JP2013072069A - Living radical polymerization initiator, star copolymer, resin composition, and die bonding film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a living radical polymerization initiator capable of allowing a star copolymer having the viscosity lower than before to be synthesized.SOLUTION: The living radical polymerization initiator has at least three branched chains, each of which has a halogen atom at the end thereof, in one molecule and at least one benzene ring on the chain between two closest halogen atoms of the plurality of halogen atoms thereof. The minimum number of atoms existing on the chain between the two halogen atoms is 9-30 and each of two atoms among the 9-30 atoms is bonded to the meta or para position of the benzene ring.

Description

  The present invention relates to a living radical polymerization initiator, a star copolymer obtained by using the polymerization initiator, a resin composition containing the copolymer, and a die bond film comprising the resin composition.

  In recent years, along with the miniaturization of semiconductor packages, CSP (Chip Size Package) that is the same size as a semiconductor chip, and stacked CSP in which semiconductor chips are stacked in multiple stages have become widespread (see, for example, Patent Documents 1 to 5). ). In order to perform adhesion on a package having unevenness, a performance for satisfactorily filling the unevenness is required.

One typical example of the semiconductor adhesive is a die bond film. Usually, a die bond film is comprised from resin and a filler, and resin is comprised combining a thermosetting component and a high molecular weight component.
As the thermosetting component, an epoxy resin is particularly preferably used from the viewpoint of heat resistance and moisture resistance, and as the high molecular weight component, a polyimide resin having a crosslinkable group, a (meth) acrylic resin, or the like is used. Among them, acrylic rubber is preferably used.

As die-bonding film characteristics, process compatibility (laminate property, dicing property, pickup property), embedding property, reliability (reflow resistance) and the like are required.
Among these, in order to satisfy the requirements for embedding, it is only necessary to increase the fluidity of the resin, specifically, to lower the viscosity at the B stage. The entanglement between each other is reduced, and the overall viscosity can be reduced.

  However, in order to satisfy the reliability requirement, the resin must have a high molecular weight, and the fluidity is lowered. In order to eliminate the trade-off relationship between fluidity and reliability, a solution has been made by using a star-shaped structural polymer (star-shaped copolymer) (see Patent Document 6).

JP 2001-279197 A JP 2002-222913 A JP 2002-359346 A JP 2001-308262 A Japanese Patent Laid-Open No. 2004-072009 JP 2009-231469 A

  However, a four-chain star polymer synthesized using a generally available tetrafunctional initiator (Pentaerythritoltetrakis (2-bromoisobutyrate)) exhibits only a melt viscosity equivalent to that of a linear structure polymer. Further improvement in fluidity was not achieved, leaving room for improvement.

  This invention is made | formed in view of the above conventional trouble, and makes it a subject to achieve the following objectives. That is, an object of the present invention is to provide a living radical polymerization initiator capable of synthesizing a star copolymer having a lower viscosity than before, a star copolymer having a low viscosity obtained by using the polymerization initiator, The object is to provide a resin composition containing a mold copolymer and a higher-bonding die-bonding film comprising the resin composition.

The present invention for solving the above problems is as follows.
(1) A living radical polymerization initiator having at least three branched chains having a halogen atom at its end in one molecule,
The halogen atom has at least one benzene ring in the bond between the two closest halogen atoms, and the minimum number of atoms bonded between the halogen atoms is 9 to 30; A living radical polymerization initiator, wherein two atoms bonded to the benzene ring among ˜30 atoms are bonded at the meta position or para position of the benzene ring.

(2) The living radical polymerization initiator according to (1), which is represented by the following general formula (1).

［一般式（１）中、Ａは少なくとも１個のベンゼン環を含む原子団を表し、Ｒ^１及びＲ^２は、それぞれ独立に、水素原子又は炭素数１〜５の脂肪族基を表し、Ｘはハロゲン原子を表し、ｎは３以上の整数を表す。］

[In General Formula (1), A represents an atomic group containing at least one benzene ring, R ¹ and R ² each independently represent a hydrogen atom or an aliphatic group having 1 to 5 carbon atoms; Represents a halogen atom, and n represents an integer of 3 or more. ]

(3) The living radical polymerization initiator according to (2), wherein the general formula (1) is represented by the following structural formula (1).

(4) The living radical polymerization initiator according to (2), wherein the general formula (1) is represented by the following structural formula (2).

(5) A star copolymer obtained by polymerizing monomer species using the living radical polymerization initiator according to any one of (1) to (4).

(6) A resin composition comprising the star copolymer according to (5), an epoxy resin, and a curing agent.

(7) The resin composition as described in (6) above, further comprising a filler, a silane coupling agent, and a curing accelerator.

(8) A die-bonding film comprising the resin composition according to (6) or (7).

According to the present invention, a living radical polymerization initiator capable of synthesizing a star copolymer having a lower viscosity than the conventional one, a low viscosity star copolymer obtained by using the polymerization initiator, and the star copolymer. It is possible to provide a resin composition containing a polymer and a higher-bonding die-bonding film comprising the resin composition.
In particular, it is possible to synthesize star-shaped polymers with a lower viscosity than four-chain star-shaped polymers synthesized using a commercially available initiator (Pentaerythritoltetrakis (2-bromoisobutyrate)), and to produce a higher-flow die-bonding film. Can be provided.

<Living radical polymerization initiator>
The living radical polymerization initiator of the present invention (hereinafter sometimes simply referred to as “the polymerization initiator of the present invention”) is a living radical polymerization initiator having at least three branched chains having a halogen atom as a terminal in one molecule. An agent having at least one benzene ring in the bond between the two closest halogen atoms among the halogen atoms, and the minimum number of atoms bonded between the halogen atoms being 9 to 30 Of the 9 to 30 atoms, two atoms bonded to the benzene ring are bonded at the meta position or para position of the benzene ring.

  That is, the polymerization initiator of the present invention has at least one benzene ring in the bond between halogen atoms, which is the starting point of living radical polymerization, and the minimum number of atoms bonded between the halogen atoms is 9 to Since it has a structure of 30, that is, a structure having a considerable distance from a branched chain having a halogen atom at its terminal, a copolymer having a star structure in which at least three polymer chains extend radially (hereinafter referred to as “star”). May be referred to as a “type copolymer”).

