficient.

[0026] The elongation rate at break is measured using the tester, with the elongation rate at the time of breakage being measured using a film made from a cured product of the same resin composition as the stretchable insulating layer.

[0027] Furthermore, the tensile stress of the stretchable insulating layer in this embodiment when it is stretched by 50% is preferably 0.1 MPa or more and 20 MPa or less. The "tensile stress when stretched by 50%" refers to the tensile stress when the elongation rate reaches 50% in the tensile test described above, and together with the tensile modulus of elasticity described above, it is an indicator of the flexibility of the stretchable insulating layer. When it is within the above range, (similar to the tensile modulus of elasticity described above) it has the advantage that it is less likely to damage the wiring and component mounting parts because it is highly conformable when deformed into any shape. A more preferable range for the tensile stress is 0.5 MPa or more and 15 MPa or less.

[0028] The first stretchable insulating layer 5 of this embodiment is preferably composed of a curable resin composition. The curable resin composition used preferably contains a thermosetting resin, and more preferably has sufficient heat resistance to not melt or decompose even at the temperatures when joining electronic components and circuit boards using a reflow oven or soldering iron with solder.

[0029] As the resin contained in the curable resin composition that can be used in the first stretchable insulating layer 5 of this embodiment, it is preferable to use a curable resin composition that contains a thermosetting resin, from the viewpoint of being able to impart functions such as excellent adhesion and heat resistance, low thermal expansion, elastic modulus control, thermal conductivity, and light reflectivity. As the thermosetting resin, it is preferable to use at least one selected from epoxy resin, urethane resin, silicone resin, polyrotaxane resin, isocyanate resin, polyol resin, hydrogenated styrene elastomer resin, and acrylic acid ester copolymer resin, and among these, it is more preferable to use epoxy resin, and even more preferable to use alkylene oxide modified epoxy resin or epoxy resin containing a divalent organic group with 2 to 5000 carbon atoms.

[0030] Furthermore, the resin composition may contain various additives such as curing agents, curing accelerators, and fillers, to the extent that they do not impair the effects of the present invention.

[0031] Specific resin compositions that can be used for the first stretchable insulating layer 5 include, for example, resin compositions containing polyrotaxane, thermosetting resin, and curing agent (for example, resin compositions described in International Publication No. 2020 / 196745, etc.).

[0032] The thickness of the first stretchable insulating layer 5 is not particularly limited, but it is preferably 10 μm or more and 500 μm or less.

[0033] The core material 11 of this embodiment is formed by laminating and integrating a conductor layer 6 onto a first stretchable insulating layer 5. The method of laminating and integrating the conductor layer 6 onto the first stretchable insulating layer 5 is not particularly limited. For example, a resin layer that will become the first stretchable insulating layer 5 may be formed on the conductor layer 6 by applying a resin varnish, etc., and then heated and dried. Alternatively, the first stretchable insulating layer 5, which is in the form of a sheet-like resin film, and the conductor layer 6 may be bonded together by molding such as heat pressing. Alternatively, the first stretchable insulating layer 5 and the conductor layer 6 may be bonded together using an adhesive, or the conductor layer 6 may be formed on the surface of the first stretchable insulating layer 5 by electroless plating, electrolytic plating, vapor deposition, etc.

[0034] In Figure 2(A), the conductor layer 6 is provided on both sides of the first stretchable insulating layer 5, but it may also be provided on only one side of the first stretchable insulating layer 5. Furthermore, the conductor layer 6 may be provided on at least a portion of the surface of the first stretchable insulating layer 5, or it may be provided on the entire surface.

[0035] Examples of the conductive layer 6 used in this embodiment include metal foil, and more specifically, copper foil, aluminum foil, nickel foil, etc. Alternatively, the conductive layer 6 may be formed using a conductive paste made of a conductive resin composition. The conductive resin composition is not particularly limited, and a resin composition containing a resin and a conductive filler, etc. (for example, a conductive resin composition described in brochure WO2021 / 241532, etc.) can be used.

