JP2006272626A - Method for manufacturing flexible laminated substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a flexible laminated substrate which can inhibit a qualitative dispersion and has excellent dimensional stability. <P>SOLUTION: This method manufactures the flexible laminated substrate comprising a conductor layer and a polyimide resin layer by applying a polyimide precursor resin solution directly to the surface of a conductor, then drying the solution, and after that, curing the dried solution thermally. The polyimide precursor resin can be obtained by adjusting the (A)/(B) molar ratio of (A) a tetracarboxylic acid or its acid anhydride to (B) a diamino compound to the range of 0.98±0.01 and setting the coefficient of linear expansion of the polyimide resin layer to not more than 10×10<SP>-6</SP>/K. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a flexible laminated substrate, and more particularly to a method for producing a flexible laminated substrate by directly applying a polyimide precursor resin solution onto a conductor.

The flexible laminated substrate is used for a flexible circuit substrate having flexibility, and among them, a flexible laminated substrate having a polyimide resin layer as an insulating resin layer is widely used because it has excellent heat resistance.
As a means for providing a polyimide resin layer on an insulating resin layer, a method is known in which a polyimide resin layer is laminated on a conductor such as copper foil by thermocompression bonding via an adhesive layer.
However, the presence of the adhesive layer has been a factor that deteriorates various characteristics of the flexible laminated substrate using the polyimide resin. For example, a conventional flexible laminated board has a polyimide film bonded onto a conductor using an adhesive such as an epoxy resin or a urethane resin, but the heat resistance of the adhesive is inferior, and when heated to high temperature with solder There has been a problem that peeling occurs or the flame retardancy of the circuit is lowered. In addition, there is a problem that the dimensions change when heated to a high temperature, or the adhesive is affected by various chemicals used when processing into a circuit and the adhesive strength is reduced.

Therefore, a method has been devised in which a flexible laminated substrate is manufactured by directly applying a polyimide precursor resin solution onto a conductor such as a copper foil.
At that time, after applying and curing the polyimide precursor resin solution, as a method of correcting the curl caused by the difference between the linear expansion coefficients of the conductor and the resin, a low linear expansion resin is applied and the linear expansion between the conductor and the insulating layer is performed. A method of reducing the difference in coefficients (see Patent Document 1), a method of preventing curling by drying a certain amount of solvent at a certain temperature range before proceeding with the curing reaction (see Patent Document 2), A method of applying a plurality of polyimide precursor resin solutions sequentially and curing the precursor resin layer by heat treatment to produce a flexible laminated substrate (see Patent Document 3) has been proposed.

However, in recent years, electronic devices have become more and more sophisticated, in particular, higher integration and higher functionality of semiconductor elements, and printed wiring boards have been required to have higher wiring density. With the method alone, it has become difficult to produce a flexible laminated substrate with excellent dimensional stability as required.
On the other hand, the polyimide resin layer used for the insulating layer is obtained by heat-treating a polyimide precursor resin solution obtained by polymerizing acid dianhydride and diamine at a charged molar ratio of 1, usually. In some cases, the molar ratio may be slightly adjusted to control the molecular weight. However, molecular weight control is mostly done to adjust the resin viscosity during the formation of an insulating layer on a laminated substrate and the production of a polyimide film, and to facilitate their production. It has not been known to control characteristics that contribute to the dimensional stability of polyimide by limiting the range. Moreover, since changing the molar ratio leads to variations in quality, it has an undesirable aspect.
Japanese Unexamined Patent Publication No. 60-243120 Japanese Unexamined Patent Publication No. 1-245587 JP-A-8-250860

  As described above, the conventional techniques have the problems that the quality of the flexible laminated substrate varies greatly and the dimensional stability is not sufficiently controlled.

  An object of the present invention is to provide a method for producing a flexible laminate substrate that suppresses variations in the quality of the flexible laminate substrate obtained by directly applying a polyimide precursor resin solution onto a conductor and then drying and curing the solution, and is excellent in dimensional stability. Is to provide.