A star-shaped copolymer has characteristics of high fluidity and low viscosity as compared with a linear polymer having the same molecular weight. This is because a linear polymer has a longer molecular chain when the molecular weight increases, and entanglement occurs between adjacent molecules, but a star copolymer has a structure in which a polymer chain extends radially from the center. It is presumed that the polymer chain part does not become longer as the polymer in the shape of a polymer and the occurrence of entanglement is less. That is, it is considered that the fluidity at the same molecular weight improves as the number of branched chains increases. However, in reality, as described above, a star copolymer synthesized using a commercially available tetrafunctional initiator (Pentaerythritoltetrakis (2-bromoisobutyrate)) is a star copolymer synthesized using a bifunctional initiator. The fluidity was almost the same as that of the star structure, and the high fluidity characteristic of the star structure could not be expressed.
As described above, the polymerization initiator of the present invention has an steric hindrance between the halogen atoms due to the presence of atoms having the above-described configuration between the closest halogen atoms among the halogen atoms as the polymerization start points. Is so far as to be negligible, and the closest halogen atoms are so spaced, so that other halogen atoms are further spaced apart. That is, it is presumed that, as a whole, it is possible to synthesize a high-fluidity star copolymer in which each branched chain is precisely extended without being affected by other steric hindrance in which the polymerization initiation point is extended.
First, the polymerization initiator of the present invention will be described in detail below.

In the polymerization initiator of the present invention, the polymerization initiator has at least three branched chains. The branched chain corresponds to the number of polymer chains of the star polymer to be synthesized. It is preferable to set according to the number of polymer chains. For example, when synthesizing a star copolymer of three polymer chains, the number of branches is three, and when synthesizing a star copolymer of four polymer chains, the number of branches is Four.
In addition, a maximum of 21-strand star polymers have been reported so far, but in order to suppress the termination reaction caused by increasing the number of branched chains, and thus the risk of gelation, the polymerization is carried out at a low monomer conversion rate. Stopped. From the above, it is considered that there are about 3 to 18 branched chains that can withstand industrially and practically.

  The polymerization initiator of the present invention has at least one benzene ring in the bond between the two closest halogen atoms among the halogen atoms. The presence of the benzene ring provides a constant separation between the halogen atoms. A distance can be secured. The number of benzene rings is preferably set as appropriate according to the number of polymer chains of the star copolymer to be synthesized. For example, when synthesizing a star copolymer of three polymer chains, 1 to 4 are preferable, and when synthesizing a star copolymer of four polymer chains, 1 to 6 are preferable, When synthesizing a star-shaped copolymer having 6 polymer chains, 2 to 10 are preferable.

On the other hand, in the polymerization initiator of the present invention, the minimum number of atoms bonded between the closest halogen atoms is defined as 9 to 30, but if it is less than 9, the distance between the closest halogen atoms becomes closer, The influence of the obstacle cannot be ignored, and if it exceeds 30, the synthesis of the polymerization initiator itself becomes difficult. The minimum number of atoms bonded between the halogen atoms is preferably 9 to 12 when the number of polymer chains of the star-shaped copolymer to be synthesized is 3, and 14 to when the number of polymer chains is 4 18 is preferred.
Furthermore, of the 9 to 30 atoms bonded between the halogen atoms, two atoms bonded to the benzene ring are bonded at the meta position or para position of the benzene ring, but should be at the meta position or para position. Thus, a certain separation distance between the halogen atoms can be ensured from the balance of the bond distance and bond angle, and the influence of the steric hindrance of the polymer chain in the case of a star copolymer can be eliminated. On the other hand, at the ortho position, the interatomic distance is short, and a constant separation distance cannot be secured, and the influence of the steric hindrance of the polymer chain cannot be ignored.
In addition, even when two or more benzene rings are present between the two closest halogen atoms, it is preferable that two atoms are bonded to each other at the meta position or the para position, but the distance between the halogen atoms. Is preferably set as appropriate so that a certain separation distance can be secured.

  Specifically, the polymerization initiator of the present invention preferably has a structure represented by the following general formula (1).

［一般式（１）中、Ａは少なくとも１個のベンゼン環を含む原子団を表し、Ｒ^１及びＲ^２は、それぞれ独立に、水素原子又は炭素数１〜５の脂肪族基を表し、Ｘはハロゲン原子を表し、ｎは３以上の整数を表す。］

[In General Formula (1), A represents an atomic group containing at least one benzene ring, R ¹ and R ² each independently represent a hydrogen atom or an aliphatic group having 1 to 5 carbon atoms; Represents a halogen atom, and n represents an integer of 3 or more. ]

  A is an atomic group containing at least one benzene ring, but may be a benzene ring itself, or a linear or branched alkyl group having 1 to 10 carbon atoms or carbon atoms on at least one benzene ring. Linear or branched alkoxyalkyl having 1 to 10 carbon atoms, cycloalkane having 3 to 10 carbon atoms, phenyl group, carbonyl group, methoxy group, aralkyl group, nitrogen-containing cyclic structure, specifically piperidyl group, pyridine group, A structure in which a pyrimidine group or the like is bonded is preferable. However, the structure bonded to the benzene ring is not limited to the above structure. A is preferably a point-symmetric or line-symmetric structure.

  X represents a halogen atom such as fluorine, chlorine or bromine, preferably chlorine or bromine, more preferably bromine.

R ¹ and R ² represent a hydrogen atom and an aliphatic group having 1 to 5 carbon atoms, and specifically, the aliphatic group represents an alkyl group having 1 to 10 carbon atoms and an alkoxyalkyl group, It may be linear or branched, and among them, a linear alkyl group having 1 to 5 carbon atoms is preferable, and a linear alkyl group having 1 to 3 carbon atoms is more preferable. Specifically, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, cyclohexyl group, heptyl group, octyl group, 2 -Ethylhexyl group, nonyl group, decyl group, dodecyl group, stearyl group, 2-methoxyethyl group, 2-ethoxyethyl group, 2-propoxyethyl group, 2-butoxyethyl group, 3-methoxypropyl group, 3-methoxybutyl Group, 4-methoxybutyl group, 2-hydroxyethyl group, 2-hydroxypropyl group and the like.

  The n corresponds to the number of branched chains of the polymerization initiator. Since the number of the branched chains has already been described, the description is omitted here.

  As a structure represented by the above general formula (1), for example, a structure represented by the following structural formula (1) or (2) is preferable.

  By using the star copolymer synthesized using the polymerization initiator of the present invention as a high molecular weight component of the die bond film, high fluidity can be ensured while having a high molecular weight. And high reliability. Next, the star copolymer synthesized using the polymerization initiator of the present invention will be described in detail.

<Star copolymer>
The star-shaped copolymer of the present invention is characterized by polymerizing monomer species using the above-described polymerization initiator of the present invention.
The star-shaped copolymer of the present invention is a copolymer having a star-shaped structure in which at least three polymer chains extend radially. Specifically, the resin classification includes (meth) acrylic resin, polyimide resin, urethane. Resins, polyphenylene ether resins, polyether imide resins, phenoxy resins, modified polyphenylene ether resins, and the like can be mentioned, among which acrylic rubber is preferable. The star copolymer preferably has a glass transition point Tg of 60 ° C. or less, more preferably 50 ° C. or less, and further preferably 40 from the viewpoint of fluidity of the resin blend and toughness of the cured product. It is below ℃.

  The acrylic rubber is a rubber mainly composed of an acrylate ester and mainly composed of a copolymer such as butyl acrylate and acrylonitrile or a copolymer such as ethyl acrylate and acrylonitrile. In the present invention, as described above, Has a star structure.

  The weight average molecular weight of the star copolymer is preferably 30,000 to 1,000,000, more preferably 60000 to 800,000, and 100,000 to 600,000 from the viewpoint of obtaining high reliability as a die bond film. Is more preferable. In addition, the said weight average molecular weight is a polystyrene conversion value using the calibration curve by a standard polystyrene by the gel permeation chromatography method (GPC). In this case, the weight average molecular weight of each polymer chain is preferably 10,000 to 300,000, more preferably 30,000 to 200,000, and further preferably 50,000 to 150,000. The weight average molecular weight of each polymer chain is a value obtained by dividing the weight average molecular weight of the whole molecule by the number of polymer chains. When the star copolymers having the same weight average molecular weight are composed of similar monomers, the greater the number of polymer chains, the shorter the polymer chains per one, so that the fluidity is improved. As a result, it is considered that the viscosity becomes low. Therefore, when it is desired to keep the weight average molecular weight as it is and to lower the viscosity, the viscosity can be lowered by increasing the number of polymer chains.

Although the specific example of a star-shaped copolymer and an example of the synthesis method are given below, the star-shaped copolymer of the present invention is not limited to the following synthesis method. The star copolymer of the present invention is, for example, one type using the polymerization initiator of the present invention, an amine compound as a ligand, and a transition metal of Group 7 to 11 elements of the periodic table as a catalyst. It can be synthesized by polymerizing the above monomer species by atom transfer radical polymerization. The number of monomer species to be polymerized is not particularly limited, and may be two or more, or may be three or more.
Below, each component used in the said synthesis method is demonstrated first.

[Monomer species]
The monomer species is not particularly limited, and various types can be used. For example, the following monomers can be mentioned. In addition, although the following structural formula shows an acryl-type thing, a methacryl-type thing can also be used. That is, in the structures (1) to (7), those in which CH ₂ ═CH— is replaced with CH ₂ ═C (CH ₃ ) — can also be used.

R in the above (1) represents an aliphatic group having 1 to 20 carbon atoms or an aromatic group having 6 to 20 carbon atoms. Specific examples of the aliphatic group include alkyl having 1 to 20 carbon atoms. Represents a group or an alkoxyalkyl group, and may be linear or branched. Among them, a linear alkyl group having 1 to 10 carbon atoms is preferable, and a linear alkyl group having 2 to 8 carbon atoms is more preferable.
Specifically, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, cyclohexyl group, heptyl group, octyl group, 2 -Ethylhexyl group, nonyl group, decyl group, dodecyl group, stearyl group, 2-methoxyethyl group, 2-ethoxyethyl group, 2-propoxyethyl group, 2-butoxyethyl group, 3-methoxypropyl group, 3-methoxybutyl Group, 4-methoxybutyl group, 2-hydroxyethyl group, 2-hydroxypropyl group and the like. On the other hand, the aromatic group represents an aryl group having 6 to 20 carbon atoms and an aralkyl group having 7 to 20 carbon atoms, and among them, an aryl group having 6 to 10 carbon atoms and an aralkyl group having 7 to 11 carbon atoms are preferable. Specific examples include a phenyl group, a toluyl group, and a benzyl group.

  R in the above (3) represents H, an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom, and among them, H or an aliphatic hydrocarbon group having 1 to 3 carbon atoms or a halogen atom is preferable. Or a C1-C2 aliphatic hydrocarbon group or a halogen atom is more preferable. For example, it represents an alkyl group having 1 to 5 carbon atoms, chlorine, and bromine, and more specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a tert-butyl group, a pentyl group, and the like.

R ¹ and R ^{2 in} the above (4) represent H or an aliphatic hydrocarbon group having 1 to 4 carbon atoms, and the aliphatic hydrocarbon group represented by R ¹ and R ² is, among others, H or carbon number. 1-3 aliphatic hydrocarbon groups are preferred. For example, it represents an alkyl group having 1 to 4 carbon atoms, and more specifically includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and the like. Moreover, the alkyl group which R < ¹ >, R < ² > represents may be substituted by the amino group.

R ^{1 in the} above (5) represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, and as the aliphatic hydrocarbon group having 1 to 4 carbon atoms represented by R ¹ , among them, it has 1 to 2 carbon atoms. Aliphatic hydrocarbon groups are preferred. For example, it represents an alkylene group having 1 to 4 carbon atoms, and more specifically includes a methylene group, an ethylene group, a propylene group, and the like. R ² and R ³ represent H, an aliphatic hydrocarbon group having 1 to 4 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, and the aliphatic hydrocarbon group represented by R ² and R ³ is Is preferably an aliphatic hydrocarbon group having 1 to 2 carbon atoms. For example, it represents an alkyl group having 1 to 4 carbon atoms, and more specifically includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and the like. Specific examples of the aromatic hydrocarbon group having 6 to 10 carbon atoms include a phenyl group, a toluyl group, and a benzyl group.

