LOW TEMPERATURE CO-FIRED SUBSTRATE COMPOSITION

Abstract

It is demanded that a LTCC substrate composition capable of maintaining low relative permittivity k and high Q value without having a reactivity with a silver which is an electrode material and causing migration of the silver during a co-firing operation at a low temperature. Provided with a low temperature co-fired substrate composition containing 83 to 91 wt. % of CaO-B.sub.2O.sub.3-SiO.sub.2 based glass powder, 7.5 to 14 wt. % of two or more kinds of nanometer-sized SiO.sub.2 powders having different ranges of particle diameter and 1.5 to 3 wt. % of β-wollastonite powder as a crystallization agent wherein the glass powder contains 40.0 to 45.0 wt. % of CaO, 9.0 to 20.0 wt. % of B.sub.2O.sub.3 and 40.0 to 46.0 wt. % of SiO.sub.2.

Claims

1. A low temperature co-fired substrate composition before a co-firing process, comprising: (A) 83 to 91 wt. % of glass powder containing CaO-B.sub.2O.sub.3-SiO.sub.2 as a basic composition; (B) 7.5 to 14 wt. % of SiO.sub.2 powder; and (C) 1.5 to 3 wt. % of β-wollastonite (CaSiO.sub.3) powder, wherein a particle diameter D.sub.50 of the glass powder (A) is 2.0 to 3.0 μm, the glass powder (A) contains 40.0 to 45.0 wt. % of CaO, 9.0 to 20.0 wt. % of B.sub.2O.sub.3 and 40.0 to 46.0 wt. % of SiO.sub.2 as a composition, the SiO.sub.2 powder (B) is a filler selected from the group consisting of (1), (2) and (3): (1) 10 to 30 wt. % of the SiO.sub.2 powder having the particle diameter D.sub.50 of 10 to 100 nm and 70 to 90 wt. % of the SiO.sub.2 powder having the particle diameter D.sub.50 of 400 to 3000 nm; (2) 60 wt. % or more of the SiO.sub.2 powder having the particle diameter D.sub.50 of 100 to 400 nm and less than 40 wt. % of the SiO.sub.2 powder having the particle diameter D.sub.50 of 400 to 3000 nm; and (3) 4 to 20 wt. % of the SiO.sub.2 powder having the particle diameter D.sub.50 of 10 to 100 nm, 60 to 95 wt. % of the SiO.sub.2 powder having the particle diameter D.sub.50 of 100 to 400 nm and 0 to 36 wt. % of the SiO.sub.2 powder having the particle diameter D.sub.50 of 400 to 3000 nm, the β-wollastonite (CaSiO.sub.3) powder (C) is another filler having the particle diameter D.sub.50 of 2.0 to 3.0 μm, when a silver paste, which functions as an electrode, is applied on a surface of a green sheet comprised of the low temperature co-fired substrate before the co-firing process and an organic binder and the co-firing process is performed, the low temperature co-fired substrate after the co-firing process has the following properties: a relative permittivity k is 6.0 or less at 2.5 GHz; a Q value which is a reciprocal of dielectric tangent is 500 or more at 2.5 GHz; and a ratio R.sub.420/R.sub.800 of a reflectance R.sub.420 in a wavelength of 420 nm with respect to a reflectance R.sub.800 in the wavelength of 800 nm is 85% or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows a temperature profile when firing a low temperature co-fired substrate composition of the present invention.

[0043] FIG. 2 is a schematic diagram showing a test body and a measurement position for measuring R.sub.420/R.sub.800.

[0044] FIG. 3 shows a reflectance profile for calculating R.sub.420/R.sub.800 of Example 12 of the present invention and Comparative example 19.

[0045] FIG. 4 is an example (Example 12) of X-ray diffraction profile of the low temperature co-fired substrate composition of the present invention after the firing process.

