JPH01313803A - Conductive paste - Google Patents

Abstract

PURPOSE:To permit acquisition of plating having its uniform thickness on the surface of a conductor prepared through a process of baking the paste in the title so as to improve the solderability of the plated conductor by having each inorganic particle prepared through a process of forming a plating film on the surface of the particle, contained in the conductive paste. CONSTITUTION:Conductive particles for a conductive paste prepared by dispersing the metallic particles 11 and inorganic particles 13 in a vehicle are formed out of metallic particles 11 and also particles prepared by forming metallic films 14 on respective surfaces of the inorganic particles 13. Accordingly, a plating film 12 may be formed on the surface of each inorganic particle 13 at the same precipitation speed as that of the metallic particle 11. This makes it possible to form the uniform plating film 12 on a conductor film 10 prepared by baking the conductive paste so that the conductive film can be acquired with its satisfactory adhesive property by means of solder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a conductive paste suitable for applying a conductive paste onto a ceramic substrate and depositing a plating film on the main surface of a fired conductor. Regarding.

[Prior Art] Conventionally, the #electroconductive paste used to form a conductor film on a ceramic substrate is AusAgs Pt%.
Precious metal particles such as Pdt Cu, N11Z 1%
It is known that conductive particles such as base metal powder such as A1 and glass frit are dispersed in a vehicle. Such conductive paste is applied to electronic parts such as ceramic substrates, ceramic capacitors, piezoelectric elements, resistors, and inductors by screen printing or other methods, and then fired to form a conductive film. be done. This conductor film is used as an electrode or a wiring conductor of the electronic component.

Among the conductive particles used in the conductive paste, Au
Since conductive materials such as sAgsPt are expensive and have large price fluctuations, base metals or relatively inexpensive particles such as Cu are used as alternative conductive materials.

In conductive electrodes formed using base metal conductive particles, the conductive metal in the electrodes has poor solder wettability, and the electrodes have poor soldering properties. In addition, conductive paste using relatively inexpensive copper particles has good solder wettability of the conductor metal itself, but the surface of the electrode depends on oxygen in the air and is easily oxidized. If the conductor is left inside for even a short time, the conductor surface will oxidize and the soldering properties will quickly deteriorate.

For this reason, when using conductive particles such as these base metals or copper, the surface of the conductor particles is coated with a gold B film to prevent oxidation, such as nickel plating or solder plating, etc.
Efforts are being made to prevent surface oxidation and improve solderability.

Furthermore, the purpose of controlling the shrinkage rate of the conductive paste when the conductive paste is applied to the substrate and fired, the purpose of increasing the adhesive strength with the ceramic substrate, and the expansion coefficient of the conductor after being fired is controlled by the ceramic. For the purpose of approximating the expansion coefficient of the substrate, particles of the same material as the ceramic base material, particles of a material forming a part of the ceramic base material, or inorganic M particles of a different type from these are added to the conductive paste. Mixing is done.

[Problems to be Solved by the Invention] When the inorganic particles are contained in the conventional conductive paste, the surface of the conductive film formed by firing the paste contains the conductive particles and the inorganic particles. The inorganic particles are randomly exposed.

However, as schematically shown in FIG. 2, when attempting to form a plating film on the surface of such a conductor 8100, the formation rate of the plating film I2 formed on the surface of the conductive particles 11 and the surface of the inorganic particles 13 are There is a large difference between the formation speed of the plating film 12 formed on the surface of the conductive particles 11, and even if a desired thickness of plating 12 is formed on the surface of the conductive particles 11, a sufficient thickness is not formed on the surface of the inorganic particles 13. The thickness of the plating M12 becomes non-uniform, such that the plating [12] is not formed.

In this way, electronic components with non-uniform plating film have, so to speak, countless holes in the plating film.
There was a problem in that the adhesion strength to solder was weak, and electronic components would fall off after soldering.

Therefore, an object of the present invention is to provide a conductive paste that can solve the above-mentioned conventional problem by incorporating particles in which a plating film is formed on the surface of inorganic particles into the conductive paste. It's true.

C Means for resolving communication] That is, 1. In order to solve the above problems, the gist of the means purchased in the present invention is as follows: First, in a conductive paste in which conductive particles and inorganic particles are dispersed in a vehicle, the conductive particles are metal particles. This is a conductive paste characterized by comprising: (1) and (n) particles having a metal coating formed on the surface of the organic particles. Furthermore, a second aspect of the present invention is a conductive paste in which conductive particles are dispersed in a vehicle, wherein the conductive particles are composed of metal particles and conductive particles having a metal coating formed on the surface of inorganic particles. It is a conductive paste.

[Function] In the conductive paste according to the present invention, inorganic particles are mixed in the vehicle as conductive particles in addition to metal particles. It reduces the shrinkage rate of the conductive paste (and reduces the stress between the ceramic substrate and the conductive paste, increasing the strength of the conductive paste. Also, due to the reaction between the inorganic particles in the conductive paste and the ceramic substrate, etc.) Since the adhesive strength is increased and the expansion coefficient of the conductor after firing is close to that of the substrate, it can withstand thermal shock after firing.

In addition to this effect of sustaining the inorganic particles, as schematically shown in FIG. The plating film 12 is formed at the same deposition rate. This makes it possible to form a uniform plating film 12 on the conductor WA10 formed by baking the conductive paste. Therefore, a conductive film with good solder adhesion can be obtained.

[Example] Next, specific examples of the present invention will be described in detail.

(Example 1) A sensitizer bath, which is an aqueous solution containing stannic chloride (SnCIa) and hydrochloric acid (MCI), and palladium chloride (P
Alumina (Al2O2) particles having an average particle diameter of 1.0 μm were sequentially immersed in an activator bath that was an aqueous solution of dC1*), and then the particles were filtered. Then, add the particles to 1000ml of pure water.
It consists of 20 g of nickel sulfate (N t S 04), 30 g of sodium citrate (NascsHsot), and 20 g of sodium hypophosphite (N a H4F O2), immersed in a nickel-plated glass preheated to a temperature of 80°C, and slowly stirred for 10 minutes. did. Thereafter, the nickel plating bath and alumina particles were separated by filtration, the alumina particles were dispersed in pure water, and the process of filtration was repeated several times.

Thereafter, it was washed and dried at a temperature of 120° C. for 1 hour. In this way, a 0.3 μm nickel film was formed on the surface of the alumina particles.

Next, separately prepared nickel metal particles (average particle size 3 μm
) For 100 parts by weight, 10 parts by weight of the alumina particles coated with nickel and 18 parts by weight of ethyl cellulose.
A conductive paste according to the present invention was prepared by blending 1 part of mff and 4 parts of butylcarpitol in a crusher for 4 hours, and further kneading in a roll mill for 1 hour.

Separately, a commercially available conductive paste is applied to barium titanate-based dielectric ceramic raw material sheets, the layers are laminated and crimped, cut to a predetermined size, and then fired. We manufactured a ceramic capacitor chip.

The ends of internal electrodes made of the conductive paste are drawn out from both end faces of this multilayer ceramic capacitor chip, and the conductive paste of the present invention is applied thereto to a thickness of about 50 μm, and then dried. 95 in a non-oxidizing atmosphere.
Baking was performed at a temperature of 0° C. for 1 hour to form external electrodes of the IO ceramic capacitor chip.

Such a multilayer ceramic capacitor chip was immersed in the nickel plating bath at a temperature of 80° C. for 15 minutes to form a nickel plating layer on the surface of the external electrode.

Further, using a commercially available solder plating solution, electrolytic solder plating was performed on the nickel film of the multilayer ceramic capacitor chip at room temperature for 30 minutes at a cathode current density of IA/da'' to form a solder plating film with a thickness of 3 μm. did.

Five hundred pieces of this multilayer ceramic capacitor chip were soldered to conductors on a printed wiring board.

Then, while reading the tensile load with a push-pull gauge, apply a maximum tensile load of 5 kg in the direction shown by the arrow in Figure 3. During this time, check whether the multilayer ceramic capacitor chip peels from the wiring board or not, and check the solder adhesion strength. A test was conducted.

In Figure 1, ■ is a wiring board, 2 is a land for soldering formed on it, 3 is a multilayer ceramic capacitor, 4 is
5 is the external electrode, 5 is the solder that is soldered to the land 2, and 6 is the tip of the hook of the push-pull gauge.

As a result, in this example, there was no case where the solder peeled off under a load of 5 kg or less.

(Example 2) In Example 1, the metal plating applied to the alumina particles was replaced with nickel plating, and 1000 ml of pure water, 15 g of copper sulfate (CCu5Oa), 15 g of tetrasodium salt of ethyldiaminetetraacetic acid, and 45 g of formalin (37% concentration) were used. 10ml sodium hydroxide (Na
The process is the same except that copper plating was performed using a copper plating bath consisting of OH) lOg at a plating bath temperature of 60°C, and that copper plating was performed on the external electrodes formed on both end surfaces of the multilayer ceramic capacitor chip. The test was conducted in the same manner as in Example 1. As a result, there were no cases where the solder peeled off under a load of 5 kg or less.

(Example 3) In Example 1, the inorganic particles were replaced with alumina particles by dielectric ceramic barium titanate particles, and the plating applied to the same particles was replaced with nickel plating, and the following Same as Example I, except that the inorganic particles were immersed in a silver plating bath containing equal amounts of liquid A and B for 10 minutes at room temperature to be silver plated. The test was then carried out.

Liquid A composition pure water 60ml Silver nitrate (AgNO3) 3.5g 7mmoni7 water (NH328%) Added until precipitated and redissolved Sodium hydroxide 2.5g B liquid composition Pure water 1000ml Glucose (Ce H+□Os) 45 Tartaric acid (Cs
He Os) 4 g Ethyl alcohol (CaH
sOH) 100rnl As a result, there were no cases where the solder peeled off under a load of 5 kg or less.

(Example 4) A test was carried out in the same manner as in Example 1 except that zinc particles were used instead of nickel particles as the money particles. As a result, there was no solder that reached ψJ under a load of 5 kg or less.

(Example 5) Same as Example 2 except that the inorganic particles in Example 1 were replaced with alumina particles by dielectric ceramic barium titanate particles, and the plating applied thereto was replaced with nickel plating. Example 1 except that copper particles were used instead of nickel as the small, residual disease particles plated with copper in the method, and the nickel plating on the external electrode was changed to copper plating.
The test was conducted in the same manner. As a result, there were no cases where the solder peeled off under a load of 5 kg or less.

(Example 6) In Example 1, the amount of nickel-plated alumina particles in the conductive paste was changed from 10 parts to 15 parts, and the amount of alumina particles not nickel-plated as inorganic particles was changed to 15 parts. Example 1 above except that parts by weight were added.
The test was conducted in the same manner. As a result, there were no cases where the solder peeled off under a load of 5 kg or less.

(Example 7) In Example 1, the number of alumina particles coated with nickel in the conductive paste was changed from 10 parts to 5 parts, and the number of alumina particles coated with nickel as inorganic particles was changed to 10 parts. The test was conducted in the same manner as in Example 1 except that parts by weight were added.

As a result, there were no cases where the solder peeled off under a load of 5 kg or less.

(Example 8) In Example 3, the copper in the conductive paste was w1f! l
Same as Example 3, except that the amount of barium titanate-based inorganic particles was changed from 10 parts to 15 parts, and 5 weight of barium titanate-based particles not coated with copper were added as inorganic particles. The test was carried out. As a result, 5Kg
There were no cases where the solder peeled off under the following loads.

(Comparative example) In Example 1, except that alumina particles not plated were added to the conductive paste instead of particles whose surfaces were plated with nickel. The test was conducted in the same manner as in Example 1.

As a result, if the solder peeled off under a load of 5 kg or less,
There were 1z out of 500.

Incidentally, in each of the above Examples, examples were shown in which alumina and barium titanate were used as the inorganic particles, but the inorganic particles used in the present invention are not limited to these. In other words, these plates containing Ti-free particles should be selected depending on the ceramic composition of the substrate. - For boat fishing, a composition close to the ceramic composition is preferable, and the amount added depends on each composition. The law will be passed accordingly. For example, the thermal expansion coefficient, curing shrinkage rate, thickness, and soldering are determined in consideration of properties and the like. Generally, a total of 1f of conductive paste
About 1% to 35% m is added to fi.

The total refraction particles mixed in the conductive paste are Zns
Cus NL A1 etc. are common, and Nis Cus Ag etc. are common for plating applied to inorganic particles.

[Effects of the Invention] As explained above, according to the present invention, inorganic particles are contained in the conductive paste, so when the conductive paste is applied and fired, the contact between the conductive paste and the substrate is reduced. The original effect of inorganic particles, which is the ability to adjust firing shrinkage, can be obtained as is. At the same time, since a gold coating was formed on the surface of the inorganic particles, the surface of the conductor obtained by firing the conductive paste could be plated with a uniform thickness, making soldering easy. It has improved adhesion to the board, and there is no chance of it falling off after soldering.

Therefore, the effect of improving the reliability of soldering can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a state in which plating is applied to a conductive film formed using the conductive paste of the present invention, and FIG. 2 is a schematic diagram showing a conductive film formed using a conventional conductive paste. FIG. 3 is an explanatory perspective view showing the method of testing the adhesion strength of the soldered parts in the examples of the present invention and the comparative examples thereof. IO... Conductor film 11... Conductive particles 12... Plated film 13... Inorganic particles 14... Plated film applied to inorganic particles

Claims (2)

[Claims] (1) In a conductive paste in which conductive particles and inorganic particles are dispersed in a vehicle, the conductive particles are composed of metal particles and inorganic particles with a metal coating formed on their surfaces. Characteristic conductive paste. (2) A conductive paste in which conductive particles are dispersed in a vehicle, wherein the conductive particles are composed of metal particles and inorganic particles with a metal coating formed on their surfaces. sex paste.