Adhesive sheet for workpieces and method for producing same

Abstract

This adhesive sheet for workpieces comprises: an adhesive layer that is configured so as to be affixed to a workpiece for an electronic device; and a release sheet that is disposed on the adhesive layer and can be removed from the adhesive layer. The release sheet has dust-free paper.

Description

Adhesive sheet for workpiece and method of manufacturing same

[0001] The present invention relates to an adhesive sheet for workpieces and a method for producing the same.

[0002] In manufacturing an electronic device such as a semiconductor device, a workpiece is first prepared, and then the workpiece is processed to form the electronic device.

[0003] During the manufacture of electronic devices, adhesive sheets are sometimes attached to workpieces for various purposes. Regarding such adhesive sheets, Patent Document 1 (JP 2021-40099 A) discloses a composite sheet for forming a protective film having a specific configuration and attached to the backside of a semiconductor wafer.

[0004] In recent years, there has been a demand for reducing carbon dioxide emissions in order to realize a sustainable world. The present inventors wondered whether it would be possible to improve the amount of carbon dioxide emissions emitted during the manufacture of adhesive sheets, which are attached to workpieces during the manufacture of electronic devices.

[0005] Therefore, an object of the present invention is to provide a technique that can improve carbon dioxide emissions from an adhesive sheet for workpieces that is attached to electronic device works.

[0006] The present inventors focused on the release sheet included in the workpiece adhesive sheet and discovered that carbon dioxide emissions can be reduced by using dust-free paper as such a release sheet, leading to the present invention.

[0007] That is, in one aspect, the adhesive sheet for a workpiece according to the present invention comprises an adhesive layer configured to be attached to a workpiece for an electronic device, and a release sheet disposed on the adhesive layer and releasable from the adhesive layer. The release sheet comprises dust-free paper.

[0008] According to the present invention, a technique is provided that can improve carbon dioxide emissions from an adhesive sheet for workpieces that is adhered to electronic device works.

[0009] Fig. 1 is a schematic cross-sectional view showing an adhesive sheet according to an embodiment, and Fig. 2 is a schematic view showing an example of a method of using the adhesive sheet.

[0010] Hereinafter, an adhesive sheet for workpieces according to an embodiment of the present invention will be described.

[0011] The adhesive sheet for workpieces according to this embodiment is an adhesive sheet that is attached to electronic device workpieces for use. As will be described in detail later, electronic device workpieces refer to workpieces used in the manufacture of electronic devices. In other words, electronic device workpieces are processed to manufacture electronic devices. The adhesive sheet according to this embodiment is attached to electronic device workpieces for use at any stage in the manufacturing process of electronic devices.

[0012] In the following description, the "adhesive sheet for workpieces" may be simply referred to as the "adhesive sheet." Furthermore, the "electronic device workpieces" may be simply referred to as the "workpieces."

[0013] (Overview) Figure 1 is a schematic cross-sectional view showing an adhesive sheet 1 according to this embodiment. As shown in Figure 1, the adhesive sheet 1 has an adhesive layer 2, a release sheet 3, and a support film 4. These are laminated in the following order: support film 4, adhesive layer 2, and release sheet 3.

[0014] The adhesive layer 2 is configured to be attached to a workpiece, i.e., the adhesive layer 2 is attached to the workpiece at some stage in the manufacturing process of an electronic device.

[0015] The release sheet 3 is disposed on the adhesive layer 2 for the purpose of protecting the adhesive layer 2. The release sheet 3 is removable from the adhesive layer 2. There are no particular limitations on the timing at which the release sheet 3 is removed. The release sheet 3 is removed from the adhesive layer 2 at any time during the manufacturing process of the electronic device.

[0016] The support film 4 is provided to support the adhesive layer 2. However, the support film 4 is not an essential component. For example, if the adhesive layer 2 is self-supporting, the support film 4 may be omitted. The support film 4 may be laminated inseparably with the adhesive layer 2. Alternatively, if the adhesive sheet is an adhesive sheet for bonding components or a film for covering the back surface of a workpiece, as described below, the support film 4 may be separable from the adhesive layer 2 and peeled from the adhesive layer 2 at any time during the manufacturing process of the electronic device. Alternatively, a core layer 6 and a second adhesive layer 2' may be laminated between the adhesive layer 2 and the support film 4, in that order from the adhesive layer 2 side, so that the adhesive sheet 1 has a so-called double-sided adhesive sheet configuration. In this case, the support film 4 laminated with the second adhesive layer 2' is separable from the second adhesive layer 2' and peeled from the adhesive layer 2 at any time during the manufacturing process of the electronic device.

[0017] In this embodiment, the release sheet 3 comprises dust-free paper. More specifically, the release sheet 3 is made of dust-free paper. Dust-free paper emits less carbon dioxide than the resin films commonly used as the release sheet 3. For example, dust-free paper can be used with approximately one-quarter the carbon dioxide emissions of polyethylene terephthalate film. According to this embodiment, because dust-free paper is used as the release sheet 3, the carbon dioxide emissions of the entire adhesive sheet 1 can be reduced.

