JP2008230113A - Metallic foil-clad laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metallic foil-clad laminate keeping excellent crack resistance and showing high adhesion to an insulating layer. <P>SOLUTION: The metallic foil-clad laminate has the metallic foil and the insulating layer wherein the metallic foil is metallic foil which is not roughened or metallic foil having an adhesive aid layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal foil-clad laminate.

  Conventionally, a laminated board used as a substrate of a printed wiring board has a predetermined number of layers of insulating layers such as a prepreg layer in which a resin having electrical insulation is used as a matrix, and a metal foil (copper foil) on one or both sides thereof. It is obtained by laminating conductive foils such as the like and integrating them by thermocompression bonding. This metal foil-clad laminate has been used by mounting electronic components after forming a circuit pattern by etching a copper foil. The copper foil used in such a printed wiring board is roughened by an electrolytic deposition method in which fine particles of copper are deposited on the surface in order to improve the adhesion to the insulator layer. The ones attached are used. The roughness obtained by this roughening treatment is a low-profile copper with a general foil having a 10-point average roughness (Rz) of about 6 μm or more, and with the aim of improving etching accuracy for high-density wiring. Rz is about 2 to 4 μm even in the foil.

  In recent years, demands for smaller, lighter, and faster electronic devices have increased, and printed wiring boards are becoming thinner and higher in density. With this trend, thin metal foil-clad laminates have also been used. However, when the insulating layer of the metal foil-clad laminate becomes thin, rigidity during handling becomes a problem. At present, high-rigidity base materials containing fillers have become mainstream in thin packages, and the base material has a structure that is easily cracked. Moreover, it is in the state which is easy to enter a crack from the fine uneven | corrugated protrusion of the copper foil provided in order to improve the adhesive force of copper foil as the starting point. Recently, low profile copper foils with small minute irregularities are commercially available.

JP 2005-74819 A

  In order to solve such a problem, in the conventional method, for example, a low profile foil having a low roughness on the surface of the metal foil is used, or a copper foil having a low roughness is further blackened to obtain finer unevenness. Thus, there has been considered a method for improving crack resistance and adhesion with an insulating layer. However, with these methods, the roughness can be reduced, but fine irregularities on the surface of the substrate remain, and it is still difficult to avoid the occurrence of cracks starting from the cracks starting from the irregularities. .

  The present invention provides a metal foil-clad laminate that eliminates the disadvantages of known methods and retains excellent crack resistance characteristics, and also provides a metal foil-clad laminate that has high adhesion to an insulating layer. To do.

The present invention relates to the following.
1. A metal foil-clad laminate comprising a metal foil and an insulating layer, wherein the metal foil is a metal foil that has not been subjected to roughening treatment or a metal foil having a layer of an adhesion assistant.
2. Item 10. The metal foil-clad laminate according to Item 1, wherein the surface of the metal foil in contact with the insulating layer has a ten-point average roughness (Rz) of 2.0 μm or less and a maximum surface roughness (Rmax) of 5 μm or less.
3. Item 3. The metal foil-clad laminate according to Item 1 or 2, wherein the adhesion auxiliary agent has a thickness of 0.1 to 15 µm.
4). Item 4. The metal foil-clad laminate according to any one of Items 1 to 3, wherein the adhesion aid is a resin having electrical insulation.

  According to the present invention, since the metal foil is not roughened, there are no conventional fine irregularities on the surface. Also, by providing an adhesion assistant between the metal foil and the insulating layer, to provide a metal foil-clad laminate that achieves both high crack resistance and adhesion with the insulating layer due to the presence of the surface insulating layer. Can do.

