WO2005086547A1 - Flexible printed wiring board and manufacturing method thereof - Google Patents

Abstract

A flexible printed wiring board having a stable quality, not generating curls on a film even after circuit process on a conductor side, and a method of manufacturing such flexible printed wiring board are provided. The flexible printed wiring board is provided with a base layer, which is composed of at least one type of low thermal expansion polyimide resin, between a bottom layer contacting the conductor and a top layer on the opposite side to the conductor. The bottom layer and the top layer are composed of a thermoplastic polyimide rein having a larger thermal expansion coefficient than that of the base layer, and a thickness P1 of the bottom layer and a thickness P2 of the top layer satisfy a condition of P1<P2.

Description

 Specification

 Flexible printed wiring board and method of manufacturing the same

 Technical field

 The present invention relates to a substrate for flexible printed wiring and a method for manufacturing the same, which meets the demands for downsizing and lightweight electronic devices. In particular, the present invention relates to a high-quality single-sided conductor flexible printed wiring board having no warpage in a polyimide film portion after wiring processing and a method of manufacturing the same.

 Background art

 [0002] In recent years, as mobile phones, digital cameras, navigators, and other various electronic devices have become more sophisticated and smaller and lighter, the use of flexible printed circuit boards as electronic wiring materials ( There is an increasing demand for smaller, higher-density, multi-layer, finer, and lower-voltage dielectric substrates. Previously, this flexible printed wiring board was manufactured by laminating a polyimide film and a metal foil with a low-temperature curable adhesive. However, the adhesive layer deteriorates the characteristics as a wiring board, and particularly impairs the excellent heat resistance and flame retardancy of the polyimide base film. Another problem with the adhesive layer is that the circuit performance of the wiring deteriorates.

[0003] Specifically, there are problems such as generation of resin smear due to drilling at the time of through-hole curing and a large dimensional change rate at the time of conductor through-hole curing. In particular, in the case of a double-sided through-hole structure, the one formed by bonding a conductor copper foil etc. to both sides of the base film, which is the insulator layer, with an adhesive, compared to a single-sided flexible printed circuit board And generally its flexibility is low. On the other hand, as the density of ICs becomes higher and the size of printed wiring becomes finer and higher, heat generation increases, and it becomes necessary to bond a good thermal conductor. In addition, there is a method of integrating the housing and the wiring in order to make the housing more compact. Further, wirings having different electric capacities are required, and wiring materials that can withstand higher temperatures are required. Therefore, there have been proposed various methods for manufacturing a flexible printed circuit board in which a polyamic acid solution before curing is directly applied to a conductor such as a copper foil without using an adhesive, and the conductor is cured by heating. [0004] For example, the thermal expansion coefficient of the cured product 3. 0 X 10- ⁵ following Jiamin and the polyamic acid which is synthesized by the tetracarboxylic acid anhydride which is cured by heating is applied to the metal foil (e.g., Patent Document 1 ), A resin solution containing a polyamideimide precursor compound having a specific structural unit is applied onto a conductor and imidized (for example, see Patent Document 2), and diamines containing diaminobenzamide or a derivative thereof. And a method of directly applying a precursor solution of an insulating material having a structural unit obtained by a reaction between the compound and an aromatic tetracarboxylic acid onto a conductor and curing the solution (for example, see Patent Document 3). Furthermore, in order to enhance the adhesion to the metal foil, a plurality of polyimide resin solutions are used on the conductor, and the coating and drying are performed multiple times to form a flexible printed wiring with multiple polyimide resin layers. A method of manufacturing a substrate (for example, see Patent Document 4) has also been proposed.

