JP2009208981A - Manufacturing method of green sheet, green sheet and silicon nitride ceramic substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the uniformity of a film thickness of a green sheet to become a silicon nitride ceramic, and also to appropriately perform the control of an orientation degree of particles and to easily manufacture a silicon nitride ceramic substrate having good characteristics. <P>SOLUTION: A sheet-shaped form is maintained, as it is, in a raw sheet 14 even after a Mylar sheet 12 is wound up by a winding side roll 16 and a raw sheet is separated from the Mylar sheet 12 (separating step). The raw sheet 14 after the separating step passes a heating device 18 (heating step). The raw sheet 14 is heated again and a binder component contained in the heating device 18 is softened. A constant shape property is obtained by evaporating an organic solvent at the drying step in the raw sheet 14. The orientation of a β-type silicon nitride particles progresses and a plane orientation degree in the silicon nitride ceramic substrate can be set at ≥0.4 by performing a rolling step at a softening temperature or above of the binder after that. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a green sheet manufacturing method used when manufacturing a silicon nitride ceramic substrate, a green sheet manufactured by the manufacturing method, and a silicon nitride ceramic substrate manufactured by firing the green sheet.

  Ceramic substrates (for example, silicon nitride ceramics) having high mechanical strength, thermal conductivity, and electrical insulation are used, for example, as power semiconductor modules capable of high voltage and large current operation as inverters for electric vehicles. . In manufacturing such a ceramic substrate, a green sheet in which the material powder constituting the ceramic is mixed with a binder, an organic solvent, and the like is formed into a regular shape, and the green sheet is fired at a high temperature to be a ceramic substrate. In general, the green sheet shrinks during the firing to become a ceramic substrate.

  At this time, it is necessary to set the thickness of the ceramic substrate to a predetermined value and make the thickness uniform, but these characteristics are mainly determined in the manufacturing process of the green sheet. That is, the green sheet is required to have an appropriate thickness, a uniform thickness, and a uniform density. Therefore, a method for producing a green sheet capable of particularly improving such characteristics has been proposed.

  Patent Document 1 describes a method for producing a green sheet of alumina ceramics, in which a green sheet is formed on a carrier film by a doctor blade method and then passed through a drying furnace and then passed between rotating rollers. Yes.

  Here, in the doctor blade method, a sheet (raw sheet) having a substantially constant thickness is formed by setting the distance between the blade edge of the doctor blade and the carrier film. However, the thickness uniformity and the density uniformity are insufficient in the raw sheet after passing through this portion. Therefore, in this case, the organic solvent in the green sheet is evaporated in a drying oven to maintain a certain degree of formability, but in a plastic state, it is passed between rotating rollers, and the thickness uniformity and density A green sheet with improved uniformity is obtained. When the green sheet produced by this method is fired, the uniformity of thickness and density is improved, and a ceramic substrate having good mechanical strength, thermal conductivity, and electrical insulation is obtained.

  In addition, when the green sheet is fired to become a sintered body, the organic component evaporates, and the constituent particles shrink because they are sintered together. This adversely affects the controllability of the thickness of the ceramic substrate. Patent Document 2 describes a manufacturing method in which the surface of a green sheet is once made uneven, and then flattened. In this method, the anisotropy is reduced by this method by randomizing the direction of the particles. Therefore, by this method, the orientation is moderately adjusted, and a ceramic substrate having good characteristics can be obtained.

  On the other hand, particularly in the case of silicon nitride ceramics, since the β-type silicon nitride particles constituting the anisotropy are high in anisotropy, the characteristics of the obtained ceramic substrate vary greatly depending on the orientation. Patent Document 3 describes that in this ceramic substrate, by setting the in-plane orientation value in the range of 0.4 to 0.8, resistance to cracks and thermal conductivity can be particularly increased. ing. This in-plane orientation degree can be adjusted by adjusting the material (green sheet material) and the like, and the value can be set in the above range.