[0036] There are no particular limitations on the thickness of the conductor layer 6, and it can be adjusted as appropriate depending on the type and application of the conductor layer 6.

[0037] In the process of preparing the core material, after creating the core material by laminating and integrating the conductor layer 6 with the first stretchable insulating layer 5, the core material 11 may have a patterned circuit on its surface by performing laser processing on the core material 11 (leftmost figure), plating on it (center figure), or etching on the conductor layer 6 to form a circuit (wiring) (rightmost figure), as shown in Figure 2(A). In addition to the methods described above, other methods for circuit formation include, for example, circuit formation by the semi-additive process (SAP) or the modified semi-additive process (MSAP).

[0038] (Coverlay film preparation process) Next, prepare the coverlay film as shown in Figure 2(B).

[0039] As shown in Figure 1, the coverlay film 10 of this embodiment is laminated in the following order: a first release sheet 2, an uncured resin layer 3 containing a thermosetting resin composition, and a second release sheet 4.

[0040] In the coverlay film of this embodiment, the peel strength of the first release sheet 2 to the uncured resin layer 3 is greater than the peel strength of the second release sheet 4 to the uncured resin layer 3.

[0041] By using the aforementioned coverlay film, the manufacturing method of this embodiment can suppress the peeling of the coverlay film during the manufacturing process of the stretchable circuit board.

[0042] In this embodiment, peel strength refers to the value (unit: N / mm) measured by cutting a sample consisting of a release sheet for measuring peel strength and an uncured resin layer containing a thermosetting resin composition into a 10mm x 150mm sheet, attaching it to a stainless steel plate (SUS plate) using an adhesive with the uncured resin layer as the bonding surface, peeling off 10mm of the release sheet by pinching it with fingers, attaching it to a universal testing machine (EZ Test manufactured by Shimadzu Corporation), and measuring the stress when the test is performed at a tensile speed of 100mm / min.

[0043] The peel strength (PB1) of the first release sheet 2 to the uncured resin layer 3 and the peel strength (PB2) of the second release sheet 4 to the uncured resin layer 3 are not particularly limited, as long as PB1 is greater than PB2. For example, the peel strength (PB1) may be approximately 0.040 N / mm or more and 0.100 N / mm or less, and the peel strength (PB2) may be approximately 0.010 N / mm or more and 0.050 N / mm or less.

[0044] Furthermore, in the coverlay film of this embodiment, the peel strength (PC1) between the cured resin layer, which is made from the cured product of the thermosetting resin composition, and the first release sheet is 0.015 N / mm or more and 0.035 N / mm or less. This has the advantage that the first release sheet does not peel off during the process and can be easily peeled off at the desired process. A more preferred range for the peel strength (PC1) is 0.15 N / mm or more and 0.30 N / mm or less, or 0.015 N / mm or more and 0.030 N / mm or less.

[0045] There are no particular limitations on the means for adjusting PB1, PB2, and PC1 as described above. For example, the peel strength of each sheet can be adjusted by adjusting the peel load of the first release sheet and the second release sheet. The peel load is a value that can be measured by the method described in the embodiments below. The preferred peel load for the first release sheet is approximately 100 mN to 10,000 mN, and the preferred peel load for the second release sheet is 50 mN to 150 mN. If the peel load exceeds the above range, the release sheet may not peel off.

[0046] Furthermore, in the coverlay film 10 of this embodiment, it is preferable that the glass transition temperature (Tg) of the first release sheet 2 is 300°C or higher. Since the first release sheet 2 may be used as a carrier film or support during the soldering process or component mounting process described later, it is preferable that it has heat resistance that can withstand soldering processes (for example, heat resistance that does not deform even when soldered using a reflow oven or soldering iron). By having a glass transition temperature of 300°C or higher for the first release sheet 2, it is possible to suppress the melting or deformation of the release sheet during the process.

