JPS63239893A - Flexible printed wiring - 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] [Industrial Application Field] The present invention relates to flexible printed wiring boards (hereinafter referred to as FPCs).
More specifically, it relates to an FPC that has stable performance against changes in humidity in the atmosphere in which it is used.

[Background Art] In recent years, the demand for FPCs has been increasing due to the demand for smaller and lighter equipment in the electrical and electronic industry fields. This FP
The general structure of C is that an electric circuit is formed on one or both sides of a base film, and a cover film is laminated on top of this circuit. Conventionally, polyimide films or polyester films have often been used as base films and cover films.Especially when immersing them in a solder bath when mounting components on an FPC, base films are often used in terms of heat resistance. An FPC using a polyimide film for both the cover film and the cover film is usually used.

[Problems to be solved by the invention] Recently, due to high-density mounting of components or miniaturization of FPCs themselves, electrical circuits of FPCs have been increased in density, that is, wiring has become thinner and the distance between adjacent wires has been shortened. There is a strong demand for

However, on the other hand, it is necessary to maintain high insulation resistance between wiring lines to prevent short circuits. The inter-line insulation resistance value is determined by the insulation performance of the adhesive or film surrounding the circuit, and if this also absorbs moisture, the insulation performance will drop significantly. Especially FP using polyimide film
In C, the water vapor permeability of the polyimide film located at the outermost layer of the FPC and in contact with the outside air is extremely high, so when the humidity of the FPC use atmosphere increases, the moisture content of adhesives, etc. increases, and the insulation resistance between lines increases. There may be cases where the value decreases.

Therefore, when designing an RPC, it is necessary to increase the distance between wires in order to provide a margin for the insulation resistance between the wires, which has been an obstacle to increasing the density of the circuit.

In addition, reliability has also been a problem in circuits used at high voltages.

An object of the present invention is to solve this problem and provide an FPC that can maintain stable line-to-line insulation resistance against changes in humidity in the atmosphere in which it is used.

[Means for Solving the Problems] The present invention provides a flexible printed wiring board having a structure in which a cover film is laminated on an electric circuit formed on at least one side of a substrate film. The outermost layer has a water vapor transmission rate of 5.0 <g
/rrf'/24hr10.1mm> This is a flexible printed wiring board characterized by being an aromatic polyamide film having the following properties.

The aromatic polyamide in the present invention is a polymer containing 50 mol% or more, preferably 70 mol% or more of the structural unit of the following formula. Here, Ar1 and ArS are halogen group, nitro group, 01-C3 alkyl group, C1-C3
alkoxy group, p and q are ○~3 alkyl groups, C1~
C3 alkoxy group, Y is -C-, -CH2-, -0-
, -8O2-, Z is a halogen group, a nitro group, C
1 to C3 alkyl group, C1 to C3 alkoxy group,
m.

n and r are integers of 0 to 3, and y has the structure 1 of either (1) or (2) of ○ or 1. This aromatic polyamide is obtained by the reaction of acid chloride and diamine or the reaction of diisocyanate and carboxylic acid.

The present invention contains 50 mol% of the structural unit represented by the above general formula.
As mentioned above, it is necessary to preferably contain 70 mol% or more, but if it is less than this range, sufficient mechanical properties and heat resistance cannot be obtained to achieve the object of the present invention. Also 5
The copolymerization component of less than 0 mol %, preferably less than 30 mol %, is not particularly limited, and may contain ester bonds, urethane bonds, imide bonds, heterocyclic bonds, etc.

Further, the aromatic polyamide of the present invention may contain lubricants, antioxidants, heat stabilizers, and other additives to the extent that the physical properties of the film are not impaired.