[0018] When the support film 4 is laminated so as not to be separable from the adhesive layer 2, it is realized by, for example, a resin film (such as a PET film). When the support film 4 can be separated from the adhesive layer 2, the support film 4 may be an adhesive layer-supporting pressure-sensitive adhesive sheet 4' having a pressure-sensitive adhesive layer for holding the adhesive layer 2, or a second release sheet 3' having the same function as the release sheet 3. When the adhesive sheet 1 has a core layer 6 and a second adhesive layer 2' and has a so-called double-sided adhesive sheet configuration, the support film 4 is usually the second release sheet 3'. When the adhesive sheet 1 has the second release sheet 3', the second release sheet 3' does not need to have dust-free paper, but from the viewpoint of reducing carbon dioxide emissions for the entire adhesive sheet 1, it is preferable that the second release sheet 3' have dust-free paper, just like the release sheet 3. In other words, it is preferable that both the release sheet 3 and the second release sheet 3' have dust-free paper.

[0019] Furthermore, adhesive sheets that are applied to electronic device workpieces are required to generate minimal amounts of foreign matter (dust, dirt, etc.) Using dust-free paper can meet this requirement.

[0020] The above is an outline of the adhesive sheet 1 according to this embodiment. Next, the adhesive sheet 1 will be described in detail.

[0021] (Method of Using the Adhesive Sheet) First, a method of using the adhesive sheet will be described. The method of using the adhesive sheet according to this embodiment includes an exposing step of exposing at least one surface of the adhesive layer as an exposed surface, an attaching step of attaching a workpiece to the exposed surface of the adhesive layer, and a peeling step of peeling the release sheet from the adhesive layer. As described above, the peeling step may be performed at any stage. For example, the exposing step may be achieved by the peeling step. That is, at least one surface of the adhesive layer may be exposed by peeling the release sheet from the adhesive layer. On the other hand, the peeling step may be performed after the attaching step. That is, the adhesive layer may be attached to the workpiece with the release sheet in place, and then the release sheet may be peeled off.

[0022] A preferred example of how to use the adhesive sheet will be described below with reference to FIG.

[0023] FIG. 2 is a schematic diagram showing an example of how to use the adhesive sheet 1. As shown in FIG. 2( a), first, the release sheet 3 is peeled off from the adhesive layer 2. This exposes one side of the adhesive layer 2. Next, the workpiece 5 is attached to the exposed surface of the adhesive layer 2. The necessary processing is then performed. This is an example of how to use the adhesive sheet 1. The adhesive layer 2 may ultimately be removed from the workpiece 5. Alternatively, the adhesive layer 2 may remain attached to the workpiece 5 as part of the final product. In either case, as in the example shown in FIG. 2, it is preferable to peel off the release sheet 3 before attaching the workpiece 5. While using dust-free paper can suppress the generation of foreign matter, it is difficult to completely eliminate the generation of foreign matter. Peeling off the release sheet 3 before attaching the workpiece 5 makes it more difficult for foreign matter originating from the dust-free paper to adhere to the workpiece 5.

[0024] When the adhesive sheet 1 has the second release sheet 3', the release sheet 3 is peeled off before the workpiece 5 is attached, and the second release sheet 3' is peeled off after the workpiece 5 is attached, thereby maintaining the handleability of the adhesive sheet 1 from the time the release sheet 3 is peeled off until the workpiece 5 is attached to the adhesive layer 2. Furthermore, if the second release sheet 3' does not contain dust-free paper, the above-mentioned effect of making it more difficult for foreign matter derived from the dust-free paper to adhere to the workpiece 5 can be obtained. On the other hand, if the second release sheet 3' is peeled off before the workpiece 5 is attached, and the release sheet 3 is peeled off after the workpiece 5 is attached, the above-mentioned effect of making it more difficult for foreign matter derived from the dust-free paper to adhere to the workpiece 5 cannot be obtained. However, having both the release sheet 3 and the second release sheet 3' contain dust-free paper has the advantage of making it possible to further reduce carbon dioxide emissions from the adhesive sheet 1 as a whole. In this case, the exposure process (the process of peeling off the second release sheet 3' instead of the release sheet 3 to expose one side of the adhesive layer 2 as an exposed surface for attachment to the workpiece 5) and the peeling process (the process of peeling off the release sheet 3) are carried out separately.

[0025] (Electronic Device Workpieces) Next, electronic device workpieces will be described. As mentioned above, electronic device workpieces are workpieces for manufacturing electronic devices. Examples of electronic device workpieces include circuit boards and semiconductor device workpieces. Examples of semiconductor device workpieces include semiconductor wafers, semiconductor chips, semiconductor packages, and chip sealing bodies produced by a fan-out packaging process. Examples of electronic device workpieces include workpieces processed by a processing method similar to the semiconductor device manufacturing process (e.g., lithography processing, etc.). For example, MEMS workpieces and wafers for forming LED chips (sapphire wafers, etc.) can also be used as electronic device workpieces. Among these, semiconductor device workpieces or workpieces processed by a processing method similar to the semiconductor device manufacturing process are preferred.

