JPS60226192A - 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] [1] Purpose of the Invention The present invention is directed to forming a conductive circuit on the surface of a thin insulating material by performing electroless plating or electrolytic plating instead of copper foil when manufacturing a laminated wiring board. This is a printed circuit board manufactured using the so-called full additive method, and is particularly suitable for the full additive method using photoresist. More specifically, a mixture consisting of a saponified product of (A) (+) ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and (2) ethylene-vinyl acetate copolymer is heated at 250°C or less. A thin-walled product obtained by extruding the thin-walled product under conditions that do not cause fish eyes at a temperature and heating and pressurizing the obtained thin-walled product at a temperature of 100°C to 400°C (B
) This relates to a printed wiring board in which a conductor circuit of 200 microns or less is formed on the surface of the above-mentioned thin material by electrolytic plating, electroless plating, and electrolytic plating, and it not only has good heat resistance but also flexibility. The purpose of this invention is to provide a printed wiring board with rich characteristics.

[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.

In particular, flexible printed wiring boards were initially used as an alternative to electric wires and cables, but due to their flexibility, they can not only be mounted three-dimensionally at high density in a narrow space, but also can be repeatedly bent. Therefore, its use is expanding as a composite component that provides wiring, cable, and connector functions for the moving parts of electronic devices.

Currently, the materials used as three-dimensional wiring materials in devices such as cameras, electric desktop devices, telephones, and printers are electrolytic copper with a thickness of 35 microns on both sides or one side of a polyimide or polyester film with a thickness of about 25 microns. The wiring pattern is formed using a flexible copper-clad board with foil bonded to it. 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 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° C. and 250° C., through-hole connection reliability is lacking. 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 (26
Although it has the advantage that solder connection can be easily performed at temperatures above 0°C, 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 the occurrence of

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.

In the method of manufacturing printed wiring boards (printed circuit boards), instead of the conventional etching method for copper-clad laminates, we apply coating technology to plastics to directly plate circuits onto resin boards by electroless plating. Additive drawing methods and substrative methods that combine plating and etching have come into use. The reason why this additive method has become popular is that it is an effective method for simultaneously forming through-holes and pattern plating for high-volume, low-mix resin laminates. The performance has been improved and it is now possible to obtain highly fine lines. Recently, a resistless method has also been developed in which ultraviolet rays are directly applied to a photoreaction catalyst mixed in the adhesive layer through a photomask to precipitate metal nuclei and electroless plating is performed.

However, the conventional paper-phenolic resin, glass-based epoxy resin, and polyimide resin substrates used in these additive methods do not have good adhesion to the plating film, resulting in blistering, peeling, etc. The coefficient of thermal expansion in the horizontal direction is large. Furthermore, when drilling holes in multilayer boards, smear occurs, which impedes the connection with the plating and reduces connection reliability. Furthermore, in etching and plating processes, large quantities of various aqueous solutions or washing water are used, so it is also an important condition that dimensional changes upon absorption of moisture be small.

[m1 Structure of the Invention Based on the above, the present inventors conducted various searches in order to improve these drawbacks and obtain a printed circuit board with good heat resistance and excellent electrical insulation properties, and as a result, (A ) A mixture consisting of saponified products of (1) ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and (2) ethylene-vinyl acetate copolymer, and the ethylene-acrylic acid occupied in the mixture is The mixing ratio of the copolymer 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 under conditions that do not cause fish eyes. things at 100°C
(B) electroless plating or electroless plating and electrolytic plating to form a conductor circuit of 200 microns or less on the surface of the thin wall object obtained by heating and pressurizing at a temperature of 400 ° C. The inventors have discovered that a printed wiring board of the following types not only has excellent flexibility and durability, but also has excellent electrical insulation properties, and has thus arrived at the present invention.

[IV] Effects of the invention The printed wiring board obtained by the invention exhibits the following effects (characteristics) 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, M electric dissipation factor performance).

(3) It has good heat resistance and can not only be plated at temperatures of 250°C or higher, but also can be electroless plated without using the adhesive by applying pressure at temperatures of 100°C or higher. Alternatively, a conductive metal thin film can be well adhered to a substrate by electrolytic plating.

(4) Excellent flexibility.

(5) In particular, the flexible printed circuit board of the present invention is characterized in that the crosslinking process is performed at a relatively high temperature (200°C or higher) as described below, compared to the case where conventionally used polyimide films and polyester films are used alone. Therefore, it is considered to have excellent dimensional stability, has good adhesion to the plating layer even at high temperatures, has good adhesion, and has extremely few residual voids.

