JPH0912982A - Adhesive sheet - Google Patents

Abstract

PURPOSE: To give an adhesive sheet having high thermal conductivity, low permittivity and excellent adhesion. CONSTITUTION: This adhesive sheet comprises a filler and a resin in which the skin layer is formed on at least one surface of the main layer. The thickness of the skin layer is 5-100μm. The 90 deg. peeling strength is >=1.0kg/cm after clamping and the main layer comprises a resin containing 30-95vol.% of boron nitride, particularly an adhesive sheet comprising an epoxy resin not perfectly cured is excellent in the strength. The sheet is useful in production of printed circuit boards because of its high thermal conductivity, low permittivity and high adhesion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an adhesive sheet used for manufacturing circuit boards, electronic parts and the like.

[0002]

BACKGROUND OF THE INVENTION Glass-epoxy resin-based, polyimide resin-based, polyester resin-based, etc. thermo-compression-bondable electrically insulating adhesive sheets are often used in the manufacture of circuit boards and the bonding of electronic parts to circuit boards. However, as the performance and diversification of electronic devices have increased in recent years, these adhesive sheets are also required to have various properties.

For example, an adhesive sheet used for a circuit board for applications such as a power source has a high heat conductivity and a low dielectric constant with an increase in heat generation due to an increase in electric power of electronic parts and a high frequency operation of a circuit. Is required. Japanese Patent Laid-Open No. 5-179
Japanese Patent Publication No. 210 discloses that an adhesive sheet is filled with an inorganic filler having a high thermal conductivity and a low dielectric constant to achieve a high thermal conductivity and a low dielectric constant.

However, highly filling the filler material
Since the ratio of the resin expressing the strength of the adhesive sheet decreases, there is a problem that the strength of the adhesive sheet decreases or the flexibility is lost.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an improvement of an adhesive sheet used for manufacturing a circuit board or the like. Specifically, because the filler is highly filled,
It is intended to improve the above-mentioned drawbacks of an adhesive sheet having a high thermal conductivity and a low dielectric constant but having insufficient adhesiveness or withstand voltage. That is, an object of the present invention is to provide an adhesive sheet which is excellent in thermal conductivity and dielectric properties and can be practically used in terms of adhesive strength and withstand voltage.

[0006]

The present invention is an adhesive sheet comprising a filler and a resin, characterized in that at least one surface of the main layer is provided with a skin layer, and further, The adhesive sheet is characterized in that the skin layer has a thickness of 5 μm or more and 100 μm or less.

Further, according to the present invention, the 90-degree peeling strength (hereinafter referred to as peel strength) after thermocompression bonding is 1.0 kg / cm.
It is characterized in that the main layer is made of a resin containing 30% by volume or more and 95% by volume or less of boron nitride. In particular, the resin of the main layer is not completely cured. The adhesive sheet is an epoxy resin.

Hereinafter, the present invention will be described in detail.

The adhesive sheet of the present invention is provided on one or both surfaces of a main layer having properties sufficient to achieve the desired high thermal conductivity and low dielectric constant under the conditions of use. And the outer skin layer. The present inventors have solved the above-mentioned drawbacks by making the skin layer bear properties such as insufficient adhesion and withstand voltage when the main layer is used alone, and have a high thermal conductivity of the main layer, Being able to exhibit excellent properties such as a low dielectric constant, in particular, for boron nitride, which has a high thermal conductivity and a low dielectric constant, and when mixed with a resin, only an adhesive sheet having a low adhesive strength can be obtained. It has been found that an adhesive sheet having a high thermal conductivity, a low dielectric constant, and an excellent adhesive force can be easily obtained because it can be highly filled. That is, the adhesive sheet of the present invention has a peel adhesion strength to the metal after thermocompression bonding of 1.0 Kg / cm or more, and has a practically sufficient adhesive force.

The main layer in the present invention is not particularly limited as long as it is a sheet having characteristics according to the final use. Generally, a resin sheet containing a filler having a thickness of 20 μm to 300 μm is used.

