JP2013199414A - Alumina ceramic and wiring board using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alumina ceramic board having high dimensional accuracy and a ceramic wiring board using the alumina ceramic board as an insulation board.SOLUTION: An alumina ceramic includes crystal particles of alumina and a grain-boundary phase and contains 3.0-5.0 mass% of Si, based on SiO, 0.3-0.5 mass% of Mg, based on MgO, 0.2-0.4 mass% of Ca, based on CaO, 3.0-6.0 mass% of Cr, based on CrO, and a combination of 0.1 mass% or less of elements other than the Si, Mg, Ca and Cr, including unavoidable impurities, relative to 100 mass% of the alumina.

Description

  The present invention relates to an alumina ceramic substrate suitable for a substrate required for dimensional accuracy, a package for housing a semiconductor element, and the like, and a wiring substrate to which the alumina ceramic substrate is applied.

  Conventionally, for example, a ceramic wiring board capable of high-density wiring design has been frequently used as a multilayer wiring board used for a package for storing electronic components such as semiconductor elements and crystal resonators.

  This type of multilayer ceramic wiring board is composed of an insulating substrate such as alumina or glass ceramic, and a wiring conductor mainly composed of W, Mo, Cu, Ag or the like formed on the surface thereof.

  In recent years, in a semiconductor element storage package that mounts semiconductor elements such as ICs and LSIs that have been highly integrated, and in a ceramic wiring substrate that is applied to a hybrid integrated circuit device in which various electronic components are mounted, Low resistance, small size, and light weight are required. For alumina ceramic materials, a low resistance conductor alumina wiring board that can be obtained by co-firing Cu-based conductors is proposed as a technique for reducing the resistance of wiring conductors. (For example, refer to Patent Document 1).

  As a method for forming such a ceramic wiring substrate, a conductor paste mainly composed of metal powder such as Cu, Ag, W, and Mo is formed on a ceramic green sheet by a screen printing method or the like, and a plurality of layers are laminated. A method of co-firing is generally used later.

  However, in the above-described manufacturing method, the ceramic green sheet shrinks by about 10 to 20% in the X, Y, and Z directions during firing, so that the shrinkage rate is controlled and a ceramic wiring board having high dimensional accuracy can be obtained. It has become difficult.

JP-A-12-114724

  Accordingly, an object of the present invention is to provide an alumina ceramic with high dimensional accuracy after firing and a wiring board using the ceramic as an insulating substrate.

Alumina ceramics of the present invention, and a crystal grain of alumina and the grain boundary phase, with respect to 100 mass% of alumina, 3.0 to 5.0 wt% of Si in terms of SiO _2, the Mg in terms of MgO 0.3 to 0.5 wt%, 0.2 to 0.4 wt% of Ca in terms of CaO, while containing 3.0-6.0 mass% in terms _{of Cr} 2 _{O 3} and Cr, including unavoidable impurities The total content of other elements excluding Si, Mg, Ca and Cr is 0.1% by mass or less.

The wiring board of the present invention has an insulating base on which a plurality of insulating layers are laminated, and a conductor layer containing at least one metal component of Mo or W provided on or inside the insulating base, The insulating layer is formed of the above-mentioned alumina ceramics.

  According to the present invention, after firing, an alumina ceramic with high dimensional accuracy and a wiring substrate using the ceramic as an insulating substrate can be obtained.

It is a graph which shows the shrinkage | contraction behavior when the molded object used as the alumina ceramic of this embodiment is heated. It is a cross-sectional schematic diagram which shows one Embodiment of the wiring board of this invention. It is a schematic diagram which shows an example when calculating | requiring the dimensional accuracy of a wiring board.

The alumina ceramic of the present embodiment has alumina (Al ₂ O ₃ ) crystal grains and a grain boundary phase. The composition of the alumina ceramic constituting the substrate is as follows: Si (silicon) is 3.0 to 5.0% by mass in terms of SiO ₂ and Mg (magnesium) is 0.3 in terms of MgO with respect to 100% by mass of alumina. -0.5 mass%, Ca (calcium) is 0.2-0.4 mass% in terms of CaO, and Cr (chromium) is 3.0-6.0 mass% in terms of Cr ₂ O ₃ . Moreover, except these Si, Mg, Ca and Cr, the total content of other elements including inevitable impurities is 0.1% by mass or less.

  FIG. 1 is a graph showing the shrinkage behavior when a molded body to be an alumina ceramic of this embodiment is heated. The shrinkage rate (%) shown in FIG. 1 is expressed as a percentage obtained by dividing the dimensions of the alumina ceramics after firing by the dimensions of the green compact before firing. The three curves shown in the graph of FIG. 1 show examples of samples in Examples described later, but the sample No. of the graph shown in FIG. 1, sample no. 3 and sample no. No. 4 has different contents of Si, Mg, Ca and Cr with respect to alumina.

  As can be seen from FIG. 1, sample 1 is a sample No. which is another sample. 3 and sample no. Compared to 4, the amount of shrinkage in the temperature range of 1550 to 1600 ° C. is small, and it can be seen that the firing shrinkage behavior of alumina ceramics varies greatly depending on the composition of additive components such as Si, Mg, Ca and Cr. .

  The alumina ceramic of this embodiment contains alumina in a mass ratio of 88% by mass or more, and is usually obtained by firing at a temperature of 1550 to 1600 ° C.

  Usually, in order to make a ceramic with a high alumina content ratio into a dense sintered body, it is necessary to add various sintering aids. As described above, depending on the composition and amount of the sintering aid, Even in the temperature range of 1550 to 1600 ° C. described above, a slight shrinkage still occurs (for example, samples 3 and 4 in FIG. 1). ).

  The alumina ceramic of the present embodiment has Si, Mg, Ca, and Cr in a predetermined composition range with respect to alumina, further defines the amount of solid solution of Cr in the alumina crystal particles, and Si, Mg Except for Ca and Cr, the total content of other elements including inevitable impurities is 0.1% by mass or less. Thereby, the shrinkage amount in the temperature range of 1550 to 1600 ° C. at which the alumina ceramics becomes dense can be reduced. As a result, even when a large number of alumina ceramics are fired at the same time, the alumina ceramics after sintering have a small variation in shrinkage, and the dimensional accuracy can be increased.

On the other hand, each content of Si, Mg, Ca and Cr with respect to 100% by mass of alumina is 3.0 to 5.0% by mass in terms of SiO ₂ and 0.3 to 0.5% by mass in terms of MgO. , In the range of 0.2 to 0.4% by mass in terms of CaO and 3.0 to 6.0% by mass in terms of Cr ₂ O ₃ , or inevitable except for Si, Mg, Ca and Cr When the total content of other elements including impurities is more than 0.1% by mass, the alumina ceramic after sintering has a large variation in shrinkage and the dimensional accuracy is lowered. Further, depending on the composition, the dielectric loss may increase.

In addition, Cr is solid-solved in the alumina crystal particles constituting the alumina ceramic of the present embodiment, and the content thereof is 3.0 to 4.0% by mass in terms of Cr ₂ O ₃ . In this case, the solid solution of Cr into the alumina crystal particles in the above composition range can suppress the solid solution of Si, Mg, and Ca, which are additional components other than Cr, into the alumina crystal particles. This suppresses the grain growth of the alumina crystal particles.

  Therefore, Si, Mg, and Ca, which are additive components other than Cr, are all combined in an oxide state to become glass, and mainly exist in the grain boundary phase of alumina crystal particles. It is densified by liquid phase sintering with glass rather than solid phase sintering in which crystal grains neck.

  Usually, the crystal growth of alumina proceeds even by liquid phase sintering involving glass, but in the case of the alumina ceramic of the present embodiment, the contents of Si, Mg, Ca and Cr are set within a predetermined range. Since the composition is almost free of other components, eutectic with other components of glass composed of Si, Mg and Ca hardly occurs in the temperature range of 1550 to 1600 ° C. In this way, the growth of crystal grains of alumina due to glass is suppressed. In this case, the total content of other elements including inevitable impurities is preferably 0.05% by mass or less.

  In the alumina ceramic thus obtained, the particle diameter of the alumina crystal particles is preferably in the range of 5 to 20 μm, and the water absorption is preferably 0.2% or less.

The alumina ceramic has a dielectric constant of 9.5 to 9.7 and a dielectric loss tangent of 3 × 10 ⁻⁴ or less.

  FIG. 2 is a schematic cross-sectional view showing an embodiment of the wiring board of the present invention. The wiring substrate shown in FIG. 1 has an insulating base 1 in which a plurality of insulating layers 1a, 1b, 1c and 1d (hereinafter sometimes referred to as 1a to 1d) are laminated, and a conductor on the surface or inside of the insulating base 1. It has a layer 3 (including a via-hole conductor), and the insulating substrate 1 is formed of the above-mentioned alumina ceramics. The conductor layer 3 contains at least one metal component of Mo or W as a main component. Since the insulating substrate 1 is formed of the above-mentioned alumina ceramics, the sintered insulating substrate 1 is also sintered even when the insulating substrate 1 is co-fired with the conductor layer 3 containing at least one metal component of Mo or W. The variation of the shrinkage amount of 1 is reduced, and a wiring board having high dimensional accuracy can be obtained.

  In the wiring board of the present embodiment, the conductor layer 3 contains alumina, the content of at least one metal component of Mo or W contained in the conductor layer 3 is 80 to 95% by volume, and the content of alumina. The amount is desirably 5 to 20% by volume. When the conductor layer 3 has the above-described configuration, the adhesive strength of the conductor layer 3 formed on the surface of the insulating substrate 1 is further increased in the wiring board obtained by simultaneous firing with the insulating substrate 1 to which the above-described alumina ceramic is applied. Can be increased.

Here, the contents of Si, Mg, Ca, and Cr contained in the alumina ceramic as the insulating substrate 1 can be obtained by dissolving the insulating substrate 1 in an acid and analyzing by ICP (Inductivity coupled plasma). In addition, with respect to 100% by mass of alumina, each element is determined as an oxide-converted value such as SiO ₂ , MgO, CaO, and Cr ₂ O ₃ .

  The water absorption rate of the insulating base 1 is obtained by the Archimedes method using a cut piece of the insulating base 1 cut out from the wiring board.

  The adhesive strength of the conductor layer 3 formed on the surface of the wiring board is such that the wiring board is cut out so as to have a predetermined shape, and a metal fitting is joined to the surface of the plating film formed on the conductor layer 3 using silver solder. The peeling load at the time of peeling off the metal fitting is measured, and the value of the obtained load is obtained as the adhesive strength.

  The dimensional accuracy of the alumina ceramic or the wiring board 1 is determined as follows. FIG. 3 is a schematic diagram illustrating an example of obtaining the dimensional accuracy of the wiring board. In this case, a plan view of the wiring board is shown. First, for example, with respect to the conductor layer 3 disposed on the surface of the sintered alumina ceramics or the wiring substrate at a predetermined interval, two directions perpendicular to the wiring substrate (in FIG. 3, the direction of the interval of X, The direction of the Y interval) is designated, and the position of at least one of these intervals is measured using a dimension measuring device. For example, by performing this measurement on 50 samples, the average value (x) and standard deviation (σ) of the dimensions are obtained, and the variation in dimensions is obtained from the standard deviation (σ) / average value (x). The variation is taken as the value of dimensional accuracy.

  The particle size of the alumina crystal particles is determined by polishing the portion of the insulating substrate cut out from the wiring board, removing the glass component on the sample surface by etching, and then taking a picture of the crystal structure using a scanning electron microscope. Draw about 50 circles on the top, select the crystal grains that fall within and around the circle, then image-process the outline of each crystal grain to determine the area of each crystal grain, and circles with the same area The diameter is calculated by substituting for the particle diameter.

  The content of Cr solid-dissolved in the crystal grains of alumina is such that a sample piece of an insulating substrate cut out from a wiring board is converted into a thin film sample piece by a microtome, an electrolytic polishing method, an ion etching method, a focused ion beam (FIB) method or the like. After processing, the thin film sample piece is obtained using a transmission electron microscope and an EDS analyzer. Specifically, the electron microscope image is enlarged until the grain boundary of the crystal grain can be confirmed at one place in one field of view, and a portion at least 0.2 μm or more inward from the grain boundary of the crystal grain is defined as the inside of the crystal grain. Define and conduct EDS analysis at that site to confirm the Cr element dissolved in the crystal grains. Next, the composition ratio of the Cr element is quantitatively determined from the EDS analysis value as mass%, the same measurement is carried out for 10 places, the composition ratio obtained at each measurement position is averaged, and the alumina crystal is obtained. The content of Cr contained in the particles is determined.

In addition, the glass comprised by the additive component containing Si, Mg, Ca which comprises the alumina ceramics of this embodiment WHEREIN: The oxide powder of the same composition as the composition which analyzed the insulating base | substrate quantitatively is 1200-1300 degreeC. The viscosity measured by the parallel plate rotation method in the temperature range should be 1 × 10 ⁶ to 1 × 10 ⁸ poise. A glass having such a viscosity characteristic causes alumina to be sintered at a temperature of 1200 ° C. to 1300 ° C., but the viscosity decrease is small at a temperature of 1500 ° C. or higher. It is to become. The glass component in the grain boundary phase of alumina ceramics is specified and the composition is determined in the same manner as the solid solution ratio of Cr dissolved in alumina. After processing into a thin film sample piece by an etching method, FIB method or the like, the thin film sample piece is obtained using a transmission electron microscope and an EDS analyzer.

  Next, the alumina ceramic of this embodiment and the manufacturing method of a wiring board using the same will be described.

  First, in order to produce an alumina ceramic to be the insulating substrate 1, an alumina powder having a purity of 99% or more and an average particle size of 1.0 to 10.0 μm is used. By making the average particle size of the alumina powder 1.0 μm or more, the sheet formability is good, and by making it 10.0 μm or less, it is possible to promote densification by firing at a temperature of 1620 ° C. or less. Become.

Next, with respect to 100% by mass of the alumina powder, the SiO ₂ powder is 3.0 to 5.0% by mass, the MgO powder is 0.3 to 0.5% by mass, and the CaO powder is 0.2 to 0.4% by mass. % And Cr ₂ O ₃ powder are added in an amount of 3.0 to 6.0% by mass to prepare a mixed powder. In this case, the SiO ₂ powder used as an additive has an average particle size of 1.0 to 5.0 μm, the MgO powder has an average particle size of 1.0 to 5.0 μm, and the CaO powder has an average particle size of 1.0 to 5 μm. As the 0.0 μm and Cr ₂ O ₃ powder, those having an average particle diameter of 1.0 to 5.0 μm are preferably used. The purity of the SiO ₂ powder, MgO powder, CaO powder and Cr ₂ O ₃ powder is preferably 99% or more. As a result, sheet formability is improved, diffusion of Si, Mg, Ca and Cr and solid solution in alumina powder can be controlled, and sinterability at a temperature of 1580 to 1620 ° C. is enhanced. be able to.

  In this case, Si, Mg, Ca, and Cr may be added as carbonates, nitrates, acetates, and the like that can form oxides by firing in addition to the above oxide powders.

  Next, an organic binder and a solvent are added to the composite powder to prepare a ceramic slurry, and then a green sheet having a predetermined thickness is formed by a molding method such as a press method, a doctor blade method, a rolling method, or an injection method. Make it. The thickness of the green sheet can be freely set to, for example, 50 to 300 μm for the reasons of design of the ceramic multilayer wiring board 1, but is not particularly limited.

