JPH07105595B2 - Method of forming insulating layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] An insulating layer forming method of forming an insulating layer having a predetermined film thickness by repeatedly applying, drying, exposing and developing a photosensitive polyimide. For the purpose of reducing the damage as much as possible, a coating step of coating a photosensitive polyimide on the laminated surface of the substrate, a drying step of drying the coated surface, and an exposure mask on the coated surface dried by the drying step. The exposure and development steps of performing exposure by superimposing and then developing after exposure, and the intermediate heating step of heating the coated surface at a temperature lower than the baking step of curing the photosensitive polyimide after the exposure and development are repeated a plurality of times. Thus, a plurality of films are laminated, and the laminated films are heated in the baking step to form an insulating layer having a predetermined thickness on the laminated surface.

TECHNICAL FIELD The present invention relates to a method for forming an insulating layer in which a photosensitive polyimide is applied, dried, exposed, and developed repeatedly to form an insulating layer having a predetermined thickness.

Recently, printed boards used in electronic devices have been multi-layered, and high-density mounting of electronic components such as semiconductor elements has been achieved.

Such a multilayer printed circuit board is formed by alternately laminating a conductive layer and an insulating layer on the laminated surface of the substrate.

Further, such an insulating layer needs to be formed to have a predetermined thickness in order to maintain electrical characteristics such as impedance in the conductive layer at a predetermined value.

Therefore, in such multi-layering, it is required to manufacture the insulating layer so that the thickness of the insulating layer has a predetermined value.

[Conventional technology]

Conventionally, it was manufactured as shown in the conventional manufacturing process diagram of FIGS. 4 (a) to (g).

As shown in FIG. 4A, a photosensitive polyimide 4 of an esterification bond type or an ionic bond type is dropped onto the laminated surface 1A of the substrate 1 made of a ceramic material or the like on which the conductive layer 3 is formed. As shown in (b), the photosensitive polyimide 4 is applied to the laminated surface 1A by spin coating so as to have a predetermined thickness.

The substrate 1 thus coated is heated at a temperature of about 80 ° C. for 1.5 hours (the heating time in this case is increased or decreased depending on the heat capacity of the substrate 1), and then, as shown in FIG. Are exposed to each other by irradiating with the light L, and the portion irradiated with the light L becomes difficult to be dissolved by this exposure.

Therefore, after the exposure, by developing with an NMP solvent, the portions not irradiated with light are dissolved by the NMP solvent,
As shown in (d), a through hole 2C is formed in the film 2A covering the conductive layer 3.

Next, the film 2A is cured by heating in the baking process.

As shown in the heating temperature graph of the baking process of FIG.
Low temperature heating of about 1.5H, and finally about 350H
The film 2A is heated to a high temperature of about 400 ° C. for about 1.5 H to cure the film 2A and form the film with a thickness t1.

On the film 2A thus formed, further, as shown in (e), the photosensitive polyimide 4 is dropped, and the laminated surface 1A on which the film 2A is formed is used as in (f). Photosensitive polyimide 4 is applied to, dried, exposed and developed.
By the baking step, as shown in (g), the insulating layer 2 having the thickness t is formed by laminating the film 2B having the thickness t1 on the upper layer of the film 2A.

It is difficult to remove a predetermined portion of the coated photosensitive polyimide 4 by exposure and development, and it becomes difficult to remove it by exposure and development when the coating becomes thicker. There is a limit to the thickness.

Therefore, the thickness of the coating film is usually set to about 20 μm so as to ensure the exposure and development.

However, in reality, the thickness of the coating film is contracted by the curing in the baking step, and the thickness t1 when formed on the film 2A is halved.

Therefore, as shown in the conventional manufacturing flowchart of FIG. 6, a coating step A for coating the photosensitive polyimide 4 on the laminated surface 1A of the substrate 1, a drying step B for drying the coated photosensitive polyimide 4, and a drying step. By exposing the coating film by overlapping the exposure mask 5 and developing with an NMP solvent, the developing step C and the baking step E of heating at a predetermined temperature are repeated n times to obtain a predetermined thickness t by t1 × n. The insulating layer 2 is formed.

[Problems to be Solved by the Invention]

Such coating process A, drying process B, exposure and development process C
By repeating the baking process E and the predetermined thickness t
By forming the insulating layer 2 as described above, in the case of manufacturing a multilayer substrate in which a plurality of conductive layers 3 and insulating layers 2 are laminated, high temperature heating by the baking step E is repeatedly applied to the substrate 1 and the lower layer. It will be.

Therefore, the substrate 1 and the lower conductive layer 3 and the insulating layer 2 are stressed by heat, which causes a problem such as peeling, disconnection, and deterioration due to heat stress.

Therefore, an object of the present invention is to reduce heat damage as much as possible when manufacturing a multilayer substrate.

[Means for Solving the Problems]

 FIG. 1 is an explanatory view of the principle of the present invention.

