JPH10273592A - Composition having excellent thermal conductivity and metal-base printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrically insulating polyimide composition showing good adhesion to metallic foils upon thermocompression bonding and having excellent thermal conductivity by mixing a noncrystalline heat-fusible aromatic polyimide with a filler effective to improve thermal conductivity and to obtain a metal-base printed circuit board excellent in thermal conductivity. SOLUTION: 5-50 wt.% noncrystalline heat-fusible aromatic polyimide is mixed with 50-95 wt.% filler effective to improve thermal conductivity to obtain an electrically insulating polyimide composition excellent in thermal conductivity. The aromatic polyimide is desirably one obtained by imidating a polymer obtained from 2,3,3',4'-biphenyltetracarboxylic acid or an ester or dianhydride thereof and an aromatic diamine having at least one ether bond and at least two phenyl groups bonded through the ether group in the main chain. A copper foil for a circuit and a metallic foil for a base board is bonded with this composition to obtain a metal-base printed circuit board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrically insulating polyimide composition having excellent thermal conductivity suitable for a metal-based printed circuit board and the like, and a metal package having excellent thermal conductivity, which is becoming popular in the field of electronics. A splint substrate;

[0002]

2. Description of the Related Art A polyimide metal-based printed circuit board is
It is mainly used as a substrate for printed wiring boards. 2. Description of the Related Art In recent years, as electronic devices using printed wiring boards have been reduced in size and density, the use of polyimide metal foil laminates capable of high-density mounting of components and elements has been increasing. Further, with high-density mounting, there is an increasing demand for a polyimide-based metal-based printed circuit board having excellent heat conductivity in order to enhance the heat dissipation of heat generated in components and elements. Attempts have been made to use a metal base plate having a high thermal conductivity, such as an aluminum plate, for the metal layer in order to enhance the heat dissipation. However, since a polyimide layer having low thermal conductivity is used as an insulating layer between the two metal foil layers, heat dissipation is not efficient due to the heat transfer resistance of the polyimide layer.

On the other hand, studies have been made to use a polyimide layer filled with a filler having good thermal conductivity in the polyimide layer. However, polyimide filled with such a filler has poor adhesion to a metal foil, so that a method of bonding a polyimide layer and a metal foil layer using an adhesive such as an epoxy resin has been adopted. The heat resistance, chemical resistance, and electrical properties of the metal-based printed circuit board manufactured in this manner are governed by the properties of the adhesive used, and the properties of polyimide are not sufficiently utilized. It was not enough.

In order to overcome the drawbacks of the conventional metal-based printed circuit board having this adhesive, a conventional adhesive solution is prepared by directly casting a polyimide solution or a polyamic acid solution as a polyimide precursor on a metal foil. Attempts have been made to obtain a metal-based printed circuit board having no agent layer and all insulating layers consisting of a polyimide layer. Also,
A polyimide precursor having an adhesive property is laminated on one or both sides of a polyimide film, and the polyimide precursor is laminated on a metal foil and heat-pressed to form a metal-based printed circuit board in which the same insulating layer is entirely made of a polyimide layer. Attempts have been made to get it. Further, a method of laminating a thermoplastic polyimide on both surfaces of a polyimide film and heat-pressing the polyimide precursor to a metal foil has also been attempted.

However, in these methods, when a polyimide layer filled with a filler is formed as in the present invention, no adhesive property is recognized, and only a method using an adhesive is practical.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to increase the demand for a metal-based printed circuit board as the demand for the metal-based printed circuit board increases, and a demand for a metal-based printed circuit board using a polyimide layer having excellent thermal conductivity as an insulating layer. In response to this demand, an electrically insulating polyimide composition having good adhesion to a metal foil by heat-pressing and having excellent heat conductivity, and a metal-based printed board having excellent heat conductivity have been provided. It is to be.

[0007]

As a result of intensive studies, the present inventor has found that by using a specific polyimide, even if an inorganic filler having a high thermal conductivity and an excellent insulating property is filled, the use of a specific polyimide can be improved. The present inventors have found that bonding can be easily achieved by thermocompression bonding, and have completed the present invention.

That is, the present invention provides an electrically insulating polyimide composition having excellent thermal conductivity, comprising a non-crystalline, heat-fusible aromatic polyimide and a filler effective for improving thermal conductivity. About.

The present invention also provides an electrically insulating polyimide composition having excellent thermal conductivity, comprising a non-crystalline, heat-fusible aromatic polyimide and a filler effective for improving thermal conductivity. The present invention relates to a metal-based printed circuit board having excellent thermal conductivity formed by joining two layers of metal foils with an insulating film made of the same.

In the present invention, it is necessary to use the above-mentioned non-crystalline and heat-fusible aromatic polyimide.
Non-crystalline refers to those in which substantially no crystallinity is observed in the X-ray diffraction spectrum by the Leuland method, preferably those having a crystallinity of less than 5%, particularly 3% or less, and especially 1 % Or less is preferred. When a non-crystalline and non-heat-fusible polyimide is used, it becomes difficult to form an insulating film by powdering an electrically insulating polyimide composition containing a filler effective for improving thermal conductivity.

The tetracarboxylic dianhydrides (acids, dianhydrides, acid esters) which can be used for the above-mentioned non-crystalline, heat-fusible aromatic polyimides include 2,3,3
3 ', 4'-biphenyltetracarboxylic dianhydrides are most preferred, but 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) e-anhydride Terdianhydrides, their acids and acid esters. Some of these acids are converted by pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride. It may be replaced.

The aromatic diamine which can be used for the polyimide in the present invention includes 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 3,3 '-Diaminodiphenyl ether, 3,3'-diaminobenzophenone, 2,2-bis (3-aminophenyl) propane,
1,4-bis (3-aminophenoxy) benzene, 4,
4'-bis (3-aminophenyl) diphenyl ether, 4,4'-bis (3-aminophenyl) diphenylmethane, 4,4'-bis (3-aminophenoxy) diphenyl ether, 4,4 ' - bis (3-aminophenoxy) diphenylmethane, a plurality of benzene rings and _O such as 2,2-bis [3- (aminophenoxy) phenyl] _{propane, CH 2, C (CH 3} ) 2, O (Bz) O ( Bz:
An aromatic diamine having a flexible structure having a group such as (benzene) or (Bz) O (Bz) in the molecular main chain and having a diamine at the meta position is suitably used.

The polyimide in the present invention is prepared by using each of the above-mentioned components in an organic solvent, preferably under an excess of tetracarboxylic dianhydride or under conditions of blocking diamine terminals with dicarboxylic anhydride. To form a solution of polyamic acid (partially imidized as long as a uniform solution state is maintained). Dicarboxylic anhydrides for capping the amine end of the polyimide, for example,
Phthalic anhydride and substituted products thereof, hexahydrophthalic anhydride and substituted products thereof, succinic anhydride and substituted products thereof, and the like may be used.

In order to obtain the above-mentioned polyimide in the present invention, an organic solvent such as N-methyl-2-pyrrolidone and N, N-dimethylacetamide is preferably used in an amount of 20 to 6%.
At a reaction temperature of 0 ° C., the amount of diamine (as moles of amino groups) used is relative to the total number of moles of acid anhydride (as total moles of tetraacid dianhydride and dicarboxylic anhydride as acid anhydride groups). The ratio is preferably 0.9 to 1.0, particularly 0.98 to 1.0, and particularly preferably 0.99 to 1.0.
0, and the amount of the dicarboxylic anhydride used to seal the terminal diamine is preferably 0.05 or less, particularly 0.0001 to 0.02, as a ratio to the molar amount of the acid anhydride group of the tetracarboxylic dianhydride. It is preferred that the components are reacted in such a ratio as follows.

If the proportion of the diamine and dicarboxylic anhydride used is outside the above range, the resulting polyamic acid, and thus the polyimide, has a low molecular weight, resulting in a decrease in the strength of the polyimide itself and the peel strength with the metal foil. . In particular, under conditions where the diamine component is excessive, the cyclization imidization of the polyamic acid or the deterioration occurs when the solvent is removed, and the peel strength tends to decrease. As the amorphous and heat-fusible polyimide used in the present invention, ηinh [0.5 g / dl (30 ° C.) in N-methyl-2-pyrrolidone] is 0.5 or more, especially 0.5
-3 are preferred.

In particular, the non-crystalline, heat-fusible aromatic polyimide according to the present invention is characterized in that the aromatic tetracarboxylic acid component is 2,3,3'4'-biphenyltetracarboxylic acid, acid ester or acid dianhydride. And at least one ether bond in the main chain as a diamine and an ether
A polyimide polymerized and imidized from an aromatic diamine having at least two phenyl groups via a tell bond is preferable.

