Adhesive tape for plating process

Abstract

To provide an adhesive tape for plating process, which is an adhesive tape to be stuck on the back side of a lead frame as a masking tape in a method of partially plating the front side of a lead frame with silver using an electrodeposited photoresist, and which can be peeled off without being soaked with plating solution or peeled off without leaving any adhesive residue, and which can suppress poor formation of a resist coating film on the overhanging portion and poor peeling of the resist coating film even when an overhanging portion (step portion) is formed on the back side of the lead frame.SOLUTION: An adhesive tape is made by laminating a substrate and a specific silicone adhesive layer, in which an ultraviolet transmittance is 70% or more at a wavelength of 365 nm from the substrate side of the adhesive tape, and a 180° peel adhesive strength of the silicone adhesive layer against a SUS plate is 0.5 to 4.5 N / 25 mm, and a bending angle of the adhesive tape measured by a specified measurement method is 130° or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This invention relates to an adhesive tape for masking the back side of a lead frame from the electrodeposited photoresist and silver plating in a method for partially plating the front side of a lead frame with silver using an electrodeposited photoresist. [Background technology]

[0002] In recent years, in response to the trend toward smaller and thinner semiconductor devices, various so-called QFN (Quad Flat Non-lead) type semiconductor devices have been proposed. These semiconductor devices use lead frames, a semiconductor element mounted on the mounting surface of which is encapsulated with encapsulating resin, and a portion of the leads is exposed on the backside. Generally, the lead frames used in manufacturing these semiconductor devices have a die pad for mounting a semiconductor chip and multiple lead terminals surrounding the die pad for connecting to the semiconductor element. A semiconductor element is mounted on the die pad of the lead frame, and the semiconductor element and the lead tips are connected with gold or other wires, followed by resin encapsulation to produce a semiconductor device. To connect the semiconductor element and the lead tips with gold or other wires, the lead tips are typically plated with highly conductive silver. A plating method using a photosensitive electrodeposited photoresist that is resistant to plating solutions is used for this silver plating (see, for example, Patent Document 1).

[0003] In this plating method using electrodeposited photoresist, the lead frame is first acid-washed and rinsed with water, after which an electrodeposited photoresist coating is formed over the entire lead frame. Next, a photomask (pattern plate) is used to expose predetermined areas to ultraviolet light, curing only the exposed areas. A development process is then performed to remove the electrodeposited photoresist from the unexposed areas, exposing the areas to be silver-plated. The lead frame is then rinsed with hot water, and the entire lead frame is immersed in a plating solution. While stirring, plating is performed at a predetermined current density and for a predetermined time, resulting in silver plating of the desired thickness on the exposed areas. The electrodeposited photoresist is then stripped using a stripper, resulting in a lead frame with silver plating only in the predetermined areas.

[0004] In this plating method, an electrodeposited photoresist coating is formed over the entire lead frame, but a photomask (pattern plate) is not required for the back side of the lead frame, which is not to be plated, and there is no need to mask it with electrodeposited photoresist; to reduce the need for expensive electrodeposited photoresist solution, the back side of the lead frame can be masked with adhesive tape or similar. In this case, the adhesive tape used for masking is first applied to the back side of the lead frame, and it must be durable and chemical-resistant so that it will not peel off even after going through all the steps of the plating method using electrodeposited photoresist (acid washing, resist electrodeposition, exposure, development, silver plating, resist stripping, electrolytic degreasing, surface roughening, etc.). Furthermore, it must be easily removable, so that the adhesive tape can be removed without leaving any adhesive residue or deforming the lead frame.

[0005] As for adhesive tape used for masking in the plating process, Patent Document 2 discloses an adhesive masking tape that simultaneously satisfies both masking properties in the plating process and removability (no adhesive residue) in the adhesive tape peeling process, and is characterized by being made from an acrylic adhesive and having a thickness of 4 μm or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 10-135391 [Patent Document 2] Patent Publication No. 2006-348212 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a masking adhesive tape such as that described in Patent Document 2 is applied to the back side of a lead frame, the resistance and chemical resistance throughout the entire process of a plating method using an electrodeposited photoresist are insufficient, and plating solution may seep in from the end face of the adhesive tape, resulting in plating adhering to the back side of the lead frame or peeling off the adhesive tape.

[0008] Furthermore, when the surface side (upper side of Figure 1) of a lead frame 10 consisting of a die pad 11 portion and leads 12 portion as shown in Figure 1, on which a semiconductor element is mounted, is sealed with resin, if a lead frame 10 is used in which overhang portions 13 (step portions) are formed on the edges of the back side of the die pad 11 and / or leads 12 by etching or the like so that the resin can partially wrap around to the back side (lower side of Figure 1) of the lead frame 10 to make it difficult for the die pad 11 and / or leads 12 to separate from the sealing resin, when adhesive tape 20 is attached as masking to the back side of the lead frame 10 where plating is not to be performed, as shown in Figure 2, a gap 14 is usually formed between the adhesive tape 20 and the overhang portion 13 on the back side of the lead frame 10, and electrodeposited photoresist liquid enters this gap 14, forming a resist coating also on the overhang portion 13 on the back side of the lead frame 10. However, when the adhesive tape 10 is applied, or due to deformation of the adhesive during each plating process or cleaning / drying, or due to bending of the film substrate, the adhesive surface of the adhesive tape 20 comes into contact with and adheres to the overhang portion 13, which blocks the gap 14 between the overhang portion 13 and the adhesive tape 20, preventing the resist liquid from entering the gap 14 and resulting in poor formation of the electrodeposited photoresist coating film, which causes plating to adhere to the overhang portion 13 on the back side of the lead frame 10, or in the resist stripping process after plating, the resist stripping liquid does not enter the gap 14, resulting in poor stripping of the resist coating film from the overhang portion 13.

