WO2013054852A1 - 窒化珪素基板および窒化珪素基板の製造方法 - Google Patents
窒化珪素基板および窒化珪素基板の製造方法 Download PDFInfo
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- WO2013054852A1 WO2013054852A1 PCT/JP2012/076339 JP2012076339W WO2013054852A1 WO 2013054852 A1 WO2013054852 A1 WO 2013054852A1 JP 2012076339 W JP2012076339 W JP 2012076339W WO 2013054852 A1 WO2013054852 A1 WO 2013054852A1
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Definitions
- the present invention relates to a silicon nitride substrate and a method for manufacturing a silicon nitride substrate.
- ceramic substrates which are ceramic sintered bodies
- insulating substrates which are members constituting circuit boards.
- a circuit board for a semiconductor module that mounts a semiconductor element that generates a large amount of electricity and generates a large amount of heat requires high mechanical strength, thermal conductivity, and electrical insulation.
- a ceramic substrate which is a bonded body is widely used.
- a metal substrate as a circuit board on which a semiconductor is mounted is bonded to one surface of a ceramic substrate, and a metal substrate as a heat dissipation plate connected to a heat dissipation member or the like is bonded to the other surface.
- the ceramic substrate and the metal substrate are bonded by a direct bonding method (DBC) or a brazing material bonding method (AMB).
- DBC direct bonding method
- AMB brazing material bonding method
- Patent Document 1 states that “a ceramic green sheet is molded, and a release agent containing BN powder having an oxygen content of 3% by weight or less and an average particle size of 20 ⁇ m or less is formed on the surface thereof by a roll coater. After coating 0.3 to 3 mg / cm 2 , stack multiple sheets, degrease, and then press the top and bottom surfaces of the laminate with a BN setter and place it in a sealed container made of the same material as the setter.
- a ceramic sintered body manufacturing method characterized in that it is housed and sintered, and a plate-like aluminum nitride sintered body having a flatness of 100 ⁇ m or less formed by the manufacturing method are disclosed.
- a plurality of silicon nitride sintered bodies are obtained by separating and then laminating and sintering a plurality of green sheets via a separating material
- the coefficient of variation Cv indicating the distribution of B amount derived from BN remaining on the surface of the silicon nitride substrate is 1.0 or less
- the silicon nitride Waviness Wa of the substrate surface is 1.5 ⁇ m or less (However, the waviness is measured by using a surface roughness meter to measure the waviness center line waviness, and the arithmetic mean waviness Wa, that is, the arithmetic mean of the absolute value of the deviation from the mean value of the surface height.
- the measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value ( ⁇ c) of 0.25 mm, a cutoff value ( ⁇ f) of 8.0 mm), and a relative density of A silicon nitride substrate characterized by being 98% or more "is disclosed.
- the green sheets which are plate-like ceramic molded bodies, are laminated and then laminated when sintered.
- the average particle size, oxygen content, coating amount, and other various conditions of the boron nitride particles constituting the separation layer interposed between the green sheets it is possible to suppress adhesion between the sintered ceramic substrates and Waviness on the surface of the substrate can be suppressed.
- the ceramic substrate is a silicon nitride substrate that is a sintered body composed of a main phase composed of silicon nitride particles and a grain boundary phase composed of a sintering aid, and has a thickness of 0.20.
- a silicon nitride substrate as thin as ⁇ 0.80 mm, it is still possible to obtain a silicon nitride substrate with a predetermined yield strength, thermal conductivity, and bondability to a metal plate with a stable yield with a surface waviness of 1.00 ⁇ m or less. It was difficult.
- the surface waviness refers to the arithmetic average waviness Wa obtained by measuring the filtered centerline waviness using a surface roughness meter.
- an amount that is an arithmetic average of absolute values of deviation from the average value of the surface height is used, and measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, and a cutoff value ( ⁇ c).
- the cut-off value ( ⁇ f) is 8.0 mm.
- the present invention has been made in view of such prior art, and is composed of a main phase made of silicon nitride particles and a grain boundary phase made of a sintering aid, which are as thin as 0.20 to 0.80 mm.
- the silicon nitride substrate which is a sintered body
- the surface waviness is 1 ⁇ m or less
- the silicon nitride substrate having desired bending strength, thermal conductivity, and bondability with a metal plate, and a plurality of layers are laminated after sintering. It is an object of the present invention to provide a manufacturing method capable of forming a silicon nitride substrate with high separability when the individual ceramic substrates are separated from the ceramic substrate in a state without damaging the ceramic substrates.
- one embodiment of the present invention is a method of manufacturing a silicon nitride substrate having a thickness t of 0.20 to 0.80 mm, wherein the silicon nitride substrate is a main phase mainly composed of silicon nitride particles. And a grain boundary phase formed mainly from a sintering aid, and using a boron nitride paste containing boron nitride powder / organic binder and organic solvent, silicon nitride powder / sintering aid powder and organic
- a separation layer forming step for forming a separation layer on the surface of the plate-shaped molded body containing the binder, and after the separation layer forming step, at a temperature higher by 15 to 450 ° C.
- said boron nitride contains 0.01 to 0.5% by mass of oxygen (O) and 0.001 to 0.5% by mass of carbon (C) in the boron nitride powder, and carbon is added to the separation layer after the degreasing step.
- the content (% by mass) of oxygen contained in the boron nitride powder of the boron nitride paste is c, and the carbon content (C) contained in the separation layer after the degreasing step
- the content (mass%) is a
- c / a is in the range of 0.02 to 10.00
- the separation layer formed on the molded body in the separation layer forming step is 0.2 to It is comprised so that 3.5 mg / cm ⁇ 2 > hexagonal boron nitride powder may be included.
- the range of the ratio of the fluorescent X-ray intensity (B / Si) of boron (B) and silicon (Si) at an arbitrary position on the surface of the silicon nitride substrate is 7. It is preferably 0 ⁇ 10 ⁇ 5 to 250 ⁇ 10 ⁇ 5 and B / C, which is the ratio of boron (B) to carbon (C), is 0.080 to 3.000. .
- the boron nitride paste contains the organic binder with respect to 100 parts by mass of boron nitride powder having an average particle size d50 of 4.0 to 20.0 ⁇ m, d10 of 0.5 to 7.0 ⁇ m, and d90 of 8 to 40 ⁇ m. It is preferable to contain 8.75 to 44 parts by mass.
- the boron nitride paste has a viscosity of 1000 to 50000 cP at 25 to 27 ° C. and a thixotropy of 1.02 to 4.00, and the separation layer forming step preferably forms the separation layer by screen printing. It is.
- thixotropy is a value defined by the ratio of the viscosity of 10 rpm to 100 rpm (viscosity of 10 rpm) / (viscosity of 100 rpm) measured with a rotational viscometer.
- the boron nitride paste preferably contains 8.75 to 44 parts by mass of the organic binder and 80 to 750 parts by mass of an organic solvent with respect to 100 parts by mass of hexagonal boron nitride powder.
- the separation layer formed on the molded body in the separation layer forming step contains 0.5 to 1.4 mg / cm 2 of hexagonal boron nitride powder, and at any place on the surface of the molded body after the degreasing step.
- the ratio (B / Si) of the characteristic X-ray intensities (B / Si) of boron (B) and silicon (Si) obtained by line analysis using an electron beam microanalyzer (EPMA) having a measurement length of 20 mm any 10. It is preferable that g / f is 0.2 to 7.0, where f is the average value of the 0 mm section and g is the average value of the 0.2 mm section included in the 10.0 mm section. .
- the exothermic peak temperature of the organic binder contained in the boron nitride paste measured by differential thermal analysis is preferably 5 ° C. or more higher than the exothermic peak temperature of the organic binder of the molded body.
- the boron nitride paste is prepared by blending 8.75 to 44 parts by mass of an organic binder and 80 to 750 parts by mass of an organic solvent with 100 parts by mass of boron nitride powder and stirring for 0.2 to 10 hours. It is preferable to do this.
- Another aspect of the present invention is a silicon nitride substrate, the silicon nitride substrate including a main phase mainly composed of silicon nitride particles and a grain boundary phase mainly formed of a sintering aid.
- the main phase is a first silicon nitride particle having a major axis length divided by a minor axis length of 3.0 or less and a major axis length of 5.0 ⁇ m or less on the substrate surface.
- a second silicon nitride particle having a major axis length and an aspect ratio both exceeding the first silicon nitride particle, and the first silicon nitride particle has a side set at an arbitrary position on the substrate surface.
- the range of the ratio of the fluorescent X-ray intensity (B / Si) of boron (B) and silicon (Si) at an arbitrary position on the substrate surface is 7.0 ⁇ . is 10 -5 ⁇ 250 ⁇ 10 -5, which is the ratio of boron (B) and carbon (C) B / There is from 0.080 to 3.000, further, waviness of the surface is not more than 1.00 .mu.m, in addition thickness t is equal to or is 0.20 ⁇ 0.80 mm.
- the waviness of the substrate surface is measured by measuring the filtered center line waviness using a surface roughness meter, and the arithmetic average waviness Wa, that is, the arithmetic average of the absolute value of the deviation from the average value of the surface height.
- the measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value ( ⁇ c) of 0.25 mm, and a cutoff value ( ⁇ f) of 8.0 mm.
- the silicon nitride substrate includes 40 or less of the first silicon nitride particles in a square region having a side of 10 ⁇ m set at an arbitrary position in the surface layer having a depth of 20 ⁇ m from the substrate surface, It is preferable that 30 or less of the first silicon nitride particles are contained in a square region having a side of 10 ⁇ m set at an arbitrary position in the inner layer whose depth from the outer layer is in a range other than the surface layer.
- the silicon nitride substrate has an aspect ratio of 5.0 to 20.0 in a square region with a side of 10 ⁇ m set at an arbitrary position on the surface layer having a depth of 20 ⁇ m from the substrate surface, It is preferable that the second silicon nitride particles having an axial length of 6.0 to 30.0 ⁇ m are included in an area ratio of 1.0 to 30.0%.
- the silicon nitride substrate includes an agglomerated portion having a maximum diameter of 25 ⁇ m or less formed by agglomerating the first silicon nitride particles in a surface layer having a depth of 20 ⁇ m from the substrate surface. Is preferred.
- the silicon nitride substrate includes 25 or less aggregated portions in a square region having a side of 100 ⁇ m set at an arbitrary position on the surface layer having a depth of 20 ⁇ m from the substrate surface.
- the silicon nitride substrate includes 25 or less aggregated portions in a square region having a side of 100 ⁇ m set at an arbitrary position on the surface layer having a depth of 20 ⁇ m from the substrate surface, and has a depth from the substrate surface. It is preferable that 20 or less of the aggregated portions are included in a square region having a side of 100 ⁇ m set at an arbitrary position in the inner layer having a length other than the surface layer.
