JPH03228389A - Thick film conductor paste - Google Patents

Abstract

PURPOSE:To reduce an air gap between glass ceramics and a via fill conductor and to form the conductor with high quality by dispersing conductive main material, low thermal expansion coefficient filler and baking assistant with organic vehicle. CONSTITUTION:Baking assistant is added to Au powder as conductive main material and inorganic powder of quartz as low expansion coefficient filler pulverized by a ball mill, kneaded with organic vehicle containing ethylcellulose, as a main agent, turpineol and fatty acid, and then pasted. Shrinkage factor at the time of baking the paste is controlled by the mixing ratio of the organic vehicle, the Au powder of the inorganic component and crystallized quartz powder and the grain size of the quartz powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] The present invention relates to thick film conductor pastes, and more particularly to via fill conductors for ceramic multilayer substrates.

[Conventional technology]

Conventionally, via fill conductors for ceramic multilayer boards often use thick film conductor paste for pattern formation, and are used differently depending on the metal system of the ceramic or multilayer board.

As a general example of use, in alumina ceramic multilayer substrates, tungsten (W), which is a metal with a higher melting point than the sintering temperature of alumina ceramic, is used.

The main material used is molybdenum (MO), with a sintering aid added as an additive and mixed with an organic vehicle.

In thick film multilayer substrates, the conductors are silver (Ag), silver palladium (AgPd), platinum (Pt), and gold (Au).

Due to the use of gold (Au) and copper (Cu), the same metals as the conductors are often used in via-fill conductors, and these metals are used as the main material and sintering aids are added as additives. A paste made by kneading , metal oxide, amorphous Niblas frit, etc. with an organic vehicle is used. Also, in recent low-temperature sintered multilayer substrates, silver palladium is used as the printed conductor on the green sheet.

The main materials are gold and copper, and sintering aids such as metal oxide and amorphous glass are added as additives, and the amount of additives added is controlled according to the firing characteristics of the green sheet to sinter the green sheet. We have obtained a via-fill conductor that matches the shrinkage rate.

[Problem that the invention is trying to solve]

However, in the above-mentioned conventional technology, the via-fill conductor is generally made of a highly conductive metal, as described above, in order to lower the conductor resistance of the circuit. Ag, and Ag
/Pd-based conductors are well known. However, the thermal expansion coefficient of a highly conductive metal is Ag#190X10
/1? :, copper about 165XIO/℃, alumina ceramic 60~80X10/C, glass ceramic 30~
It is large compared to s o x io-'/°C, which causes problems in bonding with aggregates such as ceramic, glue, and glass ceramic blocks. -As an example, we will introduce via fill formation for thick film multilayer substrates.

First, a thick film dielectric paste is printed on an alumina substrate to form a pier hole, and then, after drying the thick film dielectric, an Ag/Pd based conductor paste is filled into the pier hole and dried to form a via fill. In this state, the thick film dielectric and via fill are fired simultaneously. At this time, a gap may be created between the peer hole and the via fill due to the difference in contraction rate and expansion rate during sintering of the dielectric and the via fill. This problem also occurs in low-temperature sintered multilayer substrates, and often poses a quality problem.

To solve these problems, in the prior art, a paste composition is prepared and the shrinkage rate is controlled by controlling the inorganic/organic ratio of the conductive paste. However, increasing the inorganic ratio causes problems in the viscosity characteristics of the paste, and the filling rate of via fill becomes a problem. Regarding the expansion coefficient, efforts have been made to add inorganic components of green roots and thick film dielectrics as fillers into the conductor paste, and to combine ceramics and glass-ceramics with the conductor paste, but the high coefficient of thermal expansion of the filler makes it difficult to achieve the intended purpose. In order to obtain a coefficient of thermal expansion of , a large amount of filler must be added, but there is a problem in that the conductivity decreases and the conductor resistance of the via fill increases.

[Means to solve the problem]

The thick film conductor paste of the present invention is made by dispersing a conductive main material, a low coefficient of thermal expansion filler, and a sintering aid in an organic vehicle.

In particular, the coefficient of thermal expansion is controlled by adding crystallized quartz, the shrinkage rate during sintering is controlled by controlling the particle size distribution of low thermal expansion filler, and the conductor resistance is controlled mainly by conductive material. This problem is solved by controlling the powder particle size distribution of the material and the low thermal expansion filler.

〔Example〕

Next, the present invention will be explained in detail.

Table 1 shows basic composition ratios for explaining the first embodiment of the present invention.

In Table 1, the Au powder as the conductive main material is a spherical powder, and is crystallized with an average particle size of 1 μm. Quartz as a low coefficient of thermal expansion filler is crushed by a ball mill and has an average particle size of 2.
．． The thickness is 5 μm. A sintering aid is added to these inorganic powders, and the mixture is kneaded with an organic vehicle containing ethyl cellulose as a main ingredient and terpineol and fatty acids to form a paste.

In this example, the shrinkage rate during paste sintering was determined based on the blending ratio of the organic vehicle, the inorganic component Au powder, and the crystalline quartz powder, and the powder particle size of the crystalline quartz. Inorganic 915wt% and organic 6.5Wt'1
At a ratio of 6, the volume shrinkage during paste firing is about 35% (comparison between dry state and sintered state), and the specific surface area of crystallized quartz changes by changing the powder particle size of crystalline quartz. You can control the shrinkage rate. In other words, the volume increases by making the crystalline quartz finer. Crystallized quartz does not soften at the sintering temperature of 900°C for this thick-film conductor paste, so its volumetric shrinkage is small, and in the inventor's experiments, the crystallized quartz powder particle size was finely pulverized to 5 μm to 0.5 μm. This made it possible to vary the shrinkage rate from 40% to 28%.

Next, by changing the Au powder particle size, the cohesive force of the Au powder can be changed, and the grain growth during sintering can be made variable. This allows the conductor resistance during sintering of the thick film conductor paste to be made variable. That is, by pulverizing the Au powder, the cohesive force of Au increases, and in the sintering process, the crystallization of Au progresses, grains grow, and the electrical resistance decreases.

The coefficient of thermal expansion will be explained by taking the formation of a via fill in low temperature sintered green 7-toe as an example.

In Fig. 1, the green sheet l is a low-temperature sintered glass ceramic type, and its main composition is B, 03-PbO-
It is made into a sheet by kneading 8i0 glass and an inorganic material with a small amount of alkali metal oxide added with an organic binder. The via fill conductor 2 has the composition shown in Table 1 above.

Pier holes 3 are now formed in the green sheet 1 and filled with via fill conductors by screen printing technology.

A plurality of these 7-sheets are laminated and sintered through a pressure release and binder removal process. In this embodiment, the shrinkage rate of the green sheet is approximately 35 inches, and the thick film conductor paste is also designed to have a shrinkage ratio of approximately 35 inches as explained above.

When sintered in this state, first, in the first half of sintering, the organic components of the green sheet and via fill conductor are decomposed and the binder is removed. The temperature at this time varies depending on the material of the green sheet, but is in the range of about 400 to 480°C.

Next, the glass of the green sheet begins to soften, and then the Au of the via fill conductor progresses to crystallization and grain growth begins.

The temperature at this time varies depending on the amount of alkali metal oxide added to the glass, but is 650 to 750°C, and the temperature at which Au crystallization starts varies depending on the particle size of the Au powder, but is 700 to 800°C.
It is ℃. By starting this Au crystallization, Au
Due to the difference in the expansion coefficients of Au and glass/ceramic, pressure is applied to the pier hole due to the expansion of Au. At this time, the glass of the glass ceramic is softened, and this pressing force is absorbed by the glass ceramic.

In general, Au has a higher coefficient of thermal expansion than glass ceramics, with Au having a coefficient of thermal expansion of 1
70XlO at 7°C and 800°C. Therefore, problems due to the difference in thermal expansion coefficient between Au and glass ceramics occur during the cooling process. In the case of conventional Au-based thick film conductor pastes, amorphous glass is often used for the glass frit.
The coefficient of thermal expansion is about 148XIO/'C800, and it is calculated that a gap of about 9 μm (4.5 μm on one side) is generated between the glass ceramic and the via fill conductor at the time of cooling. Also, since the frit is amorphous glass, it melts during sintering, so the specific surface area of the glass decreases and the packing density improves, but on the other hand, the void between the glass ceramic and the via fill conductor is larger than the calculated value 9 According to the inventor's evaluation, voids of about 30 to 50 μm are generated.

In this example, since crystalline quartz is used as the filler, it has low thermal expansion and does not melt at the sintering temperature of glass-ceramic. The calculated value is approximately 8 μm (4 μm on one side)
), and it was confirmed that this value was almost the same because there was no shrinkage of the filler.

〔Effect of the invention〕

Overall, the present invention as described above has the effect that by adding a low coefficient of thermal expansion filler to the thick film conductor paste, the gap between the glass cellar i7 and the via-fill conductor can be made small, and a high-quality via-fill conductor can be formed. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of a low-temperature sintered multilayer substrate for explaining the characteristics of the thick film conductor paste of the present invention. l... Green sheet, 2... Via fill conductor, 3... Pier hole.

Claims (1)

[Claims] Thick film conductor paste featuring conductive coverage, low thermal expansion filler, and sintering aid dispersed in an organic vehicle.