JP2728694B2 - Flexible printed circuit board - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improved flexible printed wiring board (hereinafter abbreviated as FPC), and more particularly, to an insulating substrate having dimensional stability against temperature and humidity. Polyparaphenylene terephthalamide (hereinafter, referred to as "polyparaphenylene terephthalamide"), which is extremely excellent in
This is related to an FPC using a film substantially consisting of PPTA).

[Conventional technology]

In recent years, demand for FPCs, which are lighter than ordinary rigid types, have a small occupied volume, and allow free three-dimensional wiring and simplification of wiring, is supported by the persistent need for smaller and lighter electronic devices in recent years.

Conventionally, polyester or polyimide films have been used as insulating base materials for FPCs. However, polyester has no solder heat resistance and is therefore used only for very limited applications. In contrast, polyimide is
Utilizing its excellent heat resistance, it is used in large quantities in FPCs.However, it has disadvantages such as dimensional stability such as heat shrinkage and dissatisfaction in terms of moisture absorption and high cost. I have.

For this reason, the use of various materials instead of polyimide and polyester for the insulating base material of FPC has been studied.

Linear coordination aromatic lamide represented by PPTA is particularly excellent in crystallinity, high melting point, and rigid molecular structure.
It has high heat resistance and high mechanical strength, and is a polymer material that has received special attention in recent years. Particularly, it is a very promising material as an FPC material because of its excellent strength and high melting point with solder heat resistance (Japanese Patent Publication No. 55-37866).

However, conventional PPTA films have the following disadvantages when used as FPC materials.

For example, JP-B-59-14567 discloses a film obtained by extruding an aromatic polyamide solution having optical anisotropy from a slit through a short air layer and into a coagulation bath. Is extremely strong in the machine direction of the film (hereinafter abbreviated as MD direction),
In a direction perpendicular to the direction (hereinafter abbreviated as TD direction), it was extremely weak and easily ruptured, and could not withstand practical use at all. Further, when immersed in a solder bath, undesired phenomena such as film shrinkage, curl generation, and dimensional change were observed.

Also, Japanese Patent Publication No. 57-17886, Japanese Patent Publication No. 57-35088, Japanese Patent Publication No. 59-5407 and Japanese Patent Publication No. 53-44957 describe an almost isotropic PPTA film. However, it was not brittle and brittle, and was not sufficient in dimensional stability (especially stability to humidity).

In order to overcome these drawbacks, JP-A-61-248305 and JP-A-61-18048 disclose extruding an optically anisotropic dope of PPTA to make it optically isotropic and then solidifying it. Therefore, PP with high strength, excellent dimensional stability, and resistant to tearing
A TA film was obtained and the use of such a film for FPC was disclosed. However, even in such a film, further improvement in dimensional stability and suppression of the moisture absorption are required.

Furthermore, Japanese Patent Publication No. 55-37866 discloses that an aromatic polyamide hydrazide film containing PPTA is used for FPC, but once it is large, that is, it has high crystallinity.
PPTA was brittle and impractical, and the other polymers had complaints of high moisture absorption and high heat shrinkage.

[Problems to be solved by the invention]

An object of the present invention is to use PPTA, which can be provided at a lower cost than polyimide because of its simple chemical structure, and to use a film whose dimensional stability and moisture absorption rate are further improved than conventionally known PPTA films. Therefore, even if placed in a high-temperature or high-humidity atmosphere, there is no problem such as warpage or peeling of the copper plate,
There is no problem in providing an FPC that can be used in high-frequency circuits and has high density wiring.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above problems, and as a result, in the process of forming a PPTA film described in JP-A-61-248305, once dried or heat-treated at a high temperature under tension, It has been found that a film having a small moisture absorption rate and extremely excellent dimensional stability against heat and moisture absorption can be obtained by relaxing the tension and heat fixing, and by using this film as an insulating substrate, And found that a high-performance FPC could be obtained.

