Light-emitting or light-receiving device

Abstract

To provide a laminate film that exhibits excellent solvent resistance and long-term reliability even when using a silicone adhesive with high heat resistance and excellent adhesive strength.SOLUTION: In a laminate film bonding a substrate film 11 having heat resistance and a metal foil 14 using an adhesive, a barrier layer 13 that prevents an agent from penetrating an adhesive layer 12 is provided between the metal foil 14 and the adhesive layer 12. The barrier layer 13 contains resin with heat resistance similar to that of the substrate film 11, and has a water absorption rate of 1% or less. The adhesive layer 12 is made of a silicone resin, and thickness thereof after dehydration is 40 μm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated film in which a metal foil is laminated on a resin film, and particularly to a laminated film suitable for flexible substrates and the like. [Background technology]

[0002] Laminated films, which are made by laminating metal foil such as copper foil directly or via adhesive onto transparent films such as polyimide, are widely used as materials for flexible printed circuits (FPCs), etc. FPCs are made by etching the copper foil of such laminated films to form the desired wiring patterns and electrodes, and then soldering components such as semiconductor elements and light-emitting elements to them, making them useful for many electronic components.

[0003] Laminated films can be broadly divided into those in which copper foil is laminated to a base film without the use of adhesive, and those in which it is laminated using an adhesive. Both have important properties such as excellent flexibility and heat resistance, but it is also necessary to use an appropriate laminated film depending on the manufacturing process for FPCs and the final electronic components, as well as the environment in which the electronic components will be used. For example, in light-emitting devices equipped with light-emitting elements, the base film often requires transparency.

[0004] Laminated films in which metal foil is laminated onto a transparent film are generally produced by a casting method in which polyimide resin (varnish before curing) is applied to metal foil and then thermally cured, a thermal lamination method in which a polyimide film and metal foil are bonded together using a polyimide resin or a thermosetting adhesive, a sputtering method, or the like (see, for example, Patent Document 1 and Patent Document 2). Of these, the casting method and thermal lamination method can be produced using simpler production equipment than the sputtering method, and are therefore widely used.

[0005] However, when using methods such as casting, when a polyimide layer is formed on a flexible material such as copper foil and then cured, if the polyimide thickness exceeds 30 μm, it will shrink as it cures, posing the problem that the contraction stress of the polyimide will cause the entire laminated film to warp.

[0006] Furthermore, thermal lamination is temperature dependent; in low temperature ranges, peeling may occur at the interface between the metal foil and the substrate film, while in high temperature ranges, the film or the polyimide used for adhesion may partially tear, resulting in pinholes or resin lumps.

[0007] On the other hand, when using an adhesive to bond metal foil and transparent polyimide, the adhesive is required to have high adhesive strength and heat resistance sufficient to withstand the use of solder, etc. For example, Patent Document 2 lists as usable resins epoxy resin, NBR-phenolic resin, phenol-butyral resin, epoxy-NBR resin, epoxy-polyester resin, epoxy-nylon resin, epoxy-acrylic resin, acrylic resin, polyamide-epoxy-phenolic resin, polyimide resin, silicone resin, and the like. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4557515 specification [Patent Document 2] Japanese Patent Application Publication No. 10-235784 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0009] Resins with a carbon backbone, such as epoxy resins and urethane resins listed in Patent Document 2, have a heat resistance temperature of 200°C or less. When soldering electronic elements such as LEDs to FPCs, the temperature reaches 230°C or higher, and even low-temperature soldering reaches 180°C or higher. Therefore, such adhesives melt or decompose the adhesive layer during soldering. Furthermore, they do not provide sufficient strength for applications requiring long-term reliability, such as automotive components. Silicone resins have higher heat resistance than carbon-based resins, but they are prone to swelling in water. They are particularly prone to swelling in water containing acids used in wet etching and wet plating. Therefore, when silicone resins are immersed in treatment water during wet etching or wet plating to form wiring patterns from metal foils, they swell due to the moisture, acid, and solvents contained in the treatment solution, which compromises the dimensional stability of the film and the wiring patterns formed on the film.