  Although it does not specifically limit as metal foil used for this invention, For example, copper foil, nickel foil, aluminum foil etc. can be used, and copper foil is normally used. The type of copper foil is not particularly limited, such as electrolytic copper foil or rolled copper foil. Further, the thickness of the metal foil to be used is not particularly limited. A metal foil having a thickness of 105 μm or less, which is generally used for a printed wiring board, may be used, and a peelable type metal foil may be used. Note that an etchable type metal foil having an aluminum carrier or a nickel carrier may be used instead of the peelable type. The roughness of the surface of the metal foil that is in contact with the insulating layer is such that the ten-point average roughness (Rz) is 2.0 μm or less and the maximum surface roughness (Rmax) is 5 μm or less in order to avoid the occurrence of cracks due to unevenness. It is preferable that If the roughness becomes rougher than this, the possibility of occurrence of cracks increases. Generally, a metal foil used for a printed wiring board is subjected to a roughening treatment. However, in order to make the surface smoother, the present invention does not perform a substantial roughening treatment and the metal foil has a foot. It is characterized by not. “The metal foil does not have legs” means that there is no metal foil unevenness for the purpose of improving adhesion. Further, as the base material structure, a multi-sheet structure is suitable for reducing warpage and improving rigidity, and it is possible to prevent the cracks from extending greatly in the Z direction.

  Examples of commercially available products include F0-WS foil manufactured by Furukawa Circuit Foil Co., Ltd. for electrolytic copper foil, HLPB foil manufactured by Nikko Materials Co., Ltd., and ZSPC foil manufactured by Microhardware Co., Ltd. for rolled copper foil.

The metal foil used in the present invention is preferably subjected to a rust prevention treatment performed on an insulating layer adhesion surface of a general metal foil. The rust prevention treatment can be performed using any of nickel, tin, zinc, chromium, molybdenum, cobalt, or an alloy thereof, but is preferably performed by at least one selected from zinc and chromium. The amount of the rust-proofing metal varies depending on the type of metal, but is preferably 10 to 2000 μg / dm ^{2 in} total. If the rust preventive treatment is too thick, it may cause etching inhibition and deterioration of electrical characteristics, and if it is too thin, it may cause a reduction in peel strength with the resin.

  Furthermore, if a chromate treatment layer is formed on the rust prevention treatment, it is useful because a reduction in peel strength with the resin can be suppressed.

  In the present invention, it is preferable that a silane coupling agent is further adsorbed on the outermost layer of the copper foil. Examples of the silane coupling agent include 3-glycidoxypropyltrimethoxysilane, epoxy-functional silanes such as 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, and N-2. Amino-functional silanes such as-(aminoethyl) 3-aminopropyltrimethoxysilane, N-2- (aminoethyl) 3-aminopropylmethyldimethoxysilane, vinyltrimethoxysilane, vinylphenyltrimethoxysilane, vinyltris (2- Olefin functional silane such as methoxyethoxy) silane, acrylic functional silane such as 3-acryloxypropyltrimethoxysilane, methacryl functional silane such as 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane Such as mercapto functional silane is used. Considering compatibility with an adhesion aid to be applied later, it is desirable to have an epoxy group or an amino group in the molecule. These can be used alone or in combination.

The adhesion aid of the present invention is desirably a thermosetting resin composition.
The thermosetting resin composition preferably includes (A) an epoxy resin, (B) a polymer component, (C) an epoxy resin curing agent, and (D) a curing accelerator.

  The component (A) preferably contains a novolac type epoxy resin or a novolac type epoxy resin. The novolac type epoxy resin in the present invention is preferably (A) a novolac type epoxy resin having a biphenyl structure. (A) The novolak-type epoxy resin having a biphenyl structure refers to a novolak-type epoxy resin containing an aromatic ring of a biphenyl derivative in the molecule. For example, the following general formula (1):

（式中、ｐは、１〜５を示す）で示されるエポキシ樹脂が挙げられる。

(Wherein, p represents 1 to 5).

  Commercially available products include Nippon Kayaku Co., Ltd. NC-3000S (epoxy resin of formula (1) where p is 1.7), NC-3000S-H (epoxy resin of formula (1) where p is 2.8) ).

  The (A) component epoxy resin can also be used in combination with a rubber-modified epoxy resin. The rubber-modified epoxy resin can be used without particular limitation as long as it is a product marketed for adhesives or paints.

  Examples of commercially available products include EPICLON TSR-960 manufactured by Dainippon Ink Co., Ltd., EPOTOOHTO YR-102 manufactured by Tohto Kasei Co., Ltd., and Sumiepoxy ESC-500 manufactured by Sumitomo Chemical Co., Ltd.

