JPH07249867A - Method of surface treating insulating film - Google Patents

Abstract

PURPOSE:To obtain an insulating film excellent in adhesion by a method wherein the surface of a first, insulating film is treated with a mixed gas of oxygen and CF4, and then a second insulating film is formed. CONSTITUTION:Varnish-like polyimide precursor is applied onto a base board 10 and burned for the formation of a lower polyimide resin' film 11 on the base board 10, and the lower polyimide resin film 11 is subjected to a surface treatment by blowing plasma gas against it. Plasma gas used for a surface treatment is a mixed gas composed of O2 and CF4 which are mixed at a ratio of 3 to 7 in flow rate. A metal thin film is formed on the lower polyimide resin film 11 subjected to a surface treatment by evaporation or sputtering, and a wiring conductor 12 is formed through a photolithography process. Furthermore, a polyimide precursor film is formed and dried out, a viahole 13 is cut in the polyimide precursor film, and the polyimide precursor film is burned into an upper polyimide resin film 14. By this setup, an insulating film cart be enhanced in adhesion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for an insulating film. More specifically, the present invention relates to a surface treatment method of an insulating film for obtaining adhesion of the insulating film on a substrate or the like on which electronic components are mounted.

[0002]

2. Description of the Related Art In recent years, multilayer substrates have come to be widely used due to the necessity of high-density mounting. A general multi-layer substrate is manufactured by forming an insulating film on a base material of the substrate and repeating a process of forming a wiring layer on the insulating film to make the wiring layer multi-layered.

[0003]

In such a multilayer substrate, it is necessary to consider the adhesiveness between the base material and the insulating film and the adhesiveness between the insulating films when they are multilayered.
That is, it is necessary to secure a sufficient adhesive force and prevent these peelings from occurring. On the other hand, in an actual board, in order to prevent cracks due to heat and enhance the reliability of the connection, the coefficient of thermal expansion of the board and the insulating film and the coefficient of thermal expansion of the semiconductor element and the electronic component mounted on the board and Matching is desirable. Generally, the coefficient of thermal expansion of a semiconductor element or an electronic component is lower than that of an insulating film, so it is desirable to use an insulating film having a coefficient of thermal expansion as low as possible.

That is, it is necessary to form an insulating film having a coefficient of thermal expansion similar to that of a semiconductor element or electronic component to be mounted while ensuring sufficient adhesion of the insulating film.

[0005]

Therefore, according to the present invention, when laminating an insulating film, the surface of the lower insulating film is surface-treated by plasma of a mixed gas of oxygen and CF4, and then the surface-treated lower insulating film is processed. This is a surface treatment method in which an upper insulating film is formed on top.

[0006]

The adhesiveness of the insulating film is improved by subjecting the insulating film formed on the base material of the substrate to the surface treatment with the plasma of the mixed gas.

[0007]

EXAMPLES Hereinafter, a polyimide resin is used as an insulating film,
An embodiment of the present invention will be described by taking the case of manufacturing a multilayer substrate as an example. Polyimide resin has a small electric conductivity of about 3 and has excellent heat resistance. Therefore, in recent years, it has been considered effective to use polyimide as an insulating film in a high-speed signal transmission board.

Generally, since polyimide is a chemically stable substance, the adhesion between the polyimide resin films is not necessarily high. Therefore, the adhesion is insufficient and peeling easily occurs between the polyimide resin films at the time of stacking, which becomes a problem when the substrate is multilayered. Therefore, conventionally, in order to solve this problem, when the polyimide resin film is laminated, the surface of the lower polyimide resin film is treated with oxygen plasma to improve the adhesion. However, there are cases where sufficient adhesion cannot be secured even by surface treatment with oxygen plasma.

In addition to this, when the polyimide resin films are laminated, the stress in the polyimide resin film increases as the number of laminated layers increases. Further, gas is generated from the polyimide resin film in the firing process. There is a possibility that the polyimide resin film may be peeled off due to the increase of the internal stress or the gas generated in the firing process. This is particularly remarkable when a low thermal expansion polyimide resin having a rigid chemical structure is used.

However, as described above, it is necessary to match the thermal expansion coefficient of the insulating film with the thermal expansion coefficient of the semiconductor element and the electronic component as much as possible. For this purpose, peeling of the polyimide resin film is likely to occur, but it is desirable to use a polyimide resin film having low thermal expansion as much as possible. Therefore, the surface treatment method of the present invention is intended to improve the adhesion while using a polyimide resin film having a relatively low thermal expansion property, and an embodiment will be described below with reference to the drawings.

