JPH07302510A - Conductive paste composition - Google Patents

Abstract

PURPOSE:To prevent the formation of cracks and leakage of glass at the time of sintering, heighten the adhesion strength between a substrate and an electrode, and prevent the electrode from being invaded by containing a silver powder as a conductive component in a prescribed condition. CONSTITUTION:As conductive components, 29-43 pts. by wt. of finely spherical silver powder, 0.5-12 pts. by wt. of roughly granular silver powder or roughly granular silver-coated nickle powder, and 26-41 pts. by wt. of flaky silver powder are contained in a conductive paste composition. In the case the average particle size of the finely spherical silver powder is less than 0.05mum, the silver powder coagulates itself easily and the dispersibility in a vehicle is lowered and thus the amount to be used is increased. In the case the size is over 0.4mum, no film with sufficient density can be obtained. In the case the average particle size of the roughly granular silver powder or the roughly granular silver-coated nickel powder is less than 0.8mum, no effect to suppress the sinterability of the film is obtained and in the case the size exceeds 3mum, the density of the film is lowered. As the flaky silver powder, one with 2-5.5mum average particle size of longer diameter is used.

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 electrodes of thick film chip resistors used in the electronics industry.

[0002]

2. Description of the Related Art The thick film chip resistor as described above is generally manufactured through the following steps. That is, a silver-palladium conductive paste is printed on the upper surface of an alumina substrate, dried, and baked to form an upper electrode, and then a ruthenium-based resistor paste is printed, dried so as to overlap a part of the upper electrode, dried,
Bake to form a resistor. A glass paste (pre-coated glass) is printed on the upper surface of the resistor, dried and then baked at a temperature of about 600 ° C. Then, a part of the resistor is destroyed by laser light to correct the resistance value, and then the resistor is re-set. A glass paste (overcoat glass) is printed on the body, dried, and baked at a temperature of about 500 to 600 ° C.

Next, the above alumina substrate is cut into small chips, a silver-palladium conductive paste is applied to the side surface by dipping or a roller, dried and then baked in air at a temperature of about 500 to 600 ° C. to form a side surface electrode. To form. Finally, the exposed top surface electrode and side surface electrode are plated with Ni, Sn-Pb, or the like to prevent the electrodes from being damaged during soldering, and a thick film chip resistor is manufactured.

Recently, in order to reduce the cost, the above-mentioned upper electrode and the resistor are simultaneously fired in one firing step. In the simultaneous firing, a silver-palladium conductive paste is printed and dried on an alumina substrate, a ruthenium-based resistance paste is printed and dried so as to overlap a part thereof, and the firing is performed at a temperature of about 850 ° C. to form a top electrode and a resistor. It is a method of forming.

However, when the above-mentioned simultaneous firing is performed, cracks may occur in the resistor near the junction between the upper electrode and the resistor due to the difference in heat shrinkage during firing, or the conductive paste component and the resistance paste component may be fired. There is a problem in that the reaction occurs inside and the foaming occurs in the overlapping portion of the upper surface electrode and the resistor, which causes variations in resistance value, deterioration of current noise, and deterioration of plating property.

Further, in the general conductive paste, it is desired to further improve the adhesive strength between the substrate and the electrode.
In the case of a chip resistor, the adhesive strength between the substrate and the electrode is significantly reduced due to the internal penetration of the plating solution in the Ni plating step and the deterioration of the adhesive layer due to hydrogen generated during plating. In order to improve the adhesive strength, a dense electrode film has to be formed. However, if the electrode film is made dense, the glass in the resistor will exude to the electrode surface during firing,
There is a problem that the adhesion of the plating is significantly reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above problems, and cracks due to a difference in heat shrinkage may occur during firing when manufacturing a thick film chip resistor or the like.
The glass in the resistor does not ooze onto the electrode surface during firing, the adhesion strength between the substrate and the electrode is high, and even if the plating adhesion is not good due to poor plating in the plating process, the electrode will not be eaten away. An object of the present invention is to provide a conductive paste composition that does not have a conductive paste.

[0008]

In order to achieve the above object, the conductive paste composition according to the present invention has the following constitution. That is, the conductive paste composition according to the present invention has at least an average particle size of 0.05 to 0.5 as a conductive component.
29 to 43 parts by weight of 0.4 μm fine spherical silver powder, 0.5 to 12 parts by weight of coarse spherical silver powder or coarse spherical silver-coated nickel powder having an average particle diameter of 0.8 to 3 μm, and the average particle diameter in the major axis is It is characterized by containing 26 to 41 parts by weight of flake-shaped silver powder of 2 to 5.5 μm.

[0009]

The above-mentioned cracks and the like are caused by the contraction timing of the upper surface electrode and the resistor during firing and the contraction amount of the upper surface electrode. The contraction speed of the electrode depends on the particle size of the silver powder used, and generally, the smaller the particle size, the more the contraction start temperature shifts to the lower temperature side and the faster the contraction speed. On the other hand, the amount of shrinkage of the electrode decreases when the filling property of the film during drying is improved.
Therefore, it is important that the silver powder has a small specific surface area, has little surface irregularity, and is well wetted with the organic vehicle. In view of this, the present inventor has found the optimum shape of the conductive component silver powder suitable for the conductive paste composition, the particle size and the blending amount thereof, and has the above-mentioned configuration, whereby cracks and the like during firing are caused. It is possible to provide a good conductive paste that does not occur.

The conductive paste of the present invention is a mixture of a vehicle in addition to the above-mentioned conductive components. Examples of the vehicle include a cellulosic or acrylic resin dissolved in a solvent such as terpineol. Conventionally known ones can be used.

The spherical shape of the above-mentioned fine spherical silver powder refers to one having a major / minor degree (major axis / minor axis) of 1 to 2.5, and particularly preferably having a major to minor degree of 1 to 1.25. The reason why a spherical shape is used is that the sinterability of the film decreases unless the shape is spherical, which is not preferable. The average particle size of the fine spherical silver powder is set to 0.05 to 0.4 μm because the average particle size is 0.
If it is less than 05 μm, the silver powders are likely to aggregate with each other, the dispersibility in the vehicle is lowered, and the amount of the vehicle used is increased. On the other hand, if the average particle size exceeds 0.4 μm, a sufficiently dense film cannot be obtained, which is not preferable. Considering the kneadability with a vehicle or the like, the average particle size of the fine spherical silver powder is more preferably about 0.1 to 0.3 μm.

The coarseness and shortness of the coarse-grained spherical silver powder or the coarse-grained spherical silver-coated nickel powder is the same as that of the fine spherical silver powder described above, and the average grain size of 0.8 to 3 μm is 0.8 μm.
If it is less than the above range, there is almost no effect of suppressing the sinterability of the film, and if the average particle size exceeds 3 μm, the denseness of the baked film is remarkably lowered and the adhesion strength with the alumina substrate or the like is weakened, which is not preferable. . The average particle diameter is more preferably 0.8 to 2 μm in the case of coarse-grained spherical silver powder and about 2 to 3 μm in the case of coarse-grained spherical silver-coated nickel powder.

Either coarse-grained spherical silver powder or coarse-grained spherical silver-coated nickel powder may be used. However, when silver-coated nickel powder is used, the solder corrosion resistance of the electrode film itself should be improved. Is more preferable because it can Further, the nickel content of the silver-coated nickel powder is preferably in the range of 20 to 60 atomic%. If it is less than 20 atomic%, the effect of preventing electrode erosion during soldering is lowered, and if it exceeds 60 atomic%. Sinterability is reduced.

Although the method for producing the silver-coated nickel powder is appropriate,
For example, it can be manufactured by an electroless plating method or the like. Specifically, for example, sodium borohydride in which nickel powder is dispersed in advance, a solution containing silver ions may be added to an aqueous solution of ascorbic acid or the like with stirring, and the amount of nickel powder may be adjusted to any value. A silver-coated nickel powder having a silver coverage is obtained. Further, for example, it can be produced also by a vapor deposition method. Specifically, for example, it suffices to pass silver vapor which has been heated and vaporized in a nickel powder filling layer, and an arbitrary amount can be obtained by controlling the vapor deposition time. A nickel powder coated with silver is obtained.

As described above, the flake-shaped silver powder has an average particle diameter in the major axis range of 2 to 5.5 μm. When the average particle diameter in the major axis is less than 2 μm,
Uniform mixing becomes difficult, and the effect of improving the filling rate of the film during drying is small. On the other hand, if it exceeds 5.5 μm, the denseness of the fired film is remarkably lowered, and the screen is likely to be clogged during screen printing or the like. Further, considering the shrinkage characteristics of the electrode film, 2.5 to 5
The range of μm is more preferable. The flake-shaped silver powder having a length of 1 to 5, more preferably 1 to 3.5 is preferably used, and the thickness thereof is 0.05 to 2 μm, more preferably 0.1 to 1.2 μm. You should use one.

The fine spherical silver powder, coarse spherical silver powder or coarse spherical silver-coated nickel powder, and flake silver powder are blended in the amount of 29 to 43 parts by weight of fine spherical silver powder, coarse spherical silver powder or Coarse-grained spherical silver-coated nickel powder is 0.5 to 12 parts by weight, and flaky silver powder is 26 to 41 parts by weight.

The reason why the amount of the fine spherical silver powder is 29 to 43 parts by weight is that when the amount is less than 29 parts by weight, the electrode film becomes porous and the adhesive strength with an alumina substrate or the like is lowered, or the conductive resistance value is increased. If the amount exceeds 43 parts by weight, the fired film becomes too dense, and the shrinkage ratio of the electrode during sintering becomes too large, so that exudation or cracking of the resistor glass is likely to occur. .

The coarse spherical silver powder or the coarse spherical silver-coated nickel powder is set within the range of 0.5 to 12 parts by weight.
This is because if the amount is less than 5 parts by weight, it is difficult to control the denseness of the fired film, and if it exceeds 12 parts by weight, the denseness of the fired film is significantly reduced, which is not preferable.

The flake-shaped silver powder is set in the range of 26 to 41 parts by weight because when it exceeds 41 parts by weight, the denseness of the fired film is lowered, the adhesive strength is lowered, and the conductive resistance value is increased, which is not preferable. If the amount is less than 26 parts by weight, shrinkage during firing becomes too large and cracks are likely to occur.

When the coarse spherical silver powder is used, 29 to 38 parts by weight of the fine spherical silver powder and 3.5 to 3.5 of the coarse spherical silver powder are used.
11.5 parts by weight of flaky silver powder 26.5 to 40.5
It is more preferable that the content is in the range of parts by weight, and if the coarse-grained spherical silver-coated nickel powder is used, the fine spherical silver powder is 29
~ 43 parts by weight, 0.8 ~ of coarse-grained spherical silver-coated nickel powder
It is more preferable that the amount of the flaky silver powder is 1.5 parts by weight and the amount of the flaky silver powder is 29 to 38 parts by weight.

Next, palladium powder may be added as a conductive component other than the above. The palladium powder is not necessarily added, but in order to prevent the sulfuration of silver, for example, when the silver forming the electrode or the like is sulfurized by the sulfur gas in the air or the like, the electrode may be broken. Is preferably added. The amount added is preferably about 0.5 to 2 parts by weight. This is because if it is less than that, the effect of preventing sulfidation is small, and if it is too much, the material cost increases. The particle size of the palladium powder is not particularly limited and may be about 0.05 to 3 μm which is generally used.

Further, in order to enhance the adhesive strength between the substrate and the electrode, it is preferable to add glass frit as a solid component and copper or copper oxide or both as an inorganic binder.
In that case, a glass frit with a yielding temperature of 400-
550 ° C and a thermal expansion coefficient of 5 to 9.5 × 10 ^-6 / ° C
It is good to use a good one.

The glass frit yielding temperature is 400-55.
The range of 0 ° C is that when the yielding temperature is less than 400 ° C, glass floats on the electrode surface or bubbles are contained in the electrode film, resulting in a decrease in plating property and an increase in conductive resistance. May occur, and the yielding temperature is 550
This is because if the temperature exceeds ℃, the glass is not sufficiently fluidized and the effect of promoting the sintering of silver and the reaction between the copper and the alumina substrate cannot be obtained.

Further, the coefficient of thermal expansion of the glass frit is set to 5
9.5 × 10 ⁻⁶ / ° C. is set because the glass frit has a thermal expansion coefficient of about 7 × 10 ⁻⁶ /
This is because when the temperature is significantly different from (° C.), excessive stress is generated in the glass phase due to heat aging and cooling / heating cycles, and the adhesive strength is reduced.

The type of glass frit is not particularly limited,
PbO-B ₂ O ₃ -SiO ₂ system, PbO-B ₂ O ₃ -Z
Various materials such as nO type and PbO—SiO ₂ —Al ₂ O ₃ type can be used. The glass frit contains Ni.
To suppress the strength deterioration of the glass phase due to plating, TiO 2
Those containing ₂ are more preferable. The content of TiO ₂ is preferably about 3 to 10% by weight. This is because if it is less than 3% by weight, the effect of improving the acid resistance of the glass phase is small, and if it exceeds 10% by weight, the yielding temperature of the glass becomes too high.

The average particle size of the glass frit is generally 1 to
A 2.5 μm one is used. The amount of glass frit compounded is preferably about 0.5 to 2 parts by weight. If the amount is less than 0.5 parts by weight, the adhesive strength between the electrode and the alumina substrate decreases, and
This is because if it exceeds the weight part, the glass is likely to seep out.

Further, if necessary, copper powder or copper oxide or both may be added as an inorganic binder as described above, and the addition amount thereof is preferably about 0.5 to 1.5 parts by weight. If it is less than 0.5 parts by weight, the adhesive strength between the electrode and the alumina substrate will be reduced, and if it exceeds 1.5 parts by weight, the resistance characteristics such as the resistance value and the temperature coefficient of resistance will be deteriorated. is there.

[0028]

EXAMPLES Specific examples and comparative examples of the conductive paste composition according to the present invention will be described below. In the examples and comparative examples described below, the following silver powder and glass frit were used.

As the silver powder, those shown in Table 1 below were used, including fine spherical silver powder, coarse spherical silver powder, and coarse flake silver powder. The spherical silver powder used is made in-house, and the flake-shaped silver powder has an average particle size of 1 to 2 μm.
The spherical silver powder was treated in an attritor mill for an arbitrary time to form flakes. The types, particle shapes and average particle diameters of these silver powders are summarized in Table 1 below.

[0030]

The spherical silver powders S1 to S6 in the above table are all spherical with a major / minor degree (major axis / minor axis) of 1 to 1.25. Further, the average particle diameters of the flaky silver powders F1 to F4 in the table are the average particle diameters of long diameters, and are obtained by directly measuring with a scanning electron microscope. Each of the flaky silver powders is in the form of flakes having a length within a range of 1 to 3.5 and a thickness of 0.1 to 1.2 μm.

Various silver-coated nickel powders prepared by electroless plating were used. The average particle size and the amount of silver coating are summarized in Table 2 below. The shape is spherical.

[0033]

Further, glass frit having the composition shown in Table 3 below was prepared. The yielding temperature and the coefficient of thermal expansion are shown together in the table. The average particle size of the glass frit was 1 to 2.5 μm.

[0035]

[Examples] In Examples 1 to 16, a silver frit, an inorganic binder, and palladium (Pd) were appropriately selected from the above silver powder or silver-coated nickel powder.
The powder and the vehicle were kneaded with a three-roll mill to prepare various pastes. Table 4 below shows the compounding ratio in each of these Examples.

[0037]

In the above examples, as the inorganic binder, as shown in the table, reagent-grade cuprous oxide (Cu ₂ O), reagent-grade cupric oxide (CuO), or metallic copper was used. Powder was used. Also, as palladium powder,
Spherical particles with an average particle size of 0.3 μm (made in-house; trade name SP
F-030) was used. Furthermore, as the vehicle, terpineol in which 15% by weight of ethyl cellulose was dissolved was used.

Comparative Example As Comparative Examples 1 to 9 with respect to Examples 1 to 16, pastes having the compounding ratios shown in Table 5 below were prepared. In addition, the manufacturing procedure of the paste and other conditions are the same as those in the above-mentioned embodiment.

[0040]

Using the pastes obtained in Examples 1 to 16 and Comparative Examples 1 to 9 described above, the adhesive strength, the occurrence of cracks,
The extent of oozing of the glass was examined. The results are shown in Table 6 below.
And shown in Table 7.

[0042]

[0043]

The above-mentioned adhesive strength was examined as follows. First, on a 1-inch square alumina substrate (Kyocera Corporation, trade name A473) having a purity of 96% by weight, the pastes obtained in the above Examples and Comparative Examples were made to have a thickness of about 8 μm when fired. A 2-mm square pad screen-printed was dried at a temperature of 120 ° C for 15 minutes, and then a peak temperature of 850 ° C x 9 was measured by a belt-type continuous firing furnace.
After firing for minutes, a nickel plating having a thickness of 5 μm was applied on the pad, and then a tin-plated copper wire having a diameter of 0.65 mm was soldered with 63 wt% Sn-37 wt% Pd solder.

Next, the above tin-plated copper wire was bent at a pad end at a right angle to the substrate, and a tensile tester was used.
The tin-plated copper wire was pulled while the substrate was fixed, and the adhesive strength was measured. In addition, the above-mentioned tensile test is performed immediately after soldering (initial strength)
The measurement was performed on two types of samples, one that was aged at 0 ° C. for 24 hours (aging strength).

The above initial strength and aging strength are
If both are 60 (N / 4 mm ² ) or more, they can be put to practical use, and all the pastes of Examples 1 to 16 according to the present invention were 60 (N / 4 mm ² ) or more. On the other hand, it was found that those of Comparative Examples 2, 3, 5, 7 and 9 were 60 or less and could not be put to practical use.

The presence or absence of cracks was examined by the following procedure. That is, 2 formed by the above adhesive strength test
After screen-printing a plurality of 1.5 mm-square pads instead of the mm-square pads and drying, a self-made resistor paste (trade name R-
12SX) was screen-printed so that the fired film thickness was 8 μm, dried and fired to prepare a co-fired test piece.

Whether or not cracks were generated in the vicinity of the joint between the electrode of the co-fired test piece and the resistor was examined by a scanning electron microscope. In Tables 6 and 7, those with no cracks were marked with a circle, and those with cracks were marked with a cross. In Examples 1 to 16 according to the present invention, cracks were observed. I was not able to admit. On the other hand, in Comparative Examples 2 to 7 and 9, cracks were generated.

Further, regarding the exudation of the glass, a co-fired test piece was used in the same manner as in the case of checking the presence of cracks as described above, and the glass was subjected to surface analysis by EDX in the vicinity of the joint between the electrode (pad) and the resistor. The bleeding of the was evaluated. In Tables 6 and 7, those having no glass bleeding are marked with a circle, and those having a glass bleeding are marked with a cross. In Examples 1 to 16 according to the present invention,
No bleeding of the glass was observed in any of them. On the other hand, in Comparative Example 1, exudation of glass was observed.

Further, the glass frit has a yielding temperature of 400.
Up to 550 ° C. and a thermal expansion coefficient of 5 to 9.5 × 10 ⁻⁶ /
The glass frit is added in an amount of 0.5 to 1.5 parts by weight, and the inorganic binder is 0.1.
It was confirmed that 5 to 1.5 parts by weight was suitable.