[0026] The thickness of the workpiece for an electronic device is not particularly limited, but in recent years, as electronic devices have become thinner, thinner workpieces than before have been adopted for electronic devices, and is, for example, about 5 to 100 μm, preferably about 10 to 70 μm. When the adhesive sheet is a back-grinding sheet described below, it is preferable that the thickness of the back surface of the workpiece after grinding is within the above range.

[0027] (Uses) The adhesive sheet according to the present embodiment may be used by being attached to a workpiece during the manufacture of an electronic device, and its specific use is not particularly limited. For example, the adhesive sheet may be at least one of an adhesive sheet for processing a workpiece, an adhesive sheet for supporting a workpiece, an adhesive sheet for joining components, a film for covering the back surface of a workpiece, a film for reinforcing bumps, and an interlayer insulating material for forming a build-up layer.

[0028] The "adhesive sheet for workpiece processing" is an adhesive sheet that is attached to a workpiece during processing of the workpiece. Examples of adhesive sheets for workpiece processing include dicing sheets, back-grinding sheets, and sheets for chip sealing processes.

[0029] A dicing sheet is a sheet for supporting a workpiece such as a semiconductor wafer when the workpiece is diced. When used as a dicing sheet, the adhesive layer is exposed, and then the workpiece is attached to the exposed surface. The workpiece is then diced, thereby forming multiple chips. After dicing, each chip is picked up from the adhesive layer. The workpiece may be diced using a mechanical means such as a blade, or the workpiece may be cut using a means such as a laser or plasma.

[0030] A backgrinding sheet is a sheet used to protect the back surface (the surface opposite to the circuit-formation surface) of a workpiece (such as a semiconductor wafer) having a circuit-formation surface when grinding the back surface. When used as a backgrinding sheet, the adhesive layer is exposed, and then the circuit-formation surface of the workpiece is attached to the exposed surface. The back surface of the workpiece is then ground. If necessary, the adhesive layer is then removed from the workpiece. The backgrinding sheet may be used in a workpiece singulation method (a so-called dicing-first method) in which the workpiece is a semiconductor wafer and the semiconductor wafer is singulated into multiple semiconductor chips by grinding along planned division lines formed by grooves pre-formed on the circuit-formation surface of the semiconductor wafer or modified regions pre-formed within the semiconductor wafer. The dicing-first method is a method suitable for obtaining thin semiconductor chips, and the resulting semiconductor chips tend to be thin.

[0031] The chip sealing process sheet is a sheet for fixing a plurality of chips (workpieces) in a predetermined arrangement on an adhesive layer of an adhesive sheet, covering the plurality of chips with a sealing material, and curing the sealing material to obtain a sealed body in which the plurality of chips are sealed. The chip sealing sheet may have a double-sided adhesive sheet configuration having a core layer and a second adhesive layer, the second adhesive layer being adhered to a support substrate such as a glass plate, and the plurality of chips (workpieces) being fixed to the support substrate via the adhesive sheet. To facilitate peeling of the workpiece or support substrate from the adhesive sheet, at least one of the adhesive layer, core layer, and second adhesive layer may contain thermally expandable particles, and the adhesive strength of the adhesive sheet to the workpiece or support substrate may be reduced by heating.

[0032] A "workpiece support adhesive sheet" is an adhesive sheet used to support workpieces (such as wafers and chips) during temporary storage or transportation. When used as a workpiece support adhesive sheet, the adhesive layer is exposed and the workpiece is attached, after which the workpiece is temporarily stored or transported. Furthermore, when the workpiece is a plurality of chips, an expanding process may be performed in which the spacing between the plurality of chips is expanded by stretching the workpiece support adhesive sheet while the plurality of chips are supported in a predetermined arrangement on the workpiece support adhesive sheet. Thereafter, the adhesive layer is removed from the workpiece as needed.

[0033] In the above-mentioned adhesive sheets (adhesive sheets for workpiece processing and adhesive sheets for workpiece support), a pressure-sensitive adhesive layer is usually used as the adhesive layer. The adhesive layer is usually supported by a support film. However, as mentioned above, if the adhesive layer is self-supporting, the support film may be omitted.

[0034] An "adhesive sheet for joining components" is a sheet used to join multiple components. The adhesive sheet for joining components is preferably a curable adhesive sheet that has curing properties, so that a strong bond can be obtained by temporarily bonding the components together with the curable adhesive sheet and then curing it. Below, the adhesive sheet for joining components will be explained using a curable adhesive sheet as an example. A curable adhesive sheet usually has a support film in addition to an adhesive layer. The adhesive layer is separable from the support film.

