JPH09282939A - Conductive copper paste composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give the excellent conductivity to a through hole part, and to enable the electrical connection with high reliability so as to prevent the occurrence of conduction failure of the through hole part with a thermal impact by a change with lapse of time, especially, after absorbing moisture. SOLUTION: This conductive copper paste composition includes copper powder, thermoplastic resin, solvent, polyhydric phenol monomer, imidazole compound as essential component, and furthermore, includes polyvinyl butyral resin as an essential component. Polyvinyl butyral resin at 100-2,500 degree of polymerization, at 20% by mole or more of content of hydroxyl group, at 70% by mole or more of butyralization, at 80 deg.C or more of glass transition point, and at 180 deg.C or more of melting temperature is desirably used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive copper paste composition having excellent reliability of through holes in a printed circuit board, and more specifically, a paper base material phenol resin base material or a glass cloth base material. After embedding a copper paste by screen printing in the through holes provided on the printed circuit board such as an epoxy resin substrate, heating and curing give good conductivity in the through holes, and even after aging, especially after moisture absorption. The present invention relates to a conductive copper paste composition that does not cause poor conductivity in a through hole portion due to thermal shock.

However, the technique of the present invention is not only used for through-hole connection, but also for circuit use, electromagnetic wave shield use, etc., in which the adhesion to the substrate of the printed circuit board or the copper foil is sufficiently high and heat resistance and flexibility are high. Effective where needed. Especially in the case of electrical connection, the adhesion of the printed circuit board to the copper foil greatly affects the reliability. Further, in the case of application to a flexible circuit board, flexibility is also required. In this way, the adhesion with the printed circuit board is strong,
The present invention relates to a highly reliable conductive copper paste composition having both heat resistance and flexibility.

[0003]

2. Description of the Related Art Through holes are provided in lands of a printed circuit board such as a paper-based phenolic resin board or a glass cloth-based epoxy resin board, and a conductive silver paste (hereinafter, referred to as a silver paste) is screen-printed there. A method of manufacturing a printed wiring board by heat curing after embedding has recently become popular. However, when silver paste is used, migration problems frequently occur especially in pattern circuits that have recently been made finer. Further, silver is an expensive metal although it has excellent conductivity.

For this reason, a conductive copper paste (hereinafter referred to as a copper paste) has recently attracted attention as an alternative. However, since copper is easily oxidized and its oxide is an insulator, it is necessary to effectively suppress the oxidation of copper and further incorporate a substance having a reducing action. As measures for preventing such oxidation, for example, JP-A-61-3154 and JP-A-63-286577 are known. However, in the case of a copper paste, ohmic contact cannot be obtained unless the copper powders are in sufficient contact with each other, and a silver paste has not yet been replaced.

[0005]

The inventors of the present invention have hitherto proposed Japanese Patent Application No. 6-2 as a copper paste for through holes.
No. 07824, Japanese Patent Application No. 6-295384, Japanese Patent Application No. 7-
No. 161224, Japanese Patent Application No. 7-177822, Japanese Patent Application No. 7
After embedding by screen printing as described in the specification of -224401 and the like, by heating and curing, good conductivity of the through-hole portion is given, and the change with time, particularly a thermal shock test and a solder dip test For example, a copper paste that does not cause poor conductivity in the through-hole portion due to thermal shock has been provided.

However, recently, in printed circuit board manufacturers, the thermal shock resistance after moisture absorption, that is, a test method for a copper clad laminate for a multilayer printed wiring board JIS standard C-64
86, MIL standard P-13949G, etc., a test in which solder dip is performed after boiling, or solder dip is performed after C treatment, that is, 40 ° C./90% RH, 96 hours treatment, and the rate of change in conduction resistance value There is a demand to keep it within 100%.

In the solder dip test after moisture absorption, the conductive copper paste cured product must withstand the stress due to the thermal expansion of the substrate and the stress due to the volume expansion associated with the rapid gasification of the absorbed water. In the present invention, in order to exhibit the above-mentioned characteristics, it is necessary to further enhance the adhesiveness with the copper foil of the land portion, to give the conductive copper paste cured product flexibility without lowering the heat resistance, and to lower the hygroscopicity. It has been found that it becomes possible by realizing the thing.

[0008]

The present invention provides a conductive copper paste composition characterized by containing a copper powder, a thermosetting resin, a polyhydric phenol monomer and a solvent as essential components, and further containing a polyvinyl butyral resin. And then
The polyvinyl butyral resin preferably has a degree of polymerization of 100.
˜2500 and / or a glass transition temperature of 80 ° C. or higher, and more preferably a hydroxyl group containing 20 to 40 mol%. Further, it is preferably a copper paste composition containing polyvinyl butyral resin in an amount of 0.5 to 20% by weight based on the solid content of the thermosetting resin.

As the copper powder used in the present invention, commercially available products can be used as they are, and any shape such as scale, dendritic, and spherical can be used, but dendritic electrolytic copper powder is particularly preferable. . The thermosetting resin used in the present invention may be an epoxy resin, a melamine resin, an unsaturated polyester resin, a phenol resin or the like, but a so-called resol type phenol resin obtained by methylating phenol and formaldehyde under an alkali catalyst is particularly preferable.

In the present invention, glycol ethers are preferable as the solvent, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether. Propyl ether, dipropylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol Monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, ethylene glycol monoallyl ether, ethylene glycol monophenyl ether, ethylene glycol dimethyl ether, diethylene glycol Dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, etc., and their esterifications are used, but the appropriate boiling point and vapor pressure may be adjusted depending on the solubility and drying of the thermosetting resin used and the curing conditions. You can choose what you have.

The polyhydric phenol monomer used in the present invention may be catechol, resorcin, hydroquinone or the like, but hydroquinone is particularly preferable. Further, this polyhydric phenol monomer, for example, hydroquinone facilitates electron conduction by forming an oxidation-reduction system, and hydrogen released from the oxidation-reduction system can reduce copper oxide, resulting in long-term reliability. can get.

The imidazole compound used in the present invention is N, N- {2methylimidazolyl- (1) -ethyl}-
In order to maintain good conductivity, it is preferable to contain at least one compound represented by the following chemical formula 1 such as eicosane dioil diamide. This blending amount is usually 0.5 to 10% by weight based on the solid content of the thermosetting resin.

[0013]

Embedded image _{R = ─ (CH 2) n} ─, n = 4~30

The polyvinyl butyral resin used in the present invention has the functions of imparting flexibility to the copper paste without lowering the heat resistance and improving the adhesion to the circuit copper foil. Polyvinyl butyral is a polymer compound which is generally represented by Chemical Formula 2, and preferably has a polymerization degree of 100 to 2500 and / or a glass transition temperature of 8
0 ° C or higher, more preferably 20 to 40 m of hydroxyl group
Those containing ol% are selected.

[0015]

Embedded image l, m, n are integers

If the degree of polymerization is less than 100, the heat resistance and flexibility may be insufficient, and if it exceeds 2500, the heat resistance may be excellent but the printability may be deteriorated due to an increase in viscosity. Further, it is considered that the hydroxyl group is one of the factors for expressing the adhesive force by hydrogen bonding with the copper foil, and together with this, reacts with the phenol resin as the binder resin as shown in Chemical Formula 3 to improve the heat resistance. Flexibility can be imparted without reduction. In order to impart such characteristics, those containing 20 mol% or more of hydroxyl groups are preferable. However, if the amount of the hydroxyl groups is too large, the water resistance is lowered, so the content should be 40 m0l% or less. The glass transition temperature is related to heat resistance, and it is desirable to use a glass transition temperature of 80 ° C. or higher to withstand the solder dip test. Further, the melting temperature is preferably 180 ° C. or higher in order to maintain and improve the heat resistance of the copper paste.

[0017]

Embedded image (PVB means polyvinyl butyral)

The content of the polyvinyl butyral resin is preferably 0.5 to 20% by weight based on the solid content of the thermosetting resin.
It is. If it is less than 0.5, the effect is small or almost zero.
If it exceeds 5% by weight, depending on the degree of polymerization, printing becomes difficult, or the shrinkage factor at the time of curing becomes small, so that the initial conductivity decreases, and as a result, the conduction resistance value tends to increase.

Although various methods can be applied to the method for producing the conductive copper paste composition, it is generally obtained by mixing the constituent components and then kneading with a three-roll mill. Further, if necessary, various antioxidants, dispersants, and
It is also possible to add fine fused silica, a coupling agent, a defoaming agent, a leveling agent and the like.

