JPS63125589A - Adhesive for printed circuit board - Google Patents

Abstract

PURPOSE:To provide the title adhesive which has excellent adhesive strength, thermal resistance and electrical insulating properties and is useful for preparing a printed circuit board with high reliability and excellent long-term stability and which comprises, as polymer components, a phenol resin prepolymer and/or an epoxy resin prepolymer and a particular nitrile rubber. CONSTITUTION:For example, emulsion polymn of 100pts.wt. in total of a mixture comprising 10-50wt% acrylonitrile (a), 30-80wt% butadiene (b) and, if necessary, 1-20wt% monomer (c) having a functional group, such as methacrylic acid, is conducted in the presence of 1-15pts.wt. nonionic activator (d) and, if necessary, 0-10pts.wt. ionic activator as emulsifiers at a temp. below the cloud point of component (d), thereby preparing a polymer latex. If necessary, 5-20pts.wt. electrolyte (f) contg. no metals, such as NH4Cl, is added to the polymer latex, and the latex is heated at 40-150 deg.C for coagulation, thereby preparing a nitrile rubber (B). 20-80wt5 phenol resin prepolymer and/or epoxy resin prepolymer is compounded with 80-20wt% component (B), optionally together with 50wt% or less in total of a flexibilizer, an inorg. filler, a flame retarder, etc. (C).

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to an adhesive used in the manufacture of printed circuit boards, which has excellent adhesive strength and causes extremely little corrosion of circuit forming metals.

With the rapid development of the electronics industry in recent years, the demand for circuit boards has shown remarkable growth. Among them, flexible printed wiring boards that are lightweight and capable of three-dimensional wiring are increasing rapidly as electronic devices become denser, lighter, thinner, and smaller.

On the other hand, with regard to copper-clad laminates as well, there has been remarkable technological progress in the additive method using chemical plating instead of the conventional method of press-bonding copper foil to the laminate and then etching it to create a wiring pattern.

Adhesives used for flexible printed wiring boards are generally composed mainly of epoxy resins and phenol resins, to which an elastomer is added for the purpose of imparting flexibility, a curing agent, and various auxiliary materials as necessary. When used, acrylonitrile-butadiene rubber or acrylic rubber is used as the elastomer from the viewpoint of compatibility with the resin and adhesive strength.

On the other hand, when forming a circuit on a laminate using the additive plating method, the laminate is coated with an adhesive layer made of a thermosetting resin containing an elastomer (phenolic resin is mainly used), and then metal plating is applied on the laminate. It is common to do so. At this time, the surface of the adhesive layer is roughened by acid treatment in advance in order to improve its adhesion to the plated part, and acrylonitrile-butadiene rubber is mainly used as the elastomer because of its ease of surface roughening. There is.

The recent development of the electronics industry has led to a demand for higher density printed wiring boards, which has made it necessary to reduce the line width of the wiring.

As a result, it has become clear that there is a danger that problems such as wire breakage or short circuits may occur due to corrosion of old metals, which had not been considered a problem in the past. This is true for both flexible printed circuit boards and rigid circuit boards.

c. Trying to solve 11 (Year plate standing) As a solution to this problem, we will use thermosetting resins and auxiliary materials to remove halogens, mainly chlorine, which are thought to be directly involved in metal corrosiveness, sodium, potassium, etc. Attempts have been made to reduce the content of alkali metals in these materials, and some success has been achieved.On the other hand, there has been a strong demand for acrylonitrile-butadiene rubber used in these products that is less corrosive to metals.

The present invention, which is a method for calculating d,
In producing rubber-like polymers through emulsion polymerization, the stability of the polymer latex under high temperatures such as in the 7-mer recovery process is ensured by carrying out emulsion polymerization using at least a nonionic activator, and at the same time, nonionic activators are used during coagulation. The purpose of this method is to utilize the properties of the activator to obtain a rubber-like polymer containing almost no metal ions or chloride ions, and to obtain an adhesive using the same.

That is, in the present invention, when obtaining a rubber-like polymer by emulsion polymerization, the emulsion polymerization is carried out using at least a nonionic activator as an emulsifier, and then the obtained polymer latex is treated with a nonionic activator and, if necessary, a metal. The present invention relates to an adhesive for printed circuit boards using nitrile rubber, characterized in that a rubbery polymer is coagulated by heating in the presence of an electrolyte that does not contain nitrile rubber.