Examples of the resin constituting the main layer include epoxy resin, acrylic resin, polyimide resin, polyester resin, phenol resin, and silicone resin.
Epoxy resins are preferred because they are economical and have excellent electrical characteristics. In the present invention, since the skin layer bears the adhesiveness, the resin constituting the main layer does not necessarily have an adhesive force, but a resin of the same type as the skin layer or a compatible resin is bonded to the skin layer. It is preferable because it has excellent strength. In particular, the epoxy resin in a state where it is not completely cured is not only economical and excellent in electrical characteristics, but also excellent in adhesive force even when the skin layer is made of a resin other than the epoxy resin, which is preferable.
Here, the epoxy resin in a state where it is not completely cured is
An epoxy resin that contains a curing agent but is not in a gel state, such as a solid epoxy resin or an epoxy resin in a semi-cured state such as a B stage state.

As the filler for the resin constituting the main layer,
Conductive inorganic filler such as gold, silver, copper, aluminum, nickel, carbon, aluminum oxide, aluminum nitride,
Examples thereof include high thermal conductivity inorganic fillers such as boron nitride, silicon oxide, and silicon nitride, and various organic fillers such as fluororesin, polyimide resin, ABS resin, and aramid resin. It is generally mixed in a volume ratio of not less than 95% by volume.

In circuit board applications where high frequency characteristics are important,
Boron nitride (hereinafter referred to as BN) having a low dielectric constant and a high thermal conductivity is preferably used, and in the present invention, the resin contains 30% by volume or more and 95% by volume or less, preferably 40% by volume or less.
It is contained in a volume ratio of 85% by volume or more. When the content is less than 30% by volume, the main layer has a certain degree of adhesiveness, so that the main layer may be put to practical use without using the present invention, and when it exceeds 95% by volume, Even with the present invention, an adhesive sheet having sufficient peel strength and flexibility cannot be obtained. When the content is 40% by volume or more and 85% by volume or less, it is possible to obtain an adhesive sheet which has a high thermal conductivity and a low dielectric constant and is sufficiently flexible for practical use.

The skin layer referred to in the present invention is a layer which can be observed by a scanning electron microscope and is a layer in which the kind of resin, the kind of filler or the content of the filler is different from the main layer. And are separated by the boundary surface. The boundary surface is a surface where any one or more of the resin type, the filler type, and the filler content rate changes abruptly, and is determined by a scanning electron micrograph by the following method.

(Boundary Surface Detection Method) The adhesive sheet is cut, and its cross section is observed with a scanning electron microscope (DS-130, manufactured by Akashi Beam Technology), for example, an accelerating voltage of 20 kV,
Shoot under the condition of 600x magnification. As for the model and conditions of the scanning electron microscope, those suitable for observation can be selected. The skin layer can be confirmed by the following method. That is, a method of taking a cross section of an adhesive sheet with a scanning electron microscope, recognizing the cross section photograph with the naked eye, and using the surface with a large change in the filler content as a boundary surface. A method of drawing a straight line parallel to the surface of the adhesive sheet at intervals of several μm on the cross section of the sheet and determining the surface with a large change in the ratio of the length that cuts the filler to the entire length, adhesive sheet by scanning electron micrograph A straight line parallel to the surface of the adhesive sheet is drawn at intervals of several μm on the cross section of the adhesive sheet, and the filling rate is calculated by volume conversion from the area occupied by the filler in the region formed by the straight line. There is a method of using the intermediate surface of as a boundary surface. In, the distance between the parallel straight lines with the interval of several μm should be as small as possible.

The thickness of the skin layer is 5 μm or more and 100 μm or less. If the thickness of the skin layer is less than 5 μm, the adhesiveness or withstand voltage cannot be improved, and if it exceeds 100 μm, the thermal conductivity or the low dielectric property of the main layer is impaired.

The structure of the skin layer may be any as long as it has characteristics that are lacking in the main layer, such as adhesiveness with a metal or the like, and withstand voltage after heat curing, and a semi-cured state such as a B stage state. Resin is used. In particular, when the adhesive sheet is used for manufacturing a circuit board, an epoxy resin having a high adhesiveness to a metal such as a metal plate or a metal foil is preferably used in a semi-cured state.

The kind and amount of the filler contained in the resin constituting the skin layer are not particularly limited as long as the role of the skin layer is not hindered. In the case of an adhesive sheet for forming a circuit, aluminum oxide (hereinafter referred to as Al2O3), silicon oxide (hereinafter referred to as SiO2), which is electrically insulating and has high thermal conductivity, and spherical particles can be easily obtained.
Relatively high filling. For high frequency applications, boron nitride (hereinafter referred to as BN) having a lower content than that of the main layer can also be used. Generally, the upper limit of the filling amount is less than 30% by volume in the case of boron nitride and less than 85% by volume in the case of aluminum oxide and silicon oxide. Generally, for the purpose of preventing a decrease in thermal conductivity, a blending ratio close to the above upper limit value is selected, and aluminum oxide is preferably used in an amount of 65% by volume or more and less than 85% by volume.

