JP5064705B2 - Method for manufacturing foam substrate - Google Patents

Description

The present invention relates to a method for producing a foam substrate having a foam molded body portion made of a specific thermoplastic polyamide resin having fine bubbles and excellent heat resistance.

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 substrate obtained by foaming is applied as a substrate for an electronic circuit, 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.
Moreover, a circuit board using thermosetting polyimide is known as an electronic circuit board having excellent heat resistance. Since the plasticizing temperature of thermosetting polyimide is about 420 ° C., it can be said that the material is excellent in solder heat resistance and reflow temperature characteristics. However, the relative dielectric constant of the material is relatively high, such as about 3.2 to 3.8, and there is no problem when used for general telecommunications equipment, but when the high-speed communication band exceeds several GHz, Problems such as transmission loss occur, which is not preferable. Further, since thermosetting polyimide does not have a clear glass transition point, it is difficult to obtain a foam having a small cell diameter and a high cell density by a microcellular process.

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

An object of the present invention is excellent in solder heat resistance, bubble size is small, and is to provide a method for producing a foam board having a foamed molded part made of a low dielectric constant thermoplastic resin.

As a result of intensive studies to achieve the above object, the inventors of the present invention molded a thermoplastic resin made of a specific polyamide resin that is a heat-resistant resin and has a glass transition temperature of 240 ° C. or higher after foam molding. The resulting molded body is contacted and infiltrated with a non-reactive gas foaming agent under pressure, and then the pressure is reduced, and the conductor is thermocompression bonded to one surface of the thermoplastic resin at a temperature at which the thermoplastic resin is softened. It is found that a foam substrate having a foam molded body part having a favorable cell diameter and a glass transition temperature of 240 ° C. or higher can be obtained by foaming the molded body part by employing a thermocompression bonding method. The present invention has been completed.

That is, the present invention is an invention related to the following (1) to ( 3 ) (hereinafter sometimes referred to as the present invention).
(1) Pressure after contacting and infiltrating a non-reactive gas with a non-reactive gas and a thermoplastic resin molded body made of a thermoplastic polyimide obtained by reacting an aromatic tetracarboxylic dianhydride and an aromatic diamine. Then, the conductor is thermocompression-bonded on one side at a temperature at which the thermoplastic resin softens, and the thermoplastic resin molded part is foamed. The glass transition temperature of the foamed molded part is 240 ° C. or higher. A method for manufacturing a foam substrate. ( 2 ) The method for producing a foam substrate according to (1), wherein an average cell diameter of the foam molded body portion in the foam substrate is 0.01 to 10 μm.
( 3 ) The method for producing a foam substrate according to (1) or (2) , wherein the conductor is one or more selected from metals, metal alloys, conductive resins, and carbon.

The foam substrate obtained by the foam substrate manufacturing method of the present invention is excellent in solder heat resistance, has a small bubble diameter, and has a low dielectric constant. It can be used for a circuit board) and is also useful as a buffer material and a heat insulating material. In addition, since the foam substrate has no adhesive layer between the resin foam and the conductor, it is halogen-free and has high environmental performance, and since the bubble diameter is small, a fine pattern can be formed.
Furthermore, according to the manufacturing method of the invention, a foam substrate having a foamed molded body part made of a specific thermoplastic polyamide resin having the above-mentioned excellent function can be easily and efficiently manufactured, and its practical value is large.

Hereinafter, the present invention will be described in detail.
(1) Measuring method of physical property In this specification, the physical property of each foam and foam substrate 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 bubble diameter The average bubble 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 displacement 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 relative permittivity was measured according to IEC 60240. The measuring instrument used was a dielectric loss measuring apparatus TR-10C (manufactured by Ando Electric Co., Ltd.), and the measurement frequency was 1 kHz.