JP-A-55-111207 JP 58-96508 A International Publication WO2006 / 118003

  In the manufacturing method of the green sheet described in Patent Documents 1 and 2, it was assumed that an alumina ceramic substrate was manufactured. On the other hand, the importance of silicon nitride has been increasing in recent years as a ceramic material with higher mechanical strength, thermal conductivity, and electrical insulation. As described in Patent Document 3, in the case of silicon nitride ceramics, particularly good characteristics can be obtained by setting the in-plane orientation degree to an appropriate range, but the uniformity of film thickness and density is improved. At the same time, there has been no green sheet manufacturing method that can easily set the degree of orientation of particles within an appropriate range.

  That is, it was difficult to easily produce a silicon nitride ceramic substrate having good characteristics by improving the uniformity of the film thickness in the green sheet to be silicon nitride ceramics and appropriately controlling the degree of orientation of particles. .

In order to solve the above problems, the present invention has the following configurations.
The gist of the invention described in claim 1 is a green sheet manufacturing method for manufacturing a green sheet to be a silicon nitride ceramic substrate after firing, wherein at least α-type silicon nitride powder, a binder, and an organic solvent are mixed. A forming step of forming a slurry as a raw sheet on a carrier film by a doctor blade method, a drying step of heating the raw sheet to evaporate the organic solvent, and releasing the raw sheet after the drying step from the carrier film A releasing step, a heating step of heating the released green sheet to a temperature equal to or higher than a softening temperature of the binder, and a rolling step of rolling the heated green sheet to produce a green sheet. The present invention resides in a method for producing a green sheet.
The gist of the invention described in claim 2 resides in the method for producing a green sheet according to claim 1, wherein the heating temperature in the heating step is 50 ° C. or higher and lower than 150 ° C.
The gist of the invention described in claim 3 is that, in the molding step, the distance between the carrier film and the doctor blade is 1.6 to 1.9 mm, and in the rolling step, the raw sheet is 0.03 to 0.00 mm. The green sheet manufacturing method according to claim 1, wherein the green sheet passes between rolling rollers having an interval of 2 mm.
The gist of the invention described in claim 4 is that the process capability index of film thickness uniformity is 1.33 or more and the density is 50% or more. It exists in the green sheet characterized by being manufactured by the manufacturing method of the green sheet of any one of Claims.
The gist of the invention described in claim 5 resides in the green sheet according to claim 4, wherein the shrinkage ratio in the thickness direction during firing is 20% or less.
The gist of the invention described in claim 6 is a silicon nitride ceramic substrate manufactured by firing the green sheet according to claim 4 or 5, wherein the in-plane orientation degree is 0.4 to 0.8. It exists in the silicon nitride ceramic substrate characterized by being the range.
The gist of the invention described in claim 7 resides in the silicon nitride ceramic substrate according to claim 6, wherein the fracture toughness value in the thickness direction is larger than the fracture toughness value in the in-plane direction.

  Since the present invention is configured as described above, the silicon nitride ceramic substrate having good characteristics can be obtained by improving the uniformity of the film thickness in the green sheet used as the silicon nitride ceramic and appropriately controlling the degree of orientation of the particles. Can be easily manufactured.

  The inventor, in particular, when manufacturing a green sheet for manufacturing a silicon nitride ceramic substrate, provides a step of rolling in a heated state after drying in the manufacturing process of the green sheet, and the heating temperature at that time It has been found that the degree of orientation can be adjusted appropriately by adjusting the angle. Here, by firing the green sheet of which the degree of orientation is adjusted, the thickness and orientation can be controlled easily and sufficiently, and a silicon nitride ceramic sheet having good characteristics can be easily manufactured.

  The present invention will be described below with reference to specific embodiments. However, the present invention is not limited to these embodiments.

  FIG. 1 is a configuration diagram of a manufacturing apparatus 10 that realizes a manufacturing method according to an embodiment of the present invention. In this manufacturing apparatus 10, the slurry 11, which is a green sheet raw material for manufacturing silicon nitride ceramics having a desired mixing ratio, is removed from the gap between the mylar sheet (carrier film) 12 and the doctor blade 13 by the doctor blade method. Then, it becomes a desired thickness substantially equal to this gap and flows out as a raw sheet 14 on the mylar sheet 12 (molding step). The flexible mylar sheet 12 is unwound from the unwinding side roll 15 and wound around the winding side roll 16. During this time, the raw sheet 14 on the mylar sheet 12 passes through the drying furnace 17 (drying process). At this time, the volatile component in the slurry 11 (raw sheet 14) is volatilized, and its regularity is obtained after passing through the drying furnace 17. For this reason, even after the mylar sheet 12 is wound up by the winding side roll 16 and the raw sheet is detached from the mylar sheet 12 (detachment process), the raw sheet 14 is maintained in a sheet-like form as it is. However, in the raw sheet 14 in this state, the sheet-like form is maintained, but the plasticity is not completely lost.

  Here, in this manufacturing apparatus 10, the raw sheet 14 after the separation process in which the regularity is maintained passes through the heating apparatus 18 (heating process). In the heating device 18, the raw sheet 14 is again heated to the softening temperature of the binder or higher, and the binder component contained therein is softened. In this heating step, unlike the drying step, since the mylar sheet 12 does not exist, the raw sheet 14 can be heated uniformly from the vertical direction in FIG.

  Thereafter, the raw sheet 14 passes between two rolling rolls 19 to become a green sheet 20 (rolling step). For convenience, FIG. 1 shows the heating device 18 and the rolling roll 19 separately, but it is also possible to provide them in the same device and simultaneously perform the heating step and the rolling step.

  The slurry 11 used here contains at least an α-type silicon nitride powder, a binder, and an organic solvent as materials constituting the raw sheet 14.

  The α-type silicon nitride powder is the main component of the green sheet 20, and after the green sheet 20 is fired, for example, as described in Patent Document 3, the aspect ratio having a (002) plane in the longitudinal direction is large. That is, it is composed of elongated particles having large anisotropy, and these elongated particles are bonded to each other to form a silicon nitride ceramic substrate. Therefore, the characteristics of the ceramic substrate, such as fracture toughness and thermal conductivity, depend on the degree of orientation of the particles.

  As the organic solvent, for example, a toluene / butanol solution is used. This organic solvent is used as a solvent in the liquid slurry 11 and becomes a volatile component that evaporates in the drying step. In the case of a toluene / butanol solution, for example, it evaporates by being heated to 50 ° C. or higher (drying step) in the drying furnace 17, and thus the raw sheet 14 after passing through the drying furnace 17 maintains the sheet shape.

  As the binder, for example, a polyvinyl organic binder (PVB) is used. This material is added to bond the silicon nitride particles in the green sheet 20 (raw sheet 14) and maintain its regularity. In the case of a polyvinyl organic binder, the softening temperature is 50 ° C. Here, in the heating device 18, the raw sheet 14 is heated to a temperature equal to or higher than the softening temperature (heating step).

Furthermore, if necessary, Y ₂ O ₃ , MgO or the like is added in combination as a sintering aid for good sintering, and for example, a cationic cellulose derivative is used as a dispersant for preventing aggregation of the raw material powder. Dimethyl phthalate or the like can be further mixed with the slurry 11 as a plasticizer for imparting plasticity to the raw sheet, such as a surfactant (trade name Leogard GP).

  As is well known, the manufactured green sheet 20 is then fired at, for example, a temperature of about 1700 to 2000 ° C. in a nitrogen atmosphere to obtain a silicon nitride ceramic substrate.