That is, the present invention provides a substantially poly-logarithmic viscosity of 3.5 or more.
A film made of paraphenylene terephthalamide having a Young's modulus in all directions of 700 kg / mm ² or more and 25 ° C. to 2
The coefficient of thermal expansion up to 50 ° C is (0-15) × 10 ^-6 mm / mm / ° C, 25
Insulates films whose thermal shrinkage at 0 ° C is 0.1% or less, the coefficient of moisture expansion at 25 ° C is 30 × 10 ^-6 mm / mm /% RH or less, and the moisture absorption at 25 ° C 65% RH is 2.5% by weight or less This is a flexible printed wiring board formed by laminating copper on at least one side of the film.

The PPTA used in the present invention is substantially And is conveniently produced from a conventionally known paraphenylenediamine and terephthaloyl chloride by a low-temperature solution polymerization method. In the polymer used in the present invention, a small amount of components other than PPTA may be copolymerized or blended.For example, metaphenylene, 4,4′-diphenylene, 4,4′-diphenylene ether, 3, Aromatic polyamide containing 4'-diphenylene ether and the like, aromatic ring-substituted PPTA and the like can be mentioned as those components.

If the degree of polymerization of the polymer of the present invention is too low, a film having good mechanical properties cannot be obtained. Therefore, the logarithmic viscosity ηinh of 3.5 or more, preferably 4.5 or more (measured at 30 ° C. by dissolving 0.5 g of the polymer in 100 ml of sulfuric acid, at 30 ° C.) The degree of polymerization which gives the given value) is selected.

The film used in the present invention should satisfy the following requirements.

First, the film used in the present invention has a Young's modulus of fragrance in all directions of 700 kg / mm ² or more. This feature has implications for dimensional stability against mechanical external forces.

FIG. 2 shows that the coefficient of thermal expansion of the film used in the present invention was measured in the range of 25 ° C. to 250 ° C. (0 to 15) × 10 ⁻⁶ mm / mm.
/ ° C. Having a coefficient of thermal expansion in this range means that even when heated to temperatures up to 250 ° C,
This means that the length hardly changes. And this figure is close to that of ceramics and slightly smaller than that of metal. Such a film with extremely excellent dimensional stability to heat prevents shrinkage during drying and keeps the plane orientation of molecular chains at a high level, and crystallizes by drying or heat treatment at 350 ° C or higher. Was achieved only by increasing A film having a coefficient of thermal expansion of 5 to 15 × 10 ⁻⁶ mm / mm / ° C. is preferred as the film used in the present invention. In the present invention, since the difference in the coefficient of thermal expansion of the copper film is small, warping and peeling do not occur even in an environment having a high temperature and a large temperature difference.

Third, the film used in the present invention should have a heat shrinkage at 250 ° C. of 0.1% or less. As described above, the heat shrinkage of the film used in the present invention is extremely small, and is superior to the polyimide film which currently occupies a large position as a heat-resistant film. The heat shrinkage is preferably 0.05% or less. The film used in the present invention, having a very low heat shrinkage, is slightly lower than the drying or heat treatment temperature without substantially reducing the orientation and crystallinity enhanced by the drying or heat treatment.
It can be obtained only by heat setting the film at a certain temperature of 250 ° C. or higher under no tension or low tension. As described above, since a film having a small heat shrinkage rate is used in the present invention, for example, even when immersed in a solder melt in an FPC mounting process, there is no warpage, peeling, change in conduction / insulation, etc. .

Fourth, the film used in the present invention has a coefficient of hygroscopic expansion at 25 ° C. of 30 × 10 ⁻⁶ mm / mm /% RH or less. The coefficient of hygroscopic expansion is preferably 20 × 10 ⁻⁶ mm / mm /% RH or less. The characteristic that the dimensional change due to moisture absorption is small as described above, regardless of the seasonal difference between hot and humid summer and low-humidity dry winter,
C is important for exhibiting certain performances and functions, and is achieved by ensuring high crystallinity and orientation by drying or heat treatment at a high temperature.

Further, the film used in the present invention has a moisture absorption at 25 ° C. and 65% RH of 2.5% by weight or less which is provided by unique high crystallinity by high-temperature drying or heat treatment. 2.5% by weight moisture absorption
The use of a larger film has the disadvantage that the electrical characteristics of the FPC (for example, insulation resistance, dielectric constant, dielectric loss tangent, etc.) fluctuate significantly, and the adhesion between copper and the film decreases over time.

The film used in the present invention preferably has the following features in addition to the above essential requirements.