R ^{1 in the} above (7) represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and among them, an aliphatic hydrocarbon group having 2 to 4 carbon atoms is preferable. For example, it represents an alkylene group having 1 to 5 carbon atoms, and more specifically includes a methylene group, an ethylene group, a propanediyl group, a butanediyl group, a pentanediyl group, and the like. R ² , R ³ and R ⁴ represent an aliphatic hydrocarbon group having 1 to 5 carbon atoms and an alkoxy group having 1 to 5 carbon atoms. Among the aliphatic hydrocarbon groups having 1 to 5 carbon atoms, An aliphatic hydrocarbon group having 1 to 4 carbon atoms is preferable, and an aliphatic hydrocarbon group having 2 to 3 carbon atoms is more preferable. For example, an alkyl group having 1 to 5 carbon atoms is represented, and more specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a tert-butyl group, a pentyl group, and the like can be given. Specific examples of the alkoxy group having 1 to 5 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group.

  Among the (1) to (7), ethyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylonitrile are preferable. The expression “(meth) acrylic acid” indicates acrylic acid and / or methacrylic acid.

  Moreover, as a monomer seed | species used in the manufacturing method of this invention, the monomer which has a crosslinkable functional group can also be used suitably. Examples thereof are shown below, but the present invention is not limited to the following.

In the above (8) and (9), R ¹ represents a divalent aliphatic hydrocarbon group having 1 to 5 carbon atoms, and examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, and a pentylene group. Of these, a methylene group is preferred. Further, the above (8) and (9) are acrylate-based examples, but methacrylate-based ones can also be used. That is, in (8) and (9), those in which CH ₂ ═CH— is replaced with CH ₂ ═C (CH ₃ ) — can be used. In the above (8) to (10), glycidyl (meth) acrylate is preferred.

  It is preferable to use (meth) acrylonitrile as one of the above monomer types (1) to (10). Moreover, it is preferable to use the monomer which has a crosslinkable functional group as at least 1 sort. Specific examples of the combination preferably include n-butyl (meth) acrylate, ethyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylonitrile, methyl acrylate, propyl acrylate, and the like. be able to.

The blending amount of the monomer is not particularly limited and can be freely set except for (meth) acrylonitrile and amino group-containing monomers. In the present invention, the blending amount of the acrylonitrile or amino group-containing monomer can be 10% or more, preferably 20% or more, more preferably 30% or more, in terms of molar fraction with respect to the total amount of the monomer species used. Preferably, 40% or more is more preferable, and the upper limit is approximately 60%. In addition, the following monomers etc. are used suitably as an amino group containing monomer here. In addition, R in the following monomers represent -CH ₃ or _-C 2 _{H 5.}

  The amount of the polyfunctional initiator used is preferably 200: 1 to 20000: 1 in molar ratio with respect to the monomer.

[Ligand]
The ligand in this synthesis method is an amine compound, and it is preferable to use an amine compound having two or more N atoms in one molecule. Examples of such amine compounds include the following.

（Ｒ^１は炭素数１〜３の脂肪族炭化水素基を示し、Ｒ^２、Ｒ^３は、Ｈ又は炭素数１〜３の脂肪族炭化水素基を示す。）

(R ¹ represents an aliphatic hydrocarbon group having 1 to 3 carbon atoms, and R ² and R ³ represent H or an aliphatic hydrocarbon group having 1 to 3 carbon atoms.)

Examples of the aliphatic hydrocarbon group having 1 to 3 carbon atoms represented by R ¹ include a methylene group, an ethylene group, and a propylene group. Examples of the aliphatic hydrocarbon group having 1 to 3 carbon atoms represented by R ² and R ³ include a methyl group, an ethyl group, and a propyl group.

  As a usage-amount of a ligand, it is preferable that it is 0.5: 1-2: 1 by molar ratio with respect to the metal to be used.

[catalyst]
The catalyst used in this synthesis method is a transition metal of Group 7 to 11 elements of the periodic table, specifically, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, Examples include palladium, platinum, copper, silver, and gold. Among these, copper, ruthenium, nickel, and iron are preferable, and copper is most preferable. In particular, when copper is used, the catalytic activity is high, and it is easy to achieve a high polymerization rate and a high molecular weight.

  The catalyst is preferably used in a molar ratio of 1: 0.5 to 1:10 with respect to the polymerization initiator.

[solvent]
Solvents that can be used in this synthesis method include hydrocarbon solvents such as dimethyl sulfoxide (DMSO), benzene and toluene, ether solvents such as diethyl ether, tetrahydrofuran and dioxane, and halogenated hydrocarbons such as methylene chloride and chloroform. Solvents, ketone solvents such as acetone and methyl ethyl ketone, alcohol solvents such as methanol, ethanol, propanol and isopropanol, nitrile solvents such as acetonitrile, propionitrile and benzonitrile, ester solvents such as ethyl acetate and butyl acetate, ethylene Carbonate solvents such as carbonate and propylene carbonate, amide solvents such as dimethylformamide, dimethylacetamide, and hexamethylphosphoric amide can be preferably used. These may be used alone or in combination. However, the examples given here are merely examples, and the present invention is not limited to these examples.

[Other ingredients]
As other components, Lewis acid (for example, aluminum alkoxide, etc.) or an inorganic salt (for example, sodium carbonate, sodium benzoate, etc.) or a reducing agent (for example, 2-ethylhexanoic acid tin) is used to increase the catalytic activity. It is also possible to add.

