Tape Casting Slurry Composition for Preparing Silicon Nitride Sintered Body

Abstract

A tape casting slurry composition for preparing a silicon nitride sintered body is provided. The tape casting slurry composition exhibits a viscosity suitable for tape casting, and thus, can easily control the area and thickness of the prepared green sheet, thereby preparing a large area silicon nitride sintered body having a thickness of a circuit board without post-processing processes such as grinding, and the like. Therefore, according to the present invention, a silicon nitride sintered body can be prepared using low cost raw materials by a simplified process, thereby securing efficiency and economic feasibility of the preparation process.

Claims

1. A tape casting slurry composition for preparing a silicon nitride sintered body, comprising: 100 parts by weight of raw material powders comprising silicon nitride powders and sintering aid powders; 50 to 100 parts by weight of a solvent; 20 to 60 parts by weight of a binder; and 3 to 10 parts by weight of a dispersant; wherein the silicon nitride powders comprise -phase silicon nitride and -phase silicon nitride at a weight ratio of 4:1 to 1:1, and the solvent comprises two or more kinds of organic solvents having different polarity.

2. The tape casting slurry composition according to claim 1, wherein the silicon nitride powders comprise -phase silicon nitride and -phase silicon nitride at a weight ratio of 2.5:1 to 1:1.

3. The tape casting slurry composition according to claim 1, wherein the silicon nitride powders have a specific surface area of 5 m.sup.2/g to 10 m.sup.2/g.

4. The tape casting slurry composition according to claim 1, wherein the sintering aid powders are included in the content of 1 parts by weight to 15 parts by weight, based on 100 parts by weight of the silicon nitride powders.

5. The tape casting slurry composition according to claim 1, wherein the sintering aid is one or more selected from the group consisting of magnesium oxide(MgO), yttrium oxide(Y.sub.2O.sub.3), gadolinium oxide(Gd.sub.2O), holmium oxide(Ho.sub.2O.sub.3), erbium oxide(Er.sub.2O.sub.3), ytterbium oxide(Yb.sub.2O.sub.3), and dysprosium oixde(Dy.sub.2O.sub.3).

6. The tape casting slurry composition according to claim 1, wherein the solvent comprises a first solvent comprising one or more selected from the group consisting of toluene, benzene, xylene and methylethylketone; and a second solvent comprising one or more selected from the group consisting of propyleneglycol monomethylether acetate, propyleneglycol monomethylether, ethanol, butanol and methanol.

7. The tape casting slurry composition according to claim 1, wherein the binder is an acryl-based binder.

8. The tape casting slurry composition according to claim 7, wherein the acryl-based binder comprises about 5 wt % to 60 wt % of (meth)acryl-based monomers having alkyl groups, and about 5 wt % to 60 wt % of (meth)acryl-based monomers having nitrile groups.

9. The tape casting slurry composition according to claim 7, wherein the dispersant is one or more selected from the group consisting of a polyester-based dispersant, a polyacrylate-based dispersant, a polyurethane-based dispersant, and a polyether-based dispersant.

10. The tape casting slurry composition according to claim 1, further comprising a plasticizer.

11. The tape casting slurry composition according to claim 10, wherein the plasticizer is included in the content of 1 wt % to 40 wt %, based on 100 wt % of the binder.

12. The tape casting slurry composition according to claim 10, wherein the plasticizer is one or more selected from the group consisting of di-2-ethylhexyl phthalate, di-normal-butyl phthalate, butyl phthalyl butyl glycolate, and dioctyl phthalate.

13. The tape casting slurry composition according to claim 1, wherein total content of the silicon nitride powders and sintering aid powders included in the composition is 30 wt % to 60 wt %.

14. The tape casting slurry composition according to claim 1, wherein viscosity of the composition at 25 C. is 100 cP to 1000 cP.

15. A method for preparing a silicon nitride sintered body, comprising: preparing a tape casting slurry composition comprising silicon nitride powders; molding the composition to prepare a green sheet; primarily heat treating the green sheet to degrease; and secondarily heat treating the degreased green sheet to sinter, wherein the tape casting slurry composition is the composition according to claim 1.

Description

EXAMPLE

Examples 1 to 5 and Comparative Example 1

[0095] Using mixed powders comprising silicon nitride powders having a specific surface area of 7.43 m.sup.2/g and consisting of 100% -phase, and silicon nitride powders having a specific surface area of 8.27 m.sup.2/g and consisting of 95% -phase at a weight ratio described in the following Table 1 as raw materials, a tape casting slurry composition was prepared by the following method, and a silicon nitride sintered body was prepared using the same.