  As a result of intensive studies on the above problems, the present inventors can solve the problem by controlling the manufacturing conditions centering on the raw material molar ratio in the polyimide precursor resin solution in manufacturing a flexible laminated substrate. The present invention has been completed.

That is, the present invention relates to a method for producing a flexible laminated substrate having a conductor layer and a polyimide resin layer by directly applying a polyimide precursor resin solution on a conductor, drying it, and then curing it by heat treatment. Is obtained by adjusting the molar ratio of (b) / (b) between the tetracarboxylic acid or its acid anhydride (b) and the diamino compound (b) within the range of 0.98 ± 0.01. The method for producing a flexible laminated substrate is characterized in that the polyimide resin layer formed by curing the polyimide precursor resin has a linear expansion coefficient of 10 × 10 ⁻⁶ / K or less.

（但し、式中Ar1は芳香環を一個以上有する4価の有機基であり、Yは直結合、−CONH−、−CO−、−O−、−COO−、−SO₂−、−CH₂のいずれかであり、またX1、X2はH、炭素数１〜５の低級アルキル基又は低級アルコキシ基、フェニル基、フェノキシ基のいずれかであり、それぞれ異なるものであってもよい。）で示される構成単位を主成分とすることが好ましい。また、硬化後のポリイミド樹脂層の厚みは、10〜50μmであることが有利である。 Here, as the polyimide precursor resin, the following general formula (1)

(In the formula, Ar1 is a tetravalent organic group having one or more aromatic rings, and Y is a direct bond, —CONH—, —CO—, —O—, —COO—, —SO ₂ —, —CH _2. X1 and X2 are either H, a lower alkyl group having 1 to 5 carbon atoms or a lower alkoxy group, a phenyl group, or a phenoxy group, which may be different from each other. It is preferable that the constituent unit is a main component. Moreover, it is advantageous that the thickness of the polyimide resin layer after curing is 10 to 50 μm.

  Furthermore, in the method for producing a flexible laminated substrate of the present invention, the viscosity of the polyimide precursor resin solution is preferably in the range of 10,000 to 40,000 cP.

  According to the present invention, a flexible laminated substrate having excellent dimensional stability can be produced without variation in quality while maintaining the heat resistance and other physical properties that are characteristic of a polyimide resin. It is possible to provide a flexible laminated substrate that meets the requirements for workability.

  Hereinafter, embodiments of the present invention will be described.

  In the present invention, the polyimide precursor resin solution is applied directly on the conductor. The conductor to which the polyimide precursor resin solution is applied is desirably a conductive metal foil. Examples of the metal foil include copper foil, stainless steel foil, and alloy foil. Here, the alloy foil refers to a metal foil containing copper foil as an essential element and containing at least one element such as chromium, nickel, zinc, silicon, etc., and means a metal foil having a copper content of 90% or more. When using metal foil, surface treatment with zinc plating, nickel plating, silane coupling material or the like may be performed.

  In recent years, with the fine pitch of metal wiring, thin metal foil has been favored and used. From such a viewpoint, the preferable thickness of the metal foil is in the range of 5 to 35 μm, more preferably 8 to 18 μm. Moreover, it is preferable that the metal foil to be used has a surface roughness (Rz) of a surface in contact with the polyimide resin layer in the range of 0.5 to 2.0 μm. If the surface roughness (Rz) is less than 0.5 μm, the adhesion between the metal foil and the polyimide resin layer may be insufficient. If the surface roughness is 2.0 μm or more, it tends to be unfavorable to cope with recent fine pitching, Further, there is a concern about the root of the metal component in the polyimide resin layer generated during circuit processing.

