KR20060129081A - 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

Flexible printed wiring board and its manufacturing method {FLEXIBLE PRINTED WIRING BOARD AND MANUFACTURING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board and a method for manufacturing the same in response to requests for downsizing and weight reduction of electronic devices. In particular, it is related with the board | substrate for flexible printed wiring of the high quality single-sided conductor in which the polyimide film part after wiring process does not produce a curvature, and its manufacturing method.

In recent years, with the progress of miniaturization and weight reduction of high-performance mobile phones, digital cameras, navigators, and various other electronic devices, the compact, high-density, multilayered, and fine (flexible printed circuit boards) as electronic wiring materials used in these devices have been developed. ), Requests for low-cost, low-cost calls, etc. are increasing. As for this flexible printed wiring board, the polyimide film and metal foil were previously manufactured by bonding with a low temperature hardenable adhesive agent. However, the adhesive layer causes the deterioration of the characteristics as the wiring board, and particularly impairs the excellent heat resistance, flame retardance, and the like of the polyimide base film. Moreover, as another problem which has an adhesive bond layer, the circuit workability of a wiring worsens.

Specifically, there are problems such as generation of resin smear due to drilling in through-hole processing, and large dimensional change rate during conductor through hole processing. In particular, in the case of a double-sided through-hole structure, the copper foil or the like formed by bonding a conductor to a base film, which is an insulator layer, on both sides thereof through an adhesive, is generally low in flexibility compared to a flexible printed circuit board having a single-sided structure. On the other hand, the heat generation increases with the increase of the IC density, the fineness and the high density of the printed wiring, and it is necessary to join a good heat conductor. Moreover, in order to make it more compact, there is also a method of integrating the housing and the wiring. On top of that, wirings with different capacitances are required, or wiring materials that withstand higher temperatures are required. Therefore, various methods of manufacturing a flexible printed circuit board which directly apply a polyamic acid solution before curing to a conductor such as copper foil and heat and harden without using an adhesive are proposed.

For example, the polyamic acid synthesize | combined by diamine and tetracarboxylic anhydride whose thermal expansion coefficient is 3.0 * 10 <^-5> or less is apply | coated to metal foil, and it hardens | cures (for example, refer patent document 1), or polyamidoimide which has a specific structural unit Insulating material which has a structural unit obtained by apply | coating and imidating the resin solution containing a precursor compound on conductor (for example, refer patent document 2), and diamine containing diaminobenzanilide or its derivative (s), and aromatic tetracarboxylic acid. And curing the precursor solution of the solution directly on the conductor (for example, refer to Patent Document 3). Moreover, in order to improve adhesiveness with metal foil, the method of manufacturing the flexible printed wiring board which has a some polyimide resin layer by apply | coating and drying several times using a some polyimide precursor resin solution on a conductor (for example, a patent) Reference 4 is also proposed.

Patent Document 1: Japanese Patent Application Laid-Open No. 1987-212140

Patent Document 2: Japanese Patent Application Laid-Open No. 1988-84188

Patent Document 3: Japanese Patent Application Laid-Open No. 1988-245988

Patent Document 4: Japanese Patent Publication No. 1994-49185

Disclosure of the Invention

Problems to be Solved by the Invention

According to the manufacturing method of the flexible printed wiring board in the said patent document 4, the curl of the board | substrate which arises from the adhesiveness of the metal foil and resin used as a conductor, and the difference of the thermal expansion coefficient of metal foil and resin is suppressed. A high quality flexible printed wiring board can be obtained. However, even in such a substrate, when the constitution of a plurality of layers of polyimide resins does not satisfy specific conditions on one side of the metal foil, when the circuit processing is actually performed on the conductor side to remove unnecessary metal foil, the exposed polyimide film is exposed. We found that there is a problem that curls are likely to occur.

The reason why such a phenomenon occurs is that it is expected that a difference occurs in the degree of orientation of the polyimide molecules in the thickness direction of the polyimide resin layer to be formed in the process of coating and drying the polyimide precursor resin solution and imidating the mixture by heat treatment. However, the mechanism has not been elucidated yet.

Therefore, it is an object of the present invention to provide a substrate for flexible printed wiring with stable quality in which curl does not occur in the film even after the circuit processing on the conductor side and a manufacturing method thereof.

Means to solve the problem

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining the said subject, the layer predicts the difference of the thermal expansion coefficient of the thickness direction resulting from the difference of the orientation degree of the polyimide molecule of the thickness direction of the polyimide layer which consists of multilayers, and the layer which contact | connects a conductor (top) The object of the present invention was found to be achieved by arranging the polyimide resin layer having a higher coefficient of thermal expansion than the base layer existing in the middle of both layers, and making the thickness of the layer in contact with the conductor smaller than the thickness of the upper layer. Was completed.

That is, the flexible printed wiring board of the present invention is a flexible printed wiring board having a multi-layer polyimide layer having a different thermal expansion coefficient on one side of the conductor, and includes a bottom layer in contact with the conductor and an upper layer opposite to the conductor. A base layer made of a low thermally expandable polyimide resin having at least one thermal expansion coefficient of 30 × 10 ⁻⁶ (1 / ° C.) or lower is disposed in the middle, and the bottom layer and the upper layer have a thermoplastic polyimide system having a larger thermal expansion coefficient than the base layer. made of a resin, the thickness of the bottom layer thickness of the P ₁ P ₂ and the upper layer is to satisfy the condition of P ₁ <P _2.

Further, in the present invention, it is preferable that the ratio P _m / (P ₁ + P ₂ ) of the total thickness of the bottom layer and the upper layer on both sides with respect to the thickness P _m of the base layer is in the range of 2 to 100.

In the present invention, it is preferable that the thickness P ₁ of the bottom layer is in the range of 0.2 to 10 µm, and the ratio P ₁ / P ₂ to the thickness P _{2 of the} top layer is in the range of 0.2 to 0.8.

The manufacturing method of the flexible printed wiring board of this invention is for flexible printed wiring which has a multilayer polyimide layer from which a thermal expansion coefficient differs by directly coating and drying a several layer polyimide precursor resin solution on one side of a conductor, and heat-hardening. In the method of manufacturing a substrate, at least one kind is formed in the middle of the bottom layer in contact with the conductor and the top layer on the opposite side of the conductor, and is converted into a low thermally expandable polyimide resin having a coefficient of thermal expansion of 30 × 10 ⁻⁶ (1 / ° C.) or less. Possible base layer is disposed, and in the bottom layer and the top layer, a polyimide precursor resin solution convertible to a thermoplastic polyimide resin having a larger coefficient of thermal expansion than the base layer, the thickness P ₁ of the bottom layer and the thickness P ₂ of the top layer are P ₁ <P After coating and drying so as to satisfy the conditions of ₂ , heat curing is performed.

Further, according to the present invention, it is preferred that in the range of 2 to 100, and the bottom layer of the total thickness of the top layer _{non-P m / (P 1 + P} 2) of both sides of the thickness P _m of the base layer.

In the present invention, the polyimide precursor resin solution is coated so that the thickness P ₁ of the bottom layer is in the range of 0.2 to 10 μm, and the ratio P ₁ / P ₂ to the thickness P _{2 of the} top layer satisfies the range of 0.2 to 0.8. It is desirable to.

Effects of the Invention

ADVANTAGE OF THE INVENTION According to this invention, even if it carries out the circuit processing to a flexible printed wiring board and removes unnecessary metal foil, a curl or curvature does not generate | occur | produce in a polyimide film, As a result, the printed wiring board excellent in dimensional stability can be manufactured.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, the best form for implementing this invention is demonstrated in detail.

