JPH04293214A - Conductive paste for chip type electronic component - Google Patents

Abstract

PURPOSE:To relieve thermal shock to a bare chip when an electrode surface is electroplated, reduce the generation of cracks in the bare chip, and prevent the deterioration of electric characteristics and bonding characteristics to a substrate, by decreasing stress and hardness which make a baked electrode layer contract which layer is the substratum electrode of a chip type electronic parts such as a chip capacitor, a chip resistor and a chip thermistor. CONSTITUTION:This invention relates to the additive to conductive paste for forming a terminal electrode 12 by baking after the surface of a bare chip 11 constituted of ceramic dielectric is coated with said paste. In addition to metal powder, glass frit, and inert organic vehicles, one or more kinds of filler for sintering control selected out of Al2O3, MgO, Cab, BaO and ZnO is contained as additive. Said filter of 0.3-5wt.% is added to metal powder.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for forming terminal electrodes of chip-type electronic components such as chip capacitors, chip resistors, and chip thermistors. More specifically, it relates to additives for conductive pastes.

0002

2. Description of the Related Art Terminal electrodes are formed on the surface of a bare chip made of a ceramic dielectric that constitutes this type of chip-type electronic component. This terminal electrode is made by applying a conductive paste made by kneading metal powder, glass frit, and an inert organic vehicle to the surface of the bare chip and drying it for 60 minutes.
It is formed by firing at a temperature of about 0 to 800°C. This chip-type electronic component is used with terminal electrodes soldered to a substrate.

Conventionally, metal powder for conductive paste contains A
Precious metals such as g, Au, Pd, and Pt, base metals such as Cu and Ni, or powders of mixtures thereof are used. Terminal electrodes formed from conductive paste containing Ag powder suffer from so-called solder erosion, in which Ag dissolves into the solder during soldering, so Ag/Pd mixed powder, which is a combination of Ag powder and Pd powder, is often used. However, if a large amount of Pd is contained, the solderability is poor and the bare chip is likely to crack during baking, so the Pd content of the Ag-Pd terminal electrode is kept relatively low at 1 to 15%. Therefore, conventional Ag-Pd
The soldering heat resistance of terminal electrodes is not very high, and the temperature range in which chip-type electronic components can be soldered is narrow. Furthermore, since the film thickness of the terminal electrode is thin, if solder is eaten away, reliability will be degraded. To solve this problem, a two-layer plating electrode layer of Ni plating, Sn or Sn/Pb plating has conventionally been formed on the surface of the baked electrode layer. The main purpose of Ni plating is to improve solder heat resistance and prevent electrode erosion by solder, and the purpose of Sn or Sn/Pb plating is to prevent oxidation and improve solder wettability.

0004

[Problems to be Solved by the Invention] However, conventional chip-type electronic components, such as chip capacitors, in which a Ni plating layer and a Sn or Sn/Pb plating layer are formed on the surface of a baked electrode layer, do not require preheating of the bare chip. If the solder layer is immersed in a solder layer at a temperature of ℃ or higher and pulled up, the tensile stress of the Ni plating layer is high when the temperature falls, and the baked electrode layer is too hard to absorb this stress, resulting in cracks in the bare chip inside the terminal electrode. is likely to occur. When cracks occur, moisture resistance decreases and moisture infiltrates through the cracks, degrading the insulation resistance of the capacitor. In addition, this chip capacitor is mounted on the surface of the board by soldering, for example, -25
If a temperature cycle test was performed in which the temperature was raised from ℃ to +85℃ via room temperature and then lowered, the above cracks would grow due to high thermal stress and the terminal electrode part would break, or the capacitor would break. Insulation resistance begins to deteriorate.

An object of the present invention is to alleviate the thermal shock to the bare chip when electrolytic plating is performed on the surface of the electrode layer by alleviating the stress and hardness of the baked electrode layer, which is the base electrode, to shrink. An object of the present invention is to provide a conductive paste for chip-type electronic components that reduces the incidence of cracks in bare chips and does not deteriorate electrical properties and adhesive properties to substrates.

[0006]

[Means for Solving the Problems] The present inventors have focused on promoting the smooth sintering of metal powder with conventional conductive pastes, and as a result, a dense and hard baked electrode layer is formed. The present invention was developed based on the discovery that thermal stress is not sufficiently relaxed when a thermal shock is applied. The present invention is a conductive paste for chip-type electronic components, which contains metal powder, glass frit, an inert organic vehicle, and additives, and which is applied to the surface of a bare chip made of a ceramic dielectric and then baked to form a terminal electrode. Its characteristic structure is that the additives are Al2O3, MgO, CaO, BaO, Zn.
The present invention includes one or more fillers for sintering control such as O, and this filler is added in an amount of 0.3 to 5% by weight based on the metal powder.

The present invention will be explained in detail below. The metal powder of the present invention includes noble metals such as Ag, Au, Pd, and Pt, Cu, N, etc.
Base metals such as i, or powders of mixtures thereof are used. The metal powder is sintered to provide electrical conductivity to the terminal electrode. Glass frits include zinc borosilicate, borosilicate glass containing alkali metals and alkaline earth metals, lead borosilicate, bismuth borosilicate, etc., zinc borate glass, cadmium borate glass, etc. used. Glass frit is used to promote sintering of the metal powder and bond the interface with the bare chip. Further, as the inert organic vehicle, a solution of methyl cellulose, ethyl cellulose, etc. in an organic solvent such as butyl carbitol, terpineol, etc. is used. The celluloses are mixed in the organic solvent in a proportion of 5 to 30% by weight. The organic vehicle is used to adjust the viscosity of the paste and facilitate its application to the bare chip surface.

[0008] Additives for the conductive paste include Al2O3,
Any one or two of MgO, CaO, BaO, ZnO
Contains more than one filler for sintering control. This additive is used to retard the sintering of metal powders. The conductive paste has a content of 65 to 80% when the paste is 100% by weight.
% by weight of metal powder, 1-30% by weight of glass frit relative to this metal powder, and 0.3% by weight relative to this metal powder.
It is comprised of ~5% by weight filler for sintering control, and the remainder is an organic vehicle. If the metal powder content is less than 65% by weight, the conductivity of the electrode will be poor, and if it exceeds 80% by weight, the adhesion to the bare chip will deteriorate. Glass frit is 1% by weight
If it is less than this, the sintered metal becomes porous and the electrolytic solution during electrolytic plating tends to penetrate into the pores. As a result, there are problems with long-term reliability, the adhesive strength between the terminal electrode and the bare chip decreases, and the moisture resistance of the terminal electrode deteriorates. In the case of a capacitor, the dielectric loss tangent (tan δ) deteriorates. If the glass frit exceeds 30% by weight, the glass frit will stand out on the surface of the electrode layer during baking, inhibiting the formation of a plating film, and resulting in insufficient soldering heat resistance. When the amount of the sintering control filler is less than 0.3% by weight, it has no effect of delaying the sintering of the metal powder, and is no different from the case where no filler is added. On the other hand, if it exceeds 5% by weight, sintering will be suppressed too much, and the sintered metal will become porous, causing the same problem as when the amount of glass frit is small.

The conductive paste of the present invention is used for terminal electrodes of chip-type electronic components such as chip capacitors, chip resistors, and chip thermistors. In particular, it is suitably used for chip-type multilayer ceramic capacitors. In this case, the ceramic dielectric constituting the capacitor is preferably a dielectric material containing lead-based perovskite or barium titanate as a main component. Dielectric materials whose main component is lead-based perovskite include Pb(Mg1/3Nb2/3)O3, Pb(
Examples include Fe1/2Nb1/2)O3, PbTiO3, and the like.

0010

[Operation] Al2O3,M in the above proportion in the conductive paste
When one or more of gO, CaO, BaO, and ZnO are added as fillers for sintering control, these metal oxides hardly react with the metal powder during baking, but rather promote the sintering of the metal powder. delay. As a result, the stress and hardness of the baked electrode layer that tends to shrink is alleviated, and the thermal shock to the bare chip when electrolytic plating is performed on the surface of this electrode layer is alleviated. Furthermore, this filler for sintering control has plating resistance, and the plating solution does not enter into the electrode during plating.

[0011]

As described above, according to the present invention, by adding a small amount of a sintering control filler made of a metal oxide such as Al2O3 to the conductive paste, the shrinkage of the baked electrode layer, which is the base electrode, can be reduced. The stress and hardness of the chip are reduced, the thermal shock is alleviated, the incidence of bare chip cracking is reduced, the electrical properties are not degraded, and the adhesion properties to the substrate are not degraded. As a result, a highly reliable chip-type electronic component can be obtained.

0012

EXAMPLES Next, examples of the present invention will be explained based on the drawings together with comparative examples. <Embodiment> As shown in FIG. 1, the chip-type electronic component in this example is a chip-type multilayer ceramic capacitor 10. This capacitor 10 has a bare chip 11 and this chip 11
and base electrodes 12 formed at both ends of the base electrode. The chip 11 is made of lead perovskite and is made of noble metal Ag70.
It has an internal electrode 13 made of /Pd30 and has a length of 3.2 m.
It has a size of 1.6 mm in width and 0.85 mm in thickness. The surface of the base electrode 12 is coated with a Ni plating layer 14 and Sn/
Pb plating layer 15 is formed in this order.

