JP2001181054A - Ceramic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic substrate which has an improved anti-bending strength, scarcely generates defects such cracks, when assembled or the like, and can form highly reliable ceramic circuit boards and highly reliable heater substrates. SOLUTION: This ceramic substrate 1 is characterized in that the surface roughness (Ra) in the short side direction S is >=1.5 times the surface roughness in the long side on an at least tensile stress-acting side among both the sides of the ceramic substrate 1. It is also preferable that the directions giving the maximum surface roughness are different each other on both the sides of the ceramic substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate, and more particularly, to forming a highly reliable ceramic circuit substrate or a heater substrate which has improved bending strength and hardly causes defects such as cracks during assembly. The present invention relates to a ceramic substrate that can be used.

[0002]

2. Description of the Related Art Conventionally, ceramics in which a wiring metal plate formed in a predetermined wiring pattern shape is directly bonded to a ceramic substrate or integrally bonded to the ceramic substrate via a brazing material layer containing an active metal. 2. Description of the Related Art A heater substrate in which a circuit board or a metal wiring layer formed of a heating resistor is integrally joined to a ceramic substrate surface is widely used in various electronic devices and semiconductor devices.

The above ceramic circuit board is made of, for example, Al
_A circuit board made of metal such as copper is directly placed on the surface of a ceramic sintered body substrate such as ₂ O ₃ or AlN, and the substrate is heated. The eutectic compound of metal and oxygen generated by the heating is used as a bonding material for the ceramic substrate. The ceramic substrate and the circuit board are integrated via a brazing material containing an active metal such as DBC (direct bonding kappa method) or an Ag-Cu-Ti paste for directly and firmly joining a metal plate such as copper to the surface. It was manufactured by the active metal method of joining.

As described above, since the circuit board is formed of copper having excellent heat conductivity and electric conductivity, the delay of circuit operation is reduced and the life of circuit wiring is also improved. In addition, the wettability to a bonding material such as solder is improved, and a semiconductor element (IC chip) or an electrode plate can be bonded to the surface of the ceramic sintered body with high bonding strength. As a result, heat dissipation from the semiconductor element can be achieved. And the operational reliability of the element can be kept good.

[0005]

[SUMMARY OF THE INVENTION However, among the ceramic circuit board, in the circuit board using the Al ₂ O ₃ substrate, good heat dissipation is obtained for the thermal conductivity of Al ₂ O ₃ is low However, there is a problem that it is not possible to sufficiently cope with heat radiation measures accompanying high-density integration and high output of semiconductor elements.

Further, when an AlN substrate is used, the heat conductivity is high and sufficient heat dissipation is obtained. However, since the strength of the AlN substrate itself is low, cracks are liable to occur due to a repeated thermal load, so-called heat resistance. There was a problem that the cycle property was poor. As a result, there has been a problem that the copper circuit board peels off due to a thermal load that repeatedly acts during use, the heat radiation property is rapidly reduced, and the operation reliability of the electronic device is reduced.

In a conventional circuit board using a ceramic substrate, it is necessary to increase the thickness of the ceramic substrate in order to secure the structural strength thereof to some extent, which has been an obstacle to high-density mounting. In addition, since a circuit board using a ceramic substrate having a large thickness has poor toughness and is unlikely to bend, for example, after bonding an IC chip to the circuit board and housing it in a package to form a module, the electronic device is screwed to a mounting board. In this case, the bending stress acting on the ceramic substrate during screwing tends to cause cracks and other defects in the ceramic circuit substrate, lowering the production yield of electronic devices, and lowering the reliability and durability of the circuit substrate. There was also.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in particular, has a high reliability in the form of a ceramic which is improved in bending strength, hardly causes defects such as cracks at the time of assembly and the like. An object is to provide a ceramic substrate on which a circuit substrate and a heater substrate can be formed.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors have investigated the causes of cracks and chipping during the assembly and use of ceramic circuit boards and heater boards, and studied countermeasures. . as a result,
It has been found that the surface roughness of the ceramic substrate that constitutes the circuit board has a significant effect on the bending strength, and that the surface roughness of the ceramic substrate surface has directionality to improve the bending strength of the ceramic substrate. It has been found that the use of such a ceramic substrate makes it possible to realize, for the first time, a circuit substrate and a heater substrate which are less likely to crack and have high reliability. The present invention has been completed based on these findings.

That is, in the ceramic substrate according to the present invention, the surface roughness (Ra) in the short side direction is smaller than the surface roughness in the long side direction at least on the surface on both sides of the ceramic substrate on which the tensile stress acts. It is characterized by being 1.5 times or more.

Further, the direction in which the surface roughness is maximum may be different between the front surface and the back surface of the ceramic substrate. In this case, the above directions are different states is not particularly limited, for example, as shown in FIG. 3, the surface of the other surface with respect to the maximum direction D ₁ of the surface roughness of the one surface of the ceramic substrate 1 up direction _{D 2} of the roughness 45 ° to 1
It is preferably in the range of 25 °. Further, it is preferable that the main component of the ceramic substrate is silicon nitride.
Further, the surface roughness (Ra) of the ceramic substrate is 0.6.
It is preferably not more than μm.

The material constituting the ceramic substrate of the present invention is not particularly limited, and an oxide ceramic sintered body such as aluminum oxide (alumina: Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄₎ ), Nitride-based ceramics sintered bodies such as aluminum nitride (AlN), and carbide-based ceramics sintered bodies such as silicon carbide (SiC) can be used. In particular, silicon nitride (Si ₃ N ₄ ) is inherently higher in bending strength than other sintered ceramics, and thus is suitable as a constituent material of the ceramic substrate of the present invention.

Conventionally, the surface roughness of a ceramic substrate surface has been studied from the viewpoint of the bonding strength of a metal circuit board or a heating resistor to be bonded to the substrate, but the surface roughness of the ceramic substrate has not been studied. It was defined uniformly regardless of the direction.

In contrast, in the present invention, a remarkable effect is obtained by giving directionality to the surface roughness of the ceramic substrate. Specifically, the surface roughness (Ra) in the short side direction is set to be at least 1.5 times the surface roughness in the long side direction on at least the surface on the side on which the tensile stress acts, of the front and back surfaces of the ceramic substrate. Thus, the effect of improving the bending strength of the ceramic substrate is obtained when the bending strength is performed with reference to the surface on which the tensile stress acts.

The surface roughness (Ra) defined in the present invention is:
Arithmetic average roughness based on B0601 of Japanese Industrial Standards (JIS).

When the surface roughness (Ra) in the short side direction is less than 1.5 times the surface roughness in the long side direction, the effect of improving the transverse rupture strength of the ceramic substrate is insufficient, and cracks and the like occur. Defects easily occur. Therefore, the magnification of the surface roughness is set to 1.5 times or more, more preferably 2.0 times or more.

The ceramic substrate has a surface roughness (R
When a) is excessively large, a fine crack is easily generated starting from the rough surface portion, and a valley portion of the rough surface portion acts as a so-called notch to easily generate a crack. Therefore, the surface roughness of the ceramic substrate is preferably 0.6 μm or less for both the back surface and the front surface.

Further, there is no particular limitation on the processing method for imparting directionality to the surface roughness of the ceramic substrate. For example, when forming a ceramic molded body before sintering, A method of forming streaks or grooves extending in a predetermined direction can be adopted. Further, a method of polishing the surface of the ceramic sintered body with a surface grinder after sintering can be adopted.

FIG. 2 is a perspective view showing one example of a processing method for giving directionality to the surface roughness. In FIG. 2, the surface of the ceramic substrate 1 is polished so that the rotary grindstone 2 of the surface grinder moves along the long side direction of the ceramic substrate 1, and a streak-like polishing mark 3 is formed on the polished surface. You.
By this polishing, the surface roughness in the long side direction of the ceramic substrate 1 decreases, while the surface roughness in the short side direction perpendicular to the long side direction increases, and the surface roughness of one surface of the ceramic substrate 1 depends on the direction. Ceramic substrates having different sizes can be obtained.

The rotary grindstone 2 of the above-mentioned surface grinding machine contains, for example, diamond abrasive grains of about # 200 to # 400 having a fine grain size and a width of the outer polished surface of about 10 mm.
A resin-bonded grindstone of about mm can be suitably used. Then, the surface roughness of the ceramic substrate 1 in each direction can be arbitrarily adjusted by appropriately selecting the particle size of the abrasive grains and polishing in a predetermined direction. Thus, a method of polishing the ceramic substrate 1 along a certain direction is preferable.

