JP2000151047A - Double-sided flexible wiring board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make conduction with high productivity and high reliability between wirings on both sides of a double-sided flexible wiring board, ensure high adhesion between an insulation layer (esp., polyimide layer) and conductive layers (esp., Cu layers) on both sides thereof, form wiring patterns by the finable additive method and avoid curling. SOLUTION: A double-sided flexible wiring board has a laminate polyimide layer 3 composed of a first, second and third polyimide layers 3a, 3b, 3c between a lower and upper wiring layers 1, 2, the absolute value of the thermal linear expansion coefficient difference between a polyimide resin of the second polyimide layer 3b and metal materials of the wiring layers 1, 2 is within 5×10-6/K, and the third polyimide layer 3c is made of sulfo group-contg. polyimide. Metal plugs 7 filled in through-holes 6 formed through the laminate layer 3 by etching make conduction between the wiring layers 1, 2, and coverlays 4, 5 are disposed on the outsides of the wiring layers 1, 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a double-sided flexible wiring board and a method for manufacturing the same.

[0002]

2. Description of the Related Art A double-sided flexible wiring board is formed by forming a through-hole with an NC drill on a double-sided copper-clad flexible substrate having a structure in which a copper layer (conductive layer) is provided on both sides of a polyimide layer (insulating layer). Attach an electroless plated copper thin film to the inner wall of
Further, a through hole is formed by forming an electrolytic copper plating film, and then a circuit is formed on the copper layers on both surfaces of the substrate by a subtractive method while protecting the inner wall of the through hole and ensuring conduction.

Here, a typical method for producing a double-sided copper-clad flexible substrate is as follows: (1) a method in which a copper foil with an adhesive is adhered to both sides of a polyimide film as an insulating material by a laminating method; Apply a thermoplastic polyimide resin solution on top
A method of preparing two dried films, laminating thermoplastic polyimide resins on each other and laminating them under a high temperature and a high pressure; (3) a commercially available polyimide film having a single-layer structure composed of an acid dianhydride and a diamine (for example, Vapor deposition on both surfaces of Kapton (DuPont) and Apical (Kanebuchi Chemical) consisting of pyromellitic dianhydride and diaminodiphenyl ether; Iupirex S (Ube Industries) consisting of diphenyltetracarboxylic dianhydride and paraphenylenediamine A method in which a metal thin film is formed by a method and a metal plating layer is formed thereon by an electrolytic plating method; the above three methods are known.

[0004]

However, when an NC drill is used to make a through-hole in a double-sided copper-clad flexible board when manufacturing a double-sided flexible wiring board, a considerably large equipment investment is required in terms of equipment. Further, there is a problem that productivity is low because the through holes are formed one by one. Moreover, there is a problem that burrs are easily generated on the surface of the opening end of the through hole, and the shape of the opening is not constant. Further, there is also a problem that the cutting powder adheres to the inner wall of the through-hole, and the conduction reliability of the through-hole is reduced. In addition, as a method applicable when forming a copper layer of a double-sided flexible substrate into a circuit pattern, an additive method in which a fine pattern can be easily formed cannot be adopted, and the method is limited to an inferior subtraction method. There is also a problem. Also, from the difference in the coefficient of linear thermal expansion between the copper layer and the polyimide layer,
If the double-sided copper layers of the double-sided flexible substrate are patterned into different patterns, there is a problem that the double-sided flexible wiring board may be curled in some cases, which hinders the mounting operation.

In producing a double-sided copper-clad flexible substrate, each of the methods (1) to (3) has the following problems.

(1) The heat resistance of the adhesive is not sufficient, and at present, a thick copper foil is used, and the copper foil is plated at the same time at the time of through-hole plating. Therefore, it is impossible to manufacture a device corresponding to a fine pattern or wire bonding.

(2) If a thermoplastic polyimide resin having good heat resistance is used to produce a flexible substrate having good heat resistance, a laminator capable of setting a high laminating temperature and pressure is required. The capital investment increases and profitability decreases, and productivity also decreases.

(3) The adhesion between the metal thin film and the polyimide film is insufficient, and the level of conduction reliability required for a wiring board cannot be ensured.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide high productivity and high reliability between wirings on both sides of a double-sided flexible wiring board, and to provide an insulating layer (particularly, Ensure high adhesion between the polyimide layer) and the conductive layers (especially the copper layer) on both sides of the polyimide layer, and allow the wiring pattern to be formed by an additive method that can be made finer, and to prevent curling. With the goal.

[0010]

The above objects of the present invention are attained by the following double-sided flexible wiring board of the present invention and a method of manufacturing the same.

That is, the present invention provides a laminated polyimide layer having a three-layer structure of a first polyimide layer, a second polyimide layer, and a third polyimide layer between a lower wiring layer and an upper wiring layer. The absolute value of the difference in coefficient of linear thermal expansion between the polyimide resin forming the polyimide layer and the metal material forming the lower wiring layer and the upper wiring layer is within 5 × 10 ⁻⁶ / K, and the third polyimide on the upper wiring layer side A laminated polyimide layer whose layer is composed of a sulfone group-containing polyimide is sandwiched, and the lower wiring layer and the upper wiring layer are filled by electroplating in through holes formed by a photolithographic method of the laminated polyimide layer. The present invention provides a double-sided flexible wiring board that is electrically connected by a metal plug and has a coverlay disposed outside the lower wiring layer and the upper wiring layer.

Further, the present invention provides the above-mentioned method for producing a double-sided flexible wiring board, which comprises the following steps (a) to (d).
(I): (a) A laminated polyimide precursor having a three-layer structure of a first polyimide precursor film, a second polyimide precursor film, and a third polyimide precursor film containing a sulfone group on the surface of the lower wiring metal layer. (B) forming a through hole in the laminated polyimide precursor film by photolithography; (c) imidizing the laminated polyimide precursor film to form a first polyimide layer, a second polyimide layer, and a second polyimide layer. A step of forming a three-layer laminated polyimide layer having a three-layer structure; (d) a step of disposing a protective film on the lower surface of the lower wiring metal layer; (F) a step of embedding a conductive material by a plating method to form a metal plug; (f) a step of forming an upper wiring layer on the upper surface of the third polyimide layer of the laminated polyimide layer by an additive method; (g) (H) removing the protective film disposed on the lower surface of the lower wiring metal layer, and then patterning the lower wiring metal layer into a lower wiring layer by a subtractive method. And (i) arranging a coverlay on the lower wiring layer.

Here, the step (f) is replaced with the following step (f)
1) to (f4): (f1) a step of forming a metal thin film on the upper surface of the third polyimide layer of the laminated polyimide layer by a dry process; (f2) forming a plating resist film having a pattern corresponding to the upper wiring on the metal thin film (F3) forming an electrolytic plating metal film on the metal thin film by electrolytic plating; and (f4) forming an upper wiring layer by removing the plating resist film and performing soft etching. Is preferred.

Step (h) is replaced with the following step (h1)
To (h3): (h1) a step of removing the protective film provided on the lower surface of the lower wiring metal layer and forming a plating resist film having a pattern corresponding to the lower wiring on the lower surface of the lower wiring metal layer; h2) The lower wiring metal layer is the first of the laminated polyimide layers.
And (h3) forming a lower wiring layer by removing a plating resist film provided on the lower surface of the lower wiring metal layer.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The double-sided flexible wiring board of the present invention is shown in FIG.
As shown in the figure, between the lower wiring layer 1 and the upper wiring layer 2,
The first polyimide layer 3a, the second polyimide layer 3b, and the third
A laminated polyimide layer 3 having a three-layer structure of the polyimide layer 3c is sandwiched, and coverlays 4 and 5 are arranged outside the lower wiring layer 1 and the upper wiring layer 2, respectively.

In the present invention, the second polyimide layer 3b
^Is adjusted to be within 5 × 10 ⁻⁶ / K of the difference in the linear thermal expansion coefficient between the polyimide resin constituting the above and the metal material constituting the lower wiring layer 1 and the upper wiring layer 2. This makes it possible to suppress the occurrence of curling of the double-sided flexible wiring board irrespective of the contents of the normal thermal history (normal temperature storage, solder dip processing, etc.).

The thermal expansion coefficient of the second polyimide layer 3b is shown in Table 1 as the thermal expansion coefficient of the metal material of the lower wiring layer 1 and the metal material of the upper wiring layer 2 generally used for a double-sided flexible wiring board. In view of the numerical value, it is preferably (10-25) × 10 ⁻⁶ / K, more preferably (17)
-23) × 10 ⁻⁶ / K.

[0019]

[Table 1]

In the double-sided flexible wiring board of the present invention, the third polyimide layer 3c provided on the upper wiring layer 2 side of the second polyimide layer 3b is made of a sulfone group-containing polyimide. Due to the presence of the sulfone group, the adhesion between the sulfone group and the metal thin film formed thereon by a dry process can be improved. In addition, stable adhesion can be ensured even by a normal heat history.

The first polyimide layer 3a may be made of a polyimide containing no sulfone group, but is preferably made of a polyimide containing a sulfone group, like the third polyimide layer 3c.

Here, as the sulfone group-containing polyimide, those obtained by imidizing a sulfone group-containing polyamic acid derived from an acid dianhydride and a diamine can be preferably used, and the sulfone group is an acid dianhydride. And at least one of diamines. In particular, a sulfone group-containing polyimide obtained when a sulfone group is present in both the acid dianhydride and the diamine can be preferably used.

Examples of the acid dianhydride include pyromellitic dianhydride (PMDA), 3,4,3 ', 4'-biphenyltetracarboxylic dianhydride (BPDA), 3,4
Preferred examples include 3 ', 4'-benzophenonetetracarboxylic dianhydride (BTDA) and 3,3', 4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA).

Examples of the diamine include 4,4'-diaminodiphenyl ether (DPE), paraphenylenediamine (PDA), 4,4'-diaminobenzanilide (DABA), and 4,4'-bis (p-aminophenoxy). ) Diphenyl sulfone (BAPS) is preferred.

The coefficient of linear thermal expansion of the first polyimide layer 3a and the third polyimide layer 3c may be such that the absolute value of the difference between them is within 5 × 10 ^-6 / K in view of the effect of suppressing curling. preferable. Of course, they may be the same,
It may be substantially the same as the second polyimide layer 3b.

Regarding the layer thickness of the first polyimide layer 3a, the second polyimide layer 3b and the third polyimide layer 3c, the thickness of the second polyimide layer 3b is determined by the first polyimide layer 3a and the third polyimide layer 3b.
It is preferably thicker than the polyimide layer 3c. Specifically, if the thickness of the second polyimide layer 3b is too small, it becomes difficult to keep the coefficient of linear thermal expansion in the range of (10 to 25) × 10 ⁻⁶ / K, and if too thick, the laminated polyimide layer itself becomes hard. As a result, it becomes impossible to wind a roll of a predetermined size, so it is preferably 5 to 100 μm, more preferably 10 to 100 μm.
It is 50 μm. On the other hand, if the thickness of the first polyimide layer 3a and the third polyimide layer 3c is too small, it is difficult to form a film. The difference between the coefficient of thermal expansion and the coefficient of linear thermal expansion of the metal material of the lower wiring layer 1 and the upper wiring layer 2 may be large.
To 10 μm, more preferably 2 to 5 μm.

In the double-sided flexible wiring board of the present invention, the lower wiring layer 1 and the upper wiring layer 2 are electrically connected by the metal plugs 7 filled in the through holes 6 formed by the photolithographic method by the electrolytic plating method. . The through hole 6 is N
The double-sided flexible wiring board is formed by using a photolithographic method capable of performing fine patterning with uniformity and good accuracy on the laminated polyimide precursor film before imidization of the laminated polyimide layer 3 instead of the C drill. Between the wirings on both sides with high productivity, high reliability and a fine pattern.

The metal plug 7 can be made of various metals that can be filled in the through-hole 6 by electrolytic plating, and preferably a copper plug from a copper sulfate bath can be used.

As the lower wiring layer 1, a material obtained by patterning a lower wiring metal layer such as a copper foil by a subtractive method can be preferably used.

As will be described later, the upper wiring layer 2
A metal thin film 2a formed by a dry process and an electrolytic plating metal film 2b formed thereon are patterned by an additive method. Therefore, the upper wiring layer 2 can be a fine pattern wiring layer.

Here, the metal thin film 2a is formed by a dry process. As the dry process, a general physical vapor deposition method (for example, a vacuum vapor deposition process, an ion plating process, a sputtering process, etc.) can be used. .

As the metal thin film 2a, Ni, Co, C
A thin film of r, Zr, Pd, Cu or an alloy thereof is preferable. In particular, in consideration of gold plating resistance, tin plating resistance, and the like, Ni-Cu formed by a sputtering process is used.
Thin film (50-500mm thick) / Copper thin film (100-2000
(Thickness) is preferable.

As the electrolytic plating metal film 2b, 5 to 50
A μm thick electrolytic copper plating film is preferred. The conditions for forming the electrolytic copper plating film can be appropriately selected. For example, the electrolytic copper plating film can be formed by plating with a copper sulfate bath having a current density of 0.2 to 10 A / dm ² .

Prior to the formation of the metal thin film 2a, the surface of the third polyimide layer 3c is subjected to a glow discharge treatment or a plasma discharge treatment (a gas such as nitrogen oxide gas, oxygen, argon or a mixed gas atmosphere), an ultraviolet irradiation treatment. It is preferable to perform a surface modification treatment such as the above from the viewpoint of improving the adhesion.

The cover lays 4 and 5 can be formed in the same manner as the cover lay used in the conventional double-sided flexible wiring board. For example, a dry lamination of a polyimide film with an adhesive or a thermoplastic polyimide resin It can be formed by applying and drying a coating liquid or applying and drying a polyamic acid varnish to imidize.

The double-sided flexible wiring board of the present invention can be manufactured according to the following steps (a) to (i).
Each step will be described with reference to the drawings.

