JPH05343853A - Formation through hole in multilayer insulating film - Google Patents

Abstract

PURPOSE:To provide a forming method for a through hole capable of avoiding the cracking in a conductor at the junction point of multilayer insulating film. CONSTITUTION:Within this through hole making method in multilayer insulating film, the through hole 7a provided in the lower insulating film 6a is made larger than the through hole 7b provided in the upper layer insulating film 6b so that the upper layer insulating film 6b may be inserted into the through hole 7a in the lower layer insulating film 6a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hybrid integrated circuit board comprising a lower layer conductor and an upper layer conductor which are insulated by an insulating film made of a polyimide resin, and more particularly to a multi-layer insulating film having a plurality of laminated layers. The present invention relates to a method of forming a through hole connecting a conductor and an upper layer conductor.

If a pinhole is present in an insulating film interposed between conductors in a hybrid integrated circuit board or the like, a short circuit may occur via the pinhole. As a means for eliminating such a short circuit, the application and curing of the resin are repeated a plurality of times to form an insulating film having a plurality of layers.

However, when a through hole is formed in such an insulating film, a conductor connecting upper and lower conductors may be cracked and broken. Therefore, there is a demand for development of a method for forming a through hole in the multilayer insulating film at which the conductor does not crack at the junction of the insulating films.

[0004]

2. Description of the Related Art FIG. 3 is a side sectional view showing a conventional through hole forming method. In the figure, according to the conventional method of forming a through hole, an insulating film made of a polyimide resin is formed on a substrate 2 having a lower conductor 1, and the insulating film is, for example, a double layer applied in a layered form to prevent a short circuit due to a pinhole or the like. It is composed of insulating films 3a and 3b.

The double insulating film is formed by exposing the photosensitive polyimide resin coated on the substrate 2 to light and developing it to pattern the insulating film 3a and then baking it. Further, the photosensitive polyimide resin applied thereon is exposed to light and developed to pattern the insulating film 3b and then baked to generate the insulating film 3b.

Through holes 5 are formed in the generated insulating film to connect the upper conductor 4 formed on the insulating film 3b to the lower conductor 1.
The through hole 5 is formed by through holes 5a and 5b provided in the insulating films 3a and 3b, respectively, and a conductor 5c penetrating the inside of the through hole.

When the conductor 5c is formed along the wall surfaces of the through holes 5a and 5b, the smaller the step on each wall surface, the easier it is to form a conductor having a uniform film thickness. Therefore, the lower insulating film 3a is provided with a through hole 5a having an outer diameter smaller than that of the through hole 5b provided in the upper insulating film 3b.

[0008]

FIG. 4 is a side sectional view showing a problem in the conventional forming method. However, in the conventional method, the lower insulating film is formed before the upper insulating film 3b is formed.
3a is baked into black polyimide, and the ultraviolet rays for exposing the upper insulating film 3b are absorbed by the lower insulating film 3a, so that the exposure amount to the peripheral portion of the through hole 5b becomes small.

Further, the developing solution for developing the upper insulating film 3b during mass production invades between the insulating films, so that the lower surface of the insulating film 3b is often eroded, and when fired, the peripheral portion of the through hole as shown in FIG. There has been a problem that the conductor that flips up and cracks occur in the conductor that connects the upper and lower conductor layers.

It is an object of the present invention to provide a method for forming a through hole in a multilayer insulating film in which a conductor is not cracked at a junction of the insulating films.

[0011]

FIG. 1 is a side sectional view showing a through hole forming method according to the present invention. Note that the same object is denoted by the same symbol throughout the drawings.

The above problem is that the upper layer conductor formed on the uppermost insulating film by laminating two or more layers of insulating film on the substrate having the lower layer conductor is converted into the lower layer conductor through the through hole provided in the insulating film. When forming a through hole in the multi-layer insulation film to be connected,
The through-hole 7a provided in the lower insulating film 6a is replaced by the upper insulating film 6b.
This is achieved by the method of forming a through hole in a multilayer insulating film according to the present invention, which is made larger than the through hole 7b provided in the above, and the upper insulating film 6b is fitted into the through hole 7a of the lower insulating film 6a.