[0009] In view of the above-mentioned problems, the present invention aims to provide an adhesive tape for a plating process, which is applied as a masking tape to the back surface of a lead frame in a method of partially plating the front surface of a lead frame with silver using an electrodeposited photoresist, and which is free from seepage of plating solution and tape peeling, can be peeled off after plating without leaving any adhesive residue, and can suppress poor formation of an electrodeposited photoresist coating film at the overhanging portion and poor peeling of the resist coating film after plating, even if an overhanging portion (step portion) is formed on the back surface of the lead frame. [Means for solving the problem]

[0010] The pressure-sensitive adhesive tape for use in a plating process of the present invention is a pressure-sensitive adhesive tape that is applied to mask the back surface of a lead frame in a method of partially plating the front surface of a lead frame with silver using an electrodeposited photoresist, the pressure-sensitive adhesive tape comprising a substrate and at least a silicone pressure-sensitive adhesive layer laminated on one surface of the substrate, the silicone pressure-sensitive adhesive layer being a cured product of an addition-cure silicone pressure-sensitive adhesive composition, the silicone pressure-sensitive adhesive composition containing 35 to 55 mass % of an MQ resin, the transmittance of ultraviolet light at a wavelength of 365 nm from the substrate surface side of the pressure-sensitive adhesive tape being 70% or more, the 180° peel adhesive strength of the silicone pressure-sensitive adhesive layer against a SUS plate being 0.5 to 4.5 N / 25 mm, and the bending angle of the pressure-sensitive adhesive tape measured by the following predetermined measuring method being 130° or less.

[0011] (Method for measuring the curvature angle) Under an environment of 23±2°C and 50±10% RH, a 25 mm wide x 150 mm long adhesive tape was attached to one side of a 52 mm wide x 75 mm long x 2 mm thick acrylic plate, with the adhesive surface (25 mm wide x 50 mm long) of the tape aligned parallel to the length of the plate, so that the tape extended 100 mm from one end of the acrylic plate in the longitudinal direction, but not across the width of the acrylic plate. Next, the acrylic plate with the attached adhesive tape was fixed with the end face of the plate facing downwards, with the length of the acrylic plate parallel to the direction of gravity. The 25 mm wide x 100 mm long portion of the adhesive tape extending beyond the top edge of the acrylic plate was tilted toward the adhesive surface under its own weight, thereby bending the adhesive tape. An image was then taken from one end face of the acrylic plate in the transverse direction to reveal the curved state of the adhesive tape. In the captured image, the start point is the longitudinal tip of the base surface of the curved portion of the adhesive tape, and the end point is a point 5 mm from the longitudinal tip of the base surface of the curved portion of the adhesive tape along the base surface of the adhesive tape toward the other longitudinal end of the adhesive tape. The line segment connecting the start point and the end point is the inclination line of the adhesive tape, and the line segment representing the base surface of the portion of the adhesive tape attached to the acrylic plate is the reference line. The angle between the line extended upward in the direction of gravity from the reference line and the line extended from the inclination line of the adhesive tape toward the end point is measured as the angle on the upward side in the direction of gravity and in the direction in which the adhesive tape is tilted. If the 25 mm wide x 100 mm long portion of the adhesive tape extending beyond the upper end of the acrylic plate does not tilt due to its own weight or tilts toward the non-adhesive side, the angle of curvature is recorded as 0°. If the line extended upward in the direction of gravity from the reference line and the line extended from the inclination line of the adhesive tape toward the end point do not intersect, the angle of curvature is recorded as 180° or more.

[0012] One embodiment of the pressure-sensitive adhesive tape for plating process of the present invention is characterized in that the substrate is a polyethylene terephthalate film having a thickness of 50 to 100 μm.

[0013] In one embodiment of the pressure-sensitive adhesive tape for plating process of the present invention, the thickness of the silicone pressure-sensitive adhesive layer is 1 to 10 μm. [Effects of the Invention]

[0014] According to the adhesive tape for use in a plating process of the present invention, in a method for partially plating the front surface of a lead frame with silver using an electrodeposited photoresist, the adhesive tape to be applied as a masking to the rear surface of the lead frame has an adhesive layer made of a specific silicone adhesive, and by specifying the ultraviolet transmittance, adhesive strength, and bending angle of the adhesive tape measured by a predetermined method of the adhesive tape, it is possible to provide an adhesive tape for use in a plating process that does not allow the plating solution to seep in or the tape to peel off, and can be peeled off without leaving any adhesive residue after plating, and that can suppress poor formation of an electrodeposited photoresist coating film at the overhanging portion and poor peeling of the resist coating film after plating, even if an overhanging portion (step portion) is formed on the rear surface of the lead frame. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view showing an example of a lead frame before the adhesive tape of the present invention is attached. [Figure 2] 1 is a schematic cross-sectional view showing an example of a lead frame having a pressure-sensitive adhesive tape of the present invention attached to its rear surface side. [Figure 3] 1 is a schematic cross-sectional view showing one embodiment of a pressure-sensitive adhesive tape of the present invention. [Figure 4] 1A and 1B are schematic diagrams illustrating a sample for measuring the bending angle of the pressure-sensitive adhesive tape of the present invention, in which FIG. 1A is a schematic top view and FIG. 1B is a schematic side view. [Figure 5] 1 is a schematic diagram illustrating the bending angle of the pressure-sensitive adhesive tape of the present invention. [Figure 6] FIG. 2 is a schematic diagram illustrating a slope line in measuring the bending angle of the pressure-sensitive adhesive tape of the present invention. [Figure 7] 1 is a process flow showing an example of a silver plating method using the pressure-sensitive adhesive tape of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the pressure-sensitive adhesive tape for use in a plating process of the present invention will be described in detail.