What is important in the present invention is that the aromatic polyamide film used has a water vapor permeability of 5.0 (g/rr?/2
4 hr/0, 1 mm> or less, preferably 2°0
(g/rrl'/24hr10.1mm) or less, more preferably 1. O(g/rr1'/24hr10.
1mm) or less, which is one to two orders of magnitude smaller than the polyimide film conventionally used in FI).For the first time, a film with such characteristics can reduce the moisture absorption rate as the humidity of the operating atmosphere increases. As a result, the moisture content of the portion in contact with the circuit can be maintained low for a long period of time, and an FPC with stable line-to-line insulation performance against humidity fluctuations can be obtained.

In order to obtain an aromatic polyamide film with low water vapor permeability, halogen groups, nitro groups present in the aromatic nucleus in the polymer,
This is also possible by selecting a polymer with a large number of substituents such as 01 to C3 alkyl groups and C1 to C3 alkoxy groups. When expressed as the ratio of amide bonds (number of substituents/number of amide bonds), it is preferably 0.2 or more, and more preferably 0.4 or more.

The moisture absorption rate of the film of the present invention is preferably 3.0% or less, and more preferably 2.5% or less. This is because if the moisture absorption rate is high, the moisture content of the adhesive that comes into contact with the film will also be high, reducing the insulation performance.If the film is directly laminated with metal by plating, vapor deposition, etc., the moisture absorption rate of the film will be low. That is more important.

The thermal expansion coefficient of the aromatic polyamide film of the present invention is 1
．． OXI○-5 or more and 4.0XIO-5 (1/'C) or less, more preferably 1.5X10-
3, OX 10-"<1/'C). This means that when bonding a metal foil, especially a copper foil, with an adhesive, and then heat-curing the adhesive, the bond between the copper and the film is f!!: 11 This is because if the tension is different, it will curl when returned to room temperature, and a similar problem will occur when immersing it in a solder bath when manufacturing an FPC and mounting components on it. arise.

Further, the dimensional change rate of the aromatic polyamide film of the present invention is preferably 2.0% or less, more preferably 1.5% or less at 250°C. This is because the temperature of the solder bath is usually 250 to 260°C, so when the FPC is immersed in the solder bath, the dimensional change rate of the film is large.
This is because it causes wrinkles on the PC.

However, in cases where the film is not heated as described above during the FPC manufacturing process or during its use, the above-mentioned ranges of thermal expansion coefficient and dimensional change rate are not satisfied and there is no need.

Next, a method for manufacturing an FPC according to the present invention will be explained.

The aromatic polyamide film of the present invention is formed from a polymer solution in which an aromatic polyamide resin is dissolved in an organic solvent by a solution molding method.

Polymerization is carried out by solution polymerization, in which a monomer is added to an organic solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, or tetramethylurea;
Alternatively, it may be carried out by an interfacial polymerization method using an aqueous medium, and depending on the constituent units of the polymer, it may be polymerized in sulfuric acid.

When forming a film, there are cases where the polymer solution after polymerization is used as is, and cases where the polymer is once reprecipitated in water etc. to isolate it, and after drying, it is dissolved again in an organic solvent and used for film formation. .

When forming a film directly from a polymer solution after polymerization, when using acid chloride and diamine as monomers,
It is necessary to neutralize hydrogen chloride produced as a by-product during polymerization, and neutralizing agents include inorganic bases such as calcium hydroxide, lithium hydroxide, calcium carbonate, and lithium carbonate, or their hydrates, ammonia, and jetanolamine. Use an organic base such as

When an inorganic base is used during neutralization, calcium chloride, lithium chloride, etc. are produced, but these inorganic salts have the effect of dissolving the polymer, and for the same reason, the above-mentioned polymer cannot be used as a solvent. These inorganic salts may also be added when redissolving in the solution.

A film is formed from the polymer solution prepared as described above by a method such as a dry method, a wet method, or a dry-wet method.

The dry method is a method in which a polymer solution is cast onto a drum, endless belt, etc., and the solvent is evaporated by heating with hot air to obtain a film. However, if the polymer solution contains an inorganic salt, this method is not preferred because the inorganic salt remains in the film and deteriorates the mechanical properties of the film.