As shown in FIG. 1, a coating step A for coating the photosensitive polyimide 4 on the laminated surface 1A of the substrate 1, a drying step B for drying the coated surface, and a coating step dried by the drying step B. The coating surface is heated at a lower temperature than the exposure and development step C in which the exposure mask 5 is overlapped on the surface and the post-exposure development is performed, and the baking step E in which the photosensitive polyimide 4 is cured after the exposure and development. By repeating the intermediate heating step D a plurality of times (n) times, a plurality of films are laminated, and the laminated films are heated in the baking step E to form a laminated surface.
The insulating layer 2 having a predetermined thickness t is formed on 1A.

By forming in this way, the above-mentioned subject is solved.

[Action]

That is, the coating step A, the drying step B, the exposure and development step C, and the intermediate heating step D are repeated a plurality of times to stack a plurality of films, and finally, a baking step E in which heating is performed at a high temperature is performed. The insulating layer 2 having a predetermined thickness t is formed.

In this case, the temperature of repeated heating is the baking step E.
Since it is heated by the lower temperature, heat stress can be reduced.

Therefore, in manufacturing a multilayer substrate, the insulating layer 2 which has already been laminated or the conductive layer 3 is not broken due to stress due to heat as in the related art, and the conductive layer 3 is not broken, so that the quality can be improved.

〔Example〕

The present invention will be described in detail below with reference to FIGS. 2 and 3. FIG. 2 is a manufacturing flow chart of one embodiment of the present invention, and FIG. 3 is a heating temperature graph of the intermediate heating step of the present invention. Throughout the drawings, the same reference numerals denote the same objects.

As shown in FIG. 2, after the coating step A in which the photosensitive polyimide 4 is coated on the laminated surface 1A of the substrate 1, the coated surface is about 80
Drying step B for drying for 1.5 hours at a temperature of ℃ is performed, and after drying,
Exposure is carried out by overlapping the exposure mask 5, and development by an NMP solvent is carried out to dissolve a portion not irradiated with light by an NMP solvent, and a film 2A for covering the conductive layer 3 is formed by a developing step C. Heating is performed by the intermediate heating step D so as to semi-cure the film 2A.

The coating step A, the drying step B, the exposure / development step C, and the intermediate heating step D are repeated n times to obtain a plurality of films 2A.
The laminated film 2A is heated in the baking step E to cure each laminated film 2A to form the insulating layer 2 having a predetermined thickness t.

In addition, the heating in the intermediate heating step D in this case is performed by adding 1.5H at about 200 ° C. as shown in FIG. 3, and the boiling point of the NMP solvent contained in the photosensitive polyimide 4 is 1
Since the temperature is 80 ° C., the polyimide group can be semi-closed by evaporating the NMP solvent by heating at about 200 ° C. in this way, and the photosensitive polyimide 4 can be semi-cured.

When semi-cured as described above, it is not dissolved in the exposure and development step C, so that the film 2A can be easily laminated on the upper layer.

Therefore, it is possible to stack a plurality of films 2A by heating at a low temperature of 200 ° C. without heating at a high temperature of 350 to 400 ° C. by the baking step E so as to completely cure the film 2A as in the conventional case. It is possible to reduce the thermal stress in the substrate 1, the lower insulating layer 2 and the conductive layer 3.

〔The invention's effect〕

As described above, according to the present invention, it is possible to stack a plurality of films by heating at a low temperature by repeating the application, drying, exposure, development and heating of the photosensitive polyimide.

Therefore, when manufacturing a conventional multilayer substrate, it is possible to prevent problems such as peeling and disconnection caused by thermal stress, improve quality, and bring great practical effects.

[Brief description of drawings]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a manufacturing flow chart of one embodiment according to the present invention, FIG. 3 is a heating temperature graph of an intermediate heating step of the present invention, and FIG. g) is a conventional manufacturing process diagram, FIG. 5 is a heating temperature graph of the baking process, and FIG. 6 is a conventional manufacturing flowchart. In the figure, A is a coating process, B is a drying process, C is an exposure and development process, D is an intermediate heating process, E is a baking process, 1 is a substrate, 2 is an insulating layer, and 1A is a laminated surface.

Claims (1)

[Claims] 1. A coating step (A) for coating a photosensitive polyimide on a laminated surface (1A) of a substrate (1), a drying step (B) for drying the coated coating surface, and a drying step (B). Exposure by superimposing an exposure mask on the coated surface dried by, and developing after the exposure, the developing step (C), the exposure,
After development, an intermediate heating step (D) of heating the coated surface at a lower temperature than a baking step (E) of curing the photosensitive polyimide (4) is repeated a plurality of times (n) times to laminate a plurality of films. A method for forming an insulating layer, comprising forming the insulating layer (2) having a predetermined thickness (t) on the laminated surface (1A) by heating the laminated film in the baking step (E).