[0013]

In FIG. 1, the through hole provided in the lower insulating film is made larger than the through hole provided in the upper insulating film, and the upper insulating film is inserted into the through hole of the lower insulating film to allow the through hole. It is possible to eliminate the junction point of the insulating film from the hole.

That is, it is possible to realize a method of forming a through hole in the multilayer insulating film at which the conductor does not crack at the junction of the insulating films.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 2 is a side sectional view showing another embodiment of the forming method according to the present invention.

In the method of forming a through hole according to the present invention shown in FIG. 1, an insulating film is formed on a substrate 2 having a lower layer conductor 1 as in the conventional case, and the insulating film is applied in layers to prevent a short circuit due to a pinhole or the like. For example, the double insulating films 6a and 6b are formed.

The double insulating film is formed by exposing the photosensitive polyimide resin coated on the substrate 2 to light and developing it to pattern the insulating film 6a and then baking it. Further, the photosensitive polyimide resin applied thereon is exposed to light and developed to pattern the insulating film 6b, and then baked to generate the insulating film 6b.

Through holes 7 for connecting the upper layer conductor 4 formed on the insulating film 6b to the lower layer conductor 1 are formed in the generated insulating film.
The through hole 7 is formed of through holes 7a and 7b provided in the insulating films 6a and 6b and a conductor 7c penetrating the inside of the through hole.

Unlike the conventional method, the lower insulating film 6a is provided with a through hole 7a having an outer diameter larger than that of the through hole 7b formed in the upper insulating film 6b, and the upper insulating film 6b is formed to reduce a step. Is configured to be fitted into the through hole 7a provided in the lower insulating film 6a.

In the above-described embodiment, the lower insulating film 6a and the upper insulating film 6b are formed to have almost the same thickness. However, as shown in FIG. 2, the lower insulating film 6a is formed. By making the thickness thicker than the thickness of the upper insulating film 6b, it becomes possible to further reduce the step.

By making the through-hole provided in the lower insulating film larger than the through-hole provided in the upper insulating film, the lower-layer conductor is provided inside the through-hole when the upper insulating film is patterned. It is exposed and does not absorb ultraviolet rays for exposure.

As a result, erosion of the lower surface of the insulating film at the time of developing the upper insulating film and curling up of the peripheral portion of the through hole at the time of baking are eliminated, and the conductor does not crack at the junction of the insulating film in the multilayer insulating film. A method of forming holes can be realized.

Moreover, since the absorption of ultraviolet rays when patterning the upper insulating film is eliminated, the exposure amount can be reduced, the processing ability of the device for patterning the insulating film is improved, and the hybrid integrated circuit substrate is manufactured. The time required for can be shortened.

[0024]

As described above, according to the present invention, it is possible to provide a method for forming a through hole in a multilayer insulating film at which a conductor does not crack at a junction of the insulating films.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a through hole forming method according to the present invention.

FIG. 2 is a side sectional view showing another embodiment of the forming method according to the present invention.

FIG. 3 is a side sectional view showing a conventional through hole forming method.

FIG. 4 is a side sectional view showing a problem in a conventional forming method.

[Explanation of symbols]

 1 Lower layer conductor 2 Substrate 4 Upper layer conductor 6a, 6b Insulating film 7 Through holes 7a, 7b Through hole 7c Conductor

Claims (2)

[Claims] 1. An upper layer conductor formed by stacking two or more layers of insulating films on a substrate having a lower layer conductor, and forming an upper layer conductor on the uppermost insulating film through a through hole provided in the insulating film. When forming a through hole in a multi-layer insulating film that is connected to a conductor, make the through hole (7a) in the lower insulating film (6a) larger than the through hole (7b) in the upper insulating film (6b). Together with the upper insulating film (6b) through hole (7a) of the lower insulating film (6a)
A method for forming a through hole in a multilayer insulating film, which is characterized in that: 2. In the method for forming a through hole in a multilayer insulating film according to claim 1, the thickness of the lower insulating film (6a) is made thicker than the thickness of the upper insulating film (6b). A method of forming a through hole in a multi-layer insulating film, characterized by: