JPS60175478A - Flexible printed 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 is intended for use at temperatures ranging from room temperature (20°C) to relatively high temperature (38°C).
) relates to a printed circuit board with excellent adhesiveness and flexibility. More specifically, a mixture consisting of a saponified product of (A) an ethylene-acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer and (B) an ethylene-vinyl acetate copolymer is heated at a temperature of 250°C or less to create a fish eye. Extrude the resulting thin product under conditions that do not cause
It relates to a flexible printed circuit board made by overlapping a polyimide film and metal foil through a thin material obtained by heating and pressurizing them at a temperature of It is an object of the present invention to provide a printed circuit board that not only has excellent adhesive properties but also has good adhesive properties even at relatively high temperatures and has excellent flexibility.

[11] 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.
In order to withstand repeated bending, its use is expanding as a composite component that functions as a wiring, cable, or connector for the moving parts of electronic devices.

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

Current flexible hybrid integrated circuit 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 by 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 (28
It has the advantage that it can be easily soldered at temperatures above 0°C, but it has the disadvantage that it is extremely difficult to bond with metal foil due to its 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 Based on the above, the present inventors conducted various searches to improve these drawbacks in order to obtain a printed circuit board with good heat resistance and excellent electrical insulation properties, and as a result, ( It is a mixture consisting of a saponified product of A) ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and (B) ethylene-vinyl acetate copolymer, and the ethylene-acrylic acid copolymer occupied in the mixture is The mixing ratio of the coalescing and/or ethylene-methacrylic acid copolymer is 20 to 80% by weight, and this mixture is extruded into a thin shape at a temperature of 250°C or lower using a strip machine that does not produce fish eyes. object 100°
A flexible printed circuit board made by overlapping and heat-pressing a polyimide film and metal foil through a thin material obtained by crosslinking reaction by heating and pressurizing at a temperature of 400°C to 400°C is durable. The inventors have discovered that not only is it good, but also that it has excellent electrical insulation properties, leading to the present invention.

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

(1) Since thermosetting resin adhesives such as epoxy resins are not used, the first step of adhesion is not only omitted;
There is no complication (such as drying) associated with the process.

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

(3) Not only does it have good heat resistance and can be melted at temperatures of 250°C or higher, but it can also be coated with copper foil, etc. without using the adhesive by applying pressure at a temperature 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 is characterized by the fact that it can be cross-linked at a relatively high temperature (200°C or higher) as described below, compared to when conventionally used polyimide films and polyester films are used alone. Because of this, it is considered to have excellent dimensional stability, has good adhesion even at high temperatures, has good adhesion, and has extremely few residual voids.

As described above, the printed circuit board of the present invention has good electrical properties such as insulation resistance and dielectric constant, as well as dimensional stability, heat resistance, chemical resistance, temperature resistance, etc. Moreover, the bending durability of the flexible 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 3
It has characteristics such as exhibiting good adhesion up to 60°C.

[V] Detailed description of the invention (^) 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 combining ethylene and acrylic acid or ethylene and methacrylic acid at high pressure (generally 50 kg/cm or less). , preferably 1
00 kg/cm') 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 lllfl%, it is impossible to obtain a uniformly thin-walled product. On the other hand, if it exceeds 50% by weight, the softening point will be too low, making handling and transportation 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 product of the present invention, it is usually desirable to have a hydrolysis jN of 90% 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 60%, particularly 5 to 6%.
0% by weight is preferred. If the copolymerization ratio of vinyl acetate in this copolymer is less than 1% by weight, a uniformly thin product cannot be obtained. On the other hand, if it exceeds 60% by weight, the softening point will drop and handling at room temperature will become 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%
% 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, carboxyl group (-COOH) (7) a is hydroxyl group (-OH) Since the number of hydroxyl groups is smaller than that of , hydroxyl groups that do not contribute to the condensation reaction remain, resulting in poor heat resistance. On the other hand, if it exceeds 80% by weight, there are too many carboxyl groups contributing to the condensation reaction, so unreacted groups remain and heat resistance and humidity 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. This 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, kneader, roll mill, and screw extruder. It can be obtained by melt-kneading using. At this time, a homogeneous mixture can be produced by rough tri-blending and melt-kneading the resulting mixture. In addition, the carboxylic acid group (-COOH) possessed by the ethylene-acrylic acid and/or ethylene-methacrylic acid copolymer used during melt-kneading and the hydroxyl group (-on ) must not undergo a crosslinking reaction (condensation reaction) in terms of wood quality and do not cause fish eyes (slight crosslinking may be allowed). 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 in the case where no crosslinking accelerator is added, it is usually 180°C or less, and 100 to 150°C is particularly preferable. 1
If the temperature is less than 00°C, these resins will not be completely melted, which is not preferable. On the other hand, a crosslinking accelerator is added (blended)
In general, the temperature is below +40°C and 10
It is carried out at temperatures below 0°C.

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 A4-impropoxide, the ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and ethylene - Vinyl acetate (can further complete the crosslinking of the polymer with the saponified product. The amount added is usually at most 0.1 parts by weight (preferably 0.01 to 0.01 parts by weight) per 100 parts of these resins. 0.05 part).

(D) Production of thin-walled products When the thin-walled products of the present invention are used in the form of a film or sheet, in the field of thermal Ijf filable resins.
A thin product can be obtained by extruding it into a film or sheet using a commonly used T-die film or an extruder that is widely used for producing films by the inflation method. At this time,
The extrusion temperature is below 250°C. Temperature: 250℃
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. By doing so, it is not possible to obtain a uniformly shaped extruded product. 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 cases described in 42 above, after manufacturing the thin-walled objects, it is possible to prevent adhesion between the thin-walled objects or between the thin-walled objects and the take-up roll, etc. 11=
A thin-walled material with good transparency is obtained by rapidly cooling it in a water-cooled roll or a water bath. The thickness of the thin-walled products thus obtained is generally between 5 microns and 400 microns.

(F) Heating ψ Pressure Treatment The thin-walled product obtained in the above manner 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 polyimide film and metal foil described later to the thin material, it is important to heat and pressurize the material in the range of 100 to 400°C. Heating temperature,
in the range of 100 to 180°C for 20 to 30 minutes, 180
10-20 minutes in the range of ~240℃, 240-400℃
In the range of 0.1 to 10 minutes by heating and pressurizing, a crosslinking reaction (condensation reaction) occurs within the resin, and the adhesiveness and heat resistance are significantly increased to IF+]-1. Since the material exhibits thermocompression bondability (adhesiveness) at temperatures of 100° C. or higher, the effects of the present invention are further expanded by performing the crosslinking treatment and adhesion to the metal at the same time. 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 heating and pressurizing at 160° C. or higher, a crosslinking reaction is caused, which allows the thin material to adhere to the polyimide film and metal foil, and furthermore, it is possible to obtain an adhesive (laminate) with excellent heat resistance.

(G) Metal foil The thickness of the metal foil used in the present invention is generally 5 to 40 mm.
0 microns, preferably 15 to 100 microns, particularly preferably 15 to 50 microns. As the metal of the metal foil, conductive metals such as copper, nickel, and aluminum, and alloys mainly composed of these metals are preferred, and electrolytic copper foil having a thickness of 15 to 40 microns is particularly preferably used.

()l) Polyimide film The thickness of the film used in the present invention is usually 20 microns to 2.0 mm, and 50 microns to 1.0 mm. flIIlm is preferred, especially 10
0 micron to 1. A material of fl+mm is suitable.

The polyimide is generally obtained by casting a polyimide acid solution obtained by a low-temperature solution polymerization method, drying it, and then subjecting it to a dehydration ring-closing reaction. Furthermore, in the present invention, polyamide-imide having an amide group in the polymer main chain of the above-mentioned polyimide can also be preferably used. The general formula of the polyimide is shown in formula (I), and the general formula of polyamideimide is shown in formula (II). These polymers are described in "Electronic Materials" June 1979 issue, page 251, as heat-resistant resins used for printed circuit boards.

Hereinafter, the present invention will be explained using the drawings. FIG. 1 is an enlarged cross-sectional view of a part of a typical example of a flexible printed circuit board for integrated circuits, which has a structure in which conductive metal foil is laminated on the lunar surface. Further, FIG. 2 is an enlarged sectional view of the = section of a typical example of a single-sided copper-clad hybrid integrated circuit multilayer flexible board having a structure in which conductive metal foils are laminated on only one side. In both FIGS. 1 and 2, 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 a polyimide film. FIG. 1 shows a structure in which a thin material 2 is pasted 4=j between a conductive metal foil 1 and a polyimide film 3 by heat-pressing. FIG. 2 shows a structure in which the same structure as in FIG. 1 is laminated in multiple layers.

The present invention not only omits the step of applying an adhesive because there is no need to use a commonly used adhesive between the conductive metal foil and the polyimide filter, but also eliminates volatile substances in the adhesive (e.g. , organic solvents), no blistering occurs when heated. In addition, during molding of thin objects and thermocompression bonding, the thermoplastic insulating adhesive resin layer undergoes a crosslinking reaction by these high-temperature heat treatments, resulting in a crosslinked thin object that has LIF flexibility and heat resistance. It has the advantage that it is significantly improved.

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

In the Examples and Comparative Examples, the heat resistance test was conducted using a polyimide film-based copper-clad printed circuit board with a test pattern shown in UL 79El (Printed Wiring Board) 7.1. Solder bath with lead/tin = 55/45 (ERRW ratio) held at °C and lead/tin = 90/10 (ERW ratio) held at 300 °C.
It was evaluated by floating it in a solder bath for 180 seconds.

Examples 1 to 5, Comparative Examples 1 to 5 Melt flow index (JIS K-6780 NiL
? : Paddle, temperature is 190°C and load is 2.18k
Measured under the conditions of g, hereinafter rM, 1. J) is 300g
Ethylene-acrylic acid copolymer (density 0
．． 854g/c rrf, acrylic acid copolymerization ratio 20
weight%) 100 parts by weight and vinyl acetate copolymerization ratio is 2
Saponified product obtained by saponifying 8% by weight of ethylene-vinyl acetate copolymer (saponification degree 97.
5%, M, 1.75g 710 minutes, density 0.951g
/cm') was triblended for 5 minutes using a Henschel mixer. The obtained mixture [hereinafter referred to as "mixture (A)"] was extruded into a cylinder as shown in Table 1 using an extruder equipped with a T-die (diameter 40!I11, die width 30cm, rotation speed 85 rpm). Films (100 microns thick) were formed at the indicated temperatures and wound around water-cooled rolls at 20± (Example 1)
-3, Comparative Examples 1-3). Also, instead of the ethylene-acrylic acid copolymer used in producing the mixture (A), M, 1. Ethylene-methacrylic acid copolymer with a density of 200 g/10 min (density 0.850 g/cm'
, methacrylic acid copolymerization ratio 25% by weight).
A mixture [hereinafter referred to as "mixture (B)" 1] was produced in the same manner as mixture (A). A film was produced from the resulting mixture in the same manner as described above (Example 4). Furthermore, the ethylene-acrylic acid copolymer (hereinafter F r
EAAJ says. Comparative Example 4) and a saponified product of ethylene-vinyl acetate copolymer (hereinafter referred to as "saponified product J"; Comparative Example 5) were used to produce films in the same manner as described above.

Each of the films obtained in this way was heated to 250°C and 300°C for 10 minutes each using a heat press machine and pressurized at 20 kg/cm' (gauge pressure) to form an electrolytic copper foil (thickness 17 microns). and a priimide film (manufactured by DuPont, trade name Kapton, thickness 100 microns) were laminated as shown in FIG. 1 to produce a printed circuit board. The properties of the film as described above are shown in Table 1. Furthermore, bonding (lamination) is performed at the bonding temperature shown in Table 2.
Table 2 shows the results of the heat resistance test of the printed circuit board.

The film obtained in Table 2 Example 3 was rated according to JIS K-8, 111.
According to 1, the volume resistivity, permittivity (l Mu,),
Dielectric loss tangent and withstand voltage were measured.

The volume resistivity is 1014Ω・Cl11, and the dielectric constant is 3
,8. Further, the dielectric loss tangent was 0.08, and the withstand voltage was 1 OKV/ll1ffi.

From the above results, the thin-walled products of the present invention not only have excellent adhesion with copper foil and polyimide film, but also have excellent heat resistance and good electrical insulation properties, making them suitable for flexible printing based on polyimide films. It is clear that it can be used as an adhesive for wiring boards.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a part of a typical example of a flexible substrate for an integrated circuit with copper cladding on one side and having a structure in which conductive metal foil is laminated on one side. Further, FIG. 2 is an enlarged sectional view of a part of a typical example of a single-sided copper-clad hybrid integrated circuit multilayer flexible board having a structure in which conductive metal foils are laminated on only one side. l... Conductive metal foil, 2... Ethylene-acrylic acid copolymer and/or
or a thin material obtained by treating a mixture of ethylene-methacrylic acid copolymer and saponified ethylene-vinyl acetate copolymer, 3...Polyimide Film Special Process 1 Applicant: Showa Denko K.K. Representative Person Patent Attorney Neto Kikuchi Figure 1 Figure 2

Claims (1)

[Claims] A mixture consisting of (A) an ethylene-acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer and (B) a saponified product of an ethylene-vinyl acetate copolymer, and the ethylene-acrylic acid copolymer that occupies the mixture. The mixing ratio of the polymer and/or ethylene-methacrylic acid copolymer is 20 to 80% by weight, and the mixture is heated at 250°C.
Extrude it into a thin shape under the conditions that fish eyes do not occur at the following temperature.
A flexible printed circuit board made by overlapping a polyimide film and a metal foil through a thin material obtained by heating and pressurizing them at a temperature of '0, and then heat and press them and integrate them.