Heat dissipation substrate and method for producing heat dissipation substrate

Abstract

A heat dissipation substrate having a metallic layer with few defects on its surface is obtained by a process including the steps of: forming a metallic layer by plating on the surface of an alloy composite mainly composed of a powder of a principal metal, additional metal and diamond; and heating and pressurizing alloy composite coated with metallic layer, at a temperature equal to or lower than melting points of the metallic layer and the alloy composite. Consequently a heat dissipation substrate is obtained which has a coefficient of linear expansion of 6.5 ppm/K or higher and 15 ppm/K or lower as well as a degree of thermal conductivity of 420 W/m.Math.K or higher, the substrate having a metallic layer with few defects in its surface layer and thereby allowing for a Ni-based plating on which the void percentage in the solder joint will be 5% or lower.

Claims

1. A method for producing a heat dissipation substrate, the method comprising: performing a plating process on a surface of an alloy composite body mainly composed of a principal metal, an additional metal which is different from the principal metal and is at least one substance selected from a group consisting of Ti, Cr, Co, Mn, Ni, Fe, B, Y, Mg and Zn, and diamond, the diamond being provided as a powder of diamond, to form a metallic layer composed of Cu, the metallic layer being formed on a surface of the alloy composite body; and mending a defect in the metallic layer by heating and pressurizing the alloy composite body coated with the metallic layer, at a temperature which is equal to or lower than a melting point of the metallic layer and equal to or lower than a melting point of the alloy composite body, wherein a coefficient of linear expansion of the heat dissipation substrate is in a range of 6.5 ppm/K or higher and 15 ppm/K or lower, a degree of thermal conductivity of the heat dissipation substrate is 420 W/m.Math.K or higher, a carbide of the additional metal is formed on a surface of the powder of diamond.

2. The method for producing a heat dissipation substrate according to claim 1, wherein a Ni-based plating process is performed after the heating and pressurizing process is performed.

3. The method for producing a heat dissipation substrate according to claim 1, wherein: the metallic layer has a thickness in a range of 5 m or larger and 200 m or smaller.

4. The method for producing a heat dissipation substrate according to claim 1, wherein the following processes are performed before the alloy layer is formed: at least one of grinding and polishing the alloy composite body; and depositing at least one substance selected from a group consisting of Ti, Cr, Au, Pt and alloys of these metals, on at least one of the ground and polished surface of the alloy composite body.

5. The method for producing a heat dissipation substrate according to claim 1, wherein the alloy composite body is created by compacting a mixed powder of the principal metal, the additional metal which is different from the principal metal, and diamond, and performing a liquid-phase sintering process on the mold-compacted mixed powder.

6. The method for producing a heat dissipation substrate according to claim 5, wherein: 95% or more of the diamond powder is a diamond powder having a particle size in a range of 10 m or larger and 1000 m or smaller; the principal metal is at least one substance selected from a group consisting of Ag, Cu, Al and alloys of these metals; and an amount of addition of the additional metal is equal to or higher than 1 vol % and equal to or lower than 15 vol % of an entire amount of the alloy composite body.

7. The method for producing a heat dissipation substrate according to claim 5, wherein: 95% or more of the diamond powder is a diamond powder having a particle size in a range of 10 m or larger and 1000 m or smaller; the principal metal is at least one substance selected from a group consisting of Ag, Cu and alloys of these metals; and the additional metal is at least one substance selected from a group consisting of Ti, Cr, Co, Mn, Ni, Fe and B, with an amount of addition being equal to or higher than 1 vol % and equal to or lower than 5 vol % of an entire amount of the alloy composite body.

8. The method for producing a heat dissipation substrate according to claim 5, wherein: 95% or more of the diamond powder is a diamond powder having a particle size in range of 10 m or larger and 1000 m or smaller; the principal metal is at least one substance selected from a group consisting of Al and Al alloy; and the additional metal further includes Si, with an amount of addition being equal to or higher than 5 vol % and equal to or lower than 15 vol % of an entire amount of the alloy composite body.

9. The method for producing a heat dissipation substrate according to claim 8, wherein 1.0 vol % of Mg is further added.

10. The method for producing a heat dissipation substrate according to claim 5, wherein the heating and pressuring process is performed in a vacuum atmosphere, low-pressure atmosphere, non-oxidizing atmosphere, reducing atmosphere, inert-gas atmosphere, fire-resistant-liquid atmosphere, or non-combustible-liquid atmosphere, at a temperature equal to or lower than a melting point of the principal metal and a melting point of an alloy of the principal metal and the additive metal, and at a pressure in a range of 50 MPa or higher and 500 MPa or lower.