In the present invention, the polyimide precursor resin solution can be obtained by appropriately selecting a known diamino compound and tetracarboxylic acid or an anhydride thereof and combining them in an organic solvent. At that time, the charged molar ratio (i) / (b) of the tetracarboxylic acid or its acid anhydride (a) and the diamino compound (b) needs to be in the range of 0.98 ± 0.01, 0.98 ± 0.005 A range is preferred.
Outside this range, the linear expansion coefficient of the cured polyimide resin layer tends to be larger than 10 × 10 ⁻⁶ / K, which is not preferable for obtaining a flexible laminated substrate having excellent dimensional stability. At the same time, if the molar ratio is less than 0.97, the molecular weight of the polyimide precursor resin solution becomes too low, and sufficient performance may not be obtained when cured to form a polyimide resin layer. On the other hand, when the molar ratio exceeds 0.99, the molecular weight becomes large and the viscosity becomes high, so that the operability may be deteriorated, for example, bubbles are involved when applying on the conductor.
Further, the viscosity when the polyimide precursor resin solution is applied on the conductor is advantageously in the range of 10,000 to 40,000 cP, more preferably in the range of 20,000 to 40,000 cP.

In the present invention, a polyimide precursor resin that gives a particularly preferable polyimide resin layer is a polyimide precursor resin containing a structural unit represented by the following general formula (1) as a main component.

In general formula (1), Ar 1 is a tetravalent organic group having one or more aromatic rings, and Y is a direct bond, —CONH—, —CO—, —O—, —COO—, —SO ₂ —, — Any one of CH ₂ , X 1 and X 2 are H, a lower alkyl group having 1 to 5 carbon atoms or a lower alkoxy group, a phenyl group, or a phenoxy group, and X 1 and X 2 are different from each other. Also good. Here, considering the balance between the heat resistance of the polyimide resin layer, the dimensional stability represented by the linear expansion coefficient, and other physical properties, those that give the acid anhydride residue and diamine residue shown below are preferable.

  In the general formula (1), Ar1 represents a tetracarboxylic acid or an anhydride thereof, and is a tetravalent organic group having one or more aromatic rings. Typical tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic Acid dianhydride, 3,3 ', 4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,3,3', 4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3 ', 4 '-Benzophenonetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 3,3', 4,4 Examples include '-diphenylmethanetetracarboxylic dianhydride. These can be used alone or in combination of two or more. Among these, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride are preferred. Mentioned as an anhydride.

In general formula (1), Y is more preferably a direct bond or —CO—, —O—, —CONH—,
X1 and X2 are more preferably H, —CH ₃ , or —0CH ₃ . Examples of preferred diamino compounds that give these diamine residues include 4,4'-diaminodiphenyl ether, 4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'- Dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diaminodiphenylmethane, 3, 3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylsulfone, 4,4'-diaminobenzanilide, 2'-methoxy-4,4'-diaminobenzanilide, etc. Can be used alone, or two or more can be used in combination.

  In the present invention, as the polyimide precursor resin used in the polyimide precursor resin solution, it is preferable to use a resin mainly composed of the structural unit represented by the general formula (1), more preferably 70 mol. % Or more, particularly preferably 80 mol% or more of the structural unit represented by the general formula (1). When using a structural unit other than the polyimide precursor represented by the general formula (1), a polyimide precursor resin used in the present invention is appropriately combined with a known tetracarboxylic acid or acid anhydride thereof and a diamino compound. be able to.

The polyimide precursor resin solution is usually applied on the conductor in a state dissolved in an appropriate solvent. By applying this polyimide precursor resin solution directly on the conductor, a stable adhesive strength of the conductor-polyimide resin layer can be obtained.
The means for applying is not particularly limited, and examples thereof include a bar code method, a gravure coating method, a roll coating method, a die coating method, and the like, but a die coating method is preferable because bubbles are not involved in the resin solution.
Examples of the solvent contained in the polyimide precursor resin solution include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), diglyme and the like.

  The polyimide precursor resin layer is coated on the conductor so that the thickness of the cured polyimide resin layer is 10 to 50 μm, more preferably 20 to 40 μm. If the thickness of the polyimide resin layer is 10 μm or less, the performance as a polyimide resin layer may not be sufficiently exhibited. In this case, the dimensional stability is inferior.