[0047] On the other hand, there is no need to specifically define an upper limit for the glass transition temperature of the first release sheet 2, but from the viewpoint of ease of availability, etc., it is usually set to 440°C or lower.

[0048] Furthermore, the tensile modulus of the first release sheet is preferably 0.5 GPa or more and 5 GPa or less. Having a tensile modulus within this range gives the first release sheet the characteristic of being harder than the first stretchable insulating layer and the second stretchable insulating layer described later. This has the advantage that the first release sheet can maintain its shape during the component mounting process described later.

[0049] Note that the glass transition temperature and tensile modulus referred to here are the same as those described above for the core material.

[0050] The first release sheet in this embodiment can be any release sheet having the above-described peel strength (PB2) and / or peel strength (PC1), without any particular limitations. Specifically, for example, resin films such as polyimide, polyarylate, and polyamideimide can be used. Among these, polyimide films and the like are preferred from the viewpoint of having a desirable range of Tg and tensile modulus.

[0051] Furthermore, it is preferable to use a release-treated resin film as the first release sheet. Specific release treatments include applying a release coating with silicone oil. This makes it possible to obtain a release sheet with a desirable peel load.

[0052] In the coverlay film 10 of this embodiment, the uncured resin layer 3 contains a thermosetting resin composition. As the thermosetting resin composition that can be used for the uncured resin layer 3, a composition similar to the thermosetting resin composition that constitutes the first stretchable insulating layer 5 of the core material 11 described above can be used. The thermosetting resin compositions of the first stretchable insulating layer 5 and the uncured resin layer 3 may be the same or different. As will be described later, when the uncured resin layer 3 is cured to form the second stretchable insulating layer 3', it is preferable that the thermosetting resin compositions of the first stretchable insulating layer 5 and the uncured resin layer 3 be the same in order to facilitate integration with the first stretchable insulating layer 5.

[0053] In this embodiment, the "uncured resin layer" refers to a layer containing uncured resin, and the resin contained therein may be either "uncured material (A stage)" or "semi-cured material (B stage)".

[0054] In this embodiment, "semi-cured product" refers to a resin composition that has been partially cured to the extent that it can be further cured. In other words, a semi-cured product is a resin composition that has been partially cured (stage B). For example, when a resin composition is heated, its viscosity gradually decreases at first, then curing begins, and the viscosity gradually increases. In such a case, a semi-cured state would be the state between when the viscosity begins to increase and when it is not yet completely cured.

[0055] In the coverlay film 10 of this embodiment, the second release sheet can be any release sheet having the above-mentioned peel strength (PB1), and is not particularly limited to those commonly used as release sheets in fields such as electronic materials.

[0056] Specifically, examples include films made of polyethylene terephthalate (PET), polyester such as polybutylene terephthalate, polyolefins such as polyethylene, polyacetal, and polycarbonate. Among these, PET film is preferably used from the viewpoint of cost and availability.

[0057] The method for manufacturing the coverlay film described above is not particularly limited, but one example is to apply a resin varnish-like resin composition to the surface of a first release sheet, dry it, and then laminate a second release sheet onto it. Examples of the application method include bar coaters, comma coaters, die coaters, roll coaters, gravure coaters, etc.

[0058] The present invention includes not only a method for manufacturing a stretchable circuit board, but also the above-mentioned coverlay film for stretchable circuit boards.

[0059] (Lamination process) Next, as shown in Figure 2(B), the second release sheet 4 is peeled off from the coverlay film 10. At this time, in areas where the coverlay is not needed, the first release sheet 2 and the uncured resin layer 3 in those areas may be removed along with the second release sheet 4.

[0060] Specifically, unwanted parts can be removed by processing using lasers, chemical etching, drills, routers, punches, die-cutting, etc. At this time, the first release sheet 2, the uncured resin layer 3, and the second release sheet 4 may be processed together, or the first release sheet 2 and the uncured resin layer 3 may be processed together and then removed together with the second release sheet 4.