- the maximum diameter of pores formed in the grain boundary phase around the first silicon nitride particles is 10 ⁇ m or less in the surface layer having a depth of 20 ⁇ m from the substrate surface. Is preferred.
- the silicon nitride substrate includes 20 or less pores in a square region having a side of 100 ⁇ m set at an arbitrary position on the surface layer having a depth of 20 ⁇ m from the substrate surface.
- the silicon nitride substrate preferably has a variation coefficient of the characteristic X-ray intensity of boron (B) on the substrate surface measured by an electron beam microanalyzer (EPMA) under the following conditions of 1.0 or less.
- the measurement condition of the electron microanalyzer is that the range of 1 mm with a beam diameter of 1 ⁇ m is scanned, and the standard deviation is divided by the average value from the value of the fluorescent X-ray intensity of boron (B) measured at intervals of 2 ⁇ m. Is the value obtained by
- the object of the present invention can be achieved.
- the inventors of the present application first studied the prior art in order to improve the undulation of the silicon nitride substrate. As a result, it has been found that the problem of surface waviness cannot be solved in the silicon nitride substrate formed by the conventional technique. The reason why this surface undulation problem is not solved is not clear, but it was estimated that the following phenomenon might be one factor.
- boron nitride contained in a separation layer formed on the surface of the green sheet may be referred to as a boron compound containing oxygen (hereinafter referred to as B compound). .) May be formed.
- B compound include diboron trioxide (B 2 O 3 ).
- the distribution of BN particles in the separation layer formed on the green sheet is sparse, and the B compound in the portion where the BN particles are densely arranged is heated when the green sheet is heated in the sintering process.
- a normal glass that acts on the sintering aid present in the grain boundary between the silicon nitride particles contained in the surface layer of the steel lowers the melting point of the sintering aid, and as a result, the sintering aid forms A grain boundary phase composed of a glass containing boron having a lower melting point (hereinafter sometimes referred to as boron glass for the sake of convenience) (hereinafter referred to as an abnormal phase for convenience of understanding). There is a possibility of forming an abnormal region having.
- Boron (B) has a relatively small ionic radius, so it is easy to diffuse. Since the edge of the abnormal region cannot be distinguished from the normal region, a clear boundary line cannot be drawn, but the concentration of boron (B) is normal. It is estimated that the portion clearly higher than the region is an abnormal region.
- the abnormal phase contained in the abnormal region on the surface layer of the green sheet has a low melting point, it melts earlier than other normal grain boundary phases, and the ⁇ -type granular silicon nitride particles 9c contained in the abnormal region are Initiate rearrangement. Since the silicon nitride particles are rearranged so that the pores included in the abnormal region that has melted and become a liquid phase disappear, the abnormal region contracts. As described above, the distribution of BN particles contained in the separation layer is sparse and dense, and when the green sheet is viewed in plan, it is estimated that a plurality of abnormal regions having different areas are scattered.
- a grain boundary phase made of normal glass formed of a sintering aid that does not act on the B compound (hereinafter, for the sake of convenience, this grain boundary phase is set to normal.
- the normal region having a phase may also be melted, and the ⁇ -type granular silicon nitride particles contained in the normal region also start to rearrange and contract.
- a time difference occurs in the rearrangement of the silicon nitride particles due to a difference in melting point of the grain boundary phase contained in both, and a time difference also occurs in the contraction timing of both. That is, it is considered that a phenomenon occurs in which the shrinkage of the normal region where the B compound does not act starts after the shrinkage of the abnormal region including the boron glass on which the B compound acts.
- silicon nitride particles grow into particles having a long major axis length by the coexistence of a rare earth oxide such as Y 2 O 3 which is a sintering aid.
- a rare earth oxide such as Y 2 O 3 which is a sintering aid.
- boron glass having a low melting temperature is mainly present. Therefore, the boron glass is dissolved before the silicon nitride particles grow, and silicon nitride particles grow.
- the space for filling is filled with liquid (referred to as densification).
- densification liquid
- the granular silicon nitride particles contained in the abnormal region are unlikely to progress, and may become silicon nitride particles having a low aspect ratio and a short major axis.
- the granular silicon nitride particles contained in the normal region have no growth inhibiting factor, they grow and become columnar silicon nitride particles having a large aspect ratio and a long major axis. Then, it is considered that the abnormal region is pushed out by the normal region including the columnar silicon nitride particles that contract thereafter and deforms so as to protrude from the surface of the normal region.
- the inventors of the present application have found that deformation generated in a minute region by the mechanism assumed as described above causes excessive undulation when viewed as the entire surface of the silicon nitride substrate WB, and the thickness is 0.20 to 0.80 mm.
- a thin silicon nitride substrate it is presumed that it is extremely difficult to make the surface waviness (Wa) 1 ⁇ m or less, and the present invention has been completed based on this. That is, a silicon nitride substrate having a reduced surface waviness could be obtained by producing a silicon nitride substrate by making the distribution of the B compound uniform on the substrate surface and reducing the concentration of the B compound.
- One embodiment of the present invention is a silicon nitride substrate that is a sintered body including a main phase mainly composed of silicon nitride particles and a grain boundary phase mainly formed from a sintering aid, wherein the main phase Is a first silicon nitride particle having a major axis length divided by a minor axis length of 3.0 or less and a major axis length of 5.0 ⁇ m or less on the substrate surface, and the first silicon nitride Second silicon nitride particles having a major axis length and an aspect ratio that exceed both of the grains, and the first silicon nitride particles are 40 in a square region having a side of 10 ⁇ m set at an arbitrary position on the substrate surface.
- the ratio of the fluorescent X-ray intensity ratios (B / Si) of boron (B) and silicon (Si) at any location on the substrate surface is 7.0 ⁇ 10 ⁇ 5 to 250 ⁇ 10 ⁇ 5, and are each fluorescent X-ray intensity ratio of B / C of boron (B) and carbon (C) .080 ⁇ is 3.000, further, waviness of the surface is not more than 1.00 .mu.m, a silicon nitride substrate, wherein the thickness t is 0.20 ⁇ 0.80 mm in addition.
- the ratio of the fluorescent X-ray intensity (B / Si) of boron (B) and silicon (Si) at an arbitrary position on the surface is 7.0 ⁇ 10 as described above. ⁇ 5 to 250 ⁇ 10 ⁇ 5 .
- This value of B / Si is that of boron (B) contained in each of BN constituting the separation layer existing on the surface of the silicon nitride substrate and boron glass existing in the abnormal region of the surface layer of the silicon nitride substrate as described above. Although the sum of the amounts is reflected, the amount of boron (B) contained in the abnormal region is indirectly shown.
- the surface of the silicon nitride substrate contains many abnormal phases containing boron glass, and by extension, the BN powder constituting the separation layer formed on one surface of the green sheet. It is considered that many B compounds were contained therein.
- the reason why the range of B / Si is set to 7.0 ⁇ 10 ⁇ 5 to 250 ⁇ 10 ⁇ 5 is as follows. That is, when B / Si is less than 7.0 ⁇ 10 ⁇ 5 , the amount of BN powder constituting the separation layer is small in the first place, and after sintering, a plurality of stacked silicon nitride substrates are combined.
- B / C which is the ratio of the fluorescent X-ray intensity of each of boron (B) and carbon (C) is 0.080 to 3.000 as described above. That is, the silicon nitride substrate of this embodiment has an appropriate amount of carbon (C) on its surface.
- This carbon (C) is a residue of carbon (C) which is reduced to harmless boron (B) by reducing oxygen (O) of the B compound contained in the separation layer as described above.
- B / C is less than 0.080, the amount of carbon (C) remaining on the surface becomes excessive, reducing the strength of the silicon nitride substrate and degrading the bondability between the metal substrate and the silicon nitride substrate.
- the main phase is such that the major surface length is 3.0 or less and the major axis length is 5.0 ⁇ m or less on the substrate surface.
- First silicon nitride particles and second silicon nitride particles having a major axis length and an aspect ratio that exceed both of the first silicon nitride particles are included. From the value of B / Si and the value of B / C on the surface of the silicon nitride substrate, there is a possibility that the B compound contained in the separation layer is reduced by C and made harmless.
- the boron in the B compound contained in the separation layer is reduced by carbon (C), and the B compound is reduced, whereby boron formed by the action of the B compound.
- C carbon
- the aspect ratio obtained by dividing the major axis length by the minor axis length is 3.0 or less, and the major axis length is 5.0 ⁇ m or less.
- the first silicon nitride particles are reduced. Specifically, 40 or less first silicon nitride particles are present in a square region having a side of 10 ⁇ m set at an arbitrary position on the surface.
- B / Si on the surface thereof is 7.0 ⁇ 10 ⁇ 5 to 250 ⁇ 10 ⁇ 5
- B / C is 0.080 to 3.000
- the undulation of the substrate surface can be 1 ⁇ m or less.
- a surface roughness meter is used to measure the filtered center line waviness, and the arithmetic average waviness Wa, that is, the arithmetic operation of the absolute value of the deviation from the average value of the surface height.
- the average amount is used, and the measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value ( ⁇ c) of 0.25 mm, and a cutoff value ( ⁇ f) of 8.0 mm.
- the silicon nitride substrate of the above-described embodiment 40 or less of the first silicon nitride particles are included in a square region having a side of 10 ⁇ m set at an arbitrary position in the surface layer whose depth from the surface is 20 ⁇ m.
- the inner layer whose depth from the surface is in a range other than the surface layer it is preferable that 30 squares or less of the first silicon nitride particles are contained in a square region having a side of 10 ⁇ m set at an arbitrary position.
- the first silicon nitride particles when a large number of the first silicon nitride particles are present in the silicon nitride substrate, it is assumed that a large number of abnormal phases exist around the first silicon nitride particles.
- the boron glass contained in the abnormal phase has a lower strength than the glass constituting the normal phase, and cracks are likely to occur when stress is applied to the silicon nitride substrate.
- the first silicon nitride particles have a granular form with an aspect ratio of 3.0 or less with respect to the columnar second silicon nitride particles, the fracture toughness is low and cracks tend to progress.
- the first silicon nitride particles are arranged in a square region having a side of 10 ⁇ m set at an arbitrary position on the surface layer having a depth from the surface of 20 ⁇ m. Therefore, the occurrence of cracks in the surface layer of the silicon nitride substrate is suppressed even when stress is applied.
- the inner layer whose depth from the surface of the silicon nitride substrate is in a range other than the surface layer 30 squares or less of the first silicon nitride particles are included in a square region having a side of 10 ⁇ m set at an arbitrary position.
- the inner layer has higher fracture toughness than the surface layer, and even when a crack occurs in the surface layer, the progress of the crack is suppressed, and the silicon nitride substrate can be prevented from being broken.