  The content of the rubber-modified epoxy resin used in combination is preferably 10 to 80% by weight of the total epoxy resin. When a rubber-modified epoxy resin is blended, the elongation at the time of curing is increased, and the adhesion to the surface of the metal foil is improved. However, if it is less than 10% by weight, the effect cannot be sufficiently exhibited, and if it exceeds 80% by weight, the heat resistance is poor. A range of 30 to 70% by weight is more preferable. Two or more kinds of rubber-modified epoxy resins may be used, but the total amount is preferably within the above-mentioned weight%.

  The component (B) is preferably composed of at least one selected from polyvinyl acetal resins and carboxylic acid-modified polyvinyl acetal resins.

  Although the kind of polyvinyl acetal resin, the amount of hydroxyl groups, and the amount of acetyl groups are not particularly limited, those having a polymerization degree of 1000 to 2500 are preferred. Within this range, solder heat resistance can be secured, and the viscosity and handling properties of the varnish are good. Here, the number average degree of polymerization of the polyvinyl acetal resin can be determined, for example, from the number average molecular weight of polyvinyl acetate as a raw material (measured using a standard polystyrene calibration curve by gel permeation chromatography). Moreover, a carboxylic acid modified product etc. can also be used.

  Polyvinyl acetal resin is, for example, trade names manufactured by Sekisui Chemical Co., Ltd., ESREC BX-1, BX-2, BX-5, BX-55, BX-7, BH-3, BH-S, KS-3Z, KS-5, KS-5Z, KS-8, KS-23Z, trade names made by Denki Kagaku Kogyo Co., Ltd., electrified butyral 4000-2, 5000A, 6000C, 6000EP, and the like can be used. These resins can be used alone or in admixture of two or more.

  (A) It is preferable that (B) component is 0.5-25 weight part with respect to 100 weight part of (A) component. If the component (B) is less than 0.5 parts by weight, the peel strength and the peel strength of the electroless plating after chemical roughening are low, and if it exceeds 25 parts by weight, the solder heat resistance and the insulation reliability decrease. It is not preferable. In particular, when the amount of each of the crosslinked rubber particles and the polyvinyl acetal resin is 1 part by weight or more, the peel strength of the metal foil and the peel strength of the electroless plating after chemical roughening are further improved.

  The component (C) is preferably a novolak type phenol resin, and if it is a triazine ring-containing novolak type phenol resin, the peel strength of the metal foil and the peel strength of the electroless plating after chemical roughening are improved. preferable.

  In the present invention, the triazine ring-containing novolak type phenol resin means a novolak type phenol resin containing a triazine ring in the main chain of the novolak type phenol resin, and may be a cresol novolak type phenol resin containing a triazine ring. The nitrogen content is preferably 10 to 25% by weight, more preferably 12 to 19% by weight in the triazine ring-containing novolac type phenol resin. When the nitrogen content in the molecule is within this range, the dielectric loss does not increase too much, and when the adhesion aid is used as a varnish, the solubility in the solvent is appropriate, and the remaining amount of undissolved substances can be suppressed. . As the triazine ring-containing novolac type phenol resin, one having a number average molecular weight of 500 to 600 can be used. These may be used alone or in combination of two or more.

  The triazine ring-containing novolak type phenol resin can be obtained by reacting phenol, aldehyde, and a triazine ring-containing compound under conditions of pH 5-9. When cresol is used instead of phenol, a triazine ring-containing cresol novolac type phenol resin is obtained. Any of o-, m-, and p-cresol can be used as the cresol, and melamine, guanamine and derivatives thereof, cyanuric acid and derivatives thereof can be used as the triazine ring-containing compound.

  As a commercially available product, Dainippon Ink & Chemicals, Inc., a triazine ring-containing cresol novolac type phenol resin phenolite LA-3018 (nitrogen content 18% by weight) can be mentioned.

(D) Any curing accelerator may be used as the component, but it is preferable to blend various imidazoles and BF ₃ amine complexes which are latent thermosetting agents. 2-Phenylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate from the viewpoint of storage stability of adhesion aid, handling property at B stage and solder heat resistance Is preferred.