As described above, the printed wiring 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. The bending durability of flexible substrates exhibits flexibility that has not been previously available. Furthermore, the adhesion to the conductive metal thin film due to the plating recipe is characterized by good adhesion even at relatively high temperatures (approximately 360° C.) by thermocompression bonding.

[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 combining ethylene and acrylic acid or ethylene and methacrylic acid at high pressure (generally 50 kg/cm' Above, preferably 1
00 kg/c rn' 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 transportation inconvenient.

(B) Saponified product of ethylene-vinyl acetate copolymer Also, the saponified product of ethylene-vinyl acetate copolymer used in the present invention can be obtained by saponifying (hydrolyzing) the ethylene-vinyl acetate copolymer. can get. 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 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 60% by weight, particularly 5 to 6% by weight.
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 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.

(G) 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. 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 mixing may be performed using a mixer such as a Banbury mixer, kneader, roll mill, or screw extruder. It can be obtained by melt-kneading using a machine. At this time, the mixture is tri-blended in advance and the resulting mixture is melt-kneaded to create a homogeneous mixture.
mixtures can be produced. In addition, the carboxylic acid group (-Cool) possessed by the ethylene-acrylic acid and/or ethylene-methacrylic acid copolymer used during melt-kneading and the hydroxyl group (-0 ) It is necessary that 1) does not cause a crosslinking reaction (condensation reaction) in terms of wood quality and does not cause fish eyes (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 the combination of crosslinking accelerators in the latter stage as well as their types and amounts added, but when no crosslinking accelerator is incorporated, it is usually 180°C or less, and 100 to 150°C is particularly preferable. 10
If the temperature is below 0°C, these resins will not be completely melted, which is not preferable. On the other hand, when a crosslinking accelerator is added (blended), it is generally 14,000 or less, and 100°
Conducted at C or above.

In producing this mixture, oxygen and light (ultraviolet!I) commonly used in the field of olefin polymers are used.
and additives such as heat stabilizers, metal deterioration inhibitors, flame retardants, electrical property improvers, antistatic agents, lubricants, processability improvers, and tack improvers. It may be added within a range that does not impair the properties (physical properties) it has. 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 Crosslinking of the ethylene-vinyl acetate copolymer with the saponified product can be further completed. The amount added is usually at most 0.1 part by weight per 100 parts by weight of these resins.
Preferably 0. 1 to 0.05 parts by weight).

(E) Production of thin-walled products When the thin-walled products of the present invention are used in the form of a film or sheet, T-Guy film, which is commonly used in the field of thermoplastic resins, is widely used when producing films by the inflation method. A thin product can be obtained by extruding it into a film or sheet using a conventional extruder. At this time, the extrusion temperature is 2
The temperature is below 50°C. On the other hand, when extruded at temperatures exceeding 250°C, some of the saponified products of ethylene-acrylic acid copolymer and/or ethylene-meth-glyric acid copolymer and ethylene-vinyl acetate copolymer crosslink, resulting in a gel-like structure. A uniform extrudate cannot be obtained due to the formation of small lumps of material. 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 with good transparency are made 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. can get. The thickness of the thin-walled material thus obtained is from 3 microns to less than 5 mm, preferably from 10 microns to 1 ffl111, preferably from 10 microns to 400 microns, taking into account flexibility and insulation.

(F) Heat/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. 100 to 400 in order to impart the above-mentioned heat resistance to the thin-walled material.
It is important to heat and pressurize within the range of ℃. When the heating temperature is in the range of 100 to 160°C, 20 to 30 minutes, 18
10-20 minutes in the range of 0-240℃, 240-400℃
℃ range, by heating and pressurizing for 0.1 to 10 minutes, a crosslinking reaction (condensation reaction) occurs within the resin, and heat resistance is significantly improved.

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 the material to 160° C. or higher, a crosslinking reaction is carried out, and a laminate with excellent heat resistance can be obtained.

(G) Electroless plating Generally, electroless plating, that is, chemical coating,
Nickel plating, highly corrosion resistant zinc/nickel alloy plating,
Copper plating is known, but for printed wiring boards, it is necessary to use a method between the material (substrate) and the plating film that has a uniform thickness on all surfaces that come into contact with the processing solution and that provides a stable plating film. Copper sulfate plating is usually put into practical use as it has excellent adhesion and ductility. This copper sulfate plating provides fine crystals and leveling (uniform thickness), as well as stable workability and excellent physical properties.

Generally, in copper sulfate plating, copper sulfate and sulfuric acid are used to supply metallic copper into the solution and improve the conductivity and uniform electrodeposition of the solution. Additionally, chloride ions (as a catalyst) and appropriate amounts of brighteners are used. Additionally, polyoxyethylene and polyoxypropylene derivatives may be used to enhance leveling. A typical composition is to add 5 to 40 g of sulfuric acid steel (CuSO4-5H20) to one aqueous solution, and further add pH adjusters (buffers) such as caustic soda (NaOH), ammonium chloride (NH, Ca1
), and to prevent abnormal precipitation of copper in an aqueous solution, for example, EDT^-2Na (sodium salt of ethylenediaminetetraacetic acid) and formalin (HCHO) as a reducing agent are added. Furthermore, metals such as copper, nickel, and gold are electroplated on the conductive surfaces (paths) of these chemical (electroless) plated to protect the surface and prevent corrosion, and solder is applied to the conductive paths through a solder bath. It is also possible to put

(H) Circuit Formation Method This is a so-called full additive method in which a circuit is formed by electroless copper plating on the surface of the thin-walled object and the inner surface of the through-hole hole by chemical plating carried out in the uninvention. It is characterized by the fact that it does not require an etching process unlike laminates. Generally, the insulating material used in the fully additive method has a plating catalyst added to it, or has an adhesive coated on its surface. "thin material obtained from a saponified product of acrylic acid copolymer and/jujube or ethylene-methacrylic acid copolymer and ethylene-vinyl acetate copolymer" (hereinafter referred to as "rE-E thin material") is an analogy. without the use of catalysts or adhesives.
Excellent adhesion to electroless copper. Furthermore, it is possible to form a conductor circuit by a general circuit forming method, for example, by cutting an E-E thin material into specified dimensions and drilling holes (punching method, drilling method, etc.). (Press processing is also possible). Next, pattern formation is performed by screen printing with a negative pattern or by masking unnecessary portions with a photosensitive agent. This masked E-E thin object is placed in an electroless copper plating solution, and copper plating of a specified thickness is deposited on the unmasked circuit portions to form a pattern. Mask printing and photosensitizers must have excellent alkali resistance because they are immersed in electroless plating solution for a long time.

Usually, a layer is formed that serves as both a photosensitive agent and an adhesive, which is used in the commonly used full additive method, and by exposing this layer to light, only the circuit area becomes a layer that is easy to bond and deposit electroless copper plating. things are being done. However, in the printed wiring board of the present invention, it is not necessary to use these, and the electroless copper plating layer is directly formed on the surface of the E-E thin object with good adhesion and adhesion, so it is suitable for mass production. Not only is it possible to form precise circuits without any defects (such as hair formation or pattern breakage) due to normal etching. After chemical plating, it is also possible to plate with gold, soot, solder, etc. for circuit protection, corrosion prevention, and for IC chip molding.

The printed wiring board of the present invention can use any of the fully additive adhesive printing method, adhesive photography method, and direct method, but the greatest feature is that the direct method can be used.

(J) Printed Wiring Board The printed wiring board obtained by the present invention will be described below with reference to the drawings. 1 to 3 are enlarged cross-sectional views of representative examples of the manufacturing process of the printed wiring board of the present invention by the direct method among the full additive methods. It should be noted that it is of course possible to manufacture in the same manner using other adhesive printing methods and adhesive photography methods.

FIG. 1 is an enlarged cross-sectional view of a portion of a representative example of a double-sided through-hole board in which areas other than circuit formation are masked by a negative method. Further, FIG. 2 is a partially enlarged sectional view of a typical example of a double-sided through-hole substrate in which an electroless copper plating film is formed on both sides and through-hole portions. Further, FIG. 3 is an enlarged sectional view of a part of a typical example of a substrate on which a so-called circuit is formed, with masked portions removed. 1st
In the figures to FIG. 3, 1 denotes E-E thin wall material
2 is a thin material obtained from a mixture consisting of a saponified product of ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer and ethylene-vinyl acetate copolymer), and 2 is the throughhole part obtained from 1. be. 3
is a resist material, and 4 is chemical plating (electroless plating)
This is a conductive metal thin film obtained by

[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 carried out by testing the obtained film on a board with the test pattern shown in UL 713B (Printed Wiring Board) 7.1.
Evaluation was made by floating for 180 seconds in a solder bath with lead/tin = 9o/10 (weight ratio) held at 00°C. The evaluation is shown in Table 1 as follows.

