JPH0687368B2 - Flexible printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention relates to an improved flexible printed wiring board (hereinafter abbreviated as "EPC"), and more specifically, to an insulating substrate with excellent surface orientation. Polyparaphenylene tetraphthalamide (hereinafter PPTA), which has extremely high strength in the same direction and has excellent dimensional stability and solder heat resistance.
Abbreviated) is related to the EPC using the film.

“Conventional technology” In recent years, supported by the persistent need for smaller and lighter electronic devices, the demand for EPCs that are lighter and have a smaller occupied area than ordinary rigid types, and that enable free wiring and simplification It is rising.

The linear coordination aromatic polyamide represented by PPTA is particularly excellent in crystallinity, high melting point, and rigid molecular structure,
It is a polymer material that is heat-resistant and has high mechanical strength, and has recently received special attention. In particular, it is an extremely promising material as an EPC material because of its excellent strength and high melting point with solder heat resistance.

However, the conventional PPTA film has large strength and structural anisotropy. For example, in JP-B-59-14567, an aromatic polyamide solution having optical anisotropy is coagulated from a slit through a short air layer. A film obtained by extrusion into a bath is disclosed. When this film is used as an EPC, it is extremely strong in the machine direction of the film (hereinafter abbreviated as MD direction), but in a direction orthogonal to it (hereinafter abbreviated as TD direction). It was extremely weak and easy to tear, and could not be put to practical use at all. Further, when immersed in a solder bath, undesired phenomena such as film shrinkage, curling, and dimensional change were also observed.

“Problems to be solved” As described above, the optically anisotropic dope of PPTA has a domain structure in which polymers are aggregated as a liquid crystal. Therefore, when the dope is formed into a film, a slight shearing force is applied to the direction in that direction. A high degree of molecular orientation occurs, and as a result, the EPC using the film as an insulating substrate easily tears in the MD direction and also has poor dimensional stability.

If an attempt is made to avoid this by using an optically isotropic dope, a useful high molecular weight PPTA polymer will have an extremely high viscosity, and film formation will be impossible unless the polymer concentration is about 5% by weight or less. Films made from isotropic dopes are apt to form voids during solidification, and their mechanical properties are completely inadequate, so they cannot be used for EPC.

Using PPTA whose fibers have already been industrially produced, it has been oriented sufficiently not only in the MD direction but also in the TD direction.As a result, it has high strength and modulus in both length and width, and a film with excellent dimensional stability. As described above, the EPC as a base has not been realized by the conventional technology.

An object of the present invention is to provide an EPC having such preferable characteristics.

“Means for Solving Problems” As a result of intensive studies for solving the above problems, the present inventors have found that in the film formation process of a PPTA film, the dope formed into a film is subjected to a specific treatment to obtain a film. By using a film obtained by controlling the density and surface orientation of the film within a certain range as an insulating substrate, the following novel EPC has been found to solve such problems, and the present invention has been completed. .

That is, the present invention is substantially PPTA having a logarithmic viscosity ηinh of 2.5 or more.
Film having a density of 1.365 to 1.405
, The crystal orientation angle of the (200) plane due to the X-rays incident at right angles to the film surface is 70 ° or more, and the crystal orientation angle of the (010) plane due to the X-rays incident on the film surface in parallel is 60 degrees. The present invention relates to an EPC in which a film having a surface orientation of not more than ° is used as an insulating substrate and copper is laminated on at least one surface of the film.

The PPTA used in the present invention is substantially It is a polymer represented by the following formula and is conveniently produced from a conventionally known paraphenylenediamine and terephthaloyl chloride by a low temperature solution polymerization method.

The degree of polymerization of the polymer of the present invention is too low to obtain an EPC having good mechanical properties, which is the object of the present invention. Therefore, the logarithmic viscosity ηinh of 2.5 or more, preferably 3.5 or more (polymer 0.2 g in 100 ml of sulfuric acid). (Measured and measured at 30 ℃)
The degree of polymerization is selected so that

The EPC base film of the present invention can achieve its purpose only when the following two requirements are satisfied.

First of all, the density must be in the range 1.365 to 1.405. This is considered to be much smaller than that of the known PPTA fibers, which is in the range 1.43 to 1.46. The reason for this is not clear, but it is conceivable that microscopic intermolecular gaps occur and the density becomes smaller than that of the uniaxial orientation, probably due to the plane orientation described later. Density is
If it is less than 1.365, the mechanical properties will deteriorate, and if it exceeds 1.405, the film will have a deteriorated plane orientation. In any case, such a small density means that a lighter weight and higher density EPC can be obtained by the present invention. The density was measured at 30 ° C. by a known density gradient tube method using carbon tetrachloride-toluene.

Secondly, the base film for EPC of the present invention must have the plane orientation defined by the crystal orientation angle by X-ray diffraction, which will be described below. That is, the crystal orientation angle of the (200) plane by the X-ray incident at right angles to the film surface is 70 °.
As described above, the crystal orientation angle of the (010) plane by the X-rays incident on the film surface in parallel must be 60 ° or less.

As shown in the drawing, the X-rays are divided into two types: one is incident on the film surface at a right angle (hereinafter referred to as TV direction) and the other is incident on the surface in parallel (hereinafter referred to as SV direction).

The crystal structure of PPTA has been widely discussed, for example, Takayanagi et al. [J. Appl. Polym. Sci., 23, 915 (197).
9)] The film of the present invention has a large diffraction peak at 2θ≈23 °, which is reflection of the (200) plane by X-rays from the TV direction, and the crystal orientation angle at 2θ≈23 ° must be 70 ° or more. . That is, it appears almost as a Debye ring in the diffraction photograph.

Furthermore, it is the reflection of the (010) plane due to the incidence from the SV direction. 2
A large diffraction peak of θ≈18 ° appears on the equator line, but the crystal orientation angle at 2θ≈18 ° must be 60 ° or less. It can be said that the film of the present invention has a structure of plane orientation only when both of these crystal orientation angles are satisfied, and a film having a crystal orientation angle outside this range cannot be said to have plane orientation. As a result, the EP, which is the object of the present invention, has high mechanical properties in both MD and TD.
I can't get C.

A known method can be adopted as a method for measuring the crystal orientation angle,
For example, do as follows. The diffraction intensity curve is obtained by placing the counter tube at a predetermined 2θ angle and rotating the film by 180 °. In this case, the maximum strength is the center and 90 ° before and after that
It is desirable to rotate between. The value, in degrees, of the arc length in the diffractogram, which corresponds to the point showing half the intensity with respect to the baseline drawn between the highest and lowest intensity points of this curve, that is, 50% with respect to the highest intensity baseline.
The angle with respect to the point is measured, and this is taken as the crystal orientation angle of the sample. If necessary, several films may be overlapped to measure the diffraction intensity.

When the cross section of the torn film of the present invention was observed with a scanning electron microscope, a layered structure parallel to the film surface was observed, which is also considered to be a fact that supports the plane-oriented structure of the base film for EPC of the present invention. To be done.

As a solvent suitable for adjusting the dope used in molding the PPTA film of the present invention, sulfuric acid having a concentration of 98% by weight or more,
It is chlorosulfuric acid, fluorosulfuric acid or a mixture thereof. Sulfuric acid may be 100% or more, that is, fuming sulfuric acid, trihalogenated acetic acid and the like may be mixed in a range not impairing the effects of the present invention.

The polymer concentration in the dope used in the present invention is at room temperature (about
It is preferably used at a concentration not lower than 20 ° C. to 30 ° C.) or higher and at which optical anisotropy is exhibited, specifically at about 10% by weight or more, preferably about 12% by weight or more. If the polymer concentration is less than this, that is, the polymer concentration does not show optical anisotropy at room temperature or higher, the molded PP
TA films often lose their desirable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 25% by weight or less, and particularly high ηinh of P
20 wt% or less is preferably used for PTA.

Whether the dope has optical anisotropy or optical isotropy is determined by Japanese Patent Publication No. Sho 50.
Although it can be investigated by the method described in JP-A-8474, its critical point depends on the type of solvent, the temperature, the polymer concentration, the degree of polymerization of the polymer, the content of the non-solvent, etc., so the relationship between them is investigated in advance. As a result, an optically anisotropic dope can be produced.

The dope of the present invention may be mixed with usual additives such as extenders, delusterants, UV stabilizers, heat stabilizers, antioxidants, pigments and solubilizers.

The PPTA film to be the base film for EPC of the present invention is preferably formed by the following method using the above-mentioned optically anisotropic dope.

First, an optically anisotropic dope is uniformly cast on a glass plate, a metal plate, or a supporting surface such as a rotating drum in which a part is immersed in a coagulation bath. It is an important feature for obtaining the film of the present invention that the film-like dope is converted from optical anisotropy to optical isotropic prior to solidification.

The method of changing the optical anisotropy to isotropic is not particularly limited, but it can be achieved, for example, by heating a film-like optically anisotropic dope on the supporting surface after absorbing moisture or while absorbing moisture. Although the mechanism for making the optical isotropic by such a method is not necessarily clear, in addition to the reduction of the optically anisotropic region of the dope due to moisture absorption, the temperature of the dope is raised by heating, and the phase of the dope is changed. This is probably because it is optically isotropic.

Absolute humidity 1g (water) / K
It can be achieved by passing it through an atmosphere of g (dry air) or more, preferably 3 g (water) / Kg (dry air) or more and a relative humidity of 99% or less. In addition, the idea of more aggressively humidifying the normal humidity atmosphere is to lower the heating temperature and shorten the time until it becomes optically isotropic.
This is the preferred embodiment.

The heating conditions depend on the polymer concentration, the degree of polymerization of the polymer, the solvent concentration, the thickness of the dope, and the degree of moisture absorption, but usually 45 ° C or higher is preferably used.
Further, the upper limit temperature is preferably not so high in general from the viewpoint of polymer decomposition, and is preferably selected so that the temperature of the film-shaped dope does not exceed 200 ° C.

Usable as the coagulating liquid are, 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 50% by weight or less of sodium chloride aqueous solution and calcium chloride aqueous solution. . The temperature of the coagulation bath is not particularly limited and is usually in the range of about -5 ° C to 50 ° C.

Since the solidified film contains 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 mechanical properties are not significantly deteriorated by heating.

The removal of acid content is specifically about 5000 ppm or less, preferably 5 ppm or less.
Should be done to below 00ppm.

Although water is usually used as the cleaning liquid, if necessary, warm water may be used, or neutralization cleaning with an alkaline aqueous solution may be performed, followed by cleaning with water or the like. As the cleaning method, the film may be run in the cleaning liquid, or the cleaning liquid may be sprayed.

The washed film then needs to be dried.
Here, drying means not only removing the cleaning liquid adhering to the film but also heat fixing, and drying under an atmosphere of a heated inert gas such as air, nitrogen, or argon, on a heating roll. The drying may be carried out in a heat atmosphere in a tenter. The drying is preferably carried out under tension or under a fixed length while limiting the shrinkage of the film.

The drying temperature is not particularly limited, but a high temperature is preferable in order to make the mechanical strength effective, and 200 ° C. or higher, in order to obtain dimensional stability when immersed in a solder bath as FPC. Is used at a temperature of 250 ° C. or higher.

The maximum temperature for drying is not particularly limited, but if considering the drying energy and the degradability of the polymer, it is 500 ° C.
The following is used:

By using the PPTA film having the density and the plane orientation in a certain range obtained by the above method as an insulating substrate, for the first time, the extremely high mechanical strength in the MD and TD directions, which is the object of the present invention, can be obtained. In addition, EPC having excellent solder heat resistance and dimensional stability can be obtained. However, in order to make full use of the performance of this substrate film, it is necessary to pay sufficient attention when laminating copper.

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

That is, as the adhesive, polyimide-based compounds and epoxy-based compounds having excellent heat resistance are preferable examples. The adhesive is generally applied in the form of a solution, and it is of course necessary to dissolve the adhesive when selecting a solvent, but it should not attack the base film. In this respect, PPTA film is the most suitable base film without being attacked by almost all of these solvents.

Examples will be shown below, but these examples are for explaining the present invention and not for limiting the present invention. In the examples, unless otherwise specified, parts by weight or% by weight.
Indicates. The logarithmic viscosity ηinh is 0.2 g of polymer in 100 ml of 95% sulfuric acid.
Was dissolved and measured at 30 ° C. by a conventional method. The viscosity of the dope is B
It was measured at a rotation speed of 1 rpm with a type viscometer. The film thickness was measured with a dial gauge having a measuring surface with a diameter of 2 mm. The strength and modulus are 100mm x 10mm for film samples by a constant-speed elongation type elongation measuring machine.
It was calculated by drawing a load-elongation curve of 5 sheets at the initial gripping length of 30 mm and pulling speed of 30 mm / min.

Reference Example PPTA was obtained by the low temperature solution polymerization method as follows. Japanese Examined Japanese Patent Sho 53
-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine was dissolved in 1000 parts of N-methylpyrrolidone. After cooling to 8 ° C., 91.4 parts of terephthalic acid dichloride was added all at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese, so the polymerization reaction product was discharged from the polymerization device according to the method described in JP-B-53-43986 and immediately transferred to a twin-screw closed type kneader. The polymerization reaction product was pulverized therein.
Next, the finely pulverized product was transferred into a Hensiel mixer, added with approximately the same amount of water and further pulverized, then washed several times in warm water and dried in hot air at 110 ° C. 95 parts of a pale yellow PPTA polymer having an ηinh of 6.5 was obtained. The polymers with different ηinh are the ratios of N-methylpyrrolidone and monomers (paraphenylenediamine and terephthalic acid dichloride),
Alternatively, it can be easily obtained by changing the ratio between the monomers.

Example 1 PPTA having ηinh of 5.0 was added to 99.7% sulfuric acid to have a polymer concentration of 13.0%.
It was dissolved at 50 ° C. to obtain a dope with optical anisotropy. The viscosity of this dope at room temperature was 14,000 poise. Place the dope in a beaker for about 70 minutes to facilitate film formation.
Kept at ℃. Even at that time, the dope shows optical anisotropy and the viscosity is
It's 4000 poise. This dope was applied onto a glass plate at 30 ° C. with an applicator having a step of 0.1 mm.
This glass plate, absolute humidity 8.7g (water) / Kg (dry air)
It was left in the atmosphere kept at 60 ° C while keeping it warm.

After 2 minutes, the dope was converted to a transparent optically isotropic dope, and the glass plate was immersed in a water bath at 10 ° C. The film thus solidified was washed with water, then the periphery was fixed to a metal frame, and dried in an air oven at 250 ° C. for 30 minutes.

The thickness of this transparent film is 22μ and the density is 1.39.
8. The orientation angle of the (200) plane in the TV direction was 96 °, and the orientation angle of the (010) plane in the SV direction was 44 °. Tensile strength at break MD direction, respectively in the TD direction ^{21.1Kg / mm 2, 20.2Kg / mm} 2, Mojiyurasu are each ^{457Kg / mm 2, 434Kg / mm} 2, ηinh of the film is 4.4
It was.

An adhesive with the above film and 35μ electrolytic copper foil represented by the following structural formula Was used for thermocompression bonding at 280 ° C.

The characteristics of the FPC thus obtained are shown in Table 1.

Example 2 PPTA having an ηinh of 6.2 was dissolved in 99.6% sulfuric acid so that the polymer concentration became 14.0% at 60 ° C. This dope exhibited optical anisotropy at 80 ° C. and its viscosity was 3300 poise. Put this dope in a tank kept at 80 ℃, and then through the gear pump from the tank to the die, keep a 1.5m curved tube at 80 ℃
I cast from a die with a slit of 00mm to a moving Hastelloy belt polished to a mirror surface. On this belt, after keeping it in the air of absolute humidity 7.0g (water) / Kg (dry air) at 20 ° C for 35 seconds, it was passed through the zone blowing hot air of 140 ° C for 4 seconds, An optically isotropic transparent dope was obtained. The dope was solidified on the moving belt with water at 5 ° C., washed with water, neutralized with 5% aqueous sodium hydroxide solution and washed with water repeatedly to adjust the concentration of the acid content to 400 ppm.

The thickness of the transparent film obtained by drying this wet film at 300 ° C for 20 minutes in a fixed length was 18μ, and the density was 1.387.
The orientation angle of the V direction (200) plane was 84 °, and the orientation angle of the SV direction (010) plane was 46 °. Tensile strength at break MD direction, respectively 24.9 kg / mm ² in the TD direction, 25.6 kg / mm ^2, each of Mojiyurasu 60
It was 6 Kg / mm ² and 568 Kg / mm ² , and the film ηinh was 5.5.

Adhesive with the following structure with the above film and 35μ electrolytic copper foil Was used for thermocompression bonding at 220 ° C.

The characteristics of the FPC thus obtained are shown in Table 1.

Example 3 When the same dope as in Example 2 was used and cast on the belt by the same film forming apparatus and then moved in the air of the same atmosphere, the absolute humidity was about 14 g (water) / by a commercially available humidifier.
While running in a box adjusted to Kg (dry air) for 15 seconds, the speed from the cast point to the hot air zone was the same as in Example 2 for 35 seconds, and then in the zone for blowing hot air at 70 ° C. After passing for 4 seconds, an optically isotropic transparent dope was obtained. The subsequent steps of coagulation, washing with water, neutralization, washing with water and drying were carried out in exactly the same manner as in Example 2. The properties of the obtained film were as follows: thickness 18 μ, density 1.383, TV (200) plane orientation angle. The orientation angle was 84 ° and the SV direction (010) plane was 43 °. Tensile strength at break MD direction, respectively 26.5 kg / mm ² in the TD direction, 26.3Kg / mm ^2, Mojiyurasu 62
It was 0 Kg / mm ² , 563 Kg / mm ² , and the film ηinh was 5.7.

The above film and 35 μm electrolytic copper foil were heat-pressed at 220 ° C. with the same adhesive as in Example 2. First, the characteristics of the obtained FPC
Shown in the table.

Comparative Example 1 In Example 2, instead of casting on the belt,
Coagulated directly into 5 ° C. water through a 1 cm air layer. The subsequent treatment was carried out in the same manner as in Example 2, and the obtained opaque film had a thickness of 24 μ and a density of 1.416, and the direction of TV (200)
The orientation angle of the plane was 44 °, and the orientation angle of the SV direction (010) plane was 57 °. Tensile breaking strength is 26.0 in MD and TD respectively
Kg / mm ² , 3.4Kg / mm ² , Modules are 647Kg / mm ² , 551K respectively
It was g / mm ² , and the film ηinh was 5.6.

Although this film was easily torn in the MD direction and difficult to handle, copper was laminated in the same manner as in Example 2.
FPC. However, when this FPC was dipped in a solder bath at 260 ° C and pulled up, it curled and could not become an FPC.

"Effects of the Invention" As shown in the examples, the FPC of the present invention is extremely balanced in the MD direction and the TD direction, and is a base film having a high strength and modularity not found in commercially available films.
It shows good mechanical properties supported by PPTA film. Furthermore, it is shown in the examples that various properties required for FPC, such as solder heat resistance, thermal dimensional stability, flexibility, chemical resistance, and electrical properties, are extremely excellent in many respects. That's right.

[Brief description of drawings]

The drawing shows X for PPTA film when determining the crystal orientation angle.
The incident direction of the line is shown.

Claims (1)

[Claims] 1. A film consisting essentially of polyparaphenylene terephthalamide having a logarithmic viscosity η inh of 2.5 or more, the density of which is in the range of 1.365 to 1.405, which is measured by X-rays which are incident on the film surface at a right angle. The crystal orientation angle of the (200) plane is 70 ° or more, and X is incident on the film surface in parallel.
A substrate for flexible printed wiring, comprising a film having a plane orientation in which the (010) plane crystal orientation angle of the line is 60 ° or less as an insulating substrate and copper is laminated on at least one side of the film.