[0061] Next, the coverlay film 10, from which the second release sheet 4 has been peeled off, is laminated onto the core material 11 that was prepared in the core material preparation step, as shown in Figure 2(C). When laminating the coverlay film onto the core material 11, it is laminated in a manner in which the uncured resin layer 3 overlaps the core material 11.

[0062] Figure 2(C) shows a configuration in which coverlay films are laminated on both sides of the core material 11, but the coverlay film may be laminated on only one side of the core material 11. Furthermore, when coverlay films are laminated on both sides of the core material 11, the coverlay films used on the front and back surfaces of the core material 11 may be the same or different.

[0063] (Second stretchable insulating layer formation process) Next, as shown in Figure 2(D), the uncured resin layer 3 of the coverlay film is cured. The cured uncured resin layer 3 becomes the second stretchable insulating layer 3'. There are no particular limitations on the means of curing the uncured resin layer 3, and it can be cured by heating the laminate obtained in the lamination process. The heating may be accompanied by pressurization, or pressurization may be performed before or after the heating. The heating may also be performed under vacuum degassing. The heating and pressurization conditions can be set to a range that is appropriate depending on the type and content of the main component resin, etc.

[0064] In this embodiment, it is preferable that the first stretchable insulating layer 5 and the second stretchable insulating layer 3' are integrated. This is considered to have the advantage of suppressing peeling during the manufacturing process and during use.

[0065] There are no particular limitations on the means of integration. For example, as described above, the first stretchable insulating layer 5 and the second stretchable insulating layer 3' can be integrated by curing the uncured resin layer 3 in contact with the first stretchable insulating layer 5.

[0066] Through the above steps, the manufacturing method of this embodiment allows for the stable acquisition of a stretchable circuit board without the first release sheet peeling off during the process.

[0067] (Component mounting process) Furthermore, the manufacturing method of this embodiment may include a component mounting step for mounting electronic components. The method for mounting electronic components on the stretchable circuit board is not particularly limited and includes methods such as using a soldering iron, printing various types of solder paste, mounting the electronic components using various component mounting devices, and then mounting them using various reflow devices. Alternatively, means for heating only the metal parts by induction heating, microwaves, etc., may be used.

[0068] More specifically, for example, component mounting can be performed by a reflow soldering process, as shown in Figures 3(E) to (G).

[0069] (Resist printing process) First, as shown in Figure 3(E), a resist 7 is printed on the conductive layer 6 to prevent excess solder from adhering during the solder printing process described later. There are no particular limitations on the means of resist printing; the resist 7 can be printed on the conductive layer 6 by methods such as applying ordinary resist ink using screen printing or inkjet printing, or by laminating a film-like photosensitive material with a vacuum laminator and then exposing and developing it.

[0070] Note that in Figure 3(E), the first release sheet 2 on the component mounting side (resist printing side), as shown in Figure 2(D), has been peeled off. However, it is not necessarily required to peel it off at this point, and it may be peeled off simultaneously with the first release sheet 2 on the opposite side of the component mounting side during the first release sheet peeling process described later.

[0071] (Solder printing process) Next, in order to bond components such as electronic components to the stretchable circuit board and mount the components onto the stretchable circuit board, solder 8 is printed on the conductive layer (circuit) 6 of the stretchable circuit board, as shown in Figure 3(F). There are no particular limitations on the method of printing the solder 8, and known means can be used. For example, solder printing using a metal mask or flexographic printing can be used.

[0072] (Component mounting process) Next, as shown in Figure 3(G), the electronic components 9 are mounted on the solder 8 printed in the above process. Specifically, after mounting the electronic components 9 on the printed solder 8, heating is performed using a reflow oven to bond the electronic components to the stretchable circuit board, thereby obtaining a stretchable circuit board with the electronic components mounted.

[0073] In this case, by using a release sheet with a glass transition temperature of 300°C or higher as the first release sheet 2, it is possible to proceed with the manufacturing process stably because it will not melt or deform due to heating in the reflow oven.