In the wet method, the polymer solution is directly extruded into a coagulation bath, or the polymer solution is once cast onto a support such as a drum and then introduced together with the support into a coagulation bath, and organic solvents and inorganic salts are extracted in the coagulation bath. A water-containing gel film is formed. The gel film is then removed from the bath and dried to form the final film. Here, the coagulation bath generally consists of an aqueous medium, and may be mixed with an organic solvent, an inorganic salt, etc.

In the dry-wet method, similar to the dry method, the polymer solution is once dried on a support to form a gel film, and then this is immersed in a solution mainly composed of water, and the same as in the wet method, the polymer solution is dried on a support and a gel film is formed. In this method, a film is formed by extracting the water and then drying the water.

In any of these methods, it is necessary to perform stretching and heat treatment during the film forming process in order to develop sufficient physical properties as a film for IrPC.

Specifically, stretching is performed at an areal magnification of 0.9 to 9 times (area magnification is the value obtained by dividing the film area after stretching by the area before stretching, where less than 1 means shrinkage), and heat treatment. is 200~
At 400°C, preferably 250-350°C, 0.1-1
By setting these stretching and heat treatment conditions according to the constituent units of the polymer, predetermined physical properties can be imparted to the film.

The aromatic polyamide film obtained in this way is used as a substrate film or cover film for FPC.
can be produced by a conventional method using a polyimide film.

First, a conductor is laminated on one or both sides of the substrate film, and the method for laminating metal foil, especially copper, as a conductor is to bond electrolytic copper foil or rolled copper foil with a heat-resistant adhesive, or There are methods such as plating and vapor deposition to deposit metal on the film surface.
Either method may be applied. However, there are some points to be careful of due to the characteristics of the aromatic polyamide film of the present invention. For example, when bonding copper foil and film using an adhesive, care must be taken in selecting the adhesive and the bonding method. be. The adhesive must have heat resistance, chemical resistance, and electrical properties that satisfy the performance as an FPC, and adhesives such as epoxy/polyamide, epoxy/polyester, modified epoxy, and acrylic are used. etc. are suitable examples. On the other hand, urethane-based adhesives that generate gas when heated are not preferred because air bubbles are formed between the copper foil and the film because the aromatic polyamide film of the present invention has a low gas permeability. For the same reason, when bonding copper foil, it is necessary to sufficiently dry the remaining solvent in the adhesive coated on the film or copper foil in advance.

As described above, the metal foil layered on the substrate film is etched into the desired pattern to form a circuit.
If the electrical circuit is multi-layered, through-hole processing is performed, a cover film is laminated on top of the circuit using a heat-resistant adhesive, etc., and the final shape is formed by drilling, punching, etc. FPC is obtained.

The aromatic polyamide film of the present invention has a strong affinity with adhesives due to the strong polarity of the amide bonds contained in the polymer, so even if the film is not surface-treated, it will be able to bond well with metal foil. Can be bonded with strength. This is a very large advantage compared to conventional polyimide films, which usually require processing such as sandblasting to increase adhesive strength. Furthermore, when the aromatic polyamide film of the present invention is subjected to surface treatment such as corona treatment or glow discharge treatment, or anchor coating, even greater adhesive strength can be achieved between the aromatic polyamide film and metal laminated by adhesive bonding, plating, vapor deposition, etc. can give.

In the FPC of the present invention, a specific aromatic polyamide film is used for the outermost layer of the FPC that comes into direct contact with the outside air, as is clear from the purpose of stabilizing against humidity changes. For example, when forming a circuit on one side of a substrate film and laminating a cover film, the aromatic polyamide film of the present invention is used for both the substrate film and the cover film, but even if another film is used for the substrate film. The aromatic polyamide film of the present invention may be further laminated on the outside thereof, and when circuits are formed on both sides of the substrate film and cover films are laminated on both sides, the two cover films may be laminated with the aromatic polyamide film of the present invention. The substrate film may be any other film as long as it is a group polyamide film. Furthermore, even in an RPC in which an electric circuit is formed by laminating three or more layers, the aromatic polyamide film of the present invention may be similarly laminated on two surfaces of the outermost layer.

