JPH04186895A - Formation of circuit - Google Patents

Abstract

PURPOSE:To highly accurately form a precise circuit on an insulator by specifying the thickness of the first covering copper layer. CONSTITUTION:The first copper film is formed on a polyimide film by electroless copper plating. The thickness of the first copper film is maintained to be less than 1.0mum.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to printed wiring boards (PWB), flexible printed circuits (FPC), tape automatic bonding (T
A B) This invention relates to a circuit forming method that improves the shape and dimensional accuracy of circuits in the manufacturing process of electronic components obtained by forming circuits on insulators such as tapes.

[Prior Art] Conventionally, the circuit formation method for electronic components such as PWB and FPCSTAB involves forming a etching resist layer on a copper film formed on an insulator, dissolving and removing the exposed portion of the copper film, and then removing the resist. The so-called subtractive method, in which layers are removed, was common. The advantages of this method are that the process is simple and economical, but the biggest disadvantage is that because the circuit is formed by etching, the cross section of the conductive layer is not rectangular but trapezoidal or semicylindrical. This is because side etching occurs.

This is because if the conductive layer is deformed into a trapezoidal or semicylindrical shape, the side in contact with the insulator needs to be longer in order to secure the same amount of electricity as a circuit with a rectangular cross section. In this case, if the distance between the conductive layers is particularly narrow as described above, poor insulation and short circuits between the conductive layers are likely to occur.

A method devised as a means to solve the above problem is to form a first copper coating layer with a thickness of 2 to 5 μm on an insulator by electroless plating or a subsequent electroplating method, and then coat the insulator with copper. After forming a resist layer on a part of the film, the part where the resist layer is not formed, that is, the first
Copper plating is performed on the exposed portion of the copper coating layer to the desired thickness by electroless plating or electroplating.
This is a so-called additive method in which a circuit is formed by forming a copper film layer, then removing the resist layer, and then removing the exposed first copper film layer using the second copper film layer as a mask. Since the conductive layer formed by this additive method has a substantially rectangular cross section, problems such as poor insulation and short circuits do not occur even if the distance between the conductive layers becomes narrow as described above.

[Problem to be solved by the invention] In recent years, with the miniaturization and weight reduction of electronic components, the above-mentioned PWB,
Electronic components such as FPCs and TABs are now required to have even higher CV and Ef, and in terms of circuit shapes, it has become necessary to narrow the width of conductive layers and the spacing between conductive layers. .

However, even with this additive method, although it is possible to obtain a conductive layer with a more rectangular cross section than with the subtractive method, a completely rectangular conductive layer cannot be obtained. Therefore, if the distance between the conductive layers becomes even narrower,
Additive method (The conductive layer obtained by this method also increases the risk of poor insulation or short circuits, and to avoid this risk, it becomes necessary to extremely narrow the width of the conductive layer, which is technically difficult. Not only will it become a problem, but you will not be able to obtain the necessary amount of electricity.

An object of the present invention is to provide a circuit formation method for forming fine circuits on an insulator with high precision.

[Means for Solving the Problems] The method of the present invention for achieving the above object is to apply a first layer of copper plating to the surface of an insulator by electroless plating or, if necessary, by subsequent electrolytic plating. After forming the
After forming a resist layer on a part of the copper plating surface and forming a second layer of copper plating film on the copper plating film on which the resist layer is not formed, by electroless plating method or electrolytic plating method, In the circuit forming method by removing the resist and removing the first copper plating layer using the second copper plating film as a mask, the thickness of the first copper film layer is set to 1.0 μm or less. It has characteristics.

The thickness of the first copper coating layer formed in the present invention is 1.
If it exceeds 0 μm, the conductive layer formed by the second copper film layer will also be clearly eroded when the first copper film is dissolved and removed, and the cross section of the conductive layer will not be rectangular, resulting in a highly reliable circuit. It cannot be formed with high precision.

[Function] The method of the present invention enables the formation of fine circuits with high precision and high reliability by reducing the thickness of the first copper film to 1.0 μm or less in the additive method. This is because removal can be carried out quickly, and at this time, the conductive layer formed by the second copper coating does not dissolve to the extent that it affects the dimensional accuracy of the circuit.

The effects obtained by the method of the invention are not particularly affected by the dissolution and removal treatment of the first copper coating. In other words, the solution for dissolution and removal may be any known solution capable of dissolving copper, and generally, ferric chloride, cupric chloride, ammonium persulfate, ammonia, sulfuric acid, hydrogen peroxide, etc. are used alone. or an aqueous solution containing two or more types is often used. Further, it is necessary to determine the optimum conditions for dissolution and removal in advance through preliminary experiments, etc., so that there is no excess or deficiency in temperature, time, etc. Further, the dissolution and removal method may be performed by immersing the substrate in a solution, or by spraying the solution in a shower onto the substrate.

[Example] A first copper coating having a thickness of 0.5 μm was formed on an NPI-50 type polyimide film manufactured by Kanekabuchi Chemical Industry Co., Ltd. by electroless copper plating. Tokyo Ohka Kogyo PM on the hindlimb copper coating
ER-HC600 type photoresist was applied uniformly to a thickness of 40 μm and baked at 70° C. for 30 minutes. Thereafter, the substrate was masked so that a circuit with a conductive layer width of 40 μm and a conductive layer interval of 40 μm was formed, the photoresist layer was irradiated with ultraviolet rays of 10,100 O/cm', and then the resist layer was developed. After that, copper electroplating is performed on the exposed copper electroless plating film under the conditions shown below.
A copper coating was formed.

(Bath composition) CuSO4'5HiOH80g/IHzSO<180g/] (Electrolysis conditions) Temperature 25°C Cathode current density: 3 A/dm Stirring
: Air agitation and cathode rocker time: 1 hour After that, the resist layer was peeled off and the exposed first copper film was dissolved and removed using the second copper film as a mask under the conditions shown below.

(Bath composition) CLIClz・2HzO' 100 g/]NH
, CI 100 g/INH=C
Om 20 g/] 29% ammonia water ° 400 m
l/1 (melting conditions) Temperature: 25°C No stirring Time: 25 seconds The cross section of the conductive layer obtained on the substrate is 40 x 35μ
m rectangular shape, and no insulation defects or short circuits between conductive layers were observed.

[Comparative Example 1] The thickness of the first copper coating layer formed on the polyimide resin was 1
．． A circuit was formed in the same manner as in Example 1 except that the thickness was 5 μm and the dissolution time of the first copper film was 90 seconds. Although no insulation defects or short circuits were observed between the conductive layers obtained, although the cross section of the conductive layer had a length of 40 μm on the side in contact with the polyimide resin, there was significant erosion on other sides and corners. linearity was lost.

[Comparative Example 2 The thickness of the first copper coating layer formed on the copolyimide resin was 1
．． A circuit was formed in the same manner as in Example 1 except that the thickness was 5 μm and the dissolution time of the first copper film was 60 seconds. Many insulation defects, short circuits, etc. were observed between the resulting conductive layers.

[Effects of the Invention] According to the method of the present invention, it is possible to stably form fine circuits on an insulator with high precision, which was difficult even with conventional additive methods.

Furthermore, the substrate obtained by this method is used for PWB and FPCS.
If it is used as an electronic component such as a TAB, it not only enables higher density wiring but also has great effects such as high reliability.

Patent applicant: Sumitomo Metal Mining Co., Ltd.

Claims (1)

[Claims] After forming a first layer of copper plating on the surface of the insulator by electroless plating or, if necessary, by subsequent electrolytic plating, a resist layer is formed on a part of the copper plating surface to form a resist layer. After forming a second layer of copper plating film on the unused copper plating film by electroless plating or electrolytic plating, the resist is removed and a second layer of copper plating is formed.
A circuit forming method in which a first copper plating layer is removed using a copper plating layer as a mask, characterized in that the first copper plating layer has a thickness of 1.0 μm or less.