The film used in the present invention preferably has extremely high transparency. High transparency, for example, 60
The transmittance of visible light having a wavelength of 0 nm is preferably 55% or more,
More preferably it has 70% or more.

Further, the film used in the present invention is preferably
Substantially free of voids.

Further, the film used in the present invention usually has a density in the range of 1.370 to 1.405 g / cm ³ . The value of this density is 30 ° C. by a density gradient tube method using carbon tetrachloride-toluene.
It was measured with. This range of densities is known
This is considerably smaller than that of TA fiber, which is in the range of 1.43 g / cm ³ to 1.46 g / cm ³ . When the density is less than 1.370 g / cm ³ , the mechanical properties are reduced. When the density is more than 1.405 g / cm ³ , the film becomes brittle and accordingly tends to be a tough film. In any case, since the density is so small,
A light and high-strength film can be obtained.

In order to obtain such a film used in the present invention, it is necessary to first prepare an optically anisotropic dope of a polymer consisting essentially of PPTA.

A suitable solvent for preparing a dope for use in film forming is sulfuric acid at a concentration of 95% by weight or more. With less than 95% sulfuric acid, it is difficult to dissolve, or the dope after dissolution becomes abnormally high in viscosity. The dope of the present invention may contain a small amount of chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, or the like. Sulfuric acid may be 100% by weight or more, but a concentration of 98 to 100% by weight is preferably used from the viewpoint of the stability and solubility of the polymer.

The concentration of the polymer in the dope is not less than the concentration exhibiting optical anisotropy at room temperature (about 20 ° C. to 30 ° C.) or higher, and specifically, about 10% by weight or more. At a polymer concentration lower than this, that is, a polymer concentration that does not exhibit optical anisotropy at room temperature or higher, the molded film often does not have favorable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 20% by weight or less, particularly preferably 18% by weight or less, particularly preferably 16% by weight or less for a polymer having a high ηinh.

The dope may contain ordinary additives, for example, extenders, delusterants, ultraviolet stabilizers, heat stabilizers, antioxidants, pigments, dissolution aids, and the like.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, for example, the method described in Japanese Patent Publication No. 50-8474, but its critical point is determined by the type of solvent, temperature, and polymer. It depends on the concentration, the degree of polymerization of the polymer, the content of the non-solvent, etc.
By making an optically anisotropic dope and changing the condition to be an optically isotropic dope, it is possible to change from optically anisotropic to optically isotropic.

It is preferable to remove the insoluble dust and foreign matter as much as possible by filtration or the like prior to molding and solidification, and to remove gases such as air generated or entrained during melting. Degassing can be performed after the dope is once prepared, or can be achieved by performing it under vacuum (reduced pressure) consistently from the stage of charging the raw materials for preparation. The preparation of the dope can be performed continuously or batchwise.

The dope thus prepared is cast on a moving supporting surface from a die, for example, a slit die, while maintaining optical anisotropy. In the present invention, the steps of casting and subsequent conversion to optical isotropic, coagulation, washing, stretching, drying and the like are preferably carried out continuously, but if necessary, all or a part of these may be carried out. It may be done intermittently, i.e. in a batch manner.

The method for obtaining a transparent film used in the present invention is to convert the dope from optically anisotropic to optically isotropic prior to solidification after casting the dope on the support surface.

In order to make the optically anisotropic from optical anisotropy, specifically, prior to solidification of the optically anisotropic dope cast on the support surface, the concentration of the solvent forming the absorbed dope is reduced, and the concentration of the solvent is reduced. The dope is transferred to the optically isotropic region by the change of the dissolving ability and the polymer concentration, or the temperature of the dope is raised by heating, and the phase of the dope is transferred to the optically isotropic, or the moisture absorption and the heating are simultaneously performed sequentially. It can be achieved by using them together.

In particular, a method utilizing moisture absorption is useful because it can efficiently optically anisotropy the optical anisotropy and can cause no decomposition of the polymer, including a method using heating in combination.

In order to absorb the dope, air at a normal temperature and humidity may be used, but preferably humidified or heated and humidified air is used. The humidified air may contain water in the form of mist exceeding the saturated vapor pressure, and may be so-called steam. However, supersaturated steam at about 45 ° C. or lower is not preferable because it often contains large granular condensed water. Moisture absorption is usually carried out with humidified air at room temperature to about 180 ° C, preferably 50 ° C to 150 ° C.