[0035] An example of a curable adhesive sheet is a die attachment film. For example, when used as a die attachment film, at least one surface of the adhesive layer is first exposed. Specifically, one of the release sheet and the support film is peeled off to expose one surface of the adhesive layer. Next, a workpiece (such as a semiconductor chip or a semiconductor wafer) is attached to the exposed surface of the adhesive layer. Thereafter, the other surface of the adhesive layer is exposed. That is, the other of the support film and the release sheet is peeled off to expose the other surface. Next, the other surface of the adhesive layer is attached to a substrate. Thereafter, the adhesive layer is cured. This allows the workpiece to be bonded to the substrate via the adhesive layer.

[0036] Another example of a curable adhesive sheet is a non-conductive adhesive film (NCF) that is interposed between the bump-forming surface of a face-down semiconductor chip and a substrate or the like to bond them together. For example, when used as an NCF, at least one surface of the adhesive layer is first exposed. Specifically, one of the release sheet and the support film is peeled off to expose one surface of the adhesive layer. Next, the bump-forming surface of a face-down semiconductor chip wafer, which is the workpiece, is attached to the exposed surface of the adhesive layer. This attachment may be performed using a vacuum laminator or the like. Thereafter, the other surface of the adhesive layer is exposed. That is, the other surface is exposed by peeling off the other of the support film and the release sheet. Next, the laminate of the adhesive sheet and the semiconductor wafer is diced to obtain a semiconductor chip with an NCF, and the other surface of the adhesive layer is attached to the substrate. The adhesive layer is then cured. This allows the workpiece to be bonded to the substrate via the adhesive layer.

[0037] Thermally conductive material-containing sinterable films can also be used as component bonding sheets. The adhesive layer of thermally conductive material-containing sinterable films contains a thermally conductive material, such as metal particles or boron nitride, preferably dispersed in particulate form in a resin. Thermally conductive material-containing sinterable films are typically used to secure power semiconductors. Specifically, one side of the adhesive layer is exposed by peeling off one of the release sheet and the support film. Next, a workpiece (such as a power semiconductor chip or a power semiconductor wafer) is attached to the exposed side of the adhesive layer. The other side of the adhesive layer is then exposed. That is, the other side is exposed by peeling off the other side of the support film and the release sheet. Next, the other side of the adhesive layer is attached to another component, such as a substrate. The adhesive layer is then sintered, bonding the workpiece to the other component via a layer made of a sintered thermally conductive material. The layer made of a sintered thermally conductive material functions as a thermal conduction path for heat generated by the power semiconductor.

[0038] A "film for covering the back surface of a workpiece" is a film for providing a covering layer of an adhesive layer on the back surface of a workpiece (e.g., a semiconductor wafer, a semiconductor chip, etc.) having a circuit-forming surface. Therefore, it adheres only to the workpiece as an adherend and is not used to join the workpiece to other components. The back surface of the workpiece here refers to the surface facing opposite the circuit-forming surface. Examples of films for covering the back surface of a workpiece include protective sheets (called chip back surface protective tape) attached to the back surface of face-down semiconductor chips and sheets (called anti-warping sheets) attached to the back surface of encapsulated bodies containing semiconductor chips to prevent warping. The covering layer may be provided directly on the back surface of the workpiece or may be provided via another layer.

[0039] For example, when used as a chip backside protection tape, after the adhesive layer is exposed, the backside of a semiconductor wafer as a workpiece is attached to the adhesive layer. The adhesive layer is then cured to form a coating layer. The semiconductor wafer is then diced using a dicing sheet as needed, and divided into multiple semiconductor chips. This results in semiconductor chips whose backsides are protected by a coating layer. Each semiconductor chip is then picked up and mounted face-down on another substrate, etc. If a support film is present on the adhesive sheet, the support film is removed at an appropriate time, such as after curing. The surface of the adhesive layer opposite the workpiece is left open, and does not adhere to other adherends.

[0040] For example, when used as an anti-warp sheet, after the adhesive layer is exposed, the backside of a semiconductor chip is attached to the exposed surface as a workpiece. Next, an encapsulating resin is supplied onto the adhesive layer so as to encapsulate the semiconductor chip. Next, the adhesive layer and the encapsulating resin are cured. This results in an encapsulated body with reduced warpage.

[0041] A "bump reinforcing film" is a film for forming a reinforcing film on a bump-forming surface of a semiconductor wafer by applying a curable reinforcing film-forming film to the bump-forming surface and curing the film, with the aim of reinforcing the bumps and the bumps themselves. For example, when used as a bump reinforcing film, at least one surface of the adhesive layer is first exposed. Specifically, one surface of the adhesive layer is exposed by peeling off one of the release sheet and the support film. Next, the bump-forming surface of the workpiece, a semiconductor wafer with bumps formed thereon, is applied to the exposed surface of the adhesive layer. This application may be performed using a vacuum laminator or the like. Thereafter, the other surface of the adhesive layer is exposed. That is, the other surface is exposed by peeling off the other of the support film and the release sheet. Next, the adhesive layer is cured. This allows a reinforcing film to be formed on the bump-forming surface of the workpiece.

