JPS6355234B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for flattening the surface of a substrate on which a wiring pattern is formed, such as a ceramic substrate or a glass-reinforced epoxy substrate.

Generally, this type of substrate is used as a substrate for mounting hybrid integrated circuits or semiconductor elements, and a thick or thin film wiring pattern is formed on its surface. Thick film patterns are formed by printing conductive ink or resistive ink using the screen printing method, but the pattern width is limited to about 100 μm because it is affected by screen thickness and ink bleeding. . On the other hand, thin film patterns are formed at a thickness of several 100 Å to several μm, so it should be possible to form fine patterns, but due to the poor surface flatness of the substrate, conventional patterns can only be formed with a width of around 100 μm. I couldn't do it.

However, recently, as the density of hybrid integrated circuits and semiconductor devices to be mounted has increased, there has been a demand for finer wiring patterns formed on substrates. Therefore, in order to satisfy this demand, it is necessary to flatten the surface of the substrate.

Polishing and glass coating are generally used as methods to flatten the surface of the substrate on which wiring patterns are formed, but these processes require time and large capital investment, making them extremely difficult to manufacture. The cost will be higher.

Therefore, for example, as disclosed in Japanese Patent Publication No. 46-38460, a method is known in which a film made of an organic material is formed on the surface of the substrate to planarize the substrate. Here, as a method for forming the above-mentioned film, there may be a method of applying a heat-resistant resin to the substrate surface by spin coating, spray coating, roller coating, dip coating, etc.
Even in this method, it is necessary to use a highly concentrated resin solution to form a thick film in order to fill in the unevenness of the substrate and cover it with a flat coating surface by one application. However, when a highly concentrated solution is used, surface tension causes bulges around the coated substrate, resulting in thicker coatings.

This phenomenon will be explained below using a spin coating method as an example. Figure 1 shows a 5 cm ceramic substrate (Kyoto, Japan) using Trenise for semiconductors as a heat-resistant resin (polyimide resin (polyamic acid resin) manufactured by Toray Industries, Inc., resin content 17%, solvent: N,N'-dimethylacetamide, viscosity 1100 cps). This shows the change in film thickness around the substrate when it was dropped onto A476 (manufactured by Ceramics Co., Ltd.) and spin-coated. In Fig. 1, when the rotation speed is 4000 rpm, the thickness of the flat part 1 of the coating film is about 3 μm, and the width of the raised part 2 is about 30 μm from the peripheral edge.
As the rotation speed is lowered to obtain a thick film, the bulge gradually increases, and when the speed is increased to 400 rpm, the film thickness becomes 12 μm, but the width of bulge 2 is approximately 7 μm.
mm and large. If the raised portion 2 is large as described above, when forming a thin film wiring pattern thereon, the adhesion of the mask becomes poor, making it difficult to form a fine wiring pattern.

In order to reduce such raised portions 2 and flatten the rough surface of the substrate, thin resin films must be coated many times with high speed rotation. For multiple coatings, it is necessary to heat the resin each time to completely remove the solvent, or to semi-cure or completely cure the resin to prevent the previously applied coating film from being redissolved by the solvent. The process of coating such thin films over and over again is extremely complicated and requires a great deal of effort to process in large quantities. Further, when a resin is spin-coated onto a square substrate, a uniform coating film is formed in a circular shape, but there is a drawback that the film thickness at the corner portions becomes extremely thin.

The purpose of this invention is to eliminate the drawbacks of the conventional methods as described above, and to provide a method that can form a thick film with a flat surface and less bulges around the periphery, and that has simple processing steps. It is said that

This invention forms a thin resin coating film with little swelling around the periphery on the surface of the substrate on which the wiring pattern is to be formed, and then fixes the resin film by pressure bonding or thermocompression bonding to completely cover the rough surface of the substrate. This is a method to flatten the surface.

This invention will be explained below with reference to Examples.

Example After cleaning and drying the ceramic substrate (described above),
It was placed on a spin coater, about 1 ml of Trenise (described above) was added dropwise, and the plate was rotated at 4000 rpm for 1 minute. Then, in a nitrogen atmosphere at 100°C for 15 minutes and at 200°C.
The solution was heated in stages for 5 minutes to volatilize the solvent. At this time, a part of the polyamic acid in Trenice was cyclized and semi-cured. Next, on top of this coating film, a 12 μm thick film prepared by completely curing Trenice using a wet casting method was laminated, that is, thermocompressed, at 200°C using a hot roll laminator. This was heated in stages at 200°C for 15 minutes and at 300°C for 15 minutes in a nitrogen atmosphere to completely cure it, forming a 15 μm thick polyimide film that integrated the paint film and the laminate film. Ta.

Figure 2 shows the surface roughness of the ceramic substrate in the above example using a surface roughness meter (manufactured by Kosaka Seisakusho).
0, the results of measuring the surface roughness of the coating surface 11 after solvent volatilization and the surface 12 of the polyimide coating after lamination are shown. As shown in FIG. 2, the surface roughness of the substrate surface 10 is approximately 2 μm, but the surface roughness of the coating film surface 11 after solvent volatilization is approximately
It can be seen that the surface roughness of the surface 12 is approximately 0.3 μm, which is a slight improvement in flatness due to the lamination of the resin film. It is also clear that the raised portion 2 at the periphery that occurred during coating film formation was also reduced by laminating the resin film.

