JP2018182088A - Heat dissipating substrate, heat dissipating substrate electrode, semiconductor package, and semiconductor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat dissipating substrate in which a decrease in the thermal conductivity in the thickness direction is small after a heat cycle test.SOLUTION: A heat dissipating substrate includes a plate-like core substrate made of Mo and having a through hole penetrating therethrough in the thickness direction, an insert made of Cu and filled in the through hole, a joining layer made of Ni and continuously or intermittently formed between the inner wall surface of the through hole and the insert, and a heat conductive layer made of Cu and formed on the front and rear surfaces of the core substrate.SELECTED DRAWING: None

Description

The present invention relates to a heat dissipation substrate and a heat dissipation substrate electrode used to release heat generated during operation of a semiconductor device, and a semiconductor package and a semiconductor module provided with a heat dissipation substrate or a heat dissipation substrate electrode.

  Semiconductor modules are widely used in various fields such as LSIs, semiconductors for radio wave communication and optical communication, power semiconductors, lasers, LEDs, and sensors.

  A semiconductor module on which a semiconductor device is mounted is an advanced precision device that performs information processing and energy conversion, and is made of various materials. Further, a heat dissipation substrate is used to release the heat generated by the operation of the semiconductor device to the outside of the semiconductor module.

  With the advancement of performance of semiconductor modules, semiconductor devices mounted on the semiconductor modules are shifting from Si semiconductors to GaN semiconductors or SiC semiconductors having a larger band gap than Si. In addition, the maximum operating temperature of the conventional semiconductor device was 125 ° C, but in recent years the maximum operating temperature of the semiconductor device has gradually increased to 150 ° C, 175 ° C, 225 ° C, and operates at the maximum temperature 250 ° C. Semiconductor devices are also beginning to be put to practical use.

  Since the size of the heat dissipation substrate is limited due to the convenience of mounting on a semiconductor module, etc., it is difficult to completely cool the heat-generating semiconductor module with only the heat dissipation substrate. Therefore, a cooling system configured to attach a cooler (a fin, a cooling plate, a radiator, a Perch device or the like) to a heat dissipation substrate mounted on a semiconductor module and transfer the heat of the semiconductor device to the cooler is used. Such cooling systems are widely used because they are simple and economical. On the other hand, it is important to match the linear expansion coefficients of the semiconductor module and the heat dissipation substrate in order to prevent the problem of distortion due to heat between the semiconductor device and the heat dissipation substrate and between the heat dissipation substrate and the cooler. Also, in order to efficiently transfer the heat of the semiconductor device to the cooler, it is naturally also required that the thermal conductivity of the heat dissipation substrate be high.

  Semiconductor modules exist in various sizes and structures depending on applications and required performance. Conventionally, the linear expansion coefficient of the heat dissipation substrate has been preferably 6.5 ppm / K, which is close to the linear expansion coefficient of ceramic, but it is difficult to obtain a heat dissipation substrate with high thermal conductivity under this limitation. In recent years, in the technological development of semiconductor packages (PKGs) and semiconductor modules, up to about 10 ppm / K is permitted.

  Under these circumstances, the maximum value of the linear expansion coefficient from room temperature (RT) to 800 ° C is 10 ppm / K or less, and in-plane (in the XY plane) parallel to the surface and in the thickness direction (Z-axis direction) In any case, a heat dissipation substrate having a thermal conductivity of 200 W / m · K or more at room temperature is required. A heat dissipation substrate of a clad structure (laminated structure) of CuW, CuMo, and CuMo, a heat dissipation substrate made of AlSiC, and the like, which are currently put into practical use, all satisfy these requirements. The temperature of 800 ° C. is the maximum temperature that can be reached in the manufacturing process of the semiconductor package. In the case where the process of manufacturing the semiconductor package includes such a process at a high temperature, the heat dissipation substrate does not cause a problem such as deformation or peeling from other members, so that it is at room temperature (RT) to 800.degree. It is required that the maximum value of the linear expansion coefficient is 10 ppm / K or less.

  Under such circumstances, in a power semiconductor module, which is an aspect of a semiconductor module, lead wires are connected to semiconductor devices mounted on a heat dissipation substrate. The miniaturization of power semiconductor modules is also in progress, and it has become difficult to secure a sufficient current-carrying capacity by means of lead wires. Therefore, development of a heat dissipating substrate electrode in which the functions of the heat dissipating substrate and the electrode are integrated has been advanced.

IACS (International Annealed Copper Standard) is known as an international standard for evaluating electric conductivity in a unified manner. This is the electrical conductivity of annealed standard soft copper (volume resistivity: 1.7241 × 10 ^-2 μΩm) as 100% IACS, and the electrical conductivity of various materials is specified as a relative value to the electrical conductivity of annealed standard soft copper. is there. When the heat dissipation substrate also functions as an electrode, it is required to have an electrical conductivity equal to or higher than that of an Al alloy conventionally used as a lead wire, that is, 50% IACS or higher.

  Also, semiconductor devices mounted on a semiconductor module may or may not require insulation. In the case of a semiconductor device requiring insulation, a DBC (Direct Bonded Copper) substrate (Cu) in which Cu having excellent conductivity is joined to a ceramic substrate as a circuit layer to a semiconductor device so that insulation can be ensured even at high temperature operation Solder an insulated circuit board such as / Ceramic / Cu) or DBA (Direct Bonded Aluminum) board (Al / Ceramic / Al), solder a heat dissipation board to it, and attach a cooler with a resin with low thermal conductivity. Cooling system is adopted.

However, the insulating circuit board is expensive, and the size is also limited due to the convenience and economy of mounting on the semiconductor module as in the case of the heat dissipation board. Furthermore, in the ceramic materials such as AlN and Si ₃ N ₄ used in the insulating circuit board, the thermal conductivity at 250 to 300 ° C. decreases to about half the thermal conductivity at room temperature. Therefore, in order to rapidly transfer the heat generated at the time of operation of the semiconductor device to the heat dissipation substrate, an insulating circuit substrate thinned to the minimum thickness capable of maintaining the strength is used. However, with an increase in the amount of current flowing through the power semiconductor module, problems occur such as the generation of heat due to the shortage of the current-carrying capacity in the Cu layer and the Al layer. In addition, although a method of insulating a high performance semiconductor device with a Cu heat dissipation board soldered with an inexpensive resin sheet was also studied, the coefficient of linear expansion of the Cu heat dissipation board is large and matched with the linear expansion coefficient of the semiconductor device. I can not do it. When a CuMo-based heat dissipation substrate is used, the matching of the linear expansion coefficient is improved but the electrical conductivity is insufficient. In addition, there is also a problem that high frequency conduction becomes unstable when a heat dissipation substrate including Mo or W in the main conduction path is used as an electrode. Furthermore, when the heat dissipation substrate becomes thin, the heat from the device is transferred to the resin sheet and heated, which results in a decrease in the insulation, and the insulation by the resin sheet is not realized. However, since the effect of performance improvement and cost reduction is great if this structure is realized, full-scale realization is being sought by various methods such as cooling the semiconductor device from both sides as well as from one side.

  The heat dissipation substrate used for the semiconductor module has (1) linear expansion coefficient and thermal conductivity, and electrical conductivity (when it also functions as an electrode) according to the performance and structure of the semiconductor module, (2) reliability It is selected in consideration of, for example, that it is possible to perform a high plating process and (3) that the operation reliability after mounting on a semiconductor module can be secured. Whether or not reliable plating can be performed is determined by a heat test that maintains the heat dissipation substrate after plating at the maximum operating temperature of the semiconductor device (for example, 250 ° C.) or 400 ° C. Ru. Further, the reliability of each member of the semiconductor module is judged by a heat cycle test which repeatedly holds the semiconductor device at the maximum operating temperature (for example, 250 ° C.) and -40 ° C. The heat cycle test of the heat dissipation substrate is very strict, and if there is a defect or a weak place in each member or its bonding surface, the place is broken and it will be rejected. In particular, these problems are manifested as the maximum operating temperature of semiconductor devices increases. Further, the semiconductor module is mounted on a cooler, and the semiconductor device is operated at ON / OFF at the maximum operating temperature of the semiconductor device to determine the operating life of the semiconductor module at the time of mounting. If a problem occurs in these tests, the material and structure of the heat dissipating substrate are reviewed to manufacture a new heat dissipating substrate, and a heat dissipating substrate free from any problems in all the tests is produced to complete the semiconductor module.

  Heretofore, the heat dissipation substrate material has been selected based on the coefficient of linear expansion at room temperature or 800 ° C. and the value of thermal conductivity at room temperature. However, manufacturers of semiconductor modules often do not necessarily disclose information on the characteristics of the heat dissipation substrate material of products developed by themselves, and in particular, the value of the coefficient of linear expansion at the maximum operating temperature of semiconductor devices is often not disclosed. Therefore, values of linear expansion coefficient and thermal conductivity at room temperature have conventionally been used as criteria for selection. On the other hand, manufacturers of ceramic packages have emphasized the value of the coefficient of linear expansion at 800 ° C., which is required at the time of manufacture.

  Designers of semiconductor modules and semiconductor packages search for materials of a heat dissipation board according to the performance and structure of each semiconductor module, and develop a heat dissipation board that passes the above test. In addition, when it is difficult to develop such a heat dissipation board, the design of the semiconductor module may be reconsidered so that a heat dissipation board that can be developed can be mounted.

  As described above, manufacturers of semiconductor modules, semiconductor packages, or heat dissipation substrates repeatedly design, manufacture, simulate, test the above, and the like the semiconductor modules, semiconductor packages, and heat dissipation substrates, and improve their products by accumulating design know-how. And development of new products. However, in recent years, the maximum operating temperature of semiconductor devices has been gradually increased, and a new heat dissipation substrate capable of coping with such an increase in operating temperature is required.

  Under these circumstances, the thermal conductivity of AlSiC decreases significantly with the rise in temperature, so when it is used as a heat dissipation substrate for high-performance semiconductor modules that operate at high temperatures such as 250 ° C, the thermal conductivity becomes insufficient. It is not selected as a candidate for substrate material. On the other hand, in the case of CuW alloy or CuMo alloy, since the decrease in the thermal conductivity with the rise in temperature is small, it is expected as a material of the heat dissipation substrate of the semiconductor module operating at high temperature. In particular, CuMo-based materials are highly expected because they are lightweight and inexpensive.

  However, in the case of a CuMo alloy, the wettability of Cu and Mo is poor, and when it is manufactured by an infiltration method in which Cu is dissolved and impregnated into a skeleton of Mo, or a sintering method in which a powder of Cu and Mo is sintered, A nest (small air gap) is generated inside. Therefore, by rolling the manufactured alloy, the cavity is crushed and used as a heat dissipation substrate. However, if the Mo exposed on the surface is pretreated to carry out Ni-based plating (plating with Ni or Ni alloy), the interface between Cu and Mo present in the surface layer is corroded and stabilized Ni-based plating The problem was that it was difficult to apply Although it is possible to improve the stability of the Ni-based plating process by repeating the heat treatment and the Ni-based plating process, there is a problem that the process of the plating process becomes complicated and the cost becomes high.