[0042] An "interlayer insulating material for forming a buildup layer" is a film-like material used to form one buildup layer that constitutes a multilayer wiring board. For example, when used as an interlayer insulating material for forming a buildup layer, at least one surface of the adhesive layer is first exposed. Specifically, one of the release sheet and the support film is peeled off to expose one surface of the adhesive layer. Next, a circuit board, which is a workpiece, is attached to the exposed surface of the adhesive layer. At this time, a lamination process in which heat and pressure are applied to the adhesive layer may be performed via the other of the release sheet and support film that have not yet been peeled off. Thereafter, the other surface of the adhesive layer is exposed. That is, the other surface is exposed by peeling off the other of the support film and the release sheet. Next, the adhesive layer is cured. This forms a buildup layer on the circuit board. The formed buildup layer may be subjected to a drilling process in which holes are drilled in the buildup layer, a roughening process in which the buildup layer is roughened, a plating process in which a conductor layer is formed by plating on the roughened surface of the buildup layer, and a circuit formation process in which a circuit is formed on the conductor layer.

[0043] Preferably, the adhesive sheet is at least one selected from the group consisting of a dicing sheet, a backgrinding sheet, a die attachment film, a chip backside protective tape, and an anti-warping sheet. These uses may be combined. For example, the adhesive sheet may have the functions of both a die attachment film and a dicing sheet.

[0044] In the adhesive sheets for workpiece processing and the adhesive sheets for workpiece support, the adhesive layer 2 is ultimately removed from the workpiece 5, whereas in the adhesive sheets for component bonding, the film for covering the back surface of a workpiece, the film for bump reinforcing, and the interlayer insulating material for forming a build-up substrate, the adhesive layer 2 remains attached to the workpiece 5 as part of the final product. Of these, the adhesive sheets for workpiece processing and the adhesive sheets for workpiece support, from which the adhesive layer 2 is ultimately removed from the workpiece 5, are used in large quantities as indirect materials in the manufacturing process of electronic devices, and there is a strong demand for reducing carbon dioxide emissions.

[0045] (Form of adhesive sheet) Next, the form in which the adhesive sheet is provided will be described. The form of the adhesive sheet is not particularly limited. For example, the adhesive sheet may be provided in a form in which a long sheet is wound around a core material (hereinafter, sometimes referred to as a roll form). Alternatively, the adhesive sheet may be provided in a form in which a plurality of individual sheets are stacked (hereinafter, sometimes referred to as an individual sheet stack form).

[0046] (Adhesive Layer) Next, the adhesive layer will be described. As the adhesive layer, for example, a resin layer is used. The specific configuration of the adhesive layer is appropriately selected depending on the application. The adhesive layer 2 may be configured as a single layer, or may have a configuration in which multiple layers are laminated.

[0047] In a preferred embodiment, the adhesive layer is photocurable.

[0048] For example, when used in applications where a workpiece is to be peeled from the adhesive layer, photocuring can facilitate peeling of the workpiece. For example, when the adhesive sheet is a pressure-sensitive adhesive sheet such as a dicing sheet or a backgrinding sheet, the adhesive layer is first attached to the workpiece. Then, after the workpiece is processed, the adhesive layer is irradiated with light to cause a curing reaction. The curing reduces the adhesive strength between the adhesive layer and the workpiece. This allows the workpiece to be easily peeled from the adhesive layer. To impart photocurability to the adhesive layer, it is generally preferable that the adhesive layer contain a photocurable compound. In this case, it is also preferable that the adhesive layer contain a photopolymerization initiator. Examples of photocurable compounds include compounds having a group containing an unsaturated carbon bond, such as a methacryloyl group or an acryloyl group. Such compounds are preferably used in combination with a photoradical polymerization initiator. Alternatively, an adhesive layer using a compound having a cyclic ether group, such as an epoxy resin, and a photocationic polymerization initiator may be used as a photocurable adhesive layer. From the viewpoint of rapidly progressing the photocuring reaction, it is preferable that the adhesive layer contain a compound having a group containing an unsaturated carbon bond and a photoradical polymerization initiator. Examples of the compound having a group containing an unsaturated carbon bond include a compound having two or more methacryloyl groups or acryloyl groups in one molecule, such as tricyclodecane dimethanol diacrylate, and examples of the photoradical polymerization initiator include an intramolecular cleavage-type radical polymerization initiator such as α-hydroxyalkylphenone.

[0049] The adhesive layer may also contain thermally expandable particles to facilitate peeling, which can reduce the adhesive strength between the adhesive layer and the object to be peeled (the workpiece or the supporting substrate) by heating, facilitating peeling.

