DE112022002949T5 - PRESSURE SENSITIVE ADHESIVE LAYER - Google Patents

Abstract

A PSA sheet is provided in which reduced adhesive transfer during removal and good conformability to the adherend surface structure are combined in a well-balanced manner. The provided PSA sheet comprises a substrate and a PSA layer disposed on at least one side of the substrate. The PSA sheet has an indentation hardness H1 of 0.10 MPa or more and 0.50 MPa or less at the PSA layer surface and an indentation hardness H2 of 0.001 MPa or more and 0.090 MPa or less measured at a distance of 4 µm from the substrate in the direction of the PSA layer surface in a cross section of the PSA sheet.

Description

[Technical area]

The present invention relates to a pressure-sensitive adhesive layer or a pressure-sensitive adhesive layer. This application claims priority from Japanese Patent Application No. 2021-115926 , filed on July 13, 2021, the entire contents of which are incorporated herein by reference.

[State of the art]

In the manufacture of semiconductor devices including semiconductor chips, the semiconductor chips may be encapsulated with a resin to prevent damage, extend metal wiring, etc. Resin encapsulation is sometimes performed on a pressure sensitive adhesive (PSA) sheet in view of workability, etc. For example, a plurality of semiconductor chips are arranged on the PSA layer of the PSA sheet as a material for temporary fixing and are all encapsulated on the PSA sheet at once. Then, the PSA sheet is removed from the structure including the encapsulation resin and the semiconductor chips in a certain post-processing process.

[Document list]

[Patent documents]

• [Patent Document 1] Japanese patent application with publication number 2001-308116
• [Patent Document 2] Japanese patent application with publication number 2001-313350

[Technical problem]

Regarding the PSA sheet used in the above method, when it is removed from the structure including the encapsulating resin and the semiconductor chips, it must not cause adhesive transfer (adhesive residue left behind) to the structure. In the PSA sheet, to reduce adhesive transfer, the PSA layer on which the semiconductor chips are placed is generally formed of a PSA having a very high elastic modulus. However, if the PSA layer has a high elastic modulus, the PSA will not adhere strongly enough to the uneven chip surface due to the potential uneven surface of the semiconductor chips due to pre-formed metal wiring, etc., which is more likely to cause a problem with the encapsulating resin penetrating into the interface between the chips and the PSA.

The present invention was made in view of the above circumstance with the object of providing a PSA sheet in which reduced adhesive transfer during removal and good conformability to the adherend surface structure (surface structure) are combined in a well-balanced manner.

[The solution of the problem]

The PSA sheet provided by this specification includes a substrate and a PSA layer disposed on at least one side of the substrate. According to an indentation hardness measurement using a nanoindenter, the PSA layer has an indentation hardness H1 of 0.10 MPa or more and 0.50 MPa or less at the PSA layer surface and an indentation hardness H2 of 0.001 MPa or more and 0.090 MPa or less, which at a distance of 4 μm from the substrate in the direction of the PSA layer surface in a cross section of the PSA layer. If the indentation hardness H1 measured at the PSA layer surface (or hereinafter at “Measuring Point A”) is 0.10 MPa or greater, adhesive transfer during removal can be reduced. If the indentation hardness H2, which is within the measuring point A (on the substrate side; in particular at a distance of 4 µm from the substrate in the direction of the PSA layer surface in a cross section of the PSA layer (or hereinafter at the “measuring point B”)) is measured is 0.090 MPa or less, the adaptability to the adherend surface structure can be improved. Consequently, the PSA layer with H1 and H2 within these ranges can combine reduced adhesive transfer during removal and good conformability of the adherend surface in a well-balanced manner.

In some embodiments, the ratio of the indentation hardness H2 (MPa) to the indentation hardness H1 (MPa) (H2/H1) is 0.002 or higher and 0.90 or lower. According to the PSA with an indentation hardness H2 at measuring point B (inside) ≤ 0.90 times the indentation hardness H1 at measuring point A (surface), reduced adhesive transfer can be combined in an advantageous manner with good surface adaptability.

In some embodiments, the PSA layer surface has a stringing index D1 of 50 nm or more and 500 nm or less in a stringing test using a nanoindenter. The PSA layer surface (measurement point A) with a stringing index D1 ≤ 500 nm is advantageous in terms of reducing adhesive transfer. In the stringing test, it preferably has a stringing index D2 of 150 nm or more and 1000 nm or less, which is determined at a distance of 4 µm from the substrate in the direction of the PSA layer surface (at the measurement point B) in a cross section of the PSA layer. The PSA layer with a stringing index D2 in this range results in good surface conformability.

In some embodiments, the ratio of the stringiness index D2 (nm) to the stringiness index D1 (nm) (D2/D1) is 0.3 or higher and 20.0 or lower. The PSA layer having a D2/D1 ratio in this range is likely to advantageously combine adhesive transfer reduction and surface conformability.

In some embodiments, in the PSA layer having an initial thickness of T0 (µm), after 4-t-butylphenyl glycidyl ether is dropped onto the PSA layer surface and left to stand for 1 minute, the PSA layer has a thickness T1 (µm) with a difference (T1 - T0; hereinafter also referred to as the "thickness change") of 20 µm or less. The PSA layer having only a small thickness change is preferable because, for example, in usage situations where semiconductor chips are arranged on the PSA layer and encapsulated with a resin, unevenness (protrusion) is less likely to be generated between the semiconductor chips and the encapsulating resin.

The PSA layer according to some embodiments has a needle probe penetration of 3.50 μm or more and 20.0 μm or less from the PSA layer surface, which is determined using a thermomechanical analyzer (TMA) at a measurement ambient temperature of 23°C and an indentation load of 0.01 N for an indentation time of 60 minutes. For example, in usage situations where semiconductor chips are placed on a PSA layer and encapsulated with a resin, the PSA layer with a penetration in this range can achieve both semiconductor chip conformability and a reduction in embedding of semiconductor chips into the PSA layer in a well-balanced manner.

In some embodiments of the PSA layer disclosed herein, the PSA layer has a thickness of 5 μm or more and 110 μm or less. The PSA layer with such a thickness can advantageously produce the effect of the property differences between the measuring points A and B.

In some embodiments, the substrate is a substrate film formed of a resin material having a glass transition temperature (Tg) of 25°C or higher. For example, in usage situations where semiconductor chips are placed on the PSA layer of the PSA sheet and encapsulated with a resin, even if heating occurs during this process, the PSA sheet with the PSA layer on such a substrate film enables a reduction in embedding of the semiconductor chips therein and a reduction in semiconductor chip/encapsulation resin non-uniformity (standoff).

The PSA sheet according to some embodiments has an adhesion strength of 0.05 N/20 mm or more and 1.00 N/20 mm or less to a polyethylene terephthalate (PET) film. Within such an area, it can preferably fix a joining part (e.g. a semiconductor chip) and reduce the load on the joining part when removing the PSA layer.

In some embodiments, the PSA layer has an anchoring strength of 4.00 N/20 mm or greater to the substrate, determined at 23°C after heating the PSA layer at 150°C for one hour. The PSA sheet having such anchoring strength is preferable because in the PSA sheet, for example, in usage situations where semiconductor chips are arranged on the PSA layer of the PSA sheet and encapsulated with a resin, even if heating occurs during this process, Adhesive transfer can be reduced in the subsequent removal process.

In some embodiments, the PSA forming at least the PSA layer surface is an acrylic PSA comprising an acrylic polymer as a base polymer. The technique disclosed herein may preferably be implemented as a PSA sheet having a PSA layer in which at least the surface (adhesion surface) is formed of an acrylic PSA.

In some embodiments, the acrylic polymer has an SP value of 18.0 to 20.0. When the adhesion surface is formed of an acrylic PSA whose base polymer is an acrylic polymer with the SP value in this range, it helps in obtaining an indentation hardness H1 in the above-mentioned range. Furthermore, for example, even in usage situations where semiconductor chips are placed on the PSA layer and encapsulated with a resin, it helps prevent excessive increase in adhesive strength on the encapsulation resin.

In some embodiments of the PSA layer disclosed herein, the PSA layer includes a layer (Layer A) that forms the PSA layer surface and a layer (Layer B) disposed adjacent the substrate, between the layer A and the PSA layer Substrate. Accordingly, the PSA layer disclosed herein may preferably be manufactured in an embodiment having a PSA layer comprising a layer A (surface layer) and a layer B (adhesion promoter layer).

The layer A preferably has a thickness L1 of, for example, 1 µm or more and 10 µm or less. The layer A having such a thickness is likely to advantageously combine reduction of adhesive transfer and surface conformability.

The layer B preferably has a thickness L2 of, for example, 4 μm or more and 100 μm or less. It is likely that a layer B with such a thickness advantageously combines reduction in adhesive transfer and surface conformability.

The ratio of the thickness L2 (µm) of layer B to the thickness L1 (µm) of layer A (L2/L1) is preferably 1.0 to 100.0.

In some embodiments, layer A has a T _2s of 45 µs or less and layer B has a T ₂ of greater than 45 µs, where T _2s is the short (S)T ₂ relaxation time component according to pulse NMR . It is likely that the PSA sheet having a PSA layer comprising layers A and B satisfying the relaxation time (T _2s ) will advantageously have a surface conformability with a reduction in component transfer between the PSA Layer and the encapsulation resin are combined.

In some embodiments, layer A is crosslinked with an epoxy-based crosslinking agent and layer B is crosslinked with an isocyanate-based crosslinking agent. The PSA layer disclosed herein may preferably be manufactured in an embodiment comprising a PSA layer having such a construction.

In some embodiments of the PSA layer disclosed herein, the PSA layer includes the substrate, the PSA layer (first PSA layer) disposed on one side of the substrate, and a second PSA layer disposed on the opposite side of the Substrate is arranged by the PSA layer. The PSA sheet in such an embodiment is useful because, for example, while fixed to a suitable support using the second PSA layer, resin encapsulation can be performed on the first PSA layer.

In some embodiments, at least the second PSA layer surface is formed from a PSA comprising thermally expandable microspheres. The PSA layer in such an embodiment is preferred because the bond between the second PSA layer and the adherend can be easily released by optionally heating as appropriate to expand the thermally expandable microspheres.

The scope of the invention for which the present patent application seeks patent protection includes a suitable combination of the respective features described herein.

[Brief description of the drawings]

• 1 shows a cross-sectional diagram schematically showing the structure of the PSA layer according to an embodiment.
• 2 (i) to (iv) show a diagram showing an example of the step of resin encapsulating semiconductor chips using the steps described in FIG 1 PPE situation shown is carried out.
• 3 shows a cross-sectional diagram that schematically shows the structure of the PPE layer according to another embodiment.
• 4 shows a cross-sectional diagram that schematically shows the structure of the PPE layer according to another embodiment.
• 5 shows a schematic diagram illustrating the definition of the thread pull index.

[Description of embodiments]

Preferred embodiments of the present invention are described below. Items required for carrying out this invention other than those specifically referred to in this description will be apparent to a person skilled in the art based on instruction regarding implementations of the invention according to this description and the common technical knowledge in the present field. The present invention can be carried out based on the content disclosed in this description and the common technical knowledge in the present field.

In the drawings referred to below, elements or locations which produce the same effects may be assigned a common reference numeral, and duplicate descriptions are sometimes omitted or simplified. The embodiments described in the drawings are schematic for a clear illustration of the present invention and do not necessarily represent the exact sizes or reduction scales of products actually provided.

As used herein, the "base polymer" of a PSA refers to a rubbery polymer in the PSA. Other than that, it is not limited to any particular interpretation. The rubbery polymer refers to a polymer that has rubbery elasticity at about room temperature. As used herein, the "major component" (primary component) refers to a component that is greater than 50% by weight.

As used herein, “acrylic polymer” refers to a polymer comprising a monomer unit derived from a monomer having at least one (meth)acryloyl group per molecule. Hereinafter, a monomer that has at least one (meth)acryloyl group per molecule is referred to as an “acrylic monomer”. Accordingly, as used herein, the acrylic polymer is defined as a polymer comprising a monomer unit derived from an acrylic monomer. Typical examples of the acrylic polymer include a polymer in which the acrylic monomer accounts for more than 50% by weight (preferably more than 70% by weight, e.g. more than 90% by weight) of all monomers used in the synthesis of the acrylic polymer become. Hereinafter, the monomers used to synthesize the polymer are also referred to as the monomers that form the polymer (polymer-forming monomers).

As used herein, the term “(meth)acryloyl” is intended to include acryloyl and methacryloyl. Accordingly, “(meth)acrylate” stands for acrylate and methacrylate and “(meth)acrylic” is intended to include acrylic or methacrylic. Accordingly, the concept of acrylic monomer herein may include both an acrylic monomer (a monomer having an acryloyl group) and a methacrylic monomer (a monomer having a methacryloyl group).

<Overview of PPE situation>

The PSA sheet disclosed herein can be conveniently used as a temporary fixing material for resin encapsulation of semiconductor chips. Specifically, the PSA sheet of this invention can be used as a temporary fixing material for the semiconductor chips in resin encapsulating them by placing semiconductor chips on a PSA layer thereof, covering them with an encapsulating resin (typically an epoxy resin), and curing the encapsulating resin. After resin encapsulation of the semiconductor chips, during certain subsequent operations (e.g. grinding away of the encapsulation resin, pattern formation, hill formation, chip formation (cutting)) removes the PSA layer from the structure comprising the encapsulation resin and semiconductor chips. The encapsulation resin has an epoxy equivalent weight of, for example, 50 g/eq. up to 500 g/eq. on.

The 1 shows a schematic cross-sectional view showing an embodiment of the PSA sheet disclosed herein. The PSA sheet 100 comprises a substrate 10 and a PSA layer (first PSA layer) 20 disposed on one side of the substrate 10. The PSA sheet 100 has an indentation hardness H1 of 0.10 MPa or more at the measurement point A on the surface of the PSA layer (first PSA layer) 20 (ie, at the measurement point A indicated by the arrow A in the 1 ) and has an indentation hardness H2 of 0.09 MPa or less measured at a distance of 4 µm from the substrate 10 in the direction of the surface of the PSA layer 20 (ie, at the measuring point B indicated by the arrow B in the 1 ) in a cross-section of the PSA layer 100.

The PSA layer 100 can be used, for example, for resin encapsulation of semiconductor chips, as described in US Pat 2 is shown. First, a plurality of semiconductor chips 1 are applied to the PSA layer (first PSA layer) of the PSA layer 100 (step (i)). Then, the semiconductor chips 1 are covered with a partially cured encapsulation resin 2' (step (ii)). The partially cured encapsulation resin 2' is allowed to harden so that the semiconductor chips 1 are encapsulated with the encapsulation resin 2 (step (iii)). For example, the partially cured encapsulating resin 2' may be formed using a composition comprising a bifunctional naphthalene-based epoxy resin (144 epoxy equivalents). Subsequently, during a certain subsequent operation, the PSA layer 100 is removed from the structure 50 comprising semiconductor chips 1 and the encapsulation resin 2 (step (iv)).

With an indentation hardness H1 of 0.10 MPa or more at measurement point A, the PSA layer disclosed herein is less likely to cause adhesive transfer to the structure 50 in step (iv) described in Figure 10 2 is shown. With an indentation hardness H2 of 0.09 MPa or less within the PSA layer (especially at measuring point B), the PSA layer can adhere well to the part surface structure (e.g. metal wire protrusions and the like, which are on the surface of the side of the PSA layer of a semiconductor chip 1 may be present) and the occurrence of mold flash (a problem that the encapsulation resin 2 penetrates into the interface between the PSA layer and the semiconductor chip 1) can be prevented.

The 3 Figure 12 is a schematic cross-sectional diagram showing another embodiment of the PPE sheet disclosed herein. In the PSA layer 200, the PSA layer 20 in the PSA layer 100, which in the 1 is shown, the layer A 22, which forms the surface (adhesive surface) of the PSA layer 20, and the layer B 24, which is arranged adjacent to the substrate 10 between the layer A 22 and the substrate 10. The PSA layer 20 with such a structure supports the adjustment of the indentation hardness H1 and H2 at the measuring points A and B to suitable ranges. Accordingly, the PSA layer disclosed herein may preferably be manufactured in an embodiment having a PSA layer 20 comprising layers A 22 and B 24 on at least one surface of the substrate 10.

The 4 Figure 12 is a schematic cross-sectional diagram showing another embodiment of the PPE sheet disclosed herein. The PSA layer 300 further included a second PSA layer 30 on the back side of the substrate 10 (ie, on the side opposite the PSA layer 20). In other words, the PSA layer 300 includes a PSA layer 20, a substrate 10 and a second PSA layer 30 in that order. With the second PSA layer 30, for example, when resin encapsulation is performed on a substrate, the PSA sheet 300 can be easily attached to the substrate by attaching the side of the second PSA layer 30 to the substrate.

In some embodiments, in the second PSA layer, at least the surface is formed with a PSA comprising thermally expandable microspheres. Such thermally expandable microsphere-containing PSA may be heated to a certain temperature or higher so that the microspheres expand to form irregularities on the PSA layer surface, whereby the adhesive strength may be reduced or lost. With at least the second PSA layer surface formed with the thermally expandable microsphere-containing PSA, when the PSA layer is applied over the second PSA layer (e.g., to a carrier), the required adhesion is obtained; and when the PSA layer is removed (e.g., from the carrier), the adhesive strength is reduced or lost by heating, whereby good removability is obtained. Between the substrate and the thermally expandable microsphere-containing PSA, an elastic intermediate layer (optionally a PSA layer) which is free of heat-expandable microspheres or contains a small (limited) amount of them.

(Indentation hardness)

With a view to reducing adhesive transfer, the PSA layer disclosed herein has an indentation hardness H1 of suitably 0.10 MPa or more (e.g. more than 0.10 MPa) or preferably 0.12 MPa or more. In some embodiments, the indentation hardness H1 may be 0.15 MPa or more, 0.18 MPa or more, or even 0.20 MPa or more. In general, in usage situations where semiconductor chips are placed on a PSA layer and encapsulated with a resin, it tends to be advantageous for the PSA layer to be advantageous in terms of reducing potential unevenness (standoff) between the semiconductor chips and the encapsulation resin has a high indentation hardness H1. The indentation hardness H1 is expediently 0.50 MPa or less or preferably 0.40 MPa or less. With a view to assisting in obtaining very good adhesion to the adherend surface and suitable tackiness to the PSA layer surface, in some embodiments, the indentation hardness H1 may be, for example, 0.30 MPa or less, 0.28 MPa or less, 0.25 MPa or less, 0.23 MPa or less or even 0.21 MPa or less.

The PSA layer disclosed here suitably has an indentation hardness H2 that is lower than the indentation hardness H1. In view of improving the conformability to the adherend surface structure, it is preferably 0.090 MPa or less. In order to obtain a better conformability, the indentation hardness H2 may also be 0.080 MPa or less, 0.060 MPa or less, or even 0.050 MPa or less in some embodiments. The minimum indentation hardness H2 is not particularly limited. It may be, for example, 0.001 MPa or more. With a view to preventing cohesive failure within the PSA layer, the indentation hardness H2 is in some embodiments suitably 0.005 MPa or more, preferably 0.010 MPa or more, optionally 0.030 MPa or more, 0.040 MPa or more, 0.050 MPa or more or even 0.060 MPa or more.

The ratio of the indentation hardness H2 (MPa) to the indentation hardness H1 (MPa) (H2/H1) is, for example, expediently 0.90 or lower, preferably 0.70 or lower, optionally 0.50 or lower, 0.40 or lower or even 0.30 or lower. The ratio (H2/H1), for example, is suitably 0.002 or higher, preferably 0.005 or higher or more preferably 0.01 or higher. In a PSA sheet with an H2/H1 ratio in such a range, in a simple manner, reduction in adhesive transfer and surface conformability are combined in a well-balanced manner.

(threading index)

In the PSA layer disclosed here, the range of the threading index D1 at the measuring point A is not specifically limited. For example, it can be 800 nm or less. In some embodiments, the threading index D1 is suitably 500 nm or less, preferably 300 nm or less, optionally 250 nm or less, 200 nm or less, or even 150 nm or less, in view of better preventing adhesive transfer. With a view to obtaining suitable tackiness on the PSA layer surface (e.g., to facilitate placement of semiconductor chips on the PSA layer), the threading index D1 is suitably 50 nm or more, optionally 80 nm or more, 100 nm or more, or even 120 nm or more.

In the PSA layer disclosed here, the range of the stringing index D2 at the measurement point B is not particularly limited. For example, it may be 100 nm or more. In view of improving the conformability to the adherend surface structure, it is preferably 150 nm or more, or more preferably 200 nm or more. In some embodiments, the stringing index D2 may be 300 nm or more, 400 nm or more, or even 500 nm or more. The stringing index D2 may be, for example, 2500 nm or less. In view of preventing cohesive failure within the PSA layer, it is preferably 1500 nm or less, more preferably 1000 nm or less, optionally 800 nm or less, or even 600 nm or less.

The ratio of the threading index D2 (nm) to the threading index D1 (nm) (D2/D1) may be, for example, 0.3 or higher, 0.5 or higher, or even 1.0 or higher. In some embodiments, the ratio (D2/D1) is preferably above 1.0 (eg, 1.2 or higher), optionally 2.5 or higher, 3.5 or higher, or even 5.0 or higher. The ratio (D2/D1) is, for example, expediently 20.0 or lower, advantageously 15.0 or lower, preferably 10.0 or lower, optionally 8.0 or lower, 7.0 or lower or even 6.0 or lower. According to the PSA position with the ratio D2/D1 in the range determined by any combination of these upper and lower limits, reduction in adhesive transfer can be easily combined with surface conformability in a well-balanced manner.

The indentation hardness H1, H2 and the stringing index D1 and D2 are determined as follows: Using a nanoindenter, an indenter is pressed vertically from the sample surface at a predetermined measuring point to a predetermined depth and then pulled out. The change in load applied to the indenter (vertical axis) during this process is plotted against the displacement of the indenter (horizontal axis) with respect to the sample surface to obtain a load (pressing)-unload (pulling back) curve. H1, H2, D1 and D2 are determined from the curve. For the measurement of the indentation hardness H1 and the stringing index D1, the measuring point (A) is on the PSA layer surface. For the measurement of the indentation hardness H2 and the stringing index D2, the measuring point (B) is at a distance of 4 µm from the substrate in the direction of the PSA layer surface in a cross section of the PSA layer.

The indentation hardness (MPa) is determined by dividing the maximum load (Pmax) (µN) on the load curve corresponding to the specified depth of penetration of the indenter by the bulging contact area (A) of the indenter, that is, by the following equation: $$\text{Impressionh}\ddot{\text{a}}\text{rt}\left(\text{MPa}\right)=\text{Pmax}/\text{A}$$

The indentation hardness can be adjusted to the above ranges by appropriately selecting the PSA layer structure and the composition of the PSA forming the PSA layer (e.g., the composition of the base polymer, the degree of crosslinking, the type of crosslinking agent, etc.).

As shown schematically in the 5 As shown, the stringing index (nm) is defined as the displacement when the unloading curve is on the negative displacement side at zero load. The stringing index can be adjusted to the above ranges by appropriately selecting the composition of the PSA (e.g., the composition of the base polymer, the degree of crosslinking, the type of crosslinking agent, etc.).

The indentation hardness and stringing properties are analyzed using a nanoindenter (TRIBOINDENTER TI-950, available from Hysitron (currently Bruker)) under the conditions shown below.

[Measurement conditions]

• Messverfahren: Einzeleindruckmessung
• Messtemperatur: Raumtemperatur (25 °C)
• Eindrucktiefe: 800 nm an der Messstelle A, 1000 nm an der Messstelle B Eindruckgeschwindigkeit: 200 nm/s
• Entfernungsgeschwindigkeit: 200 nm/s

Indenter used: Berkovich (trigonal pyramid) diamond indenter

• Measuring method: individual impression measurement
• Measuring temperature: room temperature (25 °C)
• Indentation depth: 800 nm at measuring point A, 1000 nm at measuring point B. Indentation speed: 200 nm/s
• Removal speed: 200nm/s

(source properties)

In some embodiments of the PSA sheet disclosed herein, at an initial thickness T0 (µm) of the PSA layer (first PSA layer), after the PSA layer surface is exposed to a drop of 4-t-butylphenyl glycidyl ether (TBPGE) thereon and allowed to stand for 1 minute, the PSA layer has a thickness T1 (µm) with a difference in T0 (T1 - T0; i.e., thickness change) of 20 µm or less. For example, in usage situations where semiconductor chips are disposed on the PSA layer and encapsulated with a resin, the PSA sheet that exhibits little thickness change upon TBPGE swelling tends to exhibit reduced transfer of constituents between the PSA layer and the encapsulating resin, thereby potentially reducing non-uniformity (standoff) between the semiconductor chips and the encapsulating resin. In some embodiments, the thickness change in this regard is preferably 15 µm or less, or more preferably 10 µm or less. The closer the thickness change is to 0 (zero) µm, the more preferred this is. It may be 0 µm. In some embodiments, for practical reasons such as balancing other properties, cost, etc., the thickness change may be, for example, 0.1 µm or less, 0.5 µm or less, 1 µm or less, 2 µm or less, or even 3 µm or less.

In some embodiments of the PSA layer disclosed herein, after dropping TBPGE onto the PSA layer surface of the adhesive layer and allowing it to stand for 1 minute, the percentage change in thickness of the PSA layer is preferably 160% or lower, or more preferably 150% or lower. When the PSA layer comprises a PSA layer with a reduced percentage change in thickness due to TBPGE swelling, for example, in use situations where semiconductor chips on the PSA layer are subjected to resin encapsulation, transfer of components between the PSA layer and the encapsulating resin tends to be reduced, thereby potentially reducing sticking. In this regard, in some embodiments, the percentage change in thickness may be, for example, 120% or lower, 100% or lower, 80% or lower, or even 60% or lower. The lower the percentage change in thickness, the more preferred. The lower limit is not specifically limited. In some embodiments, for practical reasons such as balancing other properties, cost, etc., the percentage change in thickness may be, for example, 5% or higher, 10% or higher, or even 20% or higher.

The thickness change is determined in the following manner: A predetermined amount of TBPGE (0.02 g using a 22 mm diameter syringe) is dropped onto the PSA layer surface and left for 1 minute in an environment at 23 °C and 50 % relative humidity (RH). After wiping off residual TBPGE on the PSA layer, the thickness of the PSA layer T1 is obtained at the point where TBPGE was dropped. From T1 and T0 (the initial thickness of the PSA layer at the same location before TBPGE was dropped), the thickness change is determined by the equation T1 - T0. From T1 and T0, the percentage change in thickness is determined by the equation (T1 - T0)/T0. For example, the thickness change and the percentage change in thickness can be adjusted to the above ranges by appropriately selecting the composition of the base polymer (e.g., acrylic polymer) of the layer A constituting at least the PSA layer surface, the degree of crosslinking, the type of the crosslinking agent, etc become. For example, when the acrylic polymer is formed from a monomer mixture containing at least 30% (more preferably at least 40%) (by weight) of an alkyl (meth)acrylate having an alkyl group having many carbon atoms (e.g. 4 or more, preferably 8 or more) at the ester end, the resulting PSA layer may have a small change in thickness and/or a small percentage change in thickness.

(TMA penetration depth)

In some embodiments of the PSA layer disclosed herein, the PSA layer may have a TMA penetration depth of about 20.0 µm or less (e.g., about 1.00 µm or more and 20.0 µm or less) in a 23°C environment. exhibit. The penetration depth of the PSA layer according to TMA at 23 °C (or hereinafter “TMA penetration depth”) represents the penetration depth 60 minutes after bringing the probe into contact with the PSA layer (first PSA layer) using a thermomechanical analyzer ( TMA). The TMA penetration depth is measured under the following conditions: Probe: With needle (cylindrical, tip diameter ø 1 mm); Nitrogen flow rate: 50.0 ml/min; Indentation load: 0.01 N. As the thermomechanical analyzer, the product designated TMA Q400 available from TA Instruments or an equivalent product can be used.

If the PSA sheet has a PSA layer on only one side of the substrate (i.e., if it does not have the second PSA layer mentioned below), the measurement is carried out after the side of the substrate opposite to the PSA layer (first PSA layer) has been provided with a standard PSA layer. The standard PSA layer is 45 µm thick and is formed using a PSA composition prepared by mixing 100 parts by weight of an acrylic polymer (formed from the following monomers: ethyl acrylate (EA)/2-ethylhexyl acrylate (2EHA)/methyl methacrylate (MMA)/2-hydroxyethyl acrylate (HEA) = 30/70/5/5 (by weight); weight average molecular weight 45*10 ⁴ ), 10 parts by weight of a tackifier (product name MIGHTY ACE G125, available from Yasuhara Chemical Co., Ltd.), 2 parts by weight of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation), 30 parts by weight of heat-expandable microspheres (product name MATSUMOTO MICROSPHERE F-190D, available from Matsumoto Yushi-Seiyaku Co., Ltd.) and toluene.

In some embodiments, the TMA penetration depth is preferably 15.0 µm or less, more preferably 10.0 µm or less, optionally 9.00 µm or less, or even 6.00 µm or less. For example, in usage situations where semiconductor chips are placed on the PSA layer and encapsulated with a resin, the PSA layer with a lower TMA penetration depth tends to reduce the embedding of the semiconductor chips into the PSA layer due to the application force on the semiconductor chips during resin encapsulation (e.g. steps (ii) and (iii) in the 2 ). In the structure with the chips and the encapsulation resin, reducing the embedding can reduce the semiconductor/encapsulation resin unevenness (sticking) caused by the embedding. A reduction in non-uniformity is also preferred for better prevention of adhesive transfer when the PSA layer is removed from the structure.

In some embodiments, with a view to improving the conformability to the adherend surface (e.g., any non-uniformity on the semiconductor chip surface), the TMA penetration depth is, for example, 1.50 µm or more, expediently 2.00 µm or more, furthermore 2.50 µm or more, 3.00 µm or more, or even 3.50 µm or more. In the PSA layer having such a TMA penetration depth, the conformability to the semiconductor chip surface can be advantageously combined with a reduction in the embedding of the semiconductor chips in the PSA layer.

The TMA penetration depth can be adjusted to these ranges by appropriately selecting, for example, the PSA layer structure (thickness, layer composition, etc.), the composition and degree of crosslinking of the base polymer (e.g., acrylic polymer) of the PSA constituting the PSA layer, the type of crosslinking agent, the type of substrate, etc.

In some embodiments of the PSA layer disclosed herein, the PSA layer has a TMA penetration depth (or hereinafter "high temperature TMA penetration depth") of suitably 2.00 μm or more and 60 μm or less in a 145 ° C environment, for example, optionally 3.00 µm or more and 50 µm or less or even 4.00 µm or more and 40 µm or less. The PSA layer with a high temperature TMA penetration depth within these ranges can advantageously reduce the embedding of semiconductor chips into the PSA layer even when exposed to high temperature environments (e.g., the heating environment during resin encapsulation). When the measurement atmosphere temperature is set to 145°C, the high-temperature TMA penetration depth is determined in the same way as the TMA penetration depth in the 23°C environment.

(probe stickiness value)

In some embodiments of the PSA layer disclosed herein, the PSA layer (first PSA layer) has a probe tack value of preferably 50 N/ø5mm or more, more preferably 75 N/ø5mm or more, or even more preferably 100 N/ø5mm or more, which is determined on the surface. A probe tack value within these ranges is preferred in view of preventing displacement of the adherend (e.g., semiconductor chips) disposed on the PSA layer. The probe tack value can be determined in an environment at 23 °C and 50% relative humidity (RH) using a commercially available probe tack tester under the following conditions: Diameter and material of the probe area: ø 5 mm SUS (stainless steel); Probe lowering speed: 30 mm/min; Contact Load: 100gf; Contact duration: 1 s; and testing speed: 30 mm/min.

(Adhesion to PET)

The adhesion strength to PET (adhesion strength to a polyethylene terephthalate film) of the PSA sheet disclosed herein is not particularly limited. For example, it may be 5.00 N/20 mm or less, 3.00 N/20 mm or less, or even 2.00 N/20 mm or less. In some embodiments, the adhesion strength to PET is preferably 1.00 N/20 mm or less, or more preferably 0.05 N/20 mm or less, in view of preventing damage to the adherend due to the load during removal of the PSA layer. In some embodiments, the adhesion strength on PET is expediently 0.03 N/20 mm or more, preferably 0.05 N/20 mm or more, optionally 0, with a view to preferentially fixing the joining part (e.g. of semiconductor chips) of the PSA layer. 10N/20mm or more or even 0.15N/20mm or more.

The adhesion strength to PET is determined by bonding a PET film (25 µm thick) as the adherend (by rolling a 2 kg roller back and forth once) to the PSA layer (first PSA layer) of the PSA layer with a width of 20 mm and a length of 140 mm, leaving the obtained article in an environment at a temperature of 23 °C for 30 minutes and performing a tensile test (at a peel angle of 180° and a tensile speed of 300 mm/min).

(tensile modulus)

In some embodiments, the first PSA layer has a tensile modulus at 25°C of preferably less than 100 MPa, more preferably 0.1 MPa to 50 MPa, or even more preferably 0.1 MPa to 10 MPa. Within these ranges, the first PSA layer is likely to have suitable bond strength in the resulting PSA sheet. The tensile modulus can be determined based on JIS K 7161:2008.

<PSA layer (first PPE layer)>

In the PSA sheet disclosed herein, as the PSA constituting the PSA layer (first PSA layer) disposed on at least one side of the substrate, any suitable PSA may be used as long as the effects of this invention can be obtained . For example, the PSA sheet may include one, two or more types selected from various known PSAs, such as an acrylic PSA, a rubber-based PSA (based on natural rubber, synthetic rubber, a blend thereof, etc.), a silicone-based PSA, a polyester-based PSA, a urethane-based PSA, a polyether-based PSA, a polyamide-based PSA and a fluorine-based PSA. In the PSA layer comprising two or more types of PSAs, there may be two or more types selected from PSAs of the same type (e.g., acrylic PSAs); or it may be one, two, or more types selected from any of two or more different types of PSAs (e.g., acrylic PSAs and polyester-based PSAs). In the PSA layer comprising two or more types of PSA, these PSAs may be uniformly mixed together, disposed at different positions (e.g., layered) in the thickness direction, or disposed at different positions (e.g., separately applied) in the plane direction. They may also have a combined or intermediate arrangement thereof.

The thickness of the first PSA layer is preferably 5 μm or more. If the first PSA layer has a thickness of at least 5 μm, it is likely to have good conformability to adherend surface structures. The maximum thickness of the first PSA layer is not particularly limited. For example, it can be 200 µm or less or even 150 µm or less. In some embodiments, the thickness of the first PSA layer is in view of preventing adhesive transfer due to cohesive failure of the PSA layer, preventing embedding of semiconductor chips in the PSA layer in usage situations in which the resin encapsulation process for semiconductor chips on the PSA layer is Layer is carried out, etc., expediently 110 µm or less, preferably 60 µm or less or more preferably 20 µm or less.

<Layer A>

The PSA layer (first PSA layer) typically includes layer A forming at least the PSA layer surface. In some embodiments, the PSA layer may have a single layer structure formed from layer A. In this case, layer A is formed by directly bonding the opposite side of the PSA layer surface to the surface of one side of the substrate. In further embodiments, the PSA layer may include another PSA layer (e.g., layer B described later) different from layer A between layer A and the one substrate surface. In such an embodiment, the differences between the PSA forming layer A and the PSA forming the another PSA layer may be, for example, one, two, or more of the following: differences in the base polymer (e.g., differences in the composition of monomers forming the base polymer, weight average molecular weight, polymer chain structure, etc.); differences in the crosslinking agent (e.g., the type and amount used); Differences in tackifying resin (e.g. presence/absence, amount included, type of tackifying resin, etc.); presence/absence of other additives, differences in their amounts and types; etc.

In some preferred embodiments, the PSA forming the layer A is an acrylic PSA comprising an acrylic polymer as a base polymer. When at least the first PSA layer surface is formed of the acrylic PSA, the effect of the invention disclosed herein can be obtained in an advantageous manner.

(acrylic polymer)

The acrylic polymer as the base polymer of the acrylic PSA is a polymerization product of monomers (a monomer mixture) which comprise an alkyl (meth)acrylate as the primary monomer and which may optionally further comprise a secondary monomer copolymerizable with the primary monomer. Here, the primary monomer refers to the main component of the monomers constituting the acrylic polymer, i.e., a component which accounts for more than 50% by weight of the monomers.

For example, a compound represented by the following formula (A) can be advantageously used as the alkyl (meth)acrylate. CH ₂ =C(R ¹ )COOR ² (A)

Wherein, R ¹ in the formula (A) is a hydrogen atom or a methyl group. R ² is an acyclic alkyl group having 1 to 20 carbon atoms (hereinafter, such a range of the number of carbon atoms may be indicated as "C _1-20 ", and an alkyl (meth)acrylate having an alkyl group having 1 to 20 carbon atoms may be indicated as "C _1-20 alkyl (meth)acrylate"). In view of easy adjustment of adhesive properties, etc., an alkyl (meth)acrylate in which R ² is a C _1-18 acyclic alkyl group is preferable, and an alkyl (meth)acrylate in which R ² is a C _1-12 acyclic alkyl group is more preferable.

Specific examples of the alkyl (meth)acrylate include C _1-20 alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, Heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate and eicosyl (meth)acrylate. In particular, it is preferred to use an alkyl (meth)acrylate having a straight or branched C _4-20 (more preferably C _6-20 , more preferably C _8-18 ) alkyl group (eg 2-ethylhexyl (meth)acrylate).

In some embodiments, a C ₄₊ straight or branched alkyl (meth)acrylate (i.e., an alkyl (meth)acrylate having a structure in which R ² in formula (A) is a straight or branched alkyl group having 4 or more carbon atoms (preferably 8 or more; and preferably 18 or less, e.g., 12 or less)) makes up at least 30 wt.% of the acrylic polymer-forming monomers. The use of such an alkyl (meth)acrylate can reduce the transfer of components between the PSA layer and the encapsulating resin. The amount of the alkyl (meth)acrylate in the monomers used for acrylic polymer synthesis is preferably 40 wt.% or higher. In some embodiments, it may be 50 wt.% or higher, or even 70 wt.% or higher. With a view to assisting in adjusting the indentation hardness H1 at the measuring point A to a suitable range, the alkyl (meth)acrylate content in the monomers is suitably 99.5 wt.% or lower, preferably 99 wt.% or lower, optionally 98 wt.% or lower, or even 97 wt.% or lower.

A secondary monomer copolymerizable with the alkyl (meth)acrylate (primary monomer) can assist in introducing crosslinking points into the acrylic polymer or in increasing the cohesive strength and heat resistance of the acrylic polymer. The secondary monomer can assist in adjusting the indentation hardness H1. As the secondary monomer, for example, only one kind or a combination of two or more kinds of the functional group-containing monomers mentioned below can be used.

Carboxy group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid;
Acid anhydride monomers such as maleic anhydride and itaconic anhydride; hydroxy group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate;
Amido-based monomers (N-substituted), such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide and N-methylol(meth)acrylamide as well as N-methylolpropane(meth)acrylamide;
Monomers having a nitrogen atom-containing ring, such as N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam and N-(meth)acryloylmorpholine;
Amino group-containing monomers such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate and t-butylaminoethyl (meth)acrylate;
Epoxy group-containing monomers such as glycidyl (meth)acrylate. Cyano group-containing monomers such as acrylonitrile and methacrylonitrile;
Sulfonate group-containing monomers such as styrenesulfonate, allylsulfonate, 2-(meth)acrylamide-2-methylpropanesulfonate, (meth)acrylamidepropanesulfonate, sulfopropyl (meth)acrylate and (meth)acryloyloxynaphthalenesulfonate;
Maleimide-based monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide and N-phenylmaleimide;
Itaconimide-based monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide and N-laurylitaconimide;
Succinimide-based monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide;
Alkoxysilyl group-containing monomers, such as alkoxysilyl group-containing (meth)acrylates, such as (3-(meth)acryloxypropyl)trimethoxysilane, (3-(meth)acryloxypropyl)triethoxysilane, (3-(meth)acryloxypropyl)methyldimethoxysilane and (3-(meth)acryloxypropyl)methyldiethoxysilane.

In addition to the functional group-containing monomers exemplified above, the monomers may include other copolymerizable monomers (comonomers) for improving cohesiveness, etc. Examples of such other comonomers include vinyl ester monomers such as vinyl acetate, vinyl propionate and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene and the like) and vinyltoluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g. phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g. phenoxyethyl (meth)acrylate) and arylalkyl (meth)acrylates (e.g. benzyl (meth)acrylate); olefinic monomers such as ethylene, propylene, isoprene, butadiene and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; glycol-based monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate and methoxypolypropylene glycol; and other monomers including hetero ring-containing monomers such as tetrahydrofurfuryl (meth)acrylate, fluoro(meth)acrylates and silicone (meth)acrylate.

As the further comonomer, the monomers may include a polyfunctional monomer for crosslinking purposes, etc. Non-limiting possible examples of such polyfunctional monomers include hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth) acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyfunctional epoxy acrylates, polyfunctional polyester acrylates and polyfunctional urethane acrylates. As the polyfunctional monomer, only one kind or a combination of two or more kinds can be used.

In some preferred embodiments, the acrylic polymer preferably comprises a constituent unit (monomeric unit) (a) derived from a monomer having a homopolymer glass transition temperature (Tg) of -5°C to 150°C (preferably 50°C to 150°C, more preferably 80°C to 120°C). The inclusion of such a constituent unit can assist in obtaining a layer A in which the molecular motion of the acrylic polymer is restricted and the ST ₂ relaxation time component is properly adjusted according to pulse NMR. With the layer A forming at least the first PSA layer surface, the resulting PSA sheet can have excellent low-temperature adhesion. Based on all the constituent units forming the acrylic polymer, the amount of the constituent unit a is preferably 0.1 to 20 wt%, more preferably 1 to 10 wt%, particularly preferably 1.5 to 8 wt%, or particularly 3 to 6 wt%.