11. The method for producing a heat dissipation substrate according to claim 5, wherein the heating and pressuring process is performed underwater by performing an electrical sintering process at a temperature equal to or lower than a melting point of the principal metal and a melting point of an alloy of the principal metal and the additive metal, and at a pressure in a range of 50 MPa or higher and 500 MPa or lower.

12. A heat dissipation substrate, comprising: an alloy composite body mainly composed of a principal metal, an additional metal which is different from the principal metal and is at least one substance selected from a group consisting of Ti, Cr, Co, Mn, Ni, Fe, B, Y, Mg and Zn, and diamond, the diamond being provided as a powder of diamond; and a metallic layer composed of Cu, the metallic layer being formed on a surface of the alloy composite body, wherein a coefficient of linear expansion of the heat dissipation substrate is in a range of 6.5 ppm/K or higher and 15 ppm/K or lower, a degree of thermal conductivity of the heat dissipation substrate is 420 W/m.Math.K or higher, a percentage of defects on the surface of the metallic layer is 5% or lower, and a carbide of the additional metal is formed on a surface of the powder of diamond.

13. The heat dissipation substrate according to claim 12, wherein the metallic layer has a thickness of 2 m or larger.

14. The heat dissipation substrate according to claim 12, wherein: the principal metal is at least one substance selected from a group consisting of Ag, Cu, Al and alloys of these metals; and an amount of addition of the additional metal is equal to or higher than 1 vol % and equal to or lower than 15 vol % of an entire amount of the alloy composite body.

15. The heat dissipation substrate according to claim 12, wherein: the principal metal is at least one substance selected from a group consisting of Ag, Cu and alloys of these metals; and the additional metal is at least one substance selected from a group consisting of Ti, Cr, Co, Mn, Ni, Fe and B, with an amount of addition being equal to or higher than 1 vol % and equal to or lower than 5 vol % of an entire amount of the alloy composite body.

16. The heat dissipation substrate according to claim 12, wherein: the principal metal is at least one substance selected from a group consisting of Al and Al alloy; and the additional metal further includes Si, with an amount of addition being equal to or higher than 5 vol % and equal to or lower than 15 vol % of an entire amount of the alloy composite body.

17. The heat dissipation substrate according to claim 16, wherein 1.0 vol % of Mg is further added.

18. The heat dissipation substrate according to claim 12, wherein a layer made of at least one substance selected from a group consisting of Ti, Cr, Au and Pt is formed between the alloy composite body and the metallic layer.

19. A package for a semiconductor, comprising the heat dissipation substrate according to claim 12.

20. A module for a semiconductor, comprising the heat dissipation substrate according to claim 12.

21. The module for a semiconductor according to claim 20, wherein a Ni-based plating and a solder joint are formed on a surface of the metallic layer, with the solder joint having a void percentage of 5% or lower.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of a system for performing a secondary process underwater.

(2) FIG. 2 is a photograph showing an enlarged view of a section of the heat dissipation substrate.

DESCRIPTION OF EMBODIMENTS

Composition

(3) It has already been reported that, when the principal metal is Ag, Cu, Al or an alloy of any of these metals, a heat dissipation substrate having a coefficient of linear expansion of 6.5 ppm/K or higher and 15 ppm/K or lower as well as a degree of thermal conductivity of 420 W/m.Math.K or higher can be produced by performing a liquid-phase sintering process on a mold-compacted body of a powder in which an additional metal and diamond are optimally mixed. However, this technique has not yet been used on a practical basis due to various problems. For example, despite the use of the additional metal, the sintered state is unstable and the relative density is low, making it impossible to secure the quality of the Ni-based final plating. Furthermore, the degree of thermal conductivity significantly varies and does not constantly achieve the level of 420 W/m.Math.K or higher.

(4) According to the present invention, a metallic layer is formed by plating on the surface of an alloy composite mainly composed of a powder of metal and diamond. The metallic layer is subsequently heated and pressurized at a temperature equal to or lower than the melting points of the metallic layer and the alloy composite (this heating and pressurizing process is hereinafter conveniently called the solid-phase sintering), so as to form a metallic layer with few defects in its surface layer and thereby improve and stabilize the thermal conductivity. The term alloy composite means an object shaped into a mass. For example, the alloy composite can be obtained by compacting a mixed powder of metal and diamond in a mold, although it is more preferable to additionally perform the liquid-phase sintering on the molded compact to create a high-density alloy composite. Other methods, such as the infiltration method, may alternatively be used to create the alloy composite.

(5) For an application which requires heat resistance, Ag, Cu or their alloy should preferably be used as the principal metal. For a large-sized heat dissipation substrate which needs to be lightweight, Al or its alloy should preferably be used as the principal metal.

(6) The additional metal may be any element which can form a carbide with diamond or can be combined with the principal metal to form an alloy. Examples include Ti, Cr, Co, Mn, Ni, Fe, B, Y, Si, Mg and Zn. The amount of addition should be equal to or higher than 1 vol % and equal to or lower than 15 vol % of the entire alloy composite. Two or more metals can be simultaneously added as long as they produce expected effects. If the amount of additional metal is lower than 1 vol % or higher than 15 vol %, the thermal conductivity cannot be 420 W/m.Math.K or higher.

(7) When the principal metal is a substance selected from the group of Ag, Cu and their alloys, the following metals can be used as the additional metal: Ti, Cr, Co, Mn, Ni, Fe and B. The amount of addition should preferably be equal to or higher than 1 vol % and equal to or lower than 5 vol % of the entire alloy composite. If the amount of addition is lower than 1 vol % or higher than 5 vol %, the thermal conductivity cannot be 420 W/m.Math.K or higher. When the principal metal is Al or its alloy, Si can be used as the additional metal. The amount of addition should preferably be equal to or higher than 5 vol % and equal to or lower than 15 vol % of the entire alloy composite. If the amount of addition is lower than 5 vol % or higher than 15 vol %, the thermal conductivity cannot be 420 W/m.Math.K or higher. Adding 1.0 vol % of Mg produces the effect of stabilizing the liquid-phase sintering (which will be described later).

(8) In order to secure a satisfactory value of thermal conductivity, 95% or more of the diamond powder should preferably have a particle size of 10 m or larger and 1000 m or smaller. If the particle size is not larger than 10 m, the thermal conductivity cannot be 420 W/m.Math.K or higher. If the particle size is not smaller than 1000 m, the thermal conductivity will barely improve, and additionally, the cutting or other work will be extremely difficult. Furthermore, the powder price will be dramatically high. However, the diamond powder may contain a small amount of particles whose size is smaller or larger than the aforementioned range as long as 95% or more of the diamond powder falls within the aforementioned range of particle size. In other words, up to 5% of the particles of the diamond powder may have a particle size smaller than 10 m or larger than 1000 m.

(9) In addition, since the diamond powder is expensive, a portion of the diamond powder may be replaced with a powder of an inexpensive material having a low coefficient of linear expansion, such as SiC, W or Wo, as long as the property requirements of the heat dissipation substrate according to the present invention are satisfied.

(10) (Liquid-Phase Sintering)

(11) The sintering process which is performed on the mold-compacted mixed powder of the principal metal, additional metal and diamond should preferably be a liquid-phase sintering process performed in a vacuum, low-pressure, high-pressure, non-oxidizing, reducing-gas, or inert-gas atmosphere at a temperature higher than the temperature at which the liquid phase of the principal metal emerges (melting point). The liquid-phase sintering causes the additional metal to react with the diamond and form a carbide on the surface layer of the diamond particle. Furthermore, the carbide, additional metal and principal metal react with each other and form an alloy layer. Consequently, an alloy composite mainly composed of the powder of metal, additive and diamond is obtained.

(12) (Metallic Layer)

(13) The metallic layer is a coating formed by plating on the liquid-phase-sintered alloy composite or on an object obtained by polishing the alloy composite. This layer should be made of Ag, Cu, Ni or an alloy of these metals, with a thickness of 5 m or larger and 200 m or smaller. Under these conditions, the metallic layer may cover the alloy composite in any form as follows: the entire surface, the upper and lower sides, or only areas on which semiconductor devices will be mounted. In particular, a metallic layer of Ag or Cu is preferable due to their softness and high degree of thermal conductivity. The plating of Ni or an alloy of these metals is effective for an aluminum-diamond-system heat dissipation substrate having a large area and large thickness. The metallic layer may have a multilayer structure formed by plating using Ag, Cu, Ni or an alloy of these metals.

(14) If the metallic layer is not thicker than 5 m, it is difficult to form the metallic layer with few defects necessary for the heat dissipation substrate over the entire area by the heating and pressurizing process. If the thickness is not smaller than 200 m, the metallic layer is likely to be extremely unstable. Furthermore, the plating process will be expensive.