Step (a) A laminated polyimide precursor comprising a first polyimide precursor film 22a, a second polyimide precursor film 22b and a third polyimide precursor film 22c containing a sulfone group is formed on the surface of the lower wiring metal layer 21. A body film 22 is formed (FIG. 2A).

Specifically, a polyamic acid varnish for forming a first polyimide film is applied on the upper surface of the lower wiring metal layer 21 by using a comma coater, a knife coater, a roll coater, a gravure coater, a lip coater, a die coater, or the like. And dried in a continuous drying oven (such as an arc furnace or a floating oven) so that the content of residual volatiles (solvent, water generated by condensation, etc.) falls within the range of 20 to 30% by weight and foaming does not occur. To produce a polyimide precursor film 22a. Here, if the residual volatile matter content is less than 20% by weight, the adhesion between the first polyimide layer and the second polyimide layer may be insufficient. The adhesion strength and shrinkage ratio with the second polyimide layer are not stabilized.

In the present specification, the content of residual volatiles means the weight percentage (% by weight) of all volatile components in the polyimide precursor film.

Next, a polyamic acid varnish for forming a second polyimide film is similarly coated on the first polyimide precursor film 22a so that the residual volatile matter content falls within the range of 30 to 50% by weight. After drying, a second polyimide precursor film 22b is prepared. Here, if the residual volatile matter content is less than 30% by weight, the adhesion between the first polyimide layer and the second polyimide layer may be insufficient, and 50% by weight.
It is not preferable if the ratio exceeds the value, since foaming occurs during imidization.

Next, a third polyimide film-forming polyamic acid varnish is similarly applied onto the second polyimide precursor film 22b so that the residual volatile matter content falls within the range of 30 to 50% by weight. After drying, a third polyimide precursor film 22c is produced. Thus, a laminated polyimide precursor film 22 having a three-layer structure is obtained.

Step (b) Next, through holes 23 are formed in the laminated polyimide precursor film 22 by a photolithographic method (FIG. 2B).

Specifically, the laminated polyimide precursor film 22
An alkali-resistant photoresist (e.g., NR-41, manufactured by Sony Chemical Co., Ltd.) that can be developed with a neutral or weakly acidic aqueous solution is applied thereto by a conventional method, exposed through a through-hole pattern mask, developed, and developed. To form

Next, 10% through an etching resist
The laminated polyimide precursor film 22 is etched with a potassium hydroxide aqueous solution to form a through hole 23. The etching resist can be stripped and removed with a weak to moderately acidic aqueous solution.

Step (c) Next, the laminated polyimide precursor film 22 is imidized,
Polyimide layer 24a, second polyimide layer 24b and third
Laminated polyimide layer 24 having a three-layer structure of polyimide layer 24c
Is formed (FIG. 2C).

In the imidation, the residual volatile matter content is preferably 7 to 10%, and the imidization ratio (infrared absorption spectrum analysis (surface reflection method (ATR method)) indicates the absorption amount of the imido group at an absorption wavelength of 1780 cm ^-1. The value calculated from the percentage of the amount of light absorbed when the sample was imidized at 100%) was 50
% Or less, preferably from 210 to 250 ° C, preferably 23 ° C.
It can be carried out by heat treatment in a continuous furnace at a temperature of 0 to 240 ° C. Here, if the residual volatile content is less than 7%, curling cannot be sufficiently suppressed, and if it exceeds 10%, blocking tends to occur, which is not preferable. If the imidation ratio exceeds 50%, curling cannot be sufficiently suppressed.

When the heating temperature is lower than 210 ° C.,
If the residual volatile matter content is less than 7%, and if it exceeds 250 ° C., the imidization ratio becomes undesirably 50% or more.

Step (d) A protective film 25 is provided on the lower surface of the lower wiring metal layer 21 (FIG. 2D). Specifically, a protective film with an acid resistant adhesive (for example, PET8184 (manufactured by Sony Chemical Co., Ltd.)) may be directly adhered to the lower wiring metal layer 21.

Step (e) A conductive material is embedded in the through-holes 23 formed in the laminated polyimide layer 24 by electrolytic plating to form metal plugs 26 (FIG. 2E). For example, a copper plug is formed by electrolytic plating from a copper sulfate bath.

Here, it is preferable that the height of the metal plug 26 be 0 to +5 μm of the thickness of the laminated polyimide layer 24. If it exceeds +5 μm, conduction reliability tends to decrease.

Step (f) Next, an upper wiring layer 27 is formed by an additive method on the surface of the third polyimide layer 24c of the laminated polyimide layer 24 on the side where the metal plug 26 is exposed (FIG. 2).
(F)).

Specifically, the following steps (f1) to (f1)
It is preferable to form the upper wiring layer 27 according to 4).

Step (f1) A metal thin film 27a is formed on the upper surface of the third polyimide layer 24c of the laminated polyimide layer 24 by a dry process (FIG. 3 (f1)).

Here, as a dry process, a general physical vapor deposition method can be used, and among them, a sputtering process is preferable.

As a material of the metal thin film 27a, particularly, in consideration of gold plating resistance and tin plating resistance, a Ni—Cu thin film (50 to 50) formed by a sputtering process is used.
A two-layer structure thin film of (0 ° thick) / copper thin film (100 to 2000 ° thick) is preferable.

Prior to the formation of the metal thin film 27a,
The surface of the third polyimide layer 24c may be subjected to a surface modification treatment such as a glow discharge treatment and a plasma discharge treatment.
It is preferable from the viewpoint of improving the adhesion.

Step (f2) A plating resist film 28 having a pattern corresponding to the upper layer wiring is formed on the metal thin film 27a (FIG. 3 (f2)).

Step (f3) An electrolytic plating metal film 27b is formed on the metal thin film 27a by an electrolytic plating method (FIG. 3 (f3)). As the electrolytic plating metal film 27b, an electrolytic copper plating film having a thickness of 5 to 50 μm is preferable. The conditions for forming the electrolytic copper plating film can be appropriately selected. For example, the electrolytic copper plating film can be formed by plating with a copper sulfate bath having a current density of 0.2 to 10 A / dm ² .

Step (f4) The plating resist film 28 is removed, soft etching is performed with a weak acid or the like, and the exposed metal thin film 27a is removed to form the upper wiring layer 27 (FIG. 3 (f4), FIG. 2 ( f)).

Step (g) A coverlay 29 is provided on the upper wiring layer 27 by a conventional method (FIG. 2G).

Step (h) After removing the protective film 25 disposed on the lower surface of the lower wiring metal layer 21, the lower wiring metal layer 21 is patterned into the lower wiring layer 30 by the subtractive method (FIG. 2).
(H)).

Specifically, the following steps (h1) to (h)
According to 3), the lower wiring layer 30 can be formed.

Step (h1) The protective film 25 disposed on the lower surface of the lower wiring metal layer 21 is removed, and a plating resist film 31 having a pattern corresponding to the lower wiring is formed on the lower surface of the lower wiring metal layer 21. (FIG. 4
(H1)).

Step (h2) The lower wiring metal layer 21 is etched until the first polyimide layer 24a of the laminated polyimide layer 24 is exposed (FIG. 4).
(H2)).

Step (h3) The lower wiring layer 30 is formed by removing the plating resist film 31 provided on the lower surface of the lower wiring metal layer 21 (FIG. 4 (h3), FIG. 2 (h)).

Step (i) A coverlay 32 is provided on the lower wiring layer 30 (FIG. 2).
(I)). Thereby, a double-sided flexible wiring board of the present invention as shown in FIG. 1 is obtained.

In the double-sided flexible wiring board of the present invention obtained as described above, the wiring between both sides is conducted with high productivity and high reliability, and the wiring between the laminated polyimide layer and the wiring layers on both sides thereof is formed. Adhesion between them is good, and the upper wiring layer can be formed by an additive method capable of making a wiring pattern finer, and curling does not occur.

[0068]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below.

Reference Example A1 (Preparation of polyamic acid varnish having sulfone group) 0.433 kg of paraphenylenediamine (PDA, manufactured by Mitsui Chemicals, Inc.) was placed in a 60-liter jacketed reactor.
(4.00 mol) and 0.801 kg of 4,4'-diaminodiphenyl ether (DPE, manufactured by Wakayama Seika)
(4.00 mol) and about 35.3 of a solvent N-methyl-pyrrolidone (NMP, manufactured by Mitsubishi Chemical Corporation) in a nitrogen gas atmosphere.
Dissolved in kg. Then, at 25 ° C., 3,3 ′,
2.690 kg of 4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA, manufactured by Nippon Rika Co., Ltd.)
(08 mol) was gradually added to the reaction. Thereby, the solid content is about 10% and the viscosity is 20 Pa · S (25
C) of a polyamic acid varnish.

The resulting polyamic acid varnish was applied on a copper foil, and the solvent was scattered in a continuous furnace at 80 to 160 ° C., and then the atmosphere temperature was raised to 230 to 350 ° C.
The mixture was treated at 30 ° C. for 30 minutes for imidization. Then, the copper foil was removed by etching with a ferric chloride solution to obtain a single-layer polyimide film having a thickness of 25 μm. Thermal expansion coefficient of the obtained polyimide film (use measuring device: thermal mechanical analyzer (TMA / SCC150CU, SI
Company I (tension method: working load 2.5g-5g))) is 36
× 10 ⁻⁶ / K.