  The polyimide precursor resin layer applied on the conductor is dried to an appropriate range in order to remove the solvent to some extent. In this case, the drying temperature is preferably such that the imidization of the polyimide precursor resin layer does not proceed. Specifically, the drying temperature is preferably 150 ° C. or less, and preferably in the range of 110 to 140 ° C. Also, if the drying time at this time is too short, drying tends to be inadequate and the linear expansion coefficient after curing tends to increase, so the amount of solvent contained in the polyimide precursor resin layer in this drying step is reduced to the polyimide precursor resin. It is desirable that the amount be 50 parts by mass or less with respect to 100 parts by mass.

As described above, when the polyimide precursor resin solution is applied on the conductor and dried, the polyimide precursor resin layer on the conductor is further heat-treated and thermally cured. Curing as used herein refers to a step of forcibly promoting imidization reaction to promote resin curing.
This imidization reaction usually proceeds rapidly at a temperature exceeding 150 ° C., particularly at a temperature exceeding 160 ° C. After evaporating a certain amount or more of the solvent as described above, curing is performed at a temperature exceeding 150 ° C. However, in this curing process, if the temperature is rapidly increased, foaming of the resin may occur. It is preferable to perform multi-stage heat treatment or continuous temperature raising treatment. In order to sufficiently perform the imidization reaction, the maximum curing temperature is 250 ° C or higher, preferably 300 ° C or higher. It should be noted that if the curing temperature is too high, the resin is decomposed. The time required for imidization is 5 minutes to 60 minutes, preferably 5 to 30 minutes.

  Although any process can be adopted as such a drying step and a curing step, it is preferable to use a floating type in which the applied conductor does not contact the apparatus. In the floating type, the conductor is dried and cured in a state where it is suspended in the airflow, and the airflow is uniformly supplied from nozzles arranged above or below the conductor surface while the conductor is continuously running. The conductor is blown out toward the conductor surface, and the running conductor is floated, and it is made to travel while curving so as to hit a wave. Heating is preferably performed by blowing hot air as an air stream, but infrared heating, electromagnetic induction heating, or the like may be used or used in combination. As the heating atmosphere, any of air, an inert gas such as nitrogen, carbon gas, and argon can be selected.

The polyimide resin layer on the flexible laminated substrate thus manufactured has a linear expansion coefficient of 10 × 10 ⁻⁶ / K or less, preferably 10 × 10 ⁻⁷ to 10 × 10 ⁻⁶ / K. Be controlled. In order to set the linear expansion coefficient range of the polyimide resin layer to 10 × 10 ⁻⁶ / K or less, tetracarboxylic acid or its acid anhydride (A) and diamino compound (B) are added to (A) / (B) The molar ratio is 0.98 ± 0.01, and the type of polyimide precursor resin and the viscosity and molecular weight range of the precursor resin can be controlled to an appropriate range as necessary. Here, the polyimide precursor resin used is preferably the polyimide precursor described above, and the viscosity is preferably in the range of 10,000 to 40,000 cP and the weight average molecular weight is in the range of 10,000 to 150,000. Moreover, since there exists a possibility that control of a linear expansion coefficient may become difficult when the thickness of a polyimide resin layer becomes too thick, the range of 10-50 micrometers in thickness after hardening becomes suitable thickness.

The insulating resin layer of the flexible laminated substrate obtained by the present invention is preferably formed only by the polyimide resin layer, but other layers are provided on the polyimide resin layer as long as the object of the present invention is not adversely affected. Also good.
As the other layer, a polyimide resin layer other than the above is preferable. The layer structure is M / PI-a, M /
Examples include PI-a / PI-b, M / PI-a / M, and M / PI-a / PI-b / M. Here, M represents a metal foil, PI-a represents a polyimide resin layer having a linear expansion coefficient of 10 × 10 ⁻⁶ / K or less, and PI-b represents another polyimide resin layer. A metal foil may be laminated on the resin layer that has been imidized, if necessary. In this case, a known method such as thermocompression bonding can be applied to the metal foil.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, of course, this invention is not limited to these Examples. In addition, evaluation of each characteristic of the flexible laminated substrate obtained by the manufacturing method of this invention is based on the following measuring method.
[viscosity]
The viscosity was measured at 25 ° C. with a cone plate viscometer (manufactured by Tokimec Co., Ltd.) equipped with a constant temperature water bath.
[Molecular weight]
The molecular weight was measured with GPC (HLC-8020, manufactured by Tosoh Corporation) at a column temperature of 40 ° C., and the weight average molecular weight in terms of polystyrene was determined.
It was.
[Linear expansion coefficient (CTE)]
The coefficient of linear expansion (CTE) is a 3mm x 15mm size polyimide film that is pulled in a temperature range of 30 ° C to 260 ° C at a constant rate of heating while applying a 5.0g load with a thermomechanical analysis (TMA) device. A test was conducted. The linear expansion coefficient was measured from the amount of elongation of the polyimide film with respect to temperature.