  (D) The compounding quantity of a component has the preferable range of 0.1-5 weight part with respect to 100 weight part of (A) epoxy resins in an adhesion adjuvant, and the range of 0.3-1 weight part is more preferable. . Within these ranges, sufficient solder heat resistance, good storage stability of the adhesion aid, and good handleability when using the B stage can be obtained.

In order to improve flame retardancy, the adhesion aid of the present invention may contain (E) a phenolic hydroxyl group-containing phosphorus compound. (E) The phenolic hydroxyl group-containing phosphorus compound has the following general formula (2):

（式中、ｎが、１の場合、Ｒ_４は、水素原子、直鎖状若しくは分枝状のアルキル基、シクロアルキル基、アリール基又はアラルキル基であり、ｎが２の場合、それぞれのＲ_４は独立して、水素原子、直鎖状若しくは分枝状のアルキル基、シクロアルキル基、アリール基又はアラルキル基であるか、２つのＲ_４は、それぞれが結合している炭素原子と一緒になって、非置換又はアルキル基若しくはシクロアルキル基で置換されているベンゼン環を形成し、ｘは、２以上の自然数である）で示されるような、フェノール性水酸基を含有するリン化合物である。これらは、単独でも、２種以上を組み合せて用いてもよい。

(In the formula, when n is 1, R ₄ is a hydrogen atom, a linear or branched alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group. ₄ is independently a hydrogen atom, a linear or branched alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, or two R ₄ together with the carbon atom to which each is attached. Thus, it is a phosphorus compound containing a phenolic hydroxyl group as shown by the following formula: benzene ring which is unsubstituted or substituted with an alkyl group or a cycloalkyl group is formed, and x is a natural number of 2 or more. These may be used alone or in combination of two or more.

In the general formula (2), when R ₄ is a linear or branched alkyl group, a C1-C6 alkyl group is preferable, and when it is a cycloalkyl group, a C6-C8 cycloalkyl group is preferable. In the case of an aryl group, a phenyl group is preferable, and in the case of an aralkyl, a C7 to C10 aralkyl group is preferable. x is preferably 2. In the general formula (2), n is 2, and two R _{4 s} are combined with the carbon atom to which each is bonded, and two R ₄ are each a carbon atom to which each is bonded, When taken together to form a benzene ring that is unsubstituted or substituted with an alkyl or cycloalkyl group, the benzene ring that is unsubstituted or substituted with a C1-C4 alkyl group or a C6-C8 cycloalkyl group is preferable.

  Specifically, the following general formula (3) or the following general formula (4):

（式中、Ｒ_５は、水素原子、メチル、エチル、ｎ−プロピル、イソプロピル、ｎ−ブチル、イソブチル、ｓｅｃ−ブチル、ｔｅｒｔ−ブチル基、シクロヘキシル基を表す）で示されるリン化合物が挙げられる。

(Wherein, R ₅ represents a hydrogen atom, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl group, or cyclohexyl group).

  In particular, 10- (2,5-dihydroxyphenyl) -9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and derivatives thereof are preferred. As a commercial item, Sanko Co., Ltd. HCA-HQ is mentioned.

  In the case of imparting flame retardancy, the blending amount of the (E) phenolic hydroxyl group-containing phosphorus compound in the adhesion aid of the present invention is 1 in terms of phosphorus atoms in the total weight of the components (A) to (E). The range is preferably from 5 to 3.5% by weight, and more preferably from 1.8 to 2.5% by weight. When the blending amount is within this range, the flame retardancy is good, the insulation reliability is excellent, and the Tg of the cured coating film is not too low.

  In order to improve reliability, the adhesion aid in the present invention may contain (F) an inorganic filler. In the present invention, the (F) inorganic filler is not particularly limited, and examples thereof include silica, fused silica, talc, alumina, aluminum hydroxide, barium sulfate, calcium hydroxide, aerosil and calcium carbonate. Inorganic fillers include those treated with various coupling agents such as silane coupling agents for the purpose of enhancing dispersibility. These may be used alone or in combination of two or more. Silica is preferred from the viewpoint of dielectric properties and low thermal expansion.