(15) (Solid-Phase Sintering)

(16) The solid-phase sintering process, which follows the plating process, can be performed in various kinds of ambience, such as vacuum, low-pressure, high-pressure, non-oxidizing, inert-gas, fire-resistant liquid, or non-combustible liquid. Performing the electrical sintering underwater is advantageous, since this method can create the product in a near-net shape and yet is inexpensive. By performing the heating and pressurizing process at a temperature equal to or lower than the melting points of the metallic layer and the alloy composite as well as at a pressure of 50 MPa or higher and 500 MPa or lower (i.e. under the conditions corresponding to the solid-phase sintering), it is possible to mend the defects in the metallic plating layer on the surface of the alloy composite, and additionally, to improve and stabilize the thermal conductivity of the alloy composite itself. Such a manufacturing process can be performed by hot-pressing, forging, electrical sintering or otherwise. By the solid-phase sintering process, the metallic layer made of Ag, Cu, Ni or an ally of these metals formed by plating on the surface of the alloy composite composed of metal and diamond can be made to have few defects as in the surface layer of the heat dissipation substrate made of Cu.

(17) For the solid-phase sintering of thin sheets or wafers, hot-pressing is effective, since this method allows those articles to be produced in a stacked form. For the near-net shaping, electrical sintering is suitable. Furthermore, by applying heat and pressure, the thermal conductivity can be improved and stabilized. Since the plating made of Ag, Cu, Ni or an alloy of these metals softens at high temperatures, the sintering process should preferably be performed at a temperature equal to or higher than 400 C. and equal to or lower than the melting point of the metal as well as at a pressure of 50 MPa or higher and 500 MPa or lower. If the temperature is not higher than 400 C., it is difficult to sufficiently mend the defects. If the temperature is not lower than 600 C., large burrs begin to extrude from jigs or electrodes, causing a noticeable decrease in the life of the jigs. When Al or its alloy is used, 500 C. or lower temperatures are preferable since the melting point is low.

(18) The pressure should preferably be set at 50 MPa or higher. Setting a lower pressure level makes it difficult to sufficiently mend the metallic layer. Setting the pressure at 500 MPa or higher is uneconomical since it requires a large pressurizing system. Furthermore, commonly used jigs and electrodes may be broken under such a high pressure level. Accordingly, it is essential to select the solid-phase sintering conditions (temperature and pressure), jigs and electrodes that are suitable for the kind of alloy composite and that of the metallic layer.

(19) Solid-phase sintering in a vacuum, gas or similar atmosphere requires a large system and a long period of time for heating and pressurizing. Furthermore, this process is difficult to automatize. Underwater solid-phase sintering can similarly produce the effect of improving the metallic plating layer. Using a commercially available resistance welder, an alloy composite coated with a metallic layer is clamped between metallic electrodes underwater, and electric current is passed to sinter it. Such a solid-phase sintering process can be completed within tens of seconds, and can be automatized. The quality of the metallic plating layer can be additionally improved by repeatedly turning on and off the current passed through the alloy composite while holding it between the electrodes. This process is also capable of the neat-net-shape mass production of heat dissipation substrates in various forms for small parts, threaded flat plates, three-dimensional shapes, etc. Furthermore, this manufacturing method can achieve a high level of surface accuracy and does not require the grinding work using a diamond wheel or cutting work. The method allows the use of diamond powder having large particle sizes, so that a heat dissipation substrate having a high degree of thermal conductivity can be obtained.

(20) During the solid-phase sintering process using heat and pressure, a portion of the metallic layer turns into burrs and makes this layer thinner. The thickness may further decrease due to the buffing work performed for improving the surface-roughness accuracy to achieve a desired surface roughness. However, no problem will arise if the eventually remaining metallic layer has a thickness of 2 m or greater over the entire surface of the alloy composite.

(21) (Working)

(22) In the case of an alloy composite of a thin sheet or wafer, the surface roughness of the jigs or electrodes is copied onto its surface. Therefore, the product is obtained by cutting the alloy composite into a predetermined form by a water jet, high-power laser, wire cut or similar device. If an even higher level of accuracy is needed, the metallic layer can be polished into a predetermined surface roughness with abrasive paper or buff before the alloy composite is cut into the predetermined form by a water jet, high-power laser, wire cut or similar device to obtain the product. Manufacturing the alloy composite in a near-net shape is advantageous in terms of the processing cost since the technique does not require the shaping work.

(23) (Final Plating)

(24) The final plating is performed to allow the bonding of various members, insulating sheets, semiconductor devices or other elements on the heat dissipation substrate by silver-brazing, soft-soldering or otherwise. If there are defects on the heat dissipation substrate, the Ni-based final plating will also be defective due to their influences, so that the silver-brazing or soft-soldering cannot be performed with a satisfactory level of quality. Forming the Ni-based plating in layers would merely copy the defects in sequence and not solve the problem. It should be noted that the term Ni-based plating means a plating of Ni or its alloy.

(25) The solder bonding of semiconductor devices on the heat dissipation substrate is the most important process for semiconductor modules. Accordingly, an extremely low level of void percentage is required. In recent years, various materials and techniques for soldering have been developed. Among those materials, SnAgCu (melting point, 218 C.) is popularly used to realize Pb-free production and to allow for high-temperature treatments. This material is also used for the assessment.