Reference Example A2 (Preparation of polyamic acid varnish having no sulfone group)
0.400 kg of 4,4'-diaminodiphenyl ether (DPE, manufactured by Wakayama Seika) similarly to Reference Example A1
(2.0 mol) and 1.81 kg (8.0 mol) of 4,4'-diaminobenzanilide (DABA, manufactured by Wakayama Seika) in a solvent N-methyl-pyrrolidone (NMP) under a nitrogen gas atmosphere. , Mitsubishi Chemical Corporation).
Thereafter, at 50 ° C., the reaction was carried out for 3 hours while gradually adding 2.97 kg (10.1 mol) of 3,4,3 ′, 4′-biphenyltetracarboxylic dianhydride (BPDA, manufactured by Mitsubishi Chemical Corporation). . Thus, a polyamic acid varnish having a solid content of about 10% and a viscosity of 20 Pa · S (25 ° C.) was prepared.

The obtained polyamic acid varnish was prepared in Reference Example A.
By performing the same treatment as in Example 1, a single-layer polyimide film was obtained (coefficient of linear thermal expansion: 18 × 10 ⁻⁶ / K).

Reference Example A3 (Preparation of polyamic acid varnish having no sulfone group)
As in Reference Example A1, 2.00 kg of 4,4'-diaminodiphenyl ether (DPE, manufactured by Wakayama Seika)
0.0 mol) with a solvent N-methyl-
It was dissolved in about 46 kg of pyrrolidone (NMP, manufactured by Mitsubishi Chemical Corporation). Then, at 50 ° C., 3,4,3 ′, 4′-
The reaction was carried out for 3 hours while gradually adding 2.96 kg (10.1 mol) of biphenyltetracarboxylic dianhydride (BPDA, manufactured by Mitsubishi Chemical Corporation). As a result, a solid content of about 10
% And a viscosity of 15 Pa · S (25 ° C.) to prepare a polyamic acid varnish.

The obtained polyamic acid varnish was prepared in Reference Example A.
By performing the same treatment as in Example 1, a single-layer polyimide film was obtained (linear thermal expansion coefficient: 35 × 10 ⁻⁶ / K).

Example 1 (Formation of Laminated Polyimide Precursor Film) 18 μm thick, 540
mm width electrolytic copper foil (CF-T9-LP, Fukuda Metal)
On top, the polyamic acid varnish of Reference Example A3 was dried to a thickness of 2 μm.
m, and dried to form a first polyimide precursor film (residual volatile content: 25%).

The polyamic acid varnish of Reference Example A2 was applied thereon so as to have a thickness of 22 μm after imidization, and dried to form a second polyimide precursor film. First
The residual volatile matter content of the laminated polyimide precursor film obtained by combining the polyimide precursor film and the second polyimide precursor film is 30%
Met.

Further, the polyamic acid varnish of Reference Example A1 was applied thereon so as to have a thickness of 3 μm after imidization, and dried to form a third polyimide precursor film.
The residual volatile matter content of the laminated polyimide precursor film obtained by combining the first polyimide precursor film, the second polyimide precursor film, and the third polyimide precursor film was 38%.

(Formation of Sulfur and Imidization) A good alkali-resistant photoresist (NR-41, manufactured by Sony Chemical Co., Ltd.) is applied on the laminated polyimide precursor film so that the thickness after drying with a solvent is 20 μm. did.

The photoresist is exposed and developed into a pattern corresponding to a through-hole pattern to form an etching resist layer, and the laminated polyimide precursor film is etched with a 10% aqueous potassium hydroxide solution and warm water until the copper foil is exposed. To form a through hole (0.3 mm diameter). Thereafter, the etching resist layer was removed by a conventional method.

The laminated polyimide precursor film on which the through holes were formed was heat-treated in a continuous furnace at 230 ° C. The residual volatile matter content at this time was 7.9%, and the imidation ratio by infrared spectrum analysis was 20%. Subsequently, for further imidization treatment, the heat-treated laminated body 1 was placed in a stainless steel tube having a diameter of 250 mm such that the copper foil was on the inside.
00m, and put into a batch oven in a nitrogen atmosphere (oxygen concentration 0.1% or less).
The temperature was raised to 350 ° C. and maintained at 350 ° C. for 15 minutes. afterwards,
The temperature was lowered to 200 ° C. in a nitrogen atmosphere and cooled in air. Thus, a 22 μm-thick single-sided copper-clad polyimide substrate having a through hole was obtained.

(Filling the copper plug in the through hole) The copper foil side of the single-sided copper-clad polyimide substrate was protected with a protect tape,
Copper was electrolytically deposited (current density: 0.8 A / dm ² ) from a copper sulfate plating bath (5%) in a through hole using a copper foil as a cathode to form a copper plug.