  In this manufacturing apparatus 10, the shape in the cross section perpendicular | vertical to the advancing direction of the raw sheet 14 before a heating process (after a drying process) is Fig.2 (a). The thickness of the raw sheet 14 is set to a thickness determined by the distance between the mylar sheet 12 and the doctor blade 13 immediately after passing through the doctor blade 13. However, when the organic solvent evaporates in the drying furnace 17, the evaporation of the organic solvent does not proceed uniformly but proceeds from the end portion, and at that time, shrinkage occurs and distortion occurs. Thus, the film thickness is nonuniform from the center to the end. However, since the raw sheet 14 in this state where the organic solvent has evaporated is still plastic, the raw sheet 14 has a cross-sectional shape shown in FIG. 2B after the rolling process. That is, the film is formed by the rolling roll 19 and the uniformity of the film thickness and density is improved. In this case, the final film thickness of the green sheet 20 is determined by the distance between the mylar sheet 12 and the doctor blade 13 and the distance between the rolling rolls 19.

  About the above effect | action and effect, it is the same as that of what was described in patent document 1. FIG. That is, the uniformity of the film thickness and density of the green sheet 20 is improved by the rolling process.

  As described above, the green sheet 20 contains α-type silicon nitride powder (particles) as its main component. The orientation of the α-type silicon nitride particles in the green sheet 20 is directly related to the orientation degree of the β-type silicon nitride particles in the silicon nitride ceramic substrate obtained by firing this, that is, the orientation degree in the silicon nitride ceramics. In particular, since the anisotropy of β-type silicon nitride particles is larger than that of alumina particles or the like, the influence of this degree of orientation on the characteristics of the silicon nitride ceramic substrate is also greater than in the case of alumina ceramics.

  In particular, when the green sheet 20 to be a silicon nitride ceramic substrate is manufactured by the manufacturing apparatus 10, in addition to the influence on the thickness uniformity, the orientation of the α-type silicon nitride particles in the green sheet 20 is also affected by this heating step. Later affected. That is, the orientation in the silicon nitride ceramic substrate obtained by firing the green sheet 20 manufactured by this manufacturing method is also affected after the heating step.

FIG. 3 shows the results of measuring the relationship between the heating temperature in the heating step and the degree of orientation of the obtained silicon nitride sintered body. Here, the composition of the slurry 11 is silicon nitride 78 mol%, MgO in terms of _{oxides: 20mol%, Y 2 O 3} : and 2 mol%, the moving speed of the drying process is carried out at 100 ° C., the overall movement speed (Mylar sheet 12 ) Was 8 cm / min. The distance between the Mylar sheet 12 and the doctor blade 13 was 1.8 mm, and the distance between the rolling rolls 18 was 0.03 mm.

  The degree of orientation referred to here is obtained from the result of X-ray diffraction performed on silicon nitride ceramics, and is the in-plane degree of orientation fa defined by Equation (1) (Patent Document 3 or FK Rotgerling). : J. Inorg, Nucl. Chem., 9 (1959) 113.).

In the formula (1), P is represented by the formula (2), and in the silicon nitride ceramic as the sample, the X-ray diffraction of the sum of the X-ray diffraction intensities of the surface having the long axis of the β-type silicon nitride particles as the normal Is the ratio to the sum of the diffraction intensities of all surfaces appearing in. On the other hand, P ₀ is represented by the formula (3) and is a value of P in a silicon nitride ceramic having no orientation (random). Here, I ₍₁₁₀₎ represents the X-ray diffraction intensity of the (110) plane in the sample, and I ′ ₍₁₁₀₎ represents the X-ray diffraction intensity of the (110) plane in the non-oriented silicon nitride ceramic. . That is, here, it is reflected that the longitudinal direction of the β-type silicon nitride particles is the (110), (200), (210), (310), (320) directions.

  The silicon nitride ceramic substrate is composed mainly of coarse columnar particles and fine particles of β-type silicon nitride, but the in-plane orientation degree fa is determined by the orientation of the coarse β-type silicon nitride columnar particles. When the in-plane orientation degree fa is 0, coarse columnar particles are randomly arranged, but when the in-plane orientation degree fa is greater than 0, the inclination of the major axis with respect to the thickness direction of the silicon nitride substrate is more than 45 °. This shows that the larger the number of columnar particles is contained, the closer the value of the in-plane orientation fa to 1, the closer the major axis direction of the columnar particles to the thickness direction of the silicon nitride substrate is closer to 90 °. Show.