[0017] As shown in Fig. 3, the pressure-sensitive adhesive tape for plating of the present invention is a pressure-sensitive adhesive tape 20 comprising at least a substrate 21 and a silicone pressure-sensitive adhesive layer 22. In a method for partially plating the front surface of a lead frame using an electrodeposited photoresist, the pressure-sensitive adhesive tape 20 to be applied as a mask to the rear surface of the lead frame has an ultraviolet transmittance of 70% or more at a wavelength of 365 nm from the side of the substrate 21 of the pressure-sensitive adhesive tape 20 that is not in contact with the silicone pressure-sensitive adhesive layer 22 (the lower side in Fig. 3). This ensures that, in a lead frame 10 having an overhang 13 formed on the rear surface to which the adhesive tape 20 is applied, even if a negative electrodeposited photoresist in which exposed portions remain after development is used, the electrodeposited photoresist coating film formed on the overhang 13 on the rear surface is sufficiently exposed and the plating resist performance is not impaired.

[0018] Furthermore, by using an addition-curing silicone adhesive, which has excellent resistance to various chemicals, and setting the 180° peel adhesive strength from the stainless steel plate to 0.5 to 4.5 N / 25 mm, it is possible to prevent plating from seeping in from the attached edge of the adhesive layer of the adhesive tape 20, ensuring resistance to tape peeling and chemical resistance in each process. Furthermore, by setting the bending angle of the adhesive tape 20, measured by a predetermined method, to 130° or less, it is possible to prevent the adhesive surface of the adhesive tape 20 from contacting the overhang portion 13 due to deformation of the adhesive tape 20, thereby preventing poor formation of a resist coating on the overhang portion 13 and poor peeling of the resist coating after plating.

[0019] <Base material> The substrate of the adhesive tape for plating process of the present invention can be suitably a film substrate made of a material that is resistant to the chemicals used in plating methods using electrodeposited photoresist. Furthermore, in lead frames with overhangs (steps) formed on the backside of the lead frame by etching or other methods, a gap is formed between the adhesive tape and the step surface of the overhang where the adhesive tape is attached, and an electrodeposited photoresist coating is formed without masking. Therefore, in the case of a negative resist in which the exposed portion remains after development, exposure of the resist coating from the adhesive tape substrate side is necessary. In this case, it is preferable that the substrate is transparent to the actinic rays used for exposure. The substrate's transparency is preferably such that its ultraviolet transmittance at a wavelength of 365 nm is 70% or more, more preferably 75% or more, and even more preferably 80% or more.

[0020] Examples of synthetic resin materials constituting such film substrates include polyester-based resins, polyolefin-based resins, cyclic polyolefin-based resins, polyamide-based resins, polyether ether ketone, polyether sulfone, etc. Among these, from the viewpoints of mechanical strength, heat resistance, and transparency, polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferred, with polyethylene terephthalate being particularly preferred.

[0021] The thickness of the substrate is preferably in the range of 50 to 250 μm, more preferably 50 to 150 μm, and further preferably 50 to 100 μm, from the viewpoints of imparting rigidity to the adhesive tape so as to satisfy the above-mentioned bending angle and of the peelability of the adhesive tape.

[0022] The surface of the substrate on which the pressure-sensitive adhesive layer is to be formed is preferably subjected to a surface treatment to improve adhesion to the pressure-sensitive adhesive layer to be laminated thereon, such as corona discharge treatment, ultraviolet irradiation treatment, plasma treatment, and primer treatment.

[0023] <Silicone adhesive layer> The adhesive layer of the pressure-sensitive adhesive tape for plating processes of the present invention uses a silicone adhesive that is resistant to the chemicals used in plating methods that use electrodeposited photoresists. Silicone adhesives are classified into addition-curing silicone adhesives, peroxide-curing silicone adhesives, etc. depending on their curing mechanism. Addition-curing silicone adhesives are preferred because they can be cured (crosslinked) at relatively low temperatures, have good productivity, do not produce by-products during curing, and are resistant to the chemicals used in plating processes.

[0024] Examples of the addition-curing silicone adhesive include a diorganopolysiloxane having an alkenyl group as a silicone rubber component and a silicone resin component having an M unit (RSiO 1 / 2 : R is an organo group) and Q unit (SiO 4 / 2 An addition-curable silicone pressure-sensitive adhesive composition containing a polyorganosiloxane (so-called MQ resin) consisting of methyl methyl siloxane (MQ resin), a crosslinker, and a curing catalyst is preferably used. A silicone pressure-sensitive adhesive layer can be formed by addition-curing this pressure-sensitive adhesive composition to crosslink the silicone rubber. By varying the molecular weight of the silicone rubber component, the crosslink density, and the MQ resin content, chemical resistance in the plating process using an electrodeposited photoresist can be ensured, and a pressure-sensitive adhesive layer with good plating masking properties and removability can be obtained.

[0025] Examples of alkenyl groups in the alkenyl-containing diorganopolysiloxane in the addition-curable silicone pressure-sensitive adhesive composition include vinyl, allyl, hexenyl, octenyl, acryloylpropyl, acryloylmethyl, methacryloylpropyl, acryloxypropyl, acryloxymethyl, methacryloxypropyl, methacryloxymethyl, cyclohexenylethyl, and vinyloxypropyl groups. Of these, lower alkenyl groups such as vinyl and allyl are preferred, with vinyl being particularly preferred from an industrial viewpoint.