(26) For the conventional heat dissipation substrate made of Cu, the plating is performed by an electrolytic Ni, electroless NiP or electroless NiB method. For a heat dissipation substrate made of CuW or CuMo system, the final plating is performed by a combination of two methods: electrolytic Ni and electroless NiP, electroless NiP and electroless NiB, or electroless Cu and electroless NiP. For AISiC, the combination of electroless NiP and electroless NiB is used. In general, in order to secure a satisfactory level of solder quality, the void quality of the soldering is assessed under the condition that the final plating is a 3-m-thick NiB plating.

(27) In advance of the Ni-based final plating, a multilayer plating process may be performed, as in the case of CuW, CuMo or AlSiC. However, in the case of the heat dissipation substrate according to the present invention, only the Ni-based plating as the final surface layer needs to be formed since the metallic layer on the surface of the alloy composite serves as the first layer. Even the Ni-based final plating can be omitted in the case where the metallic plating layer is a Ni-based plating formed by electrolytic Ni, electroless NiP or electroless NiB plating.

(28) The solder quality has often been assessed according to JIS Z3197 (which corresponds to ISO 94455), which requires that the solder have a spread area of 80% or higher. However, this standard is not strict enough to meet actual situations. Accordingly, a new standard has recently been used, which requires that the void area be 5% or lower.

(29) If the final plating is a 3-m-thick NiB plating, the assessment condition of the SnAgCu soldering (melting point, 218 C.) is extremely strict: it is commonly known that no problem related to the silver brazing, other kinds of soldering, resin adhesion or similar processes occurs if the void percentage determined by an ultrasonic measurement is 5% or lower. The voids which occur in the soldering process reflect the pinholes which exist on the surface of the heat dissipation substrate before the Ni-based final plating is performed. Therefore, it is possible to satisfy the assessment condition of the SnAgCu soldering (melting point, 218 C.) by using a heat dissipation substrate with a pinhole (defect) area ratio of 5% or lower on its surface. This assessment condition can also be used to determine whether or not the requirements of the heat dissipation substrate according to the present invention are satisfied.

(30) <Assessment of Heat Dissipation Substrate>

(31) (Measurement of Coefficient of Linear Expansion)

(32) Test pieces measuring 10 mm in length, 5 mm in width, and 2-2.5 mm in thickness were cut out from a solid-phase-sintered sample (an alloy composite with a metallic layer formed on its surface) measuring 25 mm25 mm2-2.5 mm using a wire electric discharge machine (WEDM) and power laser. Their coefficient of linear expansion at room temperature (25 C.) was measured with a thermal expansion coefficient meter (manufactured by Seiko Instruments Inc.).

(33) (Measurement of Thermal Conductivity)

(34) Test pieces measuring 10 mm in diameter and 2-2.5 mm in thickness were cut out from a solid-phase-sintered sample (an alloy composite with a metallic layer formed on its surface) measuring 25 mm25 mm2-2.5 mm using a WEDM and power laser. Their degree of thermal conductivity at room temperature (25 C.) was measured with a laser-flash thermal conductivity meter (TC-7000, manufactured by Advance Riko, Inc.).

(35) (Adhesion Test of Metallic Layer)

(36) A solid-phase-sintered sample (an alloy composite with a metallic layer formed on its surface) measuring 25 mm25 mm2-2.5 mm was held in the air at 450 C. for 30 minutes. Its appearance was visually observed through a microscope with a magnification of 10 times. The sample was rated as OK (if the metallic plating layer had no blister) or NG (if there was a blister, regardless of its size).

(37) (Measurement of Solder Void Quality)

(38) A solid-phase-sintered sample (an alloy composite with a metallic layer formed on its surface) measuring 25 mm25 mm was prepared. After the sample was deburred and buffed, a 3-m-thick NiB plating was formed on its surface to obtain a heat dissipation substrate. A silicon device measuring 10 mm10 mm0.7 mm having metallic electrodes was bonded on the substrate with a high-temperature solder of SnAgCu (melting point, 218 C.). The void area was investigated by ultrasonic waves and rated as OK (if the void area was 5% or lower) or NG (if the void area was higher than 5%). This assessment is extremely strict: it is commonly known that no problem related to the silver brazing, other kinds of soldering, resin adhesion or similar processes occurs if the void percentage determined by this measurement is 5% or lower.

EXAMPLE

Example 1; Heat Dissipation Substrate Sample of AgTi-Diamond, Sample No. 9

(39) A mixed powder of Ag (69 vol %), Ti (1 vol %) and 30-m diamond (30 vol %) was compacted in a 25-mm25-mm mold at a pressure of 500 MPa by a pressing machine. Next, the liquid-phase sintering was performed in vacuum at 1100 C. for 60 minutes to obtain an alloy composite. After a 5-m-thick metallic layer was formed on the alloy composite by an Ag-plating process, the solid-phase sintering was performed by hot-pressing under the condition that the alloy composite was held at 400 C. under 50 MPa for 30 minutes. After deburring, the blister test was performed. Subsequently, a 3-m-thick NiB plating was formed, and the void quality of the soldering was assessed.

(40) The result is shown in Table 1.

Example 2; Heat Dissipation Substrate Sample of CuCr-Diamond, Sample No. 15

(41) A mixed powder of Ag (35 vol %), Cr (5 vol %) and 100-m diamond (60 vol %) was compacted in a 25-mm25-mm mold at a pressure of 500 MPa by a pressing machine. Next, the liquid-phase sintering was performed in a hydrogen atmosphere at 1200 C. for 60 minutes to obtain an alloy composite. Subsequently, a 50-m-thick metallic layer was formed on the alloy composite by a Cu-plating process. Then, with the alloy composite placed in a ceramic jig and pressurized at 300 MPa between the upper and lower electrodes of an electrical sintering device, the solid-phase sintering was performed under the condition that the alloy composite was heated at 600 C. for 5 minutes by passing electric current. After deburring, the blister test was performed. Subsequently, a 3-m-thick NiB plating was formed, and the void quality of the soldering was assessed.

(42) The result is shown in Table 1.

Example 3; Heat Dissipation Substrate of AgTi-Diamond-Cu (bal.), Sample No. 24

(43) A powder of Ag (10 vol %), Cu (37 vol %), Ti (3 vol %) and 100-m diamond (30 vol %) was mixed with a powder of 30-m diamond (20 vol %). The mixed powder was compacted in a 25-mm25-mm mold at a pressure of 500 MPa by a pressing machine. Next, the liquid-phase sintering was performed in vacuum at 1000 C. for 60 minutes to obtain an alloy composite. Subsequently, a 100-m-thick metallic layer was formed on the alloy composite by a Cu-plating process. Then, as shown in FIG. 1, with the plated alloy composite 1 placed in a ceramic jig 4 and pressurized at 100 MPa between the upper and lower substrates 2 and 3 of a resistance welder underwater 6, the solid-phase sintering was performed under the condition that the alloy composite was maintained at 500 C. for 2 seconds by continuously passing electric current. The current-passing operation for increasing the temperature to 500 C. was repeated three times while maintaining the pressure. After deburring, the blister test was performed. Subsequently, a 3-m-thick NiB plating was formed, and the void quality of the soldering was assessed.

(44) The result is shown in Table 1.

Example 4; Heat Dissipation Substrate Sample of AlSiMg-Diamond, Sample No. 27

(45) A powder of Al (29 vol %), Si (10 vol %), Mg (1 vol %) and 50-m diamond (60 vol %) was compacted in a 25-mm25-mm mold at a pressure of 500 MPa by a pressing machine. Next, the liquid-phase sintering was performed in a nitrogen atmosphere at 600 C. for 60 minutes to obtain an alloy composite. After the surface of the obtained alloy composite was grounded, Ti and Ni were deposited to a total thickness of 0.3 m. Furthermore, a 10-m-thick metallic layer was formed by a Ni-plating process. Subsequently, the solid-phase sintering was performed by hot-pressing under the condition that the alloy composite was held in vacuum at 450 C. under 100 MPa for 10 minutes. After deburring, the blister test was performed. Subsequently, a 3-m-thick NiB plating was formed, and the void quality of the soldering was assessed.

(46) The result is shown in Table 2.

Example 5: Assessment of Semiconductor Module Including Semiconductor Device Mounted on Heat Dissipation Substrate in Package

(47) Members made of ceramics, Kovar and other materials were silver-brazed on the heat dissipation substrate of Example 3 (coefficient of thermal expansion, 8.3 ppm/K; thermal conductivity, 555 W/m.Math.K) in a hydrogen atmosphere at 750 C. After confirming that there was neither separation nor crack, a package was created. On this package, the metallic electrodes of a silicon device measuring 10 mm10 mm0.7 mm was bonded with a high-temperature AuSn solder (melting point, 280 C.) at 300 C. Using ultrasonic waves, it was confirmed that the obtained semiconductor module had a void area of 3% or lower. For this semiconductor module, a heat cycle test was conducted (from 40 C. to 125 C., 3000 times). Meanwhile, for comparison, another package was similarly created using a heat dissipation substrate (with a CuW content of 20 wt %) in the same size as aforementioned, with a coefficient of thermal expansion of 8.3 ppm/K (the same as Example 3) and a thermal conductivity of 200 W/m.Math.K. After mounting the devices, the heat cycle test was conducted (from 40 C. to 125 C., 3000 times).

(48) The result confirmed that separation, crack or other problems did not occur on any of the two samples.

Examples 1, 2 and 3

(49) TABLE-US-00001 TABLE 1 Heat Dissipation Substrate Made of Metal-Diamond Composite Metallic Composition Layer Solid-Phase Principal Liquid-Phase Sintering Plating Sintering Metal Additive Diamond Equipment Temper- Thick- Equipment Ag Cu Ti Cr Dia Size and ature ness and No (vol %) (vol %) (vol %) (vol %) (vol %) (m) Atmosphere ( C.) Kind (m) Atmosphere 1 75 0 25 30 furnace, 1100 none none vacuum 2 70 0 30 30 furnace, 1100 none none vacuum 3 69.5 0.5 30 30 furnace, 1100 none none vacuum 4 69 1 30 30 furnace, 1100 none none vacuum 5 69 1 30 30 furnace, 1100 Ag 2.5 hot-press, vacuum vacuum 6 69 1 30 30 furnace, 1100 Ag 5 hot-press, vacuum vacuum 7 69 1 30 30 furnace, 1100 Ag 5 hot-press, vacuum vacuum 8 69 1 30 30 furnace, 1100 Ag 5 none vacuum 9 69 1 30 30 furnace, 1100 Ag 5 hot-press, vacuum vacuum 10 69 2 30 100 furnace, 1100 Ag 100 hot-press, vacuum vacuum 11 38 2 60 5 furnace, 1200 Cu 50 electrical hydrogen welder, vacuum 12 38 2 60 10 furnace, 1200 Cu 50 electrical hydrogen welder, vacuum 13 38 2 60 10 furnace, 1200 Cu 50 electrical hydrogen welder, vacuum 14 38 3 60 10 furnace, 1200 Cu 50 electrical hydrogen welder, vacuum 15 35 5 60 100 furnace, 1200 Cu 50 electrical hydrogen welder, vacuum 16 35 5 60 300 furnace, 1200 Cu 100 electrical hydrogen welder, vacuum 17 35 5 60 300 furnace, 1200 Cu 200 electrical hydrogen welder, vacuum 18 35 6 60 300 furnace, 1200 Cu 200 electrical hydrogen welder, vacuum 20 48 2 50 100 furnace, 1100 Cu 100 welder, vacuum underwater 21 48 3 50 1000 furnace, 1100 Cu 100 welder, vacuum underwater 22 48 2 50 1200 furnace, 1100 Cu 100 welder, vacuum underwater 23 48 3 50 100 furnace, 1200 Cu 100 welder, hydrogen underwater 22 10 38 2 50 100 furnace, 1000 Cu 100 welder, vacuum underwater 24 10 87 3 30 100 furnace, 1000 Cu 100 welder, 20 30 vacuum underwater Assessment Result Solid-Phase Sintering Properties Rating Temper- Adhesion of Coefficient of Thermal Final Solder Void ature Pressure Metallic Layer Linear Expansion Conductivity Plating Percentage No ( C.) (Mpa) No blister (ppm/K) (W/m .Math. K) NiB(m) (5% is OK) 1 21 202 3 NG 2 23 315 3 NG 3 17 380 3 NG 4 15 418 3 NG 5 400 50 OK 15 435 3 NG 6 350 50 OK 15 428 3 NG 7 400 25 OK 15 427 3 NG 8 NG properties unmeasurable 9 400 50 OK 15 433 3 OK 10 400 100 OK 15 450 3 OK 11 600 300 OK 6.6 405 3 OK 12 350 300 OK 6.6 427 3 NG 13 600 25 OK 6.6 426 3 NG 14 600 300 OK 6.5 430 3 OK 15 600 300 OK 6.5 433 3 OK 16 600 300 OK 6.5 530 3 OK 17 600 500 OK 6.5 531 3 OK 18 700 600 NG (jigs broken) 20 500 100 OK 8.4 560 3 OK 21 500 100 OK 8.4 829 3 OK 22 500 100 OK 8.4 830 3 OK 23 500 100 OK 7.4 550 3 OK 22 500 100 OK 7.7 500 3 OK 24 500 100 OK 7.7 555 3 OK

