JP3119714B2 - Conductive paste composition and wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste composition used for forming terminal electrodes of a wiring board and a wiring board.

[0002]

2. Description of the Related Art In recent years, substrate materials and internal conductors have been
Development of a multilayer wiring board obtained by simultaneous firing at a low temperature of 0 ° C. or lower has been advanced. Insertion of the multilayer wiring board into a circuit is performed by attaching a lead wire to an Ag alloy-based conductor formed on the substrate surface or the like with solder, and incorporating the lead wire into the circuit.

[0003] However, since there is a strong demand for improvement in mounting density and mounting performance, the use of a surface mounting device (SMD) for a multilayer wiring board is being studied. In order to form an SMD, it is necessary to use a leadless material. For this reason, a terminal electrode mainly composed of Ag is formed at a portion where a lead is attached, and electrical connection with the outside is ensured. In the terminal electrode, an inorganic binder such as glass frit is added at the paste stage in order to improve the adhesiveness to the substrate, and this inorganic binder acts as a permanent binder.

[0004] On the other hand, a plating film is formed on the surface of the terminal electrode in order to improve solderability, solder breakability and solder wettability. This plating film is made of Sn or solder (S
n-Pb) or the like, and Ni or Cu
Is provided.

[0005] However, when a plating film is formed on the surface of the terminal electrode, the plating solution degrades the inorganic binder, causing peeling of the terminal electrode and a decrease in adhesive strength.

[0006] Such a situation is not limited to the terminal electrodes of the multilayer wiring board, but also applies to the terminal electrodes of other surface mount elements and the external conductors of various elements.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and when a plating film for improving solder wettability and preventing solder cracking is formed, peeling does not occur and adhesion strength is reduced. It is an object of the present invention to provide a wiring board having terminal electrodes that hardly occur, and to provide a conductive paste composition used for forming such terminal electrodes and the like.

[0008]

This and other objects are achieved by the present invention which is defined below as (1) to (8).

(1) A conductive paste composition in which a conductive material mainly composed of Ag and an inorganic binder containing glass frit are dispersed in a vehicle, wherein the glass frit contains ZnO: 30 to 65% by weight, B ₂ O _3: 10~30 wt%, SiO _2: 5 to 20 wt%, MnO: 1 to 20 wt% and TiO _2: conductive paste composition characterized in that it contains 0.1 to 5 wt% .

(2) The conductive paste composition according to the above (1), wherein the content of the glass frit with respect to the conductive material is 1 to 10% by weight.

(3) The conductor paste composition according to the above (1) or (2), wherein a part or all of ZnO in the glass frit is substituted with PbO.

(4) The conductor paste composition according to any one of (1) to (3), wherein the glass frit has an average particle size of 0.1 to 20 μm.

(5) The conductor paste composition according to any one of the above (1) to (4), wherein the inorganic binder contains 5% by weight or less of TiO ₂ with respect to the conductive material.

(6) The average particle size of the TiO ₂ is 0.1 to
The conductor paste composition according to the above (5), which has a thickness of 20 μm.

(7) A wiring board having terminal electrodes formed by firing the conductive paste composition according to any one of (1) to (6).

(8) The wiring board according to (7), wherein a plating film is provided on a surface of the terminal electrode.

[0017]

The glass frit of the above composition contained in the conductor paste composition of the present invention is not easily attacked by the plating solution.
Terminal electrodes formed using this conductor paste composition have extremely good plating solution resistance. Therefore, when a plating film for improving solder wettability and preventing solder cracking is formed on the terminal electrode, peeling of the terminal electrode and lowering of the adhesive strength are prevented.

[0018]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

The conductor paste composition of the present invention contains a conductive material and an inorganic binder. This inorganic binder serves as a permanent binder for the conductive material, and contains glass frit as a main component.