[0026] The organo group of the diorganopolysiloxane having an alkenyl group is, for example, a hydrocarbon group having 1 to 8 carbon atoms, preferably a hydrocarbon group having 1 to 4 carbon atoms, and more preferably an alkyl group (which may be linear or branched) having 1 to 4 carbon atoms. A typical example of the organo group is a methyl group.

[0027] The diorganopolysiloxane having an alkenyl group is preferably a diorganopolysiloxane having two or more vinyl groups per molecule, and examples thereof include linear diorganopolysiloxanes having vinyl groups only at both ends, linear diorganopolysiloxanes having vinyl groups at both ends and in side chains, branched diorganopolysiloxanes having vinyl groups only at the ends, and branched diorganopolysiloxanes having vinyl groups at the ends and in side chains.

[0028] The weight-average molecular weight of the alkenyl group-containing diorganopolysiloxane is usually in the range of 20,000 to 1,300,000, and from the viewpoint of ensuring good plating masking properties and removability and adhesive strength, it is preferably in the range of 50,000 to 1,000,000, and more preferably in the range of 70,000 to 700,000. Note that the weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0029] The addition-curable silicone pressure-sensitive adhesive composition may contain two or more types of alkenyl group-containing diorganopolysiloxanes.

[0030] The addition-curable silicone pressure-sensitive adhesive composition contains M units (RSiO 1 / 2 : R is an organo group) and Q unit (SiO 4 / 2 Preferably, the MQ resin contains an MQ polyorganosiloxane consisting of the organo group. The organo group is the same as the examples of the organo group in the diorganopolysiloxane having an alkenyl group. More preferably, the MQ resin is a non-reactive MQ resin in which the organo group does not have a reactive substituent such as a hydroxyl group or an alkenyl group.

[0031] The molar ratio of M units to Q units (M units / Q units) of the MQ resin is preferably in the range of 0.5 to 1.7, more preferably in the range of 0.7 to 1.5, from the viewpoint of imparting adhesiveness.

[0032] The weight average molecular weight of the MQ resin is preferably in the range of 1,000 to 15,000, more preferably in the range of 3,000 to 10,000, and even more preferably in the range of 5,000 to 8,000, from the viewpoint of imparting adhesiveness and suppressing plating penetration.

[0033] The content of the MQ resin in the addition-curable silicone pressure-sensitive adhesive composition is preferably 35 to 55% by mass. By keeping the content of the MQ resin within this range, it is possible to suppress plating penetration and adhesive residue when peeling off the tape.

[0034] The addition-curable silicone pressure-sensitive adhesive composition may contain two or more types of MQ resins.

[0035] As the crosslinking agent in the addition-curable silicone pressure-sensitive adhesive composition, for example, an organohydrogenpolysiloxane having an SiH group (hydrosilyl group) in the molecule can be suitably used. The organohydrogenpolysiloxane preferably has three or more SiH groups in one molecule, and the molecular shape can be linear, branched, or cyclic. The organo group is the same as the example of the organo group in the diorganopolysiloxane having an alkenyl group. The SiH group of the crosslinking agent undergoes an addition reaction with the alkenyl group in the diorganopolysiloxane having an alkenyl group to form a silicone cured product (crosslinked structure).

[0036] The weight average molecular weight of the organohydrogenpolysiloxane used as the crosslinking agent is preferably in the range of 300 to 5,000, more preferably in the range of 500 to 3,000.

[0037] From the viewpoint of curability and crosslink density, the amount of crosslinking agent added is preferably such that the molar ratio to the alkenyl groups in the alkenyl group-containing diorganopolysiloxane (SiH groups / alkenyl groups) is 0.5 to 5.0, and more preferably 1.0 to 3.0.

[0038] The curing catalyst in the addition-curing silicone pressure-sensitive adhesive composition promotes the addition curing reaction, and conventionally known platinum-based catalysts can be suitably used. Examples of platinum-based catalysts include chloroplatinic acid, an alcohol solution of chloroplatinic acid, a reaction product of chloroplatinic acid and an alcohol, a reaction product of chloroplatinic acid and an olefin compound, a reaction product of chloroplatinic acid and a vinyl group-containing siloxane, a platinum-olefin complex, and a platinum-vinyl group-containing siloxane complex. These catalysts may be used alone or in combination of two or more.

[0039] In addition to the above components, the addition-curable silicone pressure-sensitive adhesive composition may also contain various additives such as reaction inhibitors and adhesion improvers.

[0040] The thickness of the silicone pressure-sensitive adhesive layer of the present invention is preferably 1 to 10 μm, more preferably 1 to 5 μm, from the viewpoints of ensuring adhesive strength, plating masking properties, and preventing contact with overhanging portions due to deformation of the pressure-sensitive adhesive layer.

[0041] The silicone pressure-sensitive adhesive layer can be formed by uniformly applying the pressure-sensitive adhesive composition, either as is or as a coating liquid with the viscosity adjusted using a solvent or the like, to a substrate to a predetermined thickness, drying the solvent, and further heating to cure the pressure-sensitive adhesive composition.

[0042] Examples of methods for applying the coating solution for the silicone pressure-sensitive adhesive layer include a gravure coater, a bar coater, a comma knife coater, and a die coater.

[0043] <Separator> In the pressure-sensitive adhesive tape for plating processes of the present invention, a separator made of a plastic film is preferably attached to the surface of the pressure-sensitive adhesive layer in order to prevent contamination and adhesion of foreign matter on the surface of the silicone pressure-sensitive adhesive layer and to improve the handling of the pressure-sensitive adhesive tape. The separator is made of a plastic film with high releasability, and if desired, a release agent may be formed on the surface of the plastic film.