Further, by preparing the ceramic substrate such that the direction in which the surface roughness becomes maximum is different between the front surface and the rear surface of the ceramic substrate, it is possible to reduce the portions where the bending strength becomes lower. In other words, if the direction in which the surface roughness is maximum coincides with the front and back surfaces of the ceramic substrate, a fragile portion that is easily damaged when bending stress is applied in a direction perpendicular to the coincident direction. Is formed. However, by changing the direction of the surface roughness between the front surface and the back surface of the ceramic substrate as described above, the number of the fragile portions is reduced, and the structural strength of the entire ceramic substrate can be increased. For example,
With respect to a ceramic substrate whose surface is polished along the lateral direction to give directionality to the surface roughness, when the direction of the surface roughness on the front side is 0 °, the surface roughness of the back side is 45 ° to 125 °. °
Is preferably polished in a certain direction. When the directionality of the surface roughness of the back surface is in the range of 0 ° to less than 45 ° and in the range of more than 125 ° to 180 °, the above-mentioned fragile portion is difficult to develop a difference in directionality from the surface roughness of the front surface. It is easy to form.

According to the ceramic substrate having the above structure, the surface roughness (Ra) in the short side direction is the surface roughness in the long side direction at least on the front and back surfaces of the ceramic substrate on the side where the tensile stress is applied. 1.5 times or more, the bending strength of the ceramic substrate is improved, cracks are less likely to occur during assembly, and a highly reliable circuit board or heater substrate can be formed with a high production yield. .

In the ceramic substrate of the present invention, as compared with the conventional case where the surface roughness is uniformly defined without considering the directionality of the surface roughness, the circuit of the ceramic substrate is modularized. It is possible to optimize the directionality of the surface roughness formed on a substrate or the like in consideration of the stress direction acting during its assembly and use, and reduce the number of polishing steps for obtaining a predetermined surface roughness. It becomes possible.

Further, by configuring the direction in which the surface roughness is maximum to be different between the front surface and the rear surface of the ceramic substrate, the fragile portion where the bending strength is particularly low is reduced, and the structure of the entire ceramic substrate is reduced. Strength can be increased.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described more specifically with reference to the accompanying drawings based on the following embodiments.

Example 1 An average particle diameter of 0.5% containing 1.3% by weight of oxygen, 0.15% by weight or less of cationic impurities, and 97% of α-phase silicon nitride.
Against silicon nitride material powder of 5 [mu] m, average particle size 0.7μm in _Y 2 _{O 3} (yttrium oxide) powder 5% by weight as a sintering aid, an average particle size of 0.5μm _Al 2 _{O 3} (alumina) 1.5 wt% of powder was added, and the mixture was wet-mixed in ethyl alcohol for 24 hours and then dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture, and the mixture is uniformly mixed.
Press molding was performed at a molding pressure of m ² to produce a large number of molded bodies. Next, after the obtained molded body was degreased in an atmosphere gas at 700 ° C. for 2 hours, the degreased body was held in a nitrogen gas atmosphere at 7.5 atm at 1900 ° C. for 6 hours to perform densification sintering. Thereafter, the amount of electricity to the heating device attached to the sintering furnace was controlled to adjust the cooling rate of the sintered body to 50 ° C./hr until the temperature in the sintering furnace dropped to 1500 ° C. The sintered body was cooled by cooling to prepare a large number of silicon nitride substrates for Example 1 having a long side length of 60 mm × a short side length of 40 mm × a thickness of 0.6 mm.

Next, the back surface of the obtained silicon nitride substrate was polished so that a rotating grindstone of a surface grinder was moved in the long side direction of the substrate, and Example 1 having a surface roughness in each direction shown in Table 1 was obtained. Was prepared.

Example 2 A silicon nitride substrate according to Example 2 was prepared in the same procedure as in Example 1 except that the surface of the silicon nitride substrate was also polished. However, the surface of the silicon nitride substrate was polished so that the rotating grindstone moved in the short side direction of the substrate.

Example 3 In Example 1, after the sintering, the back surface of the silicon nitride substrate was not polished by a rotating grindstone, and the width of the back surface was 0.3 μm and the depth was 0.3 μm in the stage of the silicon nitride molded body. A silicon nitride substrate according to Example 3 was prepared according to the same procedure as in Example 1 except that a number of stripe-like grooves having a pitch of 0.3 μm and a pitch of 10 μm were formed.