・Explanation of component (B) The nitrile rubber produced by emulsion polymerization of the present invention is not only a normal acrylonitrile-butadiene copolymer (NBR) but also contains epoxy groups, hydroxyl groups, carboxyl groups, amino groups, alkyl ester groups, etc. as necessary. A modified acrylonitrile-butadiene copolymer (modified NBR) containing at least one functional group selected from the group consisting of:

Specific examples of such modified NBR include (a) monomers having at least one functional group selected from the group of epoxy groups, hydroxyl groups, carboxyl groups, amino groups, and alkyl ester groups, such as methacrylic acid and acrylic acid; acid,
Fumaric acid, itaconic acid, maleic acid, glycidyl (meth)acrylate, glycidyl allyl ether, glycidyl vinyl ether, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate , dipropylaminoethyl (meth)acrylate, diethylaminopropyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, etc. from 1 to 20%, (b) acrylonitrile 10
Examples include polymers obtained by emulsion polymerization of 50% by weight of (c) butadiene and 30 to 80% by weight of (c) butadiene.

In general, most rubbery copolymers, especially rubbery copolymers containing a diene component, are synthesized by emulsion polymerization.

However, in ordinary emulsion polymerization methods, anionic activators containing alkali metals such as potassium and sodium are widely used as emulsifiers, and sodium chloride is also used as a coagulant in the process of separating the produced polymer latex. , calcium chloride, and other metal compounds are used.

Therefore, these metal ions remain in the polymer, and these metal ions can hardly be removed even if the polymer latex is coagulated and washed with water.

For this reason, nitrile rubber produced by ordinary emulsion polymerization has a problem with metal corrosion, making it difficult to use it as an adhesive for modern printed circuit boards having fine wiring. On the other hand, polymerization of NBR in various organic solvents is known as one way to obtain polymers that do not contain the above metals, corrosive halogens, or alkali metals; It is difficult to obtain a polymer having the molecule (1), and the cost is also high.

When obtaining a polymer by emulsion polymerization, a nonionic (nonionic) surfactant is used as an emulsifier, and after emulsion polymerization is performed at a temperature below the convex point of the nonionic surfactant, the obtained polymer latex is applied to the convex point. By heating to the above temperature, nitrile rubber with a low content of metals and minerals can be used.

Alternatively, after performing emulsion polymerization using an ionic activator and a nonionic activator as an emulsifier, an electrolyte that does not contain metal is added to the obtained polymer latex, and then heated to produce a polymer containing metals and halogens. A small amount of nitrile rubber can be obtained.

The nonionic activator used in the emulsion polymerization of the present invention is one that does not ionize in an aqueous solution among substances that exhibit remarkable surface activity at low concentrations, and specifically, for example, polyoxyethylene alkyl ether, polyoxy Ethylene alkyl allyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene oxypropylene broth polymer,
Examples include alkylsulfinyl alcohol and fatty acid monoglyceride.

When an aqueous solution of a nonionic activator is heated, the temperature at which cloudiness occurs for the first time is called the 0 point, which is a unique phenomenon that causes an aqueous solution of a nonionic activator to form.

Thermodynamically, the 0 point is the lower critical solution temperature (LCST).
) corresponds to Here, the lower critical melting temperature is as follows. That is, when a nonionic agent-water system mutual solubility curve is drawn, it is generally referred to as a convex point curve. Below this curve is a homogeneous one-phase system, and above this curve is a two-phase system. The temperature at the point corresponding to the bottom of this curve is called LCST, and the temperature corresponding to the point on the curve for each composition is called 0 point.

Therefore, when the temperature of a nonionic activator aqueous solution with a certain composition is increased, a phenomenon called white turbidity-phase separation appears at a temperature above the point where the curve intersects with the above-mentioned curve, that is, above the convex point, and the system that was a homogeneous phase changes. It separates into two phases: an aqueous phase and an active agent phase. This phenomenon can be said to be a decrease in the concentration of the nonionic activator in the aqueous phase, in other words, the activator has become poorly soluble in water, and this phenomenon is characteristic of nonionic activators.

In this way, at temperatures above the convex point, nonionic surfactants become poorly soluble in water and lose their activity as surfactants. This corresponds to the conventional separation step of reducing the water solubility and coagulating the polymer latex.