In the case of the method by heating, the heating means is not particularly limited, and includes a method of applying humidified air such as steam to the casting dope, a method of irradiating an infrared lamp, a method of dielectric heating, and the like.

The casting dope optically isotropic on the support surface is then subjected to solidification. The coagulating liquid of the dope can be, for example, water, about 70% by weight or less of dilute sulfuric acid, about 20% by weight or less of sodium hydroxide aqueous solution and ammonia water, about 10% by weight or less of sodium sulfate, sodium chloride aqueous solution and chloride. Calcium aqueous solution and the like.

The temperature of the coagulating liquid is preferably 15 ° C. or lower, more preferably 5 ° C. or lower. This is because, generally, it has been found that the lower the coagulating liquid temperature, the smaller the void contained in the film.

Since the coagulated film contains an acid as it is, it is necessary to wash and remove the acid component as much as possible in order to produce a film in which a mechanical substance is hardly reduced by heating. Specifically, it is desirable that the removal of the acid content be performed up to about 500 PPm or less. Water is usually used as the washing liquid, but if necessary, washing may be carried out with warm water, or after neutralizing and washing with an aqueous alkaline solution, followed by washing with water or the like. The cleaning is performed by, for example, running the film in the cleaning liquid or spraying the cleaning liquid.

The washed film is then dried. When the film is placed under no tension due to drying, that is, a decrease in water content, the film generally shrinks.However, in obtaining the film used in the present invention, it is important to not shrink the film in the drying step. It is. Here, the expression “no shrinkage” should be understood to include two things: drying with a fixed length and drying while stretching. Then, for example, the film is stretched only in one direction,
A mode in which the other direction remains at a fixed length is also allowed. It is also important to select a drying temperature, either at an ambient temperature of 350 ° C or higher (T ₁ ° C), or after drying at an arbitrary temperature,
It is carried out by heat treatment at a temperature of not less than ℃ (T ₁ ℃) without shrinkage. Here, drying means removal of water from the film, and the subsequent change of the physical structure (for example, crystal state) of the film is called heat treatment. In any case, it is necessary to perform the fixing of the structure under tension at a temperature T ₁ of the above 350 ° C., this was reduced Yotsute, the hygroscopic expansion coefficient, it is possible to suppress moisture absorption.

After drying or heat treatment at a temperature T ₁ (° C.) of 350 ° C. or more, then T ₂ (° C.) satisfying 250 T ₂ T ₁ -30
In performing the no tension or under a heat treatment under low tension 0~0.8kg / mm ² is also important. This means that the so-called thermal fixation is performed under substantially no tension, and the thermal fixation can reduce the heat shrinkage and can improve the tear resistance as a secondary effect.

In order to perform drying or heat treatment without causing the above-described shrinkage, for example, a method such as inserting a tenter or a metal frame into an oven, and drying under relaxation or low tension is performed in a state where the oven is in a free end state. Lowering the temperature by more than about 50 ° C by using a fixed length or tenter (that is, T ₁ −T ₂ ≧ 50
(° C.)) method, a method of slightly shortening the holding interval of the tenter, or the like. Other conditions relating to drying and heat treatment are not particularly limited, such as a method using a heating gas (air, nitrogen, argon, etc.) or a normal temperature gas, a method using radiant heat such as an electric heater or an infrared lamp, and a dielectric heating method. You can choose freely from the means.

In the method of the present invention, it is one of the preferred embodiments that the film is manufactured while running the film continuously throughout the entire process. However, if desired, the film may be partially batchwise operated. Also, an oil agent, a dye for identification, or the like may be applied to the film in an arbitrary step.

In addition, in order to obtain a film with excellent transparency, that is, a film having an extremely high light transmittance, the dope is, of course, a garbage such as a gas for absorption of moisture, a gas for heating, a support surface, a coagulating liquid, a cleaning liquid, and a dry gas. It is preferable to reduce the content of chile as much as possible. In this regard, producing a film in a so-called clean room or clean water is also a preferred embodiment.