  On the other hand, instead of a single composition material such as a CuMo alloy, a Cu / CuMo / Cu clad structure, a Cu / Mo / Cu clad structure, or a Cu / Mo / Cu /.../ Cu multilayer clad structure (these will be summarized below) Development of a heat dissipation substrate called “CuMo-based clad structure”. In these heat sinks, if the coefficient of linear expansion is about the same as that of a heat sink made of CuMo alloy or the like, the thermal conductivity of the CuMo clad structure is greater than that of a heat sink such as CuMo alloy. The potential as a material of the heat dissipation substrate is highly expected and development has been advanced. Further, in the case of the heat dissipation substrate of the clad structure, since the Cu layer having high thermal conductivity is provided on the surface, there is an advantage that the thermal conductivity in the XY plane is high. Furthermore, since a stable Ni-based plating process can be easily applied to the Cu layer on the surface of the heat dissipation substrate, the above-described steps such as heat treatment are unnecessary, and it can be manufactured at a lower cost than CuMo alloy etc. It is expected.

  However, if the Cu layer on the surface is thickened to increase the thermal conductivity in the heat dissipation substrate of the Cu / CuMo / Cu clad structure or the Cu / Mo / Cu clad structure, the outermost surface layer (the part located on the outermost side of the surface layer) There is a problem that the effect of suppressing the linear expansion coefficient of Cu by CuMo or Mo of the core material can not be sufficiently obtained, the linear expansion coefficient of the surface layer becomes large, and the problem of low thermal conductivity in the Z-axis direction . Also, as the maximum operating temperature of semiconductor devices increases, failures frequently occur in the heat cycle test corresponding to the temperature. Also, when the operating life was tested on a semiconductor module loaded with semiconductor devices operating at 250 ° C., it was also found that the desired thermal conductivity could not be obtained.

  The heat dissipation substrate of the CuMo clad structure is manufactured by a rolling method, a brazing method, a solid phase diffusion bonding method (HP method, heat pressure bonding method, hot uniaxial processing method, thermocompression bonding, etc.). As described above, these heat dissipation boards are mounted on a semiconductor module equipped with a semiconductor device operating at 250 ° C. to perform an operation life test, even if the desired thermal conductivity is obtained at the time of manufacture of the heat dissipation board. The desired thermal conductivity may not be obtained. This is because if the semiconductor module is mounted and repeatedly operated, the bonding strength at the bonding portion (interface) between Cu and Mo inside the heat dissipation substrate is reduced to cause peeling, or voids or defects in the bonding portion are taken as the starting point It is considered that the thermal conductivity in the Z-axis direction particularly decreases due to cracking and peeling. It is difficult to judge from the appearance a small crack or peeling of the joint of the heat dissipation substrate of the clad structure.

  On the other hand, a Mo plate member (core base material; also referred to as "via Mo") in which a hole (via) penetrating in the thickness direction is formed as a heat dissipation substrate that solves the problem of increasing the thermal conductivity in the Z axis direction. A Cu / via Mo / Cu three-layer heat dissipation substrate (hereinafter referred to as a “hybrid structure”) is proposed in which Cu is introduced into the inside of the via). The heat dissipation substrate of such a hybrid structure, for example, dissolves Cu and causes it to flow into the via for bonding (total dissolution bonding), or locally melts the interface between the via Mo and the Cu introduced into the inside for bonding ( It is manufactured by the method of carrying out local melt bonding). In the heat dissipation substrate of the hybrid structure, by using a core substrate made of a metal having a small linear expansion coefficient such as Mo, Cu inside the via and Cu layers located on the front and back of the core substrate are formed as via Mo layers even under high temperatures. Since it is restrained and expansion and contraction are suppressed, it is expected that high thermal conductivity can be obtained while keeping the linear expansion coefficient low.

(Prior art)
Hereinafter, the contents of the disclosure in the prior art documents investigated by the inventor of the above-mentioned various heat dissipation substrates and related techniques will be described.

  Patent Document 1 relates to a heat dissipation substrate having a clad structure, and forms a thin coated layer of copper, gold, silver or an alloy thereof on one side or both sides of a Mo plate, and copper, nickel, gold, or the like on the thin coated layer. It is described that silver metal sheets or their alloy sheets are joined by overlapping and heating and pressing.

  Patent Document 2 is a document relating to a heat dissipation substrate of a clad structure, particularly a heat dissipation substrate of a Cu / Mo / Cu clad structure or a Cu / W / Cu clad structure, and a hot press or hot isostatic pressure instead of a conventional rolling method. It is described that heating and pressure bonding of each layer is carried out by a hot uniaxial processing method using a pressing device. Specifically, a Cu material and a Mo material are directly laminated, or a surface of the Mo material is plated using a material of Cu or Ni or a combination thereof, and then the Cu material and the Mo material are superposed. It is described that heating and pressure bonding is carried out.

  Patent Document 3 also relates to a heat dissipation substrate having a clad structure, and a CuMo alloy or a CuW alloy in place of Mo or W of a Cu / Mo / Cu clad structure or a Cu / W / Cu clad structure, which has been used until then. A heat dissipation substrate using a Cu / CuMo / Cu clad structure or a Cu / CuW / Cu clad structure is described. It is described that, in these heat dissipation substrates, the thermal conductivity in the Z-axis direction is higher and the linear expansion coefficient is lower than that of the conventional heat dissipation substrates. Also, a manufacturing method is described in which a CuMo alloy or a CuW alloy formed by an infiltration method or a sintering method is plated with Ni to overlap Cu and subjected to hot rolling or hot uniaxial pressing.

  Patent Document 4 is a document relating to a method of producing a CuMo composite alloy, and it is described that a green compact made of Cu powder and Mo powder is prepared, sintered, and then rolled to produce a CuMo composite rolled sheet. It is done.

  Patent Document 5 discloses a heat dissipation substrate having a multilayer clad structure manufactured by joining a structure formed by alternately laminating a layer formed of Cu or an alloy thereof and a layer formed of Mo or W by a hot uniaxial process. Is described. It is described that the thermal expansion substrate of the multilayer clad structure has a lower linear expansion coefficient than that of the clad structure.

  In Patent Document 6, a core substrate in which a through hole (via) penetrating in the thickness direction is formed in a plate-like member made of a material having a small linear expansion coefficient such as Invar or Mo is produced, and the core substrate is penetrated While inserting the heat conduction member which consists of Cu which has an outside diameter smaller than the internal diameter of a hole, Cu layer is formed also in front and back of a core base material, and the hybrid type heat dissipation which solid-phase-diffusion joins each member The substrate is described. In this document, it is described that a linear expansion coefficient of the core base material is maintained as it is even if Cu inside the through hole is expanded and contracted by heat because a space is formed between the through hole and the inner wall of the through hole. There is.

  Patent Document 7 is a document according to the present invention and the present inventor, and describes a hybrid heat dissipating substrate. This heat dissipation substrate is a hybrid heat dissipation substrate in which a heat transfer member made of Cu is introduced into a through hole formed in a plate-like core substrate made of Mo having a small linear expansion coefficient as in Patent Document 6, but Unlike Patent Document 6, they are joined by locally melting the interface between Mo and Cu inside the via, or by flowing molten Cu into the via.

JP-A-57-221041 Japanese Patent Application Laid-Open No. 6-268115 Japanese Patent Application Laid-Open No. 6-268117 Unexamined-Japanese-Patent No. 5-125407 Unexamined-Japanese-Patent No. 2010-56148 JP, 2010-245496, A Patent No. 6041117 specification

  It has been found that a heat dissipation substrate having a hybrid structure having high thermal conductivity not only in the XY direction but also in the Z-axis direction can be obtained by manufacturing the method proposed in Patent Document 7 by the inventor of the present invention. However, when manufacturing a plurality of heat dissipation substrates and mounting them on a semiconductor module and testing the operation life, it has been newly found that the desired thermal conductivity may not necessarily be obtained.

  In many cases, a large and thin heat dissipation substrate is first manufactured, and then the individual heat dissipation substrates are manufactured by cutting out the substrate from a predetermined size. The above problem in the heat dissipation substrate of the hybrid structure is that the internal structure is complicated in the heat dissipation substrate of the hybrid structure, and particularly in a large heat dissipation substrate, the gas released from Cu dissolved inside the via remains in the heat dissipation substrate. It is presumed that this tends to result in voids, which causes variations in the internal structure of each heat dissipation substrate.

  As described above, one of the tests for a heat dissipation board is an operating life test at the time of mounting on a semiconductor module, but this test requires steps of mounting and operating a cooler, etc., and is expensive and time consuming. . Therefore, until now, the thermal expansion coefficient and thermal conductivity of a single heat dissipation substrate were measured at room temperature for a plurality of heat dissipation substrates, and semiconductor packages and semiconductors were obtained using only those for which desired values were obtained. The module was fabricated, heat cycle test was conducted, and the operation life test was conducted only for the heat dissipation board which passed the test. Therefore, in the stage of design and trial manufacture of the heat dissipation substrate, first, the requirements of the characteristics (linear expansion coefficient, thermal conductivity and electrical conductivity, etc.) of the heat dissipation substrate alone, and heat in a state of being attached to the semiconductor package or semiconductor module It is required to have the property of passing the cycle test. In addition, there is also a demand for a simple test method capable of determining pass / fail by the operation life test at the time of mounting on a semiconductor module, which is more expensive and time-consuming than other evaluation methods.

  This time, a heat cycle substrate (a test that repeatedly performs heating to 250 ° C and cooling to -40 ° C) that assumes the operating temperature of the semiconductor device is 250 ° C, which is not usually performed on a single heat dissipation substrate alone, The change in characteristics before and after the heat cycle test was compared with the change in appearance for each of the heat dissipation substrates of the hybrid structure. However, it was difficult to judge the peeling of the bonding interface between Cu and Mo from the appearance, and it was not possible to confirm that the bonding surface was curled up at the end. However, before and after the heat cycle test, the value of the thermal conductivity in the Z-axis direction was significantly reduced, which strongly suggested that the peeling occurred at the bonding interface of Cu and Mo.

  It is conventionally known that the wettability between Cu and Mo is worse than the wettability between Cu and W, and that these bonding is difficult. Nevertheless, the reason why a heat dissipation substrate of a CuMo-based clad structure or a hybrid structure is developed prior to a CuW-based heat dissipation substrate is because Mo is lighter and cheaper than W. However, in the above-mentioned infiltration method and sintering method, it is difficult to produce a good heat dissipation substrate because there are cavities on the surface and inside. Therefore, it has been tried to improve wettability by adding metals such as Ni, Cr, Co, Fe, Ti, Ag, etc., but another factor is that the added metal is dissolved in Cu and the thermal conductivity is significantly reduced. Problems have arisen and have not been put to practical use. In particular, when 0.05 to 2 wt% of Ni was added, a good composite alloy could be produced, but the thermal conductivity was significantly reduced, so that it could not be put to practical use, and subsequently a heat dissipation substrate with a clad structure by brazing. Also, we have shifted to the development of heat dissipation substrates of multilayer clad structure by solid phase diffusion bonding using hot press method, or the development of heat dissipation substrates of Cu / CuMo / Cu clad structure by rolling method or CuW heat dissipation substrate.

