JPH0353935A - Preventive method of copper diffusion into polyimide precursor - Google Patents

Abstract

PURPOSE:To prevent almost completely melting/diffusion of copper into a polyimide precursor, by a method wherein after depositing a nickel plated layer whose thickness is specific on the surface of the copper with an electroless plating method, to which the whole aromatic polyamic acid solution is applied. CONSTITUTION:After the whole aromatic polyamic acid solution is applied to a board on which a copper circuit pattern is formed, the same is made into imide by heat-treating and a polyimide layer is added. In this instance, after depositing of a nickel plated layer whose thickness is at least 0.05mum and not exceeding 1.0mum with an electroless plating method, a polyamic acid solution is applied to the same. The whole aromatic polyamic acid solution is obtained by a method wherein aromatic tetracarboxylic acid dianhydride and aromatic diamine are reacted with each other, concentration of which is regulated with an appropriate solvent and polyimide precursor varnish is formed. Formation of an electroless nickel plated layer is performed with a normal method by making use of nickel/boron electroless plating bath or nickel/phosphorus electroless plating bath on the market. However, it is preferable that purity of the nickel deposited with this method is high.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a copper polyimide multilayer substrate with excellent insulation and dielectric properties.

(Conventional technology) In recent years, with the advancement of electronic materials, technology for forming multilayer wiring has become an important issue, and multilayer wiring boards using various materials suitable for this and their manufacturing methods are being developed. Among these, polyimide is used as an insulator.
s 81IiI polyimide) Fr! The substrate is attracting attention because of its excellent electrical properties, such as good heat resistance, low dielectric constant, and high insulation properties.

The method for producing a copper polyimide multilayer board is usually to use a copper foil and polyimide film bonded together as a starting material, and to produce a board on which a grooved wiring pattern is formed on the surface.
The so-called sequential lamination method is used to laminate the substrates by sandwiching and gluing prepreg or semi-cured resin sheets, but when using this method, the polyimide film used as the substrate material It is not only difficult to obtain a thin multilayer board because it is not possible to make the copper foil very thin.
There is a problem that the excellent heat resistance and electrical properties of polyimide resin deteriorate due to the influence of the adhesive used in laminating the substrates, and recently, an alternative method for producing multilayer substrates is the so-called build-up lamination method. A law is proposed.

This pill-up lamination method repeats two unit processes: the process of forming a metal circuit pattern on a polyimide film, and the process of forming a polyimide insulating layer by thermal treatment on the surface of the substrate on which the circuit pattern is formed. In order to form the polyimide insulating layer, a solution prepared by adjusting the concentration of fully aromatic polyamic acid, which is a polyimide precursor, with an organic solvent, that is, a polyimide precursor layer, is used to form the circuit pattern. The polyimide is formed by coating the surface of the substrate on which it has been formed and heating it.

This method does not use an adhesive method when laminating the substrates, so thin substrates can be used for the structure or material, and the laminated film can be applied in a thin layer by coating, so it is more efficient than the sequential lamination method. As a result, multilayer boards can be made thinner, and since adhesives are not used for lamination, the good heat resistance and excellent electrical properties characteristic of polyimide resin are not impaired. This method is attracting attention as an excellent method for manufacturing copper-polyimide multilayer substrates because its advantages can be effectively utilized as is.

{Problem to be solved by the invention} However, when adopting the pilt-up method by applying the polyimide precursor varnish, it is difficult to convert the polyimide precursor varnish applied onto the copper thin film circuit pattern formed on the substrate into polyimide. Usually 200℃
As mentioned above, it is necessary to perform thermal curing by performing dehydration ring closure of the imide ring by ripening at a temperature of 400°C or less, and at this time, dissolution of copper occurs at the copper-polyimide precursor varnish interface. It is known that copper ions diffuse into the polyimide layer.

To explain this situation in more detail, if a polyimide precursor varnish containing polyamic acid as the main ingredient is applied onto a copper thin film and then heated to a temperature of 200°C or higher to imidize the polyamic acid, the resulting The polyimide film turned brown, and polyamic acid was imidized on the glass in the same way. The color tone will be significantly different from that obtained if the

The interface between the copper and polyimide film at this time was observed using a transmission electron microscope (
1'DI), there are countless precipitated particles with a diameter of around 50 nm in the polyimide layer near the interface, and on the other hand, the presence of such particles in the polyimide film that has been converted into Glass-L. It has been found that these precipitated particles are the cause of discoloration of the polyimide film.

According to the electron diffraction results, these precipitated particles contain a large amount of copper oxide, which indicates that copper is dissolved in the face during the process of imidization of polyamic acid by heating on the copper thin film. It is thought that during the process of diffusion into the chemically formed polyimide film, a part of it was oxidized to become copper oxide, which aggregated and precipitated.

It has also been confirmed that the precipitation of impurities as described above has an adverse effect on the structural strength and electrical properties of the polyimide film.

Regarding the formation of a metal circuit pattern layer, which is another step in multilayering a board, since copper is added on top of something that has already been made into polyimide, copper is added to the polyimide film. Even if it does diffuse, the amount of diffusion is extremely small because it is between solid phases.

On the other hand, in the process of forming a polyimide layer using a polyimide precursor varnish, which is the subject of the present invention, the main cause of copper diffusion is rather the dissolution of copper in the polyamic acid solution before imidization. Since the amount is large, it is an important issue to establish measures to prevent this.

One of the countermeasures has been to heat a polyamic acid solution that has been applied as a polyimide precursor on a copper thin film, and when it is imitated, the dissolution of the copper is accelerated by the oxygen in the air. In order to prevent this, methods have been proposed in which heating is performed in an atmosphere of an inert gas or reducing gas. However, even with these methods, it has not been possible to sufficiently prevent C from dissolving and diffusing copper into a polyimide film.

(Means for Solving the Problems) 6 The present invention aims to solve the above-mentioned problems, and includes polyamic acid as a main precept on a substrate on which a circuit pattern is formed using a copper thin film. A method for manufacturing a copper polyimide multilayer substrate, which includes a step of adding a polyimide layer on the substrate by applying a polyimide precursor varnish and heating it to imidize the polyamic acid in the varnish. This suppresses the dissolution and diffusion of copper into the polyamic acid solution at the stage of applying polyimide precursor varnish to the polyimide, and prevents impurities such as copper oxide from forming in the polyimide film formed by imidization of polyamic acid after heat treatment. The purpose of the present invention is to provide a method for preventing copper from diffusing into a polyimide precursor in such a way that copper is not contained in the polyimide precursor and electrical properties such as insulation are not impaired thereby.

That is, in order to achieve the above object, the present invention applies a wholly aromatic polyamic acid solution onto a substrate on which a copper circuit pattern is formed, and then heat-processes the solution to imidize it and form a polyimide layer on the substrate. In the method for manufacturing a copper polyimide multilayer board, which includes the step of adding a layer of
The method is characterized in that the polyamic acid solution is applied after depositing a nickel plating layer having a thickness of less than m.

<Function> In making the present invention, the inventors prepared pure silver pieces and pure nickel pieces each having an equal surface area of 6−,
Using diethylene glycol dimethyl ether as a solvent, a total of 3 mQ. 4 at room temperature in a solution of
After immersion for 00 hours, the amount of metal dissolved into each polyamic acid solution was measured. The results are not shown in Table I.

Table 1 Initial liquid phase components PAA ten solvent PAA ten solvent Metal immersed in solvent only Ni Cu Cu
Elution amount μg/■6 230 <1 As can be seen from the results in Table 1, the amount of nickel dissolved in the polyamic acid solution was about 1/40th that of copper. From this, nickel has the property of being less soluble in fully aromatic polyamic acid than copper, and therefore, when adding a nickel layer to a substrate on which a copper layer has been formed, this prevents the elution of copper by polyamic acid. It was confirmed that it acts as a barrier layer to prevent this.