As the other filler effective for improving the thermal conductivity of the polyimide composition layer of the present invention, crystalline silica powder, silicon nitride powder, aluminum nitride powder, boron nitride, alumina powder, magnesium oxide powder, A typical example is silicon carbide powder or a mixture thereof.

The mixing ratio of the polyimide and the filler is 5 to 50% by weight in 100% by weight of the whole composition.
The filler is preferably 50 to 95% by weight based on the weight%.
More preferably, the content of the filler is 55 to 90% by weight with respect to 10 to 45% by weight of the polyimide, because the thermal conductivity is high.

The method of filling the filler material which is effective for improving the thermal conductivity of the polyimide insulating film of the present invention is not particularly limited, but a specific example is a pre-polymerized polyimide precursor. A method of mixing a predetermined amount of filler powder in a polyamic acid organic solvent solution in a container and stirring and mixing with a stirrer such as a homomixer, or dispersing the filler in a polymerization solvent in advance when polymerizing polyamic acid. Here, a method of polymerizing and mixing the polyamic acid in the filler dispersion solvent and the like can be mentioned.

The thickness of the polyimide insulating film in the present invention is not particularly limited, but is usually 5 to 150 μm, preferably 8 to 50 μm.

The metal-based printed circuit board of the present invention comprises two layers of metal foil joined by an insulating film made of the above-mentioned electrically insulating polyimide composition having excellent heat conductivity. Here, one of the two layers of metal foil is a circuit (conductive) metal foil,
It is preferably a copper foil, and the other metal foil is a metal foil for a base substrate (including a so-called plate), preferably a copper foil.
Aluminum foil, stainless steel foil or iron foil.

Although the thickness of the metal foil used in the present invention is not particularly limited, it is 3 to 3 for a circuit (conductive) metal foil.
175 μm, preferably 8 to 105 μm, and 50 μm for metal foil (plate) for a base substrate
Thicknesses of up to 3000 μm are preferably used. Although the surface roughness of the surface of the metal foil bonded to the polyimide is not particularly limited, the center line average roughness (hereinafter referred to as R) in JIS B O6O1 (definition and display of surface roughness) is used.
a) and ten-point average roughness (hereinafter referred to as Rz) are Ra 0.1%.
Those having a diameter of less than μm and Rz of less than 1.00 μm are particularly effective and preferred. Among them, those satisfying these conditions at the same time are particularly preferable.

The metal foil in the present invention includes:
Inorganic coatings such as simple metals and their oxides on the surface,
Alternatively, a material treated with a coupling agent such as aminosilane or epoxysilane, or a material subjected to a treatment such as a sandplast treatment, a hole treatment, a corona treatment, a plasma treatment, or an etching treatment can be used.

In the present invention, the surface of the polyimide insulating film may be subjected to honing treatment, corona treatment, plasma treatment,
A process such as an etching process may be performed.

The method for producing the metal-based printed circuit board of the present invention is not particularly limited. As a specific example, a polyamide acid dope, which is a polyimide precursor filled with a filler in advance, is formed into a film and heated. Alternatively, a chemically imidized film is produced, and then the polyimide film is sandwiched between metal foils and heated and pressed by a heat press.Polyamic acid oxide, a polyimide precursor in which one metal foil is filled with a filler, is used. -Apply
After heating, drying and imidizing, the other metal foil may be heated and pressed. The imidization is carried out by the polyamic acid dope applied as described above.
It is preferable to heat the resin to 150 to 250 ° C. or add an imidizing agent and react at a temperature of 150 ° C. or less, particularly 15 to 50 ° C., to effect imide cyclization.

Although there is no particular limitation on the method of coating,
Known coating devices such as a comma coater, knife coater, roll coater, reverse coater, die coater, gravure coater, wire bar and the like can be used. .
In addition, as a heating method, known methods such as hot air, hot nitrogen, far infrared rays, and high-frequency induction heating can be used.

The temperature condition of the thermocompression bonding is preferably higher than the glass transition point of the polyimide layer used in the present invention. Specifically, a temperature range of 250 to 350 ° C. is preferable. If the temperature is lower than this, sufficient adhesive strength cannot be obtained, and if the temperature is higher than this, bubbles tend to be trapped during bonding.