(2) Thermoplastic resin The thermoplastic resin used in the present invention is described below.
The thermoplastic resin used in the present invention has a glass transition temperature (Tg) of the thermoplastic polyamide resin composition comprising the following to be 240 ° C. or more exemplary thermoplastic polyamide resin (A) or additives after the foam molding (B ).
In addition, since the Tg before and after foaming when foaming a molded product obtained by melt molding is almost the same, molding obtained by melt molding (including heat treatment after melt molding) is substantially used in the present invention. A thermoplastic resin having a Tg of 240 ° C. or higher can be used.
(I) Thermoplastic resin (A)
The thermoplastic resin (A) used as a raw material for the foam base material of the present invention has a glass transition temperature of 240 ° C. or higher after foam molding, and easily penetrates non-reactive gas used as a foaming agent under pressure. Those are preferred. Such thermoplastic resin (A), aromatic diamine and the polyimide synthesized from aromatic tetracarboxylic dianhydride, or a composition consisting mainly of the polyimide can be exemplified as described below.

Examples of the aromatic diamine include 4,4-bis (3-aminophenoxy) biphenyl (hereinafter sometimes referred to as APBI) and 1,3-bis (3-aminophenoxy) benzene (hereinafter referred to as APBE). And at least one aromatic diamine selected from 4,4′-diaminodiphenyl ether and the like.
Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride (hereinafter sometimes referred to as PMDA), 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride, 3 , 3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic acid At least one aromatic tetracarboxylic dianhydride selected from dianhydrides (hereinafter sometimes referred to as PSTC) is preferred.
As the thermoplastic resin (A), for example, synthesized from the above-mentioned aromatic diamine and aromatic tetracarboxylic dianhydride, specifically, a polymer of APBI and PMDA (Mitsui Chemicals, Inc.) Product name: Aurum, etc.), and a polymer of PSTC and aromatic diamine (trade names: Rika Coat (SN-20, PN-20, etc.) manufactured by Shin Nippon Rika Co., Ltd.).

Specific examples of the thermoplastic resin (A) include polyimide synthesized from APBI and PMDA (hereinafter sometimes referred to as APBPM).
APBPM can be synthesized by, for example, reacting APBI and PMDA to synthesize a polyimide precursor (polyamide acid) and dehydrating and ring-closing the polyimide precursor. The polyimide precursor can be obtained, for example, by reacting approximately equimolar amounts of an aromatic tetracarboxylic dianhydride and an aromatic diamine in an organic solvent for about 3 to 20 hours under heating. The dehydration cyclization reaction of the polyimide precursor is performed, for example, by the action of a dehydrating cyclization agent such as a mixture of acetic anhydride and pyridine.
The neat APBPM thus obtained has a glass transition temperature of 245 ° C., but can be raised to about 260 ° C. by heat treatment after molding.

(Ii) Thermoplastic resin composition (B)
When the thermoplastic resin composition (B) is used as the thermoplastic resin of the present invention, various additives including other thermoplastic resins (C) having the above-mentioned thermoplastic resin (A) as a main component, etc. It is possible to mix.
For example, APBPM is a crystalline polyimide, for crystallization speed is slow, be formulated other thermoplastic resins such as polyimide obtained from APBE and PMDA to promote crystallization of (C) as an additive it can. Such a modified thermoplastic resin ( C ) can be appropriately selected from the above-mentioned examples of polyimide, and the particularly preferred blending ratio thereof is the glass transition temperature after foam molding (or after melt molding). Thermoplastic resin (A) of 240 ° C. or higher 90 to 100% by mass, preferably 95 to 100% by mass, particularly preferably 97 to 100% by mass, and glass transition temperature (including those before and after melt molding) of 200 Thermoplastic polyimide ( C ) synthesized from the above-mentioned specific diamine and a specific tetracarboxylic dianhydride having a temperature of 0 ° C. or more, 0 to 10% by mass, preferably 0 to 5% by mass, particularly preferably 0 to 3% by mass. A plastic polyimide mixture can also be used as a material for the foam and the foam substrate of the present invention.

  In addition, various additives usually used for foam molding can be appropriately added to the thermoplastic resin composition (B). For example, bubble nucleating agents, lubricants, colorants, ultraviolet absorbers, antioxidants, crystal nucleating agents, plasticizers, flame retardants, antistatic agents, and the like can be used. The addition amount is preferably an addition amount used for molding a normal thermoplastic resin.

(3) Thermoplastic resin molded body The thermoplastic resin molded body used when contacting and permeating non-reactive gas under pressure is different from, for example, a conventional thermosetting polyimide in the case of a thermoplastic polyimide. The film can be formed not only by the casting method but also by the extrusion method or the like, and is advantageous in terms of cost when producing a thick film of about 100 μm. The polyimide precursor may be formed into a film, sheet, etc., and then dehydrated and closed to form a polyimide molded body. Further, after the thermoplastic resin is applied in a molten state or using a solvent, the sheet or film It can also be shaped. In addition, the shape in particular is not limited with the molded object in this invention, Other square shaped articles, such as a sheet | seat, a film, and a rectangular parallelepiped, may be sufficient.

(4) Non-reactive gas foaming agent In the production method of the present invention, the gas used as the foaming agent is non-reactive with respect to the heat-resistant thermoplastic resin and can penetrate into the thermoplastic resin. If it is a thing, there will be no restriction | limiting in particular, For example, a carbon dioxide, nitrogen gas, air etc. are mentioned. These gases may be used alone or in combination. Among these, practically, it is particularly preferable to use carbon dioxide having a large amount of penetration into the thermoplastic resin and a high penetration rate.
(5) foam molded body in the foam substrate of the foamed molded part <br/> present invention, the thermoplastic resin (A) or the thermoplastic resin composition (B) in the addition of non-reactive gas blowing agent A foam having a glass transition temperature of 240 ° C. or higher obtained by foam molding near the softening temperature. As the foam molding method, it is particularly desirable to use the microcellular process. If a thermoplastic resin (A) or a thermoplastic resin composition (B) having a glass transition temperature of 240 ° C. or higher is used, a foam having a glass transition temperature of 240 ° C. or higher can be easily obtained. However, even if another plastic resin of about 200 ° C. or higher is used, it may have a physical property that results in a glass transition temperature of 240 ° C. or higher due to heat treatment or the like when obtaining a molded body.

(6) Foam substrate (i) Average cell diameter, dielectric constant, etc. of foam molded body part The foam molded body part made of thermoplastic resin preferably has an average cell diameter of 0.01 to 10 µm. .
The average cell diameter of the foamed molded part, the foaming conditions and the thermoplastic resin molded article in the shape, the average cell diameter and volume expansion ratio than the thickness differ, 0.01 to 10 [mu] m by the manufacturing method described below, preferably It exists in the range of about 0.05-5 micrometers.

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, if the relative permittivity of a thermoplastic resin, particularly thermoplastic polyimide, is 3.0 to 4.0, the equivalent relative permittivity is lowered 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 is necessary when 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. As described above, the volume foaming rate may differ even under the same foaming conditions depending on the thickness of the sheet or film, but the same effect can be obtained in terms of lowering the dielectric constant.

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 preferably 2.9 or less, the lower limit is usually about 1.2 in view of the strength of the foam.
The foamed molded part obtained by the method described later has excellent heat resistance, uniform and fine bubbles, and a low dielectric constant and relative density. Accordingly, it can be suitably used as, for example, a circuit board of an electronic device or the like due to its excellent properties such as heat resistance, mechanical properties, and wear resistance.

The (ii) the foam board foam board, it is necessary to laminate the conductor on one surface of the foamed molded part by the method described below. Examples of such a conductor 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.
The method for producing a foam substrate according to the present invention is a method in which a molded body such as a sheet or a film in which carbon dioxide gas or the like is infiltrated under pressure in a high-pressure vessel is pressure- released and then thermocompression-bonded with a conductor using a hot press machine. It is the method of making it foam simultaneously.
( Iii ) Flexible printed circuit board Foamed substrate is excellent in solder heat resistance, has a small bubble diameter, and has a low dielectric constant. Therefore, it can be used for a flexible printed circuit board for high-value-added high-speed communication and high frequency. .

(Iv) a physical blowing agent, in the method for manufacturing a foaming temperature such <br/> foam substrate, the glass transition temperature after foaming molding obtained by molding the thermoplastic resin to be 240 ° C. or higher, the green body Contact and permeate under pressure with non-reactive gas (gas permeation process), then reduce the pressure (pressure reduction process), and then foam by heating and softening using the thermocompression bonding method described later (heating foaming process) ).
The physical foaming agent used for foaming can be selected as appropriate. For example, when carbon dioxide is used, the pressure at the time of permeation is several MPa to 100 MPa, preferably 5 MPa or more, and below the critical pressure of the foaming agent gas. It is preferable to select these conditions. The preferable conditions for the temperature in the gas infiltration step vary depending on the type of gas used, the glass transition temperature of the thermoplastic resin, and the like. The gas permeation time also varies depending on the type of gas used, the volume of the high-pressure vessel, the temperature during permeation, and the thickness and shape of the thermoplastic resin film. For example, when carbon dioxide gas permeates a thermoplastic polyimide film having a thickness of several tens to 100 μm, the permeation time is about several tens of minutes to several hours depending on temperature and pressure conditions.

  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 thermoplastic resin in a high-pressure container with respect to a molded body such as a sheet or film. Thereafter, the gas in the high-pressure vessel is suddenly released to bring the gas that has penetrated into the thermoplastic resin into a supersaturated state, so that the gas is slightly grown. This becomes the core of the bubble, and by heating the thermoplastic resin sheet, film, etc. in this state to the temperature at which the material softens, the core of the bubble is grown to obtain a resin foam. It is possible to obtain a uniform and fine foam molded article having an average foam diameter of 0.01 to 10 μm.

Further, in a preferred embodiment of the method of the present invention, the thermoplastic resin becomes too soft and bubbles grow excessively, outgassing, the bubbles coalesce and the density of bubbles is reduced, and the thermoplastic resin in the bubble growth process In order to prevent deformation, for example, the softening temperature is set to a temperature that is about 1 × 10 ⁷ Pa to 1 × 10 ¹¹ Pa (elastic modulus measured in an unfoamed state of the thermoplastic resin). desirable. These steps can be performed in a batch mode or a continuous mode.

The foam substrate thus obtained is excellent in heat resistance, has uniform and fine bubbles, and has a low relative density. For example, the average cell diameter of the foamed molded part is in the range of about 0.01 to 10 μm, preferably about 0.01 to 1 μm.

( V ) Method for Producing Foam Substrate As a method for producing the foam substrate of the present invention, a thermocompression bonding method is used. The manufacturing method of this method is different from the conventional method in which a metal body and a resin sheet are laminated with a thermosetting adhesive, and a conductor is directly laminated on a thermoplastic resin molded body without using an adhesive. Therefore, it can be said to be a low-cost and halogen-free method.
Thermocompression bonding of the present invention, a sheet impregnated with carbon dioxide gas in the pressure in the high pressure vessel, a molded body such as a film, at the same time to conductor thermocompression bonding by hot press machine After pressure release This is a foaming method .

In the method for producing a foam substrate of the present invention, a molded product obtained by molding a thermoplastic resin having a glass transition temperature of 240 ° C. or higher after foam molding is brought into contact with and infiltrated with a non-reactive gas under pressure. A foam having a foam part having a glass transition temperature of 240 ° C. or more by reducing pressure and then thermocompression bonding the conductor on one side at a temperature at which the thermoplastic resin softens and foaming the molded part A substrate is obtained.
Although the manufacturing method of this invention is illustrated below, the manufacturing method of this invention is not limited to this.
In the present invention , a non-reactive gas is brought into contact with and infiltrated under pressure into a thermoplastic resin molded article having a glass transition temperature of 240 ° C. or higher after foam molding, and then the pressure is reduced to infiltrate the non-reactive gas. A molded body is obtained.
Next, the molded body and conductor are infiltrated with non-reactive gas, and set in a press machine, etc., and heated by a roller or the like while being heated near the temperature at which the used thermoplastic resin is softened. And the conductor is thermocompression bonded.

Hereinafter, the present invention will be described in more detail with reference to Examples and Reference Examples , but the present invention is not limited thereto.
The thermoplastic polyimide used in the examples and reference examples is a thermoplastic polyimide (APBPM) synthesized from pyromellitic dianhydride (PMDA) and 4,4-bis (3-aminophenoxy) biphenyl (APBI). (Trade name: “Aurum (PI-PA)”, manufactured by Mitsui Chemicals, Inc.).
[ Reference Example 1]
A film (glass transition temperature: 258 ° C.) having a thickness of 50 μm obtained by molding the thermoplastic polyimide (APBPM) by an extrusion molding method (T-die method) is placed in a pressure vessel, and 6.0 MPa of carbonic acid therein. Gas was introduced and allowed to stand for 30 minutes to infiltrate carbon dioxide. Next, the film is infiltrated with carbon dioxide gas and held in a pneumatic circulation thermostat set at a temperature for softening the resin (about 240 to 300 ° C.) for several tens of seconds. A 20% foamed thermoplastic polyimide film was produced.
The obtained thermoplastic thermoplastic polyimide film had a glass transition temperature of 258 ° C., and the dielectric constant was measured. As a result, the relative dielectric constant decreased to 3.1 after foaming and to 2.6 after foaming. .

[Comparative Example 1]
Using a thermosetting polyimide (trade name: Kapton, manufactured by Toray DuPont Co., Ltd.) sheet having a thickness of 50 μm, the same operation as described in Reference Example 1 was performed to produce a foam. The foaming temperature is 400 ° C. However, a good foamed molded product was not obtained. No significant difference was observed in the measured dielectric constant of the thermosetting polyimide before and after foaming.

[ Reference Example 2]
A film (glass transition temperature: 258 ° C.) having a thickness of 50 μm obtained by molding the thermoplastic polyimide (APBPM) by an extrusion molding method was placed in a pressure vessel, and 6.0 MPa of carbon dioxide gas was introduced therein. The carbon dioxide gas was infiltrated by leaving it for 30 hours.
Next, the film infiltrated with carbon dioxide gas is held for several minutes in a pneumatic circulating thermostat set to a temperature at which the resin softens the resin (240 to 300 ° C.) and foamed to obtain an average bubble diameter of about 500 nm and volume. A foamed thermoplastic polyimide film having a foaming rate of 30% was produced.
Next, the foam and a copper foil having a thickness of 10 μm were set in a hot press machine, and a composite of resin and metal foil (foamed resin substrate) was produced by applying pressure and heating.
The glass transition temperature of the foam part in the foamed resin substrate was 258 ° C.

[Example 1 ]
A 50 μm-thick film (glass transition temperature: 258 ° C.) obtained by molding the thermoplastic polyimide (APBPM) by an extrusion molding method was placed in a pressure vessel, and 6.0 MPa carbon dioxide gas was introduced therein, By allowing to stand for 30 minutes, carbon dioxide gas was infiltrated, and then the pressure was reduced. Next, the film and a copper foil having a thickness of 10 μm were set in a hot press machine, and a composite of resin and metal foil was formed by applying pressure (4.9 MPa) and heating (300 ° C.).
The carbon dioxide gas inside the resin was foamed by heating when forming the composite, and a foam substrate having an average cell diameter of about 500 nm and a volume foaming rate of 10% was formed.
The glass transition temperature of the foam part in the foamed resin substrate was 258 ° C.

[ Reference Example 3 ]
A film having a thickness of 50 μm (glass transition temperature: 258 ° C.) obtained by molding the thermoplastic polyimide (APBPM) by an extrusion molding method and a copper foil having a thickness of 10 μm are set in a hot press machine and pressed and heated. Thus, a composite of resin and metal foil was formed. Thereafter, the composite material was placed in a pressurized container, and 6.0 MPa of carbon dioxide gas was introduced therein and allowed to stand for 30 minutes, whereby carbon dioxide gas was permeated. Then the carbon dioxide gas and penetration film was held for several minutes on the set pneumatic circulation constant temperature bath at a temperature (240 to 300 ° C.) to the resin is softened, by foaming, average cell diameter 300nm approximately, the volume expansion ratio 20 % Foamed resin substrate.
The glass transition temperature of the foam part in the foamed resin substrate was 258 ° C.

[ Reference Example 4 ]
A 50 μm-thick film (glass transition temperature: 258 ° C.) obtained by molding the thermoplastic polyimide (APBPM) by an extrusion molding method was placed in a pressure vessel, and 6.0 MPa carbon dioxide gas was introduced therein, Carbon dioxide gas was infiltrated by leaving it for 30 minutes.
Then the carbon dioxide gas and penetration film several tens of seconds holding at the set pneumatic circulation thermostat to a temperature (240 to 300 ° C.) to the resin is softened, by foaming, average cell diameter 500nm approximately, volume expansion A 20% foamed thermoplastic polyimide film was produced. After depositing the foamed resin film to a thickness of 0.1 μm by electroless nickel plating, copper was laminated to a thickness of 5 μm by electrolytic plating. As a result, it was possible to obtain a foamed resin substrate having conductive layers on both surfaces of the foam.
The glass transition temperature of the foam part in the foamed resin substrate was 258 ° C.
Furthermore, this foamed resin substrate was left in an air circulation thermostat set at 240 ° C. for 1 minute to confirm whether swelling occurred at the interface between the resin and the metal body, but no problem in appearance was observed.

[ Reference Example 5 ]
A 100 μm-thick film (glass transition temperature: 258 ° C.) obtained by molding the thermoplastic polyimide (APBPM) by an extrusion molding method was placed in a pressure vessel, and 6.0 MPa carbon dioxide gas was introduced therein, Carbon dioxide gas was infiltrated by leaving it for 30 minutes.
Then the carbon dioxide gas and penetration film several tens of seconds holding at the set pneumatic circulation thermostat to a temperature (240 to 300 ° C.) to the resin is softened, by foaming, average cell diameter 500nm approximately, volume expansion A foamed thermoplastic polyimide film having a rate of 45% was produced. After depositing the foamed resin film to a thickness of 0.1 μm by electroless nickel plating, copper was laminated to a thickness of 5 μm by electrolytic plating. As a result, a flexible foamed resin substrate (copper-clad laminate) having conductive layers provided on both surfaces of the foam could be obtained.
The copper-clad laminate was used to form a circuit pattern on the copper surface by etching, and then a double-sided flexible printed circuit board on which a coverlay film was laminated for conductor protection was produced. Next, Pb-free solder bumps were formed on the substrate surface, and electronic components such as resistors were mounted on the surface to perform reflow soldering. The temperature profile at this time is 245 ° C. (less than 10 seconds). After reflowing, it was confirmed that the soldering part was not properly joined and the base material was swollen. However, no appearance problems were observed.

[ Reference Example 6 ]
In foamed thermoplastic polyimide films made created in Reference Example 5 were carried out relative dielectric constant measured in GHz band by volumetric method. The measuring instrument used is an impedance analyzer (HP4291B) manufactured by Hewlett-Packard. As a result, at the measurement frequency of 1 GHz, the film after foaming was 2.1 with respect to the relative dielectric constant 3.1 before foaming. Next, a double-sided conductive layer was laminated on the two films before foaming and after foaming in the same manner as in Reference Example 5, and a flexible printed board provided with a test print pattern with a circuit length of 100 mm was produced by etching. As a result of measuring the propagation time of the electrical signal by the TDR (time domain reflection) measurement method, the propagation time was about 1.2 ns for the non-foamed substrate, but about 20% was improved to 1 ns or less for the foamed substrate. The effect was obtained.

The foam substrate having a foamed molded body portion made of the specific thermoplastic polyamide resin of the present invention has excellent heat resistance of solder and a small bubble diameter and a low dielectric constant. It can be used for a circuit board (flexible circuit board, printed wiring board). The foam substrate of the present invention can be applied not only to a circuit board but also to an insulator, a heat insulator, a buffer material, and the like.

Claims (3)

Reduce the pressure after contacting and infiltrating a non-reactive gas with a non-reactive gas thermoplastic resin molding made of thermoplastic polyimide obtained by reacting an aromatic tetracarboxylic dianhydride and an aromatic diamine. Then, a foamed body having a glass transition temperature of 240 ° C. or higher of the foamed molded body portion is formed by thermocompression bonding the conductor on one surface at a temperature at which the thermoplastic resin is softened and foaming the thermoplastic resin molded body portion. A method for manufacturing a substrate. 2. The method for producing a foam substrate according to claim 1 , wherein an average cell diameter of a foam molded body portion in the foam substrate is 0.01 to 10 μm. The manufacturing method of the foam board | substrate of Claim 1 or 2 whose said conductor is 1 or more types selected from a metal, a metal alloy, a conductive resin, and carbon.