Ceramic Substrate

Abstract

Provided is a ceramic substrate including aluminum oxide (Al.sub.2O.sub.3) with an average grain size between 1.31 and 1.55 m; Zirconium dioxide (ZrO.sub.2) with an average grain size between 0.65 and 0.75 m, Yttrium oxide (Y.sub.2O.sub.3) and further components.

Claims

1. A ceramic substrate comprising: aluminum oxide (Al.sub.2O.sub.3) with an average grain size from 1.31 to 1.55 m (measured by planimetric method); Zirconium dioxide (ZrO.sub.2) with an average grain size from 0.65 to 0.75 m (measured by planimetric method), Yttrium oxide (Y.sub.2O.sub.3), silicon oxide (SiO.sub.2) and further components.

2. The ceramic substrate according to claim 1, comprising 85-95 wt % (based on the overall weight of the ceramic substrate) of aluminum oxide (Al.sub.2O.sub.3) with an average grain size from 1.31 to 1.55 m (measured by planimetric method), 4-14 wt %, (based on the overall weight of the ceramic substrate) of zirconium dioxide (ZrO.sub.2) with an average grain size from 0.65 to 0.75 m (measured by planimetric method), 0.2-0.8 wt %; (based on the overall weight of the ceramic substrate) of yttrium oxide (Y.sub.2O.sub.3), 0.1-0.5 wt % (based on the overall weight of the ceramic substrate) of silicon oxide (SiO.sub.2), and Less than 0.6 wt %; (based on the overall weight of the ceramic substrate) further components, wherein the sum of all ingredients always adds up to 100 wt %.

3. The ceramic substrate according to claim 1, having a bending strength (measured according to ASTM C1499-15) of more than 620 MPa.

4. The ceramic substrate according to claim 1, having a thermal conductivity (measured at 20 C. according to ISO 18755:2005) of more than 20 W/m*K.

5. The ceramic substrate according to claim 1, having a Modulus of elasticity (Young's Modulus) of more than 310 GPa.

6. The ceramic substrate according to claim 1, having a fracture toughness K.sub.Ic Niihara (measured according to the IF-method) of 3-5 MPa m.sup.1/2.

7. The ceramic substrate according to claim 1, having a surface roughness Ra (measured according to DIN EN ISO 4288) of less than 0.5 m.

8. A method for obtaining a ceramic substrate according to claim 1 comprising the following steps providing a first mixture of at least one first type of aluminum oxide having a particle size (d50) from 0.1 to 0.8 m and at least one second type of aluminum oxide having a particle size (d50) from 0.9 to 1.7 m; providing a second mixture of at least one first type of yttria stabilized zirconium oxide having a particle size (d50) from 0.2 to 0.5 m and at least one second type of yttria stabilized zirconium oxide having a particle size (d50) from 0.8 to 1.4 m; combining the aluminum oxide mixture and the zirconium oxide mixture and optionally further additives, and dispersing the mixture in a mill, adding a binder to the dispersed mixture of aluminum oxide and zirconium oxide, shaping the dispersed mixture of aluminum oxide, zirconium oxide and binder into a desired form, and sintering the molded mixture to provide the ceramic substrate.

9. The method according to claim 8, wherein first mixture comprises 42.5-47.5 wt % of the at least one first type of aluminum oxide having a particle size (d50) from 0.1 to 0.8 m and 42.5-47.5 wt % of the at least one second type of aluminum oxide having a particle size (d50) from 0.9 to 1.7 m.

10. The method according to claim 8, wherein the second mixture comprises 2.8-9.8 wt % of the at least one first type of zirconium oxide having a particle size between (d50) from 0.2 to 0.5 m, and 1.2-4.2 wt % of the at least one second type of zirconium oxide having a particle size (d50) from 0.8 to 1.4 m.

11. The method according to claim 8, wherein sintering aids such as SiO.sub.2 and/or organic compounds are added.

12. The method according to claim 8, wherein the sintering step is carried out at temperatures between from 1400 C. to 1700 C.

13. (canceled)

14. An electronic device comprising a ceramic substrate according to claim 1.

Description

DETAILED DESCRIPTION

[0091] The solution is now explained in more detail with reference to the examples.

[0092] The following Examples are included to demonstrate certain aspects and embodiments of the disclosure as described in the claims. It should be appreciated by those of skill in the art, however, that the following description is illustrative only and should not be taken in any way as a restriction of the disclosure.

I. Synthesis

[0093] The starting materials ZrO.sub.2, Al.sub.2O.sub.3 and SiO.sub.2 are subjected to an incoming raw material inspection. Two different grades are used for both the Al.sub.2O.sub.3 and the ZrO.sub.2 to achieve the grain size distributions shown in the final product.

[0094] The mass preparation (slurry) takes place in a mill. The mass preparation contains mixing of the raw materials, meaning the ceramic starting material and the organic compounds. The slurry is cast to form a ceramic green film. The green film is cut to specified dimensions. The ceramic films are sintered at 1400 bis 1700 C.

II. Analytics

[0095] Grain size: planimetric method applied to the sintered ceramic substrate

[0096] The planimetric method applied for determining the average crystal grain size of alumina and zirconia is now described. First, the surface of the ceramic substrate 1 is subjected to mirror finishing and is heat-treated in a temperature range from 50 to 100 C. lower than the firing temperature. The heat-treated surface is then used as a measurement surface and is photographed at a multiplication factor of 5000 times using an SEM. Next, the photographed image data is analyzed using image analysis software (for example, Win ROOF available from the Mitani Corporation). As a result, the data for the respective crystal grain sizes of alumina and zirconia present in the image data can be obtained.

[0097] Although the ceramic substrate may contain crystals with a crystal grain size of less than 0.05 mm, only crystals with a crystal grain size of at least 0.05 mm are targeted in the analysis by the image analysis software. In addition, when image analysis software such as that described above is used, separate measurements are possible because there is a difference in color tone between alumina crystal grains and zirconia crystal grains.

[0098] The average value of an equivalent circle diameter of each crystal grain calculated from the area of each crystal grain of alumina is the average crystal grain size of alumina, and the average value of an equivalent circle diameter of each crystal grain calculated from the area of each crystal grain of zirconia is the average crystal grain size of zirconia.

[0099] The standard deviation of the crystal grain size of alumina can be determined by the same method as that used to determine the average crystal grain size described above from the data of the crystal grain size of alumina obtained using image analysis software.

Determination of the Fracture Toughness (KIc Value) of Ceramic Substrates According to the IF Method with Evaluation According to Niihara and Anstis

[0100] The KIc value was determined using the IF method as described in A. G. Evans, E. A. Charles, J. Am. Ceram. Soc. 1976, 56, 371-372. Und G. R. Anstis, P. Chantikul, et al., J. Am. Ceram. Soc. 1981, 64, 533-538.

[0101] In short: substrates were supplied. A sample was broken out of each substrate, embedded in Clarocit and ground and polished.

[0102] Subsequently, a large number of Vickers indentations were made in each substrate so that there were at least 5 (but usually up to 10) indentations of sufficient quality. Sufficient quality means that the cracks running away from the corners of the indentations were clearly identifiable (one clean, relatively straight crack each with a relatively clearly identifiable crack end and no branching) and no large breakouts were visible on the indentation. The creation of these clear cracks without large break-outs in the indentation first required the determination of the appropriate indentation load. If the indentation load is too low, no cracks will appear. If the indentation load is too high, either the substrate breaks or massive chipping occurs in the indentation, making it impossible to evaluate the indentation. With lower indentation loads, no or too short cracks occur.

[0103] The evaluation and thus the calculation of the K.sub.Ic value was done according to the formula of Niihara as well as Anstis:

[00001]$K_{\mathrm{Ic},\mathrm{Niihara}}=0,018H\sqrt{a}{\left(\frac{E}{H}\right)}^{0,4}{\left(\frac{c}{a}-1\right)}^{-0,5}$ [0104] KIC, Niihara=fracture toughness [MPam]. [0105] HH=Vickers hardness value in MPa [0106] EE=E-modulus [MPa] [0107] c=crack length+half diagonal of the hardness indentation [m]. [0108] aa=half diagonal of the hardness impression [m].

[00002]$K_{\mathrm{Ic},\mathrm{Anstis}}=0,032H\sqrt{a}{\left(\frac{E}{H}\right)}^{0,5}{\left(\frac{c}{a}\right)}^{-1,5}$ [0109] KIC, Anstis=fracture toughness [MPam] [0110] HH=Vickers hardness value in MPa [0111] EE=E-modulus [MPa] [0112] c=crack length+half diagonal of the hardness indentation [m]. [0113] aa=half diagonal of the hardness impression [m].