[0074] The electronic components 9 that can be used in this embodiment are not particularly limited, and examples include transistors, signal-emitting elements, light-emitting elements, solar power generation elements, diodes, switching elements, capacitors, coils, liquid crystals, wireless modules such as Bluetooth®, various sensors such as acceleration sensors, humidity sensors, and temperature sensors, and chip components used in RFID, etc.

[0075] (First release sheet peeling process) The manufacturing method of this embodiment may further include a step of peeling off the first release sheet 2, as shown in Figure 3(H), after the component mounting step described above.

[0076] In this case, by using a release sheet having the aforementioned peel strength (PB2) and / or peel strength (PC1) as the first release sheet 2, it is considered that the substrate can be peeled off with an appropriate peeling force without unnecessarily pulling it too hard and damaging it. [Examples]

[0077] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0078] First, the various materials used in this embodiment are as follows:

[0079] (base material) • Base material 1: Polyimide resin "UPIREX S (product name)" (manufactured by Ube Industries, Ltd., Tg: 359℃) Thickness: 0.025, 0.050, 0.075 mm • Base material 2: Polyamide resin "Mictron (product name)" (manufactured by Toray Industries, Inc., Tg: 309℃), thickness: 0.050mm • Base material 3: Polyphenylene sulfide resin "Torelina (product name)" (manufactured by Toray Industries, Inc., Tg: 98℃), thickness: 0.050mm • Base material 4: Polyethylene naphthalate resin "Teonex Q51 (product name)" (manufactured by Toyobo Co., Ltd., Tg: 165℃), thickness: 0.050mm • Base material 5: Polyethylene terephthalate resin "Lumirror X10S (product name)" (manufactured by Toray Industries, Inc., Tg: 86℃) Thickness: 0.025, 0.050, 0.075 mm

[0080] (Preparation of release sheet) Using the above-mentioned substrates, release sheets 1 to 13 were prepared by performing a release treatment with silicone oil to achieve the peel loads shown in Tables 1 and 2 below.

[0081] The peel load shown here is the value (mN) measured when polyester adhesive tape No. 31B (50 mm wide, manufactured by Nitto Denko Corporation) is attached to the release surface of the release sheet, mounted on a universal testing machine (AGS-X, manufactured by Shimadzu Corporation), and tested at a tensile speed of 300 mm / min.

[0082] [Table 1]

[0083] [Table 2]

[0084] (Example 1) (Creation of coverlay film) First, as thermosetting resin composition 1, 89.85 parts by mass of Teisan Resin "PMS-14-67EK40" (ethyl ethyl ketone dissolved product, solid content ratio 40.0% by weight) manufactured by Nagase ChemteX, a curing agent (Shin Nippon Rika Co., Ltd. "Ricacid TBN-100", 3.67 parts by mass) and a reaction initiator (Shikoku Chemicals, Ltd. "2PZ-CN", 0.40 parts by mass) were mixed, and a solvent (methyl ethyl ketone) was added so that the solid content of the composition was approximately 40.0% by mass to prepare a resin varnish. After degassing by standing, the resin varnish was applied to the release sheet 1 obtained above as the first release sheet (support) using a bar coater. Next, a semi-cured resin layer (uncured resin layer) was formed on the first release sheet by heating in an oven at 80°C for 60 minutes. Subsequently, the release sheet 11 obtained above was laminated on the formed semi-cured resin layer as a second release sheet (protective sheet) to produce a coverlay film.

[0085] (Peel strength: Measurement of PB1, PB2, and PC1) A sample consisting of a release sheet and a thermosetting resin composition was laminated and cut to 10 mm x 150 mm. The uncured resin layer was used as the bonding surface and attached to a stainless steel plate (SUS plate) using adhesive. The release sheet was pinched with fingers and peeled off by 10 mm. The sample was then mounted on a universal testing machine (EZ Test, manufactured by Shimadzu Corporation) and tested at a tensile speed of 100 mm / min. By measuring the stress, the peel strength of the first release sheet relative to the uncured resin layer (PB1) and the peel strength of the second release sheet relative to the uncured resin layer (PB2) were measured.