[0046] FIGS. 5A to 5C are electron microscope photographs showing a surface state (effect of adding the β-wollastonite powder and effect of adding two kinds or more nanometer-sized SiO.sub.2 powder) after the co-firing process.

MODES FOR CARRYING OUT THE INVENTION

Screening of Glass Composition

[0047] Before exploiting the present invention, screening of glass composition was performed for determining the glass composition suitable for being used for the present invention. First, a green sheet was manufactured from the glass powder by the method shown below (without adding the SiO.sub.2 powder and the β-wollastonite) and the green sheet was fired by the temperature profile shown in FIG. 1. Thus, the substrate after the firing process was obtained. The relative permittivity k and tan δ (Q value) of the substrate after the firing process were measured. The result is shown in Table 1. The glass composition codes (a), (b), (c) and (d) were selected as the glass powder A for the reasons described in the paragraph [0017].

EXAMPLES

Preparation of Glass Powder A

[0048] As a raw material, a raw material batch formed by mixing SiO.sub.2, CaCO.sub.3, B.sub.2O.sub.3 or H.sub.3BO.sub.3, Al(OH).sub.3 or Al.sub.2O.sub.3, ZrO.sub.2 and MgCO.sub.3 to have an oxide ratio (wt. %) shown in (a), (b), (c) or (d) of Table 1 was filled in a platinum crucible, the mixture was melted in an electric furnace in conditions of 1450° C. to 1500° C. and 60 to 180 minutes, and the molten material was entered into water to cool and dry the molten material. Thus, the glass having the compositions shown in (a), (b), (c) or (d) were obtained. The obtained glass was classified using a sieve having a mesh size of 4 mm. The glass passed through the sieve was crushed and classified using an ultrafine grinder incorporating a medium stirring type classifier where the crushing condition was adjusted so that the particle diameter D.sub.50 was 2.0 to 3.0 μm. Thus, the glass powder A having the particle diameter D.sub.50 shown in FIG. 3 was obtained. The particle diameter D.sub.50 was measured by a laser diffraction method using a particle-size-distribution measurement device LA-950V2 manufactured by HORIBA, Ltd.. The measurement result is shown in Table 3.

Preparation of SiO.SUB.2 .Powder B

[0049] Regarding the SiO.sub.2 powder B, AEROSIL (registered trademark) R805 manufactured by NIPPON AEROSIL CO., LTD. was used as the powder of 10 to 100 nm, SO-C1 manufactured by Admatechs Company Limited was used as the powder of 100 to 400 nm, and SO-C2 manufactured by Admatechs Company Limited or Fuselex/X manufactured by TATSUMORI LTD. was used as the powder of 400 to 3000 nm. The compounding ratio of each particle diameter of SiO.sub.2 powder is shown in Table 3.

Preparation of β-wollastonite Powder C

[0050] Commercially available crystal powder of β-wollastonite was crushed using a dry ball mill while adjusting the crushing time so that the particle diameter D.sub.50 was 2.0 to 3.0 μm and classified using a sieve having a mesh size of 100 μm. Thus, the β-wollastonite powder having the particle diameter D.sub.50 of 2.4 μm was obtained.

Manufacturing of Green Sheet for Low Temperature Co-fired Substrate

[0051] Each of composition materials A, B and C was weighed so that the ratio (wt. %) shown in Table 3 was satisfied and they are mixed together with an organic binder having the composition (wt. %) shown in Table 2 in a resin-made pot having alumina balls for 16 to 24 hours. Thus, a green sheet precursor slurry was obtained. The amount of the organic binder contained in the slurry was 46 to 49 wt. %. The obtained slurry was deaerated in a vacuum by a rotary pump, a film having a gap of approximately 0.35 mm was formed by a comma direct method and the film was passed through drying zones set to 60° C., 95° C. and 100° C. for three minutes each. Thus, a green sheet having a thickness of approximately 0.12 mm was obtained.