[0010] Furthermore, in order to increase the strength and adhesive strength of the FPC, the adhesive layer must be thick enough to ensure sufficient adhesive force, but in this case, the problems caused by the adhesive layer mentioned above become even more severe.

[0011] The present invention aims to provide a laminated film having a structure in which a metal foil and a base film are bonded together using an adhesive, which can avoid problems of peeling and tearing during the production of the laminated film, and which has heat resistance, dimensional stability, and long-term reliability. [Means for solving the problem]

[0012] The present invention solves the above problems by providing a laminated film with a four-layer structure including a barrier layer with low water absorption.

[0013] That is, the laminated film of the present invention is a laminated film in which a metal foil is laminated on a heat-resistant film via an adhesive layer, and is characterized by including an acid-resistant barrier layer between the metal foil and the adhesive layer, the barrier layer being made of a resin with a water absorption rate (JIS: K7209:2000) of 1% or less. In one embodiment of the laminated film of the present invention, a highly heat-resistant silicone adhesive is used as the adhesive layer, and a polyimide is used as the barrier layer.

[0014] The light emitting device of the present invention uses a flexible substrate in which a wiring pattern is formed on the metal foil of the above-mentioned laminated film.

[0015] The method for manufacturing a light-emitting device of the present invention includes the steps of forming a wiring pattern on the metal foil of the above-mentioned laminated film by wet etching, and joining the terminals of the light-emitting element onto the wiring pattern via a conductive adhesive. [Effects of the Invention]

[0016] The present invention provides a four-layer structure in which a barrier layer is interposed between the metal foil and the adhesive layer, thereby preventing peeling and tearing of the film. Even when a silicone-based adhesive is used as the adhesive layer, it is possible to provide a laminated film that is heat-resistant and highly reliable over the long term without incurring dimensional changes due to swelling. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view showing one embodiment of a laminated film of the present invention. [Figure 2] 1A to 1C are diagrams showing an example of a method for manufacturing a laminated film. [Figure 3] 1A to 1C are diagrams showing an example of a method for manufacturing a light-emitting device using a laminated film of the present invention. [Figure 4] FIG. 2 is a graph showing the total light transmittance of laminate films of Examples and Comparative Examples. [Figure 5] 6 is a graph showing the relationship between the thickness of the adhesive layer and the peel strength in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the laminated film of the present invention will be described. As shown in FIG. 1, the laminated film 10 of this embodiment is a laminated film having a structure in which a heat-resistant base film 11 and a metal foil 14 are bonded together with an adhesive, and a low-water-absorbent barrier layer 13 is interposed between the adhesive layer 12 and the metal foil 14.

[0019] The base film 11 can be made of a resin that is heat resistant to temperatures of 200°C or higher, specifically, polyimide, polycarbonate, polyamide, polyester, liquid crystal polymer, etc., but a polyimide film is particularly suitable from the viewpoints of heat resistance, flexibility, and acid resistance. The base film may be required to be transparent for applications such as light emitting devices, but for applications that do not require transparency, a colored film (such as Kapton (trademark): colored polyimide) may be used.

[0020] Although there are no limitations on the thickness of the base film 11, when used for an FPC, it is preferable to use one in the range of 10 to 50 μm. By setting the thickness in this range, high flexibility can be obtained and the occurrence of warping when laminated can be suppressed.

[0021] From the viewpoints of adhesive strength, heat resistance, flexibility, etc., a silicone-based adhesive is preferable for the adhesive layer 12. Silicone-based resins are based on a polysiloxane structure in which functional groups such as alkyl groups are bonded to silicon, but those with some phenyl groups bonded thereto or epoxy-modified silicone resins may also be used. When a silicone-based adhesive is used, the thickness of the adhesive layer 12 is preferably 40 μm or more in dry thickness. By making the thickness 40 μm or more, sufficient adhesive strength can be obtained while maintaining flexibility.

