JPH0415270A - Electrically conductive paste - Google Patents

Abstract

PURPOSE:To provide an electrically conductive paste with excellent skinning resistance when it is stored, adhesiveness with a metallic conductor, electric conductivity etc., by compounding a binder resin wherein a phenol resin and a specified bisoxazoline deriv. are essential ingredients with a copper powder. CONSTITUTION:A bisoxazoline deriv. is prepd. by reacting a bisoxazoline compd. such as 2,2'-(1,2-ethylene)-bis(2-oxazoline) or 2,2'-(1,4-buthylene)-bis(2-oxazoline) with a carboxylic acid (e.g. adipic acid). Then, a binder resin is prepd. by mixing this bisoxazoline deriv. and a phenol resin (e.g. resol phenol resin). This binder resin is compounded and mixed with a copper powder to prepare an electrically conductive paste. An electrically conductive circuit prepd. by using this paste exhibits high electric conductivity and has high electric reliability.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a highly conductive and highly reliable conductive paste used for printed wiring boards. The present invention relates to a conductive paste that has excellent adhesion to conductors and has excellent peeling resistance during storage.

(Prior Art and Problems to be Solved by the Invention) In recent years, copper has been evaluated for its resistance to migration and low cost compared to silver, and copper pastes using copper powder as a filler have been developed.

However, resin-curing copper paste, which is made by blending copper powder with thermosetting resin, tends to oxidize the surface of the copper powder when it is thermally cured after printing, so it cannot be used as a low-resistance conductive circuit. It has the disadvantage that it is difficult to obtain, and that circuit resistance is likely to increase due to subsequent changes over time.

Therefore, in order to prevent copper powder from oxidizing, copper paste must use a reducing resin such as phenol resin as the binder resin, and must also contain additives such as reducing agents to prevent oxidation with low resistance. It is made to be difficult.

However, copper paste is rarely used alone to form conductive circuits, and is usually used to form conductive circuits using copper foil or copper plating, for example, when copper paste is used for jumper circuits or for forming EMR shield layers. Since copper paste is often used in conductive circuits in combination with conductors such as copper foil, not only the characteristics of the copper paste itself but also the reliability of the connection between the copper paste and the conductor such as copper foil are extremely important.

However, since conventional copper paste uses a reducing resin as a binder resin as mentioned above, it has poor adhesion to conductors made of copper foil or copper plating, and
The paint film has poor flexibility and is prone to cracking, and
Adhesion is adversely affected by the addition of reducing agents, etc.
There are other problems.

It has been empirically found that adhesion can be improved by subjecting the conductor to oxidation treatment by heating before printing the copper paste. However, this method has problems such as an increase in the number of steps, and a copper paste that can ensure adhesion without oxidation treatment is desired.

In view of the above-mentioned problem that conventional copper paste has insufficient adhesion to conductors such as copper foil and lacks electrical reliability as a conductor circuit, the inventors have developed a highly conductive and highly reliable paste. As a binder resin composition suitable for a copper paste having properties, a copper paste has been found which is characterized by having a phenol resin and a bisoxazoline compound as essential components, and incorporating copper powder into the binder resin composition.

However, bisoxazoline compounds tend to cause skinning (a film formed on the surface of the copper paste), and it is necessary to add a skinning improver separately.

(Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, it was discovered that by using a bisoxazoline derivative, skin elasticity can be improved while retaining the characteristics of the bisoxazoline compound, and the present invention has been achieved. It was.

That is, the conductive paste of the present invention is characterized in that it is made by mixing copper powder with a binder resin whose essential component is a bisoxazoline derivative obtained by heating a phenol resin, a bisoxazoline compound, and a carboxylic acid. It is something to do.

The bisoxazoline compound in the present invention is 2.2'
-(1,2-ethylene)-bis(2-oxacillin)
, 2.2'-(1,4-butylene)-bis(2-oxazoline), 2.2'-(1,3-phenylene)-bis(2-oxazoline), 2.2'-(1,4 -phenylene)-bis(2-oxacillin), 2.2'-(1,3-phenylene)-bis(5-methylene-2-oxazoline), and the like.

In addition, the carboxylic acids to be reacted with the bisoxazoline compound include adipic acid and sebacic acid which are aliphatic dicarboxylic acids, terephthalic acid which is an aromatic dicarboxylic acid, and cyclohexadicarboxylic acid which is an alicyclic dicarboxylic acid.
It is a polyhydric carboxylic acid with more than a functional level.

The bisoxazoline derivative of the present invention is obtained by the reaction of a bisoxazoline compound and carboxylic acid class i, and specifically, the bisoxazoline compound and the carboxylic acid class i are mixed in a ratio of, for example, 2:l, 3:1, etc. like,
It is obtained by mixing so that the bisoxazoline compound is in excess of the carboxylic acid and carrying out a closed reaction under heating for a predetermined time while stirring.

The phenolic resin in the present invention is a resol-type phenolic resin or a mixture of a resol-type phenolic resin and a novolac-type phenolic resin.