[0044] <Adhesive strength> The 180° peel adhesive strength of the adhesive tape for use in a plating process of the present invention against a SUS plate is preferably 0.5 to 4.5 N / 25 mm, more preferably 1.0 to 4.5 N / 25 mm. If the adhesive strength is less than 0.5 N / 25 mm, plating may adhere to the backside of the lead frame due to seepage of plating solution from the adhesive tape's attached edge, or the tape may peel off during each processing step. On the other hand, if the adhesive strength exceeds 4.5 N / 25 mm, when the adhesive surface of the adhesive tape comes into contact with an overhang on the backside of the lead frame, it will adhere to the overhang and easily seal the gap. Furthermore, when the adhesive tape is peeled from the lead frame after plating, warping of the lead frame and deformation of the fine lead terminals are likely to occur. The adhesive strength in this specification is measured using a 180° peel method in accordance with JIS Z0237:2022 using a 25 mm wide test piece 30 minutes after application of the adhesive tape.

[0045] <Bending angle> The pressure-sensitive adhesive tape for plating processes of the present invention preferably has a curved angle of 130° or less, as measured by the following predetermined measurement method. If the curved angle exceeds 130°, the pressure-sensitive adhesive tape is prone to deformation. When the tape is applied to a lead frame having an overhang formed on the back side of the lead frame, the adhesive surface may come into contact with the overhang during each processing step or during cleaning and drying, blocking the gap in the overhang, resulting in poor formation of the resist coating and reduced resist performance. Furthermore, blocking the gap in the overhang may result in poor peeling of the resist coating after plating.

[0046] (Method for measuring the curvature angle) Fig. 4 shows a schematic diagram of a sample for measuring a curvature angle (A is a schematic top view, and B is a schematic side view), Fig. 5 shows a schematic diagram illustrating the curvature angle to be measured, and Fig. 6 shows a schematic diagram illustrating the slope line used in measuring the curvature angle. The curvature angle was measured in an environment of 23±2°C and 50±10% RH. First, as shown in Fig. 4, adhesive tape 20 measuring 25 mm in width and 150 mm in length was attached to one surface of acrylic plate 30 measuring 52 mm in width, 75 mm in length, and 2 mm in thickness, such that the length of the adhesive tape 20 was parallel to the length direction M of acrylic plate 30, and the adhesive surface of adhesive tape 20 (25 mm in width and 50 mm in length) of adhesive tape 20 extended 100 mm in the length direction from one end ma of acrylic plate 30 but did not extend beyond the width direction N of acrylic plate 30. 5, the acrylic plate 30 with the adhesive tape 20 attached is fixed with the longitudinal end mb surface, where the adhesive tape 20 does not protrude, facing downward, so that the longitudinal direction of the acrylic plate 30 is parallel to the direction of gravity G, and the 25 mm wide × 100 mm long portion of the adhesive tape protruding from the upper end of the acrylic plate 30 is tilted toward the adhesive surface by its own weight, thereby curving the adhesive tape 20. Next, an image is taken from one widthwise end na side of the acrylic plate 30 so that the curved state of the adhesive tape 20 can be seen. In the photographed image, as shown in Fig. 6, the tip of the base surface 21a of the curved portion of the adhesive tape 20 in the longitudinal direction is set as a start point 40a, and a point 5 mm from the tip of the base surface 21a of the curved portion of the adhesive tape toward the other end in the longitudinal direction along the base surface 21a of the adhesive tape is set as an end point 40b, and the line segment connecting the start point 40a and the end point 40b is set as the inclination line 40 of the adhesive tape. Next, as shown in Fig. 5, the line segment indicating the base surface 21a of the portion of the adhesive tape 20 attached to the acrylic plate 30 is set as a reference line, and the angle between an extension line 50 of the reference line upward in the direction of gravity and an extension line 41 of the inclination line 40 of the adhesive tape toward the end point 40b is measured as the curvature angle θ. If the 25 mm wide x 100 mm long portion of the adhesive tape 20 that protrudes from the upper end of the acrylic plate 30 does not tilt due to its own weight, or if it tilts toward the non-adhesive side, the bending angle is set to 0°. If the extension line 50 of the reference line upward in the direction of gravity and the extension line 41 of the inclination line 40 of the adhesive tape toward the end point 40b do not intersect, the bending angle is set to 180° or more.

[0047] The adhesive tape for plating of the present invention is an adhesive tape that is applied to the back side of a lead frame that is not to be plated, and is used as a masking tape to protect it from the electrodeposited photoresist and plating in a method of partially plating the front side of a lead frame using electrodeposited photoresist. Masking the back side of the lead frame with adhesive tape reduces the amount of expensive electrodeposited photoresist solution used. Figure 7 shows a process flow of an example of a method for partially plating a lead frame with negative electrodeposited photoresist using the adhesive tape of the present invention.

[0048] In the method for selectively plating the front surface of a lead frame according to this embodiment, first, a lead frame is prepared by etching a flat plate of a lead frame material (Fe-Ni alloy or Cu alloy) having a predetermined thickness (usually 100 to 300 μm), and (a) adhesive tape is attached to the rear surface of the lead frame, which is not to be plated. For example, a lamination method is preferably used as the adhesive tape attachment method.

[0049] Next, as a pretreatment, (b) pickling treatment is performed to remove oxides and the like from the metal surface on the front side of the lead frame. For the pickling treatment, an inorganic acid such as dilute sulfuric acid can be used. After pickling, it is preferable to further rinse with water.