In the present invention, ZnO: 30 to 65% by weight, preferably 50 to 60% by weight, B ₂ O ₃ : 10 to 30% by weight, preferably 15 to 23% by weight, SiO ₂ : 5 to 20% by weight , preferably 8-15 wt%, MnO: 1 to 20 wt%, preferably from 2 to 15 wt%, and TiO _2: 0.1 to 5 wt%, the glass preferably contains 0.2 to 3 wt% Use a frit. The glass frit is made of crystallized glass.

The reasons for limiting the glass frit composition are as follows.

When ZnO is less than the above range, plating solution resistance cannot be obtained, and crystallization becomes difficult. Also, Zn
If O exceeds the above range, the glass is likely to float on the surface of the electrode after firing, resulting in poor plating ability. As a result, the adhesion strength of the plating film becomes insufficient.

It is to be noted that part or all of ZnO may be substituted with PbO. Although the effect is the same in this case, it is particularly effective for improving the fixing strength described in the embodiment. However, when ZnO is contained, the balance among tensile strength, fixing strength, flexural strength and the like is improved.

When at least one of B ₂ O ₃ and SiO ₂ is less than the above range, vitrification becomes difficult, and
If at least one of them exceeds the above range, the softening point becomes too high, glass remains in the electrode after firing and glass floats, and good plating property cannot be obtained. For this reason, the adhesion strength of the plating film becomes insufficient.

When the content of at least one of MnO and TiO ₂ is less than the above range, the adhesive strength to a substrate such as a substrate becomes insufficient.
_{For the} same reason as ₂ O ₃ or SiO ₂ , the adhesion strength of the plating film becomes insufficient.

The glass having such a composition has a softening point of about 500 to 600 ° C.

In addition to the glass frit having the above composition,
A glass frit such as P ₂ O ₅ , BaO, CaO, or SrO may be contained. Such a glass frit deviating from the above composition is 10% of the entire glass frit.
% By weight or less.

The content of the glass frit in the conductive paste composition is 1 to 10% by weight, especially 1.5 to 10% by weight based on the conductive material.
Preferably it is 5% by weight. If the content of the glass frit is less than the above range, sufficient adhesive strength is not obtained,
If it exceeds the above range, the glass floats on the electrode surface after firing, and the adhesion strength of the plating film becomes insufficient.

The average particle size of the glass frit is not particularly limited, but is usually preferably 0.1 to 20 μm.

The inorganic binder may contain other inorganic particles in addition to the glass frit. Such inorganic particles include TiO ₂ , ZrO ₂ , CoO, NiO, Al
One or more of ₂ O ₃ , CuO, Cr ₂ O _{3 and the} like can be mentioned, and among them, TiO ₂ is particularly preferable. TiO ₂ acts as an aid for nucleation of crystallized glass, suppresses excessive diffusion of glass into the matrix, and also acts as an anchoring agent.

The content of these inorganic particles is preferably 5% by weight or less based on the conductor. Content is 5% by weight
Exceeds, the diffusion of glass into the substrate becomes insufficient,
Further, since the inorganic particles themselves do not diffuse into the substrate, the glass and the inorganic particles float on the electrode surface, and the plating property is reduced.

The average particle size of these inorganic particles is 0.1 to 2
It is preferably 0 μm.

In the present invention, a particulate conductive material mainly composed of Ag is used. The terminal electrode formed by using the conductor paste composition of the present invention has a plating film formed on the surface thereof for improving solder wettability and solder breakability. For this reason, although solder wettability and solder breakability are inferior to Ag-Pd and Ag-Pt, Ag which is inexpensive and has high conductivity can be used as the conductive material. Further, Ag has a higher sintering property than an Ag alloy and is less likely to penetrate the plating solution, so that the effect of the present invention is further improved.

However, Ag-Pd, Ag-Pt, Ag
An Ag alloy such as -Pd-Pt may be used. Although Ag is used for the internal electrodes and the internal conductor, when Ag is also used for the terminal electrodes, cracks may occur in the substrate due to the stress accompanying shrinkage during firing. Pd or Pt may be added to alleviate this stress. In this case, Pd or P
The amount of t added is at most 3% by weight, usually 1% by weight.
It is as follows.

In the conductive paste composition,
Ag and Pd and / or Pt may be present separately. In this case, an Ag alloy is obtained by subsequent firing.

The average particle size of the conductive material particles is 0.01 to 10
It is preferable to set it to about μm. The reason is that if the average particle size is less than 0.01 μm, the shrinkage becomes too large, and if it exceeds 10 μm, the printability and dispersibility of the conductive paste composition deteriorate.

The vehicle in which the conductive material and the inorganic binder are dispersed may be formed from a binder such as ethylcellulose, nitrocellulose or an acrylic resin, a solvent such as terpineol or butyl carbitol, or other dispersants or activators, if necessary. It is appropriately selected.

Generally, the content of the vehicle in the conductive paste composition is about 10 to 70% by weight.

The conductive paste composition of the present invention is produced by mixing conductive material particles and an inorganic binder, adding a vehicle such as a binder and a solvent thereto, kneading them, and forming a slurry. The viscosity of the conductor paste composition is 3
It is better to adjust to about 10,000 to 300,000 cps.

The conductor paste composition of the present invention is usually used by printing a predetermined pattern on the end surface of a wiring board and baking it.

The wiring board in this case may be a wiring board on which various surface-mounted components are soldered, but in the present invention, in particular, the terminal electrode of the multilayer wiring board itself used as a surface-mounted component is used. It is suitable for. FIG. 2 shows an example of such a multilayer wiring board.

The multilayer wiring board 1 shown in FIG. 1 has a plurality of insulating substrates laminated and integrated by firing, and an internal conductor having a predetermined pattern is formed at the interface between the respective layers. A terminal electrode is formed on a portion exposed on the surface of the substrate. On the surface of the terminal electrode, an Sn plating film or an Sn-P film is usually provided via a Ni plating film or a Cu plating film.
A b plating film is formed. The plating film of Ni or Cu is S
Ag of terminal electrode when forming n or Sn-Pb plating film
Provided to prevent fraying. In addition, Sn or Sn
The -Pb plating film is provided for improving solder wettability and solder breakability. Then, when the solder 2 adheres to the surface of the plating film, the multilayer wiring board 1
Fixed on the surface of

As a material of the insulating substrate constituting the multilayer wiring board, alumina-borosilicate glass, alumina-lead borosilicate glass, alumina-barium borosilicate glass,
A low-temperature fired material containing glass and an oxide aggregate such as alumina-calcium borosilicate glass, alumina-strontium borosilicate glass, and alumina-magnesium borosilicate glass is preferable.

In such a substrate material, the glass content is generally preferably about 50 to 80% by weight.

The internal conductors are usually wired in multiple layers and are electrically connected to each other through through holes formed in the thickness direction of the insulating substrate. The inner conductor is preferably a conductor mainly composed of Ag, particularly Ag, from the viewpoint of giving priority to good conductivity. The composition for an internal conductor preferably contains a conductive material and about 5 to 10% by weight of glass frit based on the conductive material.

The thickness of the internal conductor is usually about 5 to 20 μm, and the thickness of the terminal electrode is usually about 5 to 20 μm. The conduction resistance of the internal conductor and the terminal electrode depends on the composition, but generally, the former is 2 to 10 mΩ /
□, the latter is preferably about 2 to 30 mΩ / □.

Such a multilayer wiring board is manufactured, for example, as follows.

First, a predetermined number of green sheets as a substrate material are prepared. This green sheet is prepared by mixing a predetermined amount of an aggregate such as alumina powder, which is a raw material of a substrate, and glass powder (for example, borosilicate glass), adding a binder resin, a solvent, and the like, kneading them, and forming a slurry. For example, it is manufactured by molding to a thickness of about 0.1 to 0.3 mm by a doctor blade method.