[0022] The barrier layer 13 functions as a moisture barrier for the adhesive layer 12 and is made of a resin with low water absorption. The water absorption rate is 1% or less, preferably 0.9% or less. The water absorption rate can be measured in accordance with JIS: K7209:2000. Specifically, a test piece made of the resin that constitutes the barrier layer is immersed in distilled water at 23°C for a predetermined time (24 hours), and then the change in mass of the test piece (the difference from the initial mass) is divided by the initial mass (%).

[0023] By providing such a low-water-absorption barrier layer 13 between the metal foil 14 and the adhesive layer 12, when the metal foil 14 is subjected to wet etching or wet plating, the treatment liquid used in the treatment can be prevented from penetrating into the adhesive layer 12, preventing swelling of the adhesive layer 12 and ensuring dimensional stability. A resin constituting such a barrier layer 13 is preferably a material that has heat resistance comparable to that of the resins constituting the base film 11 and the adhesive layer 12 and that can provide high adhesive strength with the adhesive layer 12. Specific examples of such a low-water-absorption resin include the same resin materials as those used for the base film 11, such as polyimide, polycarbonate, polyamide, polyester, and liquid crystal polymer, with polyimide resin being particularly preferred.

[0024] The thickness of the barrier layer 13 is preferably 3 μm or more to form a stable barrier layer, and is preferably 20 μm or less to prevent warping of the laminated film due to the barrier layer 13. The thickness is more preferably 5 to 15 μm, and even more preferably 5 to 13 μm.

[0025] Copper foil is generally used as the metal foil 14, but it is not limited to copper foil, and aluminum foil, stainless steel foil, nickel foil, etc. can also be used as long as it is a conductive metal that can be laminated with the base film via an adhesive and that can be etched to form a wiring pattern. The metal foil 14 usually has a thickness of 12 to 35 μm.

[0026] 1 shows a laminate film consisting of four layers: base film 11, adhesive layer 12, barrier layer 13, and metal foil 14, but if necessary, a layer (easy-adhesion layer) for improving the adhesion between base film 11 and adhesive layer 12 may be provided, or an easy-adhesion treatment may be applied to the surface of base film 11. Furthermore, although the figure shows a laminate film in which metal foil 14 or the like is adhered to one side of base film 11, it is also possible to laminate metal foil 14 or the like on both sides, and such laminate films are also encompassed by the present invention.

[0027] Next, an example of a method for producing the laminated film of this embodiment will be described. As shown in Figure 2, a liquid (varnish) made by adding a solvent to the resin that constitutes the barrier layer 13 is uniformly applied to the metal foil 14 and then heated and dried to form a transparent barrier layer 13. Common coating methods such as die coating, spin coating, bar coating, and spray coating can be used for coating, resulting in a barrier layer with a wet thickness of 20 μm or less and a dry thickness of 5 to 20 μm. The drying conditions for the barrier layer are, for example, low-oxygen conditions with an oxygen concentration of 100 ppm or less, and the temperature is increased at a rate of 5°C / min, for example, for 30 minutes at 100°C and 30 minutes at 300°C.

[0028] An adhesive composition containing a silicone resin is applied onto the barrier layer 13 to a wet thickness of 50 to 60 μm. The application method can be the same as that used to apply the varnish to the barrier layer. Immediately after applying the adhesive composition, a transparent substrate film (thickness 25 to 50 μm) is laminated onto the adhesive composition, and the adhesive composition is vacuum-laminated and dried. Alternatively, lamination by pressure is also possible, for example, at 120°C and 1 N / mm 2 The adhesive is then heated and cured in stages at 150°C for 30 minutes, after which it is dried at atmospheric pressure for 30 minutes. This stepwise heating and curing process prevents voids from forming in the adhesive layer.

[0029] Through the above steps, a laminated film having a four-layer structure in which the metal foil 14 and the base film 11 are laminated via the barrier layer 13 and adhesive layer 12 is obtained.

[0030] However, the method for producing the laminated film of the present invention is not limited to the above-mentioned method. For example, it is also possible to produce a laminate of a metal foil 14 and a barrier layer 13, apply an adhesive composition to the substrate film 11, and then bond this laminate so that the barrier layer 13 is in contact with the adhesive-coated surface.