In the present invention, the fully aromatic polyamic acid solution to be applied onto the copper circuit pattern forming substrate with a nickel barrier layer is made by reacting an aromatic tetracarboxylic dianhydride with an aromatic diamine and adjusting the concentration using an appropriate solvent. A polyimide precursor varnish is formed by adjusting the polyimide precursor varnish. Dimethylacetamide, dimethylformamide, N-methyl birrolidone, diethylene glycol dimethyl ether, etc. are used as the solvent for concentration adjustment. Adjustment of solution concentration, coating amount, etc. are appropriately determined depending on the desired thickness of the polyimide layer. The coating on the substrate may be performed using any conventional coating method such as spin coating, bar coating, or roll coating.

In the present invention, the electroless nickel plating layer is formed on the copper layer by a conventional method using a commercially available nickel/boron electroless plating bath, nickel/phosphorous electroless plating bath, or the like. However, it is desirable that the purity of the nickel deposited by this method be high.

The formation of this nickel plating layer can also be done by electrolytic plating, but in that case, it is necessary to supply power for plating to all of the target copper circuit patterns, and there may be isolated parts in the circuit patterns. Sometimes it is not possible to plate this area. Due to these drawbacks, electroplating is not a suitable method in this case.

The thickness of the nickel plating layer in the present invention is desirably at least 0.05 μm or more in order to effectively prevent dissolution and diffusion of copper into the polyimide precursor as a barrier layer.

Furthermore, as the thickness of the plating layer increases, the precipitated nickel film tends to peel off from the copper surface due to stress problems, so the thickness is required to be 1.0 μm or less.

It is generally known that the so-called skin effect, where current flows only near the conductor surface, increases as the frequency of the current increases, and therefore the electrical conductivity of the conductor surface is considered to be a particularly important factor in high-frequency circuits. It will be done. In this sense, the additional deposition of a nickel layer on the copper layer is an important matter when deterioration of high frequency conduction properties is a problem, and in this case, as a countermeasure, increasing the nickel purity in the deposited layer increases the electrical resistance. Although it is conceivable to suppress this as much as possible, it is more desirable to make the thickness of the precipitated layer as thin as possible. This is because in the high-frequency signal frequency band of around 100HLlz, which is currently mainly used in IC circuits, the range where high current density can be obtained due to the skin effect extends to a depth of several μm below the surface of the conductor. This is because if the thickness of the nickel layer is kept within a sufficiently low value below this depth, no problems will occur in practice.

Next, embodiments of the present invention will be described.

11 (Example) Example 1 A J-thickness of 35 μm was formed on a 50 μm thick polyimide film (“Kapton 200HJ” manufactured by Toray Teibon Co., Ltd.) by a conventional method.
A nickel-boron based electroless nickel plating bath (rBEL Nickel manufactured by Hmura Kogyo Co., Ltd.) was applied to the surface of the copper circuit pattern of the copper polyimide substrate on which the copper circuit pattern of m was formed.
Ni-B plated N (Ni
: about 99% by weight, B: about 1% by weight> was precipitated.

Next, a polyamic acid obtained by reacting penzophenone dianhydride with the same mole of diaminobenzophenone in diethylene glycol dimethyl ether was applied to the circuit pattern surface of the substrate on which the electroless plating layer had been formed. A polymer solution whose concentration was further adjusted with diethylene glycol dimethyl ether was applied to an acid solution (R Larc TPI varnish type-1 manufactured by Mitsui Toatsu Chemical Co., Ltd.),
After drying, this was heat-treated (maximum heating temperature 300° C.) to imidize it to form a polyimide layer with a thickness of 20 μm.

l2 No brown coloring was observed in the polyimide layer thus formed on the copper circuit pattern, and when the interface between the formed polyimide layer and the copper layer and the inside of the polyimide layer were observed using a transmission electron microscope, No precipitated particles due to copper dissolution/diffusion were observed.