A base electrode was formed under the following conditions. When the conductive paste is 100% by weight, 75% by weight of metal powder, 10% by weight of glass frit based on this metal component, and 0.3 to 5% by weight based on the metal powder as shown in Table 1. A conductive paste was prepared by kneading nine types of sintering control fillers blended within the range and the remainder being an inert organic vehicle. Here, the metal powder is Ag100
% by weight, and the glass frit contains CdO (15% by weight).
)-PbO (25% by weight)-B2O3 (20% by weight)-
Consists of SiO2 (40% by weight). The organic vehicle used was a mixture of ethyl cellulose, butyl carbitol, and terpineol. Filler for sintering control is Al
Any one of 2O3, MgO, CaO, BaO, ZnO
A mixture of seeds, Al2O3 and MgO was used. This paste was applied by dipping to both ends of the bare chip so that the thickness after baking was 90 μm, and the paste was applied under atmospheric pressure.
It was dried at 150°C for 10 minutes. The chip was heated to 680°C under atmospheric pressure at a rate of 25°C/min, held there for 5 minutes, and then cooled to room temperature at a rate of 20 minutes/min to remove Ag.
A base electrode was obtained.

A Ni plating layer and a Sn/Pb plating layer were formed under the following conditions. Nickel sulfamate (Ni(NH2SO3)2.4H2 at pH 4.0 and temperature 50°C)
O) A 2 μm thick Ni plating layer was formed on the surface of the base electrode by electrolytic barrel plating using a bath with a composition of 120 g/L. Tin (Sn) and lead (Pb) at pH 4.5 and temperature 25°C
Ni was deposited by electrolytic barrel plating using a bath with a composition of 9:1.
A 6 μm thick Sn/Pb plating layer was formed on the surface of the plating layer. As a result, a multilayer ceramic capacitor was obtained in which two further plating layers were formed on the base electrode.

<Comparative Example> As shown in Table 1, a conductive paste containing no filler for sintering control, or an Al2
A conductive paste containing a filler for sintering control consisting of any one of O3, MgO, and ZnO in an amount outside the range of 0.3 to 5% by weight was applied to both ends of the same bare chip as in the example. A multilayer ceramic capacitor was obtained in the same manner as in the example except that the capacitor was baked.

<Measurement method> The following characteristics (a) to (d) were measured for the multilayer ceramic capacitors with plating layers manufactured in the above Examples and Comparative Examples, and in the above implementation except that two plating layers were not provided. The following characteristics (a) to (c) were measured for the same multilayer ceramic capacitors as those in the examples and comparative examples. The number n in parentheses is the number of samples tested. (a) Dielectric loss tangent (%) (n=30) Measured at 1 kHz and 1 Vrms. (b) Cracks on the inside of the base electrode after thermal shock (n = 100) A sample held with metal tweezers was immersed in eutectic solder (Sn63/Pb37) at 350°C for 1 second without preheating, and then pulled out. The base electrode was removed by boiling and dissolving it in hot concentrated nitric acid, and it was examined whether there were any cracks in the bare chip inside the base electrode. (c) Tensile strength (n=10) A 0.8 mm soldered steel wire was soldered to the base electrode of a multilayer ceramic capacitor on a hot plate at 230°C with eutectic cream solder (SPT-55-2062-M manufactured by Senju Metal Co., Ltd.).
10), and the tensile strength was measured by pulling the steel wire. (d) Reliability (humidity load test) (n=20) +85°C
The presence or absence of deterioration was examined for 1000 hours by applying a DC voltage of 50 V at a temperature of 85% and a relative humidity of 85%.

<Measurement Results and Evaluation> Table 1 shows the results of (a) to (d) above. From Table 1, the multilayer ceramic capacitors of the four comparative examples have a high crack occurrence rate on the inside of the base electrode, and among the four comparative examples, the ones containing more than 5% by weight of filler for sintering control (Comparative Example 3, In Comparative Example 4), the values of dielectric loss tangent and adhesive strength varied greatly depending on the presence or absence of a plating layer, and furthermore, those in which the amount of sintering control filler added was outside the predetermined range deteriorated within 350 hours. On the other hand, in the multilayer ceramic capacitors of the nine types of Examples, variations in the values of dielectric loss tangent and adhesive strength were extremely small regardless of the presence or absence of a plating layer. Furthermore, the rate of occurrence of cracks on the inside of the base electrode was extremely low, and no deterioration was observed even after 1000 hours had passed when the amount of sintering control filler added was within a predetermined range.

[0017]

[Table 1]

[Brief explanation of drawings]

FIG. 1 is a sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention.

[Explanation of symbols]

10 Multilayer ceramic capacitor 11 Bare chip 12 Base electrode 13 Internal electrode 14,15 Plating layer

Claims (3)

[Claims] 1. A conductive paste for chip-type electronic components, which contains metal powder, glass frit, an inert organic vehicle, and additives, and which is applied to the surface of a bare chip made of a ceramic dielectric and then baked to form a terminal electrode. The additives include Al2O3, MgO, CaO, BaO, ZnO.
A conductive paste for chip-type electronic components, characterized in that it contains one or more fillers for sintering control, and the filler is added in an amount of 0.3 to 5% by weight based on the metal powder. 2. The conductive paste for a chip-type electronic component according to claim 1, wherein the chip-type electronic component is a ceramic capacitor. 3. The conductive paste for a chip-type electronic component according to claim 2, wherein the ceramic dielectric material contains lead-based perovskite or barium titanate as a main component.