The first object of the present invention is to provide a highly reliable and high-density wiring that is free from degeneration, deterioration, and warpage in a severe environment by using a film having special characteristics obtained by the above method as an insulating substrate. A possible FPC is obtained. However, in order to make full use of the performance of the substrate film, it is necessary to pay sufficient attention in laminating copper.

As a method of laminating copper as a conductor, a method of bonding electrolytic copper foil or rolled copper foil with an adhesive having excellent heat resistance is generally used. The selection and bonding method of the adhesive are important points.

That is, polyimide-based compounds, epoxy-based compounds, and thermosetting polyphenylene oxide-based compounds excellent in heat resistance are preferable examples of the adhesive. The adhesive is generally applied in the form of a solution. In selecting a solvent, it is of course necessary to dissolve the adhesive, but it must not damage the base film. In this respect, the film of the present invention can be said to be an optimal base film without being affected by almost all of these solvents.

(Examples) Examples will be shown below, but these examples are intended to explain the present invention and do not limit the present invention.
Unless otherwise specified in the examples, parts or parts by weight are indicated. Logarithmic viscosity ηinh is 98% sulfuric acid 100ml and polymer 0.
5 g was dissolved and measured at 30 ° C. by a conventional method. For the elongation and Young's modulus, a film sample was cut into a 100 mm × 10 mm rectangle by a constant-speed elongation type
Draw a load-elongation curve 5 times at 0 mm and a pulling speed of 30 mm / min.
It is calculated from this.

To measure the expansion coefficient, use a thermomechanical analyzer, width 5 mm
A sample having a length of 15 mm between the gripping portions was applied with a load of 0.05 kg / mm ² . In the case of the coefficient of thermal expansion, the dimensional change of the sample was measured between 25 and 250 ° C., and the rate of change between 25 and 250 ° C. was calculated by dividing by 225.

On the other hand, in the case of the coefficient of hygroscopic expansion, at 25 ° C.,
After maintaining the relative humidity at 20%, the humidifier was humidified until the relative humidity increased to 80%, and the dimensional change rate during this period was calculated by dividing by 60.

The moisture absorption was calculated from the weight of the film which was left standing at 25 ° C. and 65% relative humidity for 48 hours and the weight of the film obtained by drying the film until it reached a constant weight in a 120 ° C. vacuum dryer. .

The heat shrinkage at 250 ° C. is calculated from a dimensional change at room temperature (25 ° C.) before and after the oven treatment, after applying a tension of 0.05 kg / mm ² and leaving the plate in an oven at 250 ° C. for 30 minutes.

Example 1 A PPTA polymer having a η inh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 11.5% to obtain a dope having optical anisotropy at 60 ° C. When the viscosity of this dope was measured at room temperature,
00 poise. The dope was degassed under vacuum while keeping the dope at about 70 ° C. to facilitate film formation. Also in this case, it had the same optical anisotropy as above, and the viscosity was 4,400 poise. Keep the 1.5m curved pipe from the tank through the filter, through the gear pump to the die at about 70 ° C, 0.1mm x 300mm
From a die having a slit of mm, cast on a tantalum belt polished to a mirror surface, and blow air at about 105 ° C with a relative humidity of about 12% to make the casting dope optically isotropic. Guided into water to solidify. Next, the coagulated film was peeled off from the belt and washed by running in warm water at about 40 ° C. The washed film was stretched 15% each in the length direction and the width direction by a tenter without drying, and then dried with a different tenter at 370 ° C. under a constant length at 370 ° C.

Further, the film was guided to a third tenter, and the clip-shaped grip portion was adjusted so that the grip length in the width direction and the length direction was reduced by 5% each, and heat-fixed at 340 ° C. At this time, the tension in the third tenter was almost 0.

The obtained film had a thickness of 20 μm, ηinh5.1, and a strength of 28.
kg / mm ² , elongation 23%, Young's modulus 760 kg / mm ² , coefficient of thermal expansion 11
× 10 ^-6 mm / mm / ° C, heat shrinkage less than 0.01%, hygroscopic expansion coefficient 21
× 10 ⁻⁶ mm / mm /% RH, moisture absorption 1.5%, light transmittance 76%, density 1.405 g / cm ³ , and a film having isotropic properties.