  Next, among the produced ceramic green sheets, for example, a conductor pattern as shown in FIG. 3 is printed on the surface of the ceramic green sheet laminated on the uppermost layer, and another ceramic green sheet not printed with the conductor pattern is attached. A plurality of sheets are stacked and pressed to produce a laminated molded body.

  Next, this laminated molded body is fired under a predetermined temperature condition. The firing conditions are such that the maximum temperature is 1580 to 1620 ° C. in a non-oxidizing atmosphere (nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen).

  When producing a wiring board, a conductor pattern designed to have a predetermined shape is formed on the surface of the ceramic green sheet by printing in the same manner as described above. A through hole of 50 to 250 μm is formed.

Next, the ceramic green sheets on which the conductor pattern is formed are aligned and laminated to form a laminated molded body, and then fired under the same conditions as described above.
The alumina ceramics produced by the method described above and the wiring board using the insulating ceramic 1 as an insulating base 1 have high dimensional accuracy.

An Al ₂ O ₃ powder with a purity of 99% and an average particle size of 1.8 μm, an SiO ₂ powder with a purity of 99% and an average particle size of 2.0 μm, an purity of 99% and an average particle size of 2 .0 μm M
gO powder, CaO powder with a purity of 99% and an average particle size of 2.0 μm, Cr ₂ O ₃ powder with a purity of 99% and an average particle size of 2.0 μm, a purity of 99% and an average particle size of 1.5 μm After mixing the TiO ₂ powder at a ratio as shown in Table 1, an acrylic binder as a molding organic resin (organic binder) and toluene as an organic solvent were mixed to prepare a ceramic slurry, and then a doctor blade The ceramic green sheet was produced by forming into a 200 μm thick sheet by the above method.

  Next, among the obtained ceramic green sheets, the conductor pattern shown in FIG. 3 is printed on the surface of the ceramic green sheet laminated on the uppermost layer, and 14 other ceramic green sheets not printed with the conductor pattern are stacked. Then, press molding was performed to produce a laminated molded body. In this case, the one in which ten rectangular conductor patterns of 2.4 mm × 28 mm were arranged for measuring the adhesive strength of the conductor layer was used.

  Next, this laminated compact was fired under the following conditions to obtain an alumina ceramic substrate. After degreasing in a nitrogen-hydrogen mixed atmosphere with a dew point of + 17.5 ° C., the temperature was raised from 1000 ° C. to 1600 ° C. at a heating rate of 150 ° C./hr and held at 1600 ° C. for 1 hour. The cooling rate was 100 ° C./hr.

  Next, the following evaluation was performed on the produced alumina ceramics and the wiring board.

  The water absorption was measured based on JIS-C2141. The number of samples was three and the average value was obtained.

  The relative dielectric constant and the dielectric loss tangent (tan δ) were measured at a frequency of 1 MHz using a bridge circuit method. The number of samples was 5 and the average value was obtained.

  The content of Cr dissolved in the crystal grains of alumina is obtained by processing a sample piece of an insulating substrate cut out from a wiring board into a thin film sample piece by a microtome, an electrolytic polishing method, an ion etching method, or a focused ion beam (FIB) method. Then, the thin film sample piece was obtained using a transmission electron microscope and an EDS analyzer. In this case, the electron microscope image is magnified until the grain boundary of the crystal grain can be confirmed in one field of view, and a portion at least 0.2 μm or more inward from the grain boundary of the crystal grain is defined as the inside of the crystal grain. Then, EDS analysis was performed at the site, and Cr element dissolved in the crystal particles was confirmed. Next, the composition ratio of the Cr element is quantitatively determined from the EDS analysis value as mass%, the same measurement is carried out for 10 places, the composition ratio obtained at each measurement position is averaged, and the alumina crystal is obtained. The content of Cr contained in the particles was determined. The number of samples was one and the average value was obtained.