[0096] (1) Preparation of a Tape Casting Slurry Composition

[0097] To 100 parts by weight of the mixed powders of -phase and -phase silicon nitride powders, 2 parts by weight of magnesium oxide(MgO) and 5 parts by weight of yttrium oxide(Y.sub.2O.sub.3) were added as sintering aids, and the mixture was used as raw material powders. And, as a binder, SOKEN LPR001, as a dispersant, DISPERBYK-112, and as a plasticizer, di-normal-butyl phthalate were used.

[0098] To 100 parts by weight of the raw material powders, 50 parts by weight of a 7:3 mixed solvent of toluene and PGMEA, 30 parts by weight of the binder, 5 parts by weight of the dispersant, and 4 parts by weight of the plasticizer were added, and mixed. And then, the mixture was ball-milled at 250 rpm for 4 hours, using 50 g of zirconia(ZrO.sub.2) balls(=5 mm), to prepare a tape casting slurry composition. The viscosities of the slurry compositions of Examples 1 to 5 at 25 C. were measured to be 200 to 1000 cP.

[0099] (2) Preparation of a Silicon Nitride Sintered Body

[0100] The slurry composition obtained in (1) was formed with doctor blade to prepare a green sheet having a thickness of 0.2 mm.

[0101] The green sheet was heat treated at 550 to 600 C. under nitrogen atmosphere, to conduct a degreasing process of removing organic substances and carbon in the green sheet. And then, the green sheet was heat treated and sintered at 1850 to 1900 C., under nitrogen atmosphere and 8 to 10 atm, using GPS equipment, to prepare a silicon nitride sintered body.

[0102] In order to examine the degree of shrinkage of each silicon nitride sintered body prepared above, the area of the green sheet and the area of the finally prepared silicon nitride sintered body were compared and shrinkage was calculated according to the following Equation 1.

d/dI100 (%) (d=area of green sheet before sinteringarea of silicon nitride sintered body after sintering, dI=area of green sheet before sintering) Equation 13

[0103] And, the external defects of the sintered body was confirmed with an unaided eye using an optical microscope, Scanning Electron Microscope(SEM), and the like, and if the number of pin holes per 1 mm.sup.2 is 0, it was evaluated as being good, if the number of pin holes is 1, evaluated as average, and if the number of pin holes is greater than 1, evaluated as bad; and in the case of cracks, if there is only one crack, it was evaluated as bad. The results were summarized in the following Table 1.

[0104] Referring to Table 1, it can be confirmed that when the mixing ratio of -phase and -phase silicon nitride fulfills the range of the present invention, a silicon nitride sintered body having low shrinkage and less external defects can be prepared.

TABLE-US-00001 TABLE 1 silicon nitride Shrinkage External weight ratio of green defects of - phase - phase sheet (%) sintered body Example 1 1 1 10 Example 2 1 1.5 12 Example 3 1 2 14 Example 4 1 2.3 15 Example 5 1 2.5 16 Comparative 1 5 25 X Example 1 * : good : average X: bad

Comparative Example 2

[0105] Using mixed powders comprising silicon nitride powders having a specific surface area of 7.43 m.sup.2/g and consisting of 100% -phase, and silicon nitride powders having a specific surface area of 8.27 m.sup.2/g and consisting of 95% -phase at a weight ratio of 6:4 as raw materials, a tape casting slurry composition was prepared by the following method.

[0106] To 100 parts by weight of the mixed powders of -phase and -phase silicon nitride powders, 2 parts by weight of magnesium oxide(MgO) and 5 parts by weight of yttrium oxide(Y.sub.2O.sub.3) were added as sintering aids, and the mixture was used as raw material powders.

[0107] To 100 parts by weight of the raw material powders, 50 parts by weight of a toluene solvent, 30 parts by weight of a binder, 5 parts by weight of a dispersant, and 4 parts by weight of a plasticizer were added, and mixed. And then, the mixture was ball-milled at 250 rpm for 4 hours, using 50 g of zirconia(ZrO.sub.2) balls(=5 mm), to prepare a tape casting slurry composition.

[0108] The viscosity of the prepared slurry composition at 25 C. was measured to be 2000 cP.

[0109] Since the viscosity of the slurry composition using toluene alone as a solvent was too high, it could not be formed using doctor blade, and thus, a green sheet could not be prepared.

[0110] It can be confirmed from Examples and Comparative Examples that the slurry composition fulfilling the composition of the present invention exhibit viscosity suitable for tape casting, and thus, the area and thickness of the prepared green sheet can be easily controlled, and a silicon nitride sintered body having a large area and a thickness of a circuit board can be prepared by a simple process without post-processing processes such as grinding, and the like. And, it can be seen that since the slurry composition of the present invention comprises -phase and -phase silicon nitride at a predetermined mixing ratio, it exhibits excellent sinterability.