JP2795467B2 - Good adhesive metal paste - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a metal paste containing a special flux. In more detail, a metal paste is printed on a ceramic substrate in a specific shape using a normal screen technique, and then the metal paste is heated to a high temperature, and a part of the paste is burned off and sintered to a ceramic substrate. The present invention relates to a paste composition that significantly improves adhesion to a ceramic substrate in a metal paste to be used as a hybrid circuit while leaving a pattern.

BACKGROUND OF THE INVENTION Metal pastes consist essentially of conductive metal, glass, metal oxide powders and vehicles.

Among them, the conductive metal sinters to serve as a conductor, and the glass and the metal oxide contribute to the adhesion between the conductor and the ceramic substrate.

The vehicle is also used to make the powder into a paste to provide desired printability and stability.

Among the physical properties required for these metal pastes, the adhesive strength is always an issue. The strength after aging is important, as well as the initial bonding, and the area of the bonding pads for mounting various components tends to be smaller than before, especially in the recent high-density mounting flow.
There is an increasing need to increase the bonding strength.

Conventionally, it is well known to add a glass powder or a metal oxide for bonding a fired metal paste. A well-known metal oxide is bismuth oxide. It is well known that bismuth oxide chemically reacts with alumina as a substrate, and is blended in many pastes. Further, the glass penetrates into the sintered layer of the metal in a wedge shape, and forms a physical adhesive layer at the interface with the alumina substrate.

[Problems to be Solved by the Invention] There are the following problems in bonding with bismuth oxide and glass as is known for many pastes. Bismuth oxide forms a strong adhesive layer on the alumina substrate, but the adhesive layer has the disadvantage that it is easily destroyed by the penetration of solder during the aging test, and is easily reduced by the reducing atmosphere during firing. It becomes metallic bismuth and causes a stain phenomenon. To avoid this, if the amount of bismuth oxide is reduced and the amount of glass is increased to cover the decrease in adhesive strength, there are problems such as poor solder wettability and a significant decrease in adhesive strength in a heat cycle test.

[Means for Solving the Problems] The present invention is a metal paste composed of a metal powder, a glass powder, a metal oxide powder and a vehicle, and it is essential that the metal paste contains ZnO powder and TiO ₂ powder as the metal oxide powder. , These Z
The total amount of the nO powder and the TiO ₂ powder is 3 to 5% (% by weight, the same applies hereinafter) of the total amount of the paste, and the TiO ₂ powder is 0.05 to 0.
5% of a metal paste. As the metal powder used here, silver powder, palladium powder, gold powder, nickel powder, zinc powder, a mixed powder thereof, or an alloy powder thereof is preferable. As the glass powder, lead borate or borosilicate glass having a softening point of preferably 300 to 700 ° C., particularly preferably 350 to 600 ° C., can be suitably used, but is not limited thereto. As the metal oxide, in addition to the specific metal oxide powders (ZnO powder and TiO ₂ powder), nickel oxide powder, manganese oxide powder,
Lead oxide powder, cadmium oxide powder, vanadium oxide powder, or the like can be used. As the vehicle, for example, a resin having a high viscosity and thixotropic properties obtained by dissolving a binder resin such as ethyl cellulose or an acrylic resin in a high boiling point solvent such as terpineol or butyl carbitol acetate can be preferably used.
It is not limited to these.

The mixing ratio of each component in the metal paste is preferably 70 to 85% by weight of the metal powder in the paste.
The glass powder is preferably 1 to 5% by weight, particularly preferably 1 to 4%, and the metal oxide powder is the above-mentioned specific metal oxide (ZnO powder and TiO ₂ powder)
Is preferably 3 to 12% by weight, particularly 5 to 10% by weight, and the vehicle is preferably 5 to 25% by weight, particularly 8%.
~ 20% is preferred.

The particle size of each powder is preferably in the range of 0.1 to 10 microns, and particularly preferably in the range of 0.5 to 5 microns from the viewpoint of conductor sintering during baking.

The shape of each powder is not particularly limited in the present invention,
Powders of various shapes such as spherical, flake, or a mixture thereof can be used. However, in order to promote sintering of the conductor at the time of baking, it is preferable to use powders of the above-mentioned shape having excellent monodispersity.

In the present invention, the most important feature is that ZnO powder and TiO ₂ powder are required to be used as the metal oxide powder, and it is notable that the amount of addition is specified. Conventionally, it has been known to mix zinc oxide into a thick film paste. However, if the compounding amount is increased to sufficiently increase the adhesive force, the solder wettability is immediately adversely affected and the compounding amount is limited. Therefore, the contribution to adhesive strength is not as high as bismuth oxide. Tokiko Sho 61-51
JP-A-361 also discloses a composition containing 1 to 3% ZnO in the paste, but recognizes that addition of 3% or more is undesirable. However, from the viewpoint of adhesive strength, it is desirable to add more. We have:
It made in view of the above circumstances, the result of so diligent studies prior art to overcome the disadvantages possessed by, the combination of TiO ₂ powder, ZnO
It has been found that the amount of powder that can sufficiently contribute to the adhesive strength can be achieved without impairing solder wetting, and the present invention has been completed.