  As described above, conventionally, heat dissipation substrates made of various materials and structures have been proposed, but a heat dissipation substrate that can reliably cope with the increase in the maximum operating temperature accompanying higher performance of semiconductor modules has not been found. In addition, no heat dissipation substrate has been proposed which solves the problem of peeling of the interface between Cu and Mo in a conventional CuMo clad structure or hybrid heat dissipation substrate.

  The inventors of the present invention have found that the heat dissipation of the hybrid structure is expected to obtain the highest characteristics of the thermal conductivity in the XY plane and in the Z-axis direction, the linear expansion coefficient, and the electrical conductivity among the various heat dissipation substrates described above. We focused on the substrate and verified its issues.

  In the invention described in Patent Document 7 by the inventor of the present invention, at the time of manufacturing a heat dissipation substrate of a Cu / via Mo / Cu hybrid structure, heating is performed while pressing from above and below to securely join Mo and Cu inside the via. Solid phase diffusion bonding was performed. However, according to this method, it was considered that pressure is unlikely to be applied in the direction of pushing the interface of Mo and Cu inside the via, and therefore it is considered that the bonding strength of the interface of Mo and Cu may not necessarily be sufficient. In addition, as proposed in Patent Document 7, in the method of locally dissolving Cu inside the via and bonding with Mo, or in the method of completely dissolving Cu and pouring it into the via and bonding with Mo, Cu It was considered that a gas generated at the time of melting may remain inside the via, particularly at the interface with Mo, and a void may be generated.

  In order to arrange and clarify the problems to be solved by the present inventor, a representative heat dissipation substrate of a CuMo clad structure or a hybrid structure that has been put into practical use or considered to be put into practical use so far (Comparative Example 1) To 5) were manufactured, and the characteristics before and after the heat cycle were evaluated.

Hereinafter, the outline and the consideration of the characteristic evaluation of Comparative Examples 1 to 5 will be described.
Comparative Example 1 is a heat dissipation substrate of a Cu / CuMo / Cu clad structure (FIG. 1A) manufactured by a rolling method. Comparative Example 2 is a heat dissipation substrate of a Cu / Mo / Cu clad structure (FIG. 1 (b)) manufactured by a brazing method. Comparative Example 3 is a heat dissipation substrate of a Cu / Mo / Cu clad structure (FIG. 1 (b)) manufactured by solid phase diffusion bonding. Comparative Example 4 is a heat dissipation substrate of a Cu / via Mo / Cu hybrid structure (FIG. 1 (c)) manufactured by solid phase diffusion bonding. Comparative Example 4 is a heat dissipation substrate of a Cu / via Mo / Cu hybrid structure (FIG. 1 (c)) manufactured by the local melting method. The content of Cu was 66 vol% in any of the heat dissipation substrates. Five heat dissipation boards were produced about each comparative example, and the characteristic before and behind a heat cycle test was evaluated. In addition, heat cycle tests were conducted by preparing those heat radiation substrates mounted on a semiconductor package. Furthermore, three mounted on a semiconductor module were prepared for each of Comparative Examples 1 to 5 to conduct a heat cycle test. In addition, an operating life test was conducted on one of those mounted on a semiconductor module.

  The linear expansion coefficient before the heat cycle test of each of the heat dissipation substrates of Comparative Examples 1 to 5 was 10 ppm / K or less. Further, the thermal conductivity in the XY plane and the thermal conductivity in the Z-axis direction were both 200 W / m · K or more. However, after the heat cycle test, the thermal conductivity of any of the heat dissipation substrates significantly decreased in the Z-axis direction. Moreover, the electrical conductivity after the heat cycle test was lower than 50% IACS in any of Comparative Examples 1 to 5.

  As described above, it is difficult to confirm the state of the interface between Cu and Mo only by the appearance, so the heat dissipation substrate after the heat cycle test was cut, and the internal state was observed. Then, in Comparative Examples 1 and 3, the interface between Cu and Mo was exfoliated. In Comparative Example 2, many large voids were generated at the interface of Cu and Mo, and the interface of Cu and Mo was exfoliated from this as a starting point. In Comparative Example 4, a void was present between the wall of the via and Cu, and Cu was separated from the wall of the via starting from this. In Comparative Example 5, micro voids were present between the wall of the via and Cu, and Cu was separated from the wall of the via starting from this.

  In the heat cycle test of the semiconductor module and the semiconductor package, peeling of the heat dissipation substrate and / or damage to the semiconductor device occur in one of five samples in Comparative Example 1 and in four of five samples in Comparative Examples 2 to 4 It was confirmed and rejected (NG). On the other hand, in Comparative Example 5, peeling of the heat dissipation substrate and damage to the semiconductor device were not observed in all five samples. Further, in the heat cycle test of the semiconductor module, one of three in Comparative Examples 1 and 5, 2 of 3 in Comparative Example 2, and all 3 of Comparative Examples 3 and 4 dissipate heat. Peeling of the substrate and / or damage to the semiconductor device was confirmed and failed (NG).

  From the above results, in any of the conventionally proposed heat dissipation substrates, the thermal conductivity is significantly reduced in the Z-axis direction after the heat cycle test, and the electrical conductivity is also less than 50% IACS, and furthermore, semiconductor packages and modules It turned out that there is a problem also in the operation reliability at the time of the implementation. In Comparative Examples 1 to 5, although relatively good results were obtained for the heat dissipation substrate of Comparative Example 5 (the heat dissipation substrate having a hybrid structure manufactured by the local melting method), the heat cycle test and the operating life test of the semiconductor module In order to put it to practical use, it is necessary to further enhance its reliability.

  The above results indicate that the solid phase diffusion bonding method and brazing method that have been proposed for the heat dissipation substrate of CuMo clad structure and hybrid structure conventionally have sufficient bonding strength that causes no problem in the heat cycle test at 250 ° C. It suggests that it is difficult to get. In addition, for the heat dissipation substrate of the hybrid structure, peeling occurs at the interface between Cu and Mo inside the via, and as a result, expansion and contraction of Cu existing inside the via is not sufficiently suppressed by Mo, and the semiconductor device is soldered. It is considered that asperities are generated on the surface of the heat dissipation substrate, and peeling and damage of the semiconductor device occur in the heat cycle test of the semiconductor module. Furthermore, it seems that peeling of the heat dissipation substrate and destruction of the semiconductor device proceed as the number of repetitions of expansion and contraction of Cu inside the via increases.

  The above-mentioned patent document 6 also describes a heat dissipation substrate of a hybrid structure. However, in the heat dissipation substrate of Patent Document 6, since the air gap is positively formed between the through hole (via) and the inner wall of the through hole (via), expansion and contraction of Cu inside the via is not suppressed. Therefore, compared to Comparative Example 4 produced by solid phase diffusion bonding as in Patent Document 6, cracks originating from the voids occur in the heat cycle test of the semiconductor package and the semiconductor module, or the above-described Cu layer on the front and back surfaces It can be easily predicted that unevenness is likely to occur.

  The problem to be solved by the present invention is to provide a heat dissipation substrate having a small decrease in thermal conductivity in the thickness direction (Z-axis direction) after a heat cycle test.

  Considering the difference in thermal conductivity in the thickness direction (Z-axis direction) of the heat dissipation substrates of Comparative Examples 1 to 5 before and after the heat cycle test in combination with the results of the heat cycle test of the semiconductor package and the semiconductor module, the semiconductor package Or that the bonding interface of the heat dissipation substrate peels off in the heat cycle test of the semiconductor module or the semiconductor device is damaged in the heat cycle test of the semiconductor module because of insufficient bonding strength between Cu and Mo of the heat dissipation substrate It is thought that this is due to the occurrence of surface peeling and defects. In addition, the inventor believes that the change (decrease) in thermal conductivity in the thickness direction (Z-axis direction) of the heat dissipation substrate can be suitably used as a benchmark (index) for evaluating these phenomena. The Therefore, the present inventors have found that the decrease in thermal conductivity in the Z-axis direction is relatively small before and after the heat cycle test of the heat dissipation substrate alone, and that there is no defect in the bonding interface between Cu and Mo, and the bonding strength is high. We studied to make a heat dissipation board.

  In the invention described in Patent Document 7 (corresponding to the heat dissipating substrate of Comparative Example 5), the present inventor introduces Cu completely melted into the inside of the via of Mo, or locally introduces Cu after introducing Cu. We considered to improve the bonding with Mo. However, it was found from the subsequent examination that in this case, bubbles generated from molten Cu may cause voids inside the vias.

  Therefore, in the present invention, which is not used in the solid phase diffusion bonding method etc., pressure is applied to the inside of the via of Mo by plastically deforming softened Cu, and Mo and Cu are joined, and the wettability to Mo and Cu is good. We considered that the bondability is enhanced and stabilized by interposing Ni as an insert metal at the interface of Mo and Cu. However, in the case of interposing an insert metal, it is necessary to prevent Cu from melting and alloying with Ni in order to prevent a decrease in thermal conductivity. Therefore, in the present invention, these are joined at a temperature lower than 1083 ° C., which is the melting point of Cu.

That is, the heat dissipation substrate according to the present invention is
a) coating the inner wall surface of the through-hole penetrating the plate-like core substrate made of Mo in the thickness direction with Ni,
b) filling the through hole with Cu by an amount corresponding to the volume of the through hole,
c) plate-like heat conduction members made of Cu are respectively disposed on the front and back surfaces of the core base material to produce a laminate;
d) The laminate can be manufactured by heating and pressurizing the laminate to a temperature lower than the melting point of Cu to soften Cu and press-fitting the inside of the through hole.

  In the above manufacturing method, the inside of the through hole (via) of the core substrate is filled with Cu in an amount corresponding to the volume of the via, and this is softened by heating and pressing to a temperature less than the melting point of Cu; It is introduced into the inside of the through hole (press fit) while Thereby, the interface of Mo and Cu can be pressurized, and they can be joined firmly without a gap. Alternatively, Cu plate members can be disposed on the front and back surfaces of the Mo core substrate on which the vias are formed, and this can be softened to press the Cu into the vias. Alternatively, it is also possible to press-in Cu into the inside of the via by inserting a columnar body, powder or the like having a volume larger than the volume of the via into the inside of the via and softening it. Moreover, these methods can also be used together.

  When Cu is pressed into the via by these methods, an extra amount of Cu or a part of the introduced insert metal is pushed out from the interface of Cu and Mo at the time of bonding on the outer periphery of the heat dissipation substrate after manufacturing and released as a bonding surplus. Be done. In other words, “joint surplus” is defined as an excess amount of Cu and / or an insert metal extruded from the interface of Cu and Mo at the time of joining, which is generated when introducing more Cu than the volume of the via. Can.

