JPH05167224A - Formation of electrode forming transfer sheet and external electrode of electronic part - Google Patents

Abstract

PURPOSE:To provide an outer electrode forming method whereby an external electrode is formed on the edge face at low cost in an excellent workability without substantially generating the problems such as lowering of reliability and the like caused by the intrusion of the conventional plating solution. CONSTITUTION:Using an electrode forming transfer sheet 1, the edge face 2a of an electronic part 2 is brought into contact with the metal composite layer 11 of the above-mentioned sheet 11 through the intermediary of conductive paste 12P. After the paste 12P has been dried up and hardened, the electronic part 2 is peeled from the sheet 1. As a result, an external electrode 3, consisting of a paste hardened layer 12 and a metal composite layer 11, is formed by transfer on the edge face 2a of the electronic part 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer sheet for forming electrodes and a method for forming external electrodes of electronic parts using the transfer sheet.

[0002]

2. Description of the Related Art In recent years, mobile communication and camera-integrated VTRs
There is a strong tendency for electronic devices to become lighter, thinner, shorter, and smaller, and along with this, electronic components are being made smaller and lighter, and in particular, a wide range of electronic components such as multilayer ceramic capacitors and semi-fixed volumes are being used. Research is ongoing.

By the way, in such electronic parts,
External electrodes for device connection are usually formed by dipping and applying a conductive paste, silver paste, to the end face of each electronic component.
After this is dried and cured, a Ni barrier layer and an S
This is carried out by a method of forming n or solder (alloy of Sn and Pb) layers respectively. Here, the Ni barrier layer is a high melting point material layer for preventing the silver paste hardened layer from being eaten away during soldering, and the outermost Sn or solder layer is a low melting point material layer. The purpose is to improve wettability when soldering.

[0004]

However, in the above-mentioned conventional method of forming an external electrode, the number of steps is large, the management of the plating solution is troublesome, the workability is poor, and the cost is high. Further, the plating solution enters the electronic parts, for example, between the internal electrode and the ceramic in the laminated ceramic capacitor, and between the resistor and the ceramic in the semi-fixed volume, respectively, to generate hydrogen gas. Also, residual conductive ions cause insulation deterioration, resistance value deterioration, etc., leading to a decrease in production yield and a decrease in reliability as an electronic component.

In view of the above conventional circumstances, the present invention can form external electrodes on the end faces of various electronic parts at low cost and with good workability, and at that time, reliability due to the penetration of a plating solution as in the conventional case. It is an object of the present invention to provide a method for forming the external electrode, which does not cause problems such as deterioration.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have conventionally used it for forming a Ni barrier layer or an Sn or solder layer for forming an electrode. The present inventors have completed the present invention, knowing that the above conventional problems can be overcome by using a specific electrode forming transfer sheet instead of the plating solution.

That is, according to the first aspect of the present invention, a metal composite layer composed of a thin film of a low melting point metal such as Sn and a thin film of a high melting point metal such as Ni is laminated and formed on the peelable substrate in the above order. The present invention relates to a transfer sheet for electrode formation.

In a second aspect of the present invention, the end face of the electronic component is brought into contact with the metal composite layer of the above-described electrode-forming transfer sheet via a conductive paste, and the paste is placed on the metal composite layer. After drying and curing, the electronic component is peeled off from the sheet to transfer and form an external electrode composed of a cured layer of the paste and a metal composite layer on the end face of the electronic component. The present invention relates to a method for forming an external electrode of a component.

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 shows an example of an electrode-forming transfer sheet 1 used in the present invention. A metal composite layer comprising a low melting point metal thin film 11a and a high melting point metal thin film 11b on a peelable substrate 10. 11 are laminated in the above order.

The peelable substrate 10 has a water contact angle (θ) of 7
A material having a temperature of 0 ° or more, preferably 100 ° or more is used, and it may be a glass plate or other thick one, but normally, a thickness capable of being processed into a roll as a transfer sheet is several μ.
A flexible plastic film of about m to 100 μm is preferably used.

Examples of the plastic film having a water contact angle of the above value include, for example, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and a copolymer of tetrafluoroethylene and hexafluoropropylene. , A fluorine-based resin film made of a copolymer of chlorotrifluoroethylene and vinylidene fluoride.

As another plastic film,
A non-peelable resin film made of polystyrene, polyethylene, polypropylene, polyester, polyamide, polyimide or the like, which has been subjected to an appropriate peeling treatment on the surface, can also be used. This peeling treatment is performed, for example, in addition to a silicone-containing compound such as a combination of dimethylpolysiloxane having a hydroxyl group or vinyl group and methylhydrogenpolysiloxane, a fluorine-based resin such as polychlorotrifluoroethane, molybdenum sulfide. It can be carried out by a method such as a coating method, a spray method, a vacuum deposition method, a sputtering method, an ion plating method, a baking method, etc.

Of the metal composite layer 11, the low melting point metal thin film 1
1a is for improving the wettability at the time of soldering, and a metal such as Sn or solder having a melting point of 500 ° C. or lower is preferably used, but other melting points such as Ag, Cu, and Au are about 1100 ° C. Metals up to can also be used. On the other hand, the high-melting-point metal thin film 11b is for preventing the conductive paste hardened layer from being eroded during soldering, and is usually N
i is used, but the melting point of Cr, Fe, etc. is 1,
Metals of 400 ° C. or higher can also be used.

The low melting point metal thin film 11a and the high melting point metal thin film 11b each have a thickness of 0.1 to 100.
μm, preferably in the range of 0.5 to 10 μm, both thin films 1
The total thickness of the metal composite layer 11 composed of 1a and 11b is 0.
It may be in the range of 2 to 100 μm, preferably 1 to 20 μm. If the thin films 11a and 11b are too thin, the film will not be a continuous film, making it difficult to form the intended electrode. Further, if the thickness of the thin films 11a and 11b or the thickness of the entire metal composite layer 11 becomes too thick, the tensile strength becomes so strong that it becomes difficult to transfer the dimensional accuracy to the electronic component with good accuracy. It easily sticks out and causes inconvenience such as poor appearance.

Such thin films 11a and 11b are generally formed by a vacuum deposition method, but other dry plating methods such as a sputtering method and an ion plating method, and electroless and electrolytic plating methods (wet plating method) and the like. May be used, and the means for forming the thin film is not particularly limited.

2 (A) and 2 (B), the electrode-forming transfer sheet 1 having the above-described structure is used to apply the present invention to an end surface of an electronic component such as a laminated ceramic capacitor or a semi-fixed volume. According to the method, a method for forming an external electrode is shown.

As shown in FIG. 1A, first, the end face 2 of the electronic component 2 is formed on the metal composite layer 11 of the transfer sheet 1 for electrode formation.
a is brought into contact via the conductive paste 12P. That is, normally, after the conductive paste 12P is dip-coated on the end surface 2a of the electronic component 2, the coated surface is pressed onto the metal composite layer 11.

The conductive paste 12P may have the same structure as the conventional one, and a silver paste is generally used. This silver paste is made of silver powder, silver / copper mixed powder, phenol-based,
It is made by kneading a binder such as an acrylic or epoxy resin or a glass frit and a small amount of a diluting solvent so that the viscosity is coatable. The coating thickness is preferably such that the thickness after drying and curing is usually about 0.1 to 50 μm.

Next, while the coated surface is pressed against the metal composite layer 11, the conductive paste 12P is usually 1 to 100 ° C. to 200 ° C., although it varies depending on the material constitution.
Dry and cure under conditions of 0 to 60 minutes. With this curing,
The metal composite layer 11 (on the high melting point metal thin film 11b side) is firmly bonded to the end surface 2a of the electronic component 2.

Thereafter, as shown in (B), when the electronic component 2 is peeled off from the sheet 1, the metal composite layer 11 is formed on the end face 2a of the electronic component 2 together with the hardened layer 12 of the paste. Transfer formed. That is, these layers 1
The external electrodes 3 are composed of 1 and 12.

The peeling operation of the electronic component 2 from the sheet 1 can be easily carried out without requiring any special force. This is because the tensile strength of the metal composite layer 11 in the sheet 1 is a peelable substrate. This is because it is smaller than the 90-degree peel strength with respect to 10. That is, the above tensile strength is 10 to 1,000 g.
/ Μm × cm, preferably 17 to 530 g / μm × cm, while the 90 degree peel strength is 10 g / cm ² or more, preferably 400 g / cm ² or more. The 180 degree peel strength is 1 g / cm or more, preferably 2 g / cm or more.

The above tensile strength is a value obtained by calculation from the tensile strength per unit cross-sectional area (kg / m ² ). The 90-degree peel strength is a value obtained by measuring the peel force per 1 cm square in the 90-degree direction with respect to the substrate by using a shocker or tensilon. Further, the 180-degree peel strength is a value obtained by measuring the peel force in the 180-degree direction per 1 cm width using a shocker or tensilon.

[0023]

As described above, according to the present invention, when the external electrode is formed on the electronic component, a specific electrode forming transfer is performed instead of the conventional Ni barrier layer or Sn or the soldering liquid for forming the solder layer. Since a sheet is used and the metal composite layer is transferred and formed on the electronic parts at the same time when the conductive paste is dried and cured, it can be applied to various electronic parts such as laminated ceramic capacitors and semi-fixed volumes. On the other hand, it is possible to form external electrodes at low cost and with good workability. Especially by processing the transfer sheet for electrode formation into a roll shape, it is possible to automate the electrode formation and expect significant labor savings. it can. Moreover, it is possible to essentially avoid the conventional problems such as the decrease in reliability due to the penetration of the plating solution.

Also, electronic parts such as semi-fixed volume
As the size of the electrodes becomes smaller, the gap between the electrodes becomes smaller,
In the prior art, a bridging phenomenon or the like occurs between electrodes during plating work for electrode formation, which may cause an electrical short circuit.However, in the present invention, electrodes are formed without using a plating solution. However, since there is no such concern and an electrode having a desired thickness can be formed in accordance with the material configuration of the transfer sheet for electrode formation, it is possible to sufficiently cope with miniaturization of electronic components.

[0025]

EXAMPLES Next, examples in which the present invention is applied to a laminated ceramic capacitor and a semi-fixed volume as electronic parts will be specifically described.

Example 1 Sn was vacuum-deposited on one surface of a polytetrafluoroethylene film (releasable substrate) having a thickness of 50 μm under the conditions of a vacuum degree of 1 × 10 ⁻⁴ Torr to obtain Sn having a thickness of 3 μm. After forming a thin film (low melting point metal thin film), Ni is vacuum-deposited on the thin film under the same conditions as described above to form N having a thickness of 1 μm.
An i thin film (high melting point metal thin film) was formed to obtain an electrode forming transfer sheet having the structure shown in FIG.

In this electrode-forming transfer sheet, the tensile strength of the metal composite layer consisting of the low-melting metal thin film and the high-melting metal thin film was 370 g / μm × cm, and the tensile strength against the peelable substrate was 90.
The peel strength was 3,000 g / cm ² , and the 180 degree peel strength was 6 g / cm.

Next, using this electrode-forming transfer sheet, external electrodes were formed on the end faces of the laminated ceramic capacitor according to the method shown in FIG. That is, first, silver paste was applied to the end surface of the capacitor so that the thickness after drying and curing was about 20 μm, and then the applied surface was pressed onto the metal composite layer of the sheet. .. 1 in this state
It was dried and cured at 20 ° C. for about 30 minutes.

Thereafter, when the capacitor is peeled off from the sheet, the metal composite layer is integrated with the hardened layer of silver paste to be peeled off from the peelable substrate and transferred to the end face of the capacitor. Was done. In this way, an external electrode composed of an integrated body of a hardened layer of silver paste and a metal composite layer is provided on the end surface of the laminated ceramic capacitor, which is simpler and less costly than the conventional method using a plating solution. In addition, it could be formed satisfactorily without causing any problems such as a decrease in reliability due to the plating solution.

Example 2 Pb having a thickness of 4 μm was vacuum-deposited on one surface of a polytetrafluoroethylene film having a thickness of 75 μm (peeling base material) under the condition of a vacuum degree of 2 × 10 ⁻⁴ Torr. After forming a thin film (low melting point metal thin film), Cr is further vacuum-deposited under the same conditions as above, and the thickness is 0.5 μm.
Cr thin film (high melting point metal thin film) was formed to obtain an electrode forming transfer sheet having the structure shown in FIG.

In this electrode forming transfer sheet, the tensile strength of the metal composite layer comprising the low melting point metal thin film and the high melting point metal thin film was 282 g / μm × cm, and the peel strength was 90
The peel strength was 2,200 g / cm ² , and the 180 degree peel strength was 6 g / cm.

Next, using this electrode-forming transfer sheet, external electrodes were formed on the end faces of the semi-fixed volume according to the method shown in FIG. That is, first, the silver paste is dried and cured to a thickness of about 1 on the end face of the semi-fixed volume.
After coating so as to have a thickness of 0 μm, this coated surface was pressed onto the metal composite layer of the above sheet. 180 ℃ in this state
And dried and cured for about 20 minutes.

Then, when the semi-fixed volume is peeled off from the sheet, the above-mentioned metal composite layer is integrated with the hardened layer of the silver paste to be peeled off from the releasable substrate, and the semi-fixed volume is removed. -It was transferred to the end face of the mu. In this way, an external electrode composed of an integrated body of the hardened layer of silver paste and the metal composite layer is provided on the end face of the semi-fixed volume with a simpler operation and compared with the conventional method using the plating solution. It could be formed favorably at low cost and without causing any problems such as a decrease in reliability associated with the plating solution.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a transfer sheet for electrode formation of the present invention.

FIG. 2 is a process diagram showing an example of an external electrode forming method of the present invention, in which (A) shows an end face of an electronic component on a metal composite layer of a transfer sheet for electrode formation via a conductive paste. FIG. 3B is a cross-sectional view showing a state in which they are brought into contact with each other, and FIG. 3B is a cross-sectional view showing a state in which the electronic component is peeled off from the sheet after the paste is dried and cured.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transfer sheet for electrode formation 10 Releasable substrate 11 Metal composite layer 11a Low melting point metal thin film 11b High melting point metal thin film 12P Conductive paste 12 Hardened layer of conductive paste 2 Electronic component 2a End surface 3 External electrode

Claims (2)

[Claims] 1. A transfer sheet for electrode formation, comprising a peelable substrate, and a metal composite layer comprising a low melting point metal thin film and a high melting point metal thin film laminated in this order. 2. An end face of an electronic component is brought into contact with the metal composite layer of the transfer sheet for electrode formation according to claim 1 through a conductive paste, and the paste is dried, After curing, by peeling off the electronic component from the sheet, an external electrode composed of a cured layer of the paste and a metal composite layer is transferred and formed on the end surface of the electronic component. Electrode forming method.