[Atom transfer radical polymerization]
The atom transfer radical polymerization employed in this synthesis method is a polymerization method in which a halogen compound or the like is used as an initiator and a transition metal is used as a catalyst, and a monomer such as an acrylic polymer is polymerized. A polymer having a narrow molecular weight distribution (Mw / Mn = 1.1 to 2.2) is obtained in which side reactions are unlikely to occur, and the molecular weight of the polymer to be produced is freely controlled by the charging ratio of the monomer and the initiator. In addition to the characteristics of the “living radical polymerization method” that can be performed, it has a halogen which is relatively advantageous for functional group conversion reaction at the end, and has a large degree of freedom in designing initiators and catalysts. It is useful as a method for producing a polymer having the same. As this atom transfer radical polymerization method, for example, Macromolecules, 1995, 28, 1721, 7901, Matyjazewski et al., Journal of American Chemical Society (J. Am. Chem. Soc). 1995) 117, 5614, Science 1996, 272, 866, WO 96/30421 pamphlet, WO 97/18247 pamphlet, WO 98/01480 pamphlet. , WO98 / 40415 pamphlet, JP-A-9-208616, JP-A-8-41117, and the like.

Next, a procedure for synthesizing the star copolymer will be described.
First, the catalyst is weighed in a container prepared for synthesis in this synthesis method, the inside of the container is decompressed and under a nitrogen atmosphere, and each monomer species, ligand, and solvent are added. Next, nitrogen is bubbled for deoxygenation. Under a nitrogen atmosphere again, a separately prepared initiator solution is added to proceed the polymerization. The temperature at this time is about 10 to 100 ° C., and finally the reaction solution is purified to obtain the target star copolymer.

  In this synthesis method, it is important to remove oxygen and moisture in the polymerization. Moreover, in order to advance a polymerization reaction smoothly, it is important to raise the purity of a monomer, an initiator, a ligand, a metal, and a solvent.

<Resin composition, die bond film>
The resin composition of the present invention is characterized by containing the above-described star copolymer of the present invention, an epoxy resin, and a curing agent. The die bond film of the present invention is characterized by comprising the resin composition of the present invention.
Hereinafter, each component will be described.

[Epoxy resin]
The resin composition (die-bonding film) of the present invention contains an epoxy resin as a curable component. The epoxy resin is not particularly limited as long as it is cured and has an adhesive action. Bifunctional epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin, novolac type epoxy resins such as phenol novolac type epoxy resin and cresol novolak type epoxy resin, and the like can be used. Moreover, what is generally known, such as a polyfunctional epoxy resin, a glycidyl amine type epoxy resin, a heterocyclic ring-containing epoxy resin, or an alicyclic epoxy resin, can be applied.

  In particular, the molecular weight of the epoxy resin is preferably 1000 or less, and more preferably 500 or less, in view of the high flexibility of the film in the B stage state. Also, bisphenol A type or bisphenol F type epoxy resin having a molecular weight of 500 or less having excellent flexibility and 50 to 90% by mass of a polyfunctional epoxy resin having a molecular weight of 800 to 3000 excellent in heat resistance of the cured product, and It is also preferable to use together.

[Curing agent]
As the curing agent for the epoxy resin, known curing agents that are generally used can be used. For example, amines, polyamides, acid anhydrides, polysulfides, boron trifluoride, bisphenol A, bisphenol F, bisphenol S. Examples thereof include bisphenols having two or more phenolic hydroxyl groups per molecule, phenol novolac resins, xylylene-modified phenol resins, bisphenol A novolac resins, cresol novolac resins, and other phenol resins.

On the other hand, in this invention, when the compatibility in the state of a varnish before die-bonding film preparation deteriorates, it can improve by changing the hardening | curing agent of an epoxy resin to a predetermined thing. Examples of the predetermined curing agent include those having a softening temperature of 150 ° C. or lower (preferably 140 ° C. or lower, more preferably 130 ° C. or lower).
Specific examples include phenolic hardeners such as phenol novolak resin, phenol aralkyl resin, cresol novolak resin, naphthol aralkyl resin, triphenolmethane resin, terpene modified phenol resin, dicyclopentadiene modified phenol resin, Novolak resins and phenol aralkyl resins are preferred. As content of a hardening | curing agent, it is preferable to mix | blend by 0.5-2 as an equivalent ratio of the number of epoxy groups of all the epoxy resins, and the number of hydroxyl groups of all the hardening | curing agents.

[Filler]
Furthermore, the resin composition (die-bonding film) of the present invention has an improved dicing property of the adhesive sheet in the B-stage state, an improved handling property of the adhesive sheet, an improved thermal conductivity, an adjustment of the melt viscosity, and a thixotropic property. For the purpose of imparting or the like, it is preferable to blend a filler, more preferably an inorganic filler.

  Inorganic fillers include aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, alumina, aluminum nitride, aluminum borate whisker, boron nitride, crystalline silica, non Examples thereof include crystalline silica and antimony oxide. In order to improve thermal conductivity, alumina, aluminum nitride, boron nitride, crystalline silica, amorphous silica and the like are preferable. For the purpose of adjusting melt viscosity and imparting thixotropic properties, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, alumina, crystalline silica, non-crystalline silica Crystalline silica and the like are preferred. In order to improve dicing properties, alumina and silica are preferable.

  In the present invention, the inclusion of 40 to 180 parts by mass of the filler with respect to 100 parts by mass of the resin improves the dicing property, and the storage elastic modulus after curing of the adhesive sheet is 20 to 600 MPa at 170 ° C., It is preferable at the point from which wire-bonding property becomes favorable, It is more preferable that it is 60-160 mass parts, It is further more preferable that it is 60-120 mass parts.

[Content of each component]
In the die bond film of the present invention, the content of each component is 10 to 40 parts by mass of the star copolymer, 30 to 45 parts by mass of the epoxy resin and the curing agent, and the filler is It is preferable that it is 40-180 mass parts with respect to 100 mass parts in total of a star-shaped copolymer, the said epoxy resin, and the said hardening | curing agent.
By setting the content of each component within the above numerical range, it is possible to bury the unevenness and ensure insulation from the semiconductor chip. The content of each component is preferably 12 to 35 parts by mass of the copolymer, 33 to 42 parts by mass of the epoxy resin and the curing agent, and the filler is the star copolymer. And the epoxy resin and the curing agent in a total of 100 parts by mass, 60 to 160 parts by mass, more preferably, the star copolymer is 15 to 30 parts by mass, and the epoxy resin and the curing An agent is 35-40 mass parts, and the said filler is 60-120 mass parts with respect to a total of 100 mass parts of the said star-shaped copolymer, the said epoxy resin, and the said hardening | curing agent.

