JPH04113608A - Multilayer ceramic capacitor, terminal electrode paste and formation of terminal electrode - Google Patents

Abstract

PURPOSE:To make solderability good, to reduce a drop in solderability when the surface of an electrode is oxidized and to relax a thermal shock to an element at a soldering operation by a method wherein the cross section of a terminal electrode part is provided with the following: a substratum layer containing an inorganic frit; and an intermediate layer as well as a surface layer which are composed of the mixed texture phase of metal phases at a specific composition. CONSTITUTION:The cross section of a terminal electrode part for a multilayer ceramic capacitor is provided with the following: a substratum layer 12 which contains inorganic frits 18 bonded to a ceramic raw body partially; an intermediate layer 13 composed of a mixed phase 17 by a metal phase composed mainly of one kind selected from (a) silver as well as (b) lead, zinc and tin, by an intermetallic compound phase or by a solid solution alloy phase and by a nickel metal phase 16; and, in addition, a surface layer 14 in which the content of said (b) component as at least one kind selected from lead, tin and zinc is more than that of said intermediate layer as an average composition. As the composition ratio of metal components contained in an electrode paste, the total weight ratio of lead, zinc and tin components is at 0.5wt.% or higher and 45wt.% or lower and the weight ratio of a nickel component is at 3wt.% or higher and 25wt.% or lower.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to the structure of a ceramic multilayer capacitor terminal electrode in which the metal part is made of a metal whose main component is silver and is baked on the internal electrode lead-out end face, and the electrode used in its manufacture. The present invention relates to a paste and a method for forming terminal electrodes of such electronic components.

In particular, the present invention relates to a structure of a terminal electrode portion that has good soldering properties and is excellent in mitigating thermal shock to an element, an inexpensive and simple method for forming terminal electrodes for electronic components, and an electrode paste.

[Prior Art] In recent years, with the progress of miniaturization and higher density of circuits, it has become common to use surface-mounted electronic components on circuit boards. It has become mainstream.

Among these, in electronic components such as fixed resistance elements and multilayer capacitor elements, the terminal electrode portion has a metal glaze type structure in which sintered metal powder is fixed to the element body with a glass frit. This part is soldered directly onto the wiring metal of the circuit board, so it has good wettability with solder.
In addition, measures are taken to prevent the so-called solder layer cracking phenomenon in which the terminal electrode portion is melted and lost by the molten solder of the solder flow.

Usually, silver electrodes that can be baked in air have been used as the metal material for the terminal electrodes of such elements, but in order to solve the above-mentioned problems, a method using a silver and palladium alloy and a method using baked copper terminals have been developed. Techniques such as applying nickel plating to the outside of the electrode and then applying tin-lead plating (solder plating) on top of that were used.

Also, when soldering the device and the wiring on the board, if the device terminal comes into contact with molten solder, a large tensile stress will be generated in a part of the device due to the difference in thermal expansion caused by the temperature difference between the terminal electrode and the device. In some cases, cracks appeared in the element. For this reason, measures have been taken to prevent rapid temperature differences by preheating the elements before soldering, if necessary.

[Problems to be Solved by the Invention] As mentioned above, forming a solder layer on the outermost layer of a terminal electrode by a plating method improves solderability and prevents oxidation of the terminal electrode surface, thereby reducing solderability. However, in addition to increasing the complexity and cost due to the increased number of steps, it is necessary to place the element in the plating solution, which may cause deterioration of the element and characteristic deterioration due to the plating solution. Furthermore, the plating method was not effective in preventing cracks from forming in the element due to the heat generated during soldering.

In view of these problems, the present invention provides an electronic component having a metal glaze type terminal electrode using copper metal, which is low in cost and has good solderability, and has little deterioration in solderability due to oxidation of the electrode surface. Soldering is sometimes used for the purpose of providing a structure of a terminal electrode part that has an excellent effect of mitigating thermal shock on an element, a method of forming an inexpensive and simple terminal electrode of an electronic component, and an electrode paste used for these. be.

[Means for Solving the Problems] The present invention has the following configuration in order to solve the above problems.

(1) A silver thread electrode metal containing (a) silver, (b) at least one selected from lead, zinc, and tin, (c) nickel, and (d) inorganic frit is attached to the inner electrode lead-out end surface. In a ceramic multilayer capacitor having terminal electrodes formed by baking, the cross section of the terminal electrode portion consists of (A) an underlayer containing an inorganic frit partially fused to the ceramic body, (B) (a) silver and ( b) a metal phase, an intermetallic compound phase, or a solid solution alloy phase containing at least one selected from lead, zinc, and tin as a main component; and (C) a nickel metal phase. and (C) a surface layer having a higher average composition of at least one component selected from lead, tin, and zinc than the intermediate layer (b). capacitor.

(2) In the electrode paste for multilayer capacitor terminal electrodes that is formed by baking on the end face of the internal electrode drawer, the electrode paste is made of (A) (a) metal powder whose main component is silver, and (b) lead, zinc, and tin. At least one metal powder selected from metal powders containing at least one selected metal powder as a main component, and metal powders consisting of intermetallic compounds and alloy powders thereof, (C) nickel metal powder, or (A') ) silver and at least one selected from lead, tin, and zinc
Alloy powder with seeds, nickel metal powder, (B) an inorganic frit or an oxide, hydroxide, metal salt, or metal organic compound component that reacts to form an inorganic frit during heating, (C) an organic binder, ( D) An electrode paste characterized by containing an organic solvent.

(3) In the composition ratio of metal components contained in the electrode paste, the total weight ratio of lead, zinc, and tin components is 0.5 wt%
45 wt% or less and the weight ratio of the nickel component is 3
The electrode paste according to item 2 above, which has a content of not less than wt% and not more than 25wt%.

(4) In the method of forming terminal electrodes for electronic components by directly baking them onto a ceramic body, the starting materials for the electrode metal include metal powder containing silver as a main component and at least one element selected from lead, zinc, and tin. A metal powder mainly composed of nickel, a metal powder mainly composed of nickel, and/or a powder consisting of an intermetallic compound powder or an alloy powder of these are used. 1. A method for forming a terminal electrode for an electronic component, which process is performed at a temperature higher than a temperature at which a liquid phase is partially formed between metals or intermetallic compounds due to eutectic phenomenon or partial melting of intermetallic powder or alloy powder.

[Function] In the capacitor according to claim 1 of the present invention, the surface layer of the terminal electrode portion is made of a metal layer containing a large amount of at least one component of the group consisting of lead, tin, and zinc. This improves the wettability of the molten solder metal and the terminal electrode portion, and prevents deterioration in soldering properties of the terminal electrode portion.

The existence of a metal phase mainly composed of nickel metal in the intermediate phase prevents the solder from being eaten away during soldering.

It also has an intermediate layer consisting of a mixed texture phase consisting of a metallic phase, an intermetallic compound phase or a solid solution alloy phase, and a nickel metallic phase, the main components of which are silver and at least one selected from lead, zinc, and tin. As a result, the thermal conductivity of the terminal electrode portion decreases, which acts to alleviate thermal shock in the vicinity of the ceramic terminal electrode interface of the element when it is immersed in solder molten metal.

In addition, as the method for forming a terminal electrode according to claim 4, baking is performed by a eutectic phenomenon caused by metal powder, intermetallic compound powder, or alloy powder during processing, or by melting one of the powders, whereby liquid is formed between the powders of the metal or intermetallic compound. By performing the treatment at a temperature higher than the temperature at which a phase is formed, the baking of the electrode may occur because components containing a large amount of at least one selected from lead, zinc, and tin, which partially become a liquid phase during the process, segregate to the surface. The initial electrode configuration can be obtained.

Further, as described in claim 2, the starting material for the electrode paste is a metal powder containing silver as a main component, a metal powder containing at least one selected from lead, zinc, and tin as a main component, and at least two of these. By using a mixture of nickel powder and a metal powder selected from metal powders consisting of intermetallic compounds and alloys, or a mixture of these alloy powders and nickel metal powder, nickel can be easily prevented from being eaten by solder in the intermediate phase. A metallic phase is generated, and a liquid phase containing a large amount of at least one selected from lead, tin, and zinc is generated during the electrode baking process, and the liquid phase component is segregated to the surface during the cooling process. It is easy to obtain a desired electrode configuration, does not require special processes such as plating, and can provide an inexpensive electrode paste.

Furthermore, by adopting the composition range according to claim 3,
It is possible to provide an electrode paste with improved soldering properties, a lower defect rate, and an improved solder erosion phenomenon.

[Example] Examples of the present invention will be described below.

Incidentally, the inorganic frit is not particularly limited, but zinc borosilicate glass frit is the most typical one. In addition, examples of oxides that react to form an inorganic frit during heating include zinc oxide, boron oxide, and silicon oxide1, and examples of hydroxides include, for example, Zn(O
Representative examples of metal salts such as H)2 include oxalates and nitrates of metal components used in inorganic frits, and representative examples of metal organic compounds include alcoholades of these metals.

In addition, examples of organic binders used in electrode pastes include acrylic resins and polyvinyl butyral resins, but are not particularly limited to these.
Various organic binders used in electrode pastes can be used. As the organic solvent, α-terpineol, carpitol acetate, butyl acetate, etc. may be used in a suitable combination, or various organic solvents used in electrode pastes may be used, without being particularly limited thereto.

Embodiments of the present invention will be described in detail below with reference to the drawings.

A ceramic multilayer capacitor element using a barium titanate dielectric and palladium internal electrodes was investigated. The device has a dielectric layer 1 with a thickness of 20 μm and a thickness of 2.1 μm.
It has a structure in which the palladium internal electrode layer 5 is laminated with a palladium internal electrode layer 5 of 60 μm in thickness, and an invalid layer of 60 μm is laminated above and below. 2mmX
1. 6mmX 0. A 7 mm element was used.

Starting materials for terminal electrodes include metallic silver, metallic lead, metallic tin, and metallic zinc powder with a particle size of about 1.5 μm and a particle size of 12 μm.
A powder containing zinc borosilicate glass frit with an average particle size of 1.8 μm and 4 wt% of the metal weight was used, and this was mixed with nickel metal powder of
000 acrylic resin at 5 wt% based on the powder weight, α-terpineol, carpitol acetate mixed solvent (64
) was added in an amount of 30 wt % based on the powder weight, mixed in a mortar and kneaded using three rolls, and the amount of solvent was adjusted to prepare an electrode paste with a viscosity of 8000 centipoise at 20°C.

Electrode paste is applied to both ends of the element using the dip method.
After drying in air at 80°C, the temperature was raised to 28,000°C over 5 hours in an electric furnace, then to 650-800°C over 30 minutes, held for 5 minutes, and then lowered to room temperature over 30 minutes.

FIG. 1 shows a schematic diagram of the cross-section of the terminal electrode portion of the produced capacitor, in which the distribution of electrode metal was evaluated using an X-ray microanalyzer and an X-ray microdiffractometer. The portion of the electrode portion closest to the element is comprised of a base layer 12 including an inorganic frit 18 partially fused to a dielectric layer 11 and electrically connected to a palladium internal electrode layer 15 . Next, the silver metal phase,
There is an intermediate layer 13 in which a nickel metal phase 16 of about 12 μm is partially dispersed together with a surface oxide layer in a mixed structure phase 17 of a lead metal phase, a tin metal phase, a zinc metal phase, their intermetallic compound phase, and an alloy phase. do. The total content of lead, tin, and zinc is 1
, 5 wt% or less, the intermediate layer 13 is confirmed as a phase in which a nickel metal phase is partially dispersed together with a surface oxidation phase in a metal phase in which lead, tin, or zinc is slightly dissolved in silver. The thickness of the intermediate layer 13 was approximately 700 μm in all cases.

Next, there is a surface layer 14 in which the content of lead, tin, and zinc components is higher than the average composition of the intermediate layer. The thickness of the surface layer is 0.5-
It was about 60 μm. Almost no surface layer is observed in samples that do not contain at least one of lead, tin, and zinc.

The capacitor with terminal electrodes formed is temporarily fixed to a glass epoxy substrate with copper wiring using an organic adhesive, and then heated at 230°.
Reflow soldering was performed using C, and the number of soldering defects among 50 samples was determined. The soldering is defective. After flow soldering, the soldered area is visually inspected, and if there is clearly a part where no solder adheres to the terminal electrode surface, it is judged as defective A1.
Those in which the terminal electrodes were missing were classified as defective B.

Table 1 shows the metal powder mixed composition ratio and the number of defects in the terminal electrode.

In addition, for comparison with the conventional method, samples No. 1 were subjected to nickel electrolytic plating on the surface of the terminal electrode by barrel plating method, and then barrel-plated in a solder plating solution (pH: 1.0) containing alkanolsulfonic acid as the main component. A solder plating layer was formed by a plating method. Created capacitor and No. 7.17
．． No. 25 capacitors were placed in a soldering bath at 350°C without any preheating treatment, and then polished to the center line including both terminal electrodes. The number of crack defects was calculated. Table 2 shows the number of crack defects (per 50 pieces).

