JPS6224392B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to a method for obtaining a silicon nitride (hereinafter referred to as Si ₃ N ₄ ) sintered body having a metallized surface, and more specifically, a method for obtaining a silicon nitride (hereinafter referred to as Si ₃ N _{4 )} sintered body having a metallized surface, and more specifically, to Si ₃ N ₄
The present invention relates to a method for forming a cermet layer that has a high chemical bonding strength with a sintered body and also has good electrical conductivity and can be effectively metalized.

Hot-pressed Si ₃ N ₄ sintered bodies have low surface porosity and are chemically extremely stable, making it difficult to metalize them. The most important things in this metallization are the leakage of the metal to Si ₃ N ₄ and the thermal expansion coefficient of the metal being close to that of Si ₃ N ₄ , but unfortunately there is no way to satisfy these two properties at the same time. There isn't.

The currently applied methods for metallizing Si ₃ N ₄ sintered bodies include (a) applying an aqueous metal salt solution to the surface of the sintered body and then firing it in a reducing atmosphere to precipitate the metal and metallize it; (b) A method in which a Mo-Mn or Mo-W paste is baked onto the surface of a sintered body to obtain a metallized surface and metallization is performed on the surface.
Once sintered, Si ₃ N ₄ has a small surface porosity and is chemically stable as described above, so it cannot be sintered with the metallized layer by either of the methods (a) and (b) above. The chemical bonding force with the body is extremely small, and when a metal lead is brazed onto this metallized layer, if an external force is applied to the lead in the direction of peeling, the metallized layer will peel off more easily than the sintered body that is the base body. It exposes the fatal flaw that it is.

The present invention relates to a method for obtaining a Si ₃ N ₄ sintered body with such a defect-free metallized surface, and the general solution is to form the metallized surface after sintering the Si ₃ N ₄ . Unlike the previous idea that the metallized surface is formed by sintering the special cermet powder for forming the metallized surface and the base Si ₃ N ₄ powder by hot pressing, the cermet layer and the cermet layer are formed. The main point is that the Si ₃ N ₄ sintered body has a high chemical bonding strength with each other, and the cermet itself has good electrical conductivity.

The present invention will be explained in further detail below.

The present invention consists of the following four steps. () Step of obtaining cermet powder, () Step of pressing (pressing) Si ₃ N ₄ powder into a desired shape, () Pressing and laminating the cermet powder on the Si ₃ N ₄ molded body of () Alternatively, a step of forming a paste of cermet powder and layering it on the Si ₃ N ₄ molded body, and () a step of sintering the whole into a single piece by hot pressing.

The most important step in the _present invention is the step () of obtaining cermet powder, which consists of _{Si 3} N ₄ powder 50-80% (by weight, the same hereinafter) and Wc powder + Co powder 50-20%. - This is the process of obtaining Wc-Co based cermet powder by mixing. Among cermet powders, as metal powders, it is ideal that they have a chemical affinity with Si ₃ N ₄ (there is leakage), have good sinterability on their own, are easy to electrolytically plate, and are compatible with brazing metals. conditions, and various metal compounds that seem to meet this line, such as TiC-Ni-Mo system,
Prior to the present invention, Cr-Al ₂ O ₃ system, TiC-TiN-Ni-Mo system, etc. were combined with Si ₃ N ₄ powder and sintered (hot press sintering), but TiC-Ni-Mo system was In _addition to poor mold releasability from the press mold, which is a carbon mold, the mold itself has poor sintering properties, resulting in numerous pores and _cracks . In addition to being defective, there is almost no chemical bonding with the Si ₃ N ₄ sintered body, and in the TiC-TiN-Ni-Mo system, there is no bonding with the Si ₃ N ₄ sintered body. Moreover, it was found that there were drawbacks such as burning into the carbon mold. Despite these failures, it was discovered that the Wc--Co system is a suitable material in combination with Si ₃ N ₄ within the above-mentioned limited range. That is, if the Si ₃ N ₄ powder in the cermet powder in the present invention is less than 50%, the thermal expansion of the cermet layer will be too large and the base Si ₃ N ₄
Cracks tend to creep into the sintered body and the cermet layer, and if it exceeds 80%, the cermet layer loses its metallic properties, causing problems in Ni plating, brazing, etc.