[Other ingredients]
The die bond film of the present invention may contain, as other components, a silane coupling agent, a titanium coupling agent, a curing accelerator, a leveling agent, an antioxidant, an ion trapping agent, and the like.

<Production of die bond film>
Next, each process for producing the die bond film of the present invention will be described. The process shown below is an example, and the die bond film of the present invention is not limited to the following process.
(1) Preparation of varnish A varnish is prepared by mixing and kneading a high molecular weight component (star copolymer), a thermosetting component mainly composed of an epoxy resin, a filler, and other components in an organic solvent.
The organic solvent used for preparing the varnish is not particularly limited as long as it can uniformly dissolve, knead or disperse the material, and conventionally known ones can be used. Examples of such a solvent include ketone solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, acetone, methyl ethyl ketone, and cyclohexanone, toluene, xylene, and the like. It is preferable to use methyl ethyl ketone, cyclohexanone, etc. in terms of fast drying speed and low price.

  There is no restriction | limiting in particular in the usage-amount of the organic solvent at the time of using for preparation of a varnish, Although an organic solvent is removed from a die-bonding film by heat drying etc., the amount of organic solvents (residual volatile matter) after die-bonding film preparation Is preferably 0.01 to 3% by mass based on the total mass, more preferably 0.01 to 2% by mass based on the total mass from the viewpoint of heat resistance reliability, and 0.01 to 1.5% by mass based on the total mass. Is more preferable.

  The above mixing and kneading can be carried out by appropriately combining dispersers such as a normal stirrer, a raking machine, a triple roll, and a ball mill.

(2) Coating to base material The varnish obtained by said (1) is coated on a base material, and the layer of a varnish is formed. As the substrate, a polyethylene terephthalate film, a polyimide film, a polyester film, a polypropylene film, a polyetherimide film, a polyether naphthalate film, a methylpentene film, or the like can be used.
For coating, a polyethylene terephthalate film, a polyimide film, or the like can be used. The coating thickness is determined in consideration of the final thickness of the die bond film, but is preferably 10 to 250 μm.

(3) Heat-drying The base material which apply | coated the varnish obtained by said (2) is heat-dried. The conditions for the heat drying are not particularly limited as long as the solvent used is sufficiently volatilized, but it is usually carried out by heating at 60 to 200 ° C. for 0.1 to 90 minutes. After heat drying, the substrate can be removed to obtain a die bond film (B stage film).

  The thickness of the die bond film is preferably 5 to 250 μm in order to be able to fill irregularities such as gold wires attached to the wiring circuit of the substrate and the lower semiconductor chip. If the thickness is less than 5 μm, the stress relaxation effect and adhesion tend to be poor. In addition, 20-100 micrometers is more preferable at the point which has high adhesiveness and can make a semiconductor device thin, More preferably, it is 40-80 micrometers.

  The die bond film of the present invention needs to have a melt viscosity that allows the substrate and the chip to be bonded to each other by thermocompression bonding and fill the substrate surface with irregularities and hollow wires with the die bond film, before curing (B stage state) The melt viscosity at 100 ° C. of the adhesive sheet is preferably 100 Pa · s or more and 2500 Pa · s or less from the viewpoint of excellent irregularities on the substrate surface and the filling property of the hollow wire, and more preferably 200 to 1500 Pa · s. Preferably, it is 300-1300 Pa.s.

  In this invention, melt viscosity can be obtained by measuring and calculating about the die-bonding film before hardening with the rotational viscoelasticity measuring apparatus mentioned later.

  As described above, the die bond film of the present invention has a tack strength before curing (B stage state) of 78.4 to 294 mN (8 to 30 gf) at 25 ° C. and 392 to 784 mN (40 to 80 gf) at 40 ° C. Although it is preferable, it is 588 to 2940 mN (60 to 300 gf) at 60 ° C. and 588 to 2940 mN (60 to 300 gf) at 80 ° C. This is preferable in that it is sticky at 60 ° C. or higher and has excellent laminate processability.

  The die bond film of the present invention needs to have a specific storage elastic modulus in order to improve processability. In the present invention, the adhesive sheet before curing (B stage state) is measured by dynamic viscoelasticity at 25 ° C. A storage elastic modulus of 200 to 3000 MPa is preferable in terms of excellent dicing properties. 500 to 2000 MPa is more preferable in terms of excellent dicing properties and excellent adhesion to the wafer. Further, when the storage elastic modulus of the adhesive sheet before curing (B stage state) measured by dynamic viscoelasticity at 80 ° C. is 0.1 to 10 MPa, it can be laminated on the wafer at 80 ° C. In particular, 0.5 to 5 MPa is more preferable in terms of high adhesion to the wafer.

  Furthermore, in the die bond film of the present invention, the storage elastic modulus by dynamic viscoelasticity measurement at 260 ° C. of the die bond film after curing (C stage state) is 5 to 200 MPa in order to obtain good wire bonding properties. preferable. The storage elastic modulus is more preferably 10 to 150 MPa, still more preferably 20 to 100 MPa.

  The die bond film of the present invention may be used not only as a single layer but also as a multilayer structure, for example, a laminate of two or more of the above-described die bond films, or the die bond film of the present invention and other die bond films. A plurality of laminated ones may be used. When laminating the die bond film of the present invention and other die bond films, the die bond film of the present invention is preferably on the dicing tape side.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
First, a ligand and a trifunctional initiator necessary for the synthesis of a three-chain star acrylic rubber were synthesized as follows.