Examples of monomers with a homopolymer Tg of -5 °C to 150 °C include 2-hydroxyethyl acrylate (Tg: -3 °C), 2-hydroxyethyl methacrylate (Tg: 77 °C), acrylic acid (Tg: 102 °C), cyclohexyl methacrylate (Tg: 83 °C), dicyclopentanyl acrylate (Tg: 120 °C), dicyclopentanyl methacrylate (Tg: 175 °C), isobornyl acrylate (Tg: 94 °C), isobornyl methacrylate (Tg: 150 °C), t-butyl methacrylate (Tg: 118 °C), methyl methacrylate (Tg: 105 °C), styrene (Tg: 80 °C), acrylonitrile (Tg: 97 °C), and N-acryloylmorpholine (Tg: 145 °C). For the glass transition temperatures of homopolymers of other monomers other than the above monomers, values given in the Polymer Handbook (3rd edition, John Wiley & Sons, Inc., 1989) are used. If the Polymer Handbook gives more than one value for a particular monomer, the highest value is used. If a specific homopolymer Tg is not specified in the known documents, the value obtained by the measurement method according to Japanese Patent Application Publication No. 2007-51271 shall be used.

Of these monomers, only one kind or a combination of two or more kinds can be used. In particular, methyl methacrylate increases the transparency of the PSA layer and is therefore preferred if the visibility of the adherend is to be increased during processing. Acrylic acid provides stronger adhesion to the adherend through intermolecular interactions and is therefore preferred when strong adhesion is required. 2-Hydroxyethyl (meth)acrylate is highly reactive with various crosslinking agents, making it suitable for forming a PSA with a short T ₂ relaxation time, as described later.

In some preferred embodiments, the acrylic polymer may comprise a structural unit derived from a carboxy group-containing monomer (“carboxyl monomer”). The amount of the carboxyl monomer-derived structural units based on all structural units constituting the acrylic polymer is preferably 0.1% by weight or more, more preferably 1% by weight or more, even more preferably 2% by weight or more; and preferably 15% by weight or less, more preferably 10% by weight or less, or even more preferably 7% by weight or less.

In some preferred embodiments, the acrylic polymer comprises a structural unit derived from a hydroxy group-containing monomer (“hydroxyl monomer”). The amount of hydroxyl monomer-derived structural units based on all structural units constituting the acrylic polymer is preferably 0.01% by weight or more, more preferably 0.03% by weight or more, for example 0.05% by weight or more; and preferably 20% by weight or less, or more preferably 10% by weight or less, for example 7% by weight or less.

(SP value)

In some embodiments, the base polymer (preferably an acrylic polymer) of the PSA forming Layer A has an SP value of, for example, suitably 10 or higher and 30 or lower, preferably 15 or higher and 25 or lower, or most preferably 18 or higher and 20 or lower. Within these ranges, transfer of components between the PSA layer and the encapsulating resin can preferably be prevented. It should be noted that the unit of numerical values indicating SP values is for all (cal/cm ³ ) ^1/2 .

The SP value is determined from the basic structure of the compound by the method proposed by Fedors. In particular, the SP value is determined from the vaporization energy Δe (cal) of each atom or group of atoms at 25 °C and the molar volume Δv (cm ³ ) of the atom or group of atoms at the same temperature by the following equation: $$\text{SP}-\text{Value}\left(\mathrm{\delta }\right)={\left({\displaystyle \sum \mathrm{\Delta }\text{e}}/{\displaystyle \sum \mathrm{\Delta }\text{v}}\right)}^{1/2}$$

(Reference: Hideki Yamamoto, “SP-value fundamentals, application, and calculation method” (4th edition), published by Johokiko Co., Ltd., April 3, 2006, pages 66-67 ).

When the polymer is a copolymer, its SP value is determined by calculating the SP values of homopolymers of the respective constituent units constituting the copolymer, multiplying these SP values by the mole fractions of the respective constituent units, and adding the products. In this case, for analysis of the respective constituent units (polymer composition analysis), only the PSA layer is conveniently taken out from the PSA sheet and immersed in an organic solvent such as dimethylformamide (DMF), acetone, methanol, tetrahydrofuran (THF), etc. The resulting solvent-soluble portion can be collected and analyzed by gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), and mass spectrometry.

(crosslinking agent)

With a view to assisting in obtaining the above-mentioned preferred indentation hardness H1, the base polymer of layer A is preferably crosslinked in the PSA forming layer A. For example, using a PSA composition comprising a base polymer and a suitable crosslinking agent, a layer A can be obtained which is formed from a PSA in which the base polymer is crosslinked with the crosslinking agent.

The type of the crosslinking agent is not particularly limited, and a suitable type can be selected and used from, for example, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. As the crosslinking agent, only one type or a combination of two or more types may be used. Particularly preferred crosslinking agents include epoxy-based crosslinking agents and isocyanate-based crosslinking agents.

Examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidylm-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (product name TETRAD C, available from Mitsubishi Gas Chemical Company, Inc.), 1,6-hexanediol diglycidyl ether (product name EPOLIGHT 1600, available from Kyoeisha Chemical Co., Ltd.), neopentyl glycol diglycidyl ether (product name EPOLIGHT 1500NP, available from Kyoeisha Chemical Co., Ltd.), ethylene glycol diglycidyl ether (product name EPOLIGHT 40E, available from Kyoeisha Chemical Co., Ltd.), propylene glycol diglycidyl ether (product name EPOLIGHT 70P, available from Kyoeisha Chemical Co., Ltd.), polyethylene glycol diglycidyl ether (product name EPIOL E-400, available from NOF Corporation), polypropylene glycol diglycidyl ether (product name EPIOL P-200, available from NOF Corporation), sorbitol polyglycidyl ether (product name DENACOL EX-611, available from Nagase ChemteX Corporation), glycerin polyglycidyl ether (product name DENACOL EX-314, available from Nagase ChemteX Corporation), pentaerythritol polyglycidyl ether, polyglycerin polyglycidyl ether (product name DENACOL EX-512, available from Nagase ChemteX Corporation), sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate, diglycidyl-o-phthalate, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol S diglycidyl ether and an epoxy resin having two or more epoxy groups in the molecule. Epoxy-based crosslinking agent(s) may be used in any suitable amount according to the desired properties. In some embodiments, the amount of epoxy-based crosslinking agent used for 100 parts by weight of the base polymer is, for example, optionally 0.01 parts by weight or more and 50 parts by weight or less, preferably 0.6 parts by weight or more and 15 parts by weight or less, more preferably 2 parts by weight or more and 13 parts by weight or less, or even more preferably 3 parts by weight or more and 10 parts by weight or less.

Specific examples of isocyanate-based crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and xylylene diisocyanate; Isocyanate adducts such as trimethylolpropane/tolylene diisocyanate trimer adduct (product name CORONATE L, available from Tosoh Corporation), trimethylolpropane/hexamethylene diisocyanate trimer adduct (product name CORONATE HL, available from Tosoh Corporation) and the isocyanurate of hexamethylene diisocyanate (product name CORONATE HX, available from Tos oh Corporation). The isocyanate-based crosslinking agent may be used in any amount appropriately selected according to the desired adhesion strength. In some embodiments, the amount of the isocyanate-based crosslinking agent based on 100 parts by weight of the base polymer is typically 0.1 part by weight or more and 20 parts by weight or less, or preferably 1 part by weight or more and 10 parts by weight or less.

In some embodiments, as the crosslinking agent used in the layer A, an epoxy-based crosslinking agent may preferably be used. With the layer A having a crosslinking structure in which the base polymer is crosslinked with an epoxy-based crosslinking agent, a preferred indentation hardness H1 disclosed herein can be obtained in an advantageous manner. The resulting PSA layer can also preferably reduce semiconductor chip/encapsulant resin unevenness. The PSA layer can also be formed with a high cohesive strength to effectively prevent displacement of the adherend.

In some embodiments, it is preferable to use as the crosslinking agent a crosslinking agent having a nitrogen atom (N). The N-containing crosslinking agent is advantageous because the catalytic activity of nitrogen atoms accelerates the crosslinking reaction (the reaction with carboxy groups in the base polymer) so as to assist in increasing the gel fraction of PSA. Specific Examples for the N-containing crosslinking agent include isocyanate-based crosslinking agents such as those described above and N-containing epoxy-based crosslinking agents (e.g., glycidylamino group-containing epoxy-based crosslinking agents such as N,N,N',N'-tetraglycidyl-m-xylenediamine and 1,3-bis(N,N-glycidylaminomethyl)cyclohexane). In some embodiments in which an N-containing crosslinking agent is used, the crosslinking agent is preferably used in an amount adjusted so that the amount of nitrogen gas generated mentioned below is 0.06 wt% or more and 1.0 wt% or less (more preferably 0.06 wt% or more and 0.9 wt% or less). Use in such an amount helps to obtain a PSA sheet in which no residue-remaining properties and surface conformability are advantageously combined.

In some embodiments, the quantitative ratio of the crosslinking agent (preferably a crosslinking agent that forms a crosslinking structure upon reaction with carboxy groups, e.g., an epoxy-based crosslinking agent, an isocyanate-based crosslinking agent, etc.) to carboxy groups in the base polymer (e.g., an acrylic polymer) is preferably 0.08 molar equivalents or higher and 2 molar equivalents or lower, or more preferably 0.1 molar equivalents or higher and 1 molar equivalent or lower. Use in such an amount can provide a preferred indentation hardness H1 disclosed herein. When the crosslinking agent is used in such an amount and allowed to undergo a crosslinking reaction with carboxy groups in the base polymer, a PSA sheet having few residual carboxy groups in the PSA layer can be obtained.

(Other additions)

The layer A-forming PSA may optionally comprise a suitable additive not mentioned above as an optional component. Examples of such additives include a tackifier, a plasticizer (e.g., a trimellitate ester-based plasticizer, a pyromellitate ester-based plasticizer, etc.), a pigment, a dye, a filler, an anti-aging agent, conductive materials, an antistatic agent, a UV absorber, a light stabilizer, a release modifier, a plasticizer, a surfactant, a flame retardant, and an antioxidant.

Any suitable tackifier can be used as the tackifier, for example a tackifier resin. Specific examples of the tackifier resin include rosin-based tackifier resins (e.g., unmodified rosin, modified rosin, rosin-phenol resins, rosin ester resins, etc.), terpene-based tackifier resins (e.g., terpene-based resins, terpene-phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, hydrogenated terpene resins), hydrocarbon tackifier resins (e.g., aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene resins, xylene resins, etc.), aliphatic/aromatic petroleum resins, aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, etc.), phenolic tackifier resins (e.g., alkylphenol resins, xylene-formaldehyde resins, resole, novolak, etc.), ketone tackifier resins, polyamide tackifier resins, epoxy tackifier resins, and elastomer tackifier resins. Particularly preferred examples include rosin tackifier resins, terpene tackifier resins, and hydrocarbon tackifier resins (styrene resins). As the tackifier, only one kind or a combination of two or more kinds may be used.

In some embodiments, a resin having a high softening point (Sp) or a high glass transition temperature (Tg) is used as the tackifier resin. When a resin having a high Sp or a high Tg is used, even in a high temperature environment (e.g., in processing for semiconductor chip encapsulation, etc.), a highly adhesive PSA layer can be formed. The Sp of the tackifier is preferably 100°C to 180°C, more preferably 110°C to 180°C, or even more preferably 120°C to 180°C. The Tg of the tackifier is preferably 100°C to 180°C, more preferably 110°C to 180°C, or even more preferably 120°C to 180°C.

In some embodiments, a low polarity tackifier resin is used as the tackifier resin. It is advantageous to use a low polarity tackifier resin in view of forming a PSA layer with a low affinity for the encapsulating material. Examples of the low polarity tackifier resin include hydrocarbon-based tackifier resins such as aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g. styrenic resins, xylene resins, etc.), aliphatic/aromatic petroleum resins (which may be referred to as C5/C9 petroleum resins). ), aliphatic/alicyclic petroleum resins and hydrogenated carbons hydrogen resins. Of these, aliphatic/aromatic petroleum resins are preferred. Such a tackifier resin has low polarity and excellent compatibility with acrylic polymers and can form a very stable PSA layer without phase separation over a wide temperature range.

The tackifier resin has an acid value of preferably 40 or lower, more preferably 20 or lower, or even more preferably 10 or lower. In such a range, a PSA layer having a low affinity with the encapsulating material can be formed. The tackifier resin has a hydroxyl value of preferably 60 or lower, more preferably 40 or lower, or even more preferably 20 or lower. In such a range, a PSA layer having a low affinity with the encapsulating material and capable of preventing transfer of components between the PSA layer and the encapsulating resin can be formed.

For example, the amount of the tackifier resin used for 100 parts by weight of the base polymer is optionally 5 parts by weight or more and 100 parts by weight or less, or preferably 8 parts by weight or more and 50 parts by weight or less. In some embodiments of the PSA sheet disclosed herein, in view of easy release of adherends, prevention of adhesive transfer, etc., the amount of the tackifier resin based on 100 parts by weight of the base polymer of the layer A-forming PSA is suitably less than 3 parts by weight, less than 1 part by weight, or less than 0.5 parts by weight. It is preferred that no tackifier (particularly tackifier resin) is added to the layer A-forming PSA.

(T ₂ relaxation time)

In some embodiments of the PSA layer disclosed herein, the layer A preferably has a short (S) T ₂ relaxation time component (T _2s ) of 45 µs or less according to pulse NMR. According to the PSA layer in which at least the first PSA layer surface is formed of a layer A with T _2s ≤ 45 µs, for example, in usage situations where semiconductor chips are arranged on the PSA layer and encapsulated with a resin, transfer of components between the PSA layer and the encapsulation resin can be reduced while the non-uniformity between the semiconductor chips and the encapsulation resin is reduced in an advantageous manner.

