JPH02279330A - Profile flexible printed wiring board - Google Patents

Abstract

PURPOSE:To obtain a profile FPC possible in molding processing while holding soldering resistance by using a heat-resistant film having a specific heat- shrinkage factor and a heat-softening point as a base film or a cover film. CONSTITUTION:A base film or cover film constituting a profile flexible printed wiring board (FPC) is composed of a heat-resistant film having a heat-shrinkage factor of 1.5% or less at 250 deg.C, a heat-softening point of 200 - 350 deg.C under load of 0.5kg/mm<2> and having no m.p. at 400 deg.C or less. The profile FPC means one not having a perfectly flat plate-shape but having unevenness at least on a part of a surface and heat-molding processing (draw forming) is applied to at least one of the base film or cover film used in the FPC. By this method, the profile FPC capable of molding processing while holding soldering resistance is obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a flexible printed wiring board (hereinafter abbreviated as FPC), and more particularly relates to an FPC having solder resistance and having an uneven surface. It is something.

[Prior Art] FPCs are being used frequently in the electric and electronic industries from the viewpoint of downsizing equipment. The general structure of this FPC is such that an electric circuit is formed on one or both sides of a base film, and a cover film is laminated thereon or a resist ink is applied thereon. Conventionally, aromatic polyimide films and polyethylene terephthalate (PET) films have been used as base films or cover films, and when mounting components, various methods such as solder bath dipping, wave soldering, and reflow soldering are used. Aromatic polyimide film is used when solder resistance is required, such as when the entire FPC or a large portion of the FPC is soldered, and PET film is used when only spot soldering is required. has been done. Aromatic polyimide films are also used when films used in FPCs are required to have self-extinguishing properties due to flame retardant regulations for electronic devices and the like.

[Problems to be solved by the invention] Conventional FPCs have been bent or bent after mounting components and incorporating them into equipment, but the FPC itself has a flat plate shape and cannot be used for electrical components. are simply arranged on a flat surface, and the mounting function of the FPC is simply that of a flat wiring board. Therefore, in the past, even if it was said to increase the packaging density of FPC, it was only possible to take a two-dimensional method such as narrowing the distance between wires.
At present, the film used for this purpose had no function beyond holding the electrical circuit flat.

It is possible to create a three-dimensional irregularly shaped FPC by adding irregularities to the surface because PET film can be drawn and formed, but PET film has poor solder resistance, so the range of applications is extremely narrow and it is not practical. lacking in sex.

On the other hand, aromatic polyimide films used in FPCs that require solder resistance generally have very poor moldability (heat forming), making it industrially impossible to manufacture anything other than flat FPCs. This has been a constraint on expanding the functions of FPC.

In order to improve the above-mentioned problems, the present invention provides an irregularly shaped FP.
The purpose is to provide an FPC with unprecedented functions.

[Means for Solving the Problems] The present invention provides a modified flexible printed wiring board (deformed FPC) having irregularities formed on its surface, in which a base film and a cover film constituting the deformed FPC are heated at 250°C. The shrinkage rate is 1.5% or less, the thermal softening point under a load of 0.5 kg/m is 200°C or more and 350°C or less, and 4
It is characterized by being made of a heat-resistant film that does not have a melting point below 00°C.

The irregularly shaped FPC of the present invention refers to one that is not completely flat but has irregularities formed on at least a part of its surface, and
At least one of the base film and the cover film used in the PC is subjected to thermoforming (drawing). There are no particular limitations on the size, shape, aperture ratio, etc. of the unevenness, and it can range from small unevenness such as a dome-shaped depression formed to create a click feeling in a membrane switch to a box-like shape in which the entire FPC is formed. Including those that have been.

The heat-resistant film in the present invention refers to a heat-resistant film that does not have a melting point below 400°C, and those having a melting point below 400°C are unsuitable because of their poor releasability from the molding die. Specific examples of the heat-resistant polymer constituting the heat-resistant film include aromatic polyamide, aromatic polyimide, polyparabanic acid, etc. Among these, aromatic polyamide is the most preferred. Pyromellitic dianhydride and 4.4'-
Polyimide films made from diaminodiphenyl ether have poor formability and are unsuitable, but recently developed polyimide films made from biphenyltetracarboxylic dianhydride and diaminodiphenyl ether show good formability.

The aromatic polyamide film in the present invention is an aromatic polyamide polymer containing repeating structural units represented by the general formula -NH-At1-NHCO-ArI-CO- or -NH-Ar3-CO, either alone or in copolymerized form. Or a film made of a mixture thereof.

Here, ArI, Ar2, and Ar3 contain at least one aromatic ring and may be the same or different, and representative examples thereof include the following.

X is selected from OCR2SO2-. In addition, some or all of the hydrogen atoms on the aromatic rings are halogen groups, nitro groups, CI to C
It also includes those substituted with a substituent selected from 3 alkyl groups and 01 to C3 alkoxy groups. Furthermore, it also includes those in which the hydrogen atom bonded to the nitrogen atom constituting the amide bond in the above general formula is substituted with a substituent.

The base film or cover film used in the FPC of the present invention has a heat shrinkage rate of 1.5% or less at 250°C, preferably 1.0% or less, and 0.5kg/m rd.
It is necessary that the thermal softening point under a load is 200°C or more and 350°C or less, preferably 200°C or more and 300°C or less. Here, the thermal softening point is 0.5 kg/m r
When the temperature of the film was raised at a rate of 5°C/min under a load of d,
It means the temperature at which the elongation of the film becomes 10% of its original length.

In a deformed FPC having solder resistance like the present invention, the heat shrinkage rate, which is the rate of dimensional change under no-load conditions, which defines the solder resistance, and the thermal softening point, which defines the moldability, are important. If the thermal shrinkage rate is greater than 165%, it is unsuitable because wrinkles may occur in the FPC during solder mounting. On the other hand, in the actual processing process, the temperature of the film is raised at a rate of several tens to hundreds of degrees Celsius/second, so consistency with measurable characteristic values has been an issue. In relation to the softening point, if the thermal softening point is higher than 350°C, the elongation rate of the film is too low at high temperatures and uniform molding is not possible, and if it is lower than 200°C, soldering may sometimes cause the film to elongate. It has been found through various experiments that flatness cannot be maintained and it is unsuitable.

[Manufacturing Method] Next, a method for manufacturing a irregularly shaped FPC of the present invention will be explained using aromatic polyamide as an example.

Polymerization of the aromatic polyamide can be carried out by known polymerization methods such as low-temperature solution polymerization in an amide solvent and interfacial polymerization using an aqueous medium, and is not particularly limited. Next, a film is formed from a polymer solution obtained by polymerization or a polymer solution obtained by redissolving the polymer in a solvent after isolation. The solvents used here include amide solvents and sulfuric acid, but systems using amide solvents are preferable from the viewpoint of corrosion of the equipment.

Film formation can be performed by a known solution film forming method, and there are distinctions among solution film forming methods such as dry method, wet method, dry-wet method, etc.
Either one is fine and there is no particular limitation.

During film formation, the film usually has a temperature of 0.1 at 250℃ to 350℃.
The film is heat treated for about 10 minutes and stretched 1.0 to 5.0 times in the longitudinal and width directions, but these operating conditions affect the film properties such as thermal shrinkage and thermal expansion coefficient. Therefore, conditions are appropriately selected depending on the polymer composition so as to obtain the characteristic values necessary for the present invention.

To manufacture an FPC using the obtained film as a base film or cover film, the same method as in the case of using a conventional aromatic polyimide film may be used. There are two ways to form an electric circuit on a base film: by laminating copper foil, aluminum foil, etc. with adhesive, by plating method, by laminating copper or aluminum by vapor deposition method, and then forming the circuit by etching method. paste,
Methods include screen printing of carbon paste, silver paste, etc., or a combination thereof, but are not particularly limited. However, from the point of view of solder resistance or electric capacity, it is preferable to laminate copper foil and then etch it.Furthermore, if the electric circuit is to be heat-formed integrally with the film, the copper foil used is better than electrolytic copper foil. Rolled copper foil is preferable from the viewpoint of malleability of the foil.

After the electric circuit is formed, through-hole processing is performed as necessary, cover film is laminated or resist ink is applied, holes are processed, and outline punching is performed to complete the FPC.
is manufactured.

Methods for imparting unevenness include molding with a mold, pressing with a heating jig, etc., but in any case, it takes only a few seconds or more.
The film may be deformed by heating the film to about 250° C. to 400° C. and applying pressure at the same time for several tens of seconds. For example, when processing with a mold, the temperature of the mold is heated to 300°C or higher, a film or flat FPC is pressed, the mold is cooled to 250°C or lower, and then the mold is released. A molded article is obtained. The process of forming the unevenness may be performed at any time, such as when forming the film alone, when forming an electric circuit, after laminating a cover film, etc., or after mounting components on a flat FPC, and is not particularly limited.

[Application] Irregular-shaped FP with uneven surface obtained as above
C can be used in electrical and electronic equipment in which FPCs have been commonly used, and is particularly preferably used when it is desirable to add functions to the FPC that go beyond just a flat wiring board. New functions resulting from the irregular shape of the FPC include, for example, forming a recess in the FPC to accommodate a pair of IC chips to facilitate IC sealing and terminal connection, and adding a dome to the contact area of a membrane switch. By creating an FPC with mold-shaped protrusions, it is possible to give the FPC itself a function that produces a click feeling when operating a switch, or to increase the density and simplify the mounting of components.

[Characteristics evaluation method] The method for evaluating characteristic values of the present invention is as follows.

(1) Heat Shrinkage A film sample with a width of 10 mm and a sample length of 100 mm was heat treated in a hot air oven at 250° C. for 10 minutes without any load, and the heat shrinkage was calculated using the following formula.

Thermal shrinkage rate (%) ■ In a thermal softening point thermomechanical analyzer (TMA), a film piece has a 0.
Set it so that a load of 5 (kg/mrrr) is applied,
The elongation of the film was measured when it was heated from room temperature at a heating rate of 5 ('C/min). The temperature at which this elongation became 10% of the length of the test piece was defined as the thermal softening point.

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

Example I Dissolving 2-chloro-p-phenyl diamine corresponding to a 0.9 molar ratio and 4,4'-diaminodiphenyl ether corresponding to a 0.1 molar ratio in N-methylpyrrolidone (NMP) Terephthalic acid chloride in a molar ratio of 0.2 and 2-chloroterephthalic acid chloride in a molar ratio of 0.8 were added thereto, and the mixture was stirred for 2 hours to complete the polymerization. This was neutralized with calcium hydroxide, and the polymer concentration was 1
An aromatic polyamide solution having a concentration of 1% by weight and a viscosity of 3200 voids was obtained.

This polymer solution was cast onto a stainless steel endless belt and heated with hot air at 150°C for 5 minutes to dry the solvent, and the film that had achieved self-retention properties was continuously peeled off from the belt. Next, the film was introduced into a water tank to extract the remaining solvent and inorganic salts generated by neutralization, and the water was dried using a stenter and heat treatment was performed to obtain an aromatic polyamide film with a thickness of 25 μm. During this time, the film was stretched 1.1 times and 1.3 times in the longitudinal direction and width direction, respectively, and the heat treatment was performed 3 times.
This was carried out at 10°C for 2 minutes.

The physical properties of the obtained film are as follows: heat shrinkage rate (250°C) is 0°8%, 0° in the longitudinal direction and the width direction.
, 5%, and the thermal softening point was 244°C, 24.0°C.

Next, a rolled copper foil with a thickness of 35 μm was laminated onto a film using a thermosetting modified epoxy adhesive to form a copper clad board.
A flat FPC was obtained by etching the copper foil to form an electric circuit.