TABLE-US-00002 TABLE 2 composition concentration (wt. %) cyclohexanone 48.61 ethanol 32.41 plasticizer 6.4 dispersant 0.85 polyvinyl butyral 11.73

Measurement of Relative Permittivity

[0052] Forty layers of the obtained green sheets were laminated by applying a hydrostatic pressure using a hot water laminator/WL28-45-200 manufactured by NIKKISO CO., LTD. in condition that the water temperature of 70° C., the pressure of 20.7 MPa and 10 minutes, and then the green sheets were fired in accordance with the temperature program shown in FIG. 1. Thus, a low temperature fired substrate was obtained. Here, the temperature rising speed was 1° C./min until 450° C. and the temperature was kept at 450° C. for 2 hours to perform a debinder treatment. After that the temperature was raised to 850° C. in 2 hours and the temperature was kept at 850° C. for 15 minutes to perform a crystallization treatment. Note that the firing process was performed by using a muffle furnace manufactured by MOTOYAMA CO., LTD while introducing approximately 100 L/min of air. The obtained low temperature fired substrate was processed to have a shape of approximately 3×4×30 mm. Then, the relative permittivity k and dielectric tangent (tan δ) were measured by a perturbation type cavity resonator method. The Q value was calculated in condition that Q=1/tan δ. Note that dielectric characteristics were measured by using a relative permittivity/dielectric tangent measurement system TMR-2A manufactured by KEYCOM Corporation. The measurement result is shown in Table 3.

Measurement of R.SUB.420./R.SUB.800

[0053] The obtained green sheet was cut into 22×22 mm and a silver paste having a dimeter of 8 mm was applied on the center of the green sheet by screen printing. Five layers of green sheets were laminated so that the applied silver pastes were overlapped with each other and the green sheets were co-fired. Thus, a measuring specimen was obtained (FIG. 2). The reflectance was measured on the silver electrode of the obtained specimen by using a spectrophotometer/V-750 manufactured by JASCO Corporation within the range of 200 to 800 nm. Then, R.sub.420/R.sub.800 was calculated from the values of the reflectance of 420 nm and 800 nm (FIG. 3). The calculation result is shown in Table 3. As understood from FIG. 3, the deterioration of the reflectance was not observed in 420 nm and R.sub.420/R.sub.800 was 88.6% in Example 12, while the deterioration of the reflectance due to the silver colloid was observed in 420 nm and R.sub.420/R.sub.800 was deteriorated to 75.2% in Comparative example 19. As the silver paste to be applied, the silver paste manufactured by NORITAKE CO., LIMITED was used.

Identification of Deposited Crystal Phase

[0054] The low temperature fired substrate after the firing process was crushed by an alumina magnetic mortar and the measurement was performed within the range of 15 to 35 degrees by using an X-ray diffraction device/X'Pert PRO manufactured by Malvern Panalytical Ltd.. Thus, the deposited crystal phase was identified from the peak positions. An example (Example 12) of the identification result is shown in FIG. 4. From the identification result, β-wollastonite was detected as the main crystal phase and CaB.sub.2O.sub.4 phase was detected as the auxiliary crystal phase.

[0055] The summary of the measurement result of the above described examples is shown in Table 3. When at least two of three kinds of nanometer-sized SiO.sub.2 powder were added at the ratio described in the claim, the interaction between the B.sub.2O.sub.3-rich remaining glass phase and the silver electrode and the migration of the silver to the B.sub.2O.sub.3-rich remaining glass phase could be suppressed (R.sub.420/R.sub.800 could be 85.0% or more) while keeping low k value and high Q value.