That is, if such a nonionic activator exists at least in the polymer latex obtained by emulsion polymerization, it becomes possible to facilitate the coagulation of the polymer by utilizing the zero point phenomenon.

However, although the zero point of the nonionic activator aqueous solution and the coagulation temperature of the polymer latex are not necessarily the same, there is a correlation between the former and the latter temperatures, and in the present invention, such nonionic activator is used as a guideline for the coagulation temperature. The 0 points are used.

As the nonionic activator used in the present invention, one of the compounds exemplified above may be used alone, or two or more thereof may be used in combination, and is appropriately selected depending on the emulsion polymerization conditions or coagulation conditions.

For example, the zero point of the nonionic activator is preferably 20 to 110°C; if it is too low, the stability of the polymer latex is insufficient, and if it is too high, a high temperature is required for coagulation, which is not practical.

In addition, if the temperature is raised by steam distillation etc. in the monomer recovery process, the temperature will exceed the convex point and the obtained polymer latex may coagulate, so a nonionic activator used during emulsion polymerization should also be used. In this case, it is preferable to select in advance a nonionic activator having a zero point equal to or higher than the temperature at which steam distillation is performed.

Furthermore, after performing emulsion polymerization and monomer recovery by using a nonionic surfactant with a high convexity point together with an ionic surfactant as an emulsifier, a nonionic surfactant with a low convexity point and other alcohols, fatty acids, etc. In addition, it is also possible to lower the solidification temperature by lowering the convex point.

The nonionic activator of the present invention may be used alone for emulsion polymerization (or may be used in combination with an ionic activator during emulsion polymerization.) Lower metal contents are possible.

The above-mentioned ionic activator is an anionic activator, a cationic activator, or an amphoteric activator.

Examples of anionic active agents include soap, funnel oil, emulsified oil, alkylnaphthalene sulfonate, dodecylbenzene sulfonate, oleate, alkylbenzene sulfonate, dialkyl sulfosuccinate, lignin sulfonate, and alcohol ethoxylate. Examples include sulfate, secondary alkanesulfonate, α-olefin sulfonic acid, and tamol.

Examples of the cationic activator include alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylpyridinium salts, and alkylbenzyldimethylammonium salts.

Furthermore, examples of the amphoteric surfactant include alkyl betaines, alkyl diethylene triaminoacetic acids, and the like.

Note that these ionic activators can be used alone or in combination of two or more.

The usage ratio of these activators is 1 to 15 parts by weight, preferably 2 to 15 parts by weight of nonionic activators per 100 parts by weight of monomer.
12 parts by weight, and 0 to 10 parts by weight of the ionic active agent, preferably 0 to 6.0 parts by weight.

If the amount of nonionic activator used is less than 1 part by weight,
As described later, even if heated after adding a metal-free electrolyte, it may not be possible to coagulate the polymer latex.On the other hand, if the amount exceeds 15 tLt, the nonionic activator (ionic If used together with bioactive agents, the viscosity of the resulting polymer latex may be too high or the stability of the latex may deteriorate.

On the other hand, if the ionic emulsifier exceeds 10 parts by weight, the coagulability of the polymer latex will be insufficient, making it impractical, and the metal content of the resulting polymer may increase.

In coagulating the polymer latex, in addition to heating, a metal-free electrolyte can be added as necessary to make coagulation easier.

Such metal-free electrolytes include, but are not limited to, inorganic salts such as ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium nitrate, and ammonium acetate.

Such metal-free electrolytes can be used alone or in combination of two or more.

The proportion of the electrolyte used is 5 to 20 parts by weight, preferably 7 to 15 parts by weight, per ioo parts by weight of the polymer component in the polymer latex; if it is less than 5 parts by weight, coagulation may be insufficient; Even if it is used in an amount exceeding 20 parts by weight, it is uneconomical and the coagulability hardly changes.

After emulsion polymerization (and monomer recovery), the resulting polymer latex is treated with conventional chlorination in the presence of a nonionic activator and a metal-free electrolyte. The polymer latex is coagulated by heating without using a metal compound such as calcium or sodium chloride as a coagulant.

The heating temperature in this case is not particularly limited,
Although it can be adjusted arbitrarily depending on the type, amount, and ratio of the ionic activator/nonionic activator used and the type and amount of the electrolyte used, it is usually adjusted to 40 to 150 ℃, preferably 60 to 120 ''C. If the temperature is lower than 40°C, the latex becomes unstable, which may cause production problems, while if the temperature exceeds 150°C, gelation of the polymer may occur, which is not preferable.

