JP2006342057A - Method of manufacturing ceramic sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a ceramic sintered compact, which is utilized for a substrate for electronic component or the like and is large in surface area and thin in thickness, without causing deflection being changed by an extrealy small external strength from the outside. <P>SOLUTION: In the manufacture of the ceramic sintered compact having ≥100 m<SP>2</SP>surface area and ≤2.0 mm thickness, the rate of cooling in the sintering is controlled to ≤20 °C/min in a range of ≥1,000°C. The thickness of a sintering tool to be used in the sintering of the ceramic is preferably ≥1.5 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a ceramic sintered body, and particularly to a method for sintering a ceramic sintered body having a small thickness and a large area.

  Conventionally, when sintering ceramics, the temperature is increased while maintaining a predetermined temperature increase rate to a predetermined temperature, the temperature is maintained for a predetermined time, and then cooled to near room temperature. The cooling rate at the time of sintering is generally that the ceramics and the sintering jig for holding the ceramics are cooled at a speed as fast as possible so that they are not destroyed by the thermal shock caused by cooling. there were.

  The reason for adopting such a cooling rate is that the faster the cooling rate after sintering, the shorter the processing time of sintering, so that the cost of the ceramic sintered body can be relatively reduced. . For this reason, there are very few reports on cooling during sintering of ceramics.

  When the ceramic sintered body is sintered, as described above, if the ceramic sintered body is cooled from a predetermined sintering temperature to near room temperature and taken out from the furnace, the sintered ceramic sintered body may be bent. In the case of a thick ceramic sintered body, the direction of warping of the ceramic sintered body due to bending does not change easily unless a considerable external force is applied, and even if the direction changes, the warp will occur if the external force is released. The direction returns to the state before applying the original external force.

  However, in the case of a ceramic sintered body having a large area and a small thickness, the bending changes with a very small external force from the outside. For example, the direction of warpage can be easily changed by simply changing the direction of the ceramic sintered body, or after changing the direction, the direction of the direction can be changed by applying a little external force to the convex surface of the warp, and even after releasing the external force. Continue to maintain the direction of the warp.

  Ceramics that are baked as described above, depending on the application and conditions of use, may cause inconveniences such as the substrate itself being deformed by slight vibrations. It cannot be used for component boards.

  In view of such conventional circumstances, the present invention provides a method for easily producing a ceramic sintered body that does not bend and changes with an extremely small external force even when the area is large and the thickness is small. The purpose is to do.

  In the present invention, the bending of the ceramic sintered body having a predetermined area or more and a predetermined thickness or less can be eliminated by optimizing the cooling rate during the sintering of the ceramic.

That is, the method for producing a ceramic sintered body provided by the present invention is a method for producing a ceramic sintered body having an area of 100 cm ² or more and a thickness of 2.0 mm or less, and the cooling rate during the ceramic sintering is 20 It is characterized by being not more than ° C / min.

  In the method for producing a ceramic sintered body according to the present invention, a temperature range in which the cooling rate is 20 ° C./min or less is 1000 ° C. or more. Moreover, when the thickness of the ceramic sintered body is 1.0 mm or less, the temperature range in which the cooling rate is 20 ° C./min or less is preferably 1200 ° C. or more.

  In the method for producing a ceramic sintered body according to the present invention, it is preferable that the thickness of the sintering jig used for sintering the ceramic is 1.5 mm or more.

  ADVANTAGE OF THE INVENTION According to this invention, about the ceramic sintered compact with a large area utilized as an electronic component board | substrate etc. and thin thickness, the bending rate which changes with the very small external force from the outside is controlled in the cooling rate at the time of sintering. Can be easily eliminated.

According to the present invention, when the area of the ceramic sintered body is 100 cm ² or more and the thickness is 2.0 mm or less, the cooling rate after sintering is set to 20 ° C./min or less to obtain the ceramic sintered body obtained. Deflection can be eliminated. When the cooling rate during sintering of the ceramic is higher than this, the ceramic sintered body is bent.

  Although the cause is not clear, it is presumed to be due to a temperature difference between the center portion and the end portion of the sintered body during cooling during ceramic sintering. In other words, the furnace temperature is generally considered to be almost uniform until just before the start of cooling, but since cooling is generally performed from the end of the sintered body, A temperature difference inevitably occurs at the end. Moreover, it is considered that the ceramic itself has some deformability near the sintering temperature. For this reason, when cooling of the ceramic sintered body is started, first, volume shrinkage occurs due to cooling at the end portion. At this time, the volume shrinkage amount is relatively high because the temperature is higher at the center portion than at the end portion. Becomes smaller. As a result, it is presumed that the difference in volume shrinkage between the end portion and the central portion becomes a stress, and the deformation is caused by the deformability of the sintered body central portion.