TABLE-US-00003 TABLE 3 Examples 1 2 3 4 5 6 7 glass powder A wt. % 87.30 87.22 87.22 85.48 84.60 87.22 87.22 SiO.sub.2 powder B 9.70 10.78 10.78 12.56 13.46 10.78 10.78 β-wollastonite 3.00 2.00 2.00 1.96 1.94 2.00 2.00 powder C other additives 0.00 0.00 0.00 0.00 0.00 0.00 0.00 particle diameter D.sub.50 μm 2.0 2.2 2.2 2.2 2.2 2.2 2.2 of glass powder A glass composition code (a) (b) (b) (b) (b) (b) (b) of glass powder A SiO.sub.2 powder B  10-100 25.00 18.18 27.27 15.92 22.29 0.00 0.00 (particle diameter 1) nm SiO.sub.2 powder B 100-400 0.00 0.00 0.00 0.00 0.00 63.64 81.82 (particle diameter 2) nm SiO.sub.2 powder B 400-3000 75.00 81.82 72.73 84.08 77.71 36.36 18.18 (particle diameter 3) nm particle diameter D.sub.50 μm 2.4 2.4 2.4 2.4 2.4 2.4 2.4 of β-wollastonite powder C main crystal phase α or β β β β β β β β (wollastonite) relative at 2.5 5.72 5.93 5.82 5.81 5.59 5.88 5.90 permittivity k GHz tan δ 0.0008 0.0009 0.0011 0.0012 0.0015 0.0009 0.0012 Q value (1/tan) 1250 1111 909 833 667 1111 833 R.sub.420/R.sub.800 (%) 88.3 86.4 85.6 87.4 87.6 85.6 89.3 Example 8 9 10 11 12 13 14 15 glass powder A wt. % 87.22 87.22 87.22 86.55 90.16 90.16 90.16 88.20 SiO.sub.2 powder B 10.78 10.78 10.78 8.56 7.84 7.84 7.84 9.80 β-wollastonite 2.00 2.00 2.00 1.98 2.00 2.00 2.00 2.00 powder C Other additive (ZrO.sub.2) 0.00 0.00 0.00 2.91 0.00 0.00 0.00 0.00 particle diameter D.sub.50 μm 2.2 2.2 2.2 2.3 2.3 2.3 2.3 2.2 of glass powder A glass composition symbol (b) (b) (b) (c) (c) (c) (c) (d) of glass powder A SiO.sub.2 powder B  10-100 4.55 9.09 13.64 11.68 6.25 12.50 18.75 30.00 (particle diameter 1) nm SiO.sub.2 powder B 100-400 63.64 63.64 63.64 0.00 93.75 87.50 81.25 0.00 (particle diameter 2) nm SiO.sub.2 powder B 400~3000 31.82 27.27 22.73 88.32 0.00 0.00 0.00 70.00 (particle diameter 3) nm particle diameter D.sub.50 μm 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 of β-wollastonite powder C main crystal phase α or β β β β β β β β β (wollastonite) relative at 2.5 5.87 5.85 5.73 5.88 5.89 5.72 5.54 5.59 permittivity k GHz tan δ 0.0010 0.0013 0.0017 0.0009 0.0010 0.0011 0.0015 0.0009 Q value (1/tan δ) 1000 769 588 1111 1000 909 667 1111 R.sub.420/R.sub.800 (%) 85.2 89.6 89.1 87.1 88.6 88.2 90.6 86.9

Comparative Examples

[0056] Comparative examples are shown in Table 4. In Comparative examples 1, 6 and 18, the densities of the glass powder A, the SiO.sub.2 powder B and the β-wollastonite powder C are out of the range of the claim. In other Comparative examples, the range of the particle diameter of the SiO.sub.2 powder B and the content amount of the SiO.sub.2 powder of that range of the particle diameter are out of the range of the claim. In Comparative example 9 and Comparative example 18, the Q value does not reach 500 which is the target value. In other Comparative examples, R.sub.420/R.sub.800 is below 85% and remarkable yellowing occurs.