There is no particular restriction on the molecular weight of the nitrile rubber used in the present invention, but preferably Mooney viscosity ML, (100
°C) ranges from 20 to 120.

- Description of component (A) The epoxy resin prepolymer that can be used in the present invention may be any of those conventionally used as adhesives for printed circuit boards, such as bisphenol-type epoxy resin, Tuvolac-type epoxy resin, and cresonyl-type epoxy resin. Epoxy resin, alicyclic epoxy resin, rubber modified epoxy resin,
Prepolymers such as ether-ester type epoxy resins having two or more epoxy groups per molecule can be mentioned, and brominated products of these can also be used.

On the other hand, the phenolic resin prepolymer used in the present invention may be either a novolac type or a cresonyl type, and is formed by a reaction between phenol and/or substituted phenols and aldehydes. The aldehyde is preferably formaldehyde.

As already shown in Japanese Patent Publication No. 53-36861, NBR/phenol resin is known to have excellent adhesive strength and heat resistance as an adhesive for printed circuit boards. The combined use of phenol resin and epoxy resin has been suggested for the purpose of improving workability and improving workability. However, the NBR used here is a normal NBR,
All conventional commercially available products do not use nonionic activators, but contain a large amount of metal ions that are polymerized using ionic activators and then coagulated using metal compounds.

Therefore, there is a problem with metal corrosion. This problem can only be solved by using the specific nitrile rubber of the present invention.

The amount of nitrile rubber used is 2 times the amount of polymer component used as an adhesive.
It is 0 to 80% by weight, preferably 30 to 60% by weight. If it is less than 20% by weight, for example, when used as an adhesive for additive chemical plating, it is difficult to roughen the surface by acid treatment in a post-process, and good adhesive strength on the plated surface cannot be obtained. Furthermore, when used as an adhesive for flexible printed circuit boards, the flexibility is insufficient.

In some cases, when the amount of nitrile rubber exceeds 80% by weight, the adhesive strength is poor and the heat resistance is also poor.

The amount of phenolic resin prepolymer and/or epoxy resin prepolymer used is 20 to 80% by weight,
Preferably it is 40 to 70% by weight.

If it is less than 20% by weight, the adhesive strength will be poor, and if it exceeds 80% by weight, the flexibility will be poor.

In order to be used as an adhesive for printed circuit boards, in addition to nitrile rubber, phenolic resin and/or epoxy resin prepolymers, various flexibilizers such as hardening oils, silica, alumina, mica, titanium oxide,
Inorganic fillers such as charcoal, flame retardants such as antimony trioxide, aluminum hydroxide, etc. can be added, and the amount thereof is preferably 50% by weight or less of the total solid content of the adhesive. (That is, the same amount or less of nitrile rubber + epoxy resin + phenol resin) The adhesive used in the present invention may be in any form conventionally known in this field. That is, it can be used as a liquid or paste type by dissolving it in a solvent, or it can also be used by preparing a laminate film by mixing each component with a dry press.

That is, as a method for applying the adhesive to the substrate, in addition to impregnating the substrate with an adhesive solution or applying it to the surface, it is also possible to stack a film on one or both sides of the substrate and heat and press it to integrate.

Ni Oshi ■ The present invention will be specifically described below with reference to Examples.

In addition, in the examples, the metal ions and water-soluble chlorine in the polymer were determined as follows.

"Quantification of metal ions in polymers" 1) Burn the polymer to ash at 700°C in a platinum crucible.

ii) Dissolve the remaining ash in 1N hydrochloric acid.

iii) Dilute to an appropriate concentration and determine the concentration of each metal in the aqueous solution using an atomic absorption spectrometer.

iv) Calculate the content of metal ions in the polymer from the value in item iii) above.

[Determination of the amount of water-soluble chlorine in the polymer] 1) Cut 5 g of the polymer into two pieces and place them in a 200 cc glass pressure bottle with 100 g of distilled water.

2) Heat and stir at 120°C for 24 hours.

3) Quantify chlorine ions in the extracted water using an ion chromatograph manufactured by DIONEX, and calculate the amount of water-soluble chlorine in the polymer.

Example 1 Emulsion polymerization was carried out at 20° C. in an autoclave with an internal volume of 20 using the emulsion polymerization Lesby shown below.