[0050] Alternatively, when the adhesive sheet is a curable adhesive sheet such as a die attachment film, and it is intended that the support film will be peeled off from the adhesive layer, the photocuring reaction can facilitate peeling of the support film from the adhesive layer. Note that when the adhesive layer of the die attachment film is photocurable, the adhesive layer generally also contains a thermosetting compound in order to obtain adhesive strength after die bonding.

[0051] Alternatively, if the adhesive sheet is a film for covering the back surface of a workpiece, after attaching the adhesive sheet to the workpiece, it is possible to obtain a hard covering layer by irradiating it with light to harden the adhesive layer.

[0052] As described above, the adhesive layer may be configured to be photocurable depending on the application. However, if the adhesive layer is photocurable, it must be shielded from light during storage to prevent unintended photocuring reactions. In this regard, according to this embodiment, dust-free paper is used as the release sheet. Dust-free paper has light-shielding properties. Therefore, the adhesive sheet according to this embodiment is preferable from the standpoint of light-shielding properties. Whether the adhesive sheet is in a roll form or a laminated form of individual sheets, the dust-free paper in the outermost layer suppresses light from entering the adhesive layer. For example, according to this embodiment, the adhesive sheet can be stored without using light-shielding packaging material. Alternatively, even if light-shielding packaging material is used, it may take some time between unpacking and use. According to this embodiment, exposure to light between unpacking and use can be prevented, thereby more reliably preventing unintended curing. When the adhesive layer contains a compound having a group containing an unsaturated carbon bond and a photoradical polymerization initiator, the photocuring reaction is likely to proceed, and therefore it is highly necessary to prevent unintended photocuring reactions from proceeding.

[0053] The thickness of the adhesive layer is set depending on the application and is not particularly limited. For example, the thickness of the adhesive layer is 1 μm to 1000 μm. When used as a dicing sheet, the thickness of the adhesive layer is, for example, 3 to 50 μm. When used as a backgrinding sheet, the thickness of the adhesive layer is, for example, 3 to 500 μm. When the backgrinding sheet is attached to the bump-formed surface of a workpiece on which bumps are formed, a third adhesive layer 2″ for embedding the bumps may be formed between the adhesive layer 2 and the support film 4. In this case, it is preferable that the total thickness of the adhesive layer 2 and the third adhesive layer 2″ is within the above range. When used as a sheet for a chip sealing process, the thickness of the adhesive layer is, for example, 2 to 300 μm. When the sheet for a chip sealing process has a configuration of a double-sided adhesive sheet having a core material layer 6 and a second adhesive layer 3′, the thickness of the second adhesive layer 3′ is, for example, 2 to 300 μm. When used as a pressure-sensitive adhesive sheet for supporting a workpiece during temporary storage or transportation of the workpiece, the thickness of the adhesive layer is, for example, 3 to 50 μm. When used as a die attachment film, the thickness of the adhesive layer is, for example, 3 to 200 μm. When used as an NCF, the thickness of the adhesive layer is, for example, 5 to 150 μm. When used as a thermally conductive material-containing firing film, the thickness of the adhesive layer is, for example, 30 to 200 μm. When used as a protective sheet (chip back surface protective tape) to be attached to the back surface of a face-down semiconductor chip, the thickness of the adhesive layer is, for example, 5 to 200 μm. When used as a sheet (referred to as an anti-warping sheet) to be attached to the back surface of an encapsulant containing a semiconductor chip to prevent warping, the thickness of the adhesive layer is, for example, 5 to 200 μm. When used as a bump reinforcing film, the thickness of the adhesive layer is, for example, 1 to 200 μm. When used as an interlayer insulating material for forming a build-up layer, the thickness of the adhesive layer is, for example, 3 to 100 μm.

[0054] (Dust-free Paper) Next, a description will be given of dust-free paper. Dust-free paper is paper that generates less dust than regular paper.

[0055] For example, dust-free paper can be used that generates 2,000 or fewer particles of airborne dust 0.3 μm or larger per cubic foot in any of the following dust generation tests: rubbing, crumpling, and tearing. Rubbing: Two A5-size (210 mm x 148 mm rectangular) test pieces are prepared, and the front and back of the test paper are overlapped and rubbed together for 200 seconds at a rate of three times every 10 seconds. Crushing: An A5-size (210 mm x 148 mm rectangular) test piece is rubbed by hand at a rate of once every 15 seconds for 200 seconds. Tearing: An A5-size (210 mm x 148 mm rectangular) test piece is torn in four places once every 5 seconds, and then rubbed for 180 seconds in the same manner as the crumpling test. The tests are conducted in a clean bench, and the number of airborne particles is measured using a light-scattering particle counter. Such a particle counter can be, for example, one manufactured by Rion Co., Ltd. In the dust generation test, the number of floating dust particles of 0.3 μm or larger generated is preferably 1,000 or less particles per cubic foot, and more preferably 300 or less particles per cubic foot.