[Method of measuring characteristics] The characteristic values of the present invention are determined by the following measurement method.

(1) Water vapor permeability The water vapor permeability was measured using a high-speed water permeability measuring instrument manufactured by Honeywell (Model: W825) or the method of JIS Z-0208.

(2) After removing the effects of thermal expansion coefficient thermal contraction and moisture absorption and desorption, the film was
80℃~15 when heated to 0℃ and gradually cooled
It was calculated from the dimensional change at 0°C when loaded on the head. The amount of dimensional change was measured using a thermomechanical analyzer (TMA).

(3) Dimensional change rate Cut the film to 10 mm wide and 250 mm long, mark 25 mm from both ends to create a 20 mm paper test piece, heat this in an atmosphere of 250 ° C for 10 minutes, The length after cooling was measured and the dimensional change rate was calculated using the following formula.

Dimensional change rate (%) = l t 7 (mm - ■heat' - mm) l X
100 test length (4) Line-to-line insulation resistance The resistance values were measured for a sample without a cover film and a sample with a cover film using the insulation resistance measurement method of JPCA (Japan Printed Circuit Industry Association) standard FC01.

(5) Moisture Absorption Rate A film that has been conditioned for 96 hours at 25° C. and 75% RH is brought to an absolutely dry state, and the moisture absorption rate is calculated as a weight % based on the weight of the polymer from the weight change before and after.

(6) Strength and elongation A sheet of paper with a width of 10 mm and a length of 50 mm was set in a Tensilon type tensile testing machine according to ASTM-D-882, and the film was pulled at a tensile speed of 300 mm for 7 minutes.The strength and elongation when the film broke. was measured.

[Example] The present invention will be explained based on examples.

Example I N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) 15
2-chloro-p-phenylenediamine 4.99 to 0fl
k (J and 4,4°-diaminodiphenylsulfone 3.7
2k () and terephthalic acid chloride (10.15k) were added thereto, and after stirring for 2 hours to complete polymerization, 3.71 kg of calcium hydroxide was added and stirred for neutralization. , a transparent aromatic polyamide solution was obtained. This polymer solution was cast onto a metal drum, dried in an atmosphere of 150°C for about 10 minutes, and the gel film that had achieved self-retention was continuously peeled off. Next, the film was introduced into a water tank and stretched 1.13 times in the longitudinal direction while immersed in water.The film was then introduced into a tenter and heated at 350°C for about 3 minutes while being stretched 1.20 times in the width direction. and thickness 16
A film of μ was obtained.

Using this film as a substrate film, apply adhesive to a coating thickness of 15 to 20 μm after drying and heat at 70°C for 30 minutes.
After drying for a minute, heat and press a 35μ electrolytic copper foil at 100°C. Next, curing was performed at 140° C. for 3 hours in a hot air oven to obtain a copper-clad board. The adhesive is “Byron 200”
” (polyester resin) [manufactured by Toyobo ■] 100 copies and “
Epicoat 871” (epoxy resin) [Shell Chemical ■
1,100 parts of the product was dissolved in 500 parts of methyl ethyl ketone,
Further, 15 parts of phthalic anhydride (hardening agent) was added to prepare the product.

Table 1 shows the properties of the copper-clad board.

A sample was prepared by etching the copper foil layer of the above-mentioned copper-clad plate to form a pattern for measuring inter-line insulation resistance. Also,
After forming an electric circuit similar to this, a sample was created in which a cover film was laminated on top of this circuit using the same film, adhesive, and bonding conditions as those for bonding the substrate film and copper foil described above.

These two samples were heated at 25°C and 150%RH for 240°C.
After conditioning the humidity for a period of time, the line-to-line insulation resistance was measured, and the sample was then moved to 40° C. and 90% RH to measure the change in the line-to-line insulation resistance over time. The results are shown in Table 1.