[0031] As described above, in the laminate film of the present invention, the low-water-absorption barrier layer 13 is disposed between the metal foil 14 and the adhesive layer 12. When the metal foil of the laminate film of the present invention is subjected to an etching process or the like, even if the adhesive layer 12 is exposed to an etching process solution such as an aqueous ferric chloride solution or an aqueous sodium hydroxide solution, the adhesive layer 12 is prevented from absorbing moisture in the process solution and swelling. Furthermore, after etching, the adhesive layer 12 is exposed, and even when wet plating or the like is performed in a subsequent process, the penetration of moisture from the acid (aqueous solution) such as hydrochloric acid or sulfuric acid used in the wet plating and the resulting swelling can be prevented.

[0032] The laminated film of the present invention, like general metal foil laminate films, can be used as a substrate for light-emitting devices used in automotive lighting fixtures and general lighting, a flexible substrate for electronic devices such as wearable devices, a flexible cable, a planar heating element, an electromagnetic shielding material, etc., and in each application, highly reliable products can be obtained, and the reliability can be maintained even when exposed to high temperature and high humidity environments for a long period of time.

[0033] Next, an embodiment of a light emitting device will be described as an example of a product using the laminated film of the present invention, in which the metal foil 14 is copper foil, the base film 11 is polyimide, the adhesive layer 12 is an adhesive layer made of a silicone resin, and the barrier layer 13 is polyimide.

[0034] 3, in the light emitting device 20 of this embodiment, a predetermined wiring pattern 14a is formed on the copper foil 14 of the laminate film 10 by wet etching. Wet etching is performed by immersing the copper foil, with a mask 15 such as a photoresist applied to it (step 301), in an etching solution such as an acid (e.g., a ferric chloride solution) or an alkali (e.g., a sodium hydroxide solution) that corrodes the copper foil for a predetermined period of time (step 302). When this process is performed, the copper foil is removed, exposing the underlying barrier layer. However, because the barrier layer is made of a low-water-absorbency resin, the moisture in the etching solution is prevented from penetrating through the barrier layer into the adhesive layer below the barrier layer, thereby suppressing swelling of the adhesive layer 12 made of a silicone-based resin.

[0035] The mask 15 remaining on the wiring pattern is then removed (step 303), and, as needed, Ni, Au, or the like is deposited on some or all of the copper foil remaining as the wiring pattern by electroplating or electroless plating, forming a plating layer 16 (step 304). In the case of electroless plating, for example, acid degreasing, acid cleaning using sulfuric acid or hydrochloric acid, and Pd activation using an activator are performed, followed by electroless nickel plating using an electroless nickel plating solution (e.g., ICP Nicoron), displacement Au plating using a bath make-up solution, or reduction Au plating. During plating, the laminate film including the wiring pattern is immersed in various treatment solutions for tens of seconds to tens of minutes. Here too, the barrier layer prevents moisture in the treatment solution from penetrating the adhesive layer, suppressing swelling of the adhesive layer and resulting dimensional changes of the laminate film.

[0036] Next, solder 17 is applied to the wiring pattern at the location where an electronic component 21, such as an LED element or a light-receiving element (hereinafter referred to as a chip), will be mounted (for example, at a power supply point formed by an Au bump, etc.), and a chip (SMD chip) 21 with a power supply terminal on its backside is soldered and fixed by reflow (step 305). In the illustrated example, one chip 21 is shown fixed as a representative, but multiple chips may also be fixed. Note that while FIG. 3 shows the case where the chip 21 is fixed by soldering, it is also possible to bond the chip by direct bonding, which uses Ag nanoparticles as a bonding material, applies pressure from the chip side, and passes a pulse current.

[0037] The completed light emitting or light receiving device is made by laminating a heat resistant base film 11, an adhesive layer 12, and a barrier layer 13 in this order from the side opposite to the side on which the LED element or light receiving element is mounted, and then forming a wiring pattern 14a on top of them. The LED element or light receiving element is mounted on the wiring pattern 14a, and the barrier layer 13 is exposed in the gaps between the wiring pattern 14a.