[0050] Next, in (c) resist formation, an electrodeposited photoresist is electrochemically formed on the metal portions of the lead frame that are not masked with adhesive tape. The electrodeposition conditions for the electrodeposited photoresist are preferably those suitable for the electrodeposited photoresist used. In the case of a negative electrodeposited photoresist, for example, in the current application step, the temperature of the electrodeposited photoresist solution is set to 25 to 50°C, preferably 30 to 45°C, and the metal portion of the resist coating film-formed product is immersed in the electrodeposition solution as the cathode, with an applied voltage of 15 to 250V, preferably 60 to 180V, and a current application time of 5 to 180 seconds, preferably 10 to 60 seconds. After electrodeposition, the resist coating film-formed product is preferably washed with water and then dried in an oven or the like to remove moisture and solvent components from the resist coating film.

[0051] Next, the formed resist coating film is exposed to ultraviolet light (d). Examples of ultraviolet light sources include high-pressure mercury lamps, metal halide lamps, and LEDs emitting light at a wavelength of 365 nm. The light intensity for exposure is 50 mJ / cm. 2 ~800mJ / cm 2 From the viewpoint of improving productivity, it is preferable to use 50 to 250 mJ / cm 2The front surface of the lead frame is exposed through a photomask (pattern plate) to print a predetermined pattern onto the resist coating. If an overhang is formed on the back surface of the lead frame, the back surface is also exposed.

[0052] The exposed resist coating film is (e) developed with a developer such as an organic acid, and the unexposed portions are dissolved and removed. The developer is an aqueous solution of an organic acid such as formic acid, acetic acid, or lactic acid, with a concentration of about 1 to 5%, and is used at a temperature in the range of 20°C to 50°C, preferably 35 to 45°C. After development, the developer is washed with water to wash away the developer.

[0053] Next, (f) silver plating is applied to the metal parts of the lead frame exposed by development. Silver plating is usually carried out by electrolytic plating using a silver plating solution whose main component is silver cyanide. The plating bath temperature for silver plating is preferably 10 to 50°C, and the current density is preferably 0.1 to 10 A / dm 2 The plating time is preferably 10 to 300 seconds, and can be changed as needed depending on the desired plating thickness.

[0054] Thereafter, (g) resist stripping is performed by stripping the resist coating film using a stripping solution. Suitable resist stripping solutions include aqueous alkaline solutions such as sodium hydroxide and potassium hydroxide. Stripping solutions based on organic acids or organic solvents that dissolve the cured resist coating film can also be used. The temperature of the stripping solution is preferably 40°C or higher to improve the solubility of the cured resist.

[0055] Further post-processing involves (h) electrolytic degreasing using an alkaline degreasing agent and (i) surface roughening using a surface roughening solution, followed by (j) peeling off the adhesive tape to obtain a lead frame with partial silver plating on the surface side of the lead frame. [Example]

[0056] EXAMPLES The pressure-sensitive adhesive tape for use in plating processes of the present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0057] <Preparation of adhesive layer coating liquid> The following materials were mixed in the amounts shown in Table 1 to prepare pressure-sensitive adhesive layer coating solutions 1 to 5. (Adhesive layer coating liquid materials) Silicone rubber A: Dimethylpolysiloxane with two or more vinyl groups per molecule (weight average molecular weight 77,000) Silicone rubber B: Dimethylpolysiloxane with two or more vinyl groups per molecule (weight average molecular weight 650,000) ·MQ resin; (CH3)3SiO 1 / 2 MQ resin (weight average molecular weight 7,400) consisting of units and SiO2 units Crosslinking agent: Methylhydrogenpolysiloxane (weight average molecular weight 1,250) Curing catalyst: Platinum catalyst (CAT-PL-56 manufactured by Shin-Etsu Chemical Co., Ltd.)

[0058] [Table 1]

[0059] <Preparation of adhesive tape> Example 1 A 50 μm thick polyethylene terephthalate (hereinafter abbreviated as PET) film that had been corona-treated on one side was used as the substrate, and coating solution 1 of the adhesive layer coating solution was applied to the corona-treated surface of the PET film using an applicator so that the adhesive layer would have a thickness of 5 μm after the solvent had dried, and then the adhesive tape of Example 1 was produced by heating and curing it for 2 minutes in a gear oven at 150°C.

[0060] Example 2 An adhesive tape of Example 2 was produced in the same manner as in Example 1, except that the thickness of the adhesive layer after drying the solvent was changed to 3 μm.

[0061] Example 3 An adhesive tape of Example 3 was produced in the same manner as in Example 1, except that the thickness of the adhesive layer after drying the solvent was changed to 1 μm.

[0062] Example 4 An adhesive tape of Example 4 was produced in the same manner as in Example 1, except that the thickness of the adhesive layer after drying the solvent was changed to 10 μm.

[0063] Example 5 An adhesive tape of Example 5 was produced in the same manner as in Example 1, except that the substrate was changed to a 100 μm thick PET film that had been corona-treated on one side.

[0064] Example 6 An adhesive tape of Example 6 was produced in the same manner as in Example 1, except that the adhesive layer coating liquid in Example 1 was changed to Coating Liquid 2.

[0065] Example 7 The adhesive tape of Example 7 was produced in the same manner as Example 1, except that in Example 1, the adhesive layer coating liquid was changed to Coating Liquid 3 and the adhesive layer thickness after drying the solvent was changed to 10 μm.

[0066] (Comparative Example 1) An adhesive tape of Comparative Example 1 was produced in the same manner as in Example 1, except that the substrate was changed to a 25 μm thick PET film that had been corona-treated on one side.

[0067] (Comparative Example 2) An adhesive tape of Comparative Example 2 was produced in the same manner as in Example 1, except that the substrate was changed to a 50 μm thick ethylene tetrafluoroethylene (ETFE) film that had been plasma-treated on one side.

[0068] (Comparative Example 3) An adhesive tape of Comparative Example 3 was produced in the same manner as in Example 1, except that in Example 1, the adhesive layer coating liquid was changed to Coating Liquid 3 and the adhesive layer thickness after drying the solvent was changed to 25 μm.

[0069] Comparative Example 4 An adhesive tape of Comparative Example 4 was produced in the same manner as in Example 1, except that the adhesive layer coating liquid in Example 1 was changed to Coating Liquid 4.

[0070] (Comparative Example 5) An adhesive tape of Comparative Example 5 was produced in the same manner as in Example 1, except that in Example 1, the adhesive layer coating liquid was changed to Coating Liquid 5 and the thickness of the adhesive layer after drying the solvent was changed to 10 μm.

[0071] <Ultraviolet transmittance measurement> For the pressure-sensitive adhesive tapes of Examples 1 to 7 and Comparative Examples 1 to 5, 50 mm square test pieces were cut out, and the transmittance of ultraviolet light at a wavelength of 365 nm from the substrate surface side of the pressure-sensitive adhesive tape was measured using a spectrophotometer (UH4150 manufactured by Hitachi High-Tech Science Corporation). The measurement results are shown in Table 2.

[0072] <Measurement of adhesive strength to SUS> Test pieces measuring 25 mm wide x 250 mm long were cut out from the pressure-sensitive adhesive tapes of Examples 1 to 7 and Comparative Examples 1 to 5, and the adhesive strength of each was measured using a 180° peel test method against a SUS plate in accordance with JIS Z0237:2022. However, the adhesive strength was measured after the pressure-sensitive adhesive tape was attached to the SUS plate and left to stand at 23±2°C and 50±10% RH for 30 minutes. The measurement results are shown in Table 2.

[0073] <Bending angle measurement> Test pieces measuring 25 mm wide x 150 mm long were cut out from the pressure-sensitive adhesive tapes of Examples 1 to 7 and Comparative Examples 1 to 5, and images of the curved pressure-sensitive adhesive tapes from the side were taken with a digital camera according to the method for measuring the curve angle described above (paragraph 0046), and the curve angle was measured on the images. The measurement results are shown in Table 2.

[0074] <Silver plating of lead frame> (adhesive tape attached) Test pieces measuring 80 mm wide x 80 mm long were cut out from the adhesive tapes of Examples 1 to 7 and Comparative Examples 1 to 5 and attached to the back side of a lead frame having the following specifications using a hand roller so as to protect the entire back side of the lead frame. Lead frame specifications: [Dimensions] Width 55mm x Length 58mm, [Arrangement] Matrix arrangement of 8 x 8 QFN patterns (total 64), [Package size] 5mm x 5mm, [Number of pins] 32, [Lead back surface] Overhangs of 100μm depth formed on the edge of the die pad and lead back surface by etching

[0075] (Electrodeposition resist formation) The lead frame with the adhesive tape attached was immersed in a 100 g / L aqueous sulfuric acid solution at room temperature for 10 seconds for acid washing, and then rinsed with deionized water. It was then immersed in a negative electrodeposition photoresist solution (Honey Resist E-2000 manufactured by Honey Chemical Co., Ltd., adjusted to a heating residue of 10% by mass) and a direct current of 150 V was applied for 10 seconds to form an 8 μm thick electrodeposition photoresist coating on the metal parts of the lead frame where the adhesive tape was not attached. The lead frame with the adhesive tape attached was then removed from the resist solution, rinsed with deionized water, and dried in an oven at 60°C for 30 seconds.

[0076] (exposure, development) The lead frame with the adhesive tape attached was removed from the oven, and a photomask (a pattern plate that masks the tip of the lead in black) was placed on the surface of the electrodeposited photoresist coating film formed on the surface of the lead frame. An LED lamp with an exposure wavelength of 365 nm was used to expose the photoresist to 250 mJ / cm. 2 The lead frame was exposed to light with a 1000 W exposure. The back side, to which adhesive tape was attached, was also exposed in the same way. The photomask was then removed, and the masked, unexposed portions of the electrodeposited photoresist coating were removed by developing for 30 seconds with a developer (Honey Chemical Co., Ltd., Honeyresist DEV-1 diluted to 4 wt%), and then rinsed with deionized water, leaving only the metal portions to be plated exposed.

[0077] (plating, resist stripping) The lead frame, with only the metal portion to be plated exposed, was immersed in a silver plating solution (Nihon Kojundo Chemical, Serena Bright C) for 30 seconds to perform electrolytic plating, plating the metal portion of the lead frame with silver. Next, the lead frame with the plated adhesive tape attached was immersed in a stripping solution (3% sodium hydroxide aqueous solution) for 30 seconds to strip and remove the electrodeposited photoresist coating.

[0078] (Removing adhesive tape) After peeling and removing the electrodeposited photoresist coating, the lead frame with the adhesive tape attached was electrolytically degreased with an alkaline degreasing agent (containing sodium hydroxide and a surfactant), and the surface of the lead frame was roughened with an acid-based roughening solution (containing hydrogen peroxide and sulfuric acid).The adhesive tape was then peeled off from the lead frame, and a plated lead frame was obtained.

[0079] <Tape peeling evaluation> The silver plating of the lead frames to which the adhesive tapes of Examples 1 to 7 and Comparative Examples 1 to 5 had been applied was visually inspected before the adhesive tapes were peeled off, and tape peeling was evaluated according to the following criteria. The evaluation results are shown in Table 2. (Evaluation criteria) ○: No peeling of the adhesive tape was observed. ×: Peeling of the adhesive tape is observed in some places.