  As will be described later, according to verification conducted by the present inventor, for example, when the planar shape is rectangular, only from the side surface corresponding to a part of the outer periphery when the heat dissipation substrate after the heating and pressure treatment is viewed in plan. Bonding surplus is released on all four sides of the outer periphery rather than pressing in an amount of Cu that discharges bonding surplus (that is, pressing in an amount equivalent to or slightly larger than the volume of vias) It has been found that the reduction of the thermal conductivity after the heat cycle test is smaller when the amount of Cu is injected (that is, the amount of Cu injected is sufficiently larger than the volume of the vias). Heretofore, in the manufacture of a heat dissipation substrate, a manufacturing method in which a bonding surplus or the like is released from a bonding surface has been avoided because it is difficult to secure dimensional accuracy and the life of a jig is shortened. Generally, as a simple evaluation of bonding, methods of evaluating by appearance such as burrs in friction welding, burrs and dusts in electric welding, and meniscus in brazing and soldering are known, and the welding surplus of this case is also one of them. It can be evaluated in the same way.

  As described above, in order to increase the bonding strength between Mo and Cu, it has been conventionally known to intervene other metals as insert metals, but the insert metal dissolves in Cu and the thermal conductivity decreases, etc. At present, it has not been used for the manufacture of a heat dissipation substrate because of the knowledge that the problem arises. However, by interposing the insert metal, there is an advantage that Mo and Cu can be joined well at a temperature below the melting point of Cu.

Cu is a metal which is softened by heating and easily deformed by pressure. Therefore, the insertion of Cu into the via can be performed, for example, by the following method.
(1) A Cu columnar body manufactured by hot extrusion or forging, which has a volume larger than that of the via is introduced into the inside of the via of Mo to add the interface between Mo and Cu. Press down.
(2) The softened Cu is pressed into the inside of the via by pressing and heating the Cu plate disposed on the front and back of the plate-like Mo core substrate with the via formed, and the interface is pressed.
(3) A protrusion is provided on the surface of the Cu plate disposed on the front and back, and the protrusion is inserted into the via to press the interface inside the via.
(4) The above methods (1) to (3) are combined.

  In the above manufacturing method, the bonding strength of Cu and Mo is increased and stabilized by coating Ni on the inner wall surface of the via of the core substrate made of Mo. In this method, since Cu is not melted, Ni, which is the insert metal, does not dissolve in Cu, and there is no concern that voids or voids will occur inside the via of the heat dissipation substrate after manufacture. That is, in the via of the Mo core substrate, Cu and Mo are bonded in a state in which they are in close contact with each other directly or with a Ni layer interposed therebetween without any gap.

  In addition, it is also considered to manufacture a heat dissipation substrate of a multilayer Cu / via Mo / Cu /.../ Cu structure (this is called “multilayer hybrid structure”), which extends the hybrid structure, using the same method as described above. did. In this case, when manufacturing a heat dissipation substrate of the same thickness, the core substrate (Mo Mo layer) of Mo having a via formed may be thinner than the via Mo layer of the heat dissipation substrate of the hybrid structure of three layers. Since it is possible, Cu can be easily pressed into the via. Further, by arranging the positions of the vias formed in each via Mo layer so as not to overlap in the upper and lower layers, the influence on the surface layer can be reduced even if Cu inside the via is expanded and contracted. Further, since the Cu layers located on the front and back surfaces of the heat dissipation substrate can be thinned, the effect of suppressing the thermal expansion of Cu can be enhanced by the via Mo layer, and the linear expansion coefficient in the surface layer can be suppressed low.

  Since the linear expansion coefficient of Cu constituting the heat dissipation substrate is 17 ppm / K and that of Mo is 5.5 ppm / K, the degree of expansion of Cu and Mo differs greatly when the temperature of the operation of the semiconductor device rises, Large stress occurs. Such stress generated inside the via becomes more remarkable as the via Mo layer becomes thicker. Since a plurality of via Mo layers are provided in the multilayer hybrid structure, as described above, when manufacturing a heat dissipation substrate of the same thickness, each via Mo layer becomes thinner than providing only one via Mo layer. Therefore, the stress generated at the interface inside the via can be reduced.

Further, the heat dissipation board according to the present invention is
a) A plate-like core substrate made of Mo, in which a through hole penetrating in the thickness direction is formed;
b) an insert made of Cu, filled in the through hole;
c) a bonding layer made of Ni continuously or intermittently formed between the inner wall surface of the through hole and the insert;
d) It has the heat conduction layer which consists of Cu formed on front and back of the above-mentioned core base material.

  As a result of measuring the characteristics of the heat dissipation substrate according to the present invention manufactured by the above method, the linear expansion coefficient is 10 ppm / K or less, and the thermal conductivity in the thickness direction after the heat cycle test is 200 W / m · K or more Met. Further, peeling of the heat dissipation substrate and breakage of the semiconductor device were not observed in the heat cycle test mounted on the semiconductor package and the semiconductor module.

  Furthermore, when the electric conductivity of the heat dissipation substrate according to the present invention was measured, it was also found that an electric conductivity of 50% IACS or more corresponding to the electric conductivity of the lead wire made of an Al alloy was obtained. Therefore, the heat dissipation substrate according to the present invention can be suitably used as a heat dissipation substrate electrode.

  Furthermore, the semiconductor package and the semiconductor module according to the present invention each include the heat dissipation substrate.

  In the method of manufacturing a heat dissipating substrate according to the present invention, the heat dissipating substrate passes the heat cycle test by enhancing the bonding property of the CuMo-based hybrid heat dissipating substrate by introducing an insert metal at the Cu / Mo interface. Succeeded in developing In addition, pressing the Cu in the solid phase solved the problem that the dissimilar metal is dissolved inside the Cu and the thermal conductivity is lowered. Thus, a heat dissipation substrate having a linear expansion coefficient of 10 ppm / K or less and a thermal conductivity of 200 W / m · K or more in the thickness direction even after the heat cycle test was obtained. Also, in the heat cycle test in which the heat dissipation substrate is mounted on a semiconductor package or a semiconductor module, favorable results were obtained such that peeling and breakage of each member and breakage of the semiconductor device did not occur.

  In addition, a highly reliable heat dissipation substrate in which a decrease in thermal conductivity after a heat cycle test is suppressed by pressing in an amount of Cu that generates bonding surplus (that is, pressing in an amount of Cu larger than the via volume). You can get Furthermore, in the above method, it is possible to confirm that Cu in an amount equal to or greater than the volume of the via is pressed in, that is, a state in which there is no void inside the via is formed by generating a bonding surplus. The excess or deficiency of the amount of press-in of Cu into the inside can be easily determined from the appearance. Conventionally, the bonding process of the heat dissipation substrate was not generally managed by the bonding surplus of the appearance, but for example, when manufacturing a large and thin heat dissipation substrate for cutting out a large number of heat dissipation substrates, appropriate positions It is possible to control the overall bonding quality by providing a window for checking the bonding surplus.

The figure explaining the cross-section of the thermal radiation board | substrate of a comparative example and an Example.

One embodiment of a method of manufacturing a heat dissipation board according to the present invention is
a) coating the insert metal on the inner wall surface of the through hole penetrating the plate-like core substrate made of the first metal in the thickness direction,
b) filling the through hole with an insert made of a second metal having a thermal conductivity higher than that of the first metal;
c) plate-like heat conduction members made of a third metal having a thermal conductivity larger than that of the first metal are disposed on the front and back surfaces of the main body, respectively, to produce a laminate;
d) heating and pressing the laminate to a temperature below the melting point of all of the first metal, the second metal, and the third metal.

  In the above manufacturing method, the first metal, the second metal, the third metal, and the insert metal may be any of a single metal and an alloy. Further, the second metal and the third metal can be the same metal. In that case, introduction of the insert into the through hole and arrangement of the plate member can be simultaneously performed using, for example, a plate member having a convex portion at a position corresponding to the position of the through hole.

  In the method of manufacturing a heat dissipation substrate according to this embodiment, the inside of the through hole is covered with an insert metal having good wettability to both the first metal and the second metal. Thereby, the bondability of the 2nd metal in the inside of a penetration hole improves. Also, the laminate is heated and pressurized to a temperature below the melting point of all of the first, second and third metals. Therefore, there is no concern that the insert metal dissolves inside the second metal and lowers the thermal conductivity of the second metal. Therefore, by using the method according to this embodiment, it is possible to obtain a heat dissipation substrate having a high thermal conductivity and a small decrease in the thermal conductivity before and after the heat cycle.

  In the heat dissipation substrate manufactured by the above method, as described above, the insert metal covering the inside of the through hole is not dissolved in the first metal or the second metal. Therefore, as in the earlier application by the present inventor, a fused portion in which the first metal and the second metal are alloyed is not formed at the interface inside the through hole, and the inside of the through hole is formed of the first metal and the second metal. In the meantime, a layer of insert metal will be formed continuously or intermittently.

That is, one embodiment of the heat dissipation substrate according to the present invention is
a) A plate-like core substrate made of a first metal, in which a through hole penetrating in the thickness direction is formed;
b) an insert made of a second metal having a thermal conductivity higher than that of the first metal, filled in the through hole;
c) a bonding layer made of insert metal, formed continuously or intermittently between the inner wall surface of the through hole and the insert;
and d) a heat conducting layer formed on the front and back surfaces of the main body and made of a third metal having a thermal conductivity higher than that of the first metal.

  Further, the heat dissipation substrate of the above embodiment can be suitably used as a heat dissipation substrate electrode. Furthermore, one embodiment of the semiconductor package and the semiconductor module according to the present invention each includes the heat dissipation substrate.

  Hereinafter, an embodiment of a heat dissipation substrate and a method of manufacturing the same according to the present invention will be described in detail. First, the core base material, the insert, the heat conduction layer, and the bonding metal layer which are the main components constituting the heat dissipation substrate of the present embodiment will be described.

(Core base material made of the first metal which is a low linear expansion coefficient material)
The role of the core base made of the first metal which is a low linear expansion coefficient material is the heat conduction layer made of the third metal disposed on the front and back of the core base, and the via formed in the core base. It is to suppress that the insert which consists of a 2nd metal introduced into an inside expand-contracts at the time of semiconductor device operation | movement. As a core base material suitable for this role, for example, one comprising any of W, Mo, CuW, CuMo, In (Invar), Kv (Kovar) having a linear expansion coefficient of 9.0 ppm / K or less is preferable. It can be used for In particular, a core substrate made of Mo can be suitably used in view of the balance between the characteristics and the cost.

  The vias formed in the core substrate may be those which penetrate the core substrate in the thickness direction, and the cross-sectional shape thereof can be appropriately determined by the manufacturer. Moreover, the cross-sectional shape does not necessarily have to be constant in the thickness direction, and may be, for example, tapered. Furthermore, the number, size, and arrangement of vias may be appropriately set according to the values of the linear expansion coefficient and the thermal conductivity to be obtained. The via can be formed by an appropriate method, such as punching, etching, electrical discharge machining, drilling and the like. Moreover, you may combine these suitably. Furthermore, the vias do not necessarily have to be arranged uniformly, and for example, the vias can be arranged intensively at positions corresponding to the portions where the semiconductor device is likely to be heated.

(Insert of second metal which is high thermal conductivity material)
The role of the second metal insert, which is a high thermal conductivity material, is to heat the heat conduction layer located on one surface of the heat dissipation substrate (the side on which the semiconductor device is mounted) to the other surface (such as metal fins) It is to efficiently transmit to the heat conduction layer located on the side where the cooler is provided. As an insert suitable for this role, for example, one made of a metal having a thermal conductivity of 390 W / m · K or more can be suitably used. In addition, when the heat dissipation substrate is also used as an electrode (hereinafter, the heat dissipation substrate in this case is also referred to as a "heat dissipation substrate electrode"), electrical conduction of 50% IACS or more equivalent to or more than a lead wire made of Al alloy. It is preferable to use what consists of a metal which has a rate. In addition to Cu used in the examples described later, Ag or an alloy thereof can be used as a material that satisfies these requirements.

  The insert made of the second metal is inserted into the via of the core base so as to press the inner wall surface (the interface with the first metal) of the via of the core base in a heating and pressurizing process described later. Therefore, it is preferable to use the second metal having a volume equal to or larger than the volume of the via as the insert. Here, “preferred” means that even if the amount of the second metal inserted into the via is slightly smaller than the volume of the via, it is disposed on the front and back of the core substrate during the heating and pressing process. This is because the third metal (described later) constituting the heat conduction layer is pushed into the via to some extent and the inside of the via is pressurized. The insert has a shape corresponding to the shape of the via, is formed to be higher than the depth of the via, or has a slightly larger outer diameter than the via (in this case, Cu is heated and softened and pressed in) Alternatively, powdery or granular ones can be used. Further, a convex portion having an outer diameter smaller than the inner diameter of the through hole and having a height higher than 1/2 of the depth of the via is formed on one surface of the heat conduction layer made of a third metal described later. The two projections can be integrated as an insert inside the via by softening by heating. Alternatively, these may be appropriately combined and used together (for example, used in combination with a powdery one and a convex portion formed on one surface of a plate-like member constituting the heat conductive layer).

The press-in of the second metal (here, Cu) into the via of the core substrate of the first metal (here, Mo) can be performed, for example, by the following method.
(1) A Cu columnar body manufactured by hot extrusion or forging, which has a volume larger than that of the via is introduced into the inside of the via of Mo to add the interface between Mo and Cu. Press down.
(2) Vias are applied by heating and pressing the plate-like member (the heat conduction layer of the heat dissipation substrate) of the third metal (here, Cu) disposed on the front and back of the plate-like Mo core substrate having the vias formed. The softened Cu is pressed into the interior to pressurize the interface.
(3) A convex portion is provided on the surface of the Cu plate-like member disposed on the front and back, and the convex portion is inserted into the via to press the interface inside the via.
(4) The above methods (1) to (3) are appropriately combined.

(Thermally conductive layer of the third metal which is a high thermal conductivity material)
The role of the heat conduction layer made of the third metal, which is a high thermal conductivity material, disposed on the front and back surfaces of the core substrate enhances the thermal conductivity in the plane parallel to the surface of the heat dissipation substrate (in the XY plane) It is. In addition, it is to be pressed into the via in a state of being softened by heating and pressing to press the inside of the via. Further, as described above, a convex portion having an outer diameter smaller than the inner diameter of the through hole and having a height higher than 1⁄2 of the depth of the via is formed on one surface of the heat conduction layer made of the third metal. It is also possible to integrate the two projections as an insert inside the via by coupling and softening by heating. In the case of manufacturing the heat dissipation substrate of the multilayer hybrid structure, the convex portions may be formed on both the front and back sides of the plate-like member constituting the heat conduction layer.

  As a member which comprises a heat conductive layer, the plate-shaped member which consists of Cu or Cu alloy which has thermal conductivity of 390 W / m * K or more can be used suitably. Alternatively, a heat conductive layer can be formed by using a powder or by a thermal spraying method. Moreover, these can be used in combination as appropriate. When the third metal is pressed into the via or released to the outside as a bonding surplus, the heat conduction layer becomes thin, but the thickness of the heat conduction layer is SUS, Fe, Mo, In, Kv, etc. It can control by using the guide which consists of. In particular, in the case of a multilayer clad structure, it is desirable to use such a guide as it works effectively to control the thickness of each heat conduction layer. When such a guide is disposed on the outer periphery of the heat dissipation substrate, it can also be handled as a heat dissipation substrate including the guide. In that case, it is desirable to apply a material having good wettability to both the Cu and the member constituting the guide as well as the insert metal on the surface of the guide. If it is necessary to reduce the surface roughness of the surface layer, light rolling and polishing may be performed.

(Bonding metal layer consisting of the fourth metal which is insert metal)
The role of the bonding metal layer made of the fourth metal which is the insert metal is to intervene between the first metal and the second and third metals to improve and stabilize the bonding strength. However, after completion of the bonding of the first metal, the second metal and the third metal, not all of the interposed insert metal may be necessarily left at the bonding interface. This is because the softened Cu may partially push out the insert metal during plastic deformation.

  As the insert metal (fourth metal), for example, Ni, Co, Cr, Ti, Zr, Hf, Nb, V, Ag, Cd, Sn, or an alloy thereof can be suitably used. Also, a plurality of these may be used, and the bonding metal layer may be multilayered. However, in many cases, it is preferable that the bonding metal layer be made of a single metal, since the single metal is higher in thermal conductivity and electrical conductivity than the alloy. Among them, pure Ni is preferable. When a metal having a melting point lower than that of the second metal is used, it melts at the time of bonding of the first metal, the second metal and the third metal, and a part thereof is released to the outside as a bonding surplus. Only a small amount may remain at the bonding interface between the metal and the second and third metals, but if the fourth metal is partially present at the bonding interface, the first metal and the second metal and the The bonding strength of the three metals is improved.

  As described above, since the bonding metal layer is for enhancing the bonding property between the first metal and the second metal, the inner wall surface of the via and the second metal of the core base made of the first metal are produced when the heat dissipation substrate is manufactured. It may be formed on any one of the outer wall surfaces of the insert made of metal. Of course, it may be formed on both sides. The bonding metal layer can be formed by an appropriate method such as plating, vapor deposition, application of metal powder, application of nano metal powder, thermal spraying, and the like. In addition, the bonding metal layer 14 is formed on one or both of the front and back surfaces of the core base made of the first metal and the surface of the heat conductive layer made of the third metal (the surface to be bonded to the core base). Is preferred. Thereby, the bondability of the core substrate and the heat conduction layer can be enhanced, and the bond interface can be made more stable.

  In addition, it is preferable that the thickness of the joining metal layer formed at the time of manufacture of a thermal radiation board | substrate exists in the range of 0.003-10 micrometers. This is because when the bonding metal layer is thinner than 0.003 μm, the effect of bonding the first metal and the second metal (and the first metal and the third metal) may not be sufficiently obtained, and conversely, it is thicker than 10 μm. Then, the thermal conductivity and the electrical conductivity of the heat dissipation substrate may be reduced by the bonding metal layer.

  The thickness of the bonding metal layer is the thickness formed at the time of manufacture of the heat dissipation substrate, and in the heating and pressing steps described later, a part thereof is used as a bonding surplus from the via together with the surplus amount of the insert made of the second metal. It is pushed out. In addition, even if the bonding metal layer is formed with a uniform thickness at the time of manufacturing the heat dissipation substrate, a portion thereof is at the interface between the first metal and the second metal (and the first metal and the third metal) in the heating and pressing steps. It may move. Therefore, in the heat dissipation substrate after manufacturing, the bonding alloy layer is not necessarily continuously formed on the interface between the first metal and the second metal (and the interface between the first metal and the third metal), and the interface In some cases, the bonding alloy layer may be present intermittently.

  The melting point of Cu is 1083 ° C., however, because of pressurization in the above manufacturing method, some of Cu (second metal, third metal) and Ni (fourth metal) may form a solid solution even at less than 1083 ° C. . Even if such a solid solution is formed at a part of the interface with the first metal, there is no concern that the thermal conductivity will be significantly reduced unless the layer of the solid solution is excessively thick. However, it is preferable that no solid solution exists at the bonding interface between the first metal and the second metal and the third metal, and from that viewpoint, the heating temperature at the time of bonding is preferably 1000 ° C. or less.

  As a typical example, when the first metal is Mo and the second metal (and the third metal) is Cu, a Ni layer of 3 μm thickness can be suitably used as the bonding alloy layer. As a result, the bonding property between Cu and Mo can be enhanced, and the heat dissipation substrate can be manufactured without affecting the thermal conductivity and the electrical conductivity. Also, Ni and Ni alloys are conventionally widely used for Ni-based plating treatment for soldering a semiconductor device to a heat dissipation substrate, and it is known that no swelling or peeling occurs even when heated to 400 ° C. ing. Therefore, using a Ni layer (or a Ni alloy layer) as a bonding metal layer does not cause a problem in the heat cycle test. Furthermore, pure Ni is soft and has a coefficient of linear expansion of 8.3 ppm / k (intermediate value between the coefficient of linear expansion of Cu and the coefficient of linear expansion of Mo), thereby relieving the stress generated between Cu and Mo to separate these particles. The effect of suppressing can also be obtained. In addition, by arranging soft Ni on the bonding surface of Cu and Mo, even if a crack or peeling is generated at the interface of Cu and Mo, it is possible to suppress its rapid progress.

  Next, the procedure of one embodiment of the method of manufacturing a heat dissipating substrate according to the present invention will be described. Here, an example of manufacturing a heat dissipation substrate of a 100 mm square, 1.5 mm thick three-layer Cu / Mo / Cu hybrid structure will be described.

(Laminate)
First, a core base material in which a plurality of through holes (vias) are formed in a 100 mm square region near the center of a 110 mm square and 0.5 mm thick plate member made of Mo which is a first metal is prepared. Then, the inner wall of the via and the plate-like member are plated with Ni, which is an insert metal (fourth metal). Next, two guides, which are frame-shaped members made of SUS having a thickness of 0.5 mm and having holes of 103 mm square and 110 mm square, are prepared. Furthermore, it is made of Cu which is the third metal, and is made of Cu which is the second metal on one side of a plate-like member 100 mm square and 0.51 mm thick, each having a diameter slightly smaller than the diameter of the via and height Two plate-like members provided with a cylindrical convex portion having 0.27 mm are prepared.

  Next, a guide is placed on the outer periphery of the plate-like member made of the third metal, the positions of the vias of the core substrate made of the first metal are made coincident with the positions of the convex portions, and the vias are inserted into the respective convex portions. Then, the convex part formed in the single side | surface of the plate-shaped member which consists of 3rd metal is inserted from the upper direction of the via | veer of the core base material which consists of 1st metal. Then, a guide is placed also on the outer periphery of the plate-like member located on the upper portion of the core base material to make a laminate. As a guide arrange | positioned on the outer periphery of a plate-shaped member, the thing of the same thickness (here 0.5 mm) as the heat conductive layer of the thermal radiation board | substrate after manufacture is used.