[0114] For the modulus of elasticity, literature values were used (360 GPa). The hardness values were determined and output directly when the hardness indentation was applied. The crack lengths and indentation diagonals were measured directly on the tester after each hardness indentation.

[0115] The hardness and KIc values of the measured samples are shown in table 1 below. The mean value with standard deviation is given in each case. As written above, the mean values were formed from at least 5 measured hardness impressions per material.

TABLE-US-00001 TABLE 1 KIc values according to the IF method and the Niihara and Anstis formulas Sample K.sub.Ic [MPa m.sup.1/2] no. Vickers hardness Niihara K.sub.Ic [MPa m.sup.1/2] Anstis 1 1790 +/ 27 4.118 +/ 0.063 2.807 +/ 0.076 2 1828 +/ 14 4.094 +/ 0.065 2.749 +/ 0.082

Specific Heat Capacity

[0116] The specific heat capacity or heat capacity is a measurable physical quantity that corresponds to the ratio of the heat supplied to an object to the resulting temperature change.

[0117] The equation is as follows:

[00003]$\mathrm{Specific}\mathrm{heat}\mathrm{capacity}=\frac{\mathrm{heat}\mathrm{flow}\left(g\right)}{\mathrm{sample}\mathrm{mass}\left(g\right)*\mathrm{change}\mathrm{in}\mathrm{temperature}\left(T\right)}\left[\mathrm{cp}\right]=\frac{J}{g.Math.K}$

[0118] The specific heat is the amount of heat needed to raise the temperature of one gram of the material by 1 degree Celsius.

[0119] DSC measurements are done according to DIN 51007 and ISO 11357-1.

Functional Principle of a Heat Flow DSC:

[0120] A DSC measuring cell consists of a furnace and an integrated sensor with corresponding footprints for sample and reference crucibles. The sensor surfaces are connected to thermocouples or are even part of the thermocouples themselves. This makes it possible to record both the temperature difference between the sample and reference sides (DSC signal) and the absolute temperature of the sample or reference side. Due to the heat capacity cp of the sample, the reference side (usually empty crucible) usually heats up faster than the sample side when heating up a DSC measuring cell, i.e. the reference temperature (TR) rises somewhat faster than the sample temperature (TP). Both curves behave parallel to each other during heating with a constant heating speeduntil a sample reaction occurs. In the present case, the sample begins to melt at t1. During the melting process, the temperature in the sample does not change; however, the temperature of the reference side remains unaffected and continues to rise linearly. After the melting is finished, the sample temperature also increases again and shows a linear slope again from time t2 onwards.

[0121] The difference signal (T) of the two temperature curves is used. In the middle area of the curve, a peak is formed by the difference formation, which represents the endothermic melting process. Depending on whether the reference temperature was subtracted from the sample temperature during the difference formation or vice versa, the resulting peak points upwards or downwards in the graph. The area of the peak is related to the heat content of the conversion (enthalpy in J/g).

E-Module (Young's Modulus)

[0122] The measurement setup consists of the Grindosonic with connected microphone or piezo sensor, a suitable clapper and a special specimen holder with supports matched to the respective specimen geometry. The device is also connected to the PC for recording the measured values. Elasticity of a material means that a material deforms under external load, but returns to its original state as soon as the load disappears. This strain is linearly proportional to the applied load (Hooke's Law). The quotient of strain and load results in a proportionality factor known as the Young's modulus of the material.

Coefficient of Thermal Expansion CTE

[0123] A measuring device from company Netzsch is used to measure the linear thermal expansion of a sample as a function of temperature. Thermal expansion is a measure of the change in volume of a body in response to changes in temperature. Measuring according to manufacturer's specification DIL 402 Expedis Select & SupremeNETZSCH Analyzing & Testing (netzsch-thermal-analysis.com)

[0124] The following table summarizes parameter values measured by standard methods table 2

TABLE-US-00002 parameter unit standard Thermal conductivity W/mK ISO 18755: 2005 Bulk density g/cm.sup.3 DIN 993-1/ISO 18754 Specific heat capacity J/gK DSC measurement as described above Electrical breakdown kV/mm Following DIN EN 60243-ff strength E-Modul GPa Grindosonic as decscribed above Bending strength MPa ASTM C1499 (Sigma und Weibull, BBF) KIC [MPa m] IF Method as described above RFA (element analyis) Wt % DIN 51001/DIN EN ISO 12677 CTE 10{circumflex over ()}6 mm/ C. Dilatometer as described above Surface roughness, Ra m following Din EN ISO 4288

[0125] In the following tables 3-4 several examples according to the disclosure (inventive examples IE 1-2) and their properties are summarized.