  In FIG. 3, when the heating step is not performed (heating temperature 20 ° C.), the in-plane orientation degree fa is less than 0.4, but when the heating temperature is 50 ° C., the in-plane orientation degree fa is 0. It has risen to around 4 and has continued to rise. When the heating temperature is 120 ° C., it can be confirmed that the in-plane orientation degree fa shows a high value of 0.4 or more. However, when the temperature exceeds 120 ° C., the influence of thermal decomposition of the binder starts to appear, and the in-plane orientation degree fa gradually decreases.

  Furthermore, a heating process and a rolling process can be performed on the raw sheet 14 a plurality of times. FIG. 4 shows the result of examining the relationship between the number of times in this case (number of times of rolling) and the in-plane orientation degree fa. It can be confirmed that the in-plane orientation degree fa is gradually improved by increasing the number of rolling. The in-plane orientation degree fa was about 0.4 or more when the number of rolling was 2 or more. Further, it has been confirmed that the same effect can be obtained by slowing the feed speed of the rolling roller instead of the number of rolling. Therefore, it is desirable to select whether to set the number of rollings or the feed rate according to the manufacturing site and the process.

  This effect is obtained because the orientation of the elongated β-type silicon nitride particles proceeds in the green sheet 20 (raw sheet 14) when rolling is performed at a temperature higher than the softening temperature of the binder. That is, in the raw sheet 14, the formability is obtained by evaporating the organic solvent in the drying process, and then the orientation of the β-type silicon nitride particles proceeds by performing a rolling process at the softening temperature of the binder or higher. The in-plane orientation degree in the silicon nitride ceramic substrate can be set to a value of 0.4 or more. Accordingly, the temperature in the heating step needs to be equal to or higher than the softening temperature of the binder. When a polyvinyl organic binder is used as the binder, the temperature is 50 ° C. or higher. On the other hand, when the temperature is 150 ° C. or higher, the binder is thermally decomposed and the shape of the raw sheet cannot be maintained. Therefore, the temperature is preferably 150 ° C. or lower. Thus, the heating temperature in the heating process using a normal binder material is performed at 50 ° C. or higher and lower than 150 ° C. As shown in FIG. 3, it is desirably 80 ° C. or higher and 120 ° C. or lower.

  By setting the in-plane orientation degree fa in the range of 0.4 to 0.8, as described in Patent Document 3, the fracture toughness value in the thickness direction is made larger than the in-plane fracture toughness value. And resistance to cracking is improved. Here, as shown in FIG. 5, the fracture toughness value is an IF (Indentation Fracture) method defined in JIS R1607 based on the size of the indentation and the size of the crack generated when a Vickers indenter is driven into a measurement point. Is calculated by

  That is, as described in Patent Document 3, a Vickers indenter is pushed into a side surface of a silicon nitride substrate with a predetermined load (for example, 2 kgf) in accordance with JIS R1607. At this time, the Vickers indenter is pushed so that one diagonal line of the Vickers indentation is perpendicular to the thickness direction of the substrate. In this case, as shown in FIG. 5, cracks are formed in the thickness direction from the upper end and the lower end of the Vickers indentation, and in the in-plane direction (direction perpendicular to the thickness direction) from the left end and the right end of the Vickers indentation, respectively. extend.