1 ■ Rikine Nyudanji (parts by weight) Bukudiene 65 Acrylonitrile 35 Water
= 220 polyoxyethylene nonylphenyl ether 01 ・5 tertiary dodecyl mercaptan: 0.35 ammonium persulfate 0.25 cyanoethylated diethanolamine: 0.15*1) Kao soap (horizontal split, emma convex point 920 cloud point 82°C After the polymerization conversion rate reached 90%, 0.2 parts by weight of hydroxylamine sulfate per 10 parts by weight of monomer was added to stop the polymerization.

Subsequently, the residual monomer was recovered by heating and steam distillation at about 70°C under reduced pressure, and then 1 part by weight of alkylated phenol was added as an antiaging agent, and then 10 parts by weight of ammonium sulfate was added to a 20% by weight aqueous solution. After adding as 90
The polymer latex was coagulated by heating to .

The generated crumb was taken out, washed with water, and dried under reduced pressure at 50°C to obtain a trill rubber (A)) as a sample for evaluation.

Using the obtained nitrile rubber (A), an adhesive for additive plating was prepared according to the following formulation (formulation-1).

(Blend-1) Nitrile rubber 50 parts by weight Resol type phenolic resin 50 Methyl ethyl ketone
200 The obtained adhesive was applied to an epoxy resin/glass cloth laminate to form an adhesive layer with a thickness of 40μ, and then 30μ chemical copper plating was performed using the usual additive method.The evaluation results are shown in Table 2. Shown below.

Examples 2 to 5, Comparative Examples 1 to 6 Nitrile rubber was polymerized by changing the type of emulsifier and monomer composition according to the emulsion polymerization Lesby shown in Example 1, and by changing the type of electrolyte and heating (coagulation) temperature. Furthermore, nitrile rubber (B
) to (F) were obtained.

Adhesives were prepared from the obtained nitrile rubbers (B) to (F) according to the formulations 1 and 2 shown in Example 1, and additive chemical copper plating was performed in the same manner as in Example 1. The evaluation results are summarized in Table 2.

(Blend-2) Nitrile rubber 50 parts by weight Labolac type phenolic resin 35 Epoxy resin
15~ (Epicoat 1001 manufactured by Yuka Shell Kiki) Methyl ethyl ketone 250 The obtained nitrile rubber was further evaluated as an adhesive for flexible printed circuit boards by the following method.

(Blend-3) Nitrile rubber 35 parts by weight Res--
Le-type phenolic resin 40 Epoxy resin
25 (manufactured by Yuka Shell Haisun Epicoat 828
) Dicyandiamide 1 Methyl ethyl ketone 200 The obtained adhesive was applied to a polyimide film (trade name "Kapton" manufactured by DuPont) to a thickness of 30 μm after drying, and dried at 120° C. for 10 minutes. Next, IQ the copper foil with a thickness of 30μ for 3 minutes at 160℃.
A flexible printed circuit board was produced by pressing under a load of kg/cnl and heating at 120'C for 60 minutes.

Table 3 shows the results of evaluating the characteristics of the obtained substrate.

As can be seen from Table 2, the additive chemical plated printed circuit board using the adhesive according to the present invention has excellent heat resistance, adhesive strength, and electrical insulation, and is extremely resistant to copper foil corrosion under high temperature and humidity. It has the characteristic of being small. Similarly, Table 3 clearly shows that the flexible printed circuit board using the adhesive according to the present invention has excellent heat resistance, adhesive strength, and low copper corrosion under high temperature and humidity, and is excellent in reliability. .

The adhesive of the present invention has strong adhesive strength, excellent heat resistance and electrical insulation properties, and is suitable as an adhesive for printed circuit boards.

Printed circuit boards obtained using this adhesive have excellent reliability, and can be used stably over long periods of time with little circuit corrosion, especially when the line width is reduced due to the demand for higher circuit densities. It has the following characteristics.

Claims (1)

[Claims] (1) After carrying out emulsion polymerization using (A) 20 to 80% by weight of a phenolic resin prepolymer and/or an epoxy resin prepolymer and (B) at least a nonionic activator as an emulsifier, the obtained polymer latex is An adhesive for printed circuit boards containing, as a polymer component, 80 to 20% by weight of nitrile rubber obtained by heating and coagulating in the presence of a metal-free electrolyte if necessary.