As described above, since the major cause of the bending is a temperature difference generated between the end portion and the center portion when the ceramic sintered body is cooled, the shape of the sintered body greatly affects. As an influence of the sintered body shape, firstly, the area of the ceramic sintered body can be mentioned. That is, a sintered body having a large area is apt to bend because a temperature distribution during cooling is inevitably increased. Specifically, it has been found that when the area of the ceramic sintered body exceeds 100 cm ² , the sintered body is likely to bend.

  The bending is also affected by the thickness of the sintered body. In a sintered body having a thickness exceeding 2.0 mm, heat transfer in the sintered body is relatively easy during the cooling process, and thus the above-described bending is difficult to occur. On the other hand, when the thickness is 2.0 mm or less, the amount of heat transferred in the sintered body is reduced, so that a temperature distribution is likely to occur during cooling, which tends to cause bending. Further, when the thickness is thin, the strength of the ceramics at a high temperature is relatively low, and the ceramic is easily deformed.

  From the above, it is possible to reduce the bending that occurs in the sintered body by cooling while reducing the temperature difference between the central portion and the end portion of the sintered body. That is, by reducing the cooling rate, it becomes possible to reduce the temperature difference between the center and the end of the sintered body, thereby reducing the difference in volume shrinkage between the center and the end. The stress generated in the body can be reduced to eliminate bending.

  Specifically, the cooling rate after sintering is set to 20 ° C./min or less. When the cooling rate exceeds 20 ° C./min, the temperature difference between the central portion and the end portion in the sintered body increases, and a shrinkage difference occurs in each portion of the sintered body during cooling, and bending tends to occur.

  Moreover, it is preferable that the temperature range of the sintered compact which makes a cooling rate 20 degrees C / min or less is 1000 degreeC or more. That is, it is preferable to cool at a cooling rate of 20 ° C./min or less until the sintered body is cooled to at least 1000 ° C. In the temperature range of 1000 ° C. or higher, ceramics are considered to have a certain degree of deformability. Therefore, the cooling rate is decreased in the temperature range of 1000 ° C. or higher, which is considered to have deformability, and the temperature distribution in the sintered body. It is possible to suppress the occurrence of bending by reducing the length.

Moreover, in a ceramic sintered body having an area of 100 cm ² or more and a thickness of 1.0 mm or less, the temperature range in which the cooling rate is 20 ° C./min or less can be set to 1200 ° C. or more. It is. Although depending on the jig used, a commonly used boron nitride jig has a lower thermal conductivity than the ceramic sintered body. Therefore, when using a boron nitride jig having a thickness of 2 mm or more, if the thickness of the ceramic sintered body is reduced, the influence of the heat capacity of the boron nitride jig is increased. It becomes possible to make the temperature range which is less than or equal to 1200 ° C. or higher.

  Further, in the ceramic sintered body having a large area and a thin thickness according to the present invention, the occurrence of bending is particularly caused when the thermal conductivity is 50 W / m · K or more and the specific heat is 0.75 J / g · K or less. It is remarkable. The reason for this is that when the sintered body has a high thermal conductivity, the outer periphery of the sintered body is heavily dissipated to the outside due to the effect of the cooled atmosphere during cooling after sintering. Thus, it is conceivable that the heat transfer inside the sintered body is hindered by the influence of the shape that the sintered body itself has a large area and a small thickness.

  Moreover, the heat transfer within the sintered body should be relatively easy due to the high thermal conductivity. However, as estimated from the experimental results in the present invention, if the thermal conductivity of the sintered body increases, the heat dissipation inside the sintered body is superior to the heat transfer inside the sintered body, and the temperature at the end of the sintered body Is lower than the inside, it is presumed that the occurrence of bending is promoted. In addition, since the thermal conductivity of the sintered body tends to be relatively low when the temperature is low, the influence of the thermal conductivity on the sintered body temperature distribution is not reduced in the cooling process during sintering. It is also speculated that there is no.

  As for the specific heat, the smaller the specific heat, the smaller the heat capacity of the sintered body, so the cooling effect against heat dissipation from the end of the sintered body to the outside increases, and the center of the sintered body and A temperature difference is likely to occur at the end. As a result, the smaller the specific heat, the easier it is to bend. From the above, the sintered body having a specific heat of 0.75 J / g · K or less is likely to be bent.