Example 2 5.70 kq (J) of 2-chloro-p-phenylenediamine and 2.0 kq (l) 4,4'-diaminodiphenyl ether were dissolved in NMP 150α, and 11.89 kq 2-taloroot terephthalic acid chloride was added thereto. After stirring for 2 hours to complete polymerization, 5.01k of calcium carbonate was added.
g was added and stirred for neutralization to obtain an aromatic polyamide solution. Using this polymer solution, a film with a thickness of 16 μm was prepared in the same manner as in Example 1. However, the stretching is 1.05 times in the longitudinal direction, 1.1 times in the width direction, and the tenter temperature is 32
It is 0°C.

This film was used as a substrate film and a cover film, and was laminated with copper foil in the same manner as in Example 1 to prepare a sample for measuring inter-line insulation resistance. Table 1 shows the results of the same measurements as in Example 1. Shown below.

Example 3 198 g of 4,4°-diaminodiphenylmethane was dissolved in 300 cc of dimethylacetamide, 102 g of 2-chloro-terephthalic acid chloride and 119 g of terephthalic acid chloride were added thereto for polymerization, and then 73.0 g of lithium carbonate was added. Neutralization was performed with 9 g to obtain an aromatic polyamide solution. This was cast onto a glass plate and dried at 150°C for 5 minutes, then the film was peeled off, fixed on a metal frame, and washed with water.

Next, heat it at 340℃ for 5 minutes and dry it to a thickness of 16μ.
obtained the film.

Using this film as a substrate film and a cover film, a sample for measuring inter-line insulation resistance was prepared in the same manner as in Example 1, and the measurement results are shown in Table 1.

Comparative Example 1 Polyimide film (manufactured by DuPont, trade name "Kapton", thickness 25μ, adhesive surface sandblasted) was used as a substrate film and a cover film,
In the same manner as in Example 1, lamination with copper foil was carried out, and a sample without a cover film and a sample with a cover film for measuring the insulation resistance between lines were prepared, and the same measurements as in Example 1 were carried out. The results are shown in Table 1. .

Comparative Example 2 An electric circuit for measuring inter-line insulation resistance was formed using a copper clad plate in which copper foil was laminated onto the film prepared in Example 1, and the polyimide film of Comparative Example 1 was laminated on top of this as a cover film. A sample was prepared using the same method as in Example 1, and the change in inter-line insulation resistance over time was measured in the same manner as in Example 1. The results are shown in Table 1.

As shown in Table 1, for example, the atmosphere of RPC is 25
When the high temperature conditions change from ℃ and 50% RH to 40℃ and 90% RH, the inter-line insulation resistance value decreases in about 30 minutes in the comparative example using polyimide film. On the other hand, although the FPC of the present invention has a film thickness of 16 μm, which is thinner than the 25 μm of the polyimide film, it still maintains a high resistance value even after 100 hours have elapsed. This shows that the FPC of the present invention is extremely stable against humidity fluctuations.

[Effects of the Invention] The FPC according to the present invention has the effect of being able to maintain stable line-to-line insulation resistance against changes in humidity in the atmosphere in which it is used.

In addition, the RPC of the present invention exhibits excellent properties in many aspects required for RPC, such as solder heat resistance, flexibility, chemical resistance, and electrical properties, and is suitable for wiring of -m electronic devices. Although it can be used as a material, it is particularly suitable when exposed to high temperature conditions, when high voltage is applied, or when high-density wiring is required for miniaturization.

Claims (1)

[Claims] In a flexible printed wiring board in which a cover film is laminated on an electric circuit formed on at least one side of a substrate film, the outermost layer on both sides of the flexible printed wiring board has a water vapor permeability of 5.0 (g/m^2/ 24 hours
1. A flexible printed wiring board characterized by being an aromatic polyamide film having a thickness of r/0.1 mm or less.