The above film and 35μ electrolytic copper foil adhesive represented by the following structural formula And heat-pressed at 280 ° C.

 Table 1 shows the characteristics of the EPC thus obtained.

Example 2 A PPTA film was produced in the same manner as in Example 1 except that the third tenter temperature was changed to 320 ° C.

The obtained film had a thickness of 20 μm, an ηinh of 5.0, and a strength of 29.
kg / mm ² , elongation 20%, Young's modulus 890 kg / mm ² , coefficient of thermal expansion 8
× 10 ^-6 mm / mm / ° C, heat shrinkage less than 0.01%, hygroscopic expansion coefficient 14
× 10 ⁻⁶ mm / mm /% RH, moisture absorption 1.8%, light transmittance 74%, density 1.402 g / cm ³ , and a film having isotropic properties.

Adhesive having the following structure with the above film and 35μ electrolytic copper foil And heated and pressed at 220 ° C.

 Table 1 shows the characteristics of the FPC thus obtained.

Example 3 PPTA having ηinh of 4.8 was dissolved in 99.5% sulfuric acid at 12% to obtain a 3,600 poise dope having optical anisotropy at 45 ° C. Degassing,
After filtration, the dope was cast on a tantalum belt from a die having a slit of 0.08 mm × 300 mm.
The casting dope is converted into a transparent optically isotropic dope by blowing air at about 75 ° C. with a relative humidity of about 80%, and then 10% of 0 ° C.
It was coagulated with an aqueous sulfuric acid solution. After peeling the solidified film from the belt, water at room temperature, 2% aqueous sodium hydroxide solution,
Washing was performed in the order of water at about 30 to 40 ° C.

The washed wet film containing about 250-350% water was dried under constant length in a tenter with circulating hot air at 180 ° C.

Next, at the tenter outlet, a 410 ° C hot plate was attached.
The film was subjected to a fixed length heat treatment from above and below the film, and further heat-set by a second tenter kept at 300 ° C. while reducing the holding length by about 8% in the width and length directions. The obtained film had a thickness of 25 μm, ηinh 4.4, a light transmittance of 76%, and a density of 1.401 g / c.
m ³ , strength 31 kg / mm ² , elongation 18%, Young's modulus 780 kg / mm ² , moisture absorption 0.9%, heat shrinkage less than 0.01%, coefficient of thermal expansion 14 × 10 ^-6 m
The film had isotropic properties of m / mm / ° C. and a coefficient of hygroscopic expansion of 10 × 10 ⁻⁶ mm / mm /% RH.

The above film and a 35 μm electrolytic copper foil were heat-pressed at 220 ° C. with the same adhesive as in Example 2. Table 1 shows the characteristics of the obtained FPC.

[Effect of the Invention] The FPC of the present invention has extremely excellent dimensional stability against temperature and humidity. It also has a low moisture absorption and is tough.

Therefore, even in a severe environment such as high temperature, high temperature and high humidity, and cold, deformation, warping, peeling, etc., of course, do not cause a failure and high reliability. Also, it is excellent in adaptability to a high frequency circuit, and high density wiring is possible.

In addition, various properties required for FPC, such as solder heat resistance, flexibility, chemical resistance, electrical properties, etc. It is.

Further, the FPC of the present invention has an advantage that it can be provided at a lower cost than the conventional FPC made of polyimide.

Therefore, the FPC of the present invention can be used for various electronic devices, cameras, clocks, and the like by utilizing these features.

Claims (1)

(57) [Claims] A film consisting essentially of poly-paraphenylene terephthalamide having a logarithmic viscosity of 3.5 or more,
All direction Young's modulus 700 kg / mm ² or more, 250 ° C. from 25 ° C.
Thermal expansion coefficient up to (0-15) × 10 ^-6 mm / mm / ℃, 250 ℃
A film having a heat shrinkage of 0.1% or less at 25 ° C., a coefficient of moisture expansion at 25 ° C. of 30 × 10 ⁻⁶ mm / mm /% RH or less, and a moisture absorption at 25 ° C. of 65% RH of 2.5% by weight or less is used as an insulating substrate. And a flexible printed circuit board formed by laminating copper on at least one side of the film.