 Patent Document 1: Japanese Patent Application Laid-Open No. 62-212140

 Patent Document 2: JP-A-63-84188

 Patent Document 3: JP-A-63-245988

 Patent Document 4: Japanese Patent Publication No. 6-49185

 Disclosure of the invention

 Problems to be solved by the invention

[0006] According to the method for manufacturing a substrate for flexible printed wiring in Patent Document 4 described above, due to the difference between the adhesion between the metal foil serving as a conductor and the resin and the coefficient of thermal expansion between the metal foil and the resin. A good quality flexible printed wiring board in which curling of the board is suppressed can be obtained. However, even with such a substrate, if the composition of the polyimide resin of multiple layers on one side of the metal foil does not satisfy the specific conditions, circuit processing is actually performed on the conductor side and unnecessary. It was found that if the unnecessary metal foil was removed, the exposed polyimide film was liable to cause curling, resulting in a problem.

 The cause of this phenomenon is that the degree of orientation of polyimide molecules in the thickness direction of the formed polyimide resin layer is different in the process of applying and drying the polyimide precursor resin solution and imidizing by heat treatment. Was expected. However, the mechanism has not been elucidated yet.

[0007] Therefore, an object of the present invention is to curl the film even after the circuit is cut to the conductor side. An object of the present invention is to provide a flexible printed wiring board having stable quality and a method of manufacturing the same.

 Means for solving the problem

 The inventors of the present invention have conducted intensive studies on the above problems, and as a result, have predicted a difference in the coefficient of thermal expansion in the thickness direction, which also causes a difference in the degree of orientation of the polyimide molecules in the thickness direction of the multilayer polyimide layer. In addition, a polyimide resin layer having a higher thermal expansion coefficient than the base layer present between the two layers is arranged on the layer in contact with the conductor and the top layer, and the thickness of the layer in contact with the conductor is greater than the thickness of the top layer. It has been found that the object of the present invention can be achieved by reducing the size, and the present invention has been completed.

That is, the flexible printed wiring board of the present invention is a flexible printed wiring board having a multilayer polyimide layer having a different thermal expansion coefficient on one surface of a conductor, and is provided with a bottom layer and a conductor that are in contact with the conductor. at least one thermal expansion coefficient is made of ^{30 X 10- 6 (1Z ° C} ) or lower thermal expansion polyimide-based榭脂base layer is disposed intermediate the opposite top layer of, and, the bottom layer and the top layer Is made of a thermoplastic polyimide resin with a larger coefficient of thermal expansion than the base layer, and the conditions of bottom layer thickness P and top layer thickness P force P

 1 2 1 2 It is characterized by satisfaction.

[0010] Further, it is desirable that the ratio P / (P + P) of the total thickness of the bottom layer and the top layer on both sides thereof to the thickness P of the base layer in the present invention is in the range of 2-100.

 Further, the thickness P of the bottom layer in the present invention is in the range of 0.2-10 / zm, and the ratio P / P to the thickness P of the top layer is in the range of 0.2-0.8. It is desirable that

 2 1 2

[0011] In the method for producing a substrate for flexible printed wiring of the present invention, a multi-layered polyimide precursor resin solution is directly applied on one side of a conductor, dried and then heat-cured to obtain a multilayer having a different coefficient of thermal expansion. In a method for manufacturing a flexible printed wiring board having a polyimide layer having a thickness of at least one kind between the bottom layer in contact with the conductor and the top layer on the side opposite to the conductor, the coefficient of thermal expansion is 30 X 10 — A base layer that can be converted to a low thermal expansion polyimide resin of ⁶ (1Z ° C) or less is provided, and the bottom layer and the top layer are made of a thermoplastic polyimide resin having a higher thermal expansion coefficient than the base layer. The polyimide resin solution that can be converted is applied so as to satisfy the conditions of the bottom layer thickness p and the top layer thickness p 1S p <p.

 1 2 1 2

And then heat-cured. In the present invention, the ratio P / (P + P) of the thickness P of the base layer to the total thickness of the bottom layer and the top layer on both sides thereof is preferably in the range of 2-100. Furthermore, in the present invention, the thickness P of the bottom layer satisfies the range of 0.2-10 / zm, and the ratio P / P to the thickness P of the top layer satisfies the range of 0.2-0.8. To polyimide

 2 1 2

 It is desirable to apply a precursor resin solution.