Example 4

(50) TABLE-US-00002 TABLE 2 Heat Dissipation Substrate Made of Metal-Diamond Composite Composition Plate Metallic Solid-Phase Prin- Liquid-Phase Sintering Grind- Layer Sintering cipal Equipment ing by Deposi- Plating Equipment Metal Additive Diamond and Temper- Diamond tion Thick- and Al Si Mg Dia Size Atmo- ature Wheel Ti + Ni ness Atmo- No (vol %) (vol %) (vol %) (vol %) (m) sphere ( C.) Yes/No (m) Kind (m) sphere 25 34 3 1 60 50 furnace, 600 Yes 0.3 Ni 10 hot-press, nitrogen vacuum 26 31 5 1 60 50 furnace, 600 Yes 0.3 Ni 10 hot-press, nitrogen vacuum 27 29 10 1 80 50 furnace, 600 Yes 0.3 Ni 10 hot-press, nitrogen vacuum 28 29 10 1 80 50 furnace, 600 No No NiB 10 hot-press, nitrogen vacuum 29 29 10 1 60 50 furnace, 600 Yes 0.3 NiB 10 hot-press, nitrogen vacuum 30 24 15 1 60 50 furnace, 600 Yes 0.3 Ni 10 hot-press, nitrogen vacuum 31 21 18 1 60 50 furnace, 600 Yes 0.3 Ni 10 hot-press, nitrogen vacuum Assessment Result Solid-Phase Sintering Properties Rating Temper- Adhesion of Coefficient of Thermal Final Solder Void ature Pressure Metallic Layer Linear Expansion Conductivity Plating Percentage No ( C.) (MPa) No blister (ppm/K) (W/m .Math. K) NiB(m) (5% is OK) 25 450 100 OK 7.5 418 3 OK 26 450 100 OK 7.3 460 3 OK 27 450 100 OK 7.2 510 3 OK 28 450 100 NG properties unmeasurable 29 450 100 OK 7.2 507 No OK 30 450 100 OK 7 500 3 OK 31 450 100 OK 7 415 3 OK

Comparative Example

(51) TABLE-US-00003 TABLE 3 Properties and Assessment Properties Rating Coefficient of Thermal Final Solder Void Heat Dissipation Substrate Linear Expansion Conductivity Plating Percentage No Made of Conventional Composite (ppm/K) (W/m .Math. K) NiP(m) NiB(m) (5% is OK) 32 Ag 19 420 0 3 OK 33 Cu 17 393 0 3 OK 34 Al 23 230 5 3 OK 35 CuW 6.5~8.3 180~200 5 3 OK 36 CuMo .sup.7~10.5 160~286 5 3 OK 37 CuMo Clad (Coated with Cu) 8.7~12.5 220~317 5 3 OK 38 AlSiC Sintered 8~15 150~200 5 3 OK (Coaled with Pure Al Layer) 39 AlSiC Pressure-Infiltrated 6.5~9 220~200 5 3 NG (Coated with Al Alloy Layer)
(Interpretation of Present Disclosure1)

(52) Thus, it is possible to satisfy the requirements of a high-performance heat dissipation substrate that is compatible with high-performance semiconductor modules which will be developed in the future.

(53) (Interpretation of Present Disclosure2)

(54) The present invention is not limited to the present mode. Other modes will also be included in the present invention as long as the objective of the present invention can be achieved. The specific structure, mode and other aspects to be considered in carrying out the present invention may be changed to other structures as long as the objective of the present invention can be achieved. For example, the present invention can be applied to secure the plating quality of a metal-diamond heat dissipation substrate manufactured by other methods.

(55) (Interpretation of Present Disclosure3)

(56) The presently disclosed embodiments and examples should be considered, in all aspects, as mere examples of non-restrictive nature. The subject matter is as set forth in patent claims and not the previous descriptions.

(57) As explained in the previous embodiment, the heat dissipation substrate according to the present invention has a high degree of thermal conductivity and a coefficient of linear expansion of 6.5 ppm/K or higher and 15 ppm/K or lower. Accordingly, it can be suitably used as a heat dissipation substrate serving as a base for high-performance semiconductor modules which have been in recent years popularly used, i.e. those which have a coefficient of linear expansion of 6.5 ppm/K or higher and 15 ppm/K or lower. A package on which such high-performance semiconductor modules are mounted can be used in a memory, IC, LSI, power semiconductor, communication semiconductor, optical device, laser, LED, sensor, and other applications.

REFERENCE SIGNS LIST

(58) 1 . . . Material produced by forming a metallic layer on an alloy composite composed of metal, additive metal and diamond 2 . . . Upper electrode, which can be vertically moved 3 . . . Lower electrode 4 . . . Ceramic jig 5 . . . Power source for the welder 6 . . . Water 7 . . . Diamond 8 . . . Metallic layer 9 . . . Magnified photograph of a section of a heat dissipation substrate