The blending amount of the inorganic filler as the component (F) is preferably in the range of 5 to 35% by volume, more preferably 10 to 30% by volume, in the total volume of the components (A) to (F). is there. When the blending amount is within this range, the thermal expansion coefficient and the dielectric loss are not increased, and a sufficient flow can be obtained for forming the insulating layer on the inner layer circuit. In order to disperse the inorganic filler in the adhesion aid of the present invention, a known kneading method such as a kneader, a ball mill, a bead mill, or a three roll can be used.
You may mix | blend additives, such as a pigment, a leveling agent, an antifoamer, and an ion trap agent, with the adhesion adjuvant in this invention as needed.

  The adhesion aid produced as described above is diluted with a solvent to form a varnish, which is applied to a copper foil. Solvents include ketones such as acetone, methyl ethyl ketone and cyclohexanone, aromatic hydrocarbons such as benzene, xylene and toluene, alcohols such as ethylene glycol monoethyl ether, esters such as ethyl ethoxypropionate, N, N -Amides such as dimethylformamide and N, N-dimethylacetamide. These solvents may be used alone or in combination of two or more. The usage-amount of the solvent with respect to an adhesion adjuvant is not specifically limited, It can be set as the quantity currently used conventionally.

Furthermore, for example, the above-mentioned adhesion assistant and the above varnish are applied to one side of the metal foil and semi-cured to obtain a metal foil with an adhesion assistant.
The thickness of the adhesion aid layer is preferably 0.1 μm or more. If the thickness is less than 0.1 μm, the resin layer does not elongate and the adhesive strength with the insulating layer is significantly reduced. On the other hand, when the thickness exceeds 15 μm, the properties of the prepreg used at the time of molding, for example, the elastic modulus as a substrate after heating and pressurization, Tg, or the like may be significantly reduced. Therefore, 15 μm or less is preferable. Furthermore, in order to fully exhibit the characteristics of the prepreg, it is more preferable that the thickness of the adhesion auxiliary agent layer is in the range of 1 to 5 μm.

When applying the adhesive auxiliary of the present invention to a metal foil or film with a comma coater or gravure coater, the amount of solvent used is adjusted so that the total solid content of the adhesive auxiliary is 10 to 30% by weight. Preferably, the amount can be adjusted according to the equipment for film formation.
The manufacturing method of the substrate using the metal foil as described above and the metal foil with an adhesive is such that the metal foil, the metal foil with an adhesive and the prepreg are laminated and integrated by a conventionally known method. Obtainable.

Example 1
One glass cloth base high Tg epoxy resin prepreg GEA-679F (thickness 0.1 mm) manufactured by Hitachi Chemical Co., Ltd. and an electrolytic copper foil (product name F0-WS12: Furukawa Circuit Foil) having a width of 510 mm and a thickness of 12 μm above and below it Rz = 1.2 μm) was laminated and press-molded for 1 hour under the conditions of 180 ° C. and 3.0 MPa to prepare a copper-clad laminate.

(Example 2)
The following resin composition A was produced.
(Preparation of resin composition A)
・ Novolac type epoxy resin having biphenyl structure, NC3000S-H (made by Nippon Kayaku Co., Ltd.); 65 parts by weight ・ Carboxylic acid modified polyvinyl acetal resin, KS-23Z (made by Sekisui Chemical Co., Ltd.); 15 parts by weight ・ Triazine Ring-containing cresol novolac type phenolic resin, phenolite LA-3018 (nitrogen content 18%, hydroxyl group equivalent 151, manufactured by Dainippon Ink & Chemicals, Inc.); 20 parts by weight imidazole derivative compound, 1-cyanoethyl-2-phenylimidazolium Trimellitate, 2PZ-CNS (manufactured by Shikoku Chemicals Co., Ltd.); 0.3 parts by weight / solvent, methyl ethyl ketone;

(Preparation of copper foil A)
The resin composition A was applied to the light selective surface of the electrolytic copper foil used in Example 1 to prepare a metal foil A. After coating, drying was performed at 160 ° C. for about 10 minutes so that the residual solvent was 5% by weight or less. The thickness of the coated resin composition A was 3 μm. A glass foil base material high-Tg epoxy resin prepreg GEA-679F (thickness 0.1 mm) manufactured by Hitachi Chemical Co., Ltd. and a metal foil A so that the surface coated with the resin composition A on the top and bottom thereof is in contact with the prepreg Laminate and press-mold at 180 ° C. and 3.0 MPa for 1 hour to produce a copper-clad laminate.