○: 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 4, Comparative Examples 1 and 2 Melt flow index (JIS K- 6760, measured at a temperature of 190°C and a load of 2.18 kg, hereinafter referred to as rM, 1.J) is 300 g /
Ethylene-acrylic acid copolymer (density 0
．． 954 g/cm', acrylic acid copolymerization ratio 20% by weight) 100 parts by weight and vinyl acetate copolymerization ratio 28
Saponified product obtained by saponifying ethylene-vinyl acetate copolymer (saponification degree 87.5 by weight)
%, M, 1.75g710min, density 0.951g/
cm') was triblended for 5 minutes using a Henschel mixer. The obtained mixture [hereinafter referred to as "mixture (A)" 1] was transferred to an extruder equipped with a T-die (diameter 40 mm, die width 30 cm, rotation speed 85
revolutions per minute) and the temperature of the cylinder is C1 = 100°C.
, film (thickness 100 microns) under the conditions of C2 = 120 °C and C3 = 140 °C and die temperature of 160 °C.
was formed and wound around a roll that was water-cooled at 20°C (
Examples 1 to 4, Comparative Example 1.2). Moreover, the mixture (A
) instead of the ethylene-acrylic acid copolymer used in producing M, 1. Ethylene-methacrylic acid copolymer with a density of 200 g/10 minutes (density 0.!350 g/10 minutes)
A mixture [hereinafter referred to as "mixture (B)" 1] was produced in the same manner as mixture (A), except that the mixture (cm', methacrylic acid copolymerization ratio: 25% by weight) was used. A film was produced from the resulting mixture in the same manner as described above (Example 4). Furthermore, saponified products of the ethylene-acrylic acid copolymer (hereinafter referred to as rEAAJ, Comparative Example 1) and ethylene-vinyl acetate copolymer (hereinafter referred to as "saponified product", Comparative Example 2) used in Example 1 were used. A film was produced in the same manner as above.

Each film obtained in this way was heated at 320°C for 10 minutes using a heat press to give a mass of 20kg/cm.
Crosslinking was carried out under a pressure of ' (gauge pressure) (thickness is shown in Table 1) to produce a sheet.

Each sheet thus obtained was masked except for the circuit using a screen printing machine.

The obtained sheet was plated at 72°C with a chemical plating solution having the following composition in an aqueous solution, and approximately 3.
A 0 micron copper plating film was obtained.

Cu5Oa・5H20Log EDTA” 2Na・2H2030g.

Hill: HO (38%) 3 m 1 NaOH 12 g After finishing the coating, the masking was washed off, washed with water, and dried.

A heat resistance test was conducted on the obtained circuit-formed substrate.

The results are shown in Table 1.

Table 1 From these results, it was found that the printed wiring board obtained by the present invention not only has a very high circuit density, but also has excellent heat resistance and is a flexible, high-quality printed wiring board. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged sectional view of a portion of a typical example of a double-sided through-hole substrate in which areas other than circuit formation are masked by a negative method. Further, FIG. 2 is a partially enlarged sectional view of a typical example of a double-sided through-hole substrate in which an electroless copper plating film is formed on both sides and through-hole portions. Further, FIG. 3 is an enlarged sectional view of a part of a typical example of a substrate on which a so-called circuit is formed, with masked portions removed. l...E-E thin material? Through-hole portion 3 obtained from l...Resist material 4... Conductive metal thin film obtained by chemical plating (electroless metal plating) Patent applicant Showa Denko K.K. Representative Patent attorney Kikuchi Spirit

Claims (1)

[Scope of Claims] (A) A mixture consisting of (1) an ethylene-acrylic acid copolymer and/or an ethylene-methacrylic acid copolymer and (2) a saponified product of an ethylene-vinyl acetate copolymer, The mixing ratio of the ethylene-acrylic acid copolymer and/or ethylene-methacrylic acid copolymer in the mixture is 20 to 80% by weight, and the mixture is heated at a temperature of 250°C or less under conditions that do not cause fish eyes. extrude into a thin shape with 100
(B) Electroless plating or electroless plating and electrolytic plating are applied to the thin walled object obtained by heating and pressurizing the object at a temperature between 'C and 400°C to form a conductor circuit of 200 microns or less on the surface of the thin walled object. Printed wiring board made by forming.