The blending ratio (solid content) of the phenol resin and the bisoxazoline derivative is preferably 50 to 95% by weight for the phenol resin and 5 to 50% by weight for the bisoxazoline derivative. If the bisoxazoline derivative is less than 5% by weight, the adhesion to conductors such as steel foil will not be improved. If the content of the bisoxazoline derivative exceeds 50% by weight, the adhesiveness is extremely good and there are no problems, but the conductivity tends to decrease.

In addition, other thermosetting resins or thermoplastic resins may be blended with the resins mainly composed of these phenol resins and bisoxazoline derivatives, as desired.

The copper powder used in the conductive paste of the present invention is not particularly limited, and various manufacturing methods and shapes such as electrolytic copper powder, atomized copper powder, and pulverized copper powder can be used. The average particle size is preferably 20 μm or less since the conductive paste is screen printed. In particular, it is preferable to use atomized copper powder with an average particle size of about 10 μm because it provides excellent printability and conductivity.

The copper powder content in the conductive paste is preferably 75 to 90% by weight based on the total weight of the solid content of the copper powder and binder resin. Furthermore, the optimum copper powder content varies depending on the properties of the copper powder used.

As additives, organic acids, organic acid salts, reducing agents, high boiling point solvents, antifoaming agents, shaking agents, etc. can be appropriately added to the binder resin. In particular, it is preferable to add a small amount of organic acid because a highly conductive conductive paste can be obtained.

The conductive paste of the present invention is printed on a substrate by screen printing, and can be used as a conductive circuit or an EMI shield layer as it is, or by plating the surface of the copper paste with a metal such as nickel or copper.

(Function) The conductive paste of the present invention contains a bisoxazoline derivative in the binder resin, so it has excellent toughness and is effective against conductors formed by copper foil or plating without impairing conductivity. It has excellent adhesive properties and also has excellent skin resistance.

As a result, the conductive paste of the present invention has excellent workability, and in conductive circuits and EMI shield layers using it, the connection between the conductive paste and the conductor formed by copper foil or plating is well bonded and strong. Therefore, a printed wiring board with excellent electrical reliability can be obtained.

(Example) The present invention will be explained below using examples.

2 manufactured by Takeda Pharmaceutical Company ■ as a bisoxazoline compound.
Using 2'-(1,3-phenylene)-bis(2-oxacillin), commonly known as 1.3-PBO, and using sebacic acid as the carboxylic acid, they were mixed at a molar ratio of 2:1,
A bisoxazoline derivative was obtained by reacting at 150°C for 30 minutes.

A resol type phenol resin was mixed in the ratio shown in Table 1, and a small amount of sleic acid and an antifoaming agent were added to prepare a binder resin.

Atomized spherical copper powder with an average particle size of 10 μm was used as the copper powder.

Copper powder and binder resin were mixed and then kneaded in a three-roll mill to form a conductive paste.

Note that the copper powder content was selected to be the value that would give the lowest specific resistance. It was set at 83% with respect to the total amount of copper powder and resin solid content.

A zigzag pattern with a line width of 2 mm and a length of 36.8 cm was printed on a glass epoxy substrate by screen printing each of the conductive pastes of Examples 1 to 3 and Comparative Example 1.2 using a stainless steel screen. After curing this for 30 minutes in a hot air constant temperature bath at 160° C., the resistance value and film thickness of the zigzag pattern circuit were measured to determine the specific resistance.

Furthermore, the copper-clad glass epoxy substrate was heated at 150℃3 in the atmosphere.
One was prepared by heating the copper foil for 0 minutes to oxidize the surface of the copper foil, and the other was not heated. The above conductive paste was applied to both substrates using the screen printing method to form a 50 mm x 2 board.
A 0-open pattern was formed and cured by heating at 160° C. for 30 minutes.

For the obtained substrate, 11 parallel lines perpendicular to each other were drawn on the coating film with a spacing of 1 interval, according to the substrate test of J15K5400.
Baseline-shaped cuts were made so that 100 drainage holes were made in cm2. Adhesion was evaluated based on the number of substrates of the coating film remaining on the substrate when the coating film was peeled off with cellophane tape.

Table 1 shows each binder resin composition and measurement results.

Comparative Example 1 had poor adhesiveness because no bisoxazolines were mixed therein, and adhesiveness could not be obtained unless the surface of the copper foil was oxidized.

Compared to Comparative Example 1, Examples 1 and 2 have extremely good adhesion even though the specific resistance is about the same, and even without oxidation on the surface of the copper foil.

Furthermore, compared to Comparative Example 2, it has excellent skin tension resistance. Example 3 has a slightly high specific resistance, but has extremely excellent adhesiveness and is resistant to skin-stretching properties.

(Effects of the present invention) As described above, the conductive paste of the present invention has excellent skin resistance, and the conductive circuit using the same has high conductivity. Because the adhesiveness of the joint with the conductor is extremely good and strong,
It has high electrical reliability.

Claims (1)

[Claims] A conductive paste characterized in that copper powder is blended into a binder resin whose essential component is a bisoxazoline derivative obtained by reacting a phenol resin, a bisoxazoline compound, and a carboxylic acid.