[0028]

The present invention will be described below with reference to examples.

Example 1 A 300 cc separable flask was charged with 200 ml of dimethylacetamide as a polymerization solvent, and 102.7 g of aluminum nitride powder was charged into the dimethylacetamide. The primary particles of aluminum nitride were placed in an ultrasonic disperser for 15 minutes. After the dispersion treatment, 21.929 g of 1,3-bis (4-aminophenoxy) benzene was charged while stirring by attaching a stirring blade, followed by stirring for 10 minutes.
2,2.071 g of 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride was charged. After reacting for 3 hours, polyamic acid (polyamic acid) which is a polyimide precursor
Was obtained. The content of aluminum nitride in this dope was 69.5% in the polyimide composition.
% By weight. Aggregates of aluminum nitride were filtered off from the polyamic acid dope under a pressure of 5 kg / cm ² using a 40 μm filter. The resulting dope had a viscosity of 900 poise.

This dope was coated on an aluminum foil of 150 μm in a thickness of 35 μm, and imidization was carried out at 250 ° C. with hot air. The obtained aluminum nitride-containing polyimide layer (thickness: 25 μm) coated on the aluminum foil was uniformly adhered on the aluminum foil. In addition, the polyimide layer
Despite being laminated, the laminate was completely free of warpage. The degree of crystallinity of this polyimide measured by the Leuland method by the X-ray diffraction method (wide-angle X-ray method) was 0%, and ηinh [N-methyl-
0.5 g / dl (at 30 ° C.) in 2-pyrrolidone].
At 7, the glass transition point (Tg) was 250 ° C. Next, a 35 μm electrolytic copper foil (manufactured by Fukuda Metals Co., Ltd.) was placed on the polyimide layer coated on the aluminum foil.
Was pressed with a hot press at a temperature of 320 ° C. With respect to the aluminum metal base printed board thus obtained, the peel strength at the metal foil / polyimide interface (18
(Measured at room temperature using a tensile strength tester) by the 0 ° peeling method. Table 1 shows the results. Further, a film having a thickness of 40 μm was prepared using the polyamic acid dope of this example, and the thermal conductivity of this film was measured using a rapid thermal conductivity meter manufactured by Kyoto Electronics Industry Co., Ltd. Table 1 shows the results.

Example 2 A polyamic acid dope having a composition containing 60% by weight of aluminum nitride in a polyimide composition was obtained in the same manner as in Example 1 except that the amount of aluminum nitride charged was changed to 66 g. The viscosity of this dope was 820 poise. Using this dope, a metal-based printed circuit board was prepared in the same manner as described in Example 1. Table 1 shows the results.

Example 3 A metal-based printed board having a polyimide layer containing 70% by weight of silicon nitride in the polyimide layer was prepared in the same manner as in Example 1 except that silicon nitride was used instead of aluminum nitride. Table 1 shows the evaluation results.

Example 4 Using the polyamide acid dope prepared in Example 1, a 150 μm thick stainless steel foil (SUS-3) was used as a metal foil.
04) on the stainless steel foil.
Then, a polyimide layer was formed on a stainless steel foil under the same conditions as in Example 1. Example 1 with copper foil
Then, a printed circuit board using stainless steel as a base metal was obtained. Table 1 shows the results.

Example 5 A metal-based printed circuit board having a polyimide layer containing aluminum nitride was prepared in the same manner as in Example 1 except that 4,4-diaminodiphenyl ether was used as the diamine component of the polyimide. . Table 1 shows the results.

Example 6 Using the polyamic acid dope prepared in Example 1, a 500 μm thick copper foil was used as a metal foil, and the polyamic acid dope was coated on this copper foil foil. A polyimide layer was formed on a copper foil under the same conditions as in Example 1. A copper foil was pressure-bonded thereto under the same conditions as in Example 1 to obtain a printed circuit board using the copper foil as a base metal. Table 1 shows the results.

Comparative Example 1 A polyimide composition was prepared in the same manner as in Example 1 except that 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride was used as the acid anhydride of the polyimide and paraphenylenediamine was used as the diamine. Was prepared. The composition was powdered and an insulating film could not be formed. A metal-based printed circuit board was prepared by the same operation except that this composition layer was used. The peel strength of the metal foil / polyimide layer of the metal base printed board was measured. Table 1 shows the results.