First, as a conductor used in this invention, conductive metal foil, such as copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zinc, and their alloys, whose thickness is 5-150 micrometers is mentioned, Preferably, Is copper. In the case of copper, although there are a rolled copper foil and an electrolytic copper foil, either can be used. Moreover, for the purpose of improving the adhesive strength, the surface may be subjected to chemical or mechanical surface treatment with siding, nickel plating, copper-zinc alloy plating, or aluminum alcoholate, aluminum chelate, silane coupling agent, or the like.

Although an insulator layer can be formed by forming a some polyimide-type resin layer in the single side | surface of the conductive metal foil which is a conductor, the polyimide resin used as an insulator layer is a generic name of resin which has an imide ring structure, for example, polyimide , Polyamidoimide, polyester imide and the like. And as a polyimide-type resin layer, the thing of low thermal expansion as described in the said patent documents 1-4, the thermoplastic polyimide etc. which melt or soften when it heats can be used, It does not specifically limit. However, a particularly preferable insulator layer is a thermoplastic polyimide system having a low thermal expansion resin layer having a coefficient of thermal expansion (or a coefficient of linear expansion) of 30 × 10 ⁻⁶ (1 / ° C.) as a base layer, and having a higher coefficient of thermal expansion than the base layer above and below. It is preferable that it consists of at least 3 layers of polyimide-type resin layers which arrange | positioned 2 layers (bottom layer and top layer) which consist of resin.

As low thermal expansion polyimide resin which forms a base layer here, the thermal expansion coefficient is preferably ^{30x10 <-6>} (1 / degreeC) or less, and it is good to have the outstanding performance in heat resistance and flexibility of a film. Here, the thermal expansion coefficient was raised to 250 ° C. using a thermomechanical analyzer (TMA) using a sample in which the imidization reaction had been sufficiently completed, and then cooled at a rate of 10 ° C./min, to 240 to 100 ° C. The average thermal expansion coefficient in the range is obtained. As a specific example of the low thermal expansion polyimide resin which has such a property, the polyimide resin which has a unit structure represented by following General formula (I) is preferable.

(Wherein R ₁ to R ₄ represent a lower alkyl group, a lower alkoxy group, a halogen group or hydrogen)

The thermoplastic polyimide resin forming the bottom layer and the top layer used above and below the base layer may have a larger coefficient of thermal expansion than the base layer and a glass transition point temperature of 350 ° C. or less. Preferably, when pressed under heat and pressure, the adhesive strength of the interface is sufficient. 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-based resin herein may not necessarily exhibit sufficient fluidity in a normal state at or above the glass transition point, and includes those capable of being adhered by pressure. As a specific example of the thermoplastic polyimide resin which has such a property, it has a unit structure represented by following formula (II) or formula (III).

(In the above formula, Ar ₁ is a divalent aromatic group and its carbon number is 12 or more.)

(In the above formula, Ar ₂ is a divalent aromatic group and its carbon number is 12 or more.)

Specific examples of divalent aromatic groups Ar ₁ or Ar _2, and the like to an aromatic group for example.

Moreover, as a method of manufacturing the board | substrate for flexible printed wiring of a single-sided conductor, as described in the said patent document 4, hardening | curing agents, such as an acid anhydride type and an amine-type hardening | curing agent known to a polyimide precursor solution or a polyimide solution, a silane coupling agent , A titanate coupling agent, an adhesive imparting agent such as an epoxy compound, and various additives such as a flexible imparting agent such as rubber and the like are added to coat one side of the conductive metal foil. Subsequently, it can thermoset by heat processing and can obtain a single-sided conductor laminated body. Moreover, the laminated body of a single-sided conductor has a thermoplastic polyimide-type resin layer with a larger thermal expansion coefficient than a base layer as a bottom layer in conductive metal foil, and at least 1 sort (s) of low thermally expandable polyimide-type resin layer for an intermediate base layer further, It is preferable to laminate | stack as an outermost upper layer in order of the thermoplastic polyimide resin layer with a larger thermal expansion coefficient than a base layer.