 The invention's effect

 According to the present invention, the polyimide film does not curl or warp even if unnecessary metal foil is removed by applying circuit strength to the substrate for flexible printed wiring, resulting in excellent dimensional stability. A printed wiring board can be manufactured.

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the present invention will be described in detail.

 First, the conductor used in the present invention is a conductive metal foil having a thickness of 5 to 150 μm, such as copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zinc, and alloys thereof. And copper is preferable. In the case of copper, there are rolled copper foil and electrolytic copper foil, both of which can be used. For the purpose of improving adhesive strength, the surface may be subjected to chemical or mechanical surface treatment such as siding, nickel plating, copper-zinc alloy plating, or aluminum alcoholate, aluminum chelate, or silane coupling agent. ,.

[0015] An insulating layer can be formed by forming a plurality of polyimide-based resin layers on one surface of a conductive metal foil as a conductor. The polyimide-based resin used as the insulating layer is as follows. This is a general term for resins having an imide ring structure, and examples thereof include polyimide, polyamide imide, and polyester imide. As the polyimide-based resin layer, those having low thermal expansion as described in the above-mentioned Patent Documents 14 and thermoplastic polyimides which melt or soften when heated can be used, and are not particularly limited. But particularly preferred insulator layer as a base layer of low thermal expansion property榭脂layer of thermal expansion coefficient (or linear expansion coefficients) 30 X 10- ⁶ (lZk), greater thermal expansion coefficient than the base layer on the upper and lower It is desirable to use at least three polyimide resin layers in which two layers (bottom layer and top layer) of thermoplastic polyimide resin are arranged. [0016] The low thermal expansion polyimide榭脂which here forms the base layer, the heat resistance of the thermal expansion coefficient of ^{3 OX 10- 6 (1Z ° C} ) or less preferred instrument films were excellent in flexibility Those with performance are good. Here, the coefficient of thermal expansion was determined by using a sample after the imidization reaction was sufficiently completed, using a thermomechanical analyzer (TMA), raising the temperature to 250 ° C, cooling at a rate of 10 ° CZ, and The average coefficient of thermal expansion in the range of 100 ° C was determined. As a specific example of the low thermal expansion polyimide resin having such properties, a polyimide resin having a unit structure represented by the following general formula (I) is desirable.

 [0017] [Formula 1]

(However, in the formula, R—R

 14 represents a lower alkyl group, a lower alkoxy group, a halogen group or hydrogen)

In addition, the thermoplastic polyimide resin used to form the bottom and top layers above and below the base layer should have a coefficient of thermal expansion greater than that of the base layer and a glass transition temperature of 350 ° C or lower. Just fine. It is preferable that the adhesive strength at the interface is sufficient when pressed under heat and pressure. In this case, the thermoplastic polyimide resin species of the bottom layer and the top layer may be the same or may have different unit structures as long as the above conditions are satisfied. The thermoplastic polyimide resin as used herein includes those which can be adhered by pressure so that they do not necessarily show sufficient fluidity in a normal state above the glass transition point. Specific examples of the thermoplastic polyimide resin having such properties include those having a unit structure represented by the following general formula (II) or general formula (III). [0019] [Formula 2] 0 tt ⁰ o>

(Wherein, Ar is a divalent aromatic group having 12 or more carbon atoms.)

(In the formula, Ar is a divalent aromatic group having 12 or more carbon atoms.)

 2

 Here, specific examples of the divalent aromatic group Ar or Ar include, for example,

 1 2

 [Formula 4]

o > c

o>

CH3

 ,

CH ₃ Etc.

 As a method for manufacturing a single-sided conductor flexible printed wiring board, as described in Patent Document 4, a polyimide precursor solution or a polyimide solution is cured by a known acid anhydride-based amine-based curing method. Metal foils by adding various additives and catalysts such as curing agents such as silane coupling agents, silane coupling agents, titanate coupling agents, adhesion-imparting agents such as epoxy compounds, and flexibility-imparting agents such as rubber. Apply to one side of Next, heat treatment is performed by heat treatment to obtain a single-sided conductor laminate. The single-sided conductor laminate has a conductive metal foil as a bottom layer, a thermoplastic polyimide resin layer having a larger coefficient of thermal expansion than the base layer, and an intermediate base layer as at least one kind of low thermal expansion polyimide resin layer. It is preferable to further laminate a thermoplastic polyimide resin layer having a larger coefficient of thermal expansion than the base layer as the outermost top layer.