(Synthesis of ligand)
A Dimroth equipped with a three-way cock and a septum mule were attached to a 50 ml two-necked eggplant flask and placed in an N ₂ atmosphere, and then 25.0 ml (521.4 mmol) of formic acid was weighed.
After cooling to 0 ° C., 10.0 ml (123.2 mmol) of formaldehyde was added, and the mixture was stirred at 0 ° C. for 1 hour. To this reaction solution, an aqueous solution prepared by dissolving 1.5 ml (10.0 mmol) of tris (2-aminoethyl) amine in 5 ml of distilled water was dropped over about 10 minutes. Thereafter, the reaction solution was returned to room temperature and under a nitrogen stream. Next, this reactor was installed in an oil bath set at 95 ° C. and gently refluxed for 10 hours. Subsequently, after returning to room temperature and removing the solvent with an evaporator, the residue was treated with a saturated aqueous NaOH solution. The organic layer was extracted, dried over magnesium sulfate, the solvent was distilled off under reduced pressure, and 1.9 g of hexamethylated tris (2-aminoethyl) amine (hereinafter referred to as Me ₆ TREN) as a light yellow liquid (yield) 86%). The structure was confirmed by ¹ H, ¹³ C-NMR.

(Synthesis of trifunctional initiator)
Phloroglucinol 1.00 g (7.93 mmol) was weighed in a 100 ml two-necked eggplant flask equipped with a three-way cock and septum mule. After making the N ₂ atmosphere, 40.0 ml of dehydrated tetrahydrofuran (hereinafter referred to as THF) was added. Further, 3.9 ml (27.8 mmol) of triethylamine (hereinafter referred to as Et ₃ N) was added and cooled to 0 ° C. Next, 2.8 ml (27.8 mmol) of 2-bromopropionic acid chloride was slowly added dropwise, and the reaction was allowed to proceed to room temperature for 2 hours. The reaction was traced using TLC (Thin Layer Chromatography), and when the spot of the raw material disappeared, the reaction was regarded as completed. After completion of the reaction, the mixture was filtered to remove the hydrochloride in the solution, and the solvent was distilled off with an evaporator. The residue was recrystallized with MeOH to obtain 2.4 g (yield 57%) of a white solid product.
The structure was confirmed by ¹ H, ¹³ C-NMR and found to be the structure represented by the structural formula (2) described above. That is, the minimum number of atoms bonded between bromine atoms which are the closest halogen atoms is nine.

(Synthesis of star-shaped acrylic rubber)
0.0457 g (1.44 mmol) of copper powder (hereinafter referred to as Cu (0)) was weighed into a 300 ml three-necked flask equipped with a three-way cock. Butyl acrylate (hereinafter referred to as BA) 29.85 g (232.89 mmol), ethyl acrylate (hereinafter referred to as EA) 22.23 g (222.03 mmol), glycidyl methacrylate (hereinafter referred to as GMA) 2.31 g (16.25 mmol), acrylonitrile 22.74 g (428.57 mmol), dehydrated dimethyl sulfoxide (hereinafter referred to as DMSO) 97.18 g, and Me ₆ TREN (0.1037 g, 0.45 mmol) were added. The solution was deoxygenated by N ₂ bubbling (500 ml / min 60 min), 0.2389 g (0.45 mmol) of the above trifunctional initiator was added, and further N ₂ bubbling (500 ml / min 15 min) was performed. The container was closed and placed in a water bath with a set temperature of 30 ° C., and the reaction was allowed to proceed for 16 hours. After completion of the reaction, the viscosity of the solution was reduced with acetone and suction filtered. The filtrate was transferred to a 500 ml three-necked flask equipped with a Teflon (registered trademark) vacuum stirrer. Pure water was added dropwise over 1 hour while stirring at 150 rpm, followed by stirring for 30 minutes. After stirring, vacuum distillation was performed to remove acetone and unreacted monomers. The aqueous solution remaining in the flask was removed with a dropper, and the remaining polymer was washed twice with water and once with methanol, and again dissolved with acetone. After dissolution, pure water was added dropwise again over 1 hour and stirred for 30 minutes. After stirring, vacuum distillation was performed, and the aqueous solution remaining in the flask was removed with a dropper, and then the remaining polymer was washed once with water and methanol. After washing, the polymer was dissolved in cyclohexanone, and the low boiling point solvent was removed by distillation under reduced pressure to obtain an acrylic rubber solution. The synthesized star acrylic rubber had a weight average molecular weight of 200,000. Moreover, the glass transition point Tg was 44 degreeC. The weight average molecular weight is a value obtained by gel permeation chromatography (GPC).

Next, varnish was prepared as follows using the obtained star-shaped acrylic rubber.
<Preparation of varnish>
17.9 g of star acrylic rubber synthesized as described above, 29.0 g of bisphenol F type epoxy resin (manufactured by Toto Kasei Co., Ltd., YDF-8170C), cresol novolac type epoxy resin (manufactured by Toto Kasei Co., Ltd., YDCN- 703) 9.7 g, xylene-modified novolak (manufactured by Mitsui Chemicals, XLC-LL) 33.8 g, curing accelerator (manufactured by Shikoku Chemicals Co., Ltd., 2PZ-CN) 0.1 g, coupling agent (Nihon Unicar Co., Ltd.) ), A-189) 0.3 g and (Nihon Unicar Co., Ltd., A-1160) 0.5 g was added to the composition, and cyclohexanone was added thereto, followed by stirring and degassing to prepare a varnish. The softening temperature of the phenol curing agent is 76.5 ° C.

<Die bond film coating>
Using an applicator automatic coating machine (manufactured by Tester Sangyo Co., Ltd.), the varnish prepared on a PET base material (A53 manufactured by Teijin DuPont Co., Ltd.) was applied, and coating was performed with an applicator with a gap adjusted. The obtained film was heat-dried in an oven at 120 ° C./20 min. Thereafter, the PET base material was peeled off to obtain a B stage film having a film thickness of 40 μm.

<Post-curing of die bond film>
The obtained film was heated and cured in an oven under the conditions of 120 ° C./30 min, 140 ° C./1 h, 175 ° C./2 h to obtain a C stage film.

[Example 2]
First, a ligand and a tetrafunctional initiator necessary for the synthesis of a four-chain star acrylic rubber were synthesized as follows.