Therefore, the above composition range is necessary to achieve the purpose.

Furthermore, in this case, it is more desirable that the content (wt%) of the Co powder to the Wc powder+Co powder is 1 to 10% for the following reason. That is, when the Co content is less than 1%, it has a somewhat negative effect on the sinterability of the cermet layer, and when it exceeds 10%, the Co content is less than the cermet layer.
This is because they each have a tendency to ooze out.

The cermet powder is mixed using an appropriate mixing means, such as a mortar mixer or a wet vibrating mill.
After mixing Co powder and Si ₃ N ₄ powder in MeOH, MeOH was removed, and about 4% solid paraffin was added as a binder in _carbon tetrachloride CCl ₄ . A mixing method in which the cermet powder is removed and sieved through 40 mesh passes to form the final cermet powder was applied as an example.

Process () is a process in which powdered Si ₃ N ₄ is formed into the desired shape under relatively low pressure in cold conditions, and Si ₃ N ₄ is 80%
Si ₃ N ₄ sintering composition containing more than 400~500
Lightly press with Kg/cm ² and form into desired shape.

In step (), the cermet powder obtained in step () is laminated under pressure to an appropriate thickness on the Si ₃ N ₄ molded body obtained in step (), or the powder is made into a paste with a paste. In the former case, it is desirable to add a small amount of a binder such as solid paraffin to improve moldability. The former is preferable when considering the bondability with the Si ₃ N ₄ sintered body that is the matrix or to obtain a cermet layer with a large thickness, and the latter is preferable to obtain a cermet layer with a complicated shape. Note that the above-mentioned layering of the powder also includes placing a cermet molded product obtained by press molding on the Si ₃ N ₄ molded body.

Step () is a step in which the whole obtained in step () is sintered into one piece by hot pressing, and the hot pressing is carried out in an ordinary carbon mold. The hot pressing conditions may be substantially the same as those for Si ₃ N ₄ and no special conditions are required.

Next, to explain the sintered body having the metallized surface obtained through the above steps () to (), FIG. 1 is a schematic perspective view thereof, and FIG. 2 is the Si ₃ N ₄ of FIG. 1.
This is a photograph (×250) showing the bonding boundary between the sintered body (base body) and the cermet layer. As shown in Figure 1, _{Si 3 N 4 -Wc} -Co The cermet layer 2 is integrally sintered to obtain the sintered body of the present invention. A photograph (x
2.0K) is shown in Figure 3, but from Figure 2, the sintered body 1
and cermet layer 2 are completely bonded, and the third
It can be seen from the figure that the cermet layer 2 itself is almost completely sintered without any pores. It is also clear that Co and W diffuse into the sintered body 1 from the cermet layer 2 and form a strong bond.

Furthermore, since the cermet layer 2 itself is sintered with Wc and Co particles filled between ceramic (Si ₃ N ₄ ) particles, it retains strong metallic properties and maintains good electrical conductivity. ing.

Since the electrolytic Ni plating layer is often placed on the cermet layer 2 of the cermet and ceramic composite sintered body 1 obtained in this way, the metal lead is bonded by pouring a brazing material on this plating layer, which is different from the conventional method.
A lead lead-out structure with a bonding strength so strong that cannot be obtained with the metallization method applied to Si ₃ N ₄ sintered bodies can be obtained. Using Ag solder as the brazing material, when the Cobar metal fitting was pulled in the peeling direction, a value of 130 Kg/cm2 ^or more was obtained, and in this case, there was no peeling on the metallized surface and the Si ₃ N ₄ sintered body 1
It was on the verge of peeling off due to cracks occurring from within. Examples of the present invention are listed below.

(Example 1) Process (): 49% Wc powder (9.8g) and 1% Co powder
Si ₃ N ₄ powder (already mentioned "SN220") was added to 50% (10 g) of mixed powder (0.2 g).
g) was prepared and mixed in a mortar to obtain a cermet powder. A small amount of solid paraffin was added to this powder.