[0056] As the material for dust-free paper, paper having a plant fiber layer and impregnated with an impregnating resin can be used. The impregnation with the impregnating resin suppresses fiber scattering, thereby achieving the function of dust-free paper. Furthermore, dust-free paper using plant fibers is more suitable because it produces particularly low carbon dioxide emissions. Examples of plant fibers include pulp, which is generally composed of polysaccharides such as cellulose and has a structure rich in hydrophilic groups such as hydroxyl groups, resulting in relatively low electrical resistance and preventing charging of the release sheet. As the impregnating resin, a water-based binder is preferred, as it has the potential to further reduce carbon dioxide emissions. For example, a water-based binder combining an acrylic resin and an ethylene vinyl acetate copolymer can be used.

[0057] As mentioned above, the use of dust-free paper can reduce carbon dioxide emissions from the entire adhesive sheet. In addition, dust-free paper is also preferable in terms of preventing blocking and reducing electrostatic charge. For example, when an adhesive sheet is provided in a roll form, the release sheet contacts the adjacent layer (e.g., the support film, or, if no support film is present, the adhesive layer of the adjacent layer) on the side opposite the adhesive layer. During use, the release sheet is peeled from the adjacent layer and unwound. During this process, blocking and peeling charge may occur. However, dust-free paper has a moderately uneven surface. Therefore, the contact area between the dust-free paper and the adjacent layer from which it is being peeled is relatively small. As a result, blocking is prevented. Furthermore, peeling charge during unwounding is also suppressed. The arithmetic mean roughness (Ra) of the surface of dust-free paper is typically about 0.5 to 5 μm.

[0058] Furthermore, when the dust-free paper has a plant fiber layer impregnated with an impregnating resin, it is preferable that the impregnating resin contains an antistatic agent. The inclusion of an antistatic agent can further suppress peeling static electricity. If a resin film is used as the release sheet, an antistatic coating layer must be formed on the resin film to impart antistatic properties. In contrast, according to this embodiment, by adding an antistatic agent to the impregnating resin, it is possible to easily impart antistatic properties to the dust-free paper used as the release sheet.

[0059] It is preferable that a release layer be provided as the outermost layer on the release surface (the surface in contact with the adhesive layer) of the dust-free paper. The provision of the release layer allows the release sheet to be easily peeled from the adhesive layer laminated on the release sheet. The release agent may be at least one selected from the group consisting of silicone-based release agents, alkyd-based release agents, polyolefin-based release agents, and urethane-based release agents. The thickness of the release layer is usually about 0.01 μm to 1 μm, and preferably 0.01 μm to 0.2 μm.

[0060] It is also preferable that a smoothing layer be provided on the release surface of the dust-free paper. As described above, the surface of the dust-free paper has a moderate amount of unevenness. However, if the release surface has unevenness, the unevenness will be transferred to the adhesive layer, and the smoothness of the adhesive layer surface will be lost. Therefore, in applications where a uniform thickness of the adhesive layer is required due to reasons such as the thinness of the workpiece (for example, applications in which the adhesive layer is attached to a workpiece for a semiconductor device or a MEMS), it is preferable that a smoothing layer be provided on the release surface.

[0061] The smoothing layer can be formed, for example, by coating a resin on the surface of dust-free paper. The resin to be coated may contain, for example, an energy ray-curable compound and be cured by irradiation with energy rays after application. Examples of energy rays include electron beams and ultraviolet rays. Alternatively, the smoothing layer can be realized by laminating a resin film (e.g., a thin polyethylene film with a thickness of 5 μm or less) on the surface of the dust-free paper. The surface of the smoothing layer typically has an arithmetic mean roughness Ra of less than 500 nm. The arithmetic mean roughness Ra of the surface of the smoothing layer is preferably 3 to 300 nm, more preferably 5 to 200 nm. Furthermore, when the release surface of the dust-free paper has both a smoothing layer and a release layer, the arithmetic mean roughness Ra of the surface of the release layer is preferably 1 to 200 nm, more preferably 3 to 100 nm.

[0062] Furthermore, when the adhesive sheet is used for applications such as an interlayer insulating material for forming build-up layers, the adhesive layer may contain a high-boiling point solvent such as naphtha. Therefore, to prevent the dust-free paper from absorbing such solvents and changing its quality, a solvent-resistant layer may be provided on the release surface of the dust-free paper. The solvent-resistant layer can be provided by coating the surface of the dust-free paper with a resin, similar to the smoothing layer, and the smoothing layer may also serve as the solvent-resistant layer.

[0063] The thickness of the dust-free paper is not particularly limited, but is, for example, 30 to 300 μm, preferably 50 to 200 μm.

[0064] (Manufacturing Method) The manufacturing method of the adhesive sheet is not particularly limited, but a preferred example of the manufacturing method of the adhesive sheet will be described below.