Here, the intermediate base layer must be a polyimide resin layer having a thermal expansion coefficient smaller than that of the thermoplastic polyimide resin layer of the bottom layer or the top layer. The base layer has a function of suppressing the occurrence of curling and warping of the substrate for flexible printed wiring board manufactured, the bottom layer in contact with the conductor has a function of securing adhesion with the conductive metal foil, and the top layer has a curl of the film alone. It is used in anticipation of the action to suppress the Moreover, in some cases, it is also used in anticipation of the effect | action which ensures the adhesiveness in the case of using as a board | substrate for flexible printed wiring boards which is a double-sided conductor by laminating | stacking and heat-compressing other electroconductive metal foil on an upper layer.

At that time, the ratio P _m / (P ₁ of the total thickness of the thermoplastic polyimide resin layers (bottom layer P ₁ and the upper layer P ₂ ) on both sides with respect to the thickness P _m of the low thermally expandable polyimide resin layer (base layer). + P ₂ ) is preferably in the range of 2 to 100, preferably in the range of 5 to 20. When this thickness ratio is smaller than 2, the thermal expansion coefficient of the whole polyimide-type resin layer becomes high compared with the thing of metal foil, the curvature and curl of the board | substrate for flexible printed wiring boards obtained become large, and the workability at the time of circuit processing falls remarkably. In addition, when the total thickness (P ₁ + P ₂ ) of the thermoplastic polyimide resin layers on both sides is too small and becomes so large that the ratio of the thickness exceeds 100, the adhesive force with the conductive metal foil may not be sufficiently exhibited.

It is important that the ratio of the thickness P ₁ of the bottom layer in contact with the conductor and the thickness P ₂ of the upper layer opposite the conductor is P ₁ <P ₂ . The ratio of the thickness varies depending on the thickness of the base layer having low thermal expansion, but is P ₁ / P ₂ = 0.2 to 0.8, more preferably 0.3 to 0.7. If it is smaller than this range, the film curl correction effect is too strong and conversely, curling occurs. On the other hand, if it is larger than this range, the film curl suppression effect is not expressed. In addition, the bottom layer thickness (P ₁₎ in contact with the conductive layer is preferably in the range of 0.2 to 10㎛. When it is thinner than this range, adhesive force with a conductor layer cannot be ensured, and when it is thick, it becomes a cause of heat resistance fall.

Coating of the polyimide precursor resin convertible into these polyimide resins onto the conductive metal foil can be carried out in the form of the resin solution. Preferably, as described in Patent Document 4 above, It is preferable to carry out the heating conversion of the precursor to the polyimide collectively after the desolvation process of collectively or sequential coating of plural precursor solutions, or below imide ring closure temperature. When another polyimide precursor solution is further coated on the layer completely converted to polyimide, and heat-treated by imide closing, the adhesive force between the polyimide resin layers may not be sufficiently exhibited. It causes the deterioration of quality.

The method of coating the polyimide precursor resin solution (polyamic acid solution) or the resin solution containing the precursor compound on the conductive metal foil is, for example, by a known method using a knife coater, a die coating, a roll coater, a curtain coater, or the like. A die coating or a knife coater is suitable for coating thickly. Moreover, although the polymer concentration of the polyimide precursor resin solution used for coating depends also on the polymerization degree of a polymer, it is 5-30 weight% normally, Preferably it is 10-20 weight%. If the polymer concentration is lower than 5% by weight, a sufficient coating thickness is not obtained by one coating. If the polymer concentration is higher than 30% by weight, the solution viscosity becomes too high, making coating difficult.