  Then, the lower punch of the carbon jig is raised to the upper side, and the laminate is placed thereon. Subsequently, the lower punch and the upper punch are set from above the laminate to fix the laminate.

  The thickness of the SUS guide plate used in the above example is appropriately changed for the thickness of the Cu plate-like member (thickness of the heat conduction layer in the heat dissipation substrate after production) disposed on the front and back surfaces of the core substrate. It can be adjusted by doing. In particular, in the case of a multilayer hybrid structure of 5 to 11 layers (the total number of layers of Cu layer and via Mo layer), the guide is effective for controlling the thickness of the internal Cu layer (Cu layers other than the front and back surfaces of the heat dissipation substrate). is there. In addition, when manufacturing the heat dissipation substrate of the multilayer clad structure, by providing the convex portions on the front and back surfaces of the Cu plate-like member, the insert is inserted from the convex portions in the same manner as the above-described heat dissipation substrate of the clad structure It can be made.

(Joining)
Next, the carbon jig to which the laminate is fixed is set in a heating and pressing device (hot press (HP) device, electric sintering device, hot isostatic pressing (HIP) device, heating and pressing furnace, etc.) Heat and pressure are applied in a non-oxidizing atmosphere (for example, a reducing gas atmosphere, an inert gas atmosphere such as Ar, N ₂ , or a vacuum atmosphere; a combination of a reducing gas and an inert gas may be used). The conditions of heating and pressing vary depending on the size of the heat dissipation substrate and the type of each metal used, but for example, a pressure in the range of 30 MPa (0.3 tf / cm ² ) to 500 MPa (5 tf / cm ² ) is applied. It may be heated to a temperature less than the melting point (1083 ° C. or less) of Cu. The heating temperature is preferably in the range of 600 ° C. to 1000 ° C. from the viewpoint of softening and not melting Cu. The laminate of this embodiment has a thickness of about 1.5 mm after heating and pressing, and Cu and Mo inserted inside the vias are joined via the insert metal (Ni). As a condition at the time of preparation of the laminate, it is preferable to set a state in which a bonding surplus is released from the bonding interface between the Cu layer and the via Mo layer after bonding. As described above, various heating and pressurizing devices can be used. However, heating and pressure equipment where local Cu may be melted and void may be formed at the interface with Mo, such as spark plasma sintering (SPS) equipment is not used or local melting does not occur. Use limited to the conditions.

  The lowest value of the above temperature range is higher than the heating temperature in the conventional solid phase diffusion bonding because the Cu insert inserted into the via and the Cu plate-like member disposed on the front and back of the core substrate are softened For press-fitting. In addition, the lower value of the above pressure range is higher than the pressure in the conventional solid phase diffusion bonding, similarly, the Cu insert inserted in the via, and the Cu plate-like member disposed on the front and back of the core substrate To soften and press fit into the via. In the heat and pressure treatment, the bonding strength of the interface between Cu and Mo inside the via may be unstable if the temperature is outside the temperature range or below the pressure range of the above embodiment. The pressure is not a problem even if the pressure is higher than the above-mentioned range, but in order to increase the pressure, it is necessary to use a large apparatus, and the manufacturing cost becomes high.

  Generally, when processing such a laminate with a heating and pressing device, a large pressure is applied to the surface of the laminate, but in a direction perpendicular to it (that is, a direction to push the Cu-Mo interface inside the via) ) Less pressure. In this embodiment, Cu is inserted into the via by press-fitting the via using a Cu insert higher than the depth of the via, or press-fitting Cu of a plate-like member disposed on the front and back of the core substrate. The insert is pushed in, thereby applying pressure also in the direction of pushing the bonding interface of Cu and Mo inside the via.

  When the laminate is heated and pressurized, bonding of Cu to Cu or Cu to Mo is started. Further, in parallel with this, the softened Cu plastically deforms, and the gap of the interface disappears. However, if the amount of Cu introduced into the inside of the via at the time of producing the laminate is small, the bonding is completed with the void remaining in the interface. In this case, since the pressure applied to the via is low and unstable, sufficient bonding strength may not be obtained. In the above manufacturing method, the amount of Cu pressed into the via from the Cu insert or the Cu insert and the Cu plate member is made larger than the volume of the via, that is, an extra amount of Cu is introduced inside the via. Since a bonding surplus corresponding to the surplus amount is generated, a stable heat dissipation substrate can be formed with high bonding strength even inside the via. The thickness of Cu can be appropriately controlled by using a guide material. As the guide material, in addition to the above-mentioned SUS, a guide made of Mo, W, In and Kv whose thickness hardly changes even when heated and pressurized like SUS can be suitably used. By removing the bonding surplus, it is possible to obtain a stable heat dissipation substrate having a CuMo-based hybrid structure without defects and having a high bonding strength between Cu and Mo.

  In the manufacturing method of the present embodiment, the bonding property of Cu and Mo is enhanced by introducing a Ni, which is an insert metal, into the CuMo-based hybrid structure of the heat dissipation substrate at the interface of Cu and Mo. In addition, by softening Cu and pressing in a solid state, the insert metal is not dissolved in Cu and the thermal conductivity does not decrease. As a result, as described later, a heat dissipation substrate having a linear expansion coefficient of 10 ppm / K or less and a thermal conductivity of 200 W / m · K or more in the thickness direction even after the heat cycle test was obtained. Further, even in the heat cycle test in which the heat dissipation substrate is mounted on a semiconductor package or a semiconductor module, problems such as peeling of the heat dissipation substrate and breakage of the semiconductor device did not occur.

  In addition, a highly reliable heat dissipation substrate in which the decrease in the thermal conductivity after the heat cycle test is suppressed by pressing in an amount of Cu that generates bonding surplus (that is, pressing in an amount of Cu larger than the via volume). You can get it. By producing a bonding surplus, it can be confirmed that Cu of an amount equal to or greater than the volume of the via is pressed, that is, a state in which no void is formed inside the via is formed. The excess or deficiency of the introduction amount of Cu to the steel can be easily judged from the appearance. Conventionally, the bonding process of the heat dissipation substrate was not generally managed by the bonding surplus of the appearance, but, for example, when manufacturing a large thin heat dissipation substrate for cutting out a large number of heat dissipation substrates, the bonding surplus By providing a window to confirm the overall bonding quality can be managed.

  The above-described manufacturing method can also be used, for example, for manufacturing a heat dissipation substrate having a multilayer hybrid structure (Cu / via Mo / Cu / via Mo /... / Cu) of 5 to 11 layers. That is, instead of the laminate prepared in the above example, an appropriate number of Cu plate-like members and Mo plate-like members (core base materials) filled with Cu inserts inside the vias are alternately arranged to make a carbon jig By setting them to, it is possible to manufacture a heat dissipation substrate of a multilayer hybrid structure having an appropriate number of layers. In the case of manufacturing a heat dissipating substrate of the same thickness, the core base material can be made thinner (that is, the vias can be made shallower) as the number of stacked layers is increased, and thus Cu can be easily pressed into the vias. Since the thickness of the above-described Mo and the like does not easily change, the thickness of the front and back surfaces of the heat dissipation substrate and the thickness of the intermediate Cu layer can be controlled by using a guide made of Mo and the like. The guide may not necessarily be used if the tolerance of the thickness of the Cu layer of the heat dissipation substrate to be manufactured has a large margin (a wide range of allowable error).

  Next, a method of evaluating the characteristics of the heat dissipation substrate manufactured as described above and the reliability thereof will be described.

  Heretofore, various characteristics of a heat dissipating substrate to be put into practical use have been shown as an average value of results of measuring a plurality of test products of the heat dissipating substrate. However, in such a method for presenting the characteristics, since the characteristics after the heat cycle test are unknown, a heat dissipation substrate whose characteristics fall below a predetermined standard is included, and it is mounted on a semiconductor package or a semiconductor module. There is a high possibility of problems with reliability. Taking this point into consideration, a plurality of heat dissipation substrates are manufactured by the method of the above embodiment, and the lowest values of characteristics measured for them (the linear expansion coefficient is the maximum value, and the thermal conductivity and the electrical conductivity are the minimum values) are evaluated. Targeted.

(Linear expansion coefficient)
The linear expansion coefficient of the heat dissipation substrate is an important characteristic that influences the manufacture and performance of the semiconductor module, and there are optimum values for each performance and structure according to the purpose of the semiconductor module.
In the past, in the case of a CuMo-based heat dissipation substrate, the Cu layer has been made thicker in order to increase the thermal conductivity, but when the Cu layer becomes thicker, the Mo layer or CuMo layer suppresses the thermal expansion of the surface layer of the Cu surface layer. However, problems such as exfoliation of the semiconductor device have arisen because the Cu surface layer (that is, the surface layer of the heat dissipation substrate) is largely expanded. Conventionally, since chamfering has been performed to remove the bonding surplus of the heat-radiating substrate after manufacturing, it has also been difficult to accurately measure the linear expansion coefficient.

  In the following description, the linear expansion coefficient is evaluated in a temperature range from room temperature (RT) to 800 ° C. However, the linear expansion coefficient at 800 ° C. is required to be 10 ppm / K or less when the semiconductor package is manufactured. In the case where the ceramic substrate is brazed to the heat dissipation substrate and the process of brazing the ceramic substrate to the heat dissipation substrate is not performed, it is not necessary to satisfy the characteristic that the linear expansion coefficient is low at a high temperature of 800.degree. When the process of manufacturing a semiconductor package includes the process of soldering a semiconductor device to a heat dissipation substrate, it is required to have a low linear expansion coefficient (eg, 10 ppm / K or less) at 400 ° C. at which the process is performed. That is, in the evaluation of the linear expansion coefficient of the heat dissipation substrate, the upper limit of the temperature range may be set to 800 ° C. or 400 ° C. according to the assumed process. On the other hand, it is an essential requirement to have an appropriate coefficient of linear expansion (i.e., the same coefficient of linear expansion as each member to which the heat dissipation substrate is attached) at the operating temperature of the semiconductor device.

  The linear expansion coefficient was measured by cutting a test piece of 20 mm long × 10 mm wide × 1.5 mm thick from a heat dissipation substrate manufactured under each condition described later using a wire electrical discharge machining (WEDM) apparatus. In order to measure the linear expansion coefficient of the surface layer of the heat dissipation substrate, the cut-out test pieces are only subjected to removal of bonding surplus, without chamfering, using a linear expansion coefficient measuring device (manufactured by Seiko Instruments Inc.) RT ~ The linear expansion coefficient was measured in a temperature range of 800 ° C., and the maximum value was determined. Then, linear expansion coefficients in one direction (X direction) parallel to the surface and in a direction (Y direction) orthogonal to the one direction were measured for five test pieces, and the maximum value of them was used as an evaluation target. .