[0038] In the light-emitting device 20 manufactured in this manner, even if the FPC is exposed to various chemicals in each step of its manufacture, the adhesive layer can be prevented from coming into direct contact with these chemicals, so even if a silicone resin that easily swells in water is used as the adhesive layer, a light-emitting device with a stable shape can be obtained while maintaining its high heat resistance and adhesive strength. Furthermore, because the adhesive layer that joins the FPC wiring pattern and the base film is made of silicone resin and its surface is protected by a barrier layer, the manufactured light-emitting device will not be damaged even if left in a harsh environment of high temperature and humidity for a long time, and the light-emitting device can maintain its long-term reliability. [Example]

[0039] Examples of the laminated film of the present invention will be described below.

[0040] Example 1 A transparent polyimide varnish (Neoprim S100, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was applied to a copper foil (35 μm thick) using a die coater with a coating width of 200 mm to a wet thickness of 105 μm and a coating length of 270 mm. The coating was then dried at 100°C for 30 minutes in a low-oxygen atmosphere (O2 concentration: 100 ppm or less), then heated to 300°C at a rate of 5°C / min and dried for an additional 30 minutes to form a polyimide barrier layer. The dried thickness of the barrier layer was 10 μm.

[0041] Next, silicone resin (dimethyl silicone resin, manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to the polyimide barrier layer formed as described above using a die coater with a coating width of 200 mm to a wet thickness of 58 μm and a coating length of 270 mm. Immediately after the silicone resin application, a transparent polyimide monolayer (thickness: 50 μm) was laminated and heated at 60°C for 4 hours, then heated to 150°C at a rate of 2°C / min and dried for an additional 4 hours to produce a copper foil-polyimide film laminate. The transparent polyimide monolayer was a film made from the same material as the transparent polyimide varnish used for the barrier layer.

[0042] The thickness of the adhesive layer (silicone resin layer) in the obtained laminate was 40 μm.

[0043] <Comparative Example 1> The same copper foil and transparent polyimide film as in Example 1 were used and, without providing a barrier layer, they were bonded together with the same silicone resin as in Example 1 to prepare a copper foil-polyimide film laminate.

[0044] <Comparative Example 2> A copper foil similar to that in Example 1 was prepared, and a transparent polyimide varnish (Neoprim S100, manufactured by Mitsubishi Gas Chemical Company) was applied to a wet thickness of 280 μm and a coating length of 270 mm using a die coater with a coating width of 200 mm so as to have the same thickness (50 μm) as the transparent polyimide monolayer in Example 1. The foil was then dried at 100°C for 30 minutes in a low-oxygen atmosphere (O2 concentration: 100 ppm or less), and then heated to 300°C at a heating rate of 5°C / min and further dried for 30 minutes to produce a copper foil-polyimide film laminate.

[0045] <Evaluation> The laminates of Example 1 and Comparative Examples 1 and 2 were evaluated for the following items. Warpage and curling: After lamination, it was visually confirmed whether the flat shape was maintained. Adhesive strength: Adhesive strength (N / cm) was measured by the 90-degree peel test according to C5016:1994. Transparency: The total light transmittance Tt was measured using an ultraviolet-visible spectrophotometer (UH4150, manufactured by Hitachi High-Tech Science). Solvent resistance: The laminate was immersed in an electroless nickel plating solution (ICP Nicoron or the like) for 45 minutes, and the presence or absence of peeling was confirmed.

[0046] The results are shown in Table 1. Regarding transparency, the results are shown in Figure 4, and Table 1 shows only the transparency value at a wavelength of 445 nm.

[0047] [Table 1]

[0048] As shown in Table 1, no warping or curling (curling up) occurred in Example 1 and Comparative Example 1, but warping occurred in Comparative Example 2 due to the effect of curing shrinkage of the resin during bonding. Comparative Example 2 had the strongest adhesive strength, but it was confirmed that Example 1 and Comparative Example 1 also had an adhesive strength of 9 (N / cm or more), which is sufficient for use as a laminated film. Regarding solvent resistance, Comparative Example 2, which does not have a barrier layer, saw the silicone adhesive layer deteriorate due to the plating treatment liquid. Adhesion The strength decreased.