The relaxation time represents the time required for the excited atoms (groups) to return to the ground state after irradiation of the atoms to be analyzed with an appropriate energy. The excited state of atoms (groups) can be adjusted by the extent and time of energy irradiation. There are various known energy relaxation mechanisms for excited atoms (groups) to return to the ground state and the relaxation time depends on the relaxation mechanism (e.g. “Overview of Modern NMR for Chemists”, Kagaku Doujin (1997)). After exciting ¹ H atoms of an acrylic PSA (essentially the acrylic polymer in the PSA) under the conditions shown below, followed by measurement of the subsequent relaxation behavior and analysis of the measured values, the present inventors have found that of these values the ST ₂ relaxation time component (T _2s ) provides useful information for understanding molecular motion related to the degree of crosslinking of the base polymer (typically an acrylic polymer) in the PSA that forms the PSA layer; and have further found that the above effect can be obtained by setting the ST ₂ relaxation time component (T _2s ). A short T _2s indicates that the molecular motion associated with the degree of crosslinking is restricted in the base polymer, that is, crosslinking has advanced, thereby reducing the mobility of the polymer as a whole. In the PSA in such a state, the base polymer has only small interpolymer spaces with a tendency toward reduced transfer of the PSA layer components to the encapsulating resin and reduced migration of low molecular weight components in the encapsulating resin to the PSA layer. As a result, when semiconductor chips on the PSA layer are subjected to resin encapsulation and the PSA layer is later removed, unevenness between the semiconductor chips and the encapsulation resin is prevented.

In view of better reducing the transfer of components from the encapsulation resin, the ST ₂ relaxation time component (T _2s ) of the layer A according to pulse NMR is preferably 40 µs or less, or more preferably 35 µs or less (eg, 30 µs or less) . The minimum relaxation time T _2s of layer A is not specifically limited. For example, it can be 5 µs or more. To assist in obtaining appropriate tack at the PSA layer surface, T _2s of layer A may be 10 µs or more, 15 µs or more, or even 20 µs or more in some embodiments. It is preferred that layer A with a view to strengthening the adhesion between Layer A and its adjacent layer (possibly a substrate, a joining part, the layer B mentioned below, etc.) do not have an excessively short T _2s .

• M(t): Freier Induktionszerfall
• α: % Protonen der kurzen (S) Relaxationszeitkomponente
• T_2s: S T₂-Relaxationszeitkomponente (ms)
• β: % Protonen der langen (L) Relaxationszeitkomponente
• T_2L: L T₂-Relaxationszeitkomponente (ms)
• t: Erfassungszeit (ms)
• Wa: Formfaktor (= 1)

The T _2s of the layer A layer can be determined by obtaining a T ₂ relaxation curve measured by the solid-state echo method using about 100 mg of the PSA constituting the layer A as a measurement sample and fitting the T ₂ relaxation curve to the equation (1) shown below. The ST ₂ relaxation time component (T _2s ) of the layer B according to pulse NMR shown below can also be determined in the same manner.
$$\text{M}\left(\text{t}\right)=\mathrm{\alpha }\cdot \text{ex}\left(-\left(\text{1}/\text{What}\right){\left(\text{t}/{\text{T}}_{\text{2s}}\right)}^{\text{What}}\right)+\mathrm{\beta }\cdot \text{ex}\left(-\left(\text{1}/\text{What}\right){\left(\text{t}/{\text{T}}_{\text{2L}}\right)}^{\text{What}}\right)$$

• M(t): Free induction decay
• α: % protons of the short (S) relaxation time component
• T _2s : ST ₂ relaxation time component (ms)
• β: % protons of the long (L) relaxation time component
• T _2L : LT ₂ relaxation time component (ms)
• t: acquisition time (ms)
• Wa: form factor (= 1)

• • 90°-Pulsbreite: 2,1 µs
• • Wiederholungszeit: 1 s
• • Anzahl der Scans: 32
• • Messtemperatur: 30 °C

The measurement was carried out under the following conditions:

• • 90° pulse width: 2.1 µs
• • Repetition time: 1 s
• • Number of scans: 32
• • Measuring temperature: 30 °C

(Gel content)

The Layer A-forming PSA has a gel content of preferably 75% or higher, more preferably 85% or higher, or even more preferably 90% or higher. Within these ranges, the molecular movement of the base polymer can preferably be restricted by cross-links to reduce transfer of constituents between the PSA layer and the encapsulating resin. In terms of reducing constituent transfer, the higher the gel content of the Layer A-forming PSA, the more advantageous it is. In terms of balancing with other properties (e.g., tack, adhesion, adherend surface conformability, and the like at the PSA layer surface, which are appropriate), the gel content of the Layer A-forming PSA can be, for example, 99.5% or higher, or even 99% or higher in some embodiments. The gel content is determined by immersing the PSA obtained from layer A in ethyl acetate for 7 days, drying it, and then calculating (dry weight of PSA after immersion/weight of PSA before immersion) × 100.

(Amount of nitrogen gas formed)

In the PSA sheet according to some embodiments, the PSA constituting Layer A generates and releases nitrogen (gas) upon heating, preferably 0.06 to 1.0 wt%, or more preferably 0.06 to 0.9 wt% of the unheated PSA (100 wt%). When the amount of nitrogen released is at least 0.06 wt%, the PSA exhibits sufficient cohesive strength and tends to be less likely to cause unevenness between semiconductor chips and the encapsulating resin by reducing the transfer of components between the PSA sheet and the encapsulating resin. It is advantageous that the nitrogen release is up to 1.0 wt% in view of reducing the displacement of the adherend disposed on the Layer A.

• • Trägergas: O₂ (300 mL/min), Ar (300 mL/min)
• • Standardprobe: Pyridin/Toluol-Lösung
• • Detektor: Chemilumineszenzdetektor mit vermindertem Druck • Bereich: Hohe Konzentration

The amount of nitrogen released is determined as follows: A 2 mg sample of the PSA obtained and weighed on a ceramic plate is placed in a pyrolysis oven (800 °C)/oxidation oven (900 °C); and the amount of nitrogen released is determined by a TN (total nitrogen analysis) device. The analytical conditions can be as follows:

• • Carrier gas: O ₂ (300 mL/min), Ar (300 mL/min)
• • Standard sample: pyridine/toluene solution
• • Detector: Reduced pressure chemiluminescence detector • Range: High concentration

<Layer B>

In some embodiments of the PSA sheet disclosed herein, the first PSA layer includes layer A forming at least the PSA layer surface and layer B disposed adjacent to the substrate between layer A and the substrate. In other words, the outer surface (adherent-side surface) of the first PSA layer is formed of layer A, and the inner surface (substrate-side surface) of the first PSA layer is formed of layer B. According to the first PSA layer having such a structure, for example, by selecting specific PSAs to form layers A and B and selecting the thickness of each layer, etc., adjustment of the properties (indentation hardness, stringing indices, ST ₂ relaxation time component, etc.) at the measurement locations A and B as well as the ratio thereof can be easily performed.

As the PSA constituting the layer B, any suitable PSA can be used. For example, the layer B may comprise one, two or more kinds of PSA selected from various known PSAs such as an acrylic PSA, a rubber-based PSA, a silicone-based PSA, a polyester-based PSA, a urethane-based PSA, a polyether-based PSA, a polyamide-based PSA and a fluorine-based PSA.

In some preferred embodiments, layer B is formed from an acrylic PSA that includes an acrylic polymer as the base polymer. In an embodiment in which the layer A is formed from an acrylic PSA, in view of improving the interlayer adhesion of the layers in the first PSA layer, it is particularly preferred to use an acrylic PSA as the layer B-forming PSA .

In an embodiment where layer B is formed from an acrylic PSA, the acrylic polymer as the base polymer of the acrylic PSA may conveniently be selected from the same types of acrylic polymers specified above as the base polymer of layer A. The acrylic polymers as base polymers of layers A and B can be the same or different. In some preferred embodiments, the acrylic polymers as base polymers of layers A and B have different monomer compositions. In some embodiments, the same acrylic polymer may be used as the base polymers of layers A and B for purposes of adhesion between layers A and B. In such an embodiment, their relative amounts and properties at measurement points A and B can be adjusted using other materials (crosslinking agents, tackifiers, etc.) in addition to the base polymer or not, and selecting particular types, amounts thereof, etc.

The base polymer of layer B is preferably crosslinked in the layer B-forming PSA. For example, a PSA composition comprising a base polymer and a suitable crosslinking agent can be used to obtain layer B made of a PSA whose base polymer is crosslinked with the crosslinking agent. The type of the crosslinking agent used in layer B is not particularly limited. For example, a suitable type can be selected from the examples of the crosslinking agent that can be used in layer A. The crosslinking agents used in layers A and B may be of the same type (e.g., the same or different isocyanate-based crosslinking agents) or different (e.g., one is epoxy-based and the other is isocyanate-based).

In some preferred embodiments, an epoxy-based crosslinker is used in layer A and an isocyanate-based crosslinker is used in layer B. In general, compared to epoxy-based crosslinkers, isocyanate-based crosslinkers tend to form a more flexible crosslinking structure. Consequently, according to these embodiments, a first PSA layer with indentation hardness H2 > indentation hardness H1 can be obtained in an advantageous manner.

When an isocyanate-based crosslinking agent is used as the crosslinking agent in layer B, the amount of the isocyanate-based crosslinking agent required for 100 parts by weight of the base poly mers of Layer B (eg, the acrylic polymer) is not particularly limited and can be appropriately adjusted to obtain desired properties. For example, in some embodiments, the amount of the isocyanate-based crosslinking agent based on 100 parts by weight of the base polymer of Layer B is, for example, 0.1 parts or more and 20 parts or less, preferably 1 part or more and 10 parts or less, more preferably 1 part or more and 7 parts or less, optionally 1 part or more and 5 parts or less, 1 part or more and 5 parts or less by weight, or even 2 parts or more and 5 parts or less.

A crosslinking catalyst can also be used to progress the crosslinking reaction more effectively. Examples of the crosslinking catalyst include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric acetylacetonate, butyltin oxide and dioctyltin dilaurate. The amount of the crosslinking catalyst is not particularly limited. In some embodiments, in view of the balance between the crosslinking reaction rate and the pot life of the PSA composition, the amount of the crosslinking catalyst used for each 100 parts by weight of the base polymer may be, for example, 0.0001 part by weight or more and 1 part by weight or less (preferably 0.001 part by weight or more and 0.5 parts by weight or less). The crosslinking catalyst can be used in layer A or in both layers A and B.

In some embodiments of the PSA layer disclosed here, in which layer B forms the first PSA layer, with a view to improving the adaptability to the surface structure of a joining part which is arranged on the layer of the PSA layer, layer B has: according to a pulse NMR, preferably a longer T _2s than layer A (T _2s : ST ₂ relaxation time component). The difference in T _2s between layers A and B is, for example, optionally 5 µs or more, advantageously 10 µs or more, more preferably 15 µs or more, more preferably 20 µs or more, further optionally 25 µs or more or even 30 µs or more. In view of preventing cohesive failure of the PSA layer, since T _2s of layer B is excessively long, the difference in T _2s between layers A and B is, for example, desirably 70 µs or less, preferably 60 µs or less, more preferably 50 µs or less, possibly 40 µs or less or even 35 µs or less.

In some embodiments, it is appropriate for T _2s of layer B to be longer than T _2s of layer A and also to be 30 µs or more (eg, 35 µs or more, 40 µs or more, or 45 µs or more). With a view to improving the adaptability to the surface of the part to be joined, it is preferably more than 45 µs, possibly 47 µs or more or even 50 µs or more. With a view to preventing cohesive failure of layer B, T _2s of layer B is suitably 80 µs or less, preferably 70 µs or less, optionally 65 µs or less, 60 µs or less, or even 57 µs or less.

In some embodiments of the PSA sheet having a PSA layer comprising layers A and B, layer B has a thickness of, for example, optionally 3 µm or more, or suitably 4 µm or more. In view of more effectively imparting surface conformability, the thickness of layer B is preferably 5 µm or more, optionally 7 µm or more, 10 µm or more, or even 15 µm or more. The maximum thickness of layer B is not particularly limited. It may be, for example, 300 µm or less, 250 µm or less, 150 µm or less, or 130 µm or less. In usage situations where semiconductor chips are encapsulated on the PSA layer with a resin, the thickness of layer B is suitably 100 µm or less, preferably 90 µm or less, optionally 70 µm or less, 50 µm or less, 30 µm or less or even 20 µm or less, with a view to reducing the embedding of the semiconductor chips in the PSA layer.

In the PSA sheet having a PSA layer comprising layers A and B, layer A may have a thickness of, for example, 1 µm or more and 20 µm or less. In order to advantageously obtain the effect of improving conformability through the contribution of layer B, the thickness of layer A is in some embodiments advantageously 15 µm or less, preferably 10 µm or less, optionally 8 µm or less, or even 6 µm or less. In order to advantageously reduce transfer of components between the PSA layer and the encapsulating resin through the contribution of layer A, the thickness of layer A is in some embodiments advantageously 2 µm or more, preferably 3 µm or more, optionally 4 µm or more, or even 5 µm or more.

In the PSA sheet with a PSA layer comprising the layers A and B, the ratio (L2/L1) of the thickness L1 (µm) of the layer A to the thickness L2 (µm) of the layer B is not specifically limited. It can be, for example, about 0.5 to 100.0. In some embodiments, with a view to assisting layers A and B to effectively perform the respective functions, the ratio L2/L1 is desirably 0.5 or higher, preferably 0.7 or higher, optionally 0.8 or higher, 0 .9 or higher or even 1.0 or higher. In the same regard, the L2/L1 ratio is suitably 20.0 or lower, 15.0 or lower, 10.0 or lower, 5.0 or lower, 3.0 or lower, or even 2.0 or lower.

<substrate>

The substrate of the PSA sheet disclosed herein may be, for example, a resin sheet, a nonwoven fabric, a paper, a metal foil, a woven fabric, a rubber sheet, a laminate thereof (particularly, a laminate comprising a resin sheet), etc. Examples of the resin constituting the resin sheet include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), polyamide (nylon), wholly aromatic polyamide (aramid), polyimide (PI), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), a fluororesin, and polyetheretherketone (PEEK). Examples of the nonwoven fabric include a nonwoven fabric made of a heat-resistant natural fiber such as a Manila hemp-containing nonwoven fabric; a synthetic resin nonwoven fabric such as a polypropylene resin nonwoven fabric, a polyethylene resin nonwoven fabric and an ester resin nonwoven fabric. Examples of the metal foil include a copper foil, a stainless steel foil and an aluminum foil. Examples of a paper include Japanese paper and kraft paper.

