JP3493671B2 - Manufacturing method of film wiring board - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a film wiring board. 2. Description of the Related Art A method for manufacturing a film wiring board is called a casting method. A polyimide precursor is applied to a metal foil such as a copper foil and cured to form a polyimide layer. There is known a method of forming leads by etching a metal foil into a predetermined pattern. by the way,
In a film wiring board manufactured by such a method, openings such as device holes and through holes are often formed in the polyimide layer. In such a case, first, as shown in FIGS. 4 (A) and 5, a polyimide layer 2 formed on an upper surface of a metal foil 1 made of copper foil or the like, An etching resist layer 4 having an opening 3 is formed by printing, photolithography, or the like. Next, wet etching is performed using an alkali etching solution such as hydrazine to form an opening 5 in the polyimide layer 2 as shown in FIG. Thereafter, when the etching resist layer 4 is peeled off, as shown in FIGS. 4C and 6, a film wiring board in which the openings 5 are formed in the polyimide layer 2 is obtained. However, in such a conventional method for manufacturing a film wiring board, since the polyimide layer 2 is wet-etched using an alkaline etching solution such as hydrazine, the isotropic method is used. Etching results in poor etching processing accuracy, and the inner wall of the opening 5 is not vertical, so that the dimensional accuracy of the opening 5 is poor and the edge strength of the opening 5 is low. An object of the present invention is to provide a method of manufacturing a film wiring board, which can improve the dimensional accuracy of an opening and can increase the strength of the edge of the opening. According to the present invention, a photoresist pattern is formed on an upper surface of a metal foil, and then a polyimide precursor layer or a polyimide layer is formed on the entire upper surface of the metal foil including the photoresist pattern. Forming, and then etching the polyimide precursor layer or polyimide layer until at least the top surface of the photoresist pattern is exposed, and removing the photoresist pattern to form an opening in the polyimide precursor layer or polyimide layer. It is formed. According to the present invention, the outer wall of the photoresist pattern formed on the upper surface of the metal foil becomes substantially vertical, and the photoresist pattern having the vertical outer wall is removed, whereby the polyimide precursor layer or polyimide is removed. Since the opening is formed in the layer, the shape of the opening depends on the shape of the photoresist pattern, so that the dimensional accuracy of the opening can be improved, and the inner wall of the opening becomes almost vertical. , The strength of the edge can be increased. 1 (A) to 1 (D) show respective manufacturing steps of a film wiring board according to an embodiment of the present invention. Therefore, referring to these figures in order,
A method for manufacturing the film wiring board of this embodiment will be described. First, FIG. 1A and FIG.
As shown in FIG. 2, a predetermined thickness of the upper surface of the copper foil 11 having a thickness of about 20 μm (that is, a portion corresponding to an opening formed in a polyimide layer to be described later) is formed by a photo process.
A positive photoresist pattern 12 of about 5 μm is formed. Here, the outer wall of the positive photoresist pattern 12 is formed almost vertically because it is formed by a photo process. Next, as shown in FIG. 1B, a polyamic acid, which is a polyimide precursor, is applied to the entire upper surface of the copper foil 11 including the positive photoresist pattern 12 by a casting method so as to have a thickness of about 30 μm. Curing (1
(Leave at a temperature of about 50 ° C. for about 30 minutes) to form the polyamic acid layer 13. Next, as shown in FIG. 1 (C), the polyamic acid layer 13 is formed at least by a positive photo-lithography using an alkali etching solution such as hydrazine, ethylenediamine, sodium hydroxide or potassium hydroxide while irradiating ultraviolet rays. Wet etching is performed until the upper surface of the resist pattern 12 is exposed. In this case, since the etching rate with the alkaline etching solution is much faster in the positive photoresist pattern than in the polyamic acid, after the upper surface of the positive photoresist pattern 12 is exposed, the positive photoresist pattern 12 It is immediately removed by etching (see FIG. 1D), during which the polyamic acid layer 13 hardly dissolves. In addition, even if the etching in this case is isotropic etching, since etching is performed on the entire surface, there is no problem in etching processing accuracy. Further, the reason for irradiating with ultraviolet light at this time is to expose the positive photoresist pattern 12 in an unexposed state so that the positive photoresist pattern 12 can be easily dissolved in an alkaline etching solution. The reason for using a positive photoresist as the photoresist is that the negative photoresist is hardly soluble in an alkaline etching solution. Next, the polyamic acid layer 13 is cured and polyimided, and as shown in FIG. 1D and FIG.
As shown in (1), a film wiring board in which the openings 15 are formed in the polyimide layer 14 is obtained. In this case, the curing step is performed by first leaving the device at about 200 ° C. for about 30 minutes, then leaving it at about 250 ° C. for about 30 minutes, and then leaving it at about 300 ° C. for about 30 minutes. , And then left at about 350 ° C. for about 30 minutes. In the film wiring board thus obtained, the polyamic acid layer 13 is formed on the entire upper surface of the copper foil 11 including the positive photoresist pattern 12 having a substantially vertical outer wall, and then at least the positive photoresist is formed. The polyamic acid layer 13 is exposed until the upper surface of the pattern 12 is exposed.
And the positive photoresist pattern 12 is removed to remove the polyamic acid layer 13 and the polyimide layer 1 obtained by curing the polyamic acid.
4, the shape of the opening 15 depends on the shape of the positive photoresist pattern 12.
Therefore, the dimensional accuracy of the opening 15 can be improved, and the inner wall of the opening 15 becomes substantially vertical, and the strength of the edge can be increased. In the above embodiment, the polyamic acid layer 1
Although the positive photoresist pattern 12 is etched and removed at the same time as the step 3 is etched, it goes without saying that the positive photoresist pattern 12 may be etched separately. As described above, according to the present invention, since the opening is formed in the polyimide layer by removing the photoresist pattern having the vertical outer wall, the shape of the opening is reduced. Depends on the shape of the photoresist pattern, so that the dimensional accuracy of the opening can be improved, and the inner wall of the opening becomes almost vertical, and the strength of the edge can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A to 1D are cross-sectional views of respective manufacturing steps of a film wiring board in one embodiment of the present invention. FIG. 2 is a plan view of FIG. FIG. 3 is a plan view of FIG. FIGS. 4A to 4C are cross-sectional views of respective manufacturing steps of a conventional film wiring board. FIG. 5 is a plan view of FIG. FIG. 6 is a plan view of FIG. [Description of Signs] 11 Copper foil 12 Photoresist pattern 13 Polyamic acid layer 14 Polyimide layer 15 Opening

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05K 3/00 C08J ⁷ /00-7/18

Claims (1)

(57) [Claim 1] A photoresist pattern is formed on the upper surface of a metal foil, and then a polyimide precursor layer or a polyimide layer is formed on the entire upper surface of the metal foil including the photoresist pattern. Then, while etching the polyimide precursor layer or the polyimide layer at least until the upper surface of the photoresist pattern is exposed, by removing the photoresist pattern, an opening is formed in the polyimide precursor layer or the polyimide layer. A method for manufacturing a film wiring board, comprising: