JPH02256106A - Copper paste for thick film - Google Patents

Abstract

PURPOSE:To improve adhesion strength especially after aging without degrading wettability to solders by composing the title paste with a copper powder, a glass powder, titanium nonoxide, and an organic vehicle. CONSTITUTION:The title paste is comprised of a copper powder, a glass powder, titanium monoxide (TiO), and an organic vehicle. Since TiO suppresses fluidity of fuses glass properly in Cu paste firing process, glass does not all move to a substrate side a proper amount of the glass is retained in a Cu film. Consequently, after firing the paste, glassy material is little in the surface area of the conductive film and between a Cu metal layer in the inside of the film and a glass layer close to the substrate, a metal-glass matrix structure where the glassy material is inserted density in the sintered Cu powder is formed. By this method, without degrading wettability to solders on the surface of the conductive film and conductivity of the film, adhesion strength of the film to the substrate is improved and especially the strength does not degrade even after the film is aged after firing process, and a high quality Cu conductive film is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive copper paste for forming a thick film copper conductor with excellent adhesion on an insulating substrate by baking.

In recent years, base metals such as Cu and Ni, which are fired in an inert atmosphere such as an N2 atmosphere, have attracted attention as thick film conductors for manufacturing wiring conductors for electronic circuits and electrodes for capacitors, resistors, etc. ing. In particular, Cu is an excellent conductive material in terms of its physical and electrical properties, and has been put to practical use as a substitute material for noble metals, but there is still room for improvement in conductivity, adhesive strength, and the like. In particular, after soldering onto a conductor made of fired Cu and a glassy binder and performing a high-temperature storage test, the adhesive strength (aging strength) decreased significantly, which caused problems in terms of reliability. Furthermore, solder wettability is usually a contradictory property to adhesive strength, and attempts to increase adhesive strength tend to impair solder wettability.

Therefore, one of the challenges is to improve adhesive strength without reducing solder wettability.

To improve the adhesion strength of copper conductors, especially aging strength,
Various studies have been made in the past. For example, special public service in Showa 61
JP-A-51361 discloses that adding Bi2O3 and ZnO to a conductive composition improves solder wettability and strength. In addition, Japanese Patent Publication No. 62-46588 suppresses the decrease in adhesive strength by using alloy powder in combination, and Japanese Patent Publication No. 63-232201 considers the particle size and blending amount of the powder used. There is.

Furthermore, in Japanese Patent Application Laid-Open No. 6:3-131405, Fe01Mn05v203,
Cr2O3, CeO2, 5b2o3, As2O5, Ni
By adding low-order oxides of polyvalent metals such as O, SnO, and Cu2O, surface oxidation of Cu powder is suppressed,
It is also described that it improves solder wettability.

JP-A-63-15866 discloses titanium dioxide Ti
The present disclosure discloses a Cu paste doped with 02 that has good adhesion to the inner wall of a laser-drilled through hole.

In recent years, there has been a strong demand for circuit miniaturization and cost reduction, and there has been a demand for smaller and smaller electrodes and conductor patterns, as well as thinner conductor films. There is a demand for a Cu conductor that has stronger properties, less deterioration over time, and even better conductivity. However, even with the above-mentioned conventional techniques, the current situation is that fully satisfactory characteristics have not yet been obtained.

The purpose of the present invention is to provide a highly reliable Cu paste that has further improved adhesive strength with a substrate after aging to 1,v without impairing other properties such as solder wettability. shall be.

Means for Solving Problem 0 The present invention provides copper powder, glass powder, titanium monoxide,
The amount of thick film copper paste consisting of an organic vehicle and titanium monoxide is 3.0 parts by weight per 100 parts by weight of Cu powder.
2. The thick film copper paste according to claim 1, wherein the thick film copper paste is less than or equal to parts by weight.

The Cu powder, glass, and organic vehicle are not particularly limited as long as they are commonly used for this type of thick film conductive paste. The blending amount of the glass powder is about 0.5 to 10 parts by weight per 100 parts by weight of the Cu powder.

The paste of the present invention may further contain additives used in ordinary Cu pastes, such as bismuth oxide, copper oxide, manganese oxide, and vanadium oxide.

By blending titanium monoxide TiO into the color gamut Cu paste, adhesive strength, especially aging strength, is significantly improved without substantially reducing solder wettability and conductivity.

TiO is considered to have the effect of appropriately suppressing the fluidity of molten glass when firing the Cu paste.

Therefore, all of the glass does not move toward the substrate, and an appropriate amount is retained in the sintered Cu layer. Therefore, after firing, there is less glass near the surface of the conductor film, and the part between the Cu metal layer inside the film and the glass layer near the substrate contains sintered Cu.
A strong metal-glass matrix structure is formed in which the glass is densely embedded between the powders, and the contact area between the glass layer and the metal layer is large, and the two are firmly bonded together, creating an ideal conductor film structure. Become.

As a result, the adhesive strength with the substrate is greatly improved with almost no effect on the solder wettability or conductivity of the conductor surface, and the strength does not deteriorate compared to conventional methods, especially when subjected to thermal aging after baking. A very good Cu conductor film is formed. Further, even when the film thickness is small, such a structure can be easily created, so that a conductor with high adhesive strength can be formed.

