JPS60201689A - Flexible printed circuit board - 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 [I] Object of the Invention The present invention relates to a flexible printed wiring board containing metal foil. More specifically, (A) a foil of a metal selected from the group consisting of aluminum, copper and iron or an alloy of these metals; (B) (1) an ethylene-acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer; It is a mixture consisting of a polymer and (2) a saponified product of ethylene-vinyl acetate copolymer, and the mixing ratio of ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer in the mixture is 20 to 20. 80% by weight, this mixture is extruded into a thin shape at a temperature of 250°C or lower under conditions that do not cause fish eyes, and the resulting thin product is extruded at 100°C.
This invention relates to a thin-walled material having a thickness of 3 microns to less than 5II 1 m obtained by heating and pressing at a temperature of 400° C. to 400° C., and (C) a flexible printed wiring board formed by sequentially laminating conductive metal foil. The object of the present invention is to provide a printed wiring board that not only has good heat resistance but also has excellent dimensional stability comparable to that of metal.

[II] Background of the Invention Recent electronic devices are rapidly becoming smaller, lighter, thinner, and more densely packaged. In particular, printed wiring boards began to be commercialized for consumer equipment such as radios, and are now being used in industrial equipment such as telephones and computers, supported by mass production and high reliability.

Flexible printed wiring boards were initially used as a substitute for electric wires and cables, but their flexibility not only allows for high-density three-dimensional mounting in narrow spaces.
To allow for repeated bending, we added wiring, cable, and connector functions to the moving parts of electronic devices. Its use as a composite part moe is being expanded.

Currently, the materials used as three-dimensional wiring materials in devices such as cameras, electric desktop calculators, telephones, and printers are:
A wiring pattern is formed using a flexible steel clad plate with electrolytic copper foil of 35 microns adhered to both or one side of a polyimide or polyester film with a thickness of about 25 microns. There is also used a wiring pattern in which through-hole plating is applied, and one surface and the outer layer are coated with a coverlay.

Current flexible printed wiring boards generally use polyimide or polyester resin films as the base material, but polyester resin has a high water absorption rate and
Since the coefficient of thermal expansion is large between 0℃ and 250℃,
Through-hole connection lacks reliability. Furthermore, during production, curing is sometimes carried out using a steam press at 170°C, which tends not only to reduce adhesiveness between resins but also to reduce flexibility when multi-layered.

On the other hand, polyimide film is soldered at the normal soldering temperature (26
It has the advantage that solder bonding can be easily carried out at temperatures above 0°C, but it has the disadvantage that it is extremely difficult to bond with metal foil due to poor surface activity. To solve this problem of adhesion, the general method is to apply a chemical treatment using caustic soda, a chromic acid mixture, aluminum hydroxide, etc. to the surface of the film, and then bond it with an adhesive. It is. However, even if these methods are used for adhesion, it is not possible to obtain a printed circuit board with sufficient adhesion, and the chemical resistance and heat resistance are poor. There are disadvantages such as occurrence.

In addition, thermosetting adhesives with excellent heat resistance (for example,
In the method of bonding with metal foil using epoxy resin,
It is necessary to overlap a polyimide film coated with an adhesive with a metal foil and heat and pressurize it in a press for about 1 to 20 hours to cure it, which poses problems in terms of productivity, mass production, cost, etc.

[m] Structure of the Invention In view of the above, the present inventors have conducted various searches to improve these drawbacks and obtain a printed wiring board with good heat resistance and excellent electrical insulation.

(A) A metal foil made of a metal selected from the group consisting of aluminum, copper and iron or an alloy of these metals and having a thickness of 5 microns to less than 100 microns, (B) (1) Ethylene-acrylic acid A mixture consisting of a polymer and/or an ethylene-methacrylic acid copolymer and (2) a saponified product of an ethylene-vinyl acetate copolymer, and the ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer occupied in the mixture The mixing ratio of the acid copolymer is 20 to 80% by weight, and this mixture is
Extrude into a thin shape at a temperature of 0.6C or less under conditions that do not cause fish eyes, and extrude the resulting thin product at 100℃ or 4.
A thin material with a thickness of 3 microns to less than 51 mm obtained by crosslinking reaction by heating and pressurizing at a temperature of 00'O, and (C) a flexible printed wiring board formed by sequentially laminating conductive metal foils, The present invention was achieved by discovering that it not only has good durability but also has excellent electrical insulation properties.

[IV] Effects of the invention The flexible printed wiring board obtained by the invention exhibits the following effects (features) including its manufacturing process.

(1) Since no thermosetting resin adhesive such as epoxy resin is used, not only the adhesion process is omitted, but also the complicated drying process that accompanies that process is eliminated.

(2) Excellent electrical properties (for example, insulation, withstand voltage, and dielectric loss tangent performance).

(3) It has good heat resistance, and can not only be used at temperatures of 250°C or higher, but also can be used with copper foil without using the adhesive by applying pressure at temperatures of 100°C or higher. Can be well adhered to metal foil or plate.

(4) Excellent flexibility.

(5) In particular, the flexible printed circuit board of the present invention has the following characteristics compared to the case where conventionally used polyimide film and polyester film are used alone.
It is considered that the dimensional stability is excellent because the crosslinking treatment is performed at a relatively high temperature (200° C. or higher) as described later.

It has good adhesion even at high temperatures, has good adhesion, and has very few residual voids.

As described above, the printed circuit board of the present invention not only has good electrical properties such as insulation resistance and dielectric constant, but also has good dimensional stability, heat resistance, chemical resistance, moisture resistance, etc., and is also flexible. The bending durability of the substrate exhibits flexibility that has not been previously available. In addition, the adhesion with metal foil can be achieved by thermocompression bonding at a relatively high temperature (approximately 36°C).
It has characteristics such as exhibiting good adhesion down to 0°C.

[V] Detailed description of the invention (A) Ethylene-acrylic acid copolymer and ethylene-
Methacrylic Acid Copolymer The ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer used in the present invention is prepared by mixing ethylene and acrylic acid or ethylene and MEC 15 acid at high pressure (generally 50 kg/c). m' or more, preferably 100 kg/cm' or more) in the presence of a free radical generator (usually an organic peroxide). The physical properties of each of these are well known. The copolymerization ratio of acrylic acid or methacrylic acid in these copolymers is 1 to 50% by weight, preferably 5 to 50% by weight.

If the copolymerization ratio of acrylic acid or methacrylic acid in these copolymers is less than 1% by weight, a uniformly thin product cannot be obtained. On the other hand, if it exceeds 50% by weight, the softening point will be too low, making handling and handling difficult.

Shipping becomes inconvenient.

(B) Saponified product of ethylene-vinyl acetate copolymer,
The saponified ethylene-vinyl acetate copolymer used in the present invention can be obtained by saponifying (hydrolyzing) the ethylene-vinyl acetate copolymer. Hydrolysis is generally carried out using caustic soda in methyl alcohol. In producing the saponified products of the present invention, it is usually desirable to have a hydrolysis rate of 80% or more. The raw material ethylene-vinyl acetate copolymer is obtained by copolymerizing ethylene and vinyl acetate in the same manner as the ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer described above. be. The copolymerization ratio of vinyl acetate in this ethylene-vinyl acetate copolymer is generally 1 to 80% by weight, particularly 5 to 5% by weight of CO
Weight percent is preferred. If the copolymerization ratio of vinyl acetate in this copolymer is less than 1% by weight, a uniform thin-walled product cannot be obtained. On the other hand, if it exceeds 60% by weight, the softening point decreases and handling at room temperature becomes difficult.

Saponified products of these ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and ethylene-vinyl acetate copolymers are industrially produced and used in a wide variety of fields, and we will discuss their manufacturing methods. is also well known.

(C) Mixing ratio The mixing ratio of ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer in the mixture of the present invention is 20 to 80% by weight (i.e., ethylene-vinyl acetate copolymer The mixing ratio is preferably 80-20% by weight), 25-75% by weight, particularly 30-70%
% by weight is preferred. If the mixing ratio of the ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer in these mixtures is less than 20% by weight, the number of carboxyl groups (-COOH) is lower than the hydroxyl group (-
OH), hydroxyl groups that do not contribute to the condensation reaction remain, resulting in poor heat resistance. On the other hand, 80
If it exceeds % by weight, on the contrary, there are too many carboxyl groups contributing to the condensation reaction, so that unreacted groups remain and heat resistance and temperature resistance are not improved, which is not desirable.

(D) Mixing method To produce the mixture of the present invention, the saponified products of the above ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and ethylene-vinyl acetate copolymer are uniformly mixed. can be achieved by

As a mixing method, tri-blending may be performed using a mixer such as a Henschel mixer, which is commonly used in the field of olefin polymers, or a mixer such as a Banbury mixer, Niegoo, roll mill, and screw extruder. It can be obtained by melt-kneading using. At this time, a homogeneous mixture can be produced by triblending in advance and melting and kneading the resulting mixture. In addition, the carboxylic acid group (-cooH) possessed by the ethylene-acrylic acid and/or ethylene-methacrylic acid copolymer used for melt mixing and the hydroxyl group (-〇 It is necessary that 〇) does not undergo a crosslinking reaction (condensation reaction) in terms of wood quality, and that there is no woody structure (it may be slightly crosslinked). From this, the melting temperature is the temperature at which the saponified products of these ethylene-acrylic acid copolymers and/or ethylene-methacrylic acid copolymers and ethylene-vinyl acetate copolymers melt, but the crosslinking reaction does not occur. (no fish eyes occur). The melting temperature varies depending on whether or not a crosslinking accelerator is added in the latter stage, as well as their type and amount, but it is usually 180°C when no crosslinking accelerator is added.
or less, and particularly preferably 100 to 150°C. 1
If the temperature is less than 00°C, these resins will not be completely melted, which is not preferable. On the other hand, when adding (blending) a crosslinking accelerator, the temperature is generally 140°C or less, and 100°C or less.
This will be carried out in step 1 below.

In producing this mixture, stabilizers against oxygen, light (ultraviolet light) and heat, metal deterioration inhibitors, flame retardants, electrical property improvers and antistatic agents commonly used in the field of olefinic polymers are used. Additives such as lubricants, processability improvers, and tackiness improvers may be added to the extent that they do not impair the characteristics (physical properties) of the thin-walled product of the present invention.

Furthermore, by adding a crosslinking accelerator such as an epoxy compound, P-)luenesulfonic acid and An-isopropoxide, the ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and ethylene - Crosslinking of the vinyl acetate copolymer with the saponified product can be further completed. The amount added is usually at most 0.1 parts by weight per 100 parts by weight of these resins (preferably from 0.01 to 0.01 to 0.01 to 0.01 parts by weight in the field of thermoplastic resins when the thin-walled material of the present invention is used in the form of a film or sheet. A thin product can be obtained by extruding the film into a film or sheet using an extruder which is widely used in the production of commonly used T-Guy films and films by the inflated film method. At this time, the extrusion temperature is 250℃ or less.
When extruded beyond this point, a portion of the saponified ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and ethylene-vinyl acetate copolymer crosslinks, producing small gel-like particles. As a result, a uniform extrusion molded product cannot be obtained. For these reasons, the extrusion temperature is in the same temperature range as in the case of melt-kneading described above, regardless of whether a crosslinking accelerator is added (blended) or not.

In any of the above cases, after manufacturing the thin-walled objects, the thin-walled objects have good transparency by rapidly cooling them in a water-cooling roll or a water bath to prevent adhesion between the thin-walled objects or between the thin-walled objects and a take-up roll, etc. is obtained. The thickness of the thin-walled products thus obtained is generally between 5 microns and 400 microns.

Small Metal Foil Also, the metal foil used in the present invention plays a role such as flexibility-1 dimensional stability and heat dissipation. The thickness of this metal foil is between 5 microns and 20 microns.
0 micron, preferably 5 micron to 100 micron, particularly 10 micron to 70 micron. In addition, the types of metals include aluminum,
Copper, iron, and alloys containing these metals as main components. Among these metals, if you use iron, copper, or alloy foil containing these metals as the main ingredients, you can also obtain a shielding effect against electromagnetic waves and magnetism, so do not place around the motor or switching area. It is valid. Among these metals, aluminum or aluminum-based alloy foils are used, and standard products are specified in JIS H-4180.

(Rei’l sex, wa.

Furthermore, the conductive metal foil used in the present invention is one that is used in circuit formation (circuit formation is generally performed by etching treatment). The thickness of this conductive metal foil is usually 5 to 400 microns, and 10 to 10 microns thick.
0 microns is preferred, and 10 to 50 microns is particularly preferred. Examples of conductive metals include copper, nickel, and aluminum metals, and alloys containing these metals as main components. Furthermore, a cladding made of two or more of these metals or alloys can also be preferably used.

Heating and Pressure Treatment The thin-walled product obtained as described above exhibits the same behavior as a normal thin-walled product because crosslinking has hardly progressed. In order to impart adhesion and heat resistance to the conductive metal foil and metal foil to the thin material, it is important to apply pressure and heat in the range of 100 to 400°C. Heating temperature is 100~
20-30 minutes at 180°C, 160-240°
By heating and pressurizing for 10 to 20 minutes in the range of C and 0.1 to 10 minutes in the range of 240 to 400°C, a crosslinking reaction (condensation reaction) occurs within the resin, improving adhesiveness and heat resistance. Significantly improved.

Since the thin-walled article obtained by the present invention exhibits thermocompression adhesion (adhesiveness) at a temperature of 100° C. or higher, the effects of the present invention can be further enhanced by bonding it to metal at the same time as the crosslinking treatment. That is, a mixture of an ethylene-acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer and a saponified product of an ethylene-vinyl acetate copolymer exhibits thermoplasticity at a temperature of 250°C or less; By subjecting it to pressure treatment on a heating table at 180° C. or higher, a crosslinking reaction occurs, which allows it to adhere to thin objects, polyimide films, and metal foils, and to provide excellent adhesion (laminates) with excellent heat resistance.

(Flexible Printed Wiring Board) Hereinafter, the flexible printed wiring board obtained by the present invention will be explained using drawings. Figure 1 shows a single-sided copper-clad flexible printed wiring board for hybrid integrated circuits with a structure in which conductive metal foil is laminated on one side. Fig. 2 is an enlarged sectional view of a part of a typical example of a wiring board. Fig. 2 is a representative board in which a thin material of the mixture used in the present invention is laminated on the metal foil shown in Fig. 1 for protection and insulation. FIG. 3 is a partially enlarged sectional view of the example.
The figure is an enlarged sectional view of a portion of a typical example of a double-sided copper-clad flexible printed wiring board having a structure in which conductive metal foil is layered on both sides. In each of FIGS. 1 to 4, l represents a conductive metal foil. In addition, 2 is a thin material obtained by treating a mixture of an ethylene-acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer and a saponified product of an ethylene-vinyl acetate copolymer (mixing ratio is 1:1). ). Furthermore, 3 is metal foil. FIG. 1 shows a structure in which a thin material 2 is pasted between a conductive metal foil 1 and a metal foil 3 by heat-pressing. FIG. 2 shows a structure similar to that of FIG. 1, with a thin layer 2 of the present invention provided on one side for insulation. Further, FIG. 3 shows a structure in which conductive metal foil is provided on both sides.

Furthermore, FIG. 4 is an enlarged cross-sectional view of a part of a typical example showing the state of adhesion between the resin layers after the circuit shown in FIG. 3 is formed.

The present invention not only omits the adhesive application step because there is no need to further use a commonly used adhesive between the conductive metal foil and the metal foil, but also eliminates the need for volatile substances in the adhesive (for example, organic Solvent) will not cause blistering during heating. In addition, during molding of thin objects and thermocompression bonding, the thermoplastic insulating adhesive resin layer undergoes a crosslinking reaction through these high-temperature heat treatments, resulting in crosslinked thin objects that are flexible and heat resistant. This has the advantage of significantly improving the

[VI] Examples and Comparative Examples The present invention will be explained in more detail with reference to Examples below.

In addition, in the Examples and Comparative Examples, the heat resistance test was performed using the obtained film as UL 79B (printed wiring board).
7.1 The board with the test pattern shown in Figure 30
Evaluation was made by floating for 180 seconds in a solder bath with lead/tin=Il]O/10 (weight ratio) maintained at 0°C. The evaluation is shown in Table 1 as follows.

0: No change in the current form ×: Changes such as peeling, cracking, and splitting were observed between the conductor circuit and the resin layer Examples 1 to 7, Comparative Examples 1 to 4 Melt flow index (JIS K- 67130, temperature 180°C and load 2.16kg
Measured under the following conditions: rM, 1. J) is 300g7
Ethylene-acrylic acid copolymer (density 0.
1354 g/cm", acrylic acid copolymerization ratio 20% by weight) 100 parts by weight and vinyl acetate copolymerization ratio 28%
% by weight of ethylene-vinyl acetate copolymer (saponification degree 97.5
%, M, 1.75g/10min, density 0. ! 351g
/ crn'') was triblended for 5 minutes using a Henschel mixer.The resulting mixture [hereinafter referred to as ``mixture (A)''] was mixed in a press-Takatsuki (Takatsuki) equipped with a T-die. Using a rotary table with a diameter of 40 mm, a die width of 30 cm, and a rotation speed of 85 times, the cylinder temperature CI = 10.
0'O, C2 = 120°C and c,, = 140°C
A film (thickness: 100 microns) was formed under the conditions of t-JJ- and die temperature of 160°C, and wound around a roll water-cooled to 20°C (Examples 1 to 6, Comparative Examples 1 to
4). Also, instead of the ethylene-acrylic acid copolymer used in producing the mixture (A), M, 1. is 20
Ethylene-methacrylic acid copolymer (
A mixture [hereinafter referred to as "mixture (B)"] was produced in the same manner as mixture (A), except that a mixture having a density of 0.950 g/c rn'' and a methacrylic acid copolymerization ratio of 25% by weight was used. A film was produced from the resulting mixture in the same manner as above (
Example 7). Furthermore, the saponified product of the ethylene-acrylic acid copolymer (hereinafter referred to as rEAAJ, Comparative Example 3) and the ethylene-vinyl acetate copolymer used in Example 1 (hereinafter referred to as "saponified product", Comparative Example 4) ) was produced in the same manner as above.

Layer L of each film thus obtained with a copper foil having a thickness of 35 microns facing down, and stack the metal foils shown in Table 1 at 320°C for 10 minutes using a heat press machine to produce 20 kg/l of each film. A flexible printed wiring board reinforced with metal foil was produced by crosslinking under pressure of cm'' (gauge pressure).The resulting film was subjected to a heat resistance test.The results are shown in Table 1. In addition, the printed wiring board obtained by Examples 7 to 7 has a diameter of 2 cm.
It was possible to wrap it around a round rod, and even after repeating this operation several times, no abnormality was observed. However, the printed wiring boards obtained in Comparative Examples 1 and 2 could not be wrapped around the round bar. Furthermore, when the printed wiring boards obtained in Comparative Examples 3 and 4 were wound around the round bar, peeling was observed between the metal foil and the thin material.

The volume resistivity, dielectric constant (I Ml , dielectric loss tangent, and withstand voltage) of the film obtained in Example 3 were measured according to JIS K-8911.

The volume resistivity is 1O18Ω·Crn, and the dielectric constant is 2.
It was 8. Further, the dielectric loss tangent was 0.08, and the withstand voltage was 30 KV/++u++.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a portion of a representative example of a single-sided copper-clad flexible printed wiring board. Further, FIG. 2 is a partial enlarged sectional view of a typical example of a single-sided copper-clad flexible printed wiring board, and FIG. 3 is a partial enlarged sectional view of a typical example of a flexible printed wiring board with metal foil provided on both sides. Further, FIG. 4 is a partially enlarged sectional view of a typical example showing the state of adhesion between insulating layers (resin layers) after circuit formation. l...Conductive metal foil 2...Crosslinked thin material of mixture 2...
Metal foil Figure 1 Figure 2

Claims (1)

[Scope of Claims] (A) A metal foil with a thickness of 5 microns to less than 100 microns made of a metal selected from the group consisting of aluminum, copper and iron or an alloy of these metals, (B) (1) Ethylene - a mixture consisting of an acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer and (2) a saponified product of an ethylene-vinyl acetate copolymer; or ethylene-methacrylic acid copolymer 4
The mixing ratio of 20 to 80% by weight is 20 to 80% by weight.
Extrude into a thin shape at a temperature of 50℃ or less under conditions that do not cause fish eyes, and then extrude the resulting thin product at a temperature of 100℃ or 40℃.
(c) A flexible printed wiring board formed by successively laminating conductive metal foils and (c) a thin material having a thickness of 3 microns to less than 5 mm obtained by heating and pressurizing at a temperature of 00°C.