Table (Continued) Table (Continued) Table (Continued) Table (Continued) Table (Continued) Note: * indicates comparative example outside the scope of the present invention ** indicates comparative example within the scope of the present invention Examples in Table 1 Note: Comparative Examples outside the scope of Claim 3 Note: The * mark indicates an example having the structure described in Claim 1, as is clear from Table 1 of Comparative Examples outside the scope of the present invention, or as described in Claim 2. Using the electrode paste,
The electrode forming method described in claim 4 is more effective in improving soldering properties and the solder erosion phenomenon than in the case of a single silver electrode. Further, the content of lead, tin, and zinc in the electrode paste is more preferably in the range described in claim 3. When a paste in this range is used, the soldering properties are improved and the melting of the electrode metal is improved. If the amount of nickel is thick (the adhesiveness between the terminal electrode part and the element body will deteriorate, and the soldering part will sometimes peel off, the rate of increase in the number of defects will be extremely reduced.) The content of nickel is also in claim 3. The described range is more preferable, and soldering can achieve a better effect of improving the solder erosion phenomenon without significantly reducing the effect of improving the properties.

Further, as is clear from Table 2, the composition described in claim 1 is particularly composed of at least one, more preferably at least two of metal silver, metal lead, metal tin, and metal zinc, and metal nickel and an intermetallic compound phase thereof. , sample No. 7.17.25, which has an intermediate layer in which the alloy phase forms a mixed texture phase, is less likely to crack due to thermal shock.
In cases where the intermediate phase is a single copper metal phase, such as No. 1, cracks are likely to occur. This means that in the configuration of the terminal electrode section according to claim 1, the difference from the conventional example is that the amount of metal silver, metal lead, metal tin, and metal zinc is small (both 1 and 1).
species, metallic nickel, and their intermetallic phases,
This shows that the intermediate phase consisting of a mixed structure phase formed by an alloy phase is effective in improving the thermal shock resistance of the device.

[Effects of the Invention] According to the present invention, an electronic component having a terminal electrode using a silver electrode metal is low in cost and has good soldering properties, and there is little deterioration in soldering properties due to oxidation of the terminal electrode surface.
Soldering can sometimes provide a configuration of a terminal electrode portion that has an excellent effect of alleviating thermal shock to the device, an inexpensive and simple method for forming the terminal electrode, and an electrode paste used therefor.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a terminal electrode portion of a ceramic multilayer capacitor element according to an embodiment of the present invention.
- Intermediate layer, 14... Surface layer, 15... Palladium internal electrode layer, 16... Nickel metal phase, 17... Mixed texture phase, 18... Inorganic frit.

Claims (4)

[Claims] (1) A silver-based electrode metal containing (a) silver, (b) at least one selected from lead, zinc, and tin, (c) nickel, and (d) inorganic frit is drawn out as an internal electrode. In a ceramic multilayer capacitor having terminal electrodes formed by baking on the end face, the cross section of the terminal electrode portion consists of (A) an underlayer containing an inorganic frit partially fused to the ceramic body, (B) (a) silver and (b) a metal phase, an intermetallic compound phase, or a solid solution alloy phase whose main component is at least one selected from lead, zinc, and tin; and (c) a nickel metal phase. It has an intermediate layer, and (C) a surface layer having a higher average composition of the component (b), which is at least one selected from lead, tin, and zinc, than the intermediate layer. Ceramic multilayer capacitor. (2) In the electrode paste for multilayer capacitor terminal electrodes that is formed by baking on the end face of the internal electrode drawer, the electrode paste is made of (A) (a) metal powder whose main component is silver, and (b) lead, zinc, and tin. At least one metal powder selected from metal powders containing at least one selected metal powder as a main component, and metal powders consisting of intermetallic compounds and alloy powders thereof, and (c) nickel metal powder, or (A') silver and at least one selected from lead, tin, and zinc
Alloy powder with seeds, nickel metal powder, (B) an inorganic frit or an oxide, hydroxide, metal salt, or metal organic compound component that reacts to form an inorganic frit during heating, (C) an organic binder, ( D) An electrode paste characterized by containing an organic solvent. (3) In the composition ratio of metal components contained in the electrode paste, the total weight ratio of lead, zinc, and tin components is 0.5 wt%
The weight ratio of nickel component is 3wt% or more and 45wt% or less
The electrode paste according to claim 2, wherein the content is 25 wt% or less. (4) In the method of forming terminal electrodes for electronic components by directly baking them onto a ceramic body, the starting materials for the electrode metal include metal powder containing silver as a main component and at least one element selected from lead, zinc, and tin. A metal powder mainly composed of nickel, a metal powder mainly composed of nickel, and/or a powder consisting of an intermetallic compound powder or an alloy powder of these are used, and during the baking process, these metal powders and intermetallic 1. A method for forming a terminal electrode for an electronic component, which process is carried out at a temperature higher than that at which a liquid phase is partially formed between metals or intermetallic compounds due to eutectic phenomenon or partial melting of compound powder or alloy powder.