An organic filler or dispersant can be added to the resin for the main layer and the skin layer as long as the characteristics of the finally obtained adhesive sheet are not impaired. Moreover, a coupling agent and a solvent can be used if necessary.

In order to obtain the adhesive sheet of the present invention, a general method for producing a sheet may be used. However, the resin, the inorganic filler and, if necessary, the solvent and the cup which respectively constitute the main layer and the skin layer are formed. After kneading additives such as ring agents and dispersants using a universal mixer or a triple roll, defoaming if necessary to make a paste, and further doctoring on a carrier sheet such as PET film. It may be formed into a sheet by a method such as a blade method, an extrusion method, or a roll coater method. The adhesive sheet of the present invention, by using any one of the above methods, by attaching a skin layer after forming the main layer, or after forming the skin layer first, the main layer, then the skin layer is sequentially attached. Alternatively, it can be obtained by separately producing the main layer and the skin layer and press-bonding each other.
Even when the skin layers are provided on both sides of the main layer by the usage of the adhesive sheet, it is not necessary to further limit that both have the same composition or the same thickness.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0022]

【Example】

[Examples 1 to 21, Comparative Example 1] 70 parts of a bisphenol A type solid epoxy resin and 30 parts of a bisphenol F type liquid epoxy resin were added to 100 parts of a toluene-methylethylketone mixed solvent (toluene / methylethylketone = 80/20) at 80 ° C. Dissolve by heating. After cooling to room temperature, 2 phenyl 4 methyl 5 as a curing agent
3 parts of hydroxymethyl imidazole and various fillers were added in a predetermined volume% to the resin component and kneaded with three rolls to prepare various slurries. In the case of acrylic resin, 22 parts of methyl methacrylate and 35 parts of 2-hydroxyethyl methacrylate were added to 40 parts of SEBS (manufactured by Shell Chemical Co .; Kraton G1650).
After dissolving at 0 ° C. and cooling to room temperature, 3 parts of Perhexa 3M (manufactured by NOF CORPORATION) as a curing agent and a predetermined amount of filler were added and kneaded with a three-roll to form a slurry. Two or more kinds of the above-mentioned various slurries were used and coated on a PET film by a doctor blade method to prepare various adhesive sheets. The adhesive sheet is sandwiched between an aluminum plate having a thickness of 1.5 mm and a copper foil having a thickness of 35 μm, and 170 ° C., 30K
Thermocompression bonding was performed for 1 hour at g / cm2 to obtain a 90 degree peeling strength (peel strength) test piece. Peel strength is JIS
It measured according to C6471. The adhesive sheet obtained in the above was sandwiched between Teflon sheets and cured under the same conditions as described above to obtain a thermal conductivity test piece by the laser flash method. An adhesive sheet without a skin layer was produced in part and used as a comparative example. The above results are summarized in Table 1.

[0023]

[Table 1]

[0024]

The present invention has excellent thermal conductivity and dielectric properties,
Moreover, it is an adhesive sheet that can be practically used in terms of adhesive strength, withstand voltage, etc., and is useful when used in processes such as circuit board manufacturing applications and adhesion of electronic components.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Kato 3-5-1, Asahimachi, Machida-shi, Tokyo Denka Kagaku Kogyo Co., Ltd.

Claims (5)

[Claims] 1. An adhesive sheet comprising a filler and a resin, characterized in that a skin layer is provided on at least one surface of a main layer. 2. The adhesive sheet according to claim 1, wherein the skin layer has a thickness of 5 μm or more and 100 μm or less. 3. The 90 ° peeling strength after thermocompression bonding is 1.0 Kg / cm or more.
The adhesive sheet described. 4. The adhesive sheet according to claim 1, wherein the main layer is made of a resin containing 30% by volume or more and 95% by volume or less of boron nitride. 5. The adhesive sheet according to claim 4, wherein the resin of the main layer is an epoxy resin which is not completely cured.