(Thermal conductivity)
The heat dissipation substrate cools the heat generated during the operation of the semiconductor device and, of course, is required to have a high thermal conductivity. If the thermal conductivity is low, the semiconductor device can not be cooled, and there is a risk that the semiconductor module may be damaged or burned. As a standard of thermal conductivity, for example, 400 W / m · K, which is a value of thermal conductivity of Cu, or 200 W / m · K, which is a half value thereof, is used.

  The heat dissipation substrate plays a role of dissipating the heat of the semiconductor device attached to one surface to a cooler attached to the surface opposite to the surface, so that the heat conduction particularly in the thickness direction (Z-axis direction) It is required that the rate is high.

  Therefore, a test piece of 20 mm in diameter and 1.5 mm in thickness is cut out from the heat dissipation substrate of each example, and heat conduction in the Z axis direction is performed using a thermal conductivity measuring apparatus (FTC-RT made by Advance Riko) at room temperature using a laser flash method The rate was measured three times. Further, the heat dissipation substrate of each example was used as it was, and the thermal conductivity in the XY plane was measured three times using a thermal conductivity measuring apparatus of laser flash method (TC-7000 manufactured by Advance Riko Co., Ltd.). The minimum value before the heat cycle test is 200 W / m · K or more in the Z axis direction and 200 W / m · K or more in the XY plane, and the minimum thermal conductivity in the Z axis direction after the heat cycle test The criterion of evaluation was that the value was 200 W / m · K or less.

(Electrical conductivity)
It is also required that the heat dissipation substrate has high electrical conductivity in order to function as an electrode. As described above, since the dimensions of the semiconductor device become smaller along with the miniaturization of the semiconductor module, and the performance is further improved, an Al alloy having a thermal conductivity of 50% IACS or higher is used instead of the Al lead wire. It is supposed to be Therefore, the heat dissipation substrate electrode is also required to have an electrical conductivity of 50% IACS. In addition, if there is W or Mo of the heating element in the main electric path, energization may be unstable. Therefore, when the heat dissipation substrate is also functioned as an electrode, it is preferable that W or Mo does not exist in the current path. Although Mo is used as the core substrate in the heat dissipating substrate of this embodiment, since the main conduction path is Cu present in the via of the core substrate, there is no concern that the current flow will be unstable.

  The electrical conductivity is a four-terminal method electrical conductivity measuring device (((stock) which is a test piece of 10 mm in diameter × 1.5 mm in thickness cut out by WEDM from the heat dissipation substrate of each example and the current and voltage terminals are welded on the upper and lower surfaces. ) Measured using Napson RT70V). Measure the electrical resistance value at RT three times, and use the evaluation criteria that the minimum value of the measurement result is higher than the electrical conductivity (50% IACS) of the Al alloy that is the lead material used in semiconductor devices. did. In addition, although a method of measuring an eddy current with a sigma tester is also known as a general measurement method of electrical conductivity, a measurement method in the case where the inside is a plurality of different structures as in the heat dissipation substrate of this embodiment. We decided that it was not suitable, and this time we used the four probe method.

(Ni plating evaluation)
The heat dissipating substrate itself of CuW alone or CuMo alone is poor in brazing characteristics and soldering characteristics, and it is difficult to perform a good Ni-based plating treatment. If there is a problem in the Ni-based plating process, the heat dissipation substrate does not come off from various members or semiconductor devices in the heat cycle test of the semiconductor package or semiconductor module, and the mounting operation test can not be performed. On the other hand, in the heat dissipation substrate of the CuMo-based hybrid structure as in this embodiment, the surface layer is Cu, and a good Ni-based plating process can be performed, so that such a problem does not occur.

  The Ni-based plating was evaluated based on the fact that no blisters were generated on the surface after being left at 400 ° C. for a predetermined time. A Ni-based plating treatment was applied to the surface of the heat-dissipation substrate of each example, in which test pieces were cut out from the heat-dissipation substrate manufactured by the above method by punching or cutting the press. This can reduce the possibility of defects such as voids in brazing or soldering performed later when a semiconductor device is attached and a semiconductor package or a semiconductor module is manufactured. Moreover, it can also prevent that Cu of a thermal radiation board | substrate is corroded by brazing and soldering.

  In addition, there are various methods based on the know-how in manufacture of a semiconductor module and a maker of a semiconductor package in Ni-based plating treatment of a heat dissipation substrate. The surface layer of the heat dissipation substrate of the clad structure or the hybrid structure is Cu, and a simple Ni plating process is possible. Also, in addition to the Ni-based plating process, there is also a method of plating Ni-P or Ni-B and a method of applying a heat treatment thereon. Furthermore, in order to improve the stability of soldering, Au plating processing may be performed.

(Evaluation of bonding strength and condition of heat dissipation substrate)
Essentially, since Cu and Mo are joined in the CuMo-based clad structure or hybrid structure of the heat dissipation board, it is necessary to measure the bonding strength before and after the heat cycle test at the time of development. However, since the heat dissipation substrate of the hybrid structure has a complicated internal structure, the success or failure of the internal state can not be determined even by ultrasonic flaw detection. Therefore, the investigation of the bonding interface is performed on the cross section, but this is only confirmation of the state of one cross section.

  Generally, since the heat dissipating substrate is thin, it is difficult to measure the bonding strength of the laminated interface of the heat dissipating substrate having a hybrid structure or a clad structure. In particular, it is difficult to measure the bonding strength of the laminated interface of the heat dissipation substrate of the hybrid structure. In a general measurement method of tensile strength, there is a possibility that the joint of Cu and Mo may be damaged when the measurement jig (shank) is attached. In addition, for the measurement of the bending strength, it was abandoned because the preparation of the test piece was difficult. However, it is possible to measure the thermal conductivity before and after the heat cycle test of the heat dissipation substrate alone, and to judge the bonding strength of the laminated interface based on the degree of change (reduction) in thermal conductivity in the thickness direction after the heat cycle test. I found that. As described above, it is meaningful to be able to predict the success or failure of a heat dissipation substrate alone before conducting a heat cycle test of a semiconductor package or a semiconductor module which is time-consuming and expensive.

(Heat cycle evaluation of semiconductor package)
Semiconductor packages are manufactured for various purposes, and their configurations are also various. Here, as a typical configuration of a semiconductor module, a 20 mm square, 1.5 mm thick heat dissipation substrate is subjected to a Ni-based plating treatment with a thickness of 5 μm, and an outer diameter of 20 mm square, an inner diameter of 15 mm square, a thickness A member such as a frame member made of ceramic and a metal terminal having a diameter of 0.5 mm was attached by Ag brazing treatment (the melting point of Ag is 780 ° C., brazing treatment at 800 ° C.). Then, assuming a semiconductor package provided with a semiconductor device operating at 250 ° C., the manufactured semiconductor package is heated to 250 ° C. and held for 5 minutes, followed by cooling to −40 ° C. and holding for 5 minutes. After repeating the cycle for 100 cycles, it was visually confirmed whether the semiconductor package had any problems. There are semiconductor packages in which various members are soldered to a heat dissipation substrate, and frame-like members made of resin or the like are attached by an insert or an adhesive. Also, although plastic packages and metal packages are also known, the heat cycle test of ceramic packages is the most severe, and it is found that no problem occurs in other types of semiconductor packages as long as the heat dissipation board passes this test. .

(Heat cycle evaluation of semiconductor modules)
The heat dissipation substrate of the semiconductor package is plated with Au, and a 10 mm square, 1.0 mm thick chip of GaN is attached with AuSi solder (melting point 380 ° C .; soldered at 400 ° C.), and a lead wire attached The semiconductor module was manufactured. The prepared semiconductor module is heated to 250 ° C. and held for 5 minutes, followed by 100 cycles of heating and cooling cycles of cooling to −40 ° C. and holding for 5 minutes, and the lid is removed after the heat cycle test. Was visually confirmed to see if it had occurred.

(Semiconductor module mounting operation life test)
In order to put a semiconductor module into practical use, a mounting operation life test is performed, but this test is expensive and time consuming. Since this test is intended to ensure the reliability of the operation of the semiconductor module, even the heat dissipation substrate material for which the thermal conductivity in the Z-axis direction was the minimum value in the heat cycle test of the single heat dissipation substrate conducted previously, It is necessary to confirm that the mounting operation life test passes.

  Also in the operation life test of the semiconductor module, similarly to the heat cycle test of the semiconductor module, the heat dissipation substrate of the semiconductor package is plated with Au, and further 10 mm square with AuSi solder (melting point 380 ° C .; soldered at 400 ° C.) After attaching a chip of GaN which is a dummy heating element of 1.0 mm in size and further attaching a lead wire, a lid was attached to fabricate a semiconductor module. In the operating life test of the semiconductor module, a cooler was further attached. Then, the GaN chip is energized, heated to 250 ° C, held for 5 minutes, subsequently cooled to -40 ° C, held for 5 minutes, repeated 100 cycles, and the lid is removed after the heat cycle test. It visually checked whether there was a problem in the module. In addition, when thermal damage occurred on the way, it was discontinued.

  The heat cycle test of the heat dissipation substrate alone, the semiconductor package and the semiconductor module described above is a destructive test, and another test piece (heat dissipation substrate) was used for each test. These heat cycle tests were conducted in the order of the heat dissipation substrate alone, the semiconductor package, and the semiconductor module, and the test piece (heat radiation substrate) to be used in the next test was determined based on the results of the previous heat cycle test. In this example, a heat cycle test was conducted using five heat dissipation boards alone cut out at different positions of a large (100 mm square) heat dissipation board, and the characteristics were the lowest (the heat conductivity was low). The heat dissipation substrate cut out at the position was used for the heat cycle test of the semiconductor package to be performed next. The same applies to the heat cycle test of the semiconductor module. That is, the following test was performed using what was cut out in the area | region where the characteristic is comparatively low among the manufactured large-sized heat dissipation boards. Also in the operation life test of the semiconductor module, the test piece (heat dissipation substrate) to be used in the same manner as described above was determined based on the results of the three types of heat cycle tests performed previously. By performing the test under such severe conditions, the reliability of the heat dissipation substrate which has passed the test, and the semiconductor package or semiconductor module on which the heat dissipation substrate is mounted is secured.

  Alternatively, a large number of large-sized heat dissipation substrates are prepared, and a test piece cut out from another large-size heat dissipation substrate at the same location as the heat dissipation substrate cut-out position having the lowest characteristics in the heat cycle test of the single heat dissipation substrate ) May be used for the heat cycle test of the semiconductor package and the heat cycle test and the operating life test of the semiconductor module. When performing each test using the number of heat dissipation boards described above, one large-size heat dissipation board for cutting out the five heat dissipation boards used for the heat cycle test of the heat dissipation board alone, and the other tests A large-sized heat dissipation substrate for cutting out the heat dissipation substrate to be used at the same position may be prepared in a total of 10 large heat dissipation substrates of 9 (= 5 + 3 + 1).