[0065] First, dust-free paper is prepared as a release sheet. Then, a composition in which a release agent is diluted with a solvent is applied to the prepared dust-free paper, and the composition is dried by heating to volatilize the solvent, thereby obtaining a release layer. Next, an adhesive composition containing a substance that will serve as a precursor to the adhesive layer is applied to the release layer. After application, the adhesive composition is dried by heating. For example, the composition in which a release agent is diluted with a solvent or the adhesive composition is dried in an oven. This forms an adhesive layer. Thereafter, a support film is attached to the adhesive layer as needed, and the adhesive sheet according to this embodiment is obtained.

[0066] The above-described manufacturing method is preferable from the viewpoint of productivity, etc. If a resin film is used as the release sheet, the resin film may shrink due to heat when the adhesive composition is dried by heating. On the other hand, dust-free paper generally has higher heat resistance than resin film. For example, when dust-free paper having a plant fiber layer, such as pulp, is used as the release sheet, dust-free paper with high heat resistance is obtained. Therefore, by using dust-free paper with high heat resistance as the release sheet, shrinkage of the release sheet can be prevented when the adhesive composition is dried by heating. This can suppress wrinkles, making it easier to obtain an adhesive sheet of the desired width. Furthermore, it becomes possible to dry the adhesive composition at a higher temperature, thereby improving the productivity of the adhesive sheet.

[0067] (Supplementary Note) The present invention has been described above using the embodiments. Representative configurations of the present invention will be summarized below as supplementary notes.

[0068] (Appendix 1) An adhesive sheet for a workpiece, comprising an adhesive layer configured to be attached to a workpiece for an electronic device, and a release sheet disposed on the adhesive layer and releasable from the adhesive layer, the release sheet having dust-free paper. (Appendix 2) The adhesive sheet for a workpiece according to Appendix 1, wherein the adhesive sheet is at least one material selected from the group consisting of an adhesive sheet for joining components, a film for covering the back surface of a workpiece, a film for reinforcing bumps, and an interlayer insulating material for forming build-up layers. (Appendix 3) The adhesive sheet for a workpiece according to Appendix 1 or 2, wherein the adhesive layer is photocurable. (Appendix 4) The adhesive sheet for a workpiece according to any of Appendices 1 to 3, wherein the dust-free paper has a release surface facing the adhesive layer and a smoothing layer provided on the release surface. (Appendix 5) The adhesive sheet for a workpiece according to any of Appendices 1 to 4, wherein the dust-free paper has a plant fiber layer impregnated with a resin. (Appendix 6) An adhesive sheet for workpieces according to Appendix 5, wherein the resin contains an antistatic agent. (Appendix 7) An adhesive sheet for workpieces according to Appendix 1 or 2, wherein the release sheet is configured to be peeled off before the adhesive layer is attached to the workpiece for an electronic device. (Appendix 8) A method for producing an adhesive sheet for workpieces according to any of Appendices 1 to 7, comprising the steps of preparing dust-free paper, applying an adhesive composition containing a substance that will be a precursor of the adhesive layer onto the dust-free paper, and, after the applying step, drying the adhesive composition by heating to form an adhesive layer.

[0069] REFERENCE SIGNS LIST 1 Work adhesive sheet 2 Adhesive layer 3 Release sheet 4 Support film 5 Work for electronic device

Claims

1. An adhesive sheet for a workpiece, comprising: an adhesive layer configured to be affixed to a workpiece for an electronic device; and a release sheet disposed on the adhesive layer and releasable from the adhesive layer, the release sheet having dust-free paper.

2. An adhesive sheet for workpieces according to claim 1, which is at least one selected from the group consisting of adhesive sheets for processing workpieces, adhesive sheets for supporting workpieces, adhesive sheets for joining components, films for covering the rear surface of workpieces, films for reinforcing bumps, and interlayer insulating materials for forming build-up layers.

3. An adhesive sheet for a workpiece according to claim 1 or 2, wherein the adhesive layer has photocuring properties.

4. An adhesive sheet for workpieces according to claim 1 or 2, wherein the dust-free paper has a release surface facing the adhesive layer, and further has a smoothing layer provided on the release surface.

5. An adhesive sheet for workpieces according to claim 1 or 2, wherein the dust-free paper has a plant fiber layer impregnated with a resin.

6. The adhesive sheet for a workpiece according to claim 5, wherein the resin contains an antistatic agent.

7. An adhesive sheet for a workpiece according to claim 1 or 2, wherein the release sheet is configured to be peeled off before the adhesive layer is attached to the electronic device workpiece.

8. A method for manufacturing an adhesive sheet for workpieces as described in claim 1 or 2, comprising the steps of: preparing the dust-free paper; applying an adhesive composition containing a substance that is a precursor of the adhesive layer onto the dust-free paper; and, after the applying step, drying the adhesive composition by heating to form the adhesive layer.

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