Furthermore, TiO functions as an oxygen scavenger to adjust the amount of O2 present in the firing atmosphere, and has the effect of reducing process sensitivity. Therefore, there is no effect even if Ti 02 is added. It has been confirmed that a portion of TiO changes to TlO2 and Ti 20a after firing.

Regarding the amount of TiO mixed, if Cu powder with small particle size and high filling properties is not used, the S structure of the sintered body will become denser and the voids in the film will become smaller, reducing the amount of glass required. ,
If less TiO is used, or if a bulky Cu powder is used, the voids in the Cu sintered body will become larger, increasing the amount of glass required, and in order to obtain a sufficient effect, it is not necessary to mix a large amount of TiO. must not. However, if too much TiO is added, solder wettability tends to deteriorate, so the amount added is desirably 3.0 parts by weight or less per 100 parts by weight of Cu powder.

The glass used in each Example and Comparative Example is a crystallized glass having the composition shown below.

8203 20.4% by weight zno23.8II B120354.3tNOMOO31,2I+ Mn○20.1 horn T1020.2 horn Example 1 C of average particle size 1.2IJIn (measured by B, E, T, method)
u powder ioo, o parts by weight glass powder 6.0 parts by weight TiO powder 0.5 parts by weight organic vehicle 11.0 parts by weight A paste having the above composition was spread on an alumina substrate so that the fired film thickness was about 15 μm. After screen printing a pattern of 5rnm x 1.5+++m and drying it at 140℃ for 10 minutes, using a far-infrared firing oven, it was printed at a printing temperature of 900℃ and 60℃ in an N2 atmosphere.
A Cu conductor was formed by firing in a minute cycle, and the following tests were conducted. The results are shown in Table 1.

Solder wettability: A solder ball with a diameter of 2.0 mm was placed on the crotch of the conductor, and the spread rate of the solder ball was examined after being left at 230° C. for 30 seconds.

Initial adhesion strength: After a solder-plated copper wire was hand-soldered with 5n-PB to the conductor film, the lead wire was pulled perpendicularly to the substrate, and the strength was measured when the conductor was peeled off from the substrate.

Aging Strength (2) After soldering, the adhesive strength after aging at 150° C. for 100 hours was measured in the same manner as the initial strength.

The resistance value was measured using a pattern of 0.6111 m wide x 60 long fences, and was converted to a film thickness of 15 μm.

Examples 2 to 3 Cu pastes were prepared in the same manner as in Example 1 except that the amounts of TiO were 1.0 parts by weight and 1.5 parts by weight, respectively, and baked on an alumina substrate. The resistance value, solder wettability, initial adhesive strength, and adhesive strength after aging of the obtained Cu conductor were measured, and the results are also shown in Table 1.

Comparative Example 1 A Cu paste was prepared in the same manner as in Example 1 except that Ti0 was not mixed, and baked onto an alumina substrate. Table 1 shows the characteristics of the obtained Cu conductor.

Table 1 As is clear from Table 1, the addition of TiO significantly improves both initial strength and aging strength, and has almost no effect on conductivity and solder wettability.

Example 4 Average particle size 0.8. Cu powder (measured by B, E, T method) 100.0 parts by weight Glass powder
3.3 parts by weight TiO powder 0.2 parts by weight Organic vehicle 16.0 parts by weight A paste having the above composition was baked onto an alumina substrate in the same manner as in Example 1 to form a Cu conductor.

The resistance value, solder wettability, initial adhesive strength, and aging strength of the obtained Cu conductor were measured, and the results are shown in Table 2.

Examples 5 to 7 Cu pastes were produced in the same manner as in Example 4, except that the amount of TiO was as shown in Table 2. For each Cu conductor obtained by baking on an alumina substrate, the resistance value,
Solder wettability, initial adhesive strength, and adhesive strength after aging were measured, and the results are also shown in Table 2.

Comparative Example 2 A Cu paste was produced in the same manner as in Example 4 except that TiO was not mixed, and baked on an alumina substrate. Table 1 shows the characteristics of the obtained Cu conductor.

Comparative Examples 3 to 7 Cu pastes were produced in the same manner as in Example 5, except that the metal oxides shown in Table 2 were used instead of TiO. Table 2 also shows the characteristics of the Cu conductor obtained by baking on the alumina substrate.

As is clear from Table 2, the C of the present invention added with TiO
The u-paste has lower initial strength and
Both aging strength has been significantly improved. Furthermore, it can be seen that it is extremely superior when compared to the case where conventionally used lower oxides of metals such as Cu2O, NiOlMNlol, Coo, etc., or PbO are added.

As described above in Kitanene and Marume, the Cu paste of the present invention has excellent solder wettability and adhesive strength with the substrate, especially adhesive strength after heat aging.
It is extremely superior to conventional materials and exhibits good adhesion even when the film thickness is thin, making it extremely reliable as a conductor material for high-density circuits.

Claims (1)

[Claims] 1. A thick film copper paste consisting of copper powder, glass powder, titanium monoxide, and an organic vehicle. 2. The thick film copper paste according to claim 1, wherein the content of titanium monoxide is 3.0 parts by weight or less per 100 parts by weight of Cu powder.