[0020]

The present invention will be described below with reference to examples and comparative examples. [Example] An electrolytic copper powder having an average particle diameter of 10 μm was used as the copper powder, and a resol-type phenol resin was used as the thermosetting resin.
As the solvent, a mixed solvent of ethylene glycol monobutyl ether, propylene glycol monobutyl ether and propylene glycol monopropyl ether was used.
The polyvinyl butyral used is the one shown below.
A copper paste composition was obtained by kneading with a triple roll according to the compounding ratio of. Sumitomo Bakelite Co., Ltd. paper base phenol resin substrate PLC
0.44 provided on -2147RH (thickness 1.6mm)
The through holes of mmφ were filled by a screen printing method and cured by a box hot air dryer at 150 ° C. for 30 minutes. The conduction performance per through hole of this test piece was measured and confirmed as a resistance value. Then, the following moisture absorption solder heat resistance test, -65 ℃, 30 minutes ← → 125 ℃,
A temperature shock test (1000 cycles) was performed for 30 minutes, and the rate of change from the initial conduction resistance was obtained. And
The inside of the through hole of this test piece was observed in cross section to confirm whether the copper paste had cracks or peeling. Table 1 shows the above results.

[0021]

[Table 1] The imidazole compound is a compound of the chemical formula (1) (n = 1
6) was used.

(Polyvinyl butyral resin used) Polyvinyl butyral-1: polymerization degree 2000, hydroxyl group 3
0 mol%, glass transition temperature 110 ° C., melting temperature 23
0 ° C. Polyvinyl butyral-2: degree of polymerization 200, hydroxyl group 25
mol%, glass transition temperature 150 ° C., melting temperature 260
° C

(Measurement method) 1. Moisture absorption solder test 1: 260 after boiling for 1 hour
℃ Dip into the solder bath for 5 seconds and repeat this twice. 2. Moisture Absorption Solder Test 2: 40 ° C., 95% RH, moisture absorption treatment for 96 hours, dip into a 260 ° C. solder bath for 5 seconds,
This is repeated twice.

Comparative Example As polyvinyl butyral,
A copper paste composition was obtained in the same manner as in Example except that the ones used in Examples and the following ones were used in the mixing ratios shown in Table 2, and evaluated in the same manner as in Examples. Table 2 shows the above results.
Shown in

[0025]

[Table 2] The imidazole compound is a compound of the chemical formula (1) (n = 1
6) was used.

(Polyvinyl butyral resin used) Polyvinyl butyral-3: polymerization degree 1000, hydroxyl group 3
0 mol%, glass transition temperature 60 ° C., melting temperature 150
C. polyvinyl butyral-4: degree of polymerization 700, hydroxyl group 13
mol%, glass transition temperature 110 ° C., melting temperature 260
C. polyvinyl butyral-5: degree of polymerization 3000, hydroxyl group 3
0 mol%, glass transition temperature 130 ° C., melting temperature 29
0 ° C

[0027]

The conductive copper paste composition of the present invention is a conductive copper paste composition having excellent reliability in the through-hole portion of a printed circuit board, and more specifically, a paper-based phenol resin substrate or glass cloth. After embedding a copper paste by screen printing in the through holes provided on the printed circuit board such as the base epoxy resin board, heat and cure it to give good conductivity to the through holes, and change over time, especially moisture absorption. Even after that, a highly reliable electrical connection that does not cause the defective conductivity of the through hole portion due to the thermal shock becomes possible. In addition, the technology of the present invention is not limited to through-hole connection applications, but is also used for circuit applications because it has high adhesion to the printed circuit board substrate or copper foil.
It is used for electromagnetic wave shield applications, etc., and is also extremely effective where heat resistance and flexibility are required such as application to flexible circuit boards.

Claims (5)

[Claims] 1. A conductive copper paste composition comprising a copper powder, a thermosetting resin, a polyhydric phenol monomer, and a solvent as essential components, and a polyvinyl butyral resin. 2. The conductive copper paste composition according to claim 1, wherein the polyvinyl butyral resin has a degree of polymerization of 100 to 2500. 3. The conductive copper paste composition according to claim 1, wherein the polyvinyl butyral resin has a glass transition temperature of 80 ° C. or higher. 4. The conductive copper paste composition according to claim 1, wherein the polyvinyl butyral resin contains a hydroxyl group in an amount of 20 to 40 mol%. 5. The conductive copper paste composition according to claim 1, wherein the polyvinyl butyral resin is contained in an amount of 0.5 to 20% by weight based on the solid content of the thermosetting resin.