[0086] Subsequently, the uncured resin layer was cured by heating it at 180°C for 90 minutes, and the peel strength (PC1) between the cured product of the thermosetting resin composition and the first release sheet was measured by the same method as described above.

[0087] The results are shown in Table 3. In the table, "Not peeled" indicates that the release sheet and the thermosetting resin composition were firmly adhered and could not be peeled off.

[0088] (Examples 2-8 and Comparative Examples 1-5) Coverlay films were prepared in the same manner as in Example 1, except that the first and second release sheets were changed to the sheets shown in Table 3. PB1, PB2, and PC1 were measured for each of these films. The results are also shown in Table 3.

[0089] <Evaluation Test> (Release properties of the second release sheet) A sample consisting of a release sheet and a thermosetting resin composition laminated together was cut to 10 mm x 150 mm. The uncured resin layer was used as the bonding surface and the sample was attached to a stainless steel plate (SUS plate) using adhesive. The release properties of the second release sheet were evaluated by pinching the edge of the release sheet with fingers and peeling it off. The evaluation criteria were: ○ "The second release sheet was peeled off without the first release sheet peeling off," and × "The first release sheet peeled off first."

[0090] (Reflow resistance) The reflow resistance of the coverlay film was evaluated by attaching the circuit boards fabricated using the methods shown in Figures 2(A) to 3(G) to a transport plate with Kapton tape, placing them in a reflow machine, and observing their appearance. The evaluation criteria were as follows: ○ "No peeling, melting, or deformation of the release sheet, and electronic components are properly mounted," × "Peeling, melting, or deformation of the release sheet, and improper mounting of electronic components."

[0091] (Release properties of the first release sheet) A sample consisting of a release sheet and a thermosetting resin composition laminated together was cut to 10 mm x 150 mm. The uncured resin layer was used as the adhesive surface and attached to a stainless steel plate (SUS plate) using adhesive. The release properties of the first release sheet were evaluated by pinching the edge of the release sheet with fingers and peeling it off.

[0092] The evaluation criteria were: ○ "No detachment of electronic components or breakage of the substrate after demolding," and × "Detachment of electronic components or breakage of the substrate after demolding, or delamination during the process."

[0093] The results for each are shown in Table 3.

[0094] [Table 3]

[0095] (Consideration) As is clear from the results in Table 3, the coverlay film of the present invention was confirmed to possess appropriate peel strength and reflow resistance.

[0096] On the other hand, in Comparative Example 1, where PB2 was larger than PB1, the thermosetting resin composition peeled off from the first release sheet when the second release sheet was peeled off, resulting in poor release properties of the second release sheet.

[0097] In Comparative Example 2, the PC1 was too low, causing delamination during the reflow process and resulting in frequent component mounting defects. In Comparative Example 3, the delamination load was too high, preventing the first release sheet from being peeled off after reflow, making it impossible to measure PC1.

[0098] Furthermore, in Comparative Examples 4 and 5, sufficient reflow resistance could not be obtained because the glass transition temperature of the substrate used for the first release sheet was 300°C or lower.