The polyimide precursor resin solution (polyamic acid solution) coated on the conductive metal foil with a uniform thickness is then subjected to heat treatment to remove the solvent, and further to imide-close the ring. In this case, if the heat treatment is rapidly performed at a high temperature, a skin layer is formed on the surface of the resin, and the solvent is difficult to evaporate or foams. Therefore, the heat treatment is preferably performed while gradually increasing the temperature from the low temperature to the high temperature. As a final heat processing temperature at this time, 300-400 degreeC is preferable normally, At 400 degreeC or more, thermal decomposition of a polyimide starts to arise gradually, and at 300 degrees C or less, a polyimide film is not fully oriented on a conductive metal foil, and planarity is carried out. Good single-sided conductor laminates are not obtained. The total thickness of the polyimide resin layer as the insulator thus formed is usually 10 to 150 m.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely according to an Example and a comparative example. In addition, in the following example, the thermal expansion coefficient, the curl and adhesive force of a single-sided copper cladding, and the curl of a film were measured with the following method.

That is, the thermal expansion coefficient was calculated by calculating the average linear expansion coefficient between 240 ° C and 100 ° C by cooling at a rate of 10 ° C / min after raising the temperature to 250 ° C using a Thermomechanical Analyzer (TMA100) manufactured by Seiko Electronics.

As the curl of the single-sided copper cladding product, after the heat treatment and imidization, the radius of curvature of the copper cladding product having a dimension of 100 mm × 100 mm was measured.

The adhesive force of a single-sided copper cladding product was calculated | required as a value (kg / cm) at the time of peeling copper foil at a speed | rate of 50 mm / min in the direction of 180 degrees using the pattern of conductor width 3mm according to JIS C5016: 7.1.

As hander heat resistance, according to the method of JIS C5016, hander bath temperature was gradually raised at the interval of 10 degreeC from 260 degreeC, and it measured to the maximum 400 degreeC.

In addition, the following symbol was used in the Example and the comparative example.

PMDA: pyromellitic anhydride

BTDA: 3,3 ', 4,4'-benzophenonetetracarboxylic anhydride

DDE: 4,4-diaminodiphenyl ether

MABA: 2'-methoxy-4,4'-diaminobenzanilide

Synthesis Example 1

2532 g of N, N-dimethylacetoamide was added to a glass reactor through nitrogen, followed by 0.5 mol of DDE and 0.5 mol of MABA under stirring, followed by complete dissolution. The solution was cooled to 10 ° C, 1 mole of PMDA was added in small portions so that the reaction solution was maintained at a temperature of 30 ° C or lower, and after completion of the addition, stirring was continued at room temperature for 2 hours to complete the polymerization reaction. The resulting polyimide precursor solution had an apparent viscosity of 1000 mPa · s at 25 ° C. by a polymer concentration of 15% by weight and a type B 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 an apparent viscosity of 300 mPa · s at 25 ° C. by a polymer concentration of 15% by weight and a type B viscometer.

Example 1

Coating the polyimide precursor solution 2 produced in the synthesis example 2 uniformly to the thickness of 20 micrometers using die-coating as a bottom layer on the rough surface of 35 micrometers roll-shaped electrolytic copper foil (made by Nikko Gould, Inc.). After that, the solvent was continuously removed by treatment in a hot air drying furnace at 120 ° C. Next, on the polyimide precursor layer, the polyimide precursor solution 1 prepared in Synthesis Example 1 was uniformly coated with a thickness of 200 μm as a base layer using a reverse roll coater, and continuously in a hot air drying furnace at 120 ° C. After the treatment to remove the solvent, the polyimide precursor solution 2 prepared in Synthesis Example 2 was uniformly applied thereon as an upper layer to a thickness of 40 μm, and then heated in a hot air drying furnace from 120 ° C. to 360 ° C. over 30 minutes. It imidated and obtained the single-sided conductor laminated body (one-sided copper cladding) a which is 25 micrometers in thickness, and has favorable flatness without curvature or curl. However, the starting point of the thickness of the bottom layer was measured as 1/2 of the surface roughness of the rough surface of the conductor. The result of measuring 180 degree peeling strength (JIS C-5016) between the copper foil layer and polyimide resin layer of this single-sided conductor laminated body a was 1.8 Kg / cm. Subsequently, the polyimide film exposed when circuit processing was performed on the conductor side of this single-sided conductor laminate a to remove unnecessary metal foil did not generate curl, and the coefficient of linear expansion of the film after etching was 23.5 × 10 ⁻⁶ (1 / ° C.). Was.