Example 4 The content of impurity oxygen was 1.5% by weight and the average particle size was 1.2 μm.
5 wt% of yttria (Y ₂ O ₃ ) as a sintering aid was mixed with aluminum nitride (AlN) powder of m, and the obtained raw material mixture was molded at a pressure of 100 MPa to obtain a molded body. When the molded body is 20 vol. % Of hydrogen gas at a temperature of 1800 ° C. for 4 hours to prepare a number of aluminum nitride substrates for Example 4 having a long side length of 60 mm × a short side length of 40 mm × a thickness of 0.6 mm. did.

Next, the back surface of the obtained aluminum nitride substrate was polished with a rotating grindstone of a surface grinder so as to move in the longitudinal direction of the substrate. Such an aluminum nitride substrate was prepared.

Example 5 96% by weight of aluminum oxide (Al ₂ O ₃ ) powder having an average particle diameter of 1 μm, 2% by weight of silicon oxide powder, 1.5% by weight of magnesium oxide powder and 0% of calcium oxide powder as sintering aids And 0.5% by weight of the mixed powder.
30 parts by weight of a binder is added to the parts by weight, and the mixture is kneaded, formed into a plate shape, and degreased.
Baking under the condition of time, long side length 60mm × short side length 40
An alumina substrate for Example 5 having a size of mm × 0.6 mm in thickness was produced.

Next, the back surface of the obtained alumina substrate was polished with a rotating grindstone of a surface grinder so as to move in the long side direction of the substrate, and the back surface of the alumina substrate according to Example 5 having surface roughness in each direction shown in Table 1 was obtained. An alumina substrate was prepared.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the back surface of the silicon nitride substrate sintered in Example 1 was polished so that the rotating grindstone of the surface grinder was moved in the short side direction of the substrate. According to the procedure, a silicon nitride substrate according to Comparative Example 1 was prepared.

Comparative Example 2 The silicon nitride (Si) obtained in Example 1 was sintered.
_{3 N 4)} without performing polishing with the grinding wheel for the rear surface of the substrate, and a silicon nitride substrate as in Comparative Example 2.

Comparative Example 3 The obtained aluminum nitride (Al) sintered in Example 4
N) The aluminum nitride substrate according to Comparative Example 3 was used without polishing the back surface of the substrate with a rotary grindstone.

Comparative Example 4 The obtained aluminum oxide (Al) sintered in Example 5
₂ O ₃ ) The aluminum oxide substrate according to Comparative Example 4 was used as it was without polishing the back surface of the substrate with a rotary grindstone.

For each of the ceramic substrates according to Examples 1 to 5 and Comparative Examples 1 to 4 prepared as described above, the surface roughness of the front and back surfaces in the long side direction and the short side direction was measured. As shown, a three-point bending test was performed to measure the bending strength. That is, both edges of the back surface of each ceramic substrate 1 in the long side direction L are connected to a pair of bending test jigs 4.
The pressing force is applied to the ceramic substrate 1 by the upper pressing jig 5 disposed at the center of the surface in a state where the ceramic substrate 1 is supported so that the supporting interval becomes 50 mm, and the maximum pressing force at the time when the ceramic substrate is broken is determined. Flexural strength was calculated.

In Examples 1 to 5 and Comparative Examples 2 to 4, the positional relationship between the bending test jig and the direction in which the surface roughness was maximized was parallel, whereas in Comparative Example 1, the position was perpendicular. did. Table 1 below shows the results of measurement and calculation of bending strength.

[0040]

[Table 1]

As is clear from the results shown in Table 1 above,
In the three-point bending test, the surface roughness Ra (S) in the short side direction S is changed to the surface roughness R in the long side direction L on the surface on which the tensile stress acts, that is, the back surface of the ceramic substrate 1.
In the ceramic substrate according to each of the examples, which was polished so as to be 1.5 times or more of a (L), the transverse rupture strength was large as compared with the ceramic substrates according to Comparative Examples 2 to 4 in which the polishing was not performed. It has been found that a circuit board and a heater board having high reliability with little cracking during assembly can be manufactured with high yield.