[0049] Regarding transparency, as shown in FIG. 4, Example 1, which has a barrier layer, has a slightly lower transmittance than Comparative Example 1, which does not have a barrier layer. However, since the transmittance is 85% or more at a wavelength of 445 nm, it was confirmed that the performance is sufficient as a material for mounting a blue LED or the like.

[0050] <Example 2> In the step of forming the barrier layer of Example 1, the amount of transparent polyimide varnish applied was changed, and the other conditions were the same as in Example 1. The dry thicknesses of the barrier layer were 20 μm (Experimental Example 1), 25 μm (Experimental Example 2), and 35 μm (Experimental Example 3), respectively. 3 ) A copper foil-polyimide film laminate was prepared.

[0051] These laminates were evaluated in the same manner as in Example 1, and the results were the same as in Example 1 for all items except for curl, but the laminates became cylindrical after lamination in Experimental Examples 2 and 3. From these results, it was found that the thickness of the barrier layer is preferably less than 25 μm, and more preferably 20 μm or less.

[0052] Example 3 In the step of forming the adhesive layer of Example 1, the amount of silicone resin applied was changed, and the other steps were the same as in Example 1, and adhesive layers with different thicknesses were formed. Copper A foil-polyimide film laminate was prepared, and the adhesive strength of the adhesive layer was measured (90-degree peel test). The results are shown in Figure 5.

[0053] As can be seen from the results in Figure 5, a thickness of 2 μm does not provide sufficient adhesive strength, but a thickness of 10 μm or more provides an adhesive strength of 6 N / cm or more, and a thickness of 35 μm or more provides an adhesive strength of 10 N / cm. These results show that a thickness of 35 μm or more is preferable for adhesive layers using silicone resin. [Explanation of symbols]

[0054] 10: Laminated film, 11: Base film (polyimide film), 12: Adhesive layer, 13: Barrier layer (polyimide layer), 14: Metal foil (copper foil), 15: Mask, 16: Plating layer, 20: Light-emitting device, 21: Light-emitting element (chip)

Claims

1. A light-emitting or light-receiving device comprising a laminated film in which a metal foil is laminated on a heat-resistant film via an adhesive layer, a light-transmitting flexible substrate in which a wiring pattern is formed on the metal foil, and a light-emitting element or a light-receiving element mounted on the wiring pattern of the flexible substrate, the laminated film includes a barrier layer between the metal foil and the adhesive layer, the barrier layer being made of a resin having a water absorption rate (JIS: K7209:2000) of 1% or less, the heat-resistant film is made of any one of polyimide, polycarbonate, polyamide, polyester, and liquid crystal polymer; the adhesive layer is a silicone adhesive, the wiring pattern includes a conductive metal formed by etching the metal foil, the barrier layer is made of any one of polyimide, polycarbonate, polyamide, polyester, and liquid crystal polymer, and has a thickness of less than 25 μm; The light emitting or receiving device has the barrier layer exposed in the gaps between the wiring patterns.

2. 2. The light emitting or receiving device according to claim 1, The light emitting or receiving device is characterized in that the light emitting or receiving element is connected to the wiring pattern across the wiring pattern.

3. The light emitting or receiving device according to claim 1 or 2 A light emitting or receiving device, characterized in that the adhesive layer has a thickness of 40 μm or more.

4. 4. The light emitting or receiving device according to claim 1, A light emitting or receiving device, wherein the resin constituting the barrier layer is a polyimide resin.

5. 5. The light emitting or receiving device according to claim 1, A light emitting or receiving device, wherein the barrier layer has a thickness of 20 μm or less.

6. 6. The light emitting or receiving device according to claim 1, A light emitting or receiving device, wherein the heat-resistant film is a light-transmitting polyimide film.

7. 7. The light emitting or receiving device according to claim 1, A light emitting or receiving device characterized in that a plating layer made of a metal different from the metal foil constituting the wiring pattern is provided on the metal foil.

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