  In particular, a structure when this silicon nitride ceramic substrate is used for a circuit substrate in a semiconductor module or the like is shown in FIG. 6 (wiring is omitted). The semiconductor module 30 is configured by mounting a semiconductor chip 34 on a metal circuit board 32 in a circuit board in which a metal circuit board 32 and a metal heat radiating plate 33 are respectively bonded to both surfaces of a silicon nitride ceramic substrate 31. . Both the metal circuit board 32 and the metal heat sink 33 are mainly composed of copper. Here, the semiconductor chip 34 generates heat during use. Therefore, heating and cooling are repeated during the use of this semiconductor module, and during the cooling and heating cycle, distortion occurs due to the difference in thermal expansion between silicon nitride and copper, and cracks 40 are generated as shown in FIG. Will occur. As shown in FIG. 6, this crack is generated, for example, from the end portion of the metal circuit board 32, and first propagates in the thickness direction, and then greatly progresses in the horizontal direction (in-plane direction). The silicon ceramic substrate 31 is destroyed. Therefore, in particular, suppressing the progress of cracks in the initial thickness direction is effective in increasing the durability (mechanical strength) of the silicon nitride ceramic substrate 31.

  Therefore, it is important here to obtain a silicon nitride ceramic substrate that is less prone to crack in the thickness direction. As a guideline for this purpose, the fracture toughness value in the thickness direction was calculated from the configuration shown in FIG. The fracture toughness value in the thickness direction is calculated by the IF method using the length of the diagonal line in the thickness direction of the Vickers indentation in FIG. 5 and the length of the crack extending from the upper end and the lower end. Similarly, the fracture toughness value in the in-plane direction is calculated by the IF method using the length of the diagonal line in the in-plane direction of the Vickers indentation in FIG. 5 and the length of the crack extending from the left end portion and the right end portion.

Here, the fracture toughness value in the thickness direction is preferably 6 MPa · m ^1/2 or more, and the fracture toughness value in the in-plane direction is preferably 3 MPa · m ^1/2 or more. Both the fracture toughness values in the thickness direction and in-plane direction are affected by the orientation of β-type silicon nitride particles, that is, the in-plane orientation degree fa, but if the orientation of β-type silicon nitride particles is advantageous to one side Obviously, it is disadvantageous to the other. Therefore, in these fracture toughness values, increasing the ratio of the fracture toughness value in the thickness direction to the fracture toughness value in the in-plane direction is effective in suppressing the occurrence of cracks. For this purpose, it is particularly effective to set the in-plane orientation degree fa in the range of 0.4 to 0.8.

  FIG. 7 shows the result of examining the relationship between the in-plane orientation degree fa of the silicon nitride ceramic substrate obtained by changing the production conditions of the green sheet as described above, and the fracture toughness value in the thickness direction and the in-plane direction. . Further, FIG. 8 shows the result of examining the relationship between the in-plane orientation degree fa and the ratio of the fracture toughness value in the thickness direction to the fracture toughness value in the in-plane direction in the same material.

From this result, the ratio of the fracture toughness value in the thickness direction to the fracture toughness value in the in-plane direction is set to 1. It is preferable to raise it to 2 or more and 2.6 or less, and this can increase the resistance against cracks of the ceramic substrate. However, when fa is larger than 0.8, the fracture toughness value in the in-plane direction becomes 3 MPa · m ^1/2 or less, the crack propagation speed in the plane increases, and a large crack is generated in the in-plane direction. For example, since the peeling of the circuit side metal plate of the semiconductor module occurs, the in-plane orientation degree fa is preferably 0.8 or less.

  In this ceramic substrate, anisotropy occurs in thermal conductivity as well as fracture toughness. In the semiconductor module 30 having the structure shown in FIG. 6, heat generated from the semiconductor chip 34 mounted on the metal circuit board 32 is transmitted to the metal heat radiating plate 33 via the silicon nitride ceramic substrate 31 and is radiated. In this case, it is particularly desirable that the thermal conductivity in the thickness direction (vertical direction in FIG. 6) is high. On the other hand, by setting the in-plane orientation degree fa to 0.4 or more, the ratio of the grain boundary phase that becomes a resistance in heat conduction can be reduced in the thickness direction. Can be kept high.

  Accordingly, by making the in-plane orientation degree fa in the range of 0.4 to 0.8 by this manufacturing method, the thermal conductivity in the thickness direction, which has high resistance to cracks and is important when used in a semiconductor module, is used. Can also be high.