(Formation of Metal Thin Film on Surface of Third Polyimide Layer by Dry Process) Using a plasma dry cleaner (PX-1000, manufactured by March), argon plasma using a high-frequency power source having a degree of vacuum of 80 mmTorr and an output of 120 W was used. Irradiation was performed on the surface of the third polyimide layer.

Next, a DC magnetron sputtering method was used to reduce the thickness of the Ni target to a thickness of 15% from the Ni 50% / Cu 50% alloy target.
A 0 ° Ni—Cu alloy thin film was formed.

Further, a copper thin film having a thickness of 1000 ° was formed from a copper target.

(Formation of Upper Wiring Layer by Additive Method) A photoresist film (SPG1
52, manufactured by Asahi Kasei Corporation), an upper layer wiring resist pattern was formed by photolithography, and copper having a thickness of 12 μm was deposited by electrolytic plating. A copper pattern having a width of 0.5 mm was prepared to measure the adhesive strength.

After removing the resist pattern, the exposed metal thin film was soft-etched and removed with a 3% hydrogen peroxide / sulfuric acid aqueous solution to form an upper wiring layer. Then, a coverlay was formed on the upper wiring layer according to a conventional method.

(Formation of Lower Wiring Layer by Substrate Method) A photoresist film (S
PG152, manufactured by Asahi Kasei Corporation), an etching resist pattern corresponding to the lower wiring pattern was formed by photolithography, copper was patterned with an acidic etching solution, and the etching resist pattern was removed to form a lower wiring layer. . Finally, a coverlay was formed on the lower wiring layer according to a conventional method. As a result, a double-sided flexible wiring board without curl was obtained.

(Evaluation) Regarding the double-sided flexible wiring board of Example 1, the adhesive strength between the lower wiring layer and the first polyimide layer and the adhesive strength between the upper wiring layer and the third polyimide layer were determined according to JISC6471. The same method (1.59mm
90 degree peel at width). A hot oil test (260 ° C 1
(A heat cycle of 0 sec. To 20 ° C. for 10 sec.), And the number of cycles at which the through hole conduction abnormality occurs was examined. Table 2 shows the obtained results.

As Comparative Example 1, a double-sided flexible substrate (SC18-50) in which a polyimide resin solution containing no sulfone group was coated on a copper foil, and the polyimide resins were laminated on each other and laminated under high temperature and high pressure. -18
WE, manufactured by Nippon Steel Chemical Co., Ltd.) and drilled with an NC drill according to a conventional method, and through-hole plated to produce a double-sided flexible wiring board. This wiring board was tested and evaluated in the same manner as in Example 1. Table 2 shows the obtained results.

[0090]

[Table 2] Evaluation items Example 1 Comparative example 1 Adhesive strength (kg / cm ² ) Between lower wiring layer and first polyimide layer 2.25 1.55 Between upper wiring layer and third polyimide layer 1.85 1.40 Throughhole reliability (number of cycles) 100 <20

From Table 2, it can be seen that the double-sided flexible wiring board of the present invention has excellent adhesive strength between the laminated polyimide layer and the lower and upper wiring layers. Also, it is understood that the conduction reliability of the through hole is excellent.

[0092]

According to the present invention, the wiring between both sides of the double-sided flexible wiring board is conducted with high productivity and high reliability, and the insulating layer (particularly, the polyimide layer) and the conductive layer (particularly, copper) on both sides thereof are provided. Layer) can be formed, and the wiring pattern can be formed by an additive method capable of making finer, and curling can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a double-sided flexible wiring board of the present invention.

FIG. 2 is an explanatory view of a manufacturing process of the double-sided flexible wiring board of the present invention.

FIG. 3 is an explanatory diagram of a partial manufacturing process of the double-sided flexible wiring board of the present invention.

FIG. 4 is a diagram illustrating a partial manufacturing process of the double-sided flexible wiring board of the present invention.

[Explanation of symbols]

1 lower wiring layer, 2 upper wiring layer, 2a metal thin film, 2
b Electroplating metal film, 3 laminated polyimide layer, 3a
1st polyimide layer, 3b 2nd polyimide layer, 3c 3rd polyimide layer, 4,5 coverlay, 6 through hole, 7
Metal plug

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B32B 27/34 B32B 27/34 H05K 1/11 H05K 1/11 N 3/16 3/16 3/28 3 / 28 F 3/38 3/38 A 3/42 620 3/42 620Z (72) Inventor Shuji Hagi 12-3 Satsukicho, Kanuma-shi, Tochigi Sony Chemical Corporation F-term (reference) 4F100 AB01A AB01E AB16E AB17E AB31E AH04D AK49B AK49C AK49D AK49K BA05 BA26 BA27 EH66E EH71E GB43 JA02B JA02C JA02D JK06 JL04 YY00C 5E314 AA36 BB02 BB12 CC01 CC15 FF06 FF17 GG03 GG12 GG17 CDG12 GG23 GG23 GG12 GG23 GG12 BB55 DD22 DD43 DD76 EE36 ER16 ER18 GG01 GG08 GG13