In some embodiments, it is preferable to use, as the substrate, a resin layer formed of a resin having a glass transition temperature (Tg) of 25°C or higher (preferably 40°C or higher, more preferably 50°C or higher). When such a resin layer is used, the substrate maintains its shape even when heated in the encapsulation process, thereby preventing semiconductor chips from being embedded in the PSA layer. As the resin constituting such a resin layer, an aromatic ring-containing polymer is preferable. Specific examples include polyethylene terephthalate (PET), polyimide, and polyethylene naphthalate.

The substrate may have any suitable thickness according to the desired strength or flexibility as well as the use, purpose, etc. The substrate thickness is preferably 1000 µm or less, more preferably 25 µm or more and 1000 µm or less, even more preferably 40 µm or more and 500 µm or less, particularly preferably 60 µm or more and 300 µm or less, or particularly 80 µm or more and 250 µm or less. In one embodiment, a substrate having a thickness of 25 µm or greater is used. With a substrate having such a thickness, the substrate easily maintains its shape even when pressed in the encapsulation process and is suitable for preventing embedding of semiconductor chips in the PSA layer.

In one embodiment, of the total thickness of the PSA layer, the substrate thickness accounts for 20% or more and 90% or less (preferably 20% or more and 89% or less, more preferably 20% or more and 88% or less). In such a range, semiconductor chips can be advantageously prevented from being embedded in the PSA layer.

The substrate can be subjected to a surface treatment. Examples of the surface treatment include corona discharge treatment, chromic acid treatment, ozone exposure, flame exposure, high voltage shock treatment, ionized radiation treatment and coating with an adhesion promoter.

An organic coating material can be used as an adhesion promoter. Examples of the organic coating material include the materials described in “Plastic Hard Coating Materials II” (published in 2004, CMC Publishing Co., Ltd.). It is preferred to use urethane-based polymers, more preferably polyacrylic urethane, polyester urethane or their precursors because they can be easily applied to and distributed on a substrate, and various commercial or industrial types can be selected inexpensively. The urethane-based polymer is formed, for example, from a reaction mixture of an isocyanate monomer and an alcoholic hydroxy group-containing monomer (e.g., a hydroxy group-containing acrylic or ester compound). As optional additives, the organic coating material may include a chain extender such as a polyamine, an anti-aging agent, an oxidation stabilizer, etc. The thickness of the organic coating layer is not particularly limited. For example, it is expediently about 0.1 µm to 10 µm, preferably about 0.1 µm to 5 µm or more preferably about 0.5 µm to 5 µm.

<Second PPE layer>

The PSA layer according to some embodiments includes the substrate, the PSA layer disposed on one side of the substrate, and a second PSA layer disposed opposite the PSA layer on the substrate. The PSA layer in such an embodiment (double-sided adhesive PSA layer with substrate) is expedient because, for example, while it is attached to the second PSA layer on a suitable carrier (e.g. an SUS plate or a SUS sheet, a glass plate , etc.) is attached, the resin encapsulation process can be carried out on the first PSA layer. The second PSA layer may be formed from any suitable PSA.

In the PSA sheet according to some embodiments, at least the surface of the second PSA layer is formed with a PSA comprising thermally expandable microspheres (or simply "microspheres"). The PSA sheet in such an embodiment is preferred because the thermally expandable microspheres can be optionally expanded by heating at an appropriate time so that the bond between the second PSA layer and the adherend (e.g., the carrier) is easily released.

The microsphere-containing PSA may be a curable (hardening) PSA (eg, an active energy beam curable PSA) or a pressure-sensitive adhesive. Examples of the pressure-sensitive adhesive include an acrylic PSA and a rubber-based PSA. For details of the PSA in the second PSA layer, reference can be made, for example, to the Japanese patent application with the publication number 2018-009050 to get expelled. The entire description of this publication is incorporated herein by reference.

As the thermally expandable microspheres, any suitable thermally expandable microspheres can be used, which microspheres can expand or foam when heated. As the heat-expandable microspheres, for example, microspheres having an easily heat-expandable substance encapsulated in elastic shells can be used. Such thermally expandable microspheres can be prepared by any suitable method such as coacervation, interfacial polymerization, etc.

Examples of the easily heat expandable substance include low boiling point liquids such as propane, propylene, butene, n-butane, isobutane, isopentane, neopentane, n-pentane, n-hexane, isohexane, heptane, octane, petroleum ether, methane halide and tetraalkylsilane; and azodicarbonamide, which becomes gaseous through thermal decomposition.

Examples of the shell-forming substance include polymers made from nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile and fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide and substituted methacrylamide. The polymer formed from these monomers may be a homopolymer or a copolymer. Examples of the copolymer include a vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, a methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, a methyl methacrylate-acrylonitrile copolymer and an acrylonitrile-methacrylonitrile-itaconic acid copolymer.

As the heat-expandable microspheres, an inorganic or organic foaming agent can be used. Examples of the inorganic foaming agent include ammonium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride and various azides. Examples of the organic foaming agent include chlorofluoroalkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarbonamide and barium azodicarboxylate; hydrazine compounds such as para-toluenesulfonyl hydrazide, diphenylsulfone-3,3'-disulfonyl hydrazide, 4,4'-oxybis(benzenesulfonyl hydrazide) and allylbis(sulfonyl hydrazide); semicarbazide compounds such as p-toluenesulfonyl semicarbazide and 4,4'-oxybis(benzenesulfonyl semicarbazide); Triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso compounds such as N,N'-dinitrosopentamethylenetetramine and N,N'-dimethyl-N,N'dinitrosoterephthalamide.

Commercially available products can also be used as the heat-expandable microspheres. Specific examples of commercially available heat-expandable microspheres include product name MATSUMOTO MICROSPHERE (grade: F-30, F-30D, F-36D, F-36LV, F-50, F-50D, F-65, F-65D, FN-100SS, FN-100SSD, FN-180SS, FN-180SSD, F-190D, F-260D, F-2800D) available from Matsumoto Yushi-Seiyaku Co., Ltd.; product name EXPANCEL (grade: 053-40, 031-40, 920-40, 909-80, 930-120) available from Japan Fillite Co., Ltd.; the product name DAIFOAM (grade: H750, H850, H1100, S2320D, S2640D, M330, M430, M520) available from Kureha Chemical Industry Co., Ltd.; and the product name ADVANCEL (grade: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501) available from Sekisui Chemical Co., Ltd.

The heat-expandable microspheres have a particle size before heating (unheated) of preferably 0.5 µm to 80 µm, more preferably 5 µm to 45 µm, even more preferably 10 µm to 20 µm, or particularly preferably 10 µm to 15 µm. With respect to the average particle diameter, the particle size before heating of the heat-expandable microspheres is preferably 6 µm to 45 µm, or more preferably 15 µm to 35 µm. The particle size and the average particle diameter are determined by means of a laser scattering particle size distribution analysis.

The thickness of the PSA layer formed from the thermally expandable microsphere-containing PSA is not particularly limited. For example, it can be 3 µm or more. In view of preventing a decrease in the smoothness of the adhesive surface due to the inclusion of thermally expandable microspheres, the thickness of the PSA layer is typically suitably 7 µm or more, preferably more than 10 µm, optionally more than 15 µm, more than 25 µm, or even more than 35 µm. The maximum thickness of the PSA layer is not particularly limited. It is typically expediently 300 µm or less, optionally 200 µm or less, 150 µm or less, 100 µm or less or even 70 µm or less. It may be advantageous for the PSA layer to have a thickness that is not excessive in order to avoid cohesive failure of the PSA layer due to expansion of the thermally expandable microspheres. In some embodiments, the thickness of the PSA layer may be 60 μm or less, 50 μm or less, or even 45 μm or less.

The PSA layer preferably has a thickness Ta that is greater than the average particle diameter D of the thermally expandable microspheres before heating. That is, Ta/D is preferably over 1.0. With regard to the smoothness of the adhesion surface, Ta/D is preferably 2.0 or higher, optionally 3.0 or higher, or even 4.0 or higher in some embodiments. In view of facilitating separation by expansion of the microspheres, Ta/D is typically suitably 50 or lower, preferably 20 or lower, 15 or lower, or even 10 or lower.

The thermally expandable microspheres have suitable strength that can withstand expansion without bursting up to a volumetric expansion ratio of at least 5 times, more preferably at least 7 times, or even more preferably at least 10 times. When such thermally expandable microspheres are used, the adhesive strength can be efficiently reduced by heating.

The content of the thermally expandable microspheres in the PSA can be suitably adjusted depending on how much the adhesive strength is to be reduced. The content of the thermally expandable microspheres based on 100 parts by weight of the base polymer of the thermally expandable microspheres-containing PSA is, for example, 1 part to 150 parts, preferably 10 parts to 130 parts, or more preferably 20 parts to 100 parts (all by weight) .

When the PSA forming the second PSA layer surface comprises thermally expandable microspheres, the second PSA layer surface has an arithmetic average roughness Ra of preferably 500 nm or less, more, before expansion (ie, before heating (not heated)). preferably 400 nm or less or even more preferably 300 nm or less. Within such a range, a PSA layer can be obtained which has excellent adhesion to adherends on the second PSA layer side. The second PSA layer can have such excellent surface smoothness if, for example, the thickness of the PSA layer is within these ranges; when a thermally expandable microsphere-containing PSA composition is applied to a release liner and allowed to dry and the resulting PSA layer is applied directly to a substrate or to a Interlayer (eg, an elastic interlayer) formed on the substrate is transferred; etc.

When the second PSA layer comprises heat-expandable microspheres, the PSA layer preferably comprises a PSA formed from a base polymer having a dynamic storage modulus in the range of 5 kPa to 1 MPa (more preferably 10 kPa to 0.8 MPa) at 80°C. With such a PSA layer, a PSA sheet can be formed which has a suitable adhesive strength before heating, but whose adhesive strength slightly decreases upon heating. The dynamic storage modulus can be determined at a frequency of 1 Hz at a heating rate of 10°C/min using a dynamic viscoelasticity analyzer (product name ARES, available from Rheometrics Scientific, Inc.).

<Method for producing the PPE layer>

The PSA sheet of this invention can be manufactured by any suitable method. For example, the PSA layer of this invention may be formed by a method of forming a PSA layer by directly applying a PSA composition comprising the components of the PSA layer (optionally the first PSA layer, layers A and B, which form the first PSA layer). layer, the second PSA layer, etc.) on a substrate or an intermediate layer (e.g. the layer B, an elastic middle layer, etc.) on the substrate, by a method in which the PSA composition on a applying any suitable separable in-process material (e.g., a release liner) thereon to form a PSA layer and transferring the PSA layer to a substrate or an intermediate layer on the substrate; or by a process combining them, etc. The PSA composition may be a solvent-based PSA composition comprising any suitable solvent.

The thermally expandable microsphere-containing PSA layer may be formed by applying a composition to a substrate, the composition comprising thermally expandable microspheres, a PSA and a suitable solvent. Alternatively, it may be formed by spreading thermally expandable microspheres on a PSA-coated layer and then embedding the microspheres into the PSA using a laminator, etc.

Regarding the methods for applying the PSA and the respective compositions, any suitable coating method can be used. For example, they may be applied to form the respective layers and then dried. The coating methods use, for example, a multi-purpose coating device, a die coating device, a gravure coating device, or an applicator. Examples of the drying method include natural drying and heat drying. For heat drying, the heating temperature can be set to any suitable temperature according to the properties of the substance to be dried.

[Examples]

Several examples of the present invention will be described below, but the present invention is not limited to these specific examples. In the following description, "parts" and "%" refer to weight unless otherwise specified.

<Test procedure>

1. Indentation hardness

Using a nanoindenter TRIBOINDENTER TI-950 available from Hysitron (currently Bruker), the indentation hardness H1 and H2 were determined using the above method.

2. Thread pulling index

Using a nanoindenter TRIBOINDENTER TI-950 available from Hysitron (currently Bruker), the threading indices D1 and D2 were determined by the above method.

3. Source check

$$\%\ddot{\text{A}}\text{nderung der Dicke}=\left(\left(\text{T}1-\text{T}0\right)/\text{T}0\right)\times 100$$

Using a syringe (ø 22 mm), 0.02 g of TBPGE was dropped onto the first PSA layer surface and left for 1 minute in an environment at 23 °C and 50% relative humidity (RH). After remaining TBPGE on the PSA layer was adsorbed and removed with wipes, the thickness of the PSA layer T1 (µm) was measured at the location where TBPGE was dropped. From T0 (µm) (the initial thickness of the PSA layer at the same location before spotting TBPGE) and T1 (µm), the change and percentage change in the thickness of the PSA layer were calculated by the following equations: $$\text{Dicken}\ddot{\text{a}}\text{change}\left(\mathrm{\mu }\text{m}\right)=\text{<figure-callout id="1" label="T" filenames="DE112022002949T5\_0006.png" state="{{state}}">T</figure-callout>}1-\text{<figure-callout id="0" label="T" filenames="DE112022002949T5\_0007.png" state="{{state}}">T</figure-callout>}0$$

$$\%\ddot{\text{A}}\text{change in thickness}=\left(\left(\text{<figure-callout id="1" label="T" filenames="DE112022002949T5\_0006.png" state="{{state}}">T</figure-callout>}1-\text{T}0\right)/\text{T}0\right)\times 100$$

4. TMA penetration depth

Using a thermomechanical analyzer with the product name TMA Q400, available from TA Instruments, with a needle tip probe (cylindrical, tip diameter ø 1 mm) at a measuring atmosphere temperature of 23 ° C, the penetration depth from the first PSA layer surface was measured in a nitrogen stream of 50.0 mL/min and an indentation load of 0.01 N were measured for a load time of 60 min. Five measurements (N = 5) were performed. Excluding the maximum and minimum values from the measured values, the average value (N = 3) was obtained as the TMA penetration depth.

If there is a PSA layer (first PSA layer) on only one side of the substrate and the opposite side (back) of the substrate is free of a second PSA layer in the PSA layer, the TMA penetration depth after the formation of a Standard PSA layer (45 µm thick PSA layer comprising 10 parts of a tackifier, 2 parts of an isocyanate-based crosslinking agent and 30 parts of thermally expandable microspheres) for every 100 parts of an acrylic polymer (EA/2EHA/MMA/ HEA = 30/70/5/5 (weight ratio)).

5. Relaxation time

About 100 mg of PSA was removed from the layer A-forming PSA by scraping. Using it as a measurement sample, a T ₂ relaxation curve was obtained by pulse NMR analysis. The curve was fitted using the above equation (1) by analysis software (TDNMR-A) and approximated a component (α) so that the ST ₂ relaxation time component was determined. The analysis was performed with all Wa values set to 1. The shortest relaxation time calculated by the analysis method was used as the ST ₂ relaxation time component (T _2s ) of layer A according to pulse NMR. In the same way, the ST ₂ relaxation time component (T _2s ) of layer B was determined according to pulse NMR. Pulse NMR measurements were carried out by the solid-state echo method using a time domain NMR instrument (model number TD-NMR the minispec mq20, available from Bruker) with a 90° pulse width of 2.1 µs and a repetition time of 1 s at a Measurement temperature of 30 °C (32 scans accumulated) was carried out.

6. Strength of pressure sensitive adhesive on PET

The PPE sheet was cut to a size 20 mm wide and 140 mm long. Using a double-sided adhesive tape (Product No. 531 available from Nitto Denko Corporation), the entire back surface (opposite the side provided with the first PSA layer) was attached to a SUS304 plate using a 2 kg hand roller . Regarding a PSA sheet having a second PSA layer on the back side of a substrate, instead of using the double-sided adhesive tape No. 531, the back side of the PSA sheet was adhered to the SUS304 board over the second PSA layer.

In an environment of 23°C and 50% relative humidity (RH), a polyethylene terephthalate (PET) film (product name LUMIRROR S10, available from Toray Industries, Inc.; 25 µm thick, 30 mm wide) was attached to the adhesive surface of the PSA sheet with the back side attached to the SUS304 plate using a 2 kg roller moved back and forth once. After the obtained article was left in the environment for 30 minutes, the load was measured with a tensile tester, while the PET film was peeled off from the PSA sheet at a peeling angle of 180° at a tensile speed of 300 mm/min. The average load during this time was used as the adhesion strength of the PSA sheet to PET. As the tensile tester, one with the product name AUTOGRAPH AG-120kN available from Shimadzu Corporation was used.

7. Anchoring strength after heating

The PSA sheet was cut into a size of 20 mm in width and 140 mm in length. Using a double-sided adhesive tape (product No. 531, available from Nitto Denko Corporation), the entire surface of the back side (opposite to the side provided with the first PSA layer) was attached to a SUS304 plate using a 2 kg hand roller. Regarding a PSA sheet having a second PSA layer on the back side of a substrate, instead of using the double-sided adhesive tape No. 531, the PSA sheet was attached to the SUS304 plate via the second PSA layer. The obtained article was left to stand in an environment at 150°C for 1 hour and then left to stand in an environment at 23°C and 50% relative humidity (RH) for 2 hours. Then, in the environment at 23°C and 50% relative humidity (RH), a deep cut was made from the first PSA layer surface through the substrate surface with a cutting knife. On the cut, a commercially available acrylic PSA tape (product No. 315, available from Nitto Denko Corporation) was adhered with pressure by a 2 kg roller moved back and forth once. The obtained article was left for 30 minutes. Then, the load was measured with the tensile tester while the acrylic PSA tape was peeled off at a pulling angle of 180° at a pulling speed of 50 mm/min. The maximum load during this was recorded as the anchoring strength after heating.

8. Adhesion strength to an encapsulation resin

The PPE sheet was cut to a size 50 mm wide and 140 mm long. A frame (with a rectangular opening 35 mm wide and 90 mm long, 564 μm thick) was attached to the first PSA layer. The area inside the frame was sprinkled with grains of an epoxy resin-based encapsulating material (G730, available from Sumitomo Bakelite Co., Ltd.) to a cured resin thickness of 0.3 mm and then covered with a silicone-treated release liner. Using NS-VPF-50 hydraulic forming machine manufactured by Meisho-Press Co., Ltd. is available, the encapsulating resin was thermoformed onto the first PSA layer at the following conditions: a temperature of 145 °C, a molding time of 600 seconds, a pressure of 0.3 MPa (300 mm square table), a vacuum time of 600 seconds and a vacuum degree of -0.1 MPa. The resulting article was heated at 150°C for 7 hours so that the encapsulating resin was cured, and then left to stand in an environment at 23°C and 50% relative humidity (RH) for 2 hours. The portion where the encapsulating resin is in contact with the first PSA layer was cut into a size having a width of 20 mm and a length of 88 mm, so that a test sample was prepared. The test sample was left in the environment at 23 °C and 50% relative humidity (RH) for 30 minutes. Then, using the tensile tester, the load was measured while peeling the PSA sheet from the encapsulating resin at a peeling angle of 180° at a pulling speed of 300 mm/min. The average load during this was used as the adhesion strength of the PSA layer to the encapsulating resin.

9. Properties that leave no residue

When measuring the adhesion strength to an encapsulating resin, the presence/absence of adhesive residue remaining on the encapsulating resin was visually observed after the PSA layer was removed. Based on the results, the properties of no residue remaining were rated as "P" (poor) when adhesive residue was observed and "G" (good) when no adhesive residue was observed.

10. Mold flash test

• Träger: SUS-Träger (ø 220 mm)
• Chip: Dummy-Chip mit einer ungleichmäßigen Oberfläche (ein Dummy-Chip mit einem 7 mm × 7 mm × 400 µm dicken Siliziumsubstrat mit einer Kupfer-Kontaktstelle auf einer Seite (Kontaktstellen-Zielhöhe: 5,5 µm, Maske: GNC-300mm-G03-A-300S), erhältlich von Global Net Corporation)
• Verbindungsvorrichtung: FC3000W, erhältlich von Toray Engineering Co. Ltd.
• Verbindungsbedingungen: Pressverbindungszeit 6 Sekunden, Pressverbindungsdruck 10 N und Pressverbindungstemperatur 23 °C
• Einkapselungsgerät: MS-150HP, erhältlich von Apic Yamada Corporation
• Einkapselungsharz: G730, erhältlich von Sumitomo Bakelite Co., Ltd.
• Vorwärmbedingung: 130 °C für 30 s
• Zeit vom Vorwärmen bis zum Beginn des Einkapselns: 1 Stunde Einkapselungstemperatur: 145 °C
• Vakuumzeit: 5 s
• Einkapselungszeit: 600 s
• Klemmkraft: 3,6 MPa
• Einkapselungsdicke: 600 µm

Semiconductor chips were resin encapsulated on the first adhesion surface of the PSA layer under the conditions shown below, and the ability to prevent encapsulation resin from entering the chip/encapsulation resin interface (mold flash) was evaluated.

• Support: SUS support (ø 220 mm)
• Chip: Dummy chip with an uneven surface (a dummy chip with a 7 mm × 7 mm × 400 µm thick silicon substrate with a copper pad on one side (pad target height: 5.5 µm, mask: GNC-300mm-G03-A-300S), available from Global Net Corporation)
• Connecting device: FC3000W, available from Toray Engineering Co. Ltd.
• Connection conditions: Press connection time 6 seconds, press connection pressure 10 N and press connection temperature 23 °C
• Encapsulation machine: MS-150HP, available from Apic Yamada Corporation
• Encapsulating resin: G730, available from Sumitomo Bakelite Co., Ltd.
• Preheating condition: 130 °C for 30 s
• Time from preheating to start of encapsulation: 1 hour Encapsulation temperature: 145 °C
• Vacuum time: 5 s
• Encapsulation time: 600 s
• Clamping force: 3.6 MPa
• Encapsulation thickness: 600 µm

• 1) Die Rückseite der PSA-Lage wurde mittels einer durch Wärme ausdehnbare Mikrokügelchen-enthaltenden PSA-Schicht an einen SUS-Träger geklebt (in einer Atmosphäre bei 23 °C, Verbindungszylinderdruck 0,1 MPa, Verbindungsgeschwindigkeit 0,5 m/min).

The encapsulation process was carried out using the following procedure.

• 1) The back side of the PSA sheet was bonded to a SUS support using a thermally expandable microsphere-containing PSA layer (in an atmosphere at 23 °C, bonding cylinder pressure 0.1 MPa, bonding speed 0.5 m/min).

As the thermally expandable microsphere-containing PSA layer, if the PSA sheet had a second PSA layer comprising thermally expandable microspheres on the substrate back, the second PSA layer was used as such. If the PSA layer did not have the second PSA layer on the substrate back, a standard PSA layer mentioned above (a 45 µm thick PSA layer containing 30 parts of thermally expandable microspheres (product name) for every 100 parts of the acrylic polymer was used MATSUMOTO MICROSPHERE F-190D available from Matsumoto Yushi-Seiyaku Co., Ltd.) and the back of the PSA layer was attached to the SUS carrier using the standard PSA layer.

2) Using the connecting device, on the first PSA layer of the PSA sheet attached to the SUS carrier, a total of 25 of the above dummy chips were arranged along eight radial straight lines with 45° central angles, the distance being expanded from the center in the direction of the outer circumference. The chips were arranged so that their irregular surface (surface with contact point) faces the first PSA layer.

3) The SUS carrier was preheated under the specified conditions while having the dummy chips with the uneven surface arranged on the first PSA layer of the PSA sheet.

4) After preheating, the obtained article was left in an environment at 23 °C and 50% relative humidity (RH) for 1 hour; then, the specified encapsulation resin was evenly spread on the dummy chips manually; and the chips were encapsulated using the specified encapsulation device under the specified encapsulation conditions.

5) The resulting laminate was heated at 150°C for 4 hours to cure the encapsulation resin.

6) After standing in an environment at 23°C and 50% relative humidity (RH) for 5 days, the thermoset laminate was heated on a hot plate so that the thermally expandable microspheres in the PSA layer forming the PSA layer were fixed to the SUS carrier, expanded and the SUS carrier was separated from the laminate.

7) After separating the SUS carrier, the PSA layer was peeled off from the laminate to obtain a structure formed of the encapsulating resin and the dummy chips with the uneven surface.

Regarding the structure, the surface in contact with the first adhesive surface was examined with a laser confocal microscope (OLS-4000, available from OLYMPUS) to confirm whether or not the encapsulation resin penetrated onto the dummy chips having the uneven surface . When a PSA residue (adhesive residue) was found on the surface, examinations were carried out after removing the residue with toluene. As a result, when penetration of an encapsulating resin was found in any of the dummy chips, it was rated as “P” (Poor: Poor anti-mold flash properties). If penetration of an encapsulating resin was not detected in any of the dummy chips, it was rated as “G” (good: good anti-mold flash properties).

11. Testing the distance

On the first adhesive surface of the PSA layer, in the same manner as in the mold flash test, but using Si mirror chips (7 mm × 7 mm × 400 µm thick) as the semiconductor chips (Si Chips), the semiconductor chips (Si chips) were encapsulated with a resin, so that a structure formed of the encapsulation resin and Si mirror chips was obtained.

Regarding the structure, the surface in contact with the first adhesive surface was examined with a laser confocal microscope (OLS-4000, available from OLYMPUS), and the protruding height (height difference at the interface between the Si chip and the encapsulating resin on the protruding surface) was measured for the Si chip located in the middle. If PSA residue (adhesive residue) was found on the surface, measurements were taken after removing the residue with toluene. As a result, if the protruding height was less than 3.3 µm, it was rated as “G” (good: protruding was greatly reduced). If the protruding height was 3.3 µm or more, it was rated as “P” (poor: reduction in protruding was insufficient).

<Example 1>

A toluene solution comprising 100 parts of a polymer P1 (an acrylic polymer formed from the monomers 2-ethylhexyl acrylate (2EHA)/acrylic acid (AA) = 95/5 (weight ratio); SP value 19.3) was added 5 parts an epoxy-based crosslinking agent (product name TETRAD C, available from Mitsubishi Gas Chemical Company, Inc.) and toluene for dilution (to a total of 100 parts) were added and mixed to prepare a PSA composition 1a. The PSA composition 1a was applied to the release surface of a release film R1 (product name CERAPEEL MDAR, available from Toray Industries, Inc.; 38 μm thick) made of polyethylene terephthalate (PET) coated on one side with a silicone-based release agent has been treated, applied and allowed to dry so that a PSA layer 1A (thickness L1 = 10 μm) was formed on the release film R1.

In the same manner as in the preparation of the PSA composition 1a, but using 3 parts of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation) instead of 5 parts of the epoxy-based crosslinking agent, a PSA was prepared -Composition 1b produced. The PSA composition 1b was applied to a surface of a PET film (product name LUMIRROR S10, available from Toray Industries, Inc.; 38 µm thick) as the substrate and allowed to dry to form a PSA layer 1B (thickness L2 = 10 µm) was formed on the surface of the substrate.

The adhesive surface of the PSA layer 1A formed on the release film R1 was adhered to the adhesive surface of the PSA layer 1B, so that a PSA sheet having a first PSA layer formed from the PSA layers 1B and 1A was obtained on a surface of the substrate (a PSA sheet having a structure of substrate/PSA layer 1B (layer B)/PSA layer 1A (layer A)).

<Example 2>

The amount of crosslinking agent used and the thicknesses of layers A and B were as shown in Table 1. Otherwise, in the same manner as in Example 1, a PSA sheet having a structure of substrate!PSA layer 2B (layer B)/PSA layer 2A (layer A) was obtained.

<Example 3>

To a toluene solution comprising 100 parts of a polymer P2 (an acrylic polymer formed from the monomers n-butyl acrylate (BA)/ethyl acrylate (EA)/AA = 50/50/5 (weight ratio); SP value 19.6), 5 parts of an epoxy-based crosslinking agent (product name TETRAD C, available from Mitsubishi Gas Chemical Company, Inc.) and toluene for dilution (to a total of 100 parts) were added and mixed to prepare a PSA composition 3a. The PSA composition 3a was applied to the release surface of the release film R1 and allowed to dry so that the PSA layer 3A (thickness L1 = 5 µm) was formed on the release film R1.

