JP2628734B2 - Conductive paste - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a highly conductive and highly reliable conductive paste used for a printed wiring board, and more particularly, to a conductive paste formed of copper foil or copper plating. The present invention relates to a copper paste having excellent adhesion to a conductor.

(Prior Art and Problems to be Solved by the Invention) In recent years, copper has been evaluated as being less likely to cause migration and lower in cost than silver, and copper paste using copper powder as a filler has been developed.

However, the resin-curable copper paste, which is obtained by mixing and mixing copper powder with a thermosetting resin, is liable to be oxidized by heating when it is printed and then heat-cured. It has a drawback that it is difficult to obtain, and the circuit resistance is likely to increase due to a change with time thereafter.

Commercially available copper paste, in order to prevent oxidation of copper powder, it is necessary to use a reducing resin such as a phenolic resin as a binder resin, and further, additives such as a reducing agent are blended. Sufficient results have not been obtained.

Further, the copper paste is rarely used to form a conductive circuit by itself. Usually, for example, copper paste is often used for a conductive circuit combined with a conductor formed by copper foil or copper plating, such as for a jumper circuit or for forming an EMI shield layer.

Regarding the electrical reliability of these conductive circuits as a whole, it can be said that not only the characteristics of the copper paste alone but also the reliability of the connection between the copper paste and a conductor such as a copper foil are extremely important.

However, since the conventional copper paste uses a reducing resin as a binder resin as described above, the adhesiveness with a copper foil or a conductor formed by copper plating is poor, and the flexibility of the coating film is low. Cracks are more likely to occur, and the addition of a reducing agent or the like adversely affects the adhesion.

It has been empirically found that the adhesion can be improved by heating and oxidizing the conductor before printing the copper paste in order to improve the adhesion. However, this method has many problems with respect to mass productivity, for example, the number of steps is increased, and it is difficult to maintain a constant oxidation state.

(Means for Solving the Problems) The present inventors have intensively studied in view of the above-mentioned problem that the conventional copper paste has insufficient adhesion to a conductor such as a copper foil and lacks electrical reliability as a conductor circuit. As a result, a binder resin composition suitable for a copper paste having high conductivity and high reliability was found, and the present invention was completed.

That is, the conductive paste of the present invention is characterized in that a copper powder is blended and mixed with a binder resin containing a phenol resin and a bisoxazoline compound as essential components.

The phenol resin in the present invention is a resol phenol resin or a mixture of a resol phenol resin and a novolak phenol resin.

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

The mixing ratio (solid content) of the phenol resin to the bisoxazoline compound is preferably 50 to 95% by weight for the phenol resin and 5 to 50% by weight for the bisoxazoline compound. When the bisoxazoline compound is less than 5% by weight,
Adhesion to conductors such as copper foil is not improved. If the bisoxazoline compound exceeds 50% by weight, the adhesion is very good and there is no problem, but the conductivity tends to decrease.

In addition, you may mix | blend other thermosetting resins or thermoplastic resins with these phenolic resins and the resin which mainly consists of a bisoxazoline compound as needed.

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

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

An organic acid, an organic acid salt, a reducing agent, a high boiling solvent, an antifoaming agent, a shaking agent and the like can be appropriately added to the binder resin as additives. In particular, it is preferable to add a small amount of an organic acid since a conductive paste having high conductivity can be obtained.

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

(Function) Since the conductive paste of the present invention contains a bisoxazoline compound in a binder resin, it has excellent toughness, and further has a conductive property with respect to a conductor formed by copper foil or plating without impairing conductivity. Has excellent adhesion.

As a result, in conductive circuits and EMI shield layers using copper paste, the connection between the copper paste and the conductor formed by copper foil or plating is well bonded and solid, and printing with excellent electrical reliability A wiring board can be obtained.

The effect of improving the adhesion of the bisoxazoline compound in the conductive paste of the present invention is remarkable when an organic acid is used as an additive.

(Examples) Hereinafter, the present invention will be described with reference to Examples.

Examples 1 to 3 and Comparative Example 1 For the bisoxazoline compound, 2,2 ′-(1,3-phenylene) -bis (2-oxazoline) manufactured by Takeda Pharmaceutical Co., Ltd., commonly called 1,3-PBO, was used. The resole type phenol resin was mixed in the ratio shown in Table 1, and a small amount of oleic acid and an antifoaming agent were further added to obtain a binder resin.

As the copper powder, an atomized spherical copper powder having an average particle diameter of 10 μm was used.

After mixing the copper powder and the binder resin, the mixture was kneaded with a three-roll mill to obtain a conductive paste.

The copper powder content was selected to have the lowest specific resistance. It was 83% based on the total amount of copper powder and resin solids.

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

In addition, a copper-clad glass epoxy substrate is
A copper foil surface was oxidized by heating for one minute, and a non-heated one was prepared. A binder of 50 mm × 20 mm was formed on both substrates by a screen printing method.
Heated for a minute to cure.

According to the cross-cut test of JISK5400, 11 mm length and width parallel lines perpendicular to each other on the coating film are 1 mm
At regular intervals, cross cuts were made to make 100 squares in 1 cm ² . The adhesiveness was evaluated based on the number of grids of the coating remaining on the substrate when the coating was peeled off with a cellophane tape from above.

Table 1 shows the respective binder resin compositions and measurement results.

In Comparative Example 1, since 1,3-PBO was not mixed, the adhesiveness was poor, and the adhesiveness could not be obtained unless the copper foil surface was oxidized.

Examples 1 and 2 are extremely superior to Comparative Example 1 in terms of adhesiveness while having substantially the same specific resistance. It is extremely excellent even without oxidation of the copper foil surface, and the effect of blending 1,3-PBO is remarkable.

In Example 3, the specific resistance was slightly large, but the adhesion was extremely excellent.

(Effects of the Present Invention) As described above, the conductive circuit using the conductive paste of the present invention has high conductivity, and the adhesiveness of the connection between the copper paste and the metal conductor formed by copper foil or plating is extremely high. Since it is good and strong, it has high electrical reliability.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H01B1 / 22 H01B1 / 22 A (56) References JP-A-1-113473 (JP, A)

Claims (1)

(57) [Claims] 1. A conductive paste comprising a binder resin containing a phenol resin and a bisoxazoline compound as essential components, and copper powder mixed and mixed.