Claims (13)

[Claims] 1. A laminated polyimide layer having a three-layer structure of a first polyimide layer, a second polyimide layer and a third polyimide layer between a lower wiring layer and an upper wiring layer, wherein the second polyimide layer is formed. The absolute value of the difference in the coefficient of linear thermal expansion between the polyimide resin to be formed and the metal material constituting the lower wiring layer and the upper wiring layer is within 5 × 10 ⁻⁶ / K, and the third polyimide layer on the upper wiring layer side is a sulfone group. The laminated polyimide layer composed of the contained polyimide is sandwiched, and the lower wiring layer and the upper wiring layer are metal plugs filled by electrolytic plating in through holes formed by the photolithographic method of the laminated polyimide layer. A double-sided flexible wiring board that is conductive and has a coverlay disposed outside the lower wiring layer and the upper wiring layer. 2. The double-sided flexible wiring board according to claim 1, wherein the absolute value of the difference between the coefficients of linear thermal expansion of the first polyimide layer and the third polyimide layer is within 5 × 10 ⁻⁶ / K. 3. The double-sided flexible according to claim 1, wherein the sulfone group-containing polyimide is derived from an acid dianhydride and a diamine, and wherein at least one of the acid dianhydride and the diamine has a sulfone group. Wiring board. 4. The double-sided flexible wiring board according to claim 3, wherein a sulfone group is present in both the acid dianhydride and the diamine. 5. The double-sided wiring according to claim 1, wherein the upper wiring layer comprises a metal thin film formed by a dry process and an electrolytic plating metal film formed thereon, and is patterned by an additive method. Flexible wiring board. 6. The double-sided flexible wiring board according to claim 5, wherein the metal thin film has a two-layer structure of a Ni—Cu thin film / copper thin film formed by a sputtering process. 7. The double-sided flexible wiring board according to claim 5, wherein the electrolytic plating metal film is an electrolytic copper plating film. 8. The double-sided flexible wiring board according to claim 1, wherein the lower wiring layer is formed by patterning a lower wiring metal layer by a subtractive method. 9. The method for manufacturing a double-sided flexible wiring board according to claim 1, wherein the following steps (a) to (i) are performed: (a) forming a first polyimide precursor film on the surface of the lower wiring metal layer; (2) a step of forming a three-layer laminated polyimide precursor film of a polyimide precursor film and a third polyimide precursor film containing a sulfone group; (b) forming through holes in the laminated polyimide precursor film by a photolithographic method (C) imidizing the laminated polyimide precursor film to form a laminated polyimide layer having a three-layer structure of a first polyimide layer, a second polyimide layer, and a third polyimide layer; (d) a metal layer for lower wiring (E) embedding a conductive material in a through-hole formed in the laminated polyimide layer by electrolytic plating to form a metal plug; (f) laminating poly. A step of forming an upper wiring layer on the upper surface of the third polyimide layer of the imide layer by an additive method; (g) a step of disposing a coverlay on the upper wiring layer; and (h) a step of disposing the coverlay on the lower surface of the lower wiring metal layer. A process of patterning the lower wiring metal layer into a lower wiring layer by a subtractive method after removing the protective film; and (i) disposing a coverlay on the lower wiring layer. 10. The process (f) includes the following processes (f1) to (f1).
(F4): (f1) a step of forming a metal thin film on the upper surface of the third polyimide layer of the laminated polyimide layer by a dry process; (f2) a step of forming a plating resist film having a pattern corresponding to the upper wiring on the metal thin film; (F3) forming an electrolytic plating metal film on the metal thin film by electrolytic plating; and (f4) forming an upper wiring layer by removing the plating resist film and performing soft etching. The manufacturing method as described. 11. The method according to claim 10, wherein a metal thin film having a two-layer structure of a Ni—Cu thin film / copper thin film is formed by a sputtering process as the metal thin film. 12. The method according to claim 10, wherein a copper plating film is formed as the electrolytic plating metal film by an electrolytic plating method. 13. The step (h) comprises the following steps (h1) to
(H3): (h1) removing the protective film disposed on the lower surface of the lower wiring metal layer and forming a plating resist film having a pattern corresponding to the lower wiring on the lower surface of the lower wiring metal layer; (h2) ) The lower metal layer for wiring is the first of the laminated polyimide layers.
10. The method according to claim 9, further comprising: etching until the polyimide layer is exposed; and (h3) forming a lower wiring layer by removing a plating resist film provided on a lower surface of the lower wiring metal layer.