JPH02127438A - Vertically orientated polyimide film - Google Patents

Abstract

PURPOSE:To obtain the title film useful as insulating layer, etc., having low linear thermal coefficient of expansion in the direction perpendicular to film face and high coefficient of thermal conductivity, comprising a polyimide having a specific repeating unit wherein molecular chain of the polyimide is orientated in the direction perpendicular to film face. CONSTITUTION:The aimed film comprising a polyimide having a repeating unit shown by formula I (Ar1 is tetrafunctional aromatic group; Ar2 is bifunctional aromatic group) wherein molecular chain of the polyimide is orientated in the direction perpendicular to film face. In production of the film, for example, preferably a solution of a polyamic acid is made into a cast film, which is heat-treated under <=0.1MV/cm field strength at >=150 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to polyimide, which is known as a heat-resistant resin, and is used in environments with significant temperature differences such as extremely low temperatures and high temperatures, and has excellent shape stability and This is a material that is used in industrial fields related to electronic components, where reliability is strongly required. The present invention relates to an insulating film, and more specifically, to an insulating film that has a small coefficient of linear expansion in a direction perpendicular to the film surface of the insulating film, a high thermal conductivity, and can absorb thermal strain in a direction parallel to the surface of the insulating film.

[Conventional technology]

Polyimide is known to have excellent properties such as heat resistance, chemical resistance, electrical properties, mechanical properties, and other properties.For example, 2 g of pyromellitic acid and 4.4'- Polyimide membranes obtained from diaminodiphenyl ether have been widely used. However, it is known that they generally have a large coefficient of linear expansion, poor thermal dimensional stability, and extremely poor thermal conductivity.

In recent years, with the increasing integration and density of electronic components, not only the wiring inside IC chips, but also the wiring inside IC chip mounting boards and the wiring inside input/output cables are becoming thinner. Important problems include contact failure due to slight thermal strain due to differences in linear expansion coefficients of constituent materials between boards and between boards and input/output cables, and temperature rise of elements due to heat generated by IC chips. In addition, in the field related to superconductivity, the quench phenomenon unique to superconductivity (a phenomenon in which a superconducting face changes to a normal conductive state due to some abnormality and suddenly heats up and the normal conductive region expands) is a problem. It has become.

[Problem to be solved by the invention]

To solve these problems, there is a strong need for the development of #thermal insulating materials with low thermal distortion and excellent thermal conductivity.

An object of the present invention is to provide a heat-resistant insulation pattern that can alleviate thermal strain caused by a difference in coefficient of linear expansion between different materials and has excellent thermal conductivity.

[Means to solve the problem]

To summarize the present invention, the present invention relates to a vertically aligned polyimide film, and includes the following - Shipman I: (wherein Ar1 is a tetravalent aromatic group, and Arc is a divalent aromatic group. A polyimide having a repeating unit represented by (shown), which is characterized in that the molecular chains of this polyimide are oriented perpendicular to the membrane surface.

Examples of the tetravalent aromatic group represented by Arl in the above-mentioned - Shipman I include: and examples of the divalent aromatic group represented by Ar2 include. These combinations are not limited to one set, but it is also possible to mix and use two or more combinations.

As is generally seen in crystalline polymers such as polyethylene, a polymer material in which molecular chains are uniaxially oriented can be easily obtained by stretching.

The tensile modulus of elasticity in the orientation direction of such -axially oriented polymers increases rapidly with the stretching ratio, while the linear expansion coefficient decreases rapidly with the stretching ratio, changing from zero to a negative value. , Ward (I.

M, Ward) IJ! , development, ments
In Oriented Polymers-1 (Develo
Polymer
s-1), Applied Sciences (London), Line I (1taz)), Qa The thermal conductivity in the direction of force increases with the stretching ratio CC, L, Choy (C, L, Choy)
f'i or journa μop polymer science polymer physics 7. zdiV x;17 (J,
Polym, Sci, Polym, Phya.

Ha, Volume 18, Page 1187 (1980)).

For example, the tensile modulus of high-density polyethylene changes from I GPa in an unstretched state to 703 Pa at a stretching ratio of 30 times.
The coefficient of linear expansion is zero at a stretching ratio of 2x from the unstretched state t2x10-'x4, and -1.2x10 at a stretching ratio of 18x.
It becomes K. Thermal conductivity is αOQ in unstretched state 5
From 5 W/aaK to 113 at a stretching ratio of 25 times
W/aaK significantly increased to 4. However, it is well known that the above characteristics in the direction perpendicular to the orientation direction exhibit slightly opposite trends.

Therefore, in the vertically oriented polyimide according to the present invention,
Because the molecular chains of polyimide are oriented perpendicular to the membrane surface! ! The tensile modulus in the direction perpendicular to one plane is large, the coefficient of linear expansion is small, and the thermal conductivity is large.

The present invention will be explained in detail below.

The polyimide represented by the general formula I of the present invention can be produced, for example, by the following method. That is, a cast film of a solution of a polyamic acid having a repeating unit represented by the following general 2H: (wherein Ar1 and Arc have the same meanings as defined in formula 1) is cast under an electric field strength of 11 MV/aw or more. K by heat treatment at a temperature of 150°C or higher.

Polyamic acid, which is a precursor of polyimide, can be produced by a known method. That is, it is obtained by using substantially equimolar amounts of the acid anhydride component and the diamine component and polymerizing them in an organic polar solvent. A cast film of polyamic acid can be obtained by applying this polyamic acid solution onto a substrate such as glass and then drying it at 120° C. for 1 hour.

When this cast film was observed under a polarizing microscope from a direction perpendicular to the film surface with the polarizer and analyzer perpendicular to each other, it was found to be in an extinction state where no light was transmitted, and the conoscopic image was clearly visible. It was observed that This indicates that in the cast film of polyamic acid, the molecular chains of polyamic acid are oriented perpendicularly to the film surface.

Polyimide can be produced by a chemical method such as dehydrating a cast film of polyamic acid by immersing it in a solvent containing a dehydrating agent at a stoichiometric or higher level and, if necessary, a catalytic amount of tertiary amines, or by using a dehydrating agent. It can be obtained by thermally dehydrating and ring-closing the polyamic acid without the addition of polyamic acid, but during the dehydration and ring-closing process of this polyamic acid, the vertically oriented polyamic acid transforms into a plane-oriented polyimide in which the molecular chains are parallel to the membrane surface. I knew it would change.

Figure 1 shows the thickness obtained by polymerizing pyromellitic dianhydride as the acid anhydride component, 4,4'-diaminodipheniμ ether μ as the diamine component, and N,N-dimethylacetamide as the solvent. 7- A diagram showing the change in the amount of transmitted light of polarized light (arbitrary scale 1 vertical axis) and polyimidation rate (%, vertical axis) as the temperature (°C, horizontal axis) increases in a polyamic acid cast film μ of (L/Jm) The polyimidation rate is 1 780 cm in the infrared absorption spectrum N.
-'' was determined from the absorbance of the absorption based on the stretching vibration of the force μ-bonyl group in the polyimide ring.It is almost in a quenching state from room temperature to around 140°C, but suddenly becomes transparent at around 150°C. It was found that a sudden change in orientation occurred from vertical orientation to planar orientation.The polyimidation rate was 120
3% at 150°C, 42% at 180°C, and 92% at 180°C, and the orientation change around 9.150°C is due to polyimidization.

It was found that the change in orientation from a vertically oriented polyamic acid cast film to a planarly oriented polyimide film can be controlled by an electric field. That is, it was found that polyimidization occurs while the vertical alignment state is maintained when heat treatment is performed while an electrostatic field is applied. As for the electric field strength, the vertical alignment state is partially maintained at l 10 Mv/es, but the almost vertical alignment state is maintained at α20 M'v/ex, and it is likely that α25 Mv/-
It was found that heat treatment can be carried out under the above electric field strength.

The degree of such vertical alignment can be qualitatively determined by observing a conoscopic image.

In addition, in the dehydration ring closure process of polyamic acid, shrinkage occurs due to dehydration. Since the vertical orientation of the molecular chains is maintained during heat treatment under an electrostatic field, the tensile modulus in the direction perpendicular to the film surface is large, but the tensile modulus in the in-plane direction is small. Therefore, it contracts exclusively in the plane direction and becomes an aggregate of vertically oriented polyimide crystal blocks. Voids are formed at the boundaries of this crystal mass due to contraction. This void serves to absorb thermal strain in the plane direction. On the other hand, the coefficient of linear expansion in the direction perpendicular to the film surface is small because the molecular chains of polyimide are oriented perpendicularly, and the thermal conductivity is large.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

Example 1 Commercially available 4,4'-diaminosopheneyete Ivt15
f1 Sublimated purified pyromellitic dianhydride L 30 f
Commercially available N,N-dimethymoacetamide 15- was charged into a glass container equipped with a nitrogen gas introduction tube, and polycondensation was carried out at room temperature for 4 hours while stirring with a magnetic stirrer.

Next, the above polyamic acid solution was applied onto sulfide glass using a spin coater and dried at 120° C. for 1 hour to obtain a polyamic acid cast film with a thickness of 40 μm. When this cast film was observed using a t<i optical a microscope, a clear conoscopic image was observed.

That is, it was confirmed that the molecular chains of polyamic acid were oriented perpendicularly to the film surface. Next, this cast film was sandwiched between slide glass plates with transparent electrodes, and
Heat treatment was performed at 300° C. for 30 minutes under vacuum under an electrostatic voltage of kV, ie, an electric field strength of Q, 10 MV/am. When the polyimide film thus obtained was observed using a polarizing microscope, conoscopic images were partially observed. That is, it was confirmed that there were portions in which the molecular chains of polyimide were oriented perpendicularly to the single plane. Electric field strength 0.10'
In hlV/rx, the vertical alignment state was only partially maintained.

Example 2 The polyamic acid solution of Example 1 was applied onto sulfide glass using a spin coater, and dried on an iron plate at 120'C for 1 hour to obtain a cast film of polyamic acid with a thickness of 20 pm.

Next, this cast film was sandwiched between slide glass plates with transparent electrodes, and the film was placed under an electrostatic voltage of (L4 kV, that is, (1
Heat treatment was performed at 300° C. for 30 minutes under vacuum with an electric field strength of 20 MV/c1 m. When the polyimide film thus obtained was observed under a polarizing microscope, a conoscopic image was observed. In other words, it was confirmed that the polyimide molecular chains were oriented perpendicular to the membrane surface. Electric field strength (L20M
In V151, the vertical alignment state was maintained almost entirely.

Example 3 The polyamic acid solution of Example 1 was applied onto sulfide glass using a spin coater, and dried at 120° C. for 1 hour to obtain a polyamic acid cast film with a thickness of 20 μm. This cast film was then sandwiched between slide glass plates with transparent electrodes and heated at 300° under vacuum under an electrostatic voltage of 0.5 kV, that is, under an electric field strength of 125 MV/ex.
It was heat-treated at C for 30 minutes. When the polyimide film thus obtained was observed using a polarizing microscope, a clear conoscopic image was observed throughout. That is, it was confirmed that the polyimide molecular chains were oriented perpendicularly to the membrane surface. At an electric field strength CL of 25 M'v/es, the vertical alignment state was maintained as a whole.

Example 4 The polyamic acid solution of Example 1 was thickly applied onto the rough surface of a commercially available electrolytic steel foil with a thickness of 55 μm for use in printed circuit boards with one side roughened, and dried at 120"C for 1 hour. Thickness 80μm
A cast film of polyamic acid was obtained. continue,
The above-mentioned electric field steel foil was laminated on top of this copper-clad Sicast film so that its rough surface was in contact with the copper-clad Sicast film, and was heated at 500°C under vacuum under a D voltage of 2kV, that is, under an electric field strength of 0.25λCV 7cm. It was heat-treated for 50 minutes. The linear expansion coefficient and thermal conductivity of the parallel plate conductor using the vertically oriented polyimide film thus obtained as insulation 1 were measured. The coefficient of linear expansion in the direction perpendicular to the conductor plane is zero, and the coefficient of linear expansion in the direction parallel to the conductor plane is the same as that of metallic copper t 4 × 10 = K”
”, and the thermal conductivity in the direction perpendicular to the conductor surface is α01W
/ It was in Tan. Also, liquid nitrogen temperature (-196゛C)
Even when heat cycling was repeated between 250° C. and 250° C., the copper foil did not peel off, and no distortion such as deformation was observed.

Comparative Example 1 The polyamic acid solution of Example 1 was sandwiched between Svinco Yast films and Sulfide glass plates and heated at 300°C under vacuum for 30 minutes.
Heat treated. When the polyimide film thus obtained was observed under a polarizing microscope, no conoscopic image was observed, and when the polyimide film was observed with the polarizer and analyzer perpendicular to each other, it was found to be a light-transmitting state trap. Ta. That is, it was confirmed that the polyimide molecular chains were oriented parallel to the membrane surface.

Comparative Example 2 A parallel plate conductor having a plane-oriented polyimide film as an insulating layer was produced in exactly the same manner as in Example 4 except that the electrostatic voltage was set to zero (electric field strength OMV/t:ni). The coefficient of linear expansion in the direction perpendicular to the conductor surface of this parallel plate conductor is 2
It is as large as 10-sK'', and its thermal conductivity is cLO02W/
51, and both values were close to the values in the non-oriented state. Note that the adhesive strength between opposing copper foils was weak, and they were easily peeled off when cooled with liquid nitrogen.

〔Effect of the invention〕

As explained above, the vertically oriented polyimide film of the present invention has a small linear expansion coefficient in the direction perpendicular to the film surface, a high thermal conductivity, and a heat resistance that can absorb thermal strain in the direction parallel to the film surface. It has the advantage of being an insulating layer. Such an insulating layer can be effectively used as an insulating layer for the internal wiring section of a circuit board on which a chip is mounted, an insulating layer for an input/output cable, or an insulating layer related to superconducting applications.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the change in the amount of transmitted polarized light and the polyimidation rate as the temperature rises in a polyamic acid cast film having a thickness of 20 pm. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. The following general formula 1: ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(1) (In the formula, Ar_1 is a tetravalent aromatic group, Ar_2 is a divalent aromatic group) The repeating unit represented by 1. A vertically oriented polyimide film characterized in that the molecular chains of this polyimide are oriented perpendicularly to the film surface.