ZnO powder, in the process of sintering the paste, prevented sintering of the metal at low temperatures and improved the volatilization of the binder, and melted in the glass, resulting in crystallization, high softening point, and high viscosity of the glass and melted. Prevents glass from migrating to the conductor surface through the sintered grain boundaries, maintains solder wettability, and at the same time contributes to adhesion by forming a strong glass adhesion layer at the interface between the conductor layer and ceramic I do. However, if the ZnO powder is increased to further increase the bonding strength, the temperature for forming the glass becomes too high, and the sintering temperature of the metal becomes lower, which results in inhibiting the sintering. However, by adding TiO ₂ powder at the same time as in the present invention, ZnO
The crystallinity of new glass formed from powder and glass decreases, and even if ZnO powder is mixed to a certain degree or more, vitrification advances at a temperature lower than the sintering temperature of the metal and increases the adhesion strength without adversely affecting solder wetting be able to.

The same effect cannot be obtained by preparing a crystalline glass from ZnO powder and glass in advance and blending it in a paste. This is because such a glass generally has a high softening point and poor fluidity, so that during the firing process, the transition to the interface between the metal layer and the ceramic is slow and an ideal adhesive layer cannot be formed. .

In the present invention, if the total amount of ZnO powder and TiO ₂ powder is less than 3% by weight of the total amount of the paste, there is little effect on the improvement of the adhesive strength, and if it exceeds 5% by weight, the solder wetting is deteriorated. Also, if the TiO ₂ powder is less than 0.05% by weight of the total amount of the paste, it has an adverse effect on solder wetting, and if it exceeds 0.5% by weight, solder wetting is worsened.

Next, a method for producing the metal paste of the present invention will be described.

The metal paste is produced by kneading and dispersing metal powder, glass powder and metal oxide powder in a vehicle.
As a kneading method, for example, a method of preliminarily kneading using a universal stirring mixer and then kneading using a three-roll mill is employed.

Then, for example, this metal paste is screen-printed on an alumina ceramic substrate, and then 150 to 170 ° C.
Dry for 10-15 minutes.

Finally, firing is performed in air or in a nitrogen atmosphere at a temperature of 800 to 900 ° C. for a total cycle time of 40 minutes including a peak temperature holding time of about 5 to 10 minutes.

[Examples] Hereinafter, the metal paste of the present invention will be described based on examples, but the present invention is not limited to the examples.

Examples 1 to 6 and Comparative Examples 1 to 5 The metal powder, metal oxide powder, glass powder and vehicle shown in Table 1 were blended according to the respective formulations, and a universal stirring mixer of this composition (Inoue Seisakusho Co., Ltd.) Was pre-kneaded for 24 hours. Next, this composition was mixed 12 times with a three-roll mill, and then subjected to vacuum defoaming in a universal stirring mixer to obtain a paste. The obtained paste was screen-printed in a suitable pattern on a substrate of 96% pure alumina ceramic (thickness: 0.635 mm), and then dried at 120 ° C. for 10 minutes using a hot air drier. After that, the peak temperature was 85 in a belt furnace in air or nitrogen.
The firing was performed with a profile of 0 ° C. or 900 ° C. and a total cycle time of 40 minutes including a peak temperature holding time of 7 minutes.

The performance of the thick film of the obtained conductor composition was evaluated according to the following method. Table 2 shows the results.

Performance evaluation method (Solder wettability) Print the following pattern, apply flux to the baked substrate, immerse this substrate in a 230 ° C ± 5 ° C solder bath for 3 ± 0.5 seconds, and pull up the pad part of the substrate Good when the solder wet area of the pad is 90% or more of the pad
When it was less than 90%, it was regarded as defective.

Solder: 63% Sn-37% Pb Flux: XA-100 manufactured by Tamura Kaken Co., Ltd. Pattern: 6 x 1mm x 1mm pads x 12 x 2mm x 1mm pads (adhesive strength) Apply flux to the substrate and place it in a solder bath at 230 ℃ ± 5 ℃ for 3 ± 0.5 seconds.
This substrate was immersed and pulled up.

Next, a tin-plated copper wire of 0.8mmφ is soldered with 2mm ×
Attached on a 2mm pad. The sample was pulled at a speed of 10 mm / min by a tensile tester (manufactured by Shimadzu Corporation), and the adhesive strength when the metal paste was peeled from the substrate was measured. As the adhesive strength, both the value before aging (initial strength) and the value after heating at 150 ± 2 ° C. for 250 hours (thermal aging strength) were measured.

Solder: 63% Sn-37% Pb Flux: XA-100 manufactured by Tamura Kaken Corporation Pattern: 8 x 2mm x 2mm pads [Effects of the Invention] The metal paste of the present invention significantly improves the adhesion between the conductor and the ceramic substrate when producing a hybrid circuit, and also provides excellent solder wettability.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shun Okada 5-765-120 Numa, Zushi City, Kanagawa Prefecture (72) Inventor Masami Sakuraba 2 Takenodai, Nagaokakyo City, Kyoto Prefecture (56) References JP-A 64-86404 (JP, A) JP-A-63-207001 (JP, A) JP-A-63-48704 (JP, A) JP-B-61-51361 (JP, B2) (58) Fields investigated (Int. Cl. ⁶⁾ H01B 1/20 H01B 1/16 H05K 1/09 C23C 24/00

Claims (2)

(57) [Claims] 1. A metal paste comprising a metal powder, a glass powder, a metal oxide powder, and a vehicle, which must contain ZnO powder and TiO ₂ powder as the metal oxide powder.
A metal paste, wherein the total amount of nO powder and TiO ₂ powder is 3 to 5% by weight of the total amount of the paste, and the TiO ₂ powder is 0.05 to 0.5% by weight of the total amount of the paste. 2. A metal powder having a weight ratio of 70 to 85% by weight, 1 to 5%.
The metal paste according to claim 1, comprising: glass powder of 3% by weight, 3 to 12% by weight of metal oxide powder, and 5 to 25% by weight of vehicle.