[0080] <Plating penetration evaluation> The backside of each plated lead frame from which the adhesive tape had been peeled off in Examples 1 to 7 and Comparative Examples 1 to 5 was visually inspected and observed under a microscope (100x magnification), and the plating penetration was evaluated according to the following criteria. The evaluation results are shown in Table 2. (Evaluation criteria) ◎: Under magnified microscope observation, no adhesion of silver plating was observed. ○: Under magnified microscope observation, some silver plating was observed on the edge of the surface where the adhesive tape had been attached. △: When observed under a magnified microscope, silver plating was observed to be attached to the entire edge of the surface where the adhesive tape had been attached. ×: Upon visual inspection, adhesion of silver plating was observed on the surface where the adhesive tape had been attached.

[0081] <Overhang part defect evaluation> The overhang portions on the backside of the plated lead frames from which the adhesive tapes had been peeled off in Examples 1 to 7 and Comparative Examples 1 to 5 were visually inspected and observed under a microscope at a magnification of 100x, and the overhang portion defects were evaluated according to the following criteria. The evaluation results are shown in Table 2. (Evaluation criteria) ◎: No plating adhesion or electrodeposited photoresist adhesion was observed under magnified microscope observation. ○: Under magnified microscope observation, adhesion of electrodeposited resist was observed in several places. △: Upon visual inspection, adhesion of electrodeposited resist was observed in several places. ×: A large amount of plating or electrodeposited photoresist coating film adhesion was observed by visual inspection.

[0082] <Adhesive residue evaluation> The backside of each plated lead frame from which the adhesive tape was peeled off was visually inspected and evaluated for adhesive residue according to the following criteria. The evaluation results are shown in Table 2. (Evaluation criteria) ○: No adhesive residue (adhesion of the adhesive layer) was observed. ×: Adhesive residue (adhesion of adhesive layer) is observed.

[0083] [Table 2] [Explanation of symbols]

[0084] 10: Lead frame 11: Die pad 12: Lead 13: Overhang 14: Gap 20: Adhesive tape 21: Base material 21a: Base material side 22: Silicone adhesive layer 30: Acrylic plate 40: Slope line 40a: Starting point of the slope line 40b: End point of the slope line 41: Extension of the slope line 50: Extension of the reference line M: Length direction ma: Lengthwise end (where the adhesive tape protrudes) mb: Lengthwise end (the end where the adhesive tape does not protrude) N: Width direction na: Width direction edge G:Gravity direction θ: Curvature angle

Claims

1. 1. A pressure-sensitive adhesive tape for a plating process, which is applied to mask the back surface of a lead frame in a method for partially plating the front surface of a lead frame with silver using an electrodeposited photoresist, the pressure-sensitive adhesive tape comprising a substrate and at least a silicone pressure-sensitive adhesive layer laminated on one surface of the substrate, the silicone pressure-sensitive adhesive layer being a cured product of an addition-curable silicone pressure-sensitive adhesive composition, the silicone pressure-sensitive adhesive composition containing 35 to 55 mass % of an MQ resin, the transmittance of ultraviolet light at a wavelength of 365 nm from the substrate surface side of the pressure-sensitive adhesive tape being 70% or more, the 180° peel adhesive strength of the silicone pressure-sensitive adhesive layer against an SUS plate being 0.5 to 4.5 N / 25 mm, and the bending angle of the pressure-sensitive adhesive tape measured by the following predetermined measuring method being 130° or less. (Method for measuring bending angle) In an environment of 23±2°C and 50±10% RH, a 25 mm wide × 150 mm long adhesive tape is attached to one surface of an acrylic plate that is 52 mm wide × 75 mm long × 2 mm thick, such that the length direction of the adhesive tape is parallel to the length direction of the acrylic plate, the adhesive surface of the adhesive tape (25 mm wide × 50 mm long) of the adhesive tape extends 100 mm in the length direction from one end of the acrylic plate in the length direction, but does not extend beyond the width direction of the acrylic plate. Next, the acrylic plate with the adhesive tape attached is fixed with the end face in the longitudinal direction where the adhesive tape does not protrude downwards, so that the longitudinal direction of the acrylic plate is parallel to the direction of gravity, and the 25 mm wide x 100 mm long portion of the adhesive tape protruding from the upper end of the acrylic plate is tilted toward the adhesive surface by its own weight, thereby bending the adhesive tape. Next, an image is taken from one end face side in the width direction of the acrylic plate so that the curved state of the adhesive tape can be seen. In the photographed image, the start point is the tip of the base surface of the curved portion of the adhesive tape in the longitudinal direction, and the end point is a point 5 mm from the tip of the base surface of the curved portion of the adhesive tape along the base surface of the adhesive tape toward the other end in the longitudinal direction, the line segment connecting the start point and the end point is the inclination line of the adhesive tape, and the line segment representing the base surface of the portion of the adhesive tape attached to the acrylic plate is the reference line, and the angle between an extension of the reference line upward in the direction of gravity and an extension of the inclination line of the adhesive tape toward the end point is measured as the curvature angle, which is the angle upward in the direction of gravity and in the direction in which the adhesive tape is tilted. If the 25 mm wide x 100 mm long portion of the adhesive tape protruding from the upper end of the acrylic plate does not tilt due to its own weight or tilts toward the non-adhesive side, the curvature angle is recorded as 0°. When the extension line of the reference line upward in the direction of gravity and the extension line of the inclination line of the adhesive tape toward the end point do not intersect, the curve angle is set to 180° or more.

2. 2. The adhesive tape for use in plating processes according to claim 1, wherein the substrate is a polyethylene terephthalate film having a thickness of 50 to 100 μm.

3. 3. The pressure-sensitive adhesive tape for use in a plating process according to claim 1, wherein the thickness of the silicone pressure-sensitive adhesive layer is 1 to 10 μm.

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