  However, according to the method of the present invention, the cooling rate can be controlled even in the case of a ceramic sintered body having a thermal conductivity of 50 W / m · K or more and a specific heat of 0.75 J / g · K or less. Therefore, the occurrence of bending can be eliminated.

  Further, regarding a sintered body whose main component of ceramic is aluminum nitride, silicon nitride, or silicon carbide, since the thermal conductivity is relatively high and the specific heat is also small, the sintered body is likely to be bent. However, it is possible to eliminate the occurrence of bending of the ceramic sintered body containing these as a main component by controlling the cooling rate by the method of the present invention.

  Further, since the bending is due to the influence of the cooling rate during cooling, it is also affected by the sintering jig that indirectly affects the cooling rate. That is, when the thickness of the sintering jig is large, the heat is relatively smoothly transferred in the jig, so that the occurrence of bending acts in a direction that is alleviated. Specifically, although depending on the type of jig to be used, using a sintered jig having a thickness of about 1.5 mm or more generally has an effect of reducing the bending of the sintered body.

  A predetermined amount of sintering aid, organic binder, and solvent are added to each powder of aluminum oxide, aluminum nitride, silicon nitride, and silicon carbide, which are the main raw materials, and after ball mill mixing, it is determined by the doctor blade method. The sheet was formed so as to have a thickness of. The composition of each powder at this time is shown in Table 1 below.

  Each sheet formed as described above was cut so that the size of the sintered body was 8 × 8 × 0.25 cm. Next, each of these sheets was degreased at 800 ° C. in nitrogen, further degreased under the conditions shown in Table 2 below, and then sintered under the same conditions as shown in Table 2. The obtained ceramic sintered bodies were measured for thermal conductivity and specific heat. The results are shown in Table 2 below. The thermal conductivity and specific heat were both measured by the laser flash method. For all the sintering, a boron nitride sintering jig having a thickness of 2 mm was used.

  Next, the results of evaluating the bending of the ceramic sintered body obtained by producing sintered bodies of various shapes under the above-described additional degreasing and sintering conditions and changing the cooling rate under the sintering conditions. Are shown in Tables 3 to 6 for each sintered body. In the cooling, cooling was performed at the indicated cooling rate above the temperature shown in the slow cooling temperature range of Table 3, and furnace cooling below the temperature shown in the slow cooling temperature range.

The bending of each ceramic sintered body obtained was evaluated by adjusting the force required when holding the both ends of the sintered body and changing the direction of warping. That is, ◎: Ceramics with no bending.
○: Slightly bent by applying external force.
Δ: The direction of bending easily changes when an external force is applied.
X: The direction of bending (warping) changes by simply turning the ceramic held horizontally upside down.

  As can be seen from the above results, for a sintered body having a large area and a small thickness, the degree of bending that occurs during cooling of sintering can be improved by slowing the cooling rate. In particular, it can be seen that the effect of preventing bending by slow cooling is remarkable for ceramics having high thermal conductivity and low specific heat.

  Furthermore, in order to confirm the effect of the thickness of the sintering jig, the sintered body of 2-2 in Table 2 above was sintered by changing the thickness of the sintering jig made of boron nitride. Slow cooling was performed under the conditions shown. The bending of each obtained sintered body was evaluated in the same manner as described above, and the results are also shown in Table 7.

  From the above results, it can be seen that the degree of bending of the obtained sintered body varies depending on the thickness of the sintering jig to be used. Further, when the thickness of the sintering jig is 0.1 cm or less, there is a tendency that the variation in the degree of bending that occurs in the sintered body increases.

Claims (6)

A method for producing a ceramic sintered body having an area of 100 cm ² or more and a thickness of 2.0 mm or less, wherein the cooling rate during ceramic sintering is 20 ° C./min or less. Production method.   The method for producing a ceramic sintered body according to claim 1, wherein a temperature range in which the cooling rate is 20 ° C / min or less is 1000 ° C or more.   The ceramic sintered body according to claim 1 or 2, wherein the ceramic sintered body has a thickness of 1.0 mm or less and a temperature range in which the cooling rate is 20 ° C / min or less is 1200 ° C or more. Body manufacturing method.   The method for producing a ceramic sintered body according to any one of claims 1 to 3, wherein a thickness of a sintering jig used at the time of ceramic sintering is 1.5 mm or more.   The ceramic sintered body according to any one of claims 1 to 4, wherein the ceramic sintered body has a thermal conductivity of 50 W / m · K or more and a specific heat of 0.75 J / g · K or less. Production method.   6. The method for producing a ceramic sintered body according to claim 1, wherein the main component of the ceramic sintered body is any one selected from aluminum nitride, silicon nitride, and silicon carbide.