JP4948211B2 - Foam, circuit board using foam, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foam of a polyimide-silica hybrid cured product having a fine cell diameter of 0.01-10 &mu;m, excellent solder heat resistance of 260&deg;C or higher, a low linear expansion coefficient of 30&times;10<SP>-6</SP>/&deg;C or less and a low relative dielectric constant of 2.9 or less, and a manufacturing method thereof. <P>SOLUTION: A polyamic acid obtained by a reaction of a tetracarboxylic acid dianhydride with a diamine is reacted with an epoxy group-containing alkoxysilane partial condensate to give a silane-modified polyamic acid, which is further reacted with a tetracarboxylic acid dianhydride and a diamine to give an alkoxy group-containing silane-modified block copolymer type polyamic acid. A polyimide-silica hybrid cured product, obtained by thermal cure of the alkoxy group-containing silane-modified block copolymer type polyamic acid, is brought into contact with a non-reactive gas under pressure to cause the gas to permeate it, subjected to pressure reduction and heating, and is caused to expand to give the foam. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

The present invention relates to a polyimide-silica hybrid cured product having fine bubbles, excellent heat resistance, low linear expansion and low dielectric constant, and a method for producing the same.

There are two types of conventional methods for producing foams such as films and sheets, chemical foaming and physical foaming.
Chemical foaming is a method of obtaining a foam by forming bubbles with a gas generated by thermal decomposition of a compound which is a foaming agent added to a resin. However, in this foaming method, a foaming agent residue tends to remain in the foam after foaming, and there is a strong demand for low contamination in applications such as electronic parts.
Physical foaming is a method in which a foaming agent is volatilized by heating after a low-boiling liquid such as hydrocarbon or fluorocarbon, which is a foaming agent, is dispersed in a resin. This method also has problems such as environmental problems and flammability due to the harmfulness of substances used as foaming agents.
Further, in the case of such a foaming method, it is a suitable method for obtaining a foam having a bubble diameter of several tens of μm or more, but a foam having a fine bubble diameter of about 0.01 to 10 μm is used. It is difficult to get.

On the other hand, as a method of obtaining a foam having a small cell diameter and a high cell density, a gas such as carbon dioxide gas is permeated into the resin molded body at a high pressure, then the pressure is released, and the resin is heated to near the glass transition temperature of the resin. Thus, a method of foaming (hereinafter, sometimes referred to as “microcellular process”) has been proposed (see Patent Document 1).
Patent Document 2 describes a heat-resistant polymer foam having a fine cell structure and a method for producing the same, using a microcellular process. However, since the glass transition temperature of the thermoplastic resin disclosed in Patent Document 2 is 120 ° C. or higher, when a foam base material obtained by foaming is applied as an electronic circuit board, solder heat resistance and reflow heat resistance are high. Not necessarily enough. It is known that the melting point of commonly used Sn—Pb solder is about 183 ° C., and some Pb-free solders have a melting point of about 220 ° C. In recent years, the mounting density of circuit boards tends to increase, and some circuit boards require reflow heat resistance of about 260 ° C.

In addition, the thermoplastic resin mentioned in Patent Document 2 has a linear expansion coefficient of 50 × 10 ⁻⁶ / ° C. or higher, and thus a low linear expansion coefficient such as copper foil (17 × 10 ⁻⁶ / ° C.). When the composite material and the thermoplastic resin foam sheet are combined to be applied as a circuit board, there is a high possibility that inconvenience in use will occur due to deformation such as warpage depending on the ambient temperature under the compounding conditions and use conditions.

A thermosetting polyimide resin such as Kapton manufactured by DuPont is known as a resin for circuit boards having excellent heat resistance and a linear expansion coefficient as low as that of copper foil. Since the plasticizing temperature of the thermosetting polyimide resin is slightly over 400 ° C., it is excellent in solder heat resistance and reflow temperature characteristics, and its linear expansion coefficient is relatively close to that of copper foil.

US Pat. No. 4,473,665 JP 2001-55464 A

However, the thermosetting polyimide resin has a relatively high relative dielectric constant of about 3.4, and there is no problem when used for general telecommunications equipment, but a high-speed communication band exceeding several tens of GHz. Then, problems such as transmission speed may occur.
The object of the present invention is to have a fine bubble diameter of 0.01 to 10 μm, an excellent solder heat resistance of 260 ° C. or higher, and a low linear expansion coefficient of 30 × 10 ⁻⁶ / ° C. or lower, 2.9. It is providing the polyimide-silica hybrid hardened | cured material foam which has the following low dielectric constants, and its manufacturing method.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have made a polyimide-silica hybrid cured product obtained by thermosetting a specific polyamic acid by foaming with a non-reactive gas, so as to have a thickness of 0.01 to 10 μm. Polyimide-silica hybrid cured product having fine bubble diameter, excellent solder heat resistance of 260 ° C. or higher, low coefficient of linear expansion of 30 × 10 ⁻⁶ / ° C. or lower, and low dielectric constant of 2.9 or lower The inventors found that a foam could be obtained and completed the present invention.

That is, the present invention relates to the following (1) to (5) (hereinafter sometimes referred to as the present invention).
(1) A tetracarboxylic dianhydride and a diamine are further added to a silane-modified polyamic acid obtained by reacting a polyamic acid obtained by reacting a tetracarboxylic dianhydride and a diamine with an epoxy group-containing alkoxysilane partial condensate. Polyimide-silica hybrid curing having an average cell diameter of 0.01 to 10 μm obtained by foaming a polyimide-silica hybrid cured product obtained by thermally curing an alkoxy group-containing silane-modified block copolymer polyamic acid obtained by reaction The foam has a glass transition temperature of 260 ° C. or higher, a linear expansion coefficient of 30 × 10 ⁻⁶ / ° C. or lower, and a relative dielectric constant of 1.5 to 2.9. Polyimide-silica hybrid cured product foam. (Embodiment 1)
(2) A circuit board in which a conductive layer is laminated on at least one surface of the foam according to (1). (Embodiment 2)
(3) The circuit board, wherein the conductive layer according to (2) is one or more selected from metals, metal alloys, conductive resins, and carbon. (Embodiment 3)
(4) The flexible circuit board which has the flexibility as described in said (2) or (3). (Embodiment 4)
(5) A tetracarboxylic dianhydride and a diamine are further added to a silane-modified polyamic acid obtained by reacting a polyamic acid obtained by reacting a tetracarboxylic dianhydride and a diamine with an epoxy group-containing alkoxysilane partial condensate. After the polyimide-silica hybrid cured product obtained by thermally curing the alkoxy group-containing silane-modified block copolymerization type polyamic acid obtained by reacting is reacted with a non-reactive gas under pressure, the pressure is reduced, Next, a method for producing a polyimide-silica hybrid cured foam obtained by foaming after heating and having an average cell diameter of 0.01 to 10 μm. (Embodiment 5)

The foam of the present invention has a fine cell diameter of 0.01 to 10 μm, excellent heat resistance of 260 ° C. or higher, and a low coefficient of linear expansion of 30 × 10 ⁻⁶ / ° C. or lower, 2.9. Since it has the following low relative dielectric constant, it can be used for circuit boards, particularly flexible circuit boards, high-value-added high-speed communication and high-frequency compatible circuit boards, and is also useful as a buffer material and a heat insulating material. Furthermore, according to the production method of the invention, the foam having the above-mentioned excellent function can be produced easily and efficiently, and its practical value is great.

Hereinafter, the present invention will be described in detail.
(1) Measuring method of physical property In this specification, the physical property of each foam was measured by the following method.
(I) Glass transition temperature The glass transition temperature was measured by a DSC method using a differential scanning calorimeter.
(Ii) Average cell diameter The average cell diameter was determined according to ASTM D3576-77. That is, a SEM photograph of the cross section of the molded body was taken, straight lines were drawn in the horizontal direction and the vertical direction on the SEM photograph, and the lengths t of the bubble chords crossed by the straight line were averaged. Assuming that the magnification of the photograph is M, the average bubble diameter d was determined by substituting it into the following equation.
d = t / (0.616 × M)
(Iii) Volume foaming rate The density (Pf) of the foam was determined by the water substitution method, and the volume foaming rate was calculated from the density (Po) of the non-foamed sheet by the following formula.
Volume foaming rate = (1−Pf / Po) × 100 (%)
(Iv) Relative permittivity The impedance of the sample was measured by the high frequency IV method, and the permittivity was calculated. The measuring instrument used was a material analyzer HP4291B (manufactured by Hewlett Packard), and the measurement frequency was 1 GHz.
(V) Linear expansion coefficient Based on JIS K7197, a linear expansion coefficient test (temperature range 50 to 200 ° C., measuring device TMA8310 manufactured by Rigaku) was performed.

(2) Polyimide-silica hybrid cured product In the present invention, an alkoxy group-containing silane-modified block copolymerized polyamic acid is thermally cured to obtain a polyimide-silica hybrid cured product, and the polyimide-silica hybrid cured product is foamed to obtain a polyimide. -Obtain a silica hybrid cured product foam.
The alkoxy group-containing silane-modified block copolymer type polyamic acid used in the present invention is a polyamic acid (1) obtained by reacting tetracarboxylic dianhydride (a) and diamine (b) with an epoxy group-containing alkoxysilane partial condensation. The silane-modified polyamic acid (α) obtained by reacting the product (2) is further reacted with tetracarboxylic dianhydride (β) and diamine (γ).
Alkoxy group-containing silane-modified block copolymer polyamic acid used in the present invention, and tetracarboxylic dianhydrides (a) and (β), diamines (b) and (γ), polyamic acid (1) ), An epoxy group-containing alkoxysilane partial condensate (2), a silane-modified polyamic acid (α), and a method of reacting them to obtain an alkoxy group-containing silane-modified block copolymer polyamic acid used in the present invention. The method and method disclosed in Japanese Patent Application No. 2005-068408 can be used.
Further, as a commercially available product of the alkoxy group-containing silane-modified block copolymerization type polyamic acid, Composeran H800 (manufactured by Arakawa Chemical Co., Ltd.) can be mentioned.

The alkoxy group-containing silane-modified block copolymeric polyamic acid of the present invention is converted into a polyimide-silica hybrid cured product by heat curing (sol-gel curing and dehydration ring closure). The method disclosed in Japanese Patent Application No. 2005-068408 can be used as a method for obtaining a polyimide-silica hybrid cured product by thermally curing an alkoxy group-containing silane-modified block copolymeric polyamic acid.
For example, after coating or casting an alkoxy group-containing silane-modified block copolymeric polyamic acid on a substrate, it is finally cured at about 300 ° C. to 500 ° C. to obtain a coating film or film. When the curing temperature is less than 300 ° C, the ring closure reaction from the amic acid group to the imide group becomes incomplete, and when it exceeds 500 ° C, the polyimide-silica hybrid cured product is thermally decomposed depending on the type of polyamic acid. Therefore, it is not preferable.
Moreover, after coating or casting an alkoxy group-containing silane-modified block copolymeric polyamic acid on a base material, the semi-cured product dried / cured at 80 to 200 ° C. may be subjected to the foam production method described later.
In addition, the shape of the polyimide-silica hybrid hardened | cured material used for this invention is not limited to acquisition, For example, a sheet | seat and a film-like shape are mentioned.

(3) Non-reactive gas In the production method of the present invention, the non-reactive gas functions as a blowing agent. Such a gas is not particularly limited as long as it is non-reactive with the heat-resistant polyimide-silica hybrid cured product and can penetrate into the polyimide-silica hybrid cured product, For example, carbon dioxide, nitrogen gas, air and the like can be mentioned. These gases may be used alone or in combination. Of these, practically, it is particularly preferable to use carbon dioxide which has a large amount of penetration into the polyimide-silica hybrid cured product and a high penetration rate.

(4) Foam The foam-molded body part in the polyimide-silica hybrid cured product foam in the present invention is obtained by bringing the polyimide-silica hybrid cured product into contact with a non-reactive gas foaming agent, and the polyimide-silica hybrid cured product. It is a polyimide-silica hybrid cured product foam having an average cell diameter of 0.01 to 10 μm obtained by foam molding near the softening temperature. As the foam molding method, it is particularly desirable to use the microcellular process. Specific examples of the method for obtaining the foam will be described later.

(5) Embodiments 1 to 5
Next, Embodiments 1 to 5 for carrying out the invention will be described.
(I) Foam according to Embodiment 1 The foam according to Embodiment 1 is obtained by reacting a polyamic acid obtained by reacting tetracarboxylic dianhydride and diamine with an epoxy group-containing alkoxysilane partial condensate. Obtained by foaming a polyimide-silica hybrid cured product obtained by thermally curing an alkoxy group-containing silane-modified block copolymerized polyamic acid obtained by further reacting silane-modified polyamic acid with tetracarboxylic dianhydride and diamine. The resulting foam is a polyimide-silica hybrid cured foam having an average cell diameter of 0.01 to 10 μm, wherein the foam has a glass transition temperature of 260 ° C. or higher, a linear expansion coefficient of 30 × 10 ⁻⁶ / ° C. or lower, and a relative dielectric constant. The rate is 1.5 to 2.9.
The average cell diameter of the foam is in the range of about 0.01 to 10 μm, preferably about 0.05 to 5 μm, according to the production method described later.

Next, it is known that the relationship between the volume expansion ratio and the equivalent relative dielectric constant is represented by the following relational expression (AS Winder's formula).
(Εi−εc) / (εi−εa) = (F / 100) × [3εc / (2εc−εa)]
Where εc is the dielectric constant of the foam, εi is the dielectric constant of the insulator,
εa: relative dielectric constant of foam (εa = 1), F: volume ratio of foam (%)
For example, when the relative permittivity of the polyimide-silica hybrid cured product is 3.0 to 4.0, the equivalent relative permittivity is reduced to 2.9 or less (relative permittivity corresponding to a liquid crystal polymer) by foaming. Considering this, a volume expansion ratio of 5% is necessary when the initial relative dielectric constant is 3.0, and 22% or more when the initial relative dielectric constant is 4.0. Note that the equivalent relative dielectric constant is further reduced by increasing the volume foaming rate, and in order to reduce it to the vicinity of PTFE resin (relative dielectric constant 2.2) known as a low dielectric constant material, the initial relative dielectric constant is required. When 3.0 is 3.0, a volume expansion ratio of 35% or more and 50% or more is required.

From the above, considering the purpose of use, the volume foaming ratio is preferably 5 to 50%, more preferably 50 to 90% in order to make the dielectric constant 2.9 or less.
Although the relative dielectric constant is desirably 2.9 or less, the lower limit is usually about 1.2, preferably about 1.5 in view of the strength of the foam.
The foam according to Embodiment 1 obtained by the method described later has uniform and fine bubbles, is excellent in heat resistance, has a low coefficient of linear expansion, a dielectric constant and a relative density, and has mechanical properties, wear resistance, etc. For example, it can be suitably used as a circuit board for electronic devices.

(Ii) Circuit board according to Embodiments 2 to 4 A circuit board according to Embodiment 2 is characterized in that a conductive layer is laminated on at least one surface of the foam described in (i). The circuit board according to 3 is characterized in that the conductive layer is at least one selected from metal, metal alloy, conductive resin, and carbon, and the circuit board according to the fourth embodiment has flexibility in the circuit board. It is characterized by having.
In order to use the foam according to Embodiment 1 as a circuit board, it is necessary to laminate a conductive layer on at least one surface of the foam by a method described later. Examples of such a conductive layer include one or more selected from metals, metal alloys, conductive resins, and carbon. Examples of the metal and metal alloy include gold, silver, platinum, ruthenium, nickel, and alloys thereof, but copper is most preferable.

Examples of a method for laminating a conductive layer on a foam when the circuit board of the present invention is manufactured include a thermocompression bonding method, a vacuum film forming method, and a plating method. The thermocompression bonding method is a method in which, for example, a foamed film, a sheet, or the like is laminated with a conductive layer by pressure-bonding the foam and the conductive layer through an adhesive layer at high temperature and high pressure. Note that acrylic, urethane, epoxy, and polyimide adhesives are mainly used for the adhesive layer.
The laminated structure includes foam / adhesive layer / conductive layer, conductive layer / adhesive layer / foam / adhesive layer / conductive layer, conductive layer / adhesive layer / foam / adhesive layer / conductive layer / adhesive layer / foam. Examples include a three-layer structure such as body / adhesive layer / conductive layer to a multilayer structure of five or more layers.
It is also possible to use a vacuum film forming method and plating together. For example, after forming a very thin conductive layer by sputtering, a conductive layer having a thickness of several μm can be formed by electrolytic plating. Further, by applying a wet process such as electroless plating, it is possible to continuously form a metal or the like at a lower cost than a vacuum film formation such as a conventional sputtering method. In this case, it is desirable to form a conductive layer having a thickness of about 0.1 to 1.0 μm by electroless plating on the foamed resin body film and then laminating a conductive layer having a thickness of several μm by electrolytic plating.

In the polyimide-silica hybrid cured foam, a conductive layer may be formed on at least one surface of the foam. For example, in the case of a shape such as a sheet or film, the conductive layer is formed on one or both sides. May be formed. Further, a structure in which a foamed resin and a conductive layer are laminated may be used. The laminated structure includes foam / conductive layer, conductive layer / foam / conductive layer, conductive layer / foam / conductive layer / foam / conductive layer. Examples of such a 2, 3 and 5 layer structure can be given.
In addition, since the polyimide-silica hybrid cured foam sheet or film has good flexibility (flexibility), the circuit board having the conductive layer has flexibility (flexibility) as well. As for the thickness of the polyimide-silica hybrid hardened | cured material foam which comprises a circuit board, 20-200 micrometers is preferable, More preferably, it is 25-100 micrometers. This is because if the thickness of the foam is less than 20 μm, the volume foaming ratio tends to be small, and it becomes difficult to control the dielectric constant. If the thickness of the foam exceeds 200 μm, the flexibility is lowered and the flexibility is reduced. This is because the properties are impaired. However, in applications that do not require flexibility, the foam may have a thickness of 200 μm or more.

(Iii) Method for producing foam according to Embodiment 5 The method for producing a foam according to Embodiment 5 includes a polyamic acid obtained by reacting tetracarboxylic dianhydride and a diamine, and an epoxy group-containing alkoxysilane partial condensate. A polyimide-silica hybrid obtained by thermally curing an alkoxy group-containing silane-modified block copolymer type polyamic acid obtained by further reacting a tetrasilane dianhydride and a diamine with a silane-modified polyamic acid obtained by reacting Polyimide-silica hybrid cured foam having an average cell diameter of 0.01 to 10 [mu] m, obtained by contacting and infiltrating a cured product with a non-reactive gas under pressure and then reducing the pressure, followed by foaming after heating. It is a manufacturing method. That is, the polyimide-silica hybrid cured product is brought into contact with and infiltrated with a non-reactive gas under pressure (gas permeation step), then the pressure is reduced (pressure reduction step), and then foamed by heating and softening (heating foaming step). ).
The non-reactive gas can be selected as appropriate. For example, when carbon dioxide is used, the pressure at the time of permeation is 1 to 10 MPa. The temperature in the gas permeation process varies depending on the type of gas used and the amount of gas permeation, and the bubble diameter tends to increase if the temperature during permeation is too high. It is the range below the glass transition temperature.

The microcellular process can be used as the foaming method. That is, in this production method, a foaming agent such as carbon dioxide gas is pressed and infiltrated into a polyimide-silica hybrid cured product in a high-pressure vessel with respect to a sheet-like or film-like molded body. Thereafter, the gas in the high-pressure vessel is rapidly released to bring the gas that has permeated into the polyimide-silica hybrid cured product into a supersaturated state, thereby causing the gas to grow slightly. This becomes a bubble nucleus, and the polyimide-silica hybrid cured sheet in this state is heated to a temperature at which the film is softened to grow the bubble nucleus to obtain a foam. It is possible to obtain a uniform and fine foam having a foam diameter of 0.01 to 10 μm.

Further, in a preferred embodiment of the method of the present invention, the polyimide-silica hybrid cured product becomes too soft and bubbles are excessively grown, outgassing, bubbles are coalesced, and the density of bubbles is reduced. In order to prevent the cured product from being deformed, for example, the softening temperature is about 1 × 10 ⁷ Pa to 1 × 10 ¹¹ Pa (elastic modulus measured in the unfoamed state of the polyimide-silica hybrid cured product). It is desirable to set the temperature.

EXAMPLES Hereinafter, although this invention is demonstrated in more detail using an Example, this invention is not limited by this.
[Example 1]
Polyimide obtained by drying / curing an alkoxy group-containing silane-modified block copolymer type polyamic acid (trade name: Composelane H800 (manufactured by Arakawa Chemical Co., Ltd.)) at 150 ° C. for 10 minutes, and further curing at 300 ° C. for 30 minutes. -Silica hybrid hardened | cured material film (thickness 25 micrometers, glass transition temperature 300 degreeC) was installed in the pressurized container, 6.0 Mpa carbon dioxide gas was introduce | transduced there, and it was left for 48 hours, and the carbon dioxide gas was infiltrated. Next, the film infiltrated with carbon dioxide gas is held for several tens of seconds in a pneumatic circulating thermostat set to a temperature (about 300 to 320 ° C.) at which the cured product is softened, and foamed, whereby an average cell diameter of 0. A polyimide-silica hybrid cured foam film having a thickness of 1 μm and a volume foaming ratio of 15% was produced.
The obtained foam had a glass transition temperature of 300 ° C., a linear expansion coefficient of 19 × 10 ⁻⁶ / ° C., and a relative dielectric constant of 3.3 before foaming, and decreased to 2.8 after foaming. Further, the obtained foam was very flexible (flexible).

[Comparative Example 1]
Using a thermosetting polyimide resin film (trade name: Kapton (manufactured by Toray DuPont)) with a thickness of 50 μm, a foam film was created in the same manner as in the example except that the foaming temperature was 400 ° C. A good foam having uniform fine foaming was not obtained. The relative dielectric constants before and after foaming were both equal to 3.4.

[Example 2]
After about 0.5 μm of copper was formed on one side of the polyimide-silica hybrid cured foam film prepared in Example 1 by a vacuum film forming apparatus (sputtering), about 5 μm was further formed thereon by electrolytic plating. Copper was deposited to prepare a one-side copper-clad laminate. The obtained one-side copper-clad laminate was very flexible (flexible).
When the copper clad laminated substrate was held in a thermostatic bath set at 260 ° C. for 60 seconds and then observed for appearance and the like, no deformation or alteration was observed. Further, as shown in Example 1, since the linear expansion coefficient of the foam used for the copper-clad laminate is 19 × 10 ⁻⁶ / ° C. and the relative dielectric constant is 2.8, the circuit for high-speed communication and high frequency is used. It can be applied to a substrate.

The foam of the present invention has a fine cell diameter of 0.01 to 10 μm, excellent heat resistance of 260 ° C. or higher, and a low coefficient of linear expansion of 30 × 10 ⁻⁶ / ° C. or lower, 2.9. Since it has the following low relative dielectric constant, it can be used for circuit boards, particularly flexible circuit boards, high-value-added high-speed communication and high-frequency compatible circuit boards, and is also useful as a buffer material and a heat insulating material. Furthermore, according to the production method of the invention, the foam having the above-mentioned excellent function can be produced easily and efficiently, and its practical value is great.

Claims (5)

A silane-modified polyamic acid obtained by reacting a polyamic acid obtained by reacting tetracarboxylic dianhydride and diamine with an epoxy group-containing alkoxysilane partial condensate is further reacted with tetracarboxylic dianhydride and diamine. Polyimide-silica hybrid cured product foam having an average cell diameter of 0.01 to 10 μm obtained by foaming a polyimide-silica hybrid cured product obtained by thermally curing the alkoxy group-containing silane-modified block copolymeric polyamic acid obtained The glass-transition temperature of the foam is 260 ° C. or higher, the linear expansion coefficient is 30 × 10 ⁻⁶ / ° C. or lower, and the relative dielectric constant is 1.5 to 2.9. Hybrid cured product foam.   The circuit board by which the conductive layer is laminated | stacked on the at least 1 surface of the foam of Claim 1.   The circuit board according to claim 2, wherein the conductive layer is at least one selected from a metal, a metal alloy, a conductive resin, and carbon. A flexible circuit board having flexibility according to claim 2 or 3.   A silane-modified polyamic acid obtained by reacting a polyamic acid obtained by reacting a tetracarboxylic dianhydride and a diamine with an epoxy group-containing alkoxysilane partial condensate is further reacted with a tetracarboxylic dianhydride and a diamine. The polyimide-silica hybrid cured product obtained by thermally curing the alkoxy group-containing silane-modified block copolymeric polyamic acid obtained in this way is contacted and infiltrated with a non-reactive gas under pressure, and then the pressure is reduced, and then after heating The manufacturing method of the polyimide-silica hybrid hardened | cured material foam which is obtained by making it foam and whose average bubble diameter is 0.01-10 micrometers.