Next, the flat FPC was pressed using a mold heated to 300°C, and after the mold had cooled to about 250°C, it was taken out. This molding process creates a depth of 5m in FI)C.
m, dome-shaped depressions with a diameter of 15 mm can be formed in several places, and the circuit will not be disconnected even in the areas where the copper foil circuit is covered with depressions.
There was no 7. Furthermore, when the obtained irregularly shaped FPC was immersed in a solder bath at 280° C. for 30 seconds, no wrinkles were formed on the FPC and it exhibited good solder resistance.

Example 2 0.0 as a diamine component. 2-chloro-p-phenylenediamine corresponding to a molar ratio of 0.8 to 2-chloro-p-phenylenediamine. Polymerization, neutralization, and film formation were carried out in the same manner as in Example 1 using 4,4'-diaminodiphenylsulfone corresponding to a molar ratio of 2 and terephthalic acid chloride as the acid chloride component to obtain a film having a thickness of 25 μm.
An aromatic polyamide film of m was obtained.

The physical properties of the obtained film were a heat shrinkage rate of 0.5% and 0.3%, and a heat softening point of 283°C and 281°C in the film longitudinal direction and width direction, respectively.

Next, in the same manner as in Example 1, copper foil lamination, etching processing,
When heat molding was performed, a deformed FPC with good moldability and no wrinkles was obtained, and the solder resistance was also good.

Comparative Example 1 A film was formed in the same manner as in Example 1 from a polymer solution in which metaphenylene isophthalamide was dissolved in NMP (polymer concentration 17% by weight, viscosity 2600 voids) to a thickness of 25
A μm aromatic polyamide film was obtained. However, the conditions during film formation were a stretching ratio of 1.4 times and 1.6 times in the longitudinal and width directions of the film, respectively, and heat treatment at 300° C. for 2 minutes.

The physical properties of the obtained film were a heat shrinkage rate of 1.8% and 18.5%, and a heat softening point of 217°C and 215°C in the film longitudinal direction and width direction, respectively.

Next, a flat FPC was prepared in the same manner as in Example 1, and heat molded. The moldability of the FPC was good, but when immersed in a solder bath at 260°C, wrinkles due to shrinkage of the film were observed. The solder resistance was poor.

Comparative Example 2 A flat FPC was produced in the same manner as in Example 1 using an aromatic polyimide film (thickness 25 μm, manufactured by Dupont) manufactured using pyromellitic dianhydride and 4,4'-diaminodiphenyl ether as raw materials. It was created. The physical properties of the film are as follows: heat shrinkage rate: 0.2%, 0°1%, heat softening point: 374°C, 375°C in the longitudinal direction and width direction, respectively.
It was °C.

I tried heat molding processing with the created FPC, but the mold temperature was 4.
Even at 00℃, the molding was poor and the FPC film part was torn.
Problems such as breakage of the copper foil circuit and generation of wrinkles around the position of the recesses occurred, making it impossible to create an irregularly shaped FPC.

[Effects of the invention] In the present invention, a heat-resistant film having a specific heat shrinkage rate and heat softening point is used as a substrate film or a cover film to manufacture an FPC, so the obtained FPC has solder resistance and can be easily molded. This makes it possible to replace the conventional flat FP.
It has become possible to create a variant FPC with functions not available in C.

Claims (2)

[Claims] (1) In a modified flexible printed wiring board (deformed FPC) with irregularities formed on the surface, the base film constituting the deformed FPC has a heat shrinkage rate of 1.5% or less at 250°C and 0.5 kg/mm. ^2Thermal softening point under load is 200
1. A irregularly shaped flexible printed wiring board characterized by being made of a heat-resistant film having a melting point of not less than 350° C. and not 400° C. or less. (2) In a modified flexible printed circuit board (deformed FPC) with irregularities formed on its surface, the cover film that constitutes the deformed FPC has a heat shrinkage rate of 1.5% at 250°C.
Below, the thermal softening point under a load of 0.5kg/mm^2 is 20
1. A irregularly shaped flexible printed wiring board comprising a heat-resistant film having a melting point of 0° C. or more and 350° C. or less and not having a melting point of 400° C. or less.