[0057] From the result of the Examples and Comparative examples, the SiO.sub.2 powder having a small particle diameter has a large specific surface area and attracts large amount of the B.sub.2O.sub.3-rich remaining glass phase. As a result, the migration of the silver to the B.sub.2O.sub.3-rich glass phase is suppressed. When the SiO.sub.2 powder having a small particle diameter is too much, the structure after the firing process is sparse and tan δ is large although R.sub.420/R.sub.800 is large (Comparative example 9). On the contrary, when the SiO.sub.2 powder having a large particle diameter is used, the structure after the firing process is relatively large and tan δ can be kept low. However, when the SiO.sub.2 powder having a large particle diameter is increased, the effect of suppressing the migration of the silver to the B.sub.2O.sub.3-rich glass phase is poor and R.sub.420/R.sub.800 is small (Comparative examples 7 and 14). As a result, only when at least two of three kinds of nanometer-sized SiO.sub.2 powder were added at the ratio described in the claim, the interaction between the B.sub.2O.sub.3-rich remaining glass phase and the silver electrode and the migration of the silver to the B.sub.2O.sub.3-rich remaining glass phase could be suppressed while keeping the k value of 6.0 or less and the tan δ of 0.002 or less (Q value of 500 or more).

TABLE-US-00004 TABLE 4 Comparative example 1 2 3 4 5 glass powder A wt. % 100.00 90.16 88.20 87.22 86.24 SiO.sub.2 powder B 0.00 7.84 9.80 10.78 11.76 β-wollastonite 0.00 2.00 2.00 2.00 2.00 powder C Other additive 0.00 0.00 0.00 0.00 0.00 particle diameter D.sub.50 μm 2.2 2.2 2.2 2.2 2.2 of glass powder A glass composition symbol (b) (b) (b) (b) (b) of glass powder A SiO.sub.2 powder  10-100 0.00 0.00 0.00 0.00 0.00 B (particle diameter 1) nm SiO.sub.2 powder 100-400 0.00 0.00 0.00 0.00 0.00 B (particle diameter 2) nm SiO.sub.2 powder 400-3000 0.00 100.00 100.00 100.00 100.00 B (particle diameter 3) nm particle diameter D.sub.50 μm — 2.4 2.4 2.4 2.4 of β-wollastonite powder C main crystal phase α or β α β β β β (wollastonite) relative at 2.5 6.40 6.18 5.96 5.93 5.84 permittivity k GHz tan δ 0.0011 0.0008 0.0009 0.0008 0.0008 Q value (1/tan δ) 909 1250 1111 1250 1250 R.sub.420/R.sub.800 (%) 76.8 77.9 78.9 79.3 82.6 Comparative example 6 7 8 9 10 glass powder A wt. % 82.32 87.22 87.22 87.22 86.35 SiO.sub.2 powder B 15.68 10.78 10.78 10.78 11.67 β-wollastonite 2.00 2.00 2.00 2.00 1.98 powder C Other additive 0.00 0.00 0.00 0.00 0.00 particle diameter D.sub.50 μm 2.2 2.2 2.2 2.2 2.2 of glass powder A glass composition symbol (b) (b) (b) (b) (b) of glass powder A SiO.sub.2 powder  10-100 0.00 4.55 9.09 63.64 8.57 B (particle diameter 1) nm SiO.sub.2 powder 100-400 0.00 0.00 0.00 0.00 0.00 B (particle diameter 2) nm SiO.sub.2 powder 400-3000 100.00 95.45 90.91 36.36 91.43 B (particle diameter 3) nm particle diameter D.sub.50 μm 2.4 2.4 2.4 2.4 2.4 of β-wollastonite powder C main crystal phase α or β β β β β β (wollastonite) relative at 2.5 5.60 5.92 5.90 5.24 5.95 permittivity k GHz tan δ 0.0008 0.0008 0.0008 0.0023 0.0009 Q value (1/tan δ) 1250 1250 1250 435 