Next, a through hole is formed in the green sheet by using a punching machine or a die press, and then a composition for an internal conductor is printed on each green sheet by, for example, a screen printing method. And filling the through holes.

Next, the green sheets are superimposed and hot-pressed (approximately 50 to 1000 kgf / cm ^{2 at} about 40 to 120 ° C.).
) To obtain a laminate of green sheets, and if necessary, a binder removal treatment and formation of a cutting groove are performed.

Thereafter, the laminate of green sheets is usually fired at a temperature of about 800 to 1000 ° C. in air to be integrated.

Next, a terminal electrode paste is applied to a predetermined position on the surface of the fired body and fired to form a terminal electrode.

When the conductor paste composition of the present invention is used as an external conductor paste, the paste is printed at a predetermined position on the surface of the fired body by a screen printing method or the like.
Fired to form an external conductor. Further, a resistor material paste or the like is printed and fired as necessary to form a resistor.

Thereafter, a plating film is formed.

The substrate may be manufactured by a printing method.

The conductive paste composition of the present invention can be used not only for the terminal electrodes of the multilayer wiring board for surface mounting but also for the wiring board 3 shown in the figure.
As described above, the present invention can also be applied to an external conductor of a wiring board on which surface components such as chip components such as chip inductors and chip capacitors, and various devices such as semiconductor integrated circuit devices and diodes are mounted. Further, the present invention can be applied not only to a multilayer wiring board but also to a single-layer wiring board. Further, the present invention can be applied to external conductors and terminal electrodes of various chip components and elements. However, since a terminal electrode of a wiring board used as a surface mount element is required to have strong adhesiveness, the conductive paste composition of the present invention is particularly suitable for forming a terminal electrode of a wiring board.

[0057]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Example 1 (1) Preparation of Conductive Paste Composition A conductive material, an inorganic binder and a vehicle were kneaded to prepare a conductive paste composition. Ag (average particle size 1μ)
m) and a glass frit (average particle size 8 μm) as the inorganic binder.
m) or additionally TiO ₂ (average particle size 10 μm)
And an ethyl cellulose-based resin and a high boiling solvent (terpineol) as a vehicle. Table 1 below shows the composition of the glass frit and the content of the inorganic binder with respect to 100 parts by weight of the conductive material. The vehicle is a conductive material 100
20 to 40 parts by weight were added to the parts by weight.

(2) Preparation of Green Sheet A green sheet having a composition of α-alumina: 40% by weight and glass powder: 60% by weight and a thickness of 100 to 300 μm was prepared (the glass in this case was Al ₂ O ₃ —B ₂ O ₃ -Si
O ₂ -MO system, where M = Ca, Ba, Sr, Mg).

(3) Preparation of Multilayer Wiring Substrate After forming an Ag internal conductor on the green sheet, the green sheet was laminated by hot pressing to obtain a green sheet laminate. After degreased, the laminate was simultaneously fired at 900 ° C. in air.

A conductor paste composition was printed on the obtained fired body by screen printing, and fired at 850 ° C. in air to form a terminal electrode. Terminal electrode thickness is 40μ
m.

Next, a Ni plating film (thickness 1 μm) and a Sn plating film (thickness 2
μm) were sequentially formed to obtain a multilayer wiring board.

The dimensions of the multilayer wiring board are 5.0 mm in length, 5.0 mm in width, and 0.8 mm in height. As shown in FIG. 1, three rows of terminal electrodes are formed on two opposing side surfaces. The part is formed so as to extend around both main surfaces of the substrate. The width of the terminal electrode is 0.
6 mm. In FIG. 1, the solder 2 is further adhered on the plating film on the surface of the terminal electrode, but the pattern of the solder is the same as the pattern of the terminal electrode.