(Example 3)
In Example 2, a substrate was produced in the same manner as in Example 2 except that the resin composition A was applied to a thickness of 5 μm.

Example 4
Using two glass cloth substrate high Tg epoxy resin prepreg GEA-679F (thickness 0.05 mm) manufactured by Hitachi Chemical Co., Ltd., and using the resin composition A coated in a thickness of 3 μm in Example 2, A substrate was produced in the same manner as in Example 2 except that the processed surface was laminated so as to be in contact with the prepreg.

(Example 5)
In Example 4, a substrate was prepared in the same manner as in Example 4 except that the resin composition A was applied to a thickness of 5 μm and laminated so that the coated surface was in contact with the prepreg.

(Comparative Example 1)
In Example 1, instead of laminating F0WS-12, F3WS-12 foil (manufactured by Furukawa Circuit Foil Co., Ltd., Rz = 3.5 μm, thickness 12 μm, electrolytic copper foil) was used in the same manner as in Example 1 A substrate was produced.

(Comparative Example 2)
In Example 2, a substrate was produced in the same manner as in Example 2 except that the resin composition A was applied to a thickness of 15 μm.

(Crack resistance test: Cylindrical mandrel test)
As a result of conducting a cylindrical mandrel test in accordance with JIS K5600-5-1 for each of three evaluation samples for Examples 1 to 5 and Comparative Examples 1 and 2, Table 1 was obtained.

(Measurement of conductor peeling strength)
The conductor peeling strength of the evaluation samples for Examples 1 to 5 and Comparative Examples 1 and 2 was measured. For peeling, the vertical peeling strength was measured. Measurements were always made at 20 ° C. The measuring method was based on JIS-C-6482.

(Hygroscopic heat resistance test)
The moisture absorption heat test of the board | substrate of Examples 1-5 and Comparative Examples 1-2 and the sample for evaluation was done. In the substrate test, each sample was treated for 2 hours under the conditions of 121 ° C, 100% humidity, and 2 atmospheres, and then immersed in a solder bath at 260 ° C for 20 seconds to check whether the substrate was swollen. It was. A saturation type PCT apparatus PC-242 manufactured by Hirayama Seisakusho was used for the test.

(Test results)
The test results are shown in Table 1. It turned out that the sample for evaluation produced in Examples 1-5 has high crack resistance. In terms of adhesion, since there was no adhesion auxiliary material in Example 1, the conductor peeling strength was a low value, but the moisture absorption heat resistance was at the same level as the low profile foil. Moreover, the sample for evaluation obtained in Comparative Example 1 was low in crack resistance as compared with Examples 1 and 2. As for Comparative Example 2, although the crack resistance was high, the layer of the adhesion auxiliary agent became thick, so that blistering occurred in the moisture absorption heat resistance test.

（表１中の基材構成；プリプレグの厚み（ｍｍ）、枚数）

(Substrate composition in Table 1; prepreg thickness (mm), number of sheets)

  As in the present invention, the 10-point average roughness (Rz) of the surface in contact with the insulating layer is 2.0 μm or less, the maximum surface roughness (Rmax) is 5 μm or less, and the surface is not roughened, or this By using one having a layer of an adhesion assistant, a laminate having excellent crack resistance and excellent adhesion to the insulating layer can be produced.

Claims (4)

  A metal foil-clad laminate comprising a metal foil and an insulating layer, wherein the metal foil is a metal foil that has not been subjected to roughening treatment or a metal foil having a layer of an adhesion assistant.   2. The metal foil-clad laminate according to claim 1, wherein the ten-point average roughness (Rz) of the surface in contact with the insulating layer of the metal foil is 2.0 μm or less and the maximum surface roughness (Rmax) is 5 μm or less.   The metal foil-clad laminate according to claim 1 or 2, wherein the adhesion auxiliary agent has a thickness of 0.1 to 15 µm.   The metal foil-clad laminate according to any one of claims 1 to 3, wherein the adhesion assistant is a resin having electrical insulation.