  In addition, in the heating step, since there is no carrier film, the raw sheet 14 can be heated uniformly and easily. Therefore, as the heating device 18 used here, one having a simple configuration can be used, and the manufacturing process thereof is not particularly complicated even when compared with the technique described in Patent Document 1, for example. That is, this manufacturing method can be easily realized.

  As described above, in this manufacturing method, the film thickness and density uniformity of the green sheet are also improved. FIG. 9 shows the relationship between the temperature in the heating process and the process capability index Cp for the uniformity of the film thickness of the green sheet. As shown in FIG. 9, a thickness distribution Cp of Cp = 1.33 or more is obtained by setting the temperature in the heating process to 50 ° C. or higher, and the thickness distribution Cp increases as the temperature increases. Although measurement above 120 ° C. is not performed, it is considered that there is a critical point between 120 ° C. and 150 ° C. because the thermal decomposition of the binder starts around 150 ° C. Therefore, it is considered that the heating temperature should be about 120 ° C. in consideration of the degree of softening of the sheet, the capacity of the heating device, and the cost. Here, Cp is defined by the following equation. The process capability index Cp is preferably a high numerical value, but is usually 1.33 or higher. Cp is generally a process capability index, but in FIG. 9, the thickness distribution Cp is shown as an index of the thickness distribution in the width direction of the green sheet.

  Here, σ is a standard deviation of the film thickness. It can be confirmed that the process capability index is improved by performing the heat rolling. FIG. 10 shows the result of examining the relationship between the process capability index Cp and the in-plane orientation degree fa, and it can be confirmed that the in-plane orientation degree fa increases as Cp improves.

  In the above manufacturing method, from the set thickness of the green sheet in the molding process and the set thickness of the green sheet after the rolling process, the distance between the carrier film and the doctor blade and the distance between the rolling rollers in the rolling process are important. Become. That is, the thickness of the sintered body is in the range of 0.3 mm ± 10%, and the thickness distribution Cp value of the sintered body is required to be 1.55 or more. On the contrary, it is necessary to obtain the thickness of the green sheet after rolling. Table 1 shows experimental examples (examples) for obtaining these intervals. By setting the distance between the carrier film and the doctor blade to 1.6 to 1.9 mm, the green sheet thickness within the setting can be obtained. Moreover, the green sheet thickness after the rolling within the setting was able to be obtained by setting the space | interval between the rolling rollers in a subsequent rolling process to 0.03-0.2 mm. In addition, No. Even when the interval between the rolling rollers is narrow with respect to the thickness of the green sheet as in 3 to 5, the thickness after rolling can be kept within the setting, but the pressing force between the rollers at this time becomes considerably high. No. in terms of such a load. It can be said that the condition 2 is preferable for mass production. On the other hand, if the distance between the carrier film and the doctor blade exceeds 1.9 mm, the green sheet becomes too thick and the waste of sheet material increases. On the other hand, it is difficult to make the interval between the rolling rollers less than 0.03 mm in terms of equipment and design. For this reason, the distance between the carrier film and the doctor blade is in the range of 1.6 to 1.9 mm, and the distance between the rolling rolls 19 in the rolling process is preferably in the range of 0.03 to 0.2 mm. It is preferable because the thickness distribution of the green sheet 20 can be improved and the density can be increased. In this case, since the shrinkage rate when the green sheet is fired to become silicon nitride ceramics is small, the design dimensions of the substrate can be easily controlled.

  Table 2 shows a conventional manufacturing method (without a heating step) using a rectangular green sheet having a long side direction of 170 mm and a short side direction of 142 mm using a similar slurry using a polyvinyl organic binder as a binder. The case where it manufactured using the manufacturing method (heating at 120 degreeC by a heating process) of the Example of invention is shown as a comparative example and an example, respectively, is shown. Here, the density of the green sheet is shown as a ratio (%) to the sintered body density. In the example, Cp having a value higher than 1.33 was obtained as compared with the comparative example, the uniformity of thickness was improved, and the density was increased to 50% or more. Reflecting this, in the examples, it was confirmed that the shrinkage rate during firing was small, and in particular, it was as small as 20% or less even in the thickness direction. The in-plane orientation degree fa of the obtained silicon nitride ceramic is 0.4 or more, and the resistance to cracks and the thermal conductivity in the thickness direction are high as described above.