Examples 2 and 3 and Comparative Examples 1 to 3

In Example 1, the thickness of the polyimide resin layer of the bottom layer, the base layer, and the upper layer was changed in various ways, and dried similarly, and then the temperature was raised from 120 ° C to 360 ° C in a hot air drying furnace for 30 minutes to form a single-sided conductor laminate. (Single-sided copper cladding) a was obtained. The state of the curl of the single-sided conductor laminate a, the occurrence of curl, the 180 ° peel strength, and the occurrence of curl of the exposed polyimide film in the case of removing the unnecessary metal foil by carrying out circuit processing on the conductor side and the linear expansion of the film after etching The coefficient etc. are put together in Table 1 and Table 2, and are shown.

The flexible printed wiring board of the present invention and a method for manufacturing the same include a low thermally expandable polyimide having at least one thermal expansion coefficient of 30 × 10 ⁻⁶ (1 / ° C.) or less in the middle of a lower sublayer in contact with a conductor and an upper layer opposite to the conductor. Since the base layer made of a system resin is disposed, and the bottom layer and the top layer are made of a thermoplastic polyimide resin having a coefficient of thermal expansion larger than that of the base layer, there is an industrial applicability of stable quality in which curl does not occur in the film even after processing. Get a high substrate.

Claims (5)

A flexible printed wiring board having a multi-layered polyimide layer having different thermal expansion coefficients on one side of a conductor, wherein at least one thermal expansion coefficient is 30 × 10 in the middle of the bottom layer in contact with the conductor and the upper layer opposite to the conductor. ^A base layer made of a low thermally expandable polyimide resin of ^-6 (1 / ° C) or less is disposed, and the bottom layer and the top layer are made of a thermoplastic polyimide resin having a larger coefficient of thermal expansion than the base layer, and the thickness of the bottom layer is P ₁ and The thickness P ₂ of an upper layer satisfy | fills the conditions of P ₁ <P ₂ , The board for flexible printed wirings characterized by the above-mentioned. The method of claim 1, Of both sides of the bottom layer and the total thickness of the top layer of the thickness of the base layer is not P _{m P m / (P 1 + P} 2) is a flexible printed wiring board to satisfy the range of 2 to 100. The method according to claim 1 or 2, The thickness P ₁ of the bottom layer is in the range of 0.2 to 10㎛, the flexible printed wiring board that ratio of the thickness of the top layer P ₂ P ₁ / P ₂ satisfies the range of 0.2 to 0.8. In the method of manufacturing the board for flexible printed wirings which has a multilayer polyimide layer from which a thermal expansion coefficient differs by directly coating and drying a several layer polyimide precursor resin solution on one side of a conductor, and heat-hardening, the bottom layer which contact | connects a conductor And a base layer composed of at least one kind in the middle of the upper layer on the opposite side of the conductor and converting into a low thermally expandable polyimide resin having a coefficient of thermal expansion of 30 × 10 ⁻⁶ (1 / ° C.) or less, and a base on the bottom layer and the top layer. Coating and drying the polyimide precursor resin solution which can be converted into a thermoplastic polyimide resin having a larger thermal expansion coefficient than the layer so that the thickness P ₁ of the bottom layer and the thickness P ₂ of the top layer satisfy the conditions of P ₁ <P ₂ , followed by heat curing. The manufacturing method of the board for flexible printed wiring characterized by the above-mentioned. The method of claim 4, wherein And a bottom layer thickness of P ₁ is in the range of 0.2 to 10㎛, the flexible printed wiring board that ratio of the thickness of the top layer P ₂ P ₁ / P ₂ is applying a polyimide precursor resin solution so as to satisfy the range from 0.2 to 0.8 Manufacturing method.