Here, the intermediate base layer must be a polyimide resin layer having a smaller thermal expansion coefficient V than the thermoplastic polyimide resin layer of the bottom layer or the top layer. The base layer has the function of suppressing curling and warpage of the manufactured flexible printed wiring board substrate, and the bottom layer in contact with the conductor has the function of ensuring adhesion to the conductive metal foil. The layer is expected to have the effect of suppressing the curl of the film alone. In some cases, it is also expected to have an effect of securing an adhesive property when used as a flexible printed wiring board substrate having double-sided conductors by laminating another conductive metal foil on the top layer and applying heat and pressure.

[0024] At this time, the ratio of the thickness P of the low thermal expansion polyimide resin layer (base layer) to the total thickness of the thermoplastic polyimide resin layers (bottom layer P and top layer P) on both sides thereof, P / ( P +

 1 2 ml

P) is in the range of 2100, preferably 520. If this thickness ratio is less than 2,

2

 On the other hand, the thermal expansion coefficient of the entire polyimide resin layer is too high as compared with that of the metal foil, and the resulting flexible printed wiring board substrate is greatly warped or curled, and the workability during circuit processing is significantly reduced. In addition, if the total thickness (P + P) of the thermoplastic polyimide resin layers on both sides is too small and the ratio of the thicknesses exceeds 100, the conductive polyimide foil and

 2

 In some cases, the adhesive strength may not be sufficiently exhibited.

 [0025] The ratio of the thickness (P) of the bottom layer in contact with the conductor to the thickness (P) of the top layer opposite to the conductor is P

 1 2 1

It is important that <P. The thickness ratio is the thickness of the base layer having low thermal expansion. Depending on the force, P / P = 0.2-0.8, more preferably 0.3-0.7. this

 1 2

 If it is smaller than the range, the effect of correcting the film curl is too strong, and the curl is generated on the contrary. The thickness (P) of the bottom layer in contact with the conductor layer is preferably in the range of 0.2 to 10 m. If the thickness is smaller than this range, the adhesive strength to the conductor layer cannot be secured, and if the thickness is larger, the heat resistance is reduced.

[0026] The application of the polyimide precursor resin which can be converted into the plurality of polyimide resins onto the conductive metal foil can be performed in the form of the resin solution. As described, there is a simultaneous or sequential application of a plurality of precursor solutions in the form of the precursor solution! /, To the polyimide of the precursor after the solvent removal treatment below the imide ring closure temperature. It is preferable to perform the heating conversion at once. If another polyimide-based precursor solution is applied on the layer completely converted to polyimide and heat-treated to close the imide ring, the adhesion between the polyimide-based resin layers may not be sufficiently exhibited, This will cause the quality of the double-sided laminate of the product to deteriorate.

 [0027] The polyimide precursor resin solution (polyamic acid solution) on the conductive metal foil is used as a method for applying the resin solution containing the precursor compound, for example, a knife coater, a die coater, a roll, or the like. The coating can be carried out by a known method using a coater, a curtain coater or the like, and a die coater or a knife coater is particularly suitable for thick coating. The polymer concentration of the polyimide precursor resin solution used for coating is usually 5 to 30% by weight, preferably 10 to 20% by weight, though it depends on the degree of polymerization of the polymer. If the polymer concentration is lower than 5% by weight, a single coating will not provide a sufficient film thickness, and if it is higher than 30% by weight, the solution viscosity will be too high to make coating difficult.