Step (): Similarly, only Si ₃ N ₄ (SN220) was placed in a mold and lightly pressed under a pressure of 445 kg/cm ² to obtain a molded body as shown in FIG.

Step (): Pour the paraffin-containing cermet powder from Step () above to a thickness of about 4 mm.
It was laminated under pressure (1335 Kg/cm ² ) onto a Si ₃ N ₄ molded body.

Step (): The molded product from Step () is filled into a carbon mold with a BN mold release agent and heated at 1660℃, 430Kg/
Hot press firing was carried out for 2 hours at a temperature and pressure of cm ² .

Metallization and lead derivation: Electrolytic Ni plating was applied to a thickness of 1μ on the cermet layer that had been sintered and integrated in step (), and a cover metal fitting was brazed thereon almost horizontally while melting Ag solder.

Peeling test: When the above-mentioned cover metal fitting was peeled off in the horizontal direction, a peel strength of 130 kg/cm ² was obtained.

(Example 2) Process (): For 20% of a mixed powder consisting of 49% Wc powder and 1% Co powder, prepare 80% Si ₃ N ₄ powder ("SN220" as described above) and mix both in a mortar. A cermet powder was obtained. A small amount of solid paraffin was added to this powder.

Process (): Si ₃ N ₄ (SN220) at a pressure of 445
The mixture was lightly compacted at a pressure of Kg/cm ² to obtain a molded product as shown in FIG.

Step (): Methanol was added to the paraffin-containing cermet powder of Step () to form a paste, which was then laminated under pressure (1335 Kg/cm ² ) on the Si ₃ N ₄ molded body to a thickness of approximately 5 mm.

Step (): The molded product from Step () is filled into a carbon mold with a BN mold release agent and heated at 1660℃, 430Kg/
Hot press firing was carried out for 2 hours at a temperature and pressure of cm ² .

Metallization and lead derivation: Electrolytic Ni plating was applied to a thickness of 1μ on the cermet layer that had been sintered and integrated in step (), and a cover metal fitting was soldered almost horizontally on top of it while melting Ag solder.

Peeling test: When the above-mentioned cover metal fitting was peeled off in the horizontal direction, a peel strength of 100 kg/cm ² was obtained.

As already understood from the description, in the present invention, the Si ₃ N ₄ -Wc-Co based cermet layer and the Si ₃ N ₄ sintered body as the base material are sintered into one piece by hot pressing. This enables the cermet layer to be chemically strongly bonded to the Si ₃ N ₄ sintered body, and at the same time improves the electrical conductivity of this cermet layer, which provides advantages that could not be obtained with conventional metallization methods. The effects of the present invention are remarkable, such as making it possible to join metal materials with a high peel strength, and also increasing productivity as it can be sintered into one piece by hot pressing in the manufacturing process.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of a sintered body obtained by the present invention, and FIG. 2 is a substitute drawing showing the state of the bonding boundary between the cermet layer and the sintered body in FIG. 1. Micrograph (×250), Figure 3 shows the junction boundary.
This is an XMA ray analysis photograph (×2.0K). Explanation of symbols: 1...Si ₃ N ₄ sintered body, 2... Cermet layer.

Claims (1)

[Claims] 1 Si ₃ N ₄ powder 50-80% (by weight), WC powder and Co
The process () of obtaining a cermet powder with a total powder content of 50 to 20% (by weight), the process () of pressure-molding the Si ₃ N ₄ powder into a desired shape, and the process () obtained by this process () The above cermet powder is laminated under pressure on the Si ₃ N ₄ molded body, or the cermet powder is made into a paste and layered on the Si ₃ N ₄ molded body (), and the whole is hot pressed. A method for manufacturing a silicon nitride sintered body having a metallized surface, comprising a step of integrally molding (). 2. The manufacturing method according to claim 1, wherein the content of the Co powder based on the (WC+Co) powder is 1 to 10% (by weight).