The solder resistance of the pastes obtained in the above Examples and Comparative Examples was also tested in the following manner. That is, instead of the pad formed in the above-described adhesive strength test, a circuit pattern having a width of 0.5 mm and a total length of 50 mm is screen-printed and baked in the same manner as described above to form an electrode, and the electrode is formed. 2 wt% Ag-62 wt% S in which the temperature of the conductor pattern sample was maintained at 250 ± 5 ° C.
It is immersed in a solder bath of n-36 wt% Pb composition for 10 seconds and then repeatedly pulled up, and the solder resistance is increased by the number of dippings until the resistance value becomes so high that the resistance value of the electrode cannot be measured. evaluated.

As a result, in the pastes of Examples 6 to 10 using the silver-coated nickel powder, the resistance value of the electrode could be measured even after dipping 10 times or more, and the silver-coated nickel powder was used. It has been found that the product has particularly good solder resistance. This is because the solder corrosion resistance of the electrode film itself is improved by using silver-coated nickel powder,
In addition, this makes it possible to prevent electrode erosion even when the plating adhesion is poor due to defective plating in the plating process. The same applies to the cases using silver-coated nickel powder as in Comparative Examples 6, 7, and 9, but
In the case of using N1 having a small amount of silver coating as in Comparative Example 8, the resistance value of the electrode cannot be measured until it is dipped several times, and the solder resistance is deteriorated when the amount of silver coating is small. Was confirmed.

[0053]

As described above, the conductive paste composition according to the present invention contains fine spherical silver powder, coarse spherical silver powder or spherical silver-coated nickel powder and flake silver powder as the conductive components under the above-mentioned conditions. By this, it is possible to provide a conductive paste having excellent characteristics such as adhesive strength, and also in the case of forming a top electrode and a resistor in one firing step when manufacturing a thick film chip resistor, for example, as in the conventional case. It is possible to prevent the generation of cracks and the exudation of glass. Further, particularly when silver-coated nickel powder is used, there is an effect that solder resistance can be greatly improved.

Claims (5)

[Claims] 1. 29 to 43 parts by weight of fine spherical silver powder having an average particle diameter of 0.05 to 0.4 μm, and coarse spherical silver powder or coarse spherical silver-coated nickel powder 0.5 having an average particle diameter of 0.8 to 3 μm. ~
12 parts by weight and the average particle diameter in the major axis is 2 to 5.5 μm
A conductive paste composition containing 26 to 41 parts by weight of the flake-shaped silver powder as described above as a conductive component. 2. A fine spherical silver powder having an average particle diameter of 0.05 to 0.4 μm, 29 to 38 parts by weight, and a coarse spherical silver powder having an average particle diameter of 0.8 to 2 μm, 3.5 to 11.5 parts by weight, Flake-shaped silver powder 26.5-4 having an average particle diameter of 2-5 μm in the major axis
A conductive paste composition containing 0.5 part by weight as a conductive component. 3. A spherical spherical silver-coated nickel having an average particle diameter of 0.05 to 0.4 μm, 29 to 43 parts by weight, and an average particle diameter of 2 to 3 μm, and a nickel content of 20 to 60 atomic%. A conductive paste composition containing 0.8 to 1.5 parts by weight of powder and 29 to 38 parts by weight of flake silver powder having an average particle diameter in the major axis of 2 to 5 μm as conductive components. 4. Palladium powder 0.5 to 2 as a conductive component
The conductive paste composition according to claim 1, 2 or 3, which is obtained by adding a part by weight. 5. A solid component having a yielding temperature of 400 to 55.
0.5 to 2 parts by weight of a glass frit having a thermal expansion coefficient of 5 to 9.5 × 10 ⁻⁶ / ° C. at 0 ° C. and copper or / and copper oxide 0.5.
To 1.5 parts by weight.
The conductive paste composition according to.