From the above results, it is clear that prior to the method of the present invention, that is, forming a polyimide layer by imidizing a polyamic acid solution coated on a substrate on which a copper circuit pattern is formed, an electroless plating layer of nickel is formed on the copper circuit pattern. It can be seen that by forming an appropriate J layer, dissolution and diffusion of copper into the polyimide precursor can be prevented.

Example 2 A nickel-phosphorous electroless plating bath (nickel-phosphorus electroless plating bath) was applied to the surface of the copper circuit pattern of a copper polyimide substrate, in which a 18-μm-thick copper circuit pattern was formed on a 25-μm-thick polyimide film (Kapton 100Hr manufactured by DuPont-Toray). Using "Naipok 1P" made by Meltex, thickness 0.8
A 13 μm thick Ni-P electroless plating layer (Ni: about 98% by weight, P: about 2% by weight) was formed. Next, on the circuit pattern surface, a boriamic acid solution (Mitsui Toatsu Chemical Co., Ltd. A polymer solution whose concentration was further adjusted with diethylene glycol dimethyl ether was applied to a ``r.larcTPI varnish styve'' manufactured by R.L.A.
A polyimide layer of 5 μm was formed.

No brown coloring was observed in the polyimide layer formed on the copper circuit pattern in this way, and when the inner surface of the formed polyimide layer and the interface between the polyimide layer and the copper layer were observed using a transmission electron microscope. , the presence of precipitated particles due to copper dissolution/diffusion was not observed at all.

Comparative Example A polyimide film with a thickness of 25) t (manufactured by DuPont-Toray Co., Ltd. "Strength 7" h 1001-1 -+) with a thickness of 1
87llll (1) Copper 14 The surface of the circuit pattern of a copper polyimide substrate with a circuit pattern formed thereon is reacted with penzophenone tetracarboxylic dianhydride and the same mole of diaminopenzophenone in diethylene glycol dimethyl ether. polyamic acid solution (Mitsui Toatsu Chemical Co., Ltd. r l.arc
1'PI varnish type'' was coated with a polymer solution whose concentration was further adjusted with diethylene glycol dimethyl ether, and after drying, heat treatment (maximum heating temperature 3
00° C.) and imidized to form a polyimide layer with a thickness of 15 μm.

When we observed the polyimide layer formed on the copper circuit pattern in this way, we found that it was different from the case according to Example 2.
A significant change in color tone was observed after heating, and browning was progressing. Furthermore, when we observed the inside of the formed polyimide layer and the interface between it and the copper layer using a transmission electron microscope, we found that the particle size was 10 to 50 nm, which is thought to be due to the dissolution and diffusion of copper.
Innumerable precipitated particles of 1 μm in the polyimide layer from the interface
They existed in countless numbers over a nearby area.

15 That is, if electroless nickel plating is not performed on the copper circuit pattern prior to forming the polyimide layer by imidizing polyamic acid, dissolution and diffusion of copper will occur during the chemical formation process of the polyimide layer. It can be seen that the resulting polyimide layer becomes contaminated with precipitated particles based thereon.

(Effects of the Invention) As described above, according to the present invention, a polyimide precursor using polyamic acid is coated on a substrate on which a copper circuit pattern is formed, and this is imidized to add a polyimide layer. In the method for manufacturing a copper polyimide multilayer board according to the present invention, the dissolution and diffusion of copper into the polyimide precursor is almost completely prevented, and a sound polyimide layer can be formed, so it can be said to be an effective invention.

Claims (1)

[Claims] (1) By applying a fully aromatic polyamic acid solution as a polyimide precursor onto a substrate on which a copper circuit pattern is formed and then heating, the fully aromatic polyamic acid is imidized and added as a polyimide layer. In the method for manufacturing a copper polyimide multilayer board including the steps 1.
A method for preventing copper diffusion into a polyimide precursor, which comprises depositing a nickel plating layer of 0 μm or less and then applying a wholly aromatic polyamic acid solution.