It is a block diagram of the manufacturing apparatus which implement | achieves the manufacturing method of the green sheet which concerns on embodiment of this invention. In the manufacturing method of the green sheet which concerns on embodiment of this invention, it is a figure which shows the cross-sectional shape (a) of the raw sheet before a heating process, and the cross-sectional shape (b) of the raw sheet after a rolling process. It is a figure which shows the relationship between the in-plane orientation degree in the silicon nitride ceramic substrate after baking a green sheet, and the heating temperature in a heating process. It is a figure which shows the relationship between the in-plane orientation degree in the silicon nitride ceramic substrate after baking a green sheet, and the frequency | count of heating and rolling. It is a figure explaining the principle which measures the fracture toughness value of thickness direction and in-plane direction. It is sectional drawing which shows the structure of the semiconductor module in which the silicon nitride ceramic substrate of this invention is used. It is the result of investigating the in-plane orientation degree dependence of the fracture toughness value in the thickness direction and in-plane direction. It is the result of investigating the in-plane orientation dependence of the ratio of the fracture toughness value in the thickness direction to the fracture toughness value in the in-plane direction. It is a figure which shows the relationship between the process capability index of the film thickness uniformity of a green sheet, and the heating temperature in a heating process. It is a figure which shows the relationship between the in-plane orientation degree in a silicon nitride ceramic substrate, and the process capability index of the film thickness uniformity of a green sheet.

Explanation of symbols

10 Green sheet manufacturing equipment 11 Slurry 12 Mylar sheet (carrier film)
13 Doctor blade 14 Raw sheet 15 Unwinding side roll 16 Winding side roll 17 Drying furnace 18 Heating device 19 Rolling roll 20 Green sheet 30 Semiconductor module 31 Silicon nitride ceramic substrate 32 Metal circuit board 33 Metal heat sink 34 Semiconductor chip 40 Crack

Claims (7)

A green sheet manufacturing method for manufacturing a green sheet to be a silicon nitride ceramic substrate after firing,
A forming step of forming a slurry in which at least α-type silicon nitride powder, a binder, and an organic solvent are mixed as a raw sheet on a carrier film by a doctor blade method;
A drying step of evaporating the organic solvent by heating the raw sheet;
A separation step of separating the green sheet after the drying step from the carrier film;
A heating step of heating the detached raw sheet to a temperature equal to or higher than a softening temperature of the binder;
A rolling step of rolling the heated raw sheet to produce a green sheet;
A method for producing a green sheet, comprising:   2. The method for producing a green sheet according to claim 1, wherein the heating temperature in the heating step is in a range of 50 ° C. or more and less than 150 ° C. 3. In the molding step, the distance between the carrier film and the doctor blade is 1.6 to 1.9 mm,
3. The green sheet manufacturing method according to claim 1, wherein in the rolling step, the green sheet passes between rolling rollers having an interval of 0.03 to 0.2 mm.   The green sheet manufacturing method according to any one of claims 1 to 3, wherein the process capability index for uniformity of film thickness is 1.33 or more and the density is 50% or more. A green sheet manufactured by the method.   The green sheet according to claim 4, wherein the shrinkage in the thickness direction during firing is 20% or less.   A silicon nitride ceramic substrate manufactured by firing the green sheet according to claim 4 or 5, wherein the in-plane orientation degree is in the range of 0.4 to 0.8. Silicon ceramic substrate.   The silicon nitride ceramic substrate according to claim 6, wherein the fracture toughness value in the thickness direction is larger than the fracture toughness value in the in-plane direction.

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