In the same manner as in the preparation of the PSA composition 3a, but using 3 parts of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation) instead of 5 parts of the epoxy-based crosslinking agent, a PSA composition 3b was prepared. The PSA composition 3b was applied to one surface of a PET film (product name LUMIRROR S10, available from Toray Industries, Inc.; 38 µm thick) as the substrate and allowed to dry so that a PSA layer 3B (thickness L2 = 35 µm) was formed on the surface of the substrate.

The adhesive surface of the PSA layer 3A formed on the release film R1 was adhered to the adhesive surface of the PSA layer 3B, so that a PSA sheet having a structure of substrate/PSA layer 3B (layer B)/PSA layer 3A (layer A)) was obtained.

<Example 4>

The layers A and B were formed to have the thicknesses shown in Table 1. Otherwise, in the same manner as in Example 3, a PSA sheet having a structure of substrate/PSA layer 4B (layer B)/PSA layer 1A (layer A)) was obtained.

<Example 5>

To a toluene solution comprising 100 parts of a polymer P3 (an acrylic polymer formed from the monomers EA/2EHA/methyl methacrylate (MMA)/2-hydroxyethyl acrylate (HEA) = 30/70/5/4 (weight ratio); SP value 20.7) were added 30 parts of heat-expandable microspheres (product name MATSUMOTO MICROSPHERE F-190D, available from Matsumoto Yushi-Seiyaku Co., Ltd.), 1.4 parts of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation), 10 parts of a tackifier (product name MIGHTY ACE G125, available from Yasuhara Chemical Co., Ltd.) and toluene for dilution (to a total of 100 parts). The resulting product was mixed to prepare a PSA composition 5c. The PSA composition 5c was applied to the release surface of the release film R1 and allowed to dry so that a PSA layer 5C (45 µm thick) was formed on the release film R1.

The adhesive surface of the PSA layer 5C, which is formed on the release film R1, was glued to the substrate back of the PSA layer according to Example 4, so that a double-sided PSA layer with a structure of PSA layer 5C (second PSA layer) /substrate/PSA layer 4B (layer B)/PSA layer 4A (layer A).

<Example 6>

To a toluene solution comprising 100 parts of the polymer P3 was added 1.5 parts of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation), 10 parts of a tackifier (product name MIGHTY ACE G125, available from Yasuhara Chemical Co., Ltd.) and toluene to dilute (to a total of 100 parts) were added and mixed. The resulting product was mixed to prepare a PSA composition 6a. The PSA composition 6a was applied to the release surface of the release film R1 and allowed to dry so that a PSA layer 6A (30 μm thick) was formed on the release film R1.

To a toluene solution comprising 100 parts of the polymer P3, 1 part of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation) and toluene for dilution (to a total of 100 parts) were added and mixed to form a PSA composition 6b was produced. The PSA composition 6b was applied to a surface of a PET film (product name LUMIRROR S10 available from Toray Industries, Inc.; 38 µm thick) as the substrate and allowed to dry so that a PSA layer 6B (thickness L2 = 20 µm) was obtained on the surface of the substrate.

The adhesive surface of the PSA layer 6A formed on the release film R1 was adhered to the adhesive surface of the PSA layer 6B, so that a PSA sheet having a structure of substrate/PSA layer 6B (layer B)/PSA Layer 6A (Layer A)) was obtained.

<Example 7>

A toluene solution containing 100 parts of a polymer P4 (an acrylic polymer formed from the monomers 2EHA/acryloylmorpholine (ACMO)/HEA = 75/25/22 (weight ratio) and further with 11 moles of 2-isocyanatoethyl methacrylate (KARENZ MOI, available from Showa Denko K.K) based on 22 moles of HEA modified), 5 parts of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation), 10 parts of a UV-curable oligomer (product name ARONIX M321, available from Toagosei Co., Ltd.), 3 parts of a photoinitiator (product name OMNIRAD 651, available from IGM Resins) and ethyl acetate for dilution were added and mixed to prepare a PSA composition 7a. The PSA composition 7a was applied to the release surface of the release film R1 and allowed to dry so that a PSA layer 7A (thickness L1 = 5 μm) was obtained on the release film R1.

To a toluene solution comprising 100 parts of the polymer P2, 1 part of an isocyanate-based crosslinking agent (product name CORONATE L, available from Tosoh Corporation), 10 parts of a UV-curable oligomer (product name ARONIX M321, available from Toagosei Co., Ltd.), 3 parts of a photoinitiator (product name OMNIRAD 651, available from IGM Resins), and ethyl acetate for dilution were added and mixed to prepare a PSA composition 7b. The PSA composition 7b was applied to one surface of a PET film (product name LUMIRROR S10, available from Toray Industries, Inc.; 38 µm thick) as the substrate and allowed to dry to form a PSA layer 7B (thickness L2 = 150 µm) on the surface of the substrate.

The adhesive surface of the PSA layer 7A formed on the release film R1 was adhered to the adhesive surface of the PSA layer 7B, so that a PSA sheet having a structure of substrate/PSA layer 7B (layer B)/PSA layer 7A (layer A)) was obtained.

The resulting PSA sheets were evaluated using the methods described above. The results are shown in Table 1. It should be noted that when measuring the anchor strength after heating, separation always developed at the interface between the acrylic PSA tape and the adhesive surface of interest and no anchor failure was observed at the interface with the substrate (PET film).
[Table 1] Table 1 Example 1 2 3 4 5 6 7 1 PSA layer Layer A (parts) P1 100 100 - - - - - P2 - - 100 100 100 - - polymer P3 - - - - - 100 - P4 - - - - - - 100 Isocyanate crosslinking agents Epoxy crosslinking agents 1.5 4.5 5 10 5 5 5 Tackifier UV-curable oligomer photoinitiator - - - - - 10 - - - - - - - 10 - - - - - - 3 Thickness of layer A L1 (µm) 10 5 5 6 6 30 5 Layer B (parts) P1 100 100 - - - - - polymer P2 - - 100 100 100 - 100 P3 - - - - - 100 - Isocyanate crosslinking agents 3 3 3 3 3 1 1 UV-curable oligomer photoinitiator - - - - - - 10 - - - - - - 3 Thickness of layer B L2 (µm) 10 5 35 10 10 20 150 Thickness ratio (L2/L1) 1.0 1.0 7.0 1.7 1.7 0.7 30.0 Total thickness (L1 + L2) (µm) 20 10 40 16 16 50 155 Substrate thickness (µm) 38 38 38 38 38 38 38 Thickness of the second PSA layer (µm) - - - - 45 - - exams Indentation hardness H1 (MPa) 0.161 0.204 0.224 0.224 0.224 0.050 0.098 H2 (MPa) 0.074 0.074 0.046 0.046 0.046 0.037 0.010 Ratio (H2/H1) 0.46 0.36 0.20 0.20 0.20 0.74 0.10 Thread pulling index D1 (nm) 124 106 135 135 135 1550 1105 D2 (nm) 796 796 534 534 534 18600 3771 Ratio (D2/D1) 6.42 7.51 3.96 3.96 3.96 12,00 3.41 Source testing Initial thickness T0 (µm) Thickness after swelling T1 (µm) 20 10 40 16 16 50 51 29 16 52 24 24 75 71 Thickness change (µm) 9 6 12 8th 8th 25 20 % Change in thickness 45% 60% 30% 50% 50% 50% 39% TMA penetration depth (µm) 4.20 4.00 9.80 4.80 4.80 8.60 10.70 T _2s -relaxation time Layer A (µs) 28 22 26 26 26 52 48 Layer B (µs) 56 56 53 53 53 55 61 Adhesion strength to PET (N/20 mm) 0.30 0.20 0.85 0.54 0.54 5.40 7.15 Anchoring strength after heating (N/20 mm) 5.80 5.50 6.10 6.20 6.20 9.40 17,75 Adhesion strength to the encapsulation resin (N/20 mm) 1.60 1.50 2.50 2.10 2.10 10.20 11,50 Properties such that no residue remains Mold flash test Standoff test G G G G G P P G G G G G G G G G G G G P P

As shown in Table 1, the PSA sheets of Examples 1 to 5 (0.10 MPa ≤ H1 ≤ 0.50 MPa, 0.001 MPa ≤ H2 ≤ 0.090 MPa) exhibited good anti-mold flash properties with good no residue properties.

Although specific embodiments of the present invention have been described in detail above, these are for illustrative purposes only and do not limit the scope of the claims. The technique according to the claims includes various modifications and changes made to the specific embodiments shown above.

[reference symbol list]

1

Semiconductor chip

2

Encapsulation resin

10

Substrate (substrate film)

20

PSA layer (first PSA layer)

22

Layer A

24

Layer B

30

Second layer of PPE

100, 200, 300

PPE situation

A

Measuring point A

b

Measuring point B

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2021115926 [0001]
• JP2001308116 [0002]
• JP 2001313350 [0002]
• JP2018009050 [0127]

Non-patent literature cited

• Hideki Yamamoto, “SP-value fundamentals, application, and calculation method” (4th edition), published by Johokiko Co., Ltd., April 3, 2006, pages 66-67 [0083]

Claims (19)

A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer disposed on at least one side of the substrate, the pressure-sensitive adhesive layer having an indentation hardness H1 of 0.10 MPa or more and 0.50 MPa or less at the pressure-sensitive adhesive layer surface and an indentation hardness H2 of 0.001 MPa or more and 0.090 MPa or less measured at a distance of 4 µm from the substrate in the direction of the pressure-sensitive adhesive layer surface in a cross section of the pressure-sensitive adhesive sheet according to an indentation hardness measurement using a nanoindenter. Pressure-sensitive adhesive layer according to Claim 1 , where the ratio of the indentation hardness H2 (MPa) to the indentation hardness H1 (MPa) (H2/H1) is 0.002 or higher and 0.90 or lower. Pressure-sensitive adhesive layer according to Claim 1 or 2 wherein the pressure-sensitive adhesive layer surface has a stringing index D1 of 50 nm or more and 500 nm or less in a stringing test using a nanoindenter; and a stringing index D2 of 150 nm or more and 1000 nm or less determined at a distance of 4 µm from the substrate in the direction of the pressure-sensitive adhesive layer surface in a cross section of the pressure-sensitive adhesive layer. Pressure-sensitive adhesive layer Claim 3 , wherein the ratio of the threading index D2 (nm) to the threading index D1 (nm) (D2/D1) is 0.3 or higher and 20.0 or lower. Pressure-sensitive adhesive layer according to one of the Claims 1 until 4 wherein, when the pressure-sensitive adhesive layer has an initial thickness T0 (µm), after 4-t-butylphenyl glycidyl ether is dropped onto the pressure-sensitive adhesive layer surface and after standing for 1 minute, the pressure-sensitive adhesive layer has a thickness T1 (µm) with a difference from the initial thickness (T1 - T0) of 20 µm or less. Pressure-sensitive adhesive layer according to one of the Claims 1 until 5 , which has a needle probe penetration of 3.50 µm or more and 20.0 µm or less from the pressure-sensitive adhesive layer surface, which was measured using a thermomechanical analyzer at a measurement ambient temperature of 23 ° C and an indentation load of 0.01 N for an indentation time of 60 minutes is measured. Pressure-sensitive adhesive layer according to one of the Claims 1 until 6 , wherein the pressure-sensitive adhesive layer has a thickness of 5 µm or more and 110 µm or less. Pressure-sensitive adhesive layer according to one of the Claims 1 until 7 wherein the substrate is a substrate film formed of a resin material having a glass transition temperature of 25 °C or higher. Pressure-sensitive adhesive layer according to one of the Claims 1 until 8th , which has an adhesion strength of 0.05 N/20 mm or more and 1.00 N/20 mm or less on a polyethylene terephthalate (PET) film. Pressure-sensitive adhesive layer according to one of the Claims 1 until 9 , which has an anchoring strength of 4.00 N/20 mm or more to the substrate, determined at 23 ° C after heating the pressure-sensitive adhesive layer at 150 ° C for one hour. Pressure-sensitive adhesive layer according to one of the Claims 1 until 10 wherein at least the pressure-sensitive adhesive layer surface is formed of an acrylic pressure-sensitive adhesive comprising an acrylic polymer as its base polymer. Pressure-sensitive adhesive layer according to Claim 11 , wherein the acrylic polymer has an SP value of 18.0 to 20.0. Pressure-sensitive adhesive layer according to one of the Claims 1 until 12 , wherein the pressure-sensitive adhesive layer comprises a layer (A) which forms the pressure-sensitive adhesive layer surface and a Layer (B) disposed adjacent to the substrate between layer A and the substrate. Pressure-sensitive adhesive layer Claim 13 , wherein the layer A has a thickness L1 of 1 μm or more and 10 μm or less. Pressure-sensitive adhesive layer according to Claim 13 or 14 , wherein layer B has a thickness L2 of 4 µm or more and 100 µm or less. Pressure-sensitive adhesive layer according to one of the Claims 13 until 15 , wherein the ratio of the thickness L2 (µm) of layer B to the thickness L1 (µm) of layer A (L2/L1) is 1.0 to 100.0. Pressure-sensitive adhesive layer according to one of the Claims 13 until 16 , wherein layer A has a T _2s of 45 µs or less and layer B has a T _2s of more than 45 µs, where T _2s is the short T ₂ relaxation time component according to a pulse NMR. Pressure-sensitive adhesive layer according to one of the Claims 13 until 17 , wherein layer A is crosslinked with an epoxy-based crosslinking agent and layer B is crosslinked with an isocyanate-based crosslinking agent. Pressure-sensitive adhesive layer according to one of the Claims 1 until 18 wherein the pressure-sensitive adhesive layer comprises the substrate, the pressure-sensitive adhesive layer is disposed on one side of the substrate, and a second pressure-sensitive adhesive layer is disposed on the opposite side of the substrate relative to the pressure-sensitive adhesive layer, wherein at least the second pressure-sensitive adhesive layer surface is formed of a pressure-sensitive adhesive is that comprises thermally expandable microspheres.

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