Comparative Example 2 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid anhydride of polyimide and 4,4 as a diamine
A polyimide composition was prepared in the same manner as in Example 1 except that 4'-diaminodiphenyl ether was used. The composition was powdered and an insulating film could not be formed. A metal-based printed circuit board was prepared by the same operation except that this composition layer was used. The metal foil of this metal-based printed circuit board /
The peel strength of the polyimide layer was measured. Table 1 shows the results.

Comparative Example 3 A metal-based printed circuit board was prepared in the same manner as in Example 1 except that paraphenylenediamine was used as the diamine component of the polyimide, and the peel strength of the metal foil / polyimide layer was measured. Table 1 shows the results.

Comparative Example 4 A polyamic acid dope containing no aluminum nitride was prepared by the same polymerization method as in Example 1 except that no aluminum nitride was added, and this dope was used to form a polyamic acid dope on a glass plate. A casting film was made. This film was imidized at a temperature of 250 ° C. to obtain a polyimide film. The thermal conductivity of this polyimide film was measured by the same method as in Example 1. Table 1 shows the results.

Example 7 The same operation as in Example 1 was carried out except that the amount of aluminum nitride was changed, and a polyamic acid oxide containing 85% by weight of aluminum nitride in the polyimide composition was obtained.
Got Using this dope, a metal-based printed circuit board was prepared in the same manner as described in Example 1. The peel strength of the metal foil / polyimide interface of this metal-based printed circuit board was 1.1 kg / cm, which is much better than that of each of the above embodiments.

[0041]

[Table 1]

Example 8 The metal-based printed circuit boards obtained in Examples 1 to 7 were bent. Even when R was bent to 3 mm to 5 mm, no breakage of the copper foil for the circuit or peeling of the insulating film layer was observed, and the bending process could be performed.

[0043]

According to the present invention, it is possible to obtain an electrically insulating polyimide composition having good heat-sealing property to a metal foil and excellent heat conductivity by thermocompression bonding.

According to the present invention, a two-layer metal foil is firmly adhered by the polyimide layer, and a metal-based printed board excellent in heat conductivity can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 3/34 C08K 3/34

Claims (8)

[Claims] 1. An electrically insulating polyimide composition having excellent thermal conductivity, comprising a non-crystalline, heat-fusible aromatic polyimide and a filler effective for improving thermal conductivity. 2. A non-crystalline, heat-fusible aromatic polyimide comprising 2,3,3 ′ as an aromatic tetracarboxylic acid component.
4′-biphenyltetracarboxylic acid, acid ester or acid dianhydride and at least one diamine in the main chain as a diamine
Polymerization from an aromatic diamine having at least two phenyl groups via two ether bonds and an ether bond,
The electrically insulating polyimide composition having excellent thermal conductivity according to claim 1, which is an imidized polyimide. 3. A filler effective for improving thermal conductivity contained in the electrically insulating polyimide composition is a crystalline silica powder,
The electrically insulating polyimide composition having excellent heat conductivity according to claim 1, which is a silicon nitride powder, an aluminum nitride powder, a boron nitride, an alumina powder, a magnesium oxide powder, a silicon carbide powder, or a mixture thereof. 4. A metal-based printed circuit board having excellent thermal conductivity obtained by joining two layers of metal foils with an insulating film comprising the electrically insulating polyimide composition having excellent thermal conductivity according to claim 1. 5. One of the two metal foil layers is a copper foil for a circuit, and the other layer is an aluminum foil, a stainless steel foil, a copper foil or an iron foil for a base substrate. 3. A metal-based printed circuit board having excellent thermal conductivity according to 1. 6. A filler contained in the polyimide composition and effective for improving thermal conductivity is a crystalline silica powder, silicon nitride powder, aluminum nitride powder, boron nitride, alumina powder, magnesium oxide powder, silicon carbide powder or The metal-based printed circuit board having excellent thermal conductivity according to claim 4, which is a mixture thereof. 7. The metal-based printed circuit board having excellent thermal conductivity according to claim 4, which is flexible and can be bent. 8. The metal-based printed circuit board having excellent thermal conductivity according to claim 4, wherein a copper foil for a circuit is processed by etching to form a wiring, and a semiconductor is mounted thereon.