1111 R.sub.420/R.sub.800 (%) 84.5 80.4 84.1 87.4 81.5 Comparative example 11 12 13 14 15 16 glass powder A wt. % 87.22 87.22 87.22 86.35 85.48 87.42 SiO.sub.2 powder B 10.78 10.78 10.78 11.67 12.56 7.64 β-wollastonite 2.00 2.00 2.00 1.98 1.96 2.00 powder C Other additive (ZrO.sub.2) 0.00 0.00 0.00 0.00 0.00 2.94 particle diameter D.sub.50 μm 2.2 2.2 2.2 2.2 2.2 2.2 of glass powder A glass composition symbol (b) (b) (b) (b) (b) (c) of glass powder A SiO.sub.2 powder B 10~100 0.00 0.00 0.00 0.00 0.00 0.00 (particle diameter 1) nm SiO.sub.2 powder B 100-400 18.18 36.36 54.55 8.57 15.92 0.00 (particle diameter 2) nm SiO.sub.2 powder B 400-3000 81.82 63.64 45.45 91.43 84.08 100.00 (particle diameter 3) nm particle diameter D.sub.50 μm 2.4 2.4 2.4 2.4 2.4 2.4 of β-wollastonite powder C main crystal phase α or β β β β β β β (wollastonite) relative at 2.5 5.95 5.99 5.88 5.94 5.84 5.93 permittivity k GHz tan δ 0.0008 0.0008 0.0009 0.0008 0.0008 0.0008 Q value 1250 1250 1111 1250 1250 1250 (1/tan δ) R.sub.420/R.sub.800 (%) 80.8 82.3 82.7 78.4 82.7 79.5 Comparative example 17 18 19 20 21 glass powder A wt. % 86.98 81.30 90.16 90.16 88.20 SiO.sub.2 powder B 8.10 14.11 7.84 7.84 9.80 β-wollastonite 1.99 1.86 2.00 2.00 2.00 powder C Other additive (ZrO.sub.2) 2.93 2.73 0.00 0.00 0.00 particle diameter D.sub.50 μm 2.3 2.3 2.2 2.3 2.2 of glass powder A glass composition symbol (c) (c) (c) (c) (d) of glass powder A SiO.sub.2 powder B 10~100 6.17 49.61 0.00 0.00 0.00 (particle diameter 1) nm SiO.sub.2 powder B 100-400 0.00 0.00 0.00 50.00 0.00 (particle diameter 2) nm SiO.sub.2 powder B 400-3000 93.83 50.39 100.00 50.00 100.00 (particle diameter 3) nm particle diameter D.sub.50 μm 2.4 2.4 2.4 2.4 2.4 of β-wollastonite powder C main crystal phase α or β β β β β β (wollastonite) relative at 2.5 5.91 4.19 5.96 5.79 5.94 permittivity k GHz tan δ 0.0009 0.0028 0.0007 0.0008 0.0005 Q value 1111 357 1429 1250 2000 (1/tan δ) R.sub.420/R.sub.800 (%) 81.6 91.3 75.2 80.2 82.6

[0058] Finally, the effect of the present invention was confirmed based on the result of observing a surface state of the LTCC substrate after the co-firing process by an electron microscope photograph (FIGS. 5A to 5C). When Comparative example 1 containing only the glass powder without containing the SiO.sub.2 powder and the β-wollastonite powder was co-fired, it was confirmed that the floating of the B.sub.2O.sub.3-rich glass phase densely existed on the surface in a grained state. In such a case, the migration of the silver to the B.sub.2O.sub.3-rich glass phase was remarkable. Thus, R.sub.420/R.sub.800 was deteriorated and disconnection or short circuiting of the electrode may occur. In the example where the β-wollastonite powder is added to Comparative example 1, although the floating of the B.sub.2O.sub.3-rich glass was reduced but did not completely disappear. In Example 14 where two or more kinds of nanometer-sized SiO.sub.2 powders having different ranges of particle diameter are added in addition to the β-wollastonite, it was confirmed that the floating of the B.sub.2O.sub.3-rich glass phase completely disappeared and the surface was fine and smooth.