- the first silicon nitride particles contained in the silicon nitride substrate and the abnormal phase that is considered to be present around the first silicon nitride particles are related to the characteristics of the silicon nitride substrate such as strength, fracture toughness, thermal conductivity, and withstand voltage. Negative impact.
- the first silicon nitride particles satisfy the above conditions, granular first silicon nitride particles having a small aspect ratio and a short major axis length are formed between the columnar second silicon nitride particles.
- the silicon nitride substrate When appropriately present in the region to be formed, high filling of silicon nitride particles is brought about in the silicon nitride substrate, the density of the silicon nitride substrate is improved, and the strength and thermal conductivity can be further improved.
- the condition is that in the surface layer whose depth from the substrate surface is in the range of 20 ⁇ m, the aspect ratio is 5.0 to 20.0 in a square region with a side of 10 ⁇ m set at an arbitrary position, and the major axis length is The second silicon nitride particles of 6.0 to 30.0 ⁇ m are included in an area ratio of 1.0 to 30.0%.
- the aspect ratio of the second silicon nitride particles is less than 5.0 or the major axis length is less than 6.0, a region of an appropriate size is not formed between the second silicon nitride particles, and the first There is no room for the silicon nitride powder to be disposed in the region, and there is no effect.
- the aspect ratio is 20.0 or the major axis length exceeds 30.0 ⁇ m, the presence of coarse silicon nitride particles causes coarse defects even when the first silicon nitride particles are present. It tends to occur and the strength decreases.
- the cross-sectional area ratio of the second silicon nitride particles is less than 1.0%, the amount of the first silicon nitride particles disposed in the region between the second silicon nitride particles is too large. As a result, coarse aggregated portions are formed, and various characteristics of the silicon nitride substrate cannot be realized.
- the cross-sectional area ratio of the second silicon nitride particles exceeds 30.0%, there is no room for the first silicon nitride particles to be disposed, and the density of the silicon nitride substrate is not improved.
- the surface layer having a depth from the substrate surface in the range of 20 ⁇ m includes an agglomerated portion formed by agglomeration of the first silicon nitride particles and having a maximum diameter of 25 ⁇ m or less. desirable.
- the agglomerated portion formed by agglomeration of the first silicon nitride particles is large, the size of the abnormal region, which is necessarily a collection of abnormal phases having low strength existing around it, also increases, and the strength of the silicon nitride substrate and Fracture toughness will be reduced. Therefore, it is desirable that the maximum diameter of the aggregated portion is 25 ⁇ m or less.
- the surface layer having a depth from the substrate surface in a range of 20 ⁇ m is configured to include 25 or less of the agglomerated portions in a square region having a side of 100 ⁇ m set at an arbitrary position. It is desirable.
- a silicon nitride substrate having desired strength and fracture toughness can be formed by setting the maximum diameter of the agglomerated portion to 25 ⁇ m or less.
- the silicon nitride substrate includes many agglomerated portions, There is a possibility that the thermal conductivity is lowered.
- a silicon nitride substrate which is a sintered body composed of a main phase composed of silicon nitride particles and a grain boundary phase composed of a sintering aid
- heat conduction is performed by phonons.
- the thermal conductivity of the sintered body is the thermal conductivity of the silicon nitride particles constituting the main phase
- the thermal conductivity of the grain boundary phase that is, the thermal conductivity inherent to the grain boundary phase, the volume of the grain boundary phase, It is governed by thickness.
- the second silicon nitride particles release the impurities in the grains during the grain growth process and become particles with few impurities, whereas the first silicon nitride particles do not progress in the grain growth. Contains many impurities.
- thermal conductivity decreases due to phonon scattering.
- the first silicon nitride particles are in a granular form with an aspect ratio of 3.0 or less, and the major axis length is as small as 5.0 ⁇ m or less. For this reason, when compared with the same volume, the surface area of the first silicon nitride particles is larger than that of the second silicon nitride particles, and there are many abnormal phases around the first silicon nitride particles. Is inhibited in the abnormal phase.
- the abnormal phase contains boron glass having a low thermal conductivity, and when a large number of agglomerated portions are present on the silicon nitride substrate, the thermal conductivity is lowered. Therefore, in order to construct a silicon nitride substrate having a high thermal conductivity, preferably having a thermal conductivity of 80 (W / m ⁇ K) or more, any surface layer having a depth of 20 ⁇ m from the substrate surface may be used. It is preferable that 25 or less of the agglomerated parts are included in a square region having a side of 100 ⁇ m.
- the surface layer whose depth from the substrate surface is in the range of 20 ⁇ m includes a 25 ⁇ m or less of the agglomerated portion in a square region set at an arbitrary position on a surface of 100 ⁇ m from the surface. It is desirable that the inner layer whose depth is in a range other than the surface layer includes 20 or less aggregated portions in a square region having a side of 100 ⁇ m set at an arbitrary position.
- the silicon nitride substrate when there are many agglomerated parts included in a predetermined area in the silicon nitride substrate, it is presumed that many abnormal regions that are a collection of abnormal phases including the agglomerated parts also exist.
- the abnormal phase included in this abnormal region has lower strength than the normal phase, and cracks are likely to occur when stress is applied to the silicon nitride substrate.
- the first silicon nitride particles forming the agglomerated portion are in a granular form with an aspect ratio of 3.0 or less, the fracture toughness is low and cracks tend to progress.
- the silicon nitride substrate of the preferred embodiment 25 or less of the aggregated portions are included in a square region having a side of 100 ⁇ m set at an arbitrary position in the surface layer whose depth from the substrate surface is in the range of 20 ⁇ m.
- the inner layer whose depth from the surface of the silicon nitride substrate is in a range other than the above surface layer is configured to include 20 or less agglomerated portions in a square region having a side set at an arbitrary position of 100 ⁇ m.
- the inner layer has higher fracture toughness than the surface layer, and even when a crack occurs in the surface layer, the progress of the crack is suppressed, and the silicon nitride substrate can be prevented from being broken.
- the maximum diameter of pores formed in the grain boundary phase around the first silicon nitride particles is 10 ⁇ m in the surface layer whose depth from the substrate surface is in the range of 20 ⁇ m.
- the following is desirable.
- the abnormal phase and the normal phase have a time difference in the contraction start time due to the difference in melting point between them, pores are likely to be generated near the boundary between the two.
- the pores contained in the silicon nitride substrate serve as a starting point of cracks when stress is applied, and cause the silicon nitride substrate to be destroyed, and lower the thermal conductivity and the withstand voltage.
- the silicon nitride substrate of the above aspect by setting the maximum diameter of the pores to 10 ⁇ m or less, it is possible to further increase the strength and thermal conductivity of the silicon nitride substrate and improve the dielectric strength. . For the same reason, it is more desirable that 20 or less pores exist in a square region of 100 ⁇ m on one side set at an arbitrary position in the surface layer having a depth of 20 ⁇ m from the substrate surface.
- the coefficient of variation of the characteristic X-ray intensity of boron (B) measured with an electron beam microanalyzer (EPMA) under the following conditions is preferably 1.0 or less.
- the electron beam microanalyzer was scanned under a 1 mm range with a beam diameter of 1 ⁇ m.
- the coefficient of variation is a value obtained by dividing the standard deviation by the average value from the characteristic X-ray intensity value of boron (B) measured at intervals of 2 ⁇ m under the above measurement conditions.
- the relationship between the coefficient of variation and the surface waviness of the silicon nitride substrate was inferred as follows.
- the value of boron (B) measured by EPMA is the value of boron (B) contained in each of BN existing on the surface of the silicon nitride substrate and boron glass existing in the abnormal region of the surface layer of the silicon nitride substrate. Although it is considered that the amount is a sum, the amount of boron (B) contained in the abnormal region is estimated.
- the distribution of BN remaining on the surface of the silicon nitride substrate is dense, when the silicon nitride substrate and the metal substrate are bonded to form a circuit board, the bonding property between the two is inhibited at the unevenly distributed portion of BN, Voids are likely to occur at the bonding interface.
- the silicon nitride substrate of this aspect since the variation coefficient of boron (B) is 1.0 or less, the BN distribution is suppressed and the uneven distribution portion is small, so that the silicon nitride substrate and the metal substrate are joined. Can increase the sex.
- the variation coefficient of boron (B) is 1 Since it is 0.0 or less, the density of the abnormal region distribution is suppressed, the unevenly distributed portion thereof is small, and the undulation of the surface of the silicon nitride substrate can be further reduced.
- the silicon nitride substrate of the present embodiment is configured as described above, a silicon nitride substrate having a bending strength of 600 (MPa) or more can be provided, and the thermal conductivity is 80 (W / m ⁇ k).
- the silicon nitride substrate as described above can be provided.
- the silicon nitride substrate of the present embodiment since it is configured as described above, it is high when a bonded body formed by bonding a metal substrate to the silicon nitride substrate is subjected to a heat cycle test.
- a silicon nitride substrate having a pass rate can be provided. Specifically, a copper plate having a thickness of 0.5 mm, a length of 37 mm, and a width of 26 mm is formed on the surface of the silicon nitride substrate having a thickness of 0.20 to 0.80 mm, a length of 40 mm, and a width of 30 mm.
- a plurality of joined bodies are prepared by joining a copper plate having a thickness of 0.5 mm, a length of 37 mm, and a width of 27 mm to the back surface through brazing material layers each formed of a brazing material and having a thickness of 20 ⁇ m.
- a silicon nitride substrate including 90% or more of joined bodies that do not break at a cycle number of 3000 or more can be provided.
- the brazing material is Ag: 70% by mass, In: 5% by mass, oxygen content of 0.1% by mass or less, and 100 parts by mass of alloy powder having an average particle diameter of 20 ⁇ m composed of the balance Cu and inevitable impurities.
- a brazing material having a melting point of 770 ° C. mixed with a hydride is composed of 5% by mass of an acrylic resin as a binder, 10% by mass of ⁇ -terpineol as a solvent, and a low molecular anionic compound as a dispersant.
- the silicon nitride substrate of the present embodiment since it is configured as described above, it is high when a bonded body formed by bonding a metal substrate to the silicon nitride substrate is subjected to an insulation test.
- a silicon nitride substrate having a pass rate can be provided.
- a silicon nitride substrate having a thickness t of 0.20 to 0.80 mm, which includes a main phase mainly composed of silicon nitride particles and a grain boundary phase mainly formed of a sintering aid.
- a boron nitride paste containing boron nitride powder / organic binder and an organic solvent is used, and a separation layer is formed on the surface of a plate-like molded body containing silicon nitride powder / sintering aid powder and organic binder.
- the separation layer and the molded body are heated at a temperature 15 to 450 ° C. higher than the exothermic peak temperature of the organic binder of the molded body.
- the boron nitride paste is a boron nitride powder Oxygen (O) inside .01 to 0.5 mass% and carbon (C) in an amount of 0.001 to 0.5 mass%, and the carbon component (C) remains in the separation layer after the degreasing step.
- the separation layer formed on the molded body in the separation layer forming step is made of 0.2 to 3.5 mg / cm 2 of hexagonal boron nitride powder. It is a manufacturing method of the silicon nitride board
- Examples of the organic binder mixed with the silicon nitride powder include polyvinyl butyral and methyl methacrylate resin, and examples of the organic binder used for the boron nitride paste include polyvinyl butyral and ethyl cellulose.
- Examples of the organic solvent used in the boron nitride paste include ethanol, butanol, ⁇ -terpineol, and the like.
- Examples of the sintering aid include Y 2 O 3 and MgO.
- the silicon nitride powder, the sintering aid powder and the organic powder formed by using a doctor blade method or other known forming method in the separation layer forming step.
- a separation layer is formed on the surface of a plate-shaped molded body (green sheet) containing a binder using boron nitride (BN) powder / boron nitride (BN) paste containing an organic binder and an organic solvent.
- BN boron nitride
- BN boron nitride
- BN paste is degreased on the surface of the green sheet that has undergone the degreasing step, and BN powder from which the organic binder and organic solvent have been removed and the carbon content (C) that is the residue of the organic binder as described later remain.
- a layer (hereinafter, the separation layer after the degreasing step may be referred to as a BN layer for convenience) is formed.
- a plurality of the green sheets on which the BN layer is formed are stacked through the BN layer, sintered in the sintering process, and formed mainly from a main phase mainly composed of silicon nitride particles and a sintering aid.
- a silicon nitride substrate including a grain boundary phase is formed.
- the BN paste used in the separation layer forming step contains 0 (O) in the BN powder. 0.01 to 0.5 mass% and carbon (C) 0.001 to 0.5 mass%, the oxygen content (mass%) contained in the BN powder of the BN paste is c, and the organic binder of the green sheet When the content of carbon (c) remaining in the BN layer after the degreasing step of degreasing the green sheet at a temperature 15 to 450 ° C. higher than the exothermic peak temperature of Is configured to be 0.02 to 10.00.
- the ratio of carbon (C) after the degreasing process is completed with respect to the ratio of oxygen (O) in the BN powder, the degreasing temperature in the degreasing process, and the ratio of oxygen (O) contained in the BN powder.
- the reason for the definition will be described below.
- the proportion of oxygen (O) in the BN powder is determined by the bonding force between the BN particles constituting the BN powder and the green sheet in the sintering process, and the melting point of the glass formed by melting the sintering aid contained in the green sheet. , From both perspectives. That is, when the proportion of oxygen (O) contained in the BN powder is less than 0.01% by mass, the reaction between the BN particles and the surface of the green sheet in contact with the BN particles is difficult to occur. The adhesion of BN particles to the surface is reduced.
- BN particles that move on the surface of the green sheet in the sintering process are generated, and the distribution of the BN powder is sparse in the sintering process, so that the separability of the sintered silicon nitride substrate is reduced. At the same time, the waviness of the surface may increase.
- the proportion of oxygen (O) contained in the BN powder is more than 0.5% by mass, excessive oxygen (O) acts on the sintering aid and lowers its melting point. In the process, the green sheet does not sufficiently shrink, and as a result, the density of the silicon nitride substrate does not increase, and a silicon nitride substrate having high strength and heat transfer rate cannot be obtained.
- the degreasing temperature is determined from the viewpoints of both the amount of carbon (C), which is the residue of the organic binder contained in the green sheet after the degreasing step, and the fact that the silicon nitride particles contained in the green sheet are not altered. That is, when the green sheet is degreased at a temperature of less than 15 ° C.
- the carbon content (C) reduces the silicon nitride particles, so that the growth of the silicon nitride particles is inhibited and the fracture toughness of the silicon nitride substrate is lowered.
- the green sheet is degreased at a temperature exceeding 450 ° C.
- the silicon nitride particles contained in the green sheet are oxidized, As a result, the density of the silicon nitride substrate does not increase, and a silicon nitride substrate having high strength and heat transfer rate cannot be obtained.
- the temperature corresponding to the peak appearing on the highest temperature side may be set as the exothermic peak temperature.
- the proportion of oxygen (O) in the BN powder is the same as that of the BN particles constituting the BN layer and the green in the sintering process. It is determined from the viewpoints of both the adhesive strength to the sheet and the melting point of the glass formed by melting the sintering aid contained in the green sheet.
- the value indicating the ratio of oxygen (O) contained in the BN powder is the value of oxygen (O) of the B compound formed on the surface of the BN particles constituting the BN powder.
- the BN paste used in the method of manufacturing the silicon nitride substrate of the present embodiment is included in the B compound that forms an abnormal phase containing boron glass as described above, that is, the BN layer that is a separation layer that has undergone a degreasing process.
- the B compound is reduced by the carbon component (C) in the sintering process and rendered harmless. That is, the BN paste of the present embodiment is degreased within the above degreasing temperature range, and then the carbon content (C) that is the residue of the organic binder remains in the BN layer in an appropriate amount.
- the carbon content (C) contained is configured to increase more than the amount of carbon (C) contained in the BN particles themselves contained in the BN paste.
- c / a is 10.
- the B compound cannot be sufficiently reduced, and an abnormal phase exceeding the allowable level is formed, and as a result, the density of the first silicon nitride particles existing in the silicon nitride substrate is increased.
- c / a is less than 0.02
- the strength of the silicon nitride substrate is reduced due to excessive carbon content (C), and because of the carbon content (C) present on the surface of the silicon nitride substrate. Bondability with the metal substrate is hindered.
- the carbon (C) originally contained in the BN powder forms a compound in the BN powder, and reduces the oxide of B compared to C remaining in the BN powder after the degreasing process. It is estimated that it is difficult to work effectively. For this reason, as described above, it is preferable that the carbon content (C) remains in an appropriate range in the BN powder after the degreasing step.
- the reason why the separation layer formed on the molded body in the separation layer forming step in the method for manufacturing the silicon nitride substrate of the present embodiment is configured to include 0.2 to 3.5 mg / cm 2 of hexagonal BN powder is as follows. It is as follows. That is, when the amount of hexagonal BN powder exceeds 3.5 mg / cm 2 , excessive hexagonal BN powder grows in the course of firing the green sheet, and columnar silicon nitride grains exposed on the surface. This is because BN powder enters the concave portions of the formed irregularities and inhibits the uniform shrinkage of the green sheet, and as a result, the undulation of the surface of the obtained silicon nitride substrate tends to increase.
- the amount of hexagonal BN powder is as small as less than 0.2 mg / cm 2, a portion with a small amount of hexagonal BN powder is formed, and a laminated silicon nitride substrate adheres in the sintering process, and the separability decreases. Because. From the same viewpoint, the amount of hexagonal BN powder contained in the separation layer is preferably 0.4 to 2.2 mg / cm 2 .
- the fluorescent X-ray intensities of boron (B) and silicon (Si) at arbitrary locations on the surface of the silicon nitride substrate is 7.0 ⁇ 10 ⁇ 5 to 250 ⁇ 10 ⁇ 5 and B / C, which is the ratio of boron (B) to carbon (C), is 0.080 to 3.000. It is comprised so that.
- the BN paste has an average particle diameter d50 of 4.0 to 20.0 ⁇ m, d10 of 0.5 to 7.0 ⁇ m, and d90 of 8 to 40 ⁇ m with respect to 100 parts by mass of boron nitride powder.
- the organic binder can be formed by adjusting so as to include 8.75 to 44 parts by mass.
- the average particle diameter d50 of the BN powder is set to 4.0 to 20.0 ⁇ m when the average particle diameter d50 is as small as less than 4.0 ⁇ m.
- the BN powder enters the concave and convex portions formed by the exposed columnar silicon nitride grains to inhibit the uniform shrinkage of the green sheet, and as a result, the undulation of the surface of the obtained silicon nitride substrate tends to increase.
- the average particle diameter d50 is larger than 20.0 ⁇ m, the adhesion of the BN powder to the surface of the green sheet is lowered, and the green sheet is easily peeled off during handling after lamination. .
- the reason why the average particle diameter d10 is set to 0.5 to 7.0 ⁇ m is that when the average particle diameter d10 is as small as less than 0.5 ⁇ m, the ratio of the B compound contained in the BN layer is too large.
- the ratio of the B compound contained in the BN layer is too small.
- the ratio of the B compound formed on the surface of the BN particles is small, the reaction between the BN particles and the surface of the green sheet in contact with the BN particles is difficult to occur, and the adhesion of the BN particles to the surface of the green sheet is reduced. . Therefore, BN particles that move on the surface of the green sheet in the sintering process are generated, and the distribution of the BN powder is sparse in the sintering process, so that the separability of the sintered silicon nitride substrate is reduced. At the same time, the waviness of the surface may increase.
- the reason why the average particle diameter d90 is set to 8 to 40 ⁇ m is that when the average particle diameter d90 is as small as less than 8 ⁇ m, the ratio of the B compound contained in the BN layer becomes too large.
- the average particle size d90 is larger than 40 ⁇ m, the particle size of the BN particles in the BN layer becomes too large, and thus waviness due to the shape of coarse BN particles is generated on the surface of the silicon nitride substrate. Because it does.
- the BN paste has a viscosity of 1000 to 50000 cP at 25 to 27 ° C. and a thixotropic property of 1.02 to 4.00
- the separation layer forming step includes: It is desirable that the separation layer be formed by screen printing.
- the thixotropy is a value defined by the ratio of the viscosity of 10 rpm to 100 rpm (viscosity of 10 rpm) / (viscosity of 100 rpm) measured with a rotational viscometer.
- a BN paste is adjusted so that it contains 8.75 to 44 parts by mass of an organic binder and 80 to 750 parts by mass of an organic solvent with respect to 100 parts by mass of hexagonal BN powder. Can be formed.
- the hexagonal BN powder can be used as the BN powder contained in the BN paste used in the method for manufacturing the silicon nitride substrate of the present embodiment.
- the separation layer is formed by screen printing in the separation layer forming step. Is formed so that the flat surface of the hexagonal BN particles is substantially parallel to the surface of the green sheet, that is, the c-axis of the hexagonal BN particles is substantially perpendicular to the surface of the green sheet. Can be formed.
- Such a separation layer and the green sheet on which the separation layer is formed are degreased together in the degreasing step, and then sintered in a state where a plurality of layers are laminated via the separation layer in the sintering step.
- the hexagonal BN particles are uniformly arranged in the above posture in the separation layer separating the stacked green sheets, the frictional resistance between the green sheets shrinking in the sintering process is reduced.
- the green sheet shrinks uniformly as a whole, it is possible to form a silicon nitride substrate with a further reduced surface waviness.
- the viscosity of the BN paste is as low as less than 1000 cP, the shape retention of the separation layer, which is a printing pattern formed by screen printing, is poor, and the thickness distribution of the separation layer varies, and the separation layer The distribution of the hexagonal BN powder contained in the sparseness is generated.
- it is higher than 50000 cP, defects such as blurring occur in the printed separation layer, and the distribution of the hexagonal BN powder similarly becomes dense.
- the hexagonal BN powder is sparsely arranged with the part in contact with the densely arranged part. There is a part in contact with the part.
- the thixotropy of the BN paste is as low as less than 1.02, it is difficult to arrange the hexagonal BN particles in the above posture because the viscosity of the BN paste is high when it is spread with a squeegee in screen printing. Thus, there is a possibility that the surface undulation of the silicon nitride substrate cannot be reduced.
- the thixotropy exceeds 4.00, the viscosity of the BN paste is low when it is spread with a squeegee in screen printing, the shape retention of the separation layer after printing is poor, and the thickness of the separation layer is low. Since the distribution varies, the distribution of the hexagonal BN powder contained in the separation layer is sparse and dense, and thus it may not be possible to reduce the undulation of the surface of the silicon nitride substrate.
- characteristic X-rays of boron (B) and silicon (Si) obtained by line analysis using an electron beam microanalyzer (EPMA) having a measurement length of 20 mm at an arbitrary position on the surface of the molded body after the degreasing step.
- EPMA electron beam microanalyzer
- the average value of an arbitrary 10.0 mm section is f
- the average value of a 0.2 mm section included in the 10.0 mm section is g / g / It is desirable that f is 0.2 to 7.0.
- each characteristic X of boron (B) and silicon (Si) obtained by line analysis with an electron beam microanalyzer (EPMA) having a measurement length of 20 mm at an arbitrary location on the surface of the molded body after the degreasing step.
- EPMA electron beam microanalyzer
- the index g / f macroscopically defines the density of the hexagonal BN powder contained in the separation layer formed on the surface of the compact, which affects the surface undulation of the silicon nitride substrate. It is.
- each characteristic X of boron (B) and silicon (Si) obtained by line analysis using an electron beam microanalyzer (EPMA) having a measurement length of 20 mm at an arbitrary position on the surface of the molded body after the degreasing step.
- the line intensity ratio (B / Si) is shown in FIG. As indicated by a solid line L1 in FIG.
- the value of the B / Si ratio at each measurement position at a measurement length of 20 mm varies within a certain variation including a large mountain M1, a small mountain M2, and the like.
- the density of the hexagonal BN powder can be defined by obtaining the dispersion of the fluctuating B / Si value.
- the dispersion value does not directly affect the waviness on the surface of the silicon nitride substrate.
- the value of a small mountain M2 that is irrelevant is also included and is not appropriate. Therefore, the inventors of the present application have conceived the above definition so that the mountain M1 having a large solid line L1 directly related to the undulation on the surface of the silicon nitride substrate can be appropriately evaluated.
- B / Si values obtained by the electron beam microanalyzer (EPMA) having a measurement length of 20 mm as described above B / of an arbitrary section N1 of 10.0 mm is obtained.
- An average value f of Si values is obtained. The reason for obtaining the average value f of the section N1 of 10.0 mm will be described later.
- an average value g is obtained as the B / Si value in the 0.2 mm section N2 included in the 10.0 mm section N1.
- the 0.2 mm section N2 may be set to an appropriate portion where the large mountain M1 exists in the 10.0 mm section N1, but for example, a plurality of arbitrarily selected sections in the 10.0 mm section N1
- An average value g in a section of 0.2 mm may be obtained at a location, and an average value further obtained from the plurality of average values g or the maximum value may be adopted as the value “g” of the index g / f.
- the average value g of the section N2 of 0.2 mm is the same as that in FIG. 1A, and only the average value g of the section N2 of 0.2 mm is obtained. It is not valid for evaluation. Therefore, the average value g in the section N2 of 0.2 mm is divided by the average value f in the section N1 of 10.0 mm, and the distribution of the hexagonal BN powder contained in the separation layer is expressed by the dimensionless index g / f. It evaluates sparseness.
- the hexagonal BN powder there are parts that are in contact with the densely arranged parts and parts that are in contact with the sparsely arranged parts.
- the shrinkage amount of each part of the green sheet is different due to the difference in frictional resistance due to the relative density of the hexagonal BN powder in the separation layer, Since the green sheet does not shrink uniformly as a whole, there is a possibility that the undulation of the surface of the silicon nitride substrate cannot be reduced.
- the exothermic peak temperature of the organic binder contained in the BN paste is 5 ° C. or more higher than the organic binder contained in the green sheet. Is desirable.
- the organic binder contained in the molded body is degreased after the organic binder contained in the BN paste, the BN powder disposed on the surface of the molded body after the degreasing of the BN paste is caused by degreasing the molded body. Due to the generated gas, there is a possibility that the density of the BN powder is formed. In order to suppress this phenomenon, the exothermic peak temperature of the organic binder contained in the BN paste is increased by 5 ° C.
- the organic binder contained in the molded body is degreased first, It is preferable that the organic binder contained in the BN paste is subsequently degreased.
- the BN paste of this embodiment 8.75 to 44 parts by mass of an organic binder and 80 to 750 parts by mass of an organic solvent are mixed with 100 parts by mass of boron nitride powder and stirred for 0.2 to 10 hours. Is preferable.
- the viscosity of the BN paste may be 1000 cP and the thixotropy may be lower than 1.02.
- the viscosity of the BN paste may exceed 50000 cP and the thixotropy may exceed 4.00.
- the viscosity of the BN paste may exceed 50000 cP and the thixotropy may exceed 4.00.
- the viscosity of the BN paste is 1000 cP and the thixo May be less than 1.02.
- the circuit board W includes a metal substrate WA bonded to the upper surface (one surface) of the silicon nitride substrate WB via the brazing material layer M1, and the silicon nitride substrate WB. It has a flat metal substrate WC joined to the lower surface (other surface) via a brazing material layer M3.
- the metal substrate WA bonded to the upper surface of the silicon nitride substrate WB functions as a circuit board on which a semiconductor element or the like is mounted, and the metal substrate WC bonded to the lower surface of the silicon nitride substrate WB functions as a heat sink. To do.
- the length of the silicon nitride substrate WB (size in the horizontal direction in FIG. 2A) of the circuit substrate W formed in each of the following examples and comparative examples is 40 mm and the width (in FIG. 2A).
- the size of the metal substrate WA is 0.5 mm in thickness, 36 mm in length, and 26 mm in width.
- the dimensions of the metal substrate WA are 0.5 mm in thickness, 37 mm in length, and 27 mm in width. It is.
- the brazing material layers M1 and M2 having substantially the same length and width as the metal substrates WA and WC have a thickness of 20 ⁇ m.
- the metal substrate WA / WC can be joined with a brazing material, and is not particularly limited as long as its melting point is higher than that of the brazing material.
- a brazing material for example, copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, nickel, nickel alloy, It is possible to use nickel plated molybdenum, nickel plated tungsten, nickel plated iron alloy, or the like.
- copper is most preferably used as a metal member from the viewpoints of electrical resistance and stretchability, high thermal conductivity (low thermal resistance), and low migration.
- the use of aluminum as a metal member has electrical resistance and high thermal conductivity (low thermal resistance), which is inferior to copper, but has the mounting reliability against the thermal cycle by utilizing the plastic deformability of aluminum. Is preferable.
- the thermal expansion coefficient thereof is a silicon nitride substrate. Since it is close to WB, the thermal stress during bonding can be reduced, which is preferable.
- circuit board W for every circuit board W, as shown to Fig.2 (a), (b).
- a plurality of circuit boards W are arranged in parallel in the vertical and horizontal directions on the large-sized silicon nitride substrate WB. Individually formed and separated into individual pieces along a broken line CB shown in the figure.
- each example and comparative example will be described by taking as an example the case of manufacturing a large silicon nitride substrate WB for forming 12 circuit boards W per sheet.
- the silicon nitride substrate WB created in each of the examples and comparative examples is formed by joining the metal substrates WA and WC on both sides to form a circuit substrate W, and is subjected to a heat cycle test and an insulation resistance test.
- the manufacturing process of the circuit board W performed after the manufacturing process of the silicon substrate WB will also be described.
- the silicon nitride substrates of Examples 1 to 43 and Comparative Examples 1 to 7 were formed by the following method.
- a silicon nitride powder blended so as to have the ratio shown in Table 1 and a mixed powder of MgO and Y 2 O 3 as sintering aids were prepared.
- the average particle diameters (d50) of the silicon nitride powder and the MgO and Y 2 O 3 powders were 0.1 to 2 ⁇ m, 0.1 to 2 ⁇ m, and 0.1 to 2 ⁇ m, respectively.
- the mixed powder and the silicon nitride balls as the grinding media were put into a resin pot of a ball mill filled with an ethanol / butanol solution (organic solvent), and wet mixed for 4 hours.
- the types and proportions of organic binders shown in Table 1 were added to the mixed powder in the pot, and wet mixed for 12 hours to obtain a sheet-forming slurry.
- the organic binder polyvinyl butyral and methyl methacrylate resin having various exothermic peak temperatures (A1) shown in Table 1 were used.
- the exothermic peak temperature (A1) of the organic binder contained in the sheet forming slurry is a temperature corresponding to the peak appearing on the highest temperature side, as measured by differential thermal analysis.
- Example 25 has a thickness of 1.3 mm
- Example 38 has a thickness of 0.32 mm
- Comparative Example 1 has a thickness of 1.6 mm
- Comparative Example 2 has a thickness of 0.3 mm
- Comparative Example 7 has a thickness of 0.48 mm. Formed.
- a BN paste containing BN powder was prepared.
- BN powder, an organic binder, and an organic solvent were blended in the composition shown in Table 2, and mixed using a planetary mixer to prepare a BN paste.
- organic binder polyvinyl butyral and ethyl cellulose having various exothermic peak temperatures (A5) shown in Table 2 were used.
- BN powder type, particle size distribution (d10, d50, d90), composition (A2), oxygen content (c), carbon content in BN powder (b), organic binder type and composition in each example and comparative example Table 2 shows the difference (A5-A1) in the exothermic peak temperature between the organic binder contained in (A4) and the organic binder contained in the compact and the composition of the organic solvent.
- the mixing time of the BN pastes of Examples 1 to 41 and Comparative Examples 1 to 6 was 40 minutes, and the viscosity and thixotropy of the formed BN paste and the method for forming a separation layer using the BN paste are shown in Table 3. It is as follows.
- the thixotropy is a value defined by the ratio of the viscosity of 10 rpm to 100 rpm (viscosity of 10 rpm) / (viscosity of 100 rpm) measured with a rotational viscometer.
- the exothermic peak temperature (A5) of the organic binder contained in the BN paste is a temperature corresponding to the peak appearing on the highest temperature side as measured by differential thermal analysis, as described above.
- the separation layer 1 was formed on the upper surface of the green sheet Wb as shown in FIG.
- Table 4 shows the thickness of the separation layer of each Example and Comparative Example, the weight per unit area of the BN powder contained in the separation layer, the average value g in the 0.2 mm section by the above-described EPMA, and the average in the 10.0 mm section. The value f and their ratio g / f are indicated.
- the thickness of the separation layer in Table 4 is a value after heating the green sheet on which the separation layer is formed at 120 ° C. to remove the organic solvent contained in the separation layer.
- d50 average particle size
- a brazing material paste m1 ⁇ m3 containing an Ag—Cu—In based active brazing material is applied on both sides of the silicon nitride substrate WB to a rectangular region with a thickness of 50 ⁇ m by screen printing. And drying in a 120 ° C. drying oven for 30 minutes to remove the solvent in the brazing paste.
- the brazing material paste m1 ⁇ m3 used in each example and comparative example is Ag: 70% by mass, In: 5% by mass, oxygen content of 0.1% by mass or less, the average particle size of 20 ⁇ m consisting of the remainder Cu and inevitable impurities.
- a copper substrate Wa.Wc which is a metal substrate having a slightly smaller vertical and horizontal dimensions than the silicon nitride substrate WB and having a thickness of 0.5 mm
- Are disposed on both sides of the silicon nitride substrate WB heated in a non-oxidizing atmosphere with a degree of vacuum of 1 Pa or less at 820 ° C. for 1 hour, and then cooled by furnace cooling, whereby the copper substrate Wa. Wb was joined to obtain a joined body.
- the brazing material paste m1 and m3 shown in FIG. 6D are indicated by broken lines.
- Etching is performed on the joined body, and as shown in FIG. 7B, in the planar direction, the dimensions and shapes corresponding to the copper substrates WA and WC of the individual circuit boards W shown in FIG.
- the gap S was formed by etching, and the copper substrates Wa and Wc (copper substrate Wc not shown) joined to the silicon nitride substrate WB were separated.
- ferric chloride (FeCl 3) is applied to the surface of the copper substrate Wa by applying a UV curable etching resist in a predetermined pattern by a screen printing method, and then the temperature of the etching liquid is set to 50 ° C.
- the joined body was immersed in the solution (46.5Be) to separate the copper substrates Wa and Wc.
- brazing material removal process After removing the etching resist, unnecessary brazing material remaining around the copper substrates WA and WC was removed with a brazing material removing solution containing hydrogen peroxide and acidic ammonium fluoride.
- Table 6 shows the density of the first silicon nitride particles on the surface and the surface layer, and the inner layer numbers in the silicon nitride substrates of Examples 1 to 43 and Comparative Examples 1 to 7 formed through the separation layer forming step to the firing step.
- 1 shows the density of the silicon nitride particles, the maximum diameter of the agglomerated part where the first silicon nitride particles agglomerated, the density of the agglomerated part of the surface and the surface layer, and the density of the agglomerated part of the inner layer. For example, as shown in FIG.
- these values are the surface layer in which the depth from the substrate surface of the silicon nitride substrate WB is 20 ⁇ m and the inner layer in which the depth from the substrate surface is in a range other than the surface layer. It was measured based on a structural photograph of an arbitrary cross section.
- reference numeral 9j is the first silicon nitride particles
- reference numeral 9k is the second silicon nitride particles
- reference numeral 9L is an agglomerated portion where the first silicon nitride particles 9j are aggregated.
- the first silicon nitride particles 9j are silicon nitride particles having an aspect ratio of 3.0 or less and a major axis length of 5.0 ⁇ m or less obtained by dividing the major axis length by the minor axis length.
- the silicon nitride particles 9k are silicon nitride particles whose major axis length and aspect ratio exceed both of the first silicon nitride particles 9j.
- the density of the first silicon nitride particles is the number of first silicon nitride particles in a 10 ⁇ m square region set at an arbitrary position on the surface or cross section. It is the number of aggregated portions of the first silicon nitride particles in a 100 ⁇ m square region set at an arbitrary position on the surface or cross section.
- the surface layer of the silicon nitride substrate refers to a range whose depth from the surface is 20 ⁇ m
- the inner phase refers to an internal range other than the surface layer.
- the maximum diameter of the agglomerated part 9L is the diameter of the minimum circle L3 including the agglomerated part 9L as indicated by reference numeral 9m in the conceptual diagram of the agglomerated part 9L shown in FIG.
- Table 7 shows that the aspect ratios of the silicon nitride substrates formed in Examples 1 to 43 and Comparative Examples 1 to 7 are 5.0 to 20.0 in the surface layer whose depth from the substrate surface is 20 ⁇ m.
- the area ratio of the second silicon nitride particles having a major axis length of 6 to 30 ⁇ m, the maximum pore diameter and density, and the thickness of the silicon nitride substrate are shown.
- the area ratio of the second silicon nitride particles having the predetermined aspect ratio and the long axis length was determined as an area ratio in a 10 ⁇ m square region set at an arbitrary position on the surface layer.
- the maximum pore diameter is the diameter of the smallest circle L4 including the pores 9n as indicated by reference numeral 9o in the conceptual diagram of the pores 9n shown in FIG. 5 (b).
- the pore density is the number of pores in a 10 ⁇ m square region set at an arbitrary position on the surface layer.
- Table 8 shows the undulation of the surface of the silicon nitride substrate formed in Examples 1 to 43 and Comparative Examples 1 to 7, and the fluorescent X-ray intensity of each of boron (B) and silicon (Si) at any location on the surface.
- the ratio (B / Si) value and the ratio (C / Si) of each fluorescent X-ray intensity of carbon (C) and silicon (Si) and the ratio B / C of both were measured with an electron beam microanalyzer (EPMA).
- EPMA electron beam microanalyzer
- the variation coefficient of boron (B) obtained by the electron beam microanalyzer was obtained by scanning the range of 1 mm with an acceleration voltage of 10 kV and a beam diameter of 1 ⁇ m, and measuring the fluorescent X-ray intensity of boron (B) measured at 2 ⁇ m intervals. It is a value obtained by dividing the standard deviation by the average value. Further, the surface waviness of the silicon nitride substrate is measured by measuring the filtered center line waviness using a surface roughness meter, and calculating the arithmetic average waviness Wa, that is, the absolute value of the deviation from the average value of the surface height.
- Example 25 An amount that is an arithmetic average is used, and the measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value ( ⁇ c) of 0.25 mm, and a cutoff value ( ⁇ f) of 8.0 mm. Furthermore, in Example 25 and Comparative Examples 1 and 2, in order to obtain silicon nitride substrates having thicknesses of 0.8, 1.0, and 0.18 mm, respectively, thicknesses of 1.0, 1.25, and 0.23 mm were obtained. Green sheets were used.
- Table 9 shows the separability, bending strength, and thermal conductivity of the silicon nitride substrates of Examples 1 to 43 and Comparative Examples 1 to 7.
- the numerical value described in the column of separability of the silicon nitride substrate is the case where, in the firing process, 10 sets of silicon nitride substrates that are laminated and sintered per set, that is, 200 silicon nitride substrates are peeled off
- the pass rate was that the silicon nitride substrate could be peeled off normally without being damaged.
- the bending strength conforms to JISR1601, and the obtained silicon nitride substrate is processed into a width of 4 mm, set in a three-point bending jig having a distance between support rolls of 7 mm, and loaded at a crosshead speed of 0.5 mm / min. was calculated from the weight applied at the time of rupture. Furthermore, the thermal conductivity was obtained by a laser flash method in accordance with JIS R1611 after processing the above silicon nitride substrate into a 5 mm square and blackening the front and back surfaces with carbon spray.
- Table 9 shows the results of the peel strength test, the thermal cycle test, and the insulation test of the circuit boards of Examples 1 to 43 and Comparative Examples 1 to 7 formed through the metal substrate bonding process to the separation process.
- the numerical value shown in the column of a peel strength test result is a pass rate at the time of attaching a peel strength test to 100 test pieces described below.
- the numerical value shown in the column of a thermal cycle test result and an insulation test result is a pass rate at the time of attaching
- a test piece T is prepared in which a copper substrate WA is disposed so that one end protrudes 5 mm from the side surface of the silicon nitride substrate WB and bonded under the same bonding conditions as the circuit board.
- the force per unit length required for pulling the protruding portion upward by 90 degrees was evaluated, and when the force was 20 kN / m or more, the test was accepted.
- the cooling / heating cycle test a temperature rising / falling cycle with cooling at ⁇ 40 ° C. for 20 minutes, holding at room temperature for 10 minutes and heating at 125 ° C. for 20 minutes was set as one cycle, and this was repeated 3000 times.
- thermal stress was applied to the circuit board and no crack was generated in the silicon nitride substrate. Furthermore, the insulation test was accepted when a voltage of 5 kV was applied to the circuit board for 1 minute and no crack was generated in the silicon nitride substrate.
- the major axis length is the minor axis length.
- first silicon nitride particle surfaces having a major axis length of 5.0 ⁇ m or less with an aspect ratio of 3.0 or less, and boron (B) and silicon
- the ratio (B / Si) of each fluorescent X-ray intensity of Si) is a
- the range is 7.0 ⁇ 10 ⁇ 5 to 250 ⁇ 10 ⁇ 5
- B / C which is the ratio of boron (B) to carbon (C)
- b is the ratio of each fluorescent X-ray intensity (C / Si)
- each silicon nitride substrate had a thickness of 0.8 mm (Example 25) and the separation layer was formed by spray coating (Example 41).
- the surface layer having a depth from the substrate surface in the range of 20 ⁇ m includes 40 or less first silicon nitride particles in a square region having a side of 10 ⁇ m set at an arbitrary position, and the depth from the substrate surface is
- the bending strength of the silicon nitride substrate is 600 (MPa).
- the aspect ratio is 5.0 to 20.0 in a square region with a side of 10 ⁇ m set at an arbitrary position on the substrate surface and a surface layer having a depth of 20 ⁇ m from the substrate surface.
- a silicon nitride substrate containing 1.0 to 30.0% of the second silicon nitride particles having an area ratio of 6.0 to 30.0 ⁇ m the bending strength of the silicon nitride substrate is 600 (MPa) or more
- the conductivity was 80 (W ⁇ mk) or higher, and the results of the heat cycle test and insulation resistance test using the circuit board using the silicon nitride substrate showed a high pass rate of 90% or higher.
- the silicon nitride substrate having a maximum diameter of 25 ⁇ m or less formed by agglomeration of the first silicon nitride particles on the substrate surface and a surface layer having a depth of 20 ⁇ m from the substrate surface
- the silicon nitride substrate The bending strength exceeded 600 (MPa)
- the result of the heat cycle test with the circuit board using the silicon nitride substrate showed a high pass rate of 90% or more.
- the area ratio of the second silicon nitride particles was 4 to 23% and the maximum diameter of the agglomerated part was 20 ⁇ m or less (other than Example 37), the effect was remarkable.
- the silicon nitride substrate including 25 or less aggregated portions in a square region having a side of 100 ⁇ m set at an arbitrary position on the substrate surface and a surface layer having a depth of 20 ⁇ m from the substrate surface
- the silicon nitride The thermal conductivity of each substrate exceeded 80 (W ⁇ mk), and the result of the heat cycle test using a circuit board using the silicon nitride substrate showed a high pass rate of 90% or more.
- the area ratio of the second silicon nitride particles is 4 to 23% and the maximum diameter of the aggregated portion is 20 ⁇ m or less, the effect is remarkable.
- a side of 100 ⁇ m includes 25 or less of the agglomerated parts, and the depth from the substrate surface is other than the surface layer.
- the bending strength of the silicon nitride substrate is 600 (MPa) or more
- the conductivity was 80 (W ⁇ mk) or more
- the result of the heat cycle test with the circuit board using the silicon nitride substrate showed a high pass rate of 90% or more.
- the area ratio of the second silicon nitride particles is 4 to 23% and the maximum diameter of the aggregated portion is 20 ⁇ m or less, the effect is remarkable.
- the maximum diameter of pores formed in the grain boundary phase around the first silicon nitride particles is 10 ⁇ m or less, preferably the substrate surface
- the bending strength of the silicon nitride substrate is 600 (MPa) or more
- the thermal conductivity is 80 (W ⁇ mk) or more
- the results of the heat cycle test and the insulation test by the circuit board using the silicon nitride substrate are both as high as 90% or higher.
- the value is shown.
- the area ratio of the second silicon nitride particles is 4 to 23% and the maximum diameter of the aggregated portion is 20 ⁇ m or less, the effect is remarkable.
- the undulation of the surface of the silicon nitride substrate is It was also confirmed to be small, preferably 0.5 or less.
- Comparative Example 1 where the thickness of the silicon nitride substrate is as thick as 1.0 mm, even when the B / C is as low as 0.05, that is, when the amount of residual carbon is small, the undulation of the surface is small, In a thick silicon nitride substrate, it has been confirmed that the present invention does not exhibit its effects.
- Example 44 corresponds to Example 9
- Example 45 corresponds to Example 6
- Example 46 corresponds to Example 7
- Example 47 corresponds to Example 8.
- Tables 10 and 11 the mixing time is basically as shown in Tables 10 and 11.
- a silicon nitride substrate and a circuit board were formed under the manufacturing conditions that were changed only. Further, the characteristics of the silicon nitride substrate and the characteristics of the circuit board were confirmed in the same manner as in Examples 1 to 43.
- the viscosity and thixotropy of the BN paste are more than those of the corresponding examples.
- the values are within an appropriate range (viscosity 1000 cP and thixotropy 1.02 in Example 9 are 3000 cP and thixotropy 1.1 in Example 44, and viscosity 47000 cP and thixotropy 3 in Example 6 are Examples.
- the viscosity was 36000 cP and the thixotropy was 2.1.
- Example 46 the viscosity was 48000 cP and the thixotropy was 3.2.
- Example 46 the viscosity was 35,000 cP and the thixotropy was 2.1. In Example 8, the viscosity was 50000 cP and the thixotropy was 4. In Example 47, the viscosity is 34000 cP and the thixotropy is 2.
- the undulation of the separation layer can be reduced when the separation layer is formed by applying and printing the BN paste on the surface of the green sheet. As a result, the silicon nitride substrate The swell can also be reduced.
- the undulation of Example 44 is 0.40 ⁇ m
- the undulation of Example 45 is 0.32 ⁇ m
- the undulation of Example 46 is 0.32 ⁇ m
- the undulation of Example 47 is 0.35 ⁇ m
- the undulation is smaller than in the corresponding ninth and sixth to eighth embodiments.
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Abstract
Description
但し、チキソ性は、回転粘度計で測定した10rpmと100rpmの粘度の比(10rpmの粘度)/(100rpmの粘度)で定義される値である。
また、前記窒化ホウ素ペーストは六方晶窒化ホウ素粉末100質量部に対し、前記有機バインダを8.75~44質量部含み、さらに有機溶剤を80~750質量部含むのが好適である。
但し、基板表面のうねりは、表面粗さ計を用いて、ろ波中心線うねりを測定して、その算術平均うねりWa、すなわち、表面高さの平均値からの偏差の絶対値の算術平均である量を用いるものとし、測定条件は評価長さ30mm、測定速度0.3mm/s、カットオフ値(λc)0.25mm、カットオフ値(λf)8.0mmとする。
但し、電子線マイクロアナライザーの測定条件は、ビーム径1μmで1mmの範囲を走査し、2μm間隔で測定したホウ素(B)の蛍光X線強度の値から、その標準偏差をその平均値で割ることによって求めた値である。
図2(a)および(b)に示すように、回路基板Wは、窒化珪素基板WBの上面(一面)に、ろう材層M1を介して接合された金属基板WAと、窒化珪素基板WBの下面(他面)にろう材層M3を介し接合された平板状の金属基板WCとを有している。ここで、窒化珪素基板WBの上面に接合された金属基板WAは、半導体素子などが搭載される回路板として機能し、窒化珪素基板WBの下面に接合された金属基板WCは、放熱板として機能する。なお、下記の各実施例および比較例で形成される回路基板Wの、窒化珪素基板WBの長さ(図2(a)において水平方向の大きさ)は40mm、幅(図2(a)において上下方向の大きさ)は30mmであり、金属基板WAの寸法は、厚み0.5mm・長さ36mm・幅26mmであり、金属基板WAの寸法は、厚み0.5mm・長さ37mm・幅27mmである。また、金属基板WAおよびWCとほぼ同じ長さおよび幅を有するろう材層M1およびM2の厚みは20μmである。
実施例1~43および比較例1~7の窒化珪素基板は、以下の方法で形成した。表1に示す割合となるよう配合した窒化珪素粉末ならびに焼結助剤であるMgOおよびY2O3の混合粉末を準備した。なお、窒化珪素粉末ならびにMgOおよびY2O3の粉末の平均粒径(d50)は、各々0.1~2μm、0.1~2μm、0.1~2μmとした。そして、エタノール・ブタノール溶液(有機溶剤)を満たしたボールミルの樹脂製ポット中に、上記混合粉末および粉砕媒体の窒化珪素製ボールを投入し、4時間、湿式混合した。次に、前記ポット中の混合粉末に対し、表1に示す種類および割合の有機バインダを添加し、12時間、湿式混合し、シート成形用スラリーを得た。なお、有機バインダとしては、表1に示す各種発熱ピーク温度(A1)を有するポリビニルブチラール、メタクリル酸メチル樹脂を使用した。シート成形用スラリーに含まれる有機バインダの発熱ピーク温度(A1)は、各々、示差熱分析で計測し、最も高温側に現れるピークに対応する温度である。
上記成形用スラリーを脱泡、溶媒除去により粘度を調整し、ドクターブレード法によりグリーンシートを成形した。次に、成形したグリーンシートを空気中で加熱し、有機溶剤を除去し、寸法が、縦150mm、横150mm、厚さが0.4mmである、表1に示す組成のグリーンシートを得た。なお、実施例25は厚みを1.3mm、実施例38は厚みを0.32mm、比較例1は1.6mm、比較例2は0.3mm、比較例7は0.48mmの厚みのグリーンシートを形成した。
上記グリーンシートの上面(一面)に分離層を形成するため、BN粉末を含むBNペーストを準備した。各実施例および比較例ごとに、表2に示す組成でBN粉末・有機バインダ・有機溶剤を配合し、プラネタリーミキサーを用いて混合を行い、BNペーストを作成した。なお、有機バインダとしては、表2に示す各種発熱ピーク温度(A5)を有するポリビニルブチラール、エチルセルロースを使用した。各実施例および比較例における、BN粉末の種類・粒度分布(d10、d50、d90)・組成(A2)・酸素量(c)、BN粉末中の炭素量(b)、有機バインダの種類・組成(A4)、BNペーストに含まれる有機バインダと成形体に含まれる有機バインダの発熱ピーク温度の差(A5-A1)、有機溶媒の組成は、表2に示すとおりである。また、実施例1~41および比較例1~6のBNペーストの混合時間は40分とし、形成されたBNペーストの粘度およびチキソ性ならびに当該BNペーストによる分離層の形成方法は、表3に示すとおりである。なお、チキソ性は、回転粘度計で測定した10rpmと100rpmの粘度の比(10rpmの粘度)/(100rpmの粘度)で定義される値である。さらに、BNペーストに含まれる有機バインダの発熱ピーク温度(A5)も、上記と同様に、示差熱分析で計測し、最も高温側に現れるピークに対応する温度である。
上記分離層1が形成されたグリーンシートWbを、大気(酸素雰囲気)中で加熱することにより有機バインダを脱脂(除去)した。各実施例における、脱脂温度(A6)、脱脂工程完了後のBN層中の炭素分(C)の割合(a)、BNペーストのBN粉末中における炭素割合(b)と脱脂工程後のBN層に含まれる炭素分(C)の割合(a)との差a-b、BNペーストのBN粉末中における酸素割合(c)と脱脂工程後のBN層に含まれる炭素分(C)の割合(a)との比c/a、グリーンシートに含まれる有機バインダの発熱ピーク温度(A1)と脱脂温度(A6)との差(A6-A1)は、表5に示すとおりである。
脱脂工程が完了したグリーンシートWbを、分離層1を介して20枚積層し、図6(b)に示すように焼成炉F中に配置し、実施例・比較例ごとに表5に示す焼成温度で、5時間、加熱し、平板状の焼結体である窒化珪素基板を得た。その後、図6(c)に示すように、焼結体WBの表面に残存する分離層1をホーニング処理し除去した。ホーニング処理は、メディアGとして平均粒径(d50)が10~100μmのアルミナ砥粒を焼結体表面に1~360秒吹き付けて行った。
図6(d)に示すように、窒化珪素基板WBの両面に、Ag-Cu-In系活性ろう材を含むろう材ペーストm1・m3をスクリーン印刷で50μmの厚みで矩形領域に塗布し、その後、120℃の乾燥炉で30分間乾燥し、ろう材ペースト中の溶媒を除去した。各実施例および比較例で使用したろう材ペーストm1・m3は、Ag:70質量%、In:5質量%、酸素含有量0.1質量%以下、残部Cu及び不可避不純物からなる平均粒子径20μmの合金粉末100質量部に対し、さらに平均粒子径10μmのAg粉末粒子を10質量部および45μm以下の粒子サイズが85%以上の水素化チタンを1質量部添加し、前記合金粉末粒子間の間隙を埋めるようにAg粉末粒子および活性金属水素化物を混合してなる融点が770℃のろう材を、全ペーストに占める割合でバインダとしてアクリル系樹脂を5質量%、溶剤としてα-テルピネオール10質量%、分散剤0.1質量%と配合したのちプラネタリーミキサーを用いて混合を行い、粘度を55Pa・sとしたものである。
上記接合体にエッチング処理を施し、図7(b)に示すように、図2(a)に示す個々の回路基板Wの銅基板WAおよびWCに対応した寸法・形状となるよう、平面方向に間隙Sをエッチングで形成し、窒化珪素基板WBに接合された銅基板WaおよびWc(銅基板Wcは不図示)を分離した。具体的には、銅基板Waの表面に、UV硬化型のエッチングレジストをスクリーン印刷法で所定のパターンで塗布し、その後、エッチング液である液温を50℃に設定した塩化第2鉄(FeCl3)溶液(46.5Be)に接合体を浸漬し、銅基板Wa・Wcを分離した。
上記エッチングレジストを除去した後、銅基板WA・WCの周囲に残存する不要なろう材を、過酸化水素および酸性フッ化アンモニウムを含むろう材除去液で除去した。
その後、図7(c)に示す破線CBに沿い窒化珪素基板WBを切断し、一枚の窒化珪素基板WBあたり12個の、図2(a)に示す回路基板Wを得た。
表6に、上記分離層形成工程~焼成工程を経て形成された実施例1~43および比較例1~7の窒化珪素基板における、表面および表層の第1の窒化珪素粒子の密度、内層の第1の窒化珪素粒子の密度、第1の窒化珪素粒子が凝集した凝集部の最大径、表面および表層の凝集部の密度、内層の凝集部の密度、を示す。これらの値は、例えば図4に示すように、いずれも窒化珪素基板WBの基板表面からの深さが20μmの範囲である表層および基板表面からの深さが前記表層以外の範囲である内層における任意の断面の組織写真に基づき測定したものである。図4において、符号9jが第1の窒化珪素粒子、符号9kが第2の窒化珪素粒子であり、符号9Lは、第1の窒化珪素粒子9jが凝集した凝集部である。ここで、第1の窒化珪素粒子9jとは、長軸長を短軸長で除したアスペクト比が3.0以下である長軸長が5.0μm以下の窒化珪素粒子であり、第2の窒化珪素粒子9kとは、第1の窒化珪素粒子9jに対し長軸長およびアスペクト比がともに超える窒化珪素粒子である。
表9に、金属基板接合工程~分離工程を経て形成された、実施例1~43および比較例1~7の回路基板の、ピール強度試験、冷熱サイクル試験、絶縁試験を行った結果を示す。なお、ピール強度試験結果の欄に示された数値は、下記説明する試験片100個をピール強度試験付した場合の合格率である。また、冷熱サイクル試験結果および絶縁試験結果の欄に示された数値は、100個の回路基板を両試験に付した場合の合格率である。
Claims (17)
- 窒化珪素粒子を主体とした主相と、主に焼結助剤から形成された粒界相とを含む厚みtが0.20~0.80mmの窒化珪素基板の製造方法であって、
窒化ホウ素粉末・有機バインダおよび有機溶剤を含む窒化ホウ素ペーストを使用し、窒化珪素粉末・焼結助剤粉末および有機バインダを含む板状の成形体の表面に、分離層を形成する分離層形成工程と、
前記分離層形成工程の後に、成形体の有機バインダの発熱ピーク温度に加えて15~450℃高い温度で前記分離層及び成形体を加熱し、前記分離層及び成形体から有機バインダを除去する脱脂工程と、
前記脱脂工程の後に、分離層を介し複数枚積層された成形体を焼結する焼結工程と、を含み、
前記窒化ホウ素ペーストは、その窒化ホウ素粉末中に酸素(O)を0.01~0.5質量%および炭素(C)を0.001~0.5質量%含み、前記脱脂工程後の分離層に炭素分(C)が残存するよう構成されており、さらに前記窒化ホウ素ペーストの窒化ホウ素粉末中に含まれる酸素の含有率(質量%)をc、前記脱脂工程後の分離層に含まれる炭素分の含有率(質量%)をaとした場合に、c/aが0.02~10.00の範囲であり、さらに前記分離層形成工程において成形体に形成された分離層は0.2~3.5mg/cm2の六方晶窒化ホウ素粉末を含むことを特徴とする窒化珪素基板の製造方法。 - 前記焼結工程が完了した後に、窒化珪素基板の表面の任意の箇所における、ホウ素(B)とシリコン(Si)の各々の蛍光X線強度の比(B/Si)の範囲が7.0×10-5~250×10-5であり、ホウ素(B)と炭素(C)の比であるB/Cが0.080~3.000となるよう構成されている請求項1に記載の窒化珪素基板の製造方法。
- 前記窒化ホウ素ペーストは、平均粒径d50が4.0~20.0μm、d10が0.5~7.0μm、d90が8~40μmの窒化ホウ素粉末100質量部に対し、前記有機バインダを8.75~44質量部含む請求項1または請求項2に記載の窒化珪素基板の製造方法。
- 前記窒化ホウ素ペーストは、25~27℃における粘度が1000~50000cP、チキソ性が1.02~4.00であり、前記分離層形成工程が、スクリーン印刷で分離層を形成する請求項3に記載の窒化珪素基板の製造方法。
但し、チキソ性は、回転粘度計で測定した10rpmと100rpmの粘度の比(10rpmの粘度)/(100rpmの粘度)で定義される値である。 - 前記窒化ホウ素ペーストは六方晶窒化ホウ素粉末100質量部に対し、前記有機バインダを8.75~44質量部含み、さらに有機溶剤を80~750質量部含む請求項4に記載の窒化珪素基板の製造方法。
- 前記脱脂工程後の成形体の表面の任意の箇所における測定長20mmの電子線マイクロアナライザー(EPMA)による線分析で得られた、ホウ素(B)とシリコン(Si)の各々の特性X線の強度の比(B/Si)のうち、任意の10.0mmの区間の平均値をf、その10.0mmの区間に含まれる0.2mmの区間の平均値をgとしたとき、g/fが0.2~7.0である請求項4または請求項5のいずれか一項に記載の窒化珪素基板の製造方法。
- 示差熱分析で計測された前記窒化ホウ素ペーストに含まれる有機バインダの発熱ピーク温度は、前記成形体の有機バインダの発熱ピーク温度よりも5℃以上高い請求項1乃至請求項6のいずれか一項に記載の窒化珪素基板の製造方法。
- 前記窒化ホウ素ペーストは、窒化ホウ素粉末100質量部に対し、有機バインダを8.75~44質量部、有機溶剤を80~750質量部配合し、0.2~10時間攪拌することにより作製する、請求項5乃至請求項7のいずれか一項に記載の窒化珪素基板の製造方法。
- 窒化珪素粒子を主体とした主相と、主に焼結助剤から形成された粒界相とを含む焼結体である窒化珪素基板であって、
前記主相は、基板表面において、長軸長を短軸長で除したアスペクト比が3.0以下であり、かつ長軸長が5.0μm以下の第1の窒化珪素粒子と、前記第1の窒化珪素粒子に対し長軸長およびアスペクト比がともに超える第2の窒化珪素粒子とを含み、
前記第1の窒化珪素粒子は、基板表面の任意の箇所に設定した一辺が10μmの正方領域に、40個以下存在し、
基板表面の任意の箇所における、ホウ素(B)とシリコン(Si)の各々の蛍光X線強度の比(B/Si)の範囲が7.0×10-5~250×10-5であり、ホウ素(B)と炭素(C)の比であるB/Cが0.080~3.000であり、
更に、表面のうねりが1.00μm以下であり、
加えて厚みtが0.20~0.80mmである、
ことを特徴とする窒化珪素基板。
但し、基板表面のうねりは、表面粗さ計を用いて、ろ波中心線うねりを測定して、その算術平均うねりWa、すなわち、表面高さの平均値からの偏差の絶対値の算術平均である量を用いるものとし、測定条件は評価長さ30mm、測定速度0.3mm/s、カットオフ値(λc)0.25mm、カットオフ値(λf)8.0mmとする。 - 基板表面からの深さが20μmの範囲である表層において任意の箇所に設定した一辺が10μmの正方領域に、前記第1の窒化珪素粒子を40個以下含み、表面からの深さが前記表層以外の範囲である内層において任意の箇所に設定した一辺が10μmの正方領域に、前記第1の窒化珪素粒子を30個以下含む、請求項9に記載の窒化珪素基板。
- 基板表面からの深さが20μmの範囲である表層において任意の箇所に設定した一辺が10μmの正方領域に、アスペクト比が5.0~20.0であり、長軸長が6.0~30.0μmの第2の窒化珪素粒子を、面積比で1.0~30.0%含む請求項9または請求項10のいずれか一項に記載の窒化珪素基板。
- 基板表面からの深さが20μmの範囲である表層において、前記第1の窒化珪素粒子が凝集して形成された最大径が25μm以下である凝集部を含む請求項11に記載の窒化珪素基板。
- 基板表面からの深さが20μmの範囲である表層において任意の箇所に設定した一辺が100μmの正方領域に、前記凝集部を25個以下含む請求項12に記載の窒化珪素基板。
- 基板表面からの深さが20μmの範囲である表層において任意の箇所に設定した一辺が100μmの正方領域に、前記凝集部を25個以下含み、基板表面からの深さが前記表層以外の範囲である内層において任意の箇所に設定した一辺が100μmの正方領域に、前記凝集部を20個以下含む、請求項13に記載の窒化珪素基板。
- 基板表面からの深さが20μmの範囲である表層において、前記第1の窒化珪素粒子の周囲の粒界相に形成された気孔の最大径は、10μm以下である請求項11乃至請求項14のいずれかに記載の窒化珪素基板。
- 基板表面からの深さが20μmの範囲である表層において任意の箇所に設定した一辺が100μmの正方領域に、前記気孔を20個以下含む請求項15に記載の窒化珪素基板。
- 下記の条件にて電子線マイクロアナライザー(EPMA)で測定した基板表面におけるホウ素(B)の特性X線強度の変動係数が1.0以下である請求項9乃至請求項16のいずれか一項に記載の窒化珪素基板。
但し、電子線マイクロアナライザーの測定条件は、ビーム径1μmで1mmの範囲を走査し、2μm間隔で測定したホウ素(B)の蛍光X線強度の値から、その標準偏差をその平均値で割ることによって求めた値である。
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