[0099] (Manufacturing of stretchable circuit boards) First, a core material 11 is prepared in which a conductor layer 6 is laminated on at least one side of the first stretchable insulating layer 5. Figure 2(A) shows a core material 11 with conductor layers 6 laminated on both sides, but it may also be on one side, and in the case of one side, it is preferable that the other side has a first release sheet laminated on it. The core material 11 is drilled using a laser or the like, and then a wiring board is obtained through a plating process and an etching process. On the other hand, as shown in Figure 2(B), unnecessary parts of the coverlay film 10 are processed using a laser or the like, and then the second release sheet 4 is peeled off, and at the same time the unnecessary first release sheet 2 and uncured resin layer 3 are removed. Next, as shown in Figure 2(C), the coverlay film from which the second release sheet 4 has been peeled off is placed with the uncured resin layer 3 facing the core material 11, and laminated using a vacuum laminator so that no air bubbles remain. Next, as shown in Figure 2(D), the stretchable circuit board 12 is introduced into a vacuum molding machine and heated at 180°C for 90 minutes under vacuum degassing and a pressure of 1.0 MPa to cure the uncured resin layer 3. At this time, the voids in the core material 11 are filled with the second stretchable insulating layer 3'. At this time, at least one of the first release sheets 2 laminated on both sides is left laminated on the stretchable circuit board 12. The other first release sheet 2 may or may not be peeled off. Next, as shown in Figure 3(E), the resist 7 is printed. Next, as shown in Figure 3(F), solder 8 is applied to the positions where the electronic components will be joined. Next, as shown in Figure 3(G), the electronic components 9 are placed. Next, as shown in Figure 3(H), the solder is melted in a reflow apparatus or the like to electrically join the stretchable circuit board 12 and the electronic components 9. Steps 3(F) to 3(G) may also be performed by electrically joining the stretchable circuit board 12 and the electronic components 9 using a soldering iron or the like. [Industrial applicability]

[0100] The present invention has broad industrial applicability in the technical fields related to various electronic materials and electronic devices. [Explanation of Symbols]

[0101] 10 Coverlay Film 11 Core material 12 Stretchable circuit board 2. First release sheet 3 Uncured resin layer 3' Second stretchable insulating layer 4. Second release sheet 5. First stretchable insulating layer 6 Conductor layers 7 Resist 8 solder 9 Electronic Components

Claims

1. A method for manufacturing a stretchable circuit board, A step of preparing a core material comprising a first stretchable insulating layer and a conductive layer overlapping at least one surface of the first stretchable insulating layer, A step to prepare a coverlay film in which a first release sheet, an uncured resin layer containing a thermosetting resin composition, and a second release sheet are laminated in this order. A step of peeling the second release sheet from the coverlay film and laminating the uncured resin layer and at least one surface of the core material, and The process includes curing the uncured resin layer to form a second stretchable insulating layer, The peel strength of the first release sheet to the uncured resin layer is greater than the peel strength of the second release sheet to the uncured resin layer. The peel strength between the cured product of the thermosetting resin composition and the first release sheet is 0.015 N / mm or more and 0.035 N / mm or less. The glass transition temperature of the first release sheet is 300°C or higher, and A method for manufacturing a stretchable circuit board, characterized in that both the first stretchable insulating layer and the second stretchable insulating layer have a glass transition temperature of 60°C or less and a tensile modulus of 0.1 MPa or more and 100 MPa or less.

2. A method for manufacturing a stretchable circuit board according to claim 1, further comprising the step of mounting electronic components.

3. The method for manufacturing a stretchable circuit board according to claim 2, wherein the step of mounting the electronic components includes a step of joining them by soldering.

4. A method for manufacturing a stretchable circuit board according to any one of claims 1 to 3, further comprising the step of peeling off the first release sheet.

5. A method for manufacturing a stretchable circuit board according to any one of claims 1 to 4, wherein the tensile modulus of the first release sheet is 0.5 GPa or more and 5 GPa or less.

6. A method for manufacturing a stretchable circuit board according to any one of claims 1 to 5, wherein the first stretchable insulating layer and the second stretchable insulating layer are integrated.

7. A first release sheet, an uncured resin layer containing a thermosetting resin composition, and a second release sheet are laminated in this order. The peel strength of the first release sheet to the uncured resin layer is greater than the peel strength of the second release sheet to the uncured resin layer. The peel strength between the cured product of the thermosetting resin composition and the first release sheet is 0.015 N / mm or more and 0.035 N / mm or less. The glass transition temperature of the first release sheet is 300°C or higher. Stretchable coverlay film for circuit boards.

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