On the other hand, in the silicon nitride substrate according to Comparative Example 1, the direction of the bending test jig is perpendicular to the maximum direction of the surface roughness, and the maximum surface roughness appears in the direction in which the bending stress acts. Has a lower bending strength than the silicon nitride substrate according to Comparative Example 2 in an unpolished state.

Comparative Examples 2 and 3 in which the predetermined polishing treatment was not performed and the directionality of the surface roughness of the ceramic substrate was not considered
In the ceramic substrate according to No. 4, it was confirmed that the transverse rupture strength was reduced as compared with the substrates of the corresponding examples.

Examples 6 to 11 In the substrate of Example 1, when the polishing direction of the front surface was set to 0 °, the back surface was polished in the angular directions shown in Table 2.
A bending strength test was performed in the same manner as in Example 1, and a bending strength test was performed from a direction changed by 90 ° with respect to the direction. The results shown in Table 2 below were obtained. The back surface was polished with the same grindstone as the one polished on the front side.

[0045]

[Table 2]

As is clear from Table 2, the direction in which the maximum surface roughness of the front and rear surfaces is changed corresponds to the direction in which the maximum surface roughness of the front and rear surfaces changes as in Example 6, for example. It was found that excellent flexural strength was obtained when the flexural strength test was performed by pressing the test jig in either direction.

Based on this result, when the direction in which the tensile stress acts is random, the direction in which the surface roughness is maximized is changed on the front and back surfaces of the ceramic substrate, so that the direction in which the stress acts from either direction This also makes it possible to obtain excellent bending strength.

In other words, it has been found that if the direction in which the tensile stress acts is always constant, it is preferable to polish the front and back surfaces in the same direction as shown in the sixth embodiment.

[0049]

As described above, according to the ceramic substrate of the present invention, the surface roughness (Ra) in the short side direction of at least the surface of the front and back surfaces of the ceramic substrate on which the tensile stress acts is reduced. Since the surface roughness is 1.5 times or more the surface roughness in the long side direction, the bending strength of the ceramic substrate is improved, cracks are less likely to occur during assembly, and highly reliable circuit boards and heater substrates are manufactured at high cost. It can be formed with a yield.

Also, in comparison with the conventional case where the surface roughness is uniformly defined without considering the directionality of the surface roughness, the ceramic substrate of the present invention is a circuit It is possible to optimize the directionality of the surface roughness formed on a substrate or the like in consideration of the stress direction acting during its assembly and use, and reduce the number of polishing steps for obtaining a predetermined surface roughness. It becomes possible.

Further, by arranging the direction in which the surface roughness is maximized on the front surface and the back surface of the ceramic substrate, the fragile portion where the transverse rupture strength is reduced is reduced, and the structure of the entire ceramic substrate is reduced. Strength can be increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state in which a bending test is performed on one embodiment of a ceramic substrate according to the present invention.

FIG. 2 is a perspective view showing an example of a polishing method for giving directionality to the surface roughness of a ceramic substrate.

FIG. 3 is a plan view showing the positional relationship of the surface roughness of the front and back surfaces of the ceramic substrate in the maximum direction (D ₁ , D ₂ ).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic substrate 2 Rotating grindstone 3 Polishing mark 4 Jig for bending test 5 Upper pressing jig

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G001 BA03 BA04 BA06 BA07 BA09 BA32 BA36 BA71 BA73 BA75 BB03 BB04 BB06 BB07 BB09 BB32 BB36 BC12 BC13 BC52 BC54 BC55 BC73 BD13 BD14 BE35 4G030 AA12 AA36 AA52 BA02 GA19 GA24 5E338A EE26

Claims (4)

[Claims] 1. A surface roughness (Ra) in a short side direction of at least 1.5 of a front side and a back side of a ceramic substrate on a side on which a tensile stress acts is smaller than a surface roughness in a long side direction.
A ceramic substrate characterized by being at least twice as large. 2. The ceramic substrate according to claim 1, wherein the direction in which the surface roughness is maximum differs between the front surface and the rear surface of the ceramic substrate. 3. The ceramic substrate according to claim 1, wherein the main component of the ceramic substrate is silicon nitride. 4. The ceramic substrate according to claim 1, wherein the surface roughness (Ra) of the ceramic substrate is 0.6 μm or less.