[0028] The polyimide precursor resin solution (polyamic acid solution) applied to the conductive metal foil to have a uniform thickness is then subjected to a heat treatment to remove the solvent and further close the imide ring. In this case, if heat treatment is performed rapidly at high temperature, a skin layer will be formed on the resin surface and the solvent will not easily evaporate or foam.Therefore, heat treatment is performed while gradually increasing the temperature from low to high. desirable. In this case, the final heat treatment temperature is usually preferably 300 to 400 ° C. Above 400 ° C, the polyimide begins to decompose gradually, and below 300 ° C, the polyimide film becomes conductive. A single-sided conductor laminate with good flatness was obtained, which was not sufficiently oriented on metal foil Rena, The overall thickness of the polyimide resin layer as an insulator thus formed is usually 10 to 150 m.

 Example

 Hereinafter, embodiments of the present invention will be specifically described based on examples and comparative examples.

 In the following examples, the coefficient of thermal expansion, the curl and adhesion of a single-sided copper-clad product, and the curl of a film were measured by the following methods.

[0030] That is, the coefficient of thermal expansion was measured using a thermomechanical analyzer (TMA100) manufactured by Seiko Denshi Kogyo Co., Ltd., and then the temperature was raised to 250 ° C and then cooled at a rate of 10 ° CZ, and the temperature was reduced to 240 ° C

The average coefficient of linear expansion between 100 ° C was calculated and determined.

As the curl of the single-sided copper-clad product, the radius of curvature of the copper-clad product having dimensions of 100 mm × 100 mm after imidization by heat treatment was measured.

[0032] The adhesive strength of a single-sided copper-clad product is the value when a copper foil is peeled off at a speed of 50mmZ in a 180 ° direction using a pattern with a conductor width of 3mm in accordance with JIS C5016: 7.1. (kgZcm).

 [0033] The solder heat resistance was measured up to a maximum of 400 ° C from 260 ° C at an interval of 10 ° C gradually according to the method of JIS C5016.

[0034] The following abbreviations were used in the examples and comparative examples.

 PMDA: pyromellitic anhydride

 BTDA: 3, 3 ', 4, 4' benzophenone tetracarboxylic anhydride

 DDE: 4,4-diaminodiphenyl ether

 MABA: 2, -Methoxy-4,4, -Diaminobenzayulide

(Synthesis Example 1)

25,2 g of N, N-dimethylacetoamide was charged into the glass reactor while passing nitrogen, and then 0.5 mol of DDE and 0.5 mol of MABA were charged with stirring, and then completely dissolved. This solution was cooled to 10 ° C, and 1 mol of PMDA was added little by little so that the reaction solution was kept at a temperature of 30 ° C or lower. After the addition was completed, stirring was continued at room temperature for 2 hours. The polymerization reaction was completed. The obtained polyimide precursor solution had a polymer concentration of 15% by weight and an apparent viscosity of 100 MPa's at 25 ° C by a B-type viscometer. (Synthesis Example 2)

 A polyimide precursor solution was prepared in the same manner as in Synthesis Example 1, except that 1 mol of DDE was used as the diamine component and 1 mol of BTDA was used as the acid anhydride component. The obtained polyimide precursor solution had a polymer concentration of 15% by weight and an apparent viscosity of 300 mPa · s at 25 ° C. by a B-type viscometer.

Example 1

The polyimide precursor solution 2 prepared in Synthetic Example 2 was uniformly coated with a thickness of 20 μm using a die coater as the bottom layer on the roughened surface of a 35 μm rolled electrolytic copper foil (manufactured by Nikko Gould). After coating, the mixture was continuously treated in a hot air drying oven at 120 ° C. to remove the solvent. Next, the polyimide precursor solution 1 prepared in Synthesis Example 1 was applied uniformly as a base layer to a thickness of 200 μm using a reverse type roll coater using a reverse roll coater at a temperature of 120 ° C. After continuous treatment in a hot-air drying oven to remove the solvent, the polyimide precursor solution 2 prepared in Synthesis Example 2 was evenly applied as a top layer with a thickness of 40 m, and then in a hot-air drying oven for 30 minutes. And heat-treated by heating from 120 ° C to 360 ° C, and imidized.The polyimide resin layer has a thickness of 25 μm and has no warpage or curl. The product a) was obtained. However, the base point of the thickness of the bottom layer was measured as 1Z2 of the surface roughness of the rough surface of the conductor. The 180 ° peel strength (JIS C-5016) between the copper foil layer and the polyimide resin layer of the single-sided conductor laminate a was 1.8 KgZcm. Next, circuit processing is performed on the conductor side of this single-sided conductor laminate a to remove unnecessary metal foil, no curl occurs on the exposed polyimide film, and the coefficient of linear expansion of the film after etching is 23. 5 was ^{X 10- 6 (lZ ° C)} .