The contents of Si, Mg, Ca and Cr contained in the alumina ceramic can be obtained by ICP analysis after dissolving the insulating substrate in an acid. In this case, SiO ₂ , MgO, It was determined as the conversion value to the CaO and _Cr 2 _{O 3.} The composition of the sintered body was consistent with the formulation composition shown in Table 1. The number of samples was one.

  The dimensional accuracy of the produced alumina ceramic substrate was measured by using a substrate having a plane area of 30 mm × 30 mm and measuring the X and Y intervals shown in FIG. This measurement was performed on 50 samples, and from the average value (x) and standard deviation (σ) of the dimensions, the dimensional variation was obtained as standard deviation (σ) / average value (x). This was taken as the value of dimensional accuracy.

The adhesion strength of the conductor layer to the insulating base is determined by applying the electroless Ni plating to the 2 mm x 25 mm conductor wiring formed on the surface of the wiring board, then joining the metal fittings using silver solder, and peeling the metal fittings The peeling load was measured. When the peeling load was 4.9 kgf or more, it was determined that the adhesive strength of the metallization was high, and when the peeling load was lower than 4.9 kgf, it was determined that the adhesive strength of the metallization was low. In this evaluation, ten conductor layers were measured and an average value was obtained. These results are shown in Table 1.

  As is clear from the results of Table 1, the dimensional accuracy was 0.03% or less in the samples (Sample Nos. 1, 6, 7, 10, 11, 14, 15, 18, 19, and 21 to 25). .

These samples have a water absorption of 0.02%, a relative dielectric constant of 9.5 to 9.7, and a dielectric loss tangent of 3
× 10 ^-4 .

In samples (sample Nos. 1, 6, 7, 10, 11, 14, 15, 18, 19 and 21 to 24) having a content of TiO ₂ of less than 0.1% by mass, all the samples have dimensional accuracy. 0.02%. In addition, among the samples (sample Nos. 1, 6, 7, 10, 11, 14, 15, 18, 19, 21, and 22) in which the composition of the metal component (W) of the conductor layer is 80 to 95% by volume. The adhesive strength of the conductor layer was 4.9 kgf or more.

Instead of TiO ₂ , V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ta, W, and rare earth element (RE) were used as sample numbers. For the alumina ceramics prepared by adding only the same molar amount as 25, Sample No. The result was the same as 25.

  Furthermore, in Table 1, although the case where the metal component of the conductor layer was W was illustrated, the same result was obtained also when Mo was applied with the same composition instead of W.

  In contrast, sample no. In 2-5, 8, 9, 12, 13, 16, 17, and 20, all the dimensional accuracy was larger than 0.03%.

1 ... Insulating substrate 1a, 1b, 1c, 1d ... Insulating layer 3 ... Conductor layer

Claims (4)

Having crystal grains of alumina and a grain boundary phase;
Relative to 100 mass% of alumina, 3.0 to 5.0 wt% of Si in terms of SiO _2, 0.3 to 0.5 mass% of Mg in terms of MgO, of Ca in terms of CaO from 0.2 to 0. 4 wt%, while containing 3.0-6.0 mass% in terms _{of Cr} 2 _{O 3} and Cr,
Aluminous ceramics characterized in that the total content of other elements including inevitable impurities, excluding Si, Mg, Ca and Cr, is 0.1% by mass or less.   2. The alumina ceramics according to claim 1, wherein the total content of the other elements is 0.05% by mass or less.   An insulating substrate in which a plurality of insulating layers are laminated, and a conductor layer containing at least one metal component of Mo or W provided on or inside the insulating substrate, wherein the insulating layer is claim 1 or A wiring board, which is formed of the alumina ceramics described in 2.   The conductor layer contains alumina, the content of the metal component contained in the conductor layer is 80 to 95% by volume, and the content of the alumina is 5 to 20% by volume. 3. The wiring board according to 3.