The following tests were performed on the obtained multilayer wiring board.

Tensile Strength Test As shown in FIG. 1, the lead wire 4 was fixed vertically to the plating film on the terminal electrode surface by the solder 2. Then, the lead wire 4 was pulled in the direction of the arrow in the figure by a tensile tester, and the load when the terminal electrode was peeled off from the multilayer wiring board 1 was measured, and this was defined as the tensile strength.

Fixing Strength Test As shown in FIG. 2, the multilayer wiring board 1 was used as a surface mount device and was fixed on a board 3 (glass epoxy board) by solder 2. Then, a load was applied in the direction of the arrow in the figure, and the load when the multilayer wiring board 1 was peeled was measured.

As shown in FIG. 3, a board 3 (glass epoxy board) having holes was prepared, and a multilayer wiring board 1 was fixed to the surface of the board 3 with solder 2 so as to cover the holes. Then, a load was applied from the back side of the substrate 3 in the direction of the arrow in the figure, and the load when the multilayer wiring board 1 was peeled was measured, and this was defined as the fixing strength in back-pressing.

Deflection Strength Test The board 3 (glass epoxy board) to which the multilayer wiring board 1 was fixed with the solder 2 was bent by applying a load from the back side of the multilayer wiring board 1 as shown in FIG. The amount of flexure when the multilayer wiring board 1 was peeled was measured, and this was defined as flexural strength.

In each of the above tests, the pressing speed was 2
0 mm / min.

The results of the above tests are shown in Table 2 below.

[0071]

[Table 1]

[0072]

[Table 2]

From the above results, the effect of the present invention is clear.

[0074]

According to the present invention, when a terminal electrode or an external conductor such as a surface mount device or a wiring board is formed using the conductive paste composition of the present invention, the surface of the terminal electrode or the external conductor can be improved in solder wettability and solder breakability. When a plating film is formed, the adhesion strength of the terminal electrode and the external conductor hardly decreases, and an extremely reliable element or substrate is realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a tensile strength test of a terminal electrode of a multilayer wiring board.

FIG. 2 is an explanatory diagram of a fixing strength test (lateral pressing and vertical pressing) of a terminal electrode of a multilayer wiring board.

FIG. 3 is an explanatory diagram of a bonding strength test (back pressing) of a terminal electrode of a multilayer wiring board.

FIG. 4 is an explanatory diagram of a bending strength test of a terminal electrode of a multilayer wiring board.

[Explanation of symbols]

 Reference Signs List 1 multilayer wiring board 2 solder 3 board

Claims (8)

(57) [Claims] 1. A conductive paste composition in which a conductive material mainly composed of Ag and an inorganic binder containing glass frit are dispersed in a vehicle, wherein the glass frit is ZnO: 30 to 65% by weight, B ₂ O _3: 10 to 30 wt%, SiO _2: 5 to 20 wt%, MnO: 1 to 20 wt% and TiO _2: conductive paste composition characterized in that it contains 0.1 to 5 wt%. 2. The conductive paste composition according to claim 1, wherein the content of the glass frit with respect to the conductive material is 1 to 10% by weight. 3. The glass frit according to claim 1, wherein part or all of ZnO in the glass frit is substituted with PbO.
3. The conductor paste composition according to item 1. 4. The glass frit has an average particle size of 0.1.
The conductive paste composition according to any one of claims 1 to 3, wherein the thickness of the conductive paste is from 20 to 20 µm. 5. The conductive paste composition according to claim 1, wherein the inorganic binder contains TiO ₂ in an amount of 5% by weight or less based on the conductive material. 6. The TiO _{2 having} an average particle size of 0.1 to 20.
The conductive paste composition according to claim 5, which has a particle size of µm. 7. A wiring board comprising terminal electrodes formed by firing the conductive paste composition according to claim 1. 8. The wiring board according to claim 7, wherein a plating film is provided on a surface of the terminal electrode.