Example 2-3 and Comparative Example 1-3

The thickness of the polyimide resin layer of the bottom layer, the base layer, and the top layer in Example 1 was changed variously, dried in the same manner, and then heated from 120 ° C to 360 ° C in a hot-air drying oven for 30 minutes. Thus, a single-sided conductor laminate (single-sided copper-clad product) a was obtained. The situation of occurrence of warpage and curl of this single-sided conductor laminate a, 180 ° peel strength, and the situation of occurrence of curl of the exposed polyimide film when circuit processing is performed on the conductor side and unnecessary metal foil is removed Tables 1 and 2 summarize the coefficient of linear expansion of the film after etching. [Table 1]

 [0040] [Table 2]

 Industrial applicability

[0041] The method for flexible printed wiring board and its manufacturing The present invention, at least one thermal expansion coefficient of 30 X 10- ⁶ to the middle of the bottom layer and the conductor opposite the top layer of which is in contact with the conductor (1Z ° C) A base layer made of the following low thermal expansion polyimide resin is disposed, and the bottom layer and the top layer are made of a thermoplastic polyimide resin having a larger thermal expansion coefficient than the base layer. A substrate with high quality, which is stable in quality and free of curling, is obtained.

Claims

The scope of the claims A flexible printed wiring board having a multilayer polyimide layer having a different coefficient of thermal expansion on one surface of a conductor, wherein at least one kind of coefficient of thermal expansion is provided between a bottom layer in contact with the conductor and a top layer on the opposite side of the conductor. There ^{30 X 10- 6 (1Z ° C} ) base layer consisting of a low thermal expansion polyimide-based榭脂is arranged, and, the bottom layer and the top layer is a thermal bulging expansion coefficient than the base layer large thermoplastic polyimide A flexible printed wiring board that is made of resin and further satisfies the condition of bottom layer thickness P and top layer thickness P force p <p  2 1 2  Board.  The ratio of the total thickness of the bottom layer and the top layer on both sides to the thickness P of the base layer P / (mm 2. The flexible printed wiring according to claim 1, wherein (P + P) satisfies the range of 2-100. 1 2  substrate.  The thickness P of the bottom layer is in the range of 0.2-10 m, and the ratio P to the thickness P of the top layer is P  1 2 1 3. The flexible printed circuit according to claim 1, wherein / P satisfies the range of 0.2 to 0.8. 2  Substrate for wire. [4] Multiple layers of polyimide precursor resin solution are directly applied on one side of the conductor, dried and then heat-cured to produce a flexible printed wiring board with multiple polyimide layers with different coefficients of thermal expansion Te you!ヽto a method of, intermediate thermal expansion coefficient also at least one force is ^{30 X 10- 6 (1Z ° C} ) or lower thermal expansion polyimide-based榭the bottom layer and the conductor opposite the top layer of which is in contact with the conductor A base layer that can be converted to a fat is placed, and a polyimide precursor resin solution that can be converted to a thermoplastic polyimide resin with a larger coefficient of thermal expansion than the base layer is placed on the bottom and top layers. Of thickness P and top layer thickness P force P <P  A method for manufacturing a substrate for flexible printed wiring, characterized by coating, drying and heat-curing so as to satisfy 1 2 1 2 conditions. [5] The thickness P of the bottom layer is in the range of 0.2-10 μm, and the ratio P to the thickness P of the top layer is P  1 2 1 Apply polyimide precursor resin solution so that ZP satisfies the range of 0.2-0.8 2  5. The method for producing a flexible printed wiring board according to claim 4.