First, the surface treatment method of the present invention will be described with reference to FIG. Base substrate 1 which is a base material for forming an insulating film
A varnish-shaped polyimide precursor is applied to No. 0 by a method such as spin coating. This is baked to form a polyimide resin film. This forms the lower layer polyimide resin film 11 (FIG. 1 (a)).

Next, surface treatment is performed by spraying a plasma gas onto the lower layer polyimide resin film 11. The plasma gas was sprayed using a reactive ion etching apparatus with plasma having a gas pressure of 10 Pa and an applying power of 600 W, and the processing time was 3 minutes. The plasma in this surface treatment has a gas flow rate ratio O2: CF4 = 3: 7.
It was realized by the mixed gas of (Fig. 1 (b)).

A metal thin film is formed on the lower polyimide resin film 11 thus surface-treated by vapor deposition or sputtering, and a wiring conductor 12 is formed by a photolithography process (FIG. 1 (c)).

On the lower layer polyimide resin film 11 and the wiring conductor 12, a polyimide precursor is further formed into a film by a method such as spin coating, and after drying, the via hole 1 is formed.
3 is formed. This is baked to form the upper polyimide resin film 1
Get 4. By repeating the above steps, wiring is connected between the upper and lower layers to form a multilayer, and a multilayer wiring board is manufactured.

The effect of improving the adhesion between the polyimide resin films according to the present invention will be described below.

FIG. 2 shows that (1) no surface treatment of the insulating film, (2) plasma treatment with pure oxygen, (3) mixed gas of O 2: CF 4 = 98: 2,
(4) With a mixed gas of O2: CF4 = 6: 4, and
(5) It is the result of evaluating the adhesiveness of the polyimide resin film by a peel test for each of the cases of using a mixed gas of O2: CF4 = 3: 7. The evaluation result shows the average value of the number of materials n = 10.

As is clear from FIG. 2, the peel strength is a little less than 700 g / cm in the plasma treatment with pure oxygen, whereas the peel strength is 840 g / cm in the plasma treatment with the mixed gas having the CF4 concentration of 70%. It can be seen that the adhesion is greatly improved.

From FIG. 2, the CF4 concentration of the mixed gas is 20%.
It will be understood that the peel strength is exceeded when the degree is exceeded than when the plasma treatment with pure oxygen is performed. Here, the concentration of CF4 in the mixed gas is 4 in order to obtain a strength sufficiently higher than that of the plasma treatment with pure oxygen.
It is desirable that the content is about 0% or more and 80% or less. Further, when the CF4 concentration is 70%, the adhesion of the polyimide resin film is the best.

In the above, the manufacturing of a multilayer substrate has been described by taking a multilayer substrate as an example. However, in addition to this, when a polyimide resin is used as an insulating film of a flexible wiring substrate typified by a TAB tape, or passivation of other electronic components. Even when a polyimide resin is used for the film, the surface treatment method of the present invention can be applied.

Although the case where the polyimide resin film is used as the insulating film has been described, the surface treatment method of the present invention is also applicable to the case where other organic materials such as Teflon and BCB are used as the insulating film. Can be applied.

Further, the insulating film to which the surface treatment method of the present invention is applied is not limited to the case where it is formed directly on the surface of the base material, and for example, when the insulating film is formed in multiple layers on the base material. It is possible to apply the surface treatment method of the present invention to a multi-layer, that is, an arbitrary insulating film in which a plurality of films are formed.

[0022]

As described in detail above, by applying the surface treatment method according to the present invention, it becomes possible to secure sufficient adhesion of the insulating film.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a surface treatment method of the present invention.

FIG. 2 is a diagram showing an evaluation result of adhesion of an insulating film.

[Explanation of symbols]

 10 ... Base substrate 11 ... Lower layer polyimide resin film 12 ... Wiring conductor 13 ... Via hole 14 ... Upper layer polyimide resin film

Claims (3)

[Claims] 1. A surface treatment method for an insulating film, comprising: forming a first insulating film on a base material; and forming a second insulating film on the surface of the insulating film. A surface treatment method for an insulating film, characterized in that the surface is treated with plasma using a mixed gas of oxygen and CF4, and then the second insulating film is formed. 2. The surface treatment method for an insulating film according to claim 1, wherein the mixing ratio of CF4 in the mixed gas is 40%.
The surface treatment method is 80% or less. 3. The surface treatment method for an insulating film according to claim 2, wherein the mixing ratio of CF 4 in the mixed gas is 70%.
The surface treatment method is characterized by: