JPS60130190A - Substrate for flexible printing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flexible printed circuit board formed by bonding a metal foil, such as a copper foil, and an insulating film with an adhesive, with or without a resistor layer.

Conventionally, polyimide films, polyester films, and epoxy resin-impregnated glass cloth have been known as insulating films used in circuit boards of this type. Among these, epoxy resin-impregnated glass cloth has relatively good dimensional stability and heat resistance, but has the disadvantage of poor flexibility, and polyester film has a problem of poor heat resistance.

On the other hand, polyimide film has excellent heat resistance, electrical insulation, chemical resistance, radiation resistance, mechanical strength, etc., and in particular, it has excellent heat resistance, solvent resistance and Since it satisfies both flexibility requirements, it is also attracting attention as an insulating film for circuit boards.

However, a circuit board made from a flexible printed circuit board using polyimide film having the above advantages as an insulating film through the required processes such as resist printing, etching, plating, cover coat lamination, and hanging, can be manufactured after the above process. Blistering, peeling, and O voids (bubbles) are likely to occur in the insulating film, which may lead to deterioration in circuit characteristics or, in extreme cases, to difficulty in using the film as a circuit board.

This problem is said to be caused by the fact that polyimide films have higher hygroscopicity than polyester films.

In other words, a circuit board having an insulating film undergoes repeated cycles of heating and drying and humidification and moisture absorption during the various steps of manufacturing the circuit board, so if the insulating film is highly hygroscopic, it will contain a large amount of moisture. During this process, the moisture is rapidly vaporized and expanded, resulting in blistering, peeling, and voids as described above.

Therefore, it is desirable for an insulating film to have as low moisture absorption as possible, but conventional polyimide films,
For example, a film made of general polyimide obtained by reacting pyromellitic anhydride and aromatic diamine,
All of them have the disadvantage of higher hygroscopicity than polyester films. For this reason, the occurrence of blistering, peeling, and voids during the heat treatment, for example during cover coat lamination or during printing, cannot be avoided.

For this reason, attempts have been made to add a vacuum drying step before heat treatment, or to store the material in a dry box after drying. However, such operations not only complicate the circuit board manufacturing process and reduce productivity, but also
Conventional polyimide films exhibit high hygroscopicity even under normal conditions, so even if the above procedure was attempted, moisture absorption during handling could not be sufficiently prevented, and as a result, the occurrence of blistering etc. could not be significantly suppressed. .

The inventors conducted various experimental studies to solve the above-mentioned problems with conventional polyimide films, and discovered that a film made of a specific polyimide that had never been used before had an extremely low moisture absorption rate. It was discovered that when applied as an insulating film for circuit boards, higher quality printed circuit boards with suppressed blistering, peeling, and voids during heat treatment as described above could be obtained, leading to the completion of this invention. Ta.

That is, the present invention provides a metal foil with or without a resistor layer, which is bonded to a metal foil using an adhesive using the general formula; 0-R6 is a hydrogen atom, a lower alkyl group or a halogenated alkyl group. This relates to a flexible printed circuit board made by laminating films.

In the flexible printed circuit board of the present invention, the insulating film is obtained mainly from a repeating unit represented by the above general formula, that is, from a biphenyltetracarphonic acid component and an aromatic ether diamine having a specific structure. This film (for example, conventional polyimide film contains a tetracarboxylic acid component such as pyromellitic anhydride or benzophenone tetracarphonic dianhydride, and 4,4'-diaminodiphenyl ether or 4-diaminodiphenyl ether). - It has the characteristic of having lower hygroscopicity than polyimide films made in combination with amines such as 4'-diaminodiphenylmethane.

In other words, the above conventional polyimide film is generally made of 25
While the moisture absorption rate at 280% relative humidity (hereinafter abbreviated as RH) at °C is about 1 to 2%, the polyimide film according to the present invention has a moisture absorption rate of 0.5% under the conditions described in (2).
Below, in terms of good and bad, it shows a low hygroscopicity of 0.3% or more. When such a low moisture absorption polyimide film is applied as an insulating film for a circuit board, it should be dried normally after humidification treatment, and then left under normal conditions before being coated with a cover coat laminate, a no-interface, etc. Even when subjected to heat treatment, the insulating film may swell, peel, or
The occurrence of voids etc. is almost no longer observed.

As described above, according to the present invention, blistering during heat treatment,
It is possible to stably provide higher quality flexible printed circuit boards with reduced problems such as peeling, and it also eliminates the need for vacuum drying before heat treatment or storage in a dry box after drying. Good results can also be obtained in improving productivity.

In addition, the moisture absorption rate described in this specification refers to the dry film dried at 50 PaC for 24 hours (usually 50±5
It is expressed as the weight change rate when saturated moisture absorption is carried out under constant temperature and humidity.
The formula for calculating the moisture absorption rate when the temperature is 5°C and 280% RH is as follows.

W.

W, ; Weight W immediately after drying at 50'C for 24 hours,
Place the dry film in a humidity-controlled atmosphere at 25°C and 280% RH.
The structure of the flexible printed circuit board of the present invention will be described in detail below with reference to the drawings. , FIG. 1 and FIG. 2 show two examples of flexible printed circuit boards of the present invention. FIG. 1 is a board without a resistor layer, and FIG. 2 is a board without a resistor layer. This is a board with In both figures, 1 is a metal foil, 2 is an insulating film made of a polyimide film bonded to the metal foil 1 via an adhesive 3, and 4 is a resistor layer formed on the metal foil 1. .

Copper foil is mainly used as the metal foil 1, but aluminum foil or other conductive metal foil may also be used. Metal foil]
The thickness is generally about 15 to 70) m. The layer 4 of the resistor is formed by forming conventionally known resistance metals such as nickel-phosphorus, tin-nickel, tin-nickel-sulfur 715, tin-nickel-copper-sulfur on the metal foil 1 by plating or other methods. , its thickness is usually about 001 to 101 inches.

It is desirable that the adhesive 3 has heat resistance and low moisture absorption, and from this point of view, thermosetting adhesives such as polyacrylic acid alkyl ester, rubber-epoxy, and polyester resin are preferred. Ru. The thickness of the adhesive 3 is usually about 5 to 51 inches.

The polyimide film constituting the insulating film 2 has the general formula; ), and to produce this polyimide, biphenyltetracarboxylic dianhydride or its derivatives represented by the general formula; An aromatic tetracarboxylic acid component and an aromatic diamine whose main component is an aromatic ether diamine represented by the general formula: (R1-R6 are as described above) are used.

Hyphenyltetra-h carboxylic acid dianhydride or its derivatives represented by the above general formula include 3, 3, 4, and 4.
'-Biphenyltetracarboxylic dianhydride, 2, 3, 3
',47-biphenyltetracarboxylic dianhydride and derivatives such as acid halides, diesters, and monoesters, and these compounds can be used singly or in combination.
Use by mixing more than one species.

Among these compounds, it is recommended to use 3,3',4,4-biphenyltetracarboxylic dianhydride in an amount of 50 mol% or more in the components represented by the above general formula in order to improve the mechanical properties of the resulting polyimide film. Preferable from the viewpoint of strength.

Other aromatic tetracarboxylic acid components used with these main components include pyromellitic acid, 3,3',
4,4'-benzophenonetetracarboxylic acid, 2,3,
・6,7-naphthalenetetracarboxylic acid, ■・4・5・
8-Naphthalenetetracarboxylic acid, 3, 3', 4, 4'
Examples include acid dianhydrides such as -diphenyl ether tetracarboxylic acid and derivatives thereof, and one or more of these compounds can be used.

Specific examples of the aromatic ether diamine represented by the above general formula include 2,2-bis[4-(4-aminophenoxy)phenyl-1propane, 2,2-his[3-methyl-
4-(4-aminophenoxy)phenyl]propane, 2
・2-bis[3-chloro-4-(4-aminophenoxy)phenyl 1-propane, ■ ・1-bis[4-(4-aminophenoxy)phenylconitane, 1,1-bis[3-
Methyl-4-(4-aminophenoxy)phenylconitane, 1,1-bis[3-chloro-4-(4-aminophenoxy)phenylconitane, ■,1-bis[3,5-dimethyl-4-(4 -aminephenoxy)phenylconitane, bis[4-(4-aminophenoxy)phenylcomethane, bis[3-methyl-4-(4-aminophenoxy)phenylcomethane, bis[3-40-4-(4- aminophenoxy) phenylconitane, bis[3,5-dimethyl-4-(4-aminophenoxy)phenylcomethane, 2,2-his[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2 -Bis [3.5
-dibromo-4-(4-aminophenoxy)phenyl]
Examples include propane, and one or more of these compounds may be used in combination.

Furthermore, among these compounds, 2,2-bis[4-(4
-aminophenoxy)phenyl-1-propane is particularly preferably used. In addition to this, 2.2-bis [4-
(4-Aminophenoxy)phenyl"hexafluoropropane and the like are also preferably used.

Other aromatic diamines used with these main components include 4,4'-diaminodiphenyl ether, 4
・4'-diaminodiphenylmethane, 4,4-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfide,
4,4'-diaminodiphenylpronofone, 4,4'-
Diaminodiphenyl, paraphenylenediamine, metaphenylenediamine, 1,5-diaminonaphthalene, 3.
3'-dimethyl-4,4'-diphenyldiamine and o,, N-C>o-Q OiIJo(yNn2, ll2
N00 building 502-C times (NNH2, 112N(FC Pesa Nl(,,, [(2N-<II) 0-C>O Benito NlI2, H2
Npesi00coo-4n0(yNn,.

etc., and one or more types of these can be used.

There are two preferred methods for MJMing a polyimide film using the above-mentioned aromatic tetracarboxylic acid component and yJ exogroup diamine.

One method is to make a polyimide precursor with polyamic acid by reacting these two components in an organic polar solvent with approximately equimolar moles, and to form a film of the polyimide precursor from a solution of this polyimide precursor. is imidized by heating.

Examples of the organic polar solvent include N-methyl-2-pyrrolidone, N-N-dimethylpolamide, N-N-dimethylacetamide, dimethyl sulfoxide, tetramethylurea, metafresol, para-cresol, meta-, para-cresol. Examples include solvents that can dissolve the polyimide precursor, such as mixtures of polyimide, xylenol, and phenol. The amount of the organic polar solvent to be used is preferably such that the concentration of both components (d) is usually 5 to 30% by weight.

In this organic solvent, approximately equal moles of the above components are usually 0 to 80
The reaction is carried out at °C for 1 to 10 hours to obtain a polyimide precursor solution. The polyimide precursor obtained at this time has a logarithmic viscosity (0.59/ in N-methyl-2-pyrrolidone),
00me (measured at 30°C with D concentration) is usually 15-6
It is preferable that the polymer has a high molecular weight within the range of .

If this value is too small, the resulting polyimide film will have low mechanical strength, which is not preferred. Note that this logarithmic viscosity is calculated using the following formula.

A polyimide precursor film can be formed from the polyimide precursor solution obtained in this manner by a known forming method. That is, a method in which a solution of a polyimide precursor is poured onto a smooth flat plate such as a stainless steel plate, a glass plate, an aluminum plate, a copper plate, etc. to form a film, and the solvent is gradually removed from this film by heating.
Alternatively, there is a method in which the solution is poured onto an endless stainless steel belt to form a film, which is then introduced into a heating furnace and the solvent is gradually removed. The film of the polyimide precursor thus obtained is usually heated at 100 to 350'C for about 30 minutes.
By heating for ~300 minutes to cause an imidization reaction,
A polyimide film of this invention with low moisture absorption can be obtained. Note that when forming a film from a polyimide precursor solution, the removal of the solvent and the heating for the imidization reaction may be performed continuously, or the second half of the solvent removal and the first half of the imidization reaction may be performed simultaneously. It's okay.

Another method for producing the polyimide film of the present invention was investigated by the inventors in order to obtain a polyimide film with low moisture absorption, and the repeating unit represented by the general formula: (R, to R6 are as described above) This discovery was made based on the knowledge that polyimide whose main component is soluble in solvents.

That is, in this production method, a solvent-soluble polyimide is obtained by reacting approximately equimolar moles of the aromatic tetracarboxylic acid component and aromatic diamine in a phenolic solvent, and a polyimide film is formed from this polyimide solution. do.

This manufacturing method does not require a high-temperature treatment process for imidization after being formed into a film, and it is possible to obtain a film of good quality because the film does not have voids due to dehydration during the imidization reaction. can.

The reaction in a phenolic solvent in this production method is
This is a polycondensation reaction consisting of a reaction to produce a polyimide precursor, such as an amidation reaction, and a subsequent imidization reaction, and is usually carried out at a temperature of 80 to 220'C for 1 to 7 hours. When the polyimide precursor is polyamic acid, water is produced as a by-product during the imidization reaction, and this water is removed by distillation out of the reaction system. Removal of water limits the reaction rate and favors the production of high molecular weight polyimides.

Since phenolic solvents are difficult to miscible with water, it is easy to distill off the by-product water, and it is economical and easy to volatilize during film formation.3 Polar solvents such as pyrrolidone are not suitable for this reaction from the above point of view. Appropriate guess. As the phenolic solvent, metacresol, para-cresol, xylenol, phenol, and mixed solvents thereof are used. A preferred method is to use an aromatic solvent such as xylene or toluene which is azeotropic with water together with these phenolic solvents to facilitate distillation of water.

The polymerization reaction product obtained in this way was not completely imidized.
/ 100 nze (Da degree"?:30"C down itq
Polymer ij having a defined logarithmic viscosity in the range of about 15 to 6
) polyimide.

This polyimide can be used as it is as a solution in the phenolic solvent used in the polymerization reaction, or if necessary, it can be purified by precipitating it in acetone or methanol, filtered and dried, and then purified using cresol or other phenolic solvent. It can be used by dissolving it in various organic solvents such as, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylpolamide, and hexamethylenephosphoramide.

The solid content concentration of the sample used is not particularly specified;
It can be selected as appropriate depending on the purpose of use, but it is preferably 25% or less.

If this solid content concentration becomes too high, the polyimide becomes insolubilized or becomes sticky during storage, so i(1,) is preferable.
. t, f This polyimide solution has good storage stability; 11)) It can be stored stably for 6 to 12 months.

To form a polyimide film from this solution of solvent iiJ-soluble polyimide, ζ1/, 7
This is carried out by pouring this solution onto a metal li plate to form a film, and gradually removing the solvent by heating. In addition, the following method may also be used.

One method is to impregnate a glass fiber cloth or carbon fiber cloth with a polyimide precursor solution obtained in the same manner as the above method, gradually remove the solvent by heating, and then further heat to initiate an imidization reaction. A polyimide-impregnated glass fiber cloth or carphone fiber cloth is obtained, and several sheets of this are laminated and pressed with a hot press to obtain a low hygroscopic polyimide m scrap film.

Still another method is to reprecipitate the polyimide precursor with water from a polyimide precursor solution obtained in the same manner as the above method and filter it to obtain a fine powder of about 5 to 301'M. Polyimide precursor fine powder is heated at 250'C for about 2 hours to dry it and completely imidized to produce polyimide powder, and this polyimide powder is pressed using a mold at 300-350'C. By molding, a polyimide film with low moisture absorption is obtained.

In addition, in order to produce the above polyimide powder, j-, i
i [! Polyimide powder can also be obtained by reprecipitation in water from a solution of this polyimide using a solvent-soluble polyimide.

The polyimide film obtained by any of the methods described above contains hyphenyltetranoJruponic acid dihydrate or its derivatives represented by the above general formula, which is present in the aromatic tetracarboxylic acid component during production. Type 1 or 2
Species JL
0 mol% or more and the other 50 mol% or more, preferably 70 mol% or more of both, so that the moisture absorption rate is 0.5 mol% or more.
% (25'C, 80% RI-1).

In particular, biphenyltetracarboxylic acid dianhydride represented by the above general formula or its derivative 3, 3, 4, 4
'-hyphenyltetracarboxylic dianhydride, and the aromatic ether diamine represented by the above general formula is 2.
・2-bis[4-(4-aminophenoxy)phenyl 1
A polyimide film made of polyimide whose main component is a repeating unit represented by the formula obtained using propane has better moisture resistance and also has excellent mechanical strength.

In addition, in the aromatic tetracarboxylic acid component, hyphenyltetracarboxylic acid dianhydride or its derivative is used at 100 mol %, and in the aromatic diamine, aromatic ether diamine represented by the above general formula], 00 Moisture absorption rate of polyimide film obtained by using mol% is 02-04%
(25°C, 80% RH), and in a more preferred embodiment, it is 0.3% or less, indicating superior moisture resistance.

The thickness of the polyimide film produced as described above is generally about 5 to 250/ffi. This film is used as the insulating film 2, and this is used as the adhesive 3.
By laminating on the metal foil ↑ with or without a layer 4 of resistor through the layer 4, a flexible printed circuit board of the invention as shown in FIGS. 1 and 2 is obtained.

The above laminating method varies depending on the type of adhesive 3 applied, but generally it is applied at 50 to 200'C and 5 to 5
0 Kg/am thermocompression bonding method is adopted. On this occasion,
Apply Kf agent 3 to metal 711 or insulating film 2.
Alternatively, it may be made into a film in advance and inserted between the metal wire 11 and the insulating film 2. The thermosetting adhesive usually hardens during the above-mentioned Lamio 1 process to form an adhesive layer with good heat resistance, but may be subjected to treatments such as after-curing if necessary.

As detailed above, according to the present invention, it is possible to stably and easily provide a high-quality flexible printed circuit board with reduced problems such as blistering and peeling during circuit board production.

Examples of this invention will be described below. In addition, 1st to 3rd
In the table, 5-BPDA is 3-3'-4-4'-biphenyltetracarphonic dianhydride, and a-BPDA is 2.3
・3,4-biphenyltetracarboxylic dianhydride, PD
A is pyromellitic dianhydride, BTDA is 3・-3′・
4,4'-benzophenonetetracarboxylic dianhydride,
BAPP is 2-2-hisc4-(4-7minophenoxy)phenyl]propane, BAPFi; i2,2-bis[
4,-(4-aminophenoxy)phenyl 1 hexafluorophore lopane, BAP84 to 2,2-J:-su[4-
(4-aminephenoxy)phenylcomethane, BAPB
rP is 2,2-bis[3,5-dibromo-4=(4-aminephenoxy)phenyl]furopane, BAPS is 4.
4'-di(m-aminophenoxy)diphenylsulfone, DADE represents 4,4'-diaminodiphenyl ether.

In addition, the logarithmic viscosity is 0.5 in N-methyl-2-pyrrolidone.
y/100me (value measured at 30'c at D concentration).

Examples 1 to 9 N-methyl-2-pyrrolidone and the aromatic diamine shown in Table 1 were placed in the separable flask No. 11 and mixed well at room temperature until the diamine was completely dissolved. The amount of N-methyl-2-pyrrolidone used was such that the monomer concentration of aromatic diamine and aromatic tetracarboxylic dianhydride was 12% by weight.

Next, aromatic tetracarboxylic dianhydrides shown in Table 1 were gradually added to the flask while suppressing heat generation.

During this time, the viscosity of the solution gradually increased. After this, 5 minutes at room temperature.
After stirring for a period of time, a solution of polyamic acid having a logarithmic viscosity shown in Table 1 was obtained.

This polyamic acid solution was poured onto a glass plate to form a film, dried in a hot air dryer at 320°C for 30 minutes, further dried at 180°C for 30 minutes, and then dried at 250°C for 30 minutes.
By heating for 31 minutes at C and imidizing, 5o±
The polyimide film with a thickness of 5P is jH.

- Each polyimide film obtained by the method described above was dried for 24 hours in a hot air dryer at 5°C, and then
After weighing it to the size of 25"C, 80".

2411=''' in a desiccator with humidity adjusted to RH.
The sample was weighed using an apparatus, and the moisture absorption rate was determined from the change in weight.The results were as shown in Table 1 below. ,In addition,
For reference, the moisture absorption rate of a polynisdel film (polyethylene terephthalate I film, tJ) having a thickness of 5 Q pm was determined in the same manner as above, and the result was 0.5%.

In Table 1, each polyimide film obtained by the above method is
．． 71) n-thick copper foil via thermosetting adhesive] 50'
C. Bonded by thermocompression under the conditions of 30Kg/crl,
A flexible full printed circuit board of the present invention as shown in FIG. 1 was obtained.

In addition, as the above-mentioned thermosetting adhesive, Epon #1001
(Product name manufactured by Shell Co., Ltd., 100 parts by weight of epoxy (711 resin), Epon #], 007 (Product name manufactured by Shell Co., Ltd.:
epoxy resin) 3 parts by weight, Hiker #I 072 (B
An adhesive composition consisting of 100 parts of acrylonitrile-butadiene copolymer resin (Carpoxol group-containing acrylonitrile-butadiene copolymer resin) and 80 parts by weight of methyl ethyl ketone was used as a film having a thickness of 25 mm.

Examples 10 to 16 Mek7 Valacresol, xylene, aromatic tetra-h luponic dianhydride and aromatic diamine not shown in Table 2 were charged into the separable flask No. 11.

The amount of meta- and para-cresol used was such that both the acid dianhydride and diamine moly/mer components were J5% by weight based on the total amount of meta- and para-cresol. In addition, the amount of xylene used is 1 of this amount of meta, para-cresol used.
0% by weight.

These mixtures were heated to 150°C for 60 minutes with stirring.
The temperature rose to . During this temperature rise, a dehydration reaction occurred at 140 to 145°C, and an azeotropic mixture of water and xylene was distilled out of the system. A homogeneous black and colored high viscosity solution of ground polyimide was obtained by reacting at 150°C for 3 hours. The logarithmic viscosity of the polyimide thus obtained was as shown in Table 2.

This polyimide solution was poured onto a glass plate to form a film, dried in a hot air dryer at 20°C for 30 minutes, and then further dried at 200°C for 60 minutes to form a film of 50±5
The moisture absorption rate of each polyimide film obtained was measured in the same manner as in Examples 1 to 9, and the results are as shown in Table 2 above. there were.

Table 2 shows that a flexible printed circuit board of the present invention having the structure shown in FIG. 1 was obtained in exactly the same manner as in Examples 1 to 9 using each polyimide film obtained by the above method. .

Comparative Examples 1 to 7 Comparative Examples 1, 2.3 and 5 were prepared in the same manner as Examples 1 to 9 using the aromatic tetracarboxylic dianhydride and aromatic diamine shown in Table 3. A solution of polyamic acid having a logarithmic viscosity was obtained, and from this solution 50 ± 577 m
A polyimide film with a thickness of . Comparative Example 4 was a commercially available 50 mm thick film (Kapton manufactured by Teyupon; PD
A polyimide film consisting of A and DADE was used. In addition, as Comparative Examples 6 and 7, solvent-soluble polyimide was prepared in the same manner as in Examples 10 to 16 using the aromatic tetracarboxylic dianhydride and y) aromatic diamine shown in Table 3. However, it became completely insolubilized by the reaction at 150''C for 1 hour, and a polyimide film could not be obtained.

-1- The moisture absorption rate of each polyimide film of Comparative Examples 1 to 5 was measured in the same manner as Examples 1 to 9, and the results were as shown in Table 3 below.

In Table 3, a comparative flexible printed circuit board having the structure shown in FIG. Obtained.

Using the circuit boards according to the above Examples 1 to 16 and Comparative Examples 1 to 5, a model circuit pattern was formed through the usual methods such as resist printing, etching, plating, cover coat lamination, bank, etc. A flexible printed circuit board (I PC-FC-200) having the following was fabricated.

During the "2nd paper production" process, a vacuum drying process (room temperature,
Changes in the properties of the polyimide film after cover coat lamination and bank treatment were examined with and without addition of J OmmHj (7 hours at 7 hours), and when no abnormality was observed in the polyimide film ( ○), cases where some voids were observed were marked as (△), and cases where voids and swelling were significant were marked as (x).The results were as shown in Table 4 of the Ichiboki1. In addition, NoJ Harcoat Laminate-1- is made by applying the same film (adhesive-based) as the base material of 25μIll thickness to 130"C and 30cm on the board on which the Motel circuit pattern is formed!?
/c.rrl, and the subsequent bank treatment was performed at 260C for 10 seconds. Furthermore, in Table 4, A indicates the case where the vacuum drying step was not added, and B indicates the case where the vacuum drying step was added.

As is clear from the results in Table 4, the flexible printed circuit board of the present invention can prevent blistering of the insulating film (polyimide film) even without troublesome pre-drying such as vacuum drying. It can be seen that a circuit board of better quality with less occurrence of voids etc. can be obtained.

Incidentally, although each of the Examples described in ``2'' is shown for an example without a resistor layer, the same results as in ``2'' were obtained even in the case of a flexible printed circuit board having a resistor layer.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one example of a flexible printed circuit board of the present invention, and FIG. 2 is a sectional view showing another example. J. Metal foil, 2. Polyimide film (insulating film)
, 3 - Adhesive, 4 Resistor layer. Patent applicant Nitto Electric Industry Co., Ltd. Figure 1

Claims (1)

[Claims] (1) Metal foil with or without a resistor layer.”
2. General formula: (wherein, R, , R7
, R3 and R4 are hydrogen atoms or halogen atoms, R5
and R6 is a hydrogen atom, a lower alkyl group, or a halogenated alkyl group.
A flexible printed circuit board made by laminating polyimide films (280% relative humidity).