  Hereinafter, the heat dissipation substrate (Examples 1 to 3) of three types of Cu / Mo / Cu hybrid structure or Cu / Mo / Cu / Mo / Cu multilayer (five-layer) hybrid structure is manufactured by the above method, and the above method Explain the result of evaluation by.

  Examples 1 and 2 are heat dissipation substrates of a three-layer hybrid structure (FIG. 1 (c)), and Example 3 is a heat dissipation substrate of a five-layer hybrid structure (FIG. 1 (d)). The coefficient of linear expansion and the thermal conductivity were measured. In Examples 1 and 3, after the heating and pressure treatment, Cu insert and Cu plate-like member are used in such an amount that bonding surplus occurs on any of the four sides of the outer periphery of the heat dissipation substrate (see Table below) In the third embodiment, the Cu insert and the Cu plate-like member are used in an amount such that bonding surplus occurs only in a part of the outer periphery of the heat dissipation substrate in Example 3 (described in the following table as “part”) . In each example, five heat dissipation substrates were mounted on the semiconductor package, and the heat cycle test of the semiconductor package was performed. Furthermore, a heat cycle test was performed by mounting three heat dissipation substrates on the semiconductor module for each example. In addition, the content ratio of Cu of Examples 1-3 was 66 vol% same as the comparative example mentioned above.

  In preparation of the thermal radiation board | substrate of Examples 1-3, the laminated body of the hybrid structure was first prepared. In a 100 mm square area of the central portion of a 110 mm square and 0.5 mm thick plate member made of a first metal (Mo), three for every 5 mm square unit area with a diameter of 2.06 mm (radius 1.03 mm) A through hole was formed. That is, a total of 1,200 through holes were formed in a 100 mm square area of the central portion of the plate-like member. In the 100 mm square area, the ratio of the through holes to the cross section of the plate-like member is about 40%.

  Then, a plating process of a fourth metal (Ni), which is an insert metal, was applied to the inner wall surface of the via and the front and back of the plate-like member to a thickness of 3 μm. Next, two guides which are plate-shaped members made of SUS with a thickness of 0.5 mm and having an outer diameter of 110 mm and a hole of 103 mm formed therein were prepared. Furthermore, the second metal (Cu) slightly smaller than the outer diameter (φ 2.06 mm) of the via on one side of two 100 mm square, 0.53 mm thick plate members made of the third metal (Cu) A convex portion having a diameter of 2.0 mm and a height of 0.27 mm was formed by etching.

  Subsequently, the Cu plate member is placed with the surface on the side on which the convex portion is formed facing upward, and the guide is placed on the outer periphery thereof. Then, vias formed in the core substrate of Mo are inserted from above the respective convex portions. Furthermore, a convex portion formed on one side of another Cu plate-like member from above is inserted into a via formed in the core substrate of Mo, and a guide is placed on the outer periphery of the via to form a laminate.

Then, the lower punch of the carbon jig was raised to the upper side to bond the respective members, the laminate was set thereon, the lower punch was lowered, and the upper punch was inserted. Next, the carbon jig to which the laminate was fixed was set in a heating and pressurizing apparatus of HP, and a pressure of 100 MPa (about 1.0 tf / cm ² ) was applied in a vacuum atmosphere to heat to 900 ° C. Then, it was held for 30 minutes and gradually cooled to 100 ° C. or less, and then taken out. The outer periphery of the heat dissipation substrate was checked to confirm the condition of the bonding surplus. And when thickness was thicker than 1.5 mm which is a design value, it adjusted to 1.5 mm thickness by grinding. Thereafter, it was cut out to a predetermined size with WEDM and used as a measurement sample. Five heat dissipation substrates of each of Examples 1 to 3 were produced, and the following evaluation was performed.

(Evaluation)
The results of the characteristic evaluation of the heat dissipation substrates of Examples 1 to 3 are shown in the following table together with the results of the characteristic evaluation of Comparative Examples 1 to 5 described above. In this table, the method of manufacturing the heat dissipation substrate of the above-described example is described as “insert metal heat and pressure bonding method”.

  Hereinafter, the result of the characteristic evaluation of Examples 1 to 3 will be considered in comparison with the characteristic evaluation of Comparative Examples 1 to 5 described above.

  As can be seen from the measurement results of the characteristics of Comparative Examples 1 to 5 and Examples 1 to 3, in Examples 1 to 3, the thickness direction after the heat cycle test in comparison with the conventional heat dissipation substrate (Comparative Examples 1 to 5) The decrease in the thermal conductivity (in the Z-axis direction) is significantly suppressed, and even after the heat cycle test, the thermal conductivity is 200 W / m · K or more.

  The degree of decrease in bonding strength can be determined from the change in the thermal conductivity (degree of decrease) before and after the heat cycle test of the heat dissipation substrate alone. In the heat dissipation substrates of Examples 1 to 3, the decrease of the thermal conductivity before and after the heat cycle is small, and the interface of Cu and Mo in the laminated structure and the interface of Cu and Mo inside the via are firmly joined. I understand. Also, as in Examples 1 and 3, when using a Cu insert containing an excess amount that causes a bonding excess on any of the four sides of the rectangular heat dissipation substrate in the heating and pressing process, an embodiment with a small excess amount. The decrease in the thermal conductivity before and after the heat cycle test was somewhat suppressed as compared to 2.

  In addition, when the heat dissipation substrate after the heat cycle test was cut and the state inside the via was observed, in each of Comparative Examples 1 to 5 as described above, voids were generated inside or the interface between Cu and Mo was peeled off. However, in Examples 1 to 3, no such void or peeling was observed. Also, no blisters were found for the Ni-based plating process.

  Furthermore, from the results of the heat cycle test of the semiconductor module, it is possible to predict the decrease in the bonding strength of the semiconductor device due to the unevenness of the surface of the heat dissipation substrate generated during the heat cycle. You can also That is, using the heat dissipation substrates of Examples 1 to 3 in which no problem occurred in all the test pieces, there is no concern that the bonding strength with the semiconductor device is reduced, and a semiconductor module having high operation reliability is manufactured. Can.

The above-described embodiment is an example, and can be appropriately modified in accordance with the spirit of the present invention.
As described above, a method of manufacturing a heat dissipation substrate using an insert metal and heating and pressurizing to a temperature below the melting point of Cu using a guide for controlling the thickness of the Cu layer to produce a bonding surplus, A heat dissipation substrate having a hybrid structure of Cu / via CuMo / Cu in which the first metal is CuMo in addition to the first metal (core base material) being Mo and the third metal (thermal conductive layer) being Cu as in the example And Cu / via CuMo / Cu / via CuMo /... / Cu. In addition, with regard to the heat dissipating substrate other than the above-described embodiment, the heat dissipating substrate alone can satisfy the above requirements and have an electrical conductivity of 50% IACS, which can also be used as a heat dissipating substrate electrode.

  The above method of interposing Ni as an insert metal with good wettability to Mo and Cu as an insert metal at the interface between Mo and Cu not only enhances the bonding strength of Cu and Mo inside the via, but also to the via Mo layer and its front and back surfaces. It is also effective in that the bonding strength of the located Cu layer is increased. That is, the present invention is effective not only to the heat dissipating substrate of the hybrid structure but also to the heat dissipating substrate of the clad structure. Furthermore, the above method can be used to manufacture a heat dissipation substrate having a structure in which a hybrid structure and a clad structure are combined. Specifically, it is possible to make the surface layer part a hybrid structure and make the inside a clad structure, or conversely make the inside a layer structure clad structure as a hybrid structure.

  In addition, since the size of the heat dissipation substrate that can be used is limited by the configuration of the semiconductor module and economic constraints, the heat dissipation of this embodiment is high for the thermal conductivity in the Z-axis direction for semiconductor devices requiring insulation. Even when the substrate is attached to one surface of the semiconductor device and cooled, the substrate may not be cooled to the heat resistant temperature of the edge resin sheet. In such a case, a large cooling plate made of Cu or Al is soldered to the heat dissipation substrate of the present embodiment, and this is attached to two sides (typically, both front and back sides) of the semiconductor device and cooled. The heat of the semiconductor device can be cooled to the heat resistant temperature of the insulating resin sheet, and the insulating property can be secured by an inexpensive resin sheet. Also, cost can be reduced.

  In addition, in the LED, the electrode configuration is shifting from the horizontal electrode type to the vertical electrode type, but in the conventional CuW and Mo heat dissipation electrodes, there is a problem that the thermal conductivity and the electrical conductivity are insufficient. Could not respond to. On the other hand, by using the heat dissipation substrate of this embodiment having large thermal conductivity and electrical conductivity, it is possible to cope with the enhancement of the performance of the LED and to reduce the cost.

  The application of the semiconductor module provided with the above-mentioned heat dissipation substrate is diverse, such as memory, IC, LSI, for communication, power semiconductor, sensor, LED, etc., and is expected to be further expanded in the future. In particular, in the case of a power semiconductor module, it is possible to efficiently cool the semiconductor device by bonding the heat dissipation substrate electrode to the upper and lower sides or one side of the semiconductor device, and to increase the conduction cross section to secure a large conduction capacity. Can. Furthermore, it is suitable for a heat dissipation substrate electrode having a structure in which a semiconductor device of an insulated gate bipolar transistor (IGBT) is cooled on both sides.

Claims (9)

a) A plate-like core substrate made of Mo, in which a through hole penetrating in the thickness direction is formed;
b) an insert made of Cu, filled in the through hole;
c) a bonding layer made of Ni continuously or intermittently formed between the inner wall surface of the through hole and the insert;
d) A heat dissipation substrate comprising: a heat conduction layer of Cu formed on the front and back surfaces of the core base material. further,
d) The heat dissipation substrate according to claim 1, further comprising: a bonding layer made of Ni continuously or intermittently formed at the interface between the core base and the heat conduction layer.   The through holes formed in the thickness direction of the plate member made of Mo are filled with Cu, Cu layers are formed on the front and back surfaces of the plate member, and the insert metal is continuously or intermittently inserted into the interface between Mo and Cu. A heat dissipation substrate characterized by the presence of Ni. A heat dissipation substrate in which the thermally conductive layer and the core base material in which the insert is filled in the through hole are alternately stacked, and the total number of layers is five to eleven. The heat dissipation substrate according to claim 1 or 2, characterized in that: The maximum value of the linear expansion coefficient in the temperature range from room temperature to 800 ° C is 10 ppm / K or less,
The heat dissipation substrate according to any one of claims 1 to 4, wherein the thermal conductivity in the direction perpendicular to the surface at room temperature is 200 W / m · K or more. It is characterized in that the heat conductivity in the direction perpendicular to the surface after the heat cycle test is 200 W / m · K or more after 100 cycles of heating to 250 ° C. and cooling to −40 ° C. The heat dissipation substrate according to any one of claims 1 to 5.   The heat dissipation substrate electrode comprising the heat dissipation substrate according to any one of claims 1 to 3, wherein the electrical conductivity is 50% IACS or more.   A semiconductor package comprising the heat dissipation substrate according to any one of claims 1 to 7.   A semiconductor module comprising the heat dissipation substrate according to any one of claims 1 to 7.

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