As described above, by thermocompression bonding the resin film onto the resin coating, even if the coating surface 11 is rough, excellent flatness can be obtained on the surface 12 after thermocompression bonding. It becomes possible to form a fine wiring pattern (metal layer) on the 12, and high density of various circuit elements can be realized.

Further, by forming the two-layer structure of the resin coating film and the resin film, sufficient thickness and flatness can be obtained as a whole even if the resin coating film is formed to be thin and have a rough surface. Moreover, the substrate can be flattened simply by thermocompression bonding the resin film. Therefore, formation of the resin coating film and fixation of the resin film are facilitated, and the processing steps are simplified.

In addition, since the resin coating film acts like an adhesive, the resin film can be firmly adhered to the substrate, thereby increasing reliability as a circuit board.

In the above embodiments, a ceramic substrate is used as the insulating substrate, but the present invention can also be used to flatten the surface of a glass-reinforced epoxy substrate or a substrate made of other insulating materials. In addition to the above-mentioned Trenice, coating resin materials include polyimide resins such as PIQ (manufactured by Hitachi Chemical, trade name), Pyraline (manufactured by Dupont, trade name), HI-600 (manufactured by Hitachi Chemical, trade name), etc. Heat-resistant resins such as polyamide resins, epoxy resins, phenol resins, polycarbonate resins, polybenzimidazole resins, and polyparabanic acid resins are used. Furthermore, the above-mentioned polyimide resin, polyamideimide resin, polycarbonate resin, polybenzimidazole resin, polyoxadiazole resin, polyparabanic acid resin, etc. can be used for the laminate film.

In the examples, the same materials were used for the coating resin and the laminate film, but a combination of different materials may be used. The rotation speed varies depending on the type of resin and solvent, but in the case of Trenise it is 2000 rpm.
The above is desirable.

In addition, the Trenice solution is dissolved in the state of polyamic acid, and when heated, a dehydration cyclization reaction occurs to form a polyimide resin. It may remain inside. If such residual moisture is present, polyimide will hydrolyze and deteriorate, but in this invention, a thin coating film is sufficient, making it easy to volatilize and remove the solvent and water, and if a film is laminated on top of it, it can be cured by high temperature heating. In some cases, the moisture is completely volatilized and removed, forming a polyimide film that does not easily deteriorate.

In addition, Trenise shrinks by several percent when it is heated and cured, but since the laminate film is already in a cured state, only small distortions due to curing shrinkage of the thin coating remain.

Furthermore, when forming a coating film using the spin coating method, 70 to 80% of the dropped resin solution is blown off to the outside of the substrate and is wasted, but with the method of this invention, this amount is extremely small, and it can be used to save resources. is also valid,
Suitable for mass processing.

As another embodiment of the present invention, the resin film may be fixed to the resin coating film not by thermocompression bonding but by simple pressure bonding without heating.

As explained above, according to the present invention, since a resin coating film and a resin film are laminated on an insulating substrate, excellent flatness can be obtained on the surface of the resin film, and fine wiring can be formed on the resin film. Can form patterns. Further, by forming the resin coating film into a two-layer structure consisting of a resin coating film and a resin film, formation of the resin coating film and fixing of the resin film are facilitated, and the processing steps can be simplified.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the relationship between the number of rotations of the coating machine and the coating film thickness near the periphery of the substrate when a resin coating film is formed on the substrate by one rotational coating, and Fig. 2 is a characteristic diagram of the present invention. FIG. 2 is a characteristic diagram showing the surface roughness of the surface of the ceramic substrate, the surface of the resin coating film, and the surface of the coating film after lamination of the resin film used in the example. 1... Flat part, 2... Surrounding raised part, 1
0...Surface of ceramic substrate, 11...Surface of resin coating film, 12...Surface of coating after lamination of resin film. In the figures, the same numbers indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first step of forming a resin coating film on an insulating substrate on which a wiring pattern is formed, and a second step of fixing a resin film on the upper surface of this resin coating film by pressure bonding or thermocompression bonding. A method for planarizing a substrate surface, comprising the steps of: 2 The insulating substrate is a ceramic substrate or a glass-reinforced epoxy substrate, and the resin coating film is made of polyimide resin, polyamideimide resin, epoxy resin, phenol resin, polycarbonate resin, polybenzimidazole resin, polyparabanic resin. At least one selected from acid-based resins
The resin film is made of at least one type of heat-resistant polymer selected from polyimide resins, polyamideimide resins, polycarbonate resins, polybenzimidazole resins, polyoxadiazole resins, and polyparabanic acid resins. A method for planarizing a surface of a substrate according to claim 1, comprising a heat-resistant polymer. 3 The above resin coating film can be applied by spin coating, spray coating,
3. The method for flattening a substrate surface according to claim 1, wherein the resin film is formed by roller coating or dip coating, and the resin film is bonded by pressure or thermocompression with a roll laminator. 4 The first step is to apply a polyamic acid solution to the surface of the substrate and heat it to volatilize the solvent to form a resin coating film made of semi-cured polyimide or polyamideimide. Step 2 is to press or thermocompress a completely cured polyimide resin or polyamideimide resin film onto the resin coating film. Flattening method.