The abbreviations in each example are as follows.
PMDA: pyromellitic dianhydride
BPDA:
3,3 ', 4,4'-biphenyltetracarboxylic dianhydride
m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl
TPE-R:
1,3-bis- (4-aminophenoxy) benzene
DMAc: Dimethylacetamide

(Synthesis Example 1)
After dissolving 0.1 mol of TPE-R and 0.9 mol of m-TB in 255 g of DMAc, PMDA
0.748 mol and BPDA 0.187 mol were gradually added and reacted to obtain a viscous polyimide precursor resin solution (polyamic acid A). The obtained resin had a viscosity of 550 cP and a weight average molecular weight of 36,953.
(Synthesis Example 2 to Synthesis Example 8)
A polyimide precursor resin solution (polyamic acid B to polyamic acid H) was obtained in the same manner as in Synthesis Example 1, except that the raw monomer charge ratio was changed to the ratio shown in Table 1.

(Example 1)
Polyamic acid C was applied onto the mirror surface of an electrolytic copper foil (thickness: 18 μm) so that the thickness of the cured resin layer was about 25 μm, and dried in a circulating hot air oven at 130 ° C. for 14 minutes. Next, heat-treat and harden the flexible multilayer substrate at 160 ° C for 4 minutes, 200 ° C for 2 minutes, 230 ° C for 2 minutes, 280 ° C for 2 minutes, 320 ° C for 2 minutes, and 380 ° C for 2 minutes. Obtained. The copper foil of the obtained flexible laminated substrate was etched to form a single-layer polyimide film, and the CTE measured was 7.9 ppm / K.
(Example 2 to Example 5, Comparative Example 1 to Comparative Example 3)
A flexible laminated substrate was obtained in the same manner as in Example 1 except that each of the polyamic acids shown in Table 2 was used. The results are summarized in Table 2.

Claims (4)

In the method of manufacturing a flexible laminated substrate having a conductor layer and a polyimide resin layer by directly applying and drying a polyimide precursor resin solution on a conductor and then drying it by heat treatment, the polyimide precursor resin is tetracarboxylic acid or The acid anhydride (a) and diamino compound (b) are obtained by adjusting the molar ratio of (a) / (b) to a range of 0.98 ± 0.01. A method for producing a flexible laminated substrate, wherein an expansion coefficient is 10 × 10 ⁻⁶ / K or less. The polyimide precursor resin is represented by the following general formula (1)

(In the formula, Ar1 is a tetravalent organic group having one or more aromatic rings, and Y is a direct bond, —CONH—, —CO—, —O—, —COO—, —SO ₂ —, —CH _2. X1 and X2 are either H, a lower alkyl group having 1 to 5 carbon atoms or a lower alkoxy group, a phenyl group, or a phenoxy group, which may be different from each other. The method for producing a flexible laminated substrate according to claim 1, comprising a structural unit as a main component.   The method for producing a flexible laminated substrate according to claim 1, wherein the polyimide resin layer has a thickness of 10 to 50 μm.   The method for producing a flexible laminated substrate according to any one of claims 1 to 3, wherein the viscosity of the polyimide precursor resin solution is 10,000 to 40,000 cP.