[0126] In table 3 type and amount of starting material is provided for the inventive examples. The first grade of Al.sub.2O.sub.3 has a particle size d50 of 0.5 m and d90 of 2.0 m and the second grade of Al.sub.2O.sub.3 has a particle size d50 of 1.3 m and d90 of 3.2 m. The first grade of ZrO.sub.2 has a particle size d50 of 0.3-0.32 m and d90 of 0.60 m and the second grade of ZrO.sub.2 has a particle size d50 of 1.17 m and d80 of 2.06 m.

[0127] Further additives that are used are SiO.sub.2 as sintering agent,

TABLE-US-00003 TABLE 3 IE1 IE2 starting material wt % wt % Al.sub.2O.sub.3 first grade 45.110 45.110 ZrO.sub.2 first grade 6.637 6.637 ZrO.sub.2 second grade 2.844 2.844 Al.sub.2O.sub.3 second grade 45.110 45.110 SiO.sub.2 0.299 0.299

[0128] Further additives may be added, wherein the sum of all ingredients always adds up to 100 wt %.

[0129] The ceramic substrate obtained contains Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3 and SiO.sub.2. Further components in the ceramic substrates can be: Na.sub.2O, MgO, K.sub.2O, CaO, TiO.sub.2, Cr.sub.2O.sub.3, Fe.sub.2O.sub.3, SrO, CeO.

[0130] Table 4 summarizes the mechanical, thermal and electrical properties of the inventive examples of Table 3.

[0131] As can be seen in Table 4, bending strength reaches a high value of over 650 MPa, even over 680 MPa while the thermal conductivity is 24-25 W/(m*K). Thus, the inventive examples combine both an excellent mechanical strength and a good thermal conductivity.

TABLE-US-00004 TABLE 4 Condition Unit IE1 IE2 Average ZrO2 grain size m 0.65 0.72 Bulk density >95% der >95% der theoretischen theoretischen Dichte Dichte Surface roughness Ra m i.O. i.O. Mechanial Bending MPa >650 >680 strenght Modulus of GPa >355 >360 elasticity Thermal CTE (20-300 C.) 10.sup.6/K i.O. i.O. (300-600 C.) (600-900 C.) Thermal 25 C. W/(m .Math. K) >24 >24 conductivity specific heat 25 C. J/(kg .Math. K) 700 670 capacity Electrical Breakdown DC kV/mm >30 >30 strength

[0132] The effect of specific ZrO.sub.2 grain size and the amount of ZrO.sub.2 used in the inventive examples IE 1 and IE2 is furthermore illustrated in Table 5 with reference to comparative examples CE1 and CE2.

[0133] Comparative Examples CE 1 and CE2 were obtained according to conventional methods as described previously. In particular, the required amounts of Al.sub.2O.sub.3, ZrO.sub.2 and SiO.sub.2 powder were mixed, pulverizing, granulating and compact sintering.

TABLE-US-00005 TABLE 5 average ZrO.sub.2 amount of amount of Bending strength size ZrO.sub.2 [wt %] Al.sub.2O.sub.3 [wt %] [MPa] CE1 0.49 3.7 96.4 <600 CE2 0.49 9.1 90.4 >620 IE1 0.65 9.4 wt % 89.9 >650 IE2 0.72 9.4 wt % 89.9 >680

[0134] As can be seen for CE2, when using ZrO.sub.2 of a smaller grain size of 0.49 m a bending strength of the final ceramic of 640 MPa is achieved. However, when using ZrO.sub.2 with grain sizes of 0.65 (IE1) and 0.72 (IE2) even higher bending strengths of over 650 and 680 MPa were detected. Thus, a ZrO.sub.2 grain size of more than 0.6 m did not hamper the mechanical strength, on the contrary it was even possible to increase the mechanical strength to a certain extent.

[0135] This effect was not to be expected and contrary to the prior art.