(Synthesis of tetrafunctional initiator)
TekP-4HBPA (5.0 g, 8.7 mmol) was weighed into a 500 ml four-necked flask equipped with a three-way cock. 100 g THF and 3.7 g (36.6 mmol) Et ₃ N were added and cooled to 0 ° C. under N ₂ atmosphere. After dropping 7.9 g (36.6 mmol) of 2-bromopropionyl bromide (3 g / min), the mixture was returned to room temperature and reacted for 12 hours. The reaction was traced using TLC, and when the raw material spot disappeared, the reaction was regarded as completed. After completion of the reaction, Et ₃ N bromate in the solution was removed by filtration, and the solvent was removed with an evaporator. The residue was washed twice with pure water and then dried in a vacuum dryer for 2 hours. The dried sample was recrystallized with ethanol to obtain 19.5 g (yield 50%) of a white solid compound. When the structure was confirmed by ¹ H NMR, it was a structure represented by the structural formula (1) described above. That is, the minimum number of atoms bonded between bromine atoms as the closest halogen atoms is fifteen.

  In Example 1 "Synthesis of star-shaped acrylic rubber", except that the initiator was changed from a trifunctional initiator to the above tetrafunctional initiator to synthesize an acrylic rubber, and a varnish was prepared using it. A die bond film was produced in the same manner as in Example 1.

[Comparative Example 1]
In Example 1 “Preparation of varnish”, instead of 17.9 g of star-shaped acrylic rubber, linear acrylic rubber (manufactured by Nagase ChemteX Corp., HTR-860P-3, weight average molecular weight: 800,000) 17 A die bond film was prepared in the same manner as in Example 1 except that varnish was prepared using .9 g. In addition, the weight average molecular weight of "HTR-860P-3" is a molecular weight by GPC.

[Comparative Example 2]
In Example 1, “Synthesis of star-shaped acrylic rubber”, the initiator was changed from a trifunctional initiator to a bifunctional initiator (Aldrich, 2,6-dibromoheptandionate) to synthesize an acrylic rubber, which was used. A die bond film was produced in the same manner as in Example 1 except that the varnish was prepared.

[Comparative Example 3]
In Example 1 "Synthesis of star-shaped acrylic rubber", an acrylic rubber was synthesized by changing the initiator from a trifunctional initiator to a tetrafunctional initiator (Aldrich, Pentaerythritoltetrakis (2-bromoisobutyrate)), and using it A die bond film was produced in the same manner as in Example 1 except that the varnish was prepared.

[Evaluation]
The following evaluation was performed about each of the die bond film of the Example obtained from the above and a comparative example.

(1) Measurement of tack force The tack force was evaluated by a probe tack test according to JIS Z0237-1991. Using a Tesca tester manufactured by Reska, the peel strength was measured under the conditions of probe diameter: φ 5.1 mm, contact speed: 2 mm / sec, and peel speed of 10 mm / sec to obtain tack force. The standard contact conditions were contact load: 0.98 N / cm ² , contact time: 1 sec, and measurement temperature: 40 ° C.

(2) Melt viscosity measurement Two uncured films with a thickness of 40 μm were laminated at 60 ° C. to give a film thickness of 80 μm, punched into a circle with a diameter of 8 mm, and sandwiched between glass plates / cover glasses. After pressure bonding at 120 ° C. and 3 kgf for 3 seconds, the melt viscosity was calculated by using Equation 1. The calculation method is shown in Equation 1. In the formula, η is the viscosity, V is the initial volume of the die bond film, t is the pressure bonding time, F is the pressure bonding pressure, Z0 is the initial film thickness, and Z is the film thickness after pressure bonding.

(3) Die shear strength measurement B-stage die bond film is punched out using a 5mm x 5mm punching die, laminated to the chip at 40 ° C, and then applied to the substrate using a thermocompression tester (manufactured by Hitachi Chemical Technoplant Co., Ltd.). Thermocompression bonding was performed.
Thereafter, it was cured by heating. Further, after standing on a hot plate at 260 ° C. for 30 seconds, the die shear strength was measured using a universal bond tester (Dage, series 4000).
Chip size: 5 mm × 5 mm × 280 μmt Substrate: 20 mm × 10 mm × 100 μmt
Solder resist: AUS308 Thermocompression bonding conditions: 120 ° C./0.5 kg / 3 s Die shear strength measurement speed: 50 μm / sec

The above evaluation results are shown in Table 1.
Table 1 is a table comparing Examples 1 and 2 and Comparative Examples 1 to 3, which were prepared using a die bond film prepared using the star copolymer of the present invention and a conventional high molecular weight component. The difference in performance from the die bond film is shown.

  From Table 1, it can be seen that there is no difference in melt viscosity in Comparative Examples 2 and 3, whereas in Examples 1 and 2, it can be seen that the melt viscosity is significantly lower than in Comparative Example 2. This indicates that the structure of the above-described structure and the structure of the star-shaped copolymer contribute to the melt viscosity of the die bond film. Moreover, the evaluation of tack force and die shear strength is also good, indicating that the star copolymer synthesized by the present invention contributes to high reliability.

Claims (8)

A living radical polymerization initiator having at least three branched chains having a halogen atom at its end in one molecule,
The halogen atom has at least one benzene ring in the bond between the two closest halogen atoms, and the minimum number of atoms bonded between the halogen atoms is 9 to 30; A living radical polymerization initiator, wherein two atoms bonded to the benzene ring among ˜30 atoms are bonded at the meta position or para position of the benzene ring. The living radical polymerization initiator according to claim 1, which is represented by the following general formula (1).

[In General Formula (1), A represents an atomic group containing at least one benzene ring, R ¹ and R ² each independently represent a hydrogen atom or an aliphatic group having 1 to 5 carbon atoms; Represents a halogen atom, and n represents an integer of 3 or more. ] The living radical polymerization initiator according to claim 2, wherein the general formula (1) is represented by the following structural formula (1).

The living radical polymerization initiator according to claim 2, wherein the general formula (1) is represented by the following structural formula (2).

  A star-shaped copolymer obtained by polymerizing one or more monomer species using the living radical polymerization initiator according to any one of claims 1 to 4.   A resin composition comprising the star copolymer according to claim 5, an epoxy resin, and a curing agent.   Furthermore, the resin composition of Claim 6 containing a filler, a silane coupling agent, and a hardening accelerator.   A die-bonding film comprising the resin composition according to claim 6.