JP4146321B2 - Ceramic circuit board - Google Patents

Description

  The present invention mainly relates to a ceramic circuit board used for mounting high-power transistors, power modules, and the like, and in particular, mounting position accuracy of mounted components such as semiconductor chips, electrode terminals, thermistors, resistors, etc. is high, and the mounted components are made conductive. The present invention relates to a ceramic circuit board that can effectively prevent solder or brazing material as a bonding material from flowing out to an adjacent circuit layer or wiring layer when bonded to a circuit layer.

  Conventionally, ceramic circuit boards and metal circuit materials such as Cu (copper) are integrated as ceramic circuit boards on which high-power transistors, power modules, etc. are mounted, such as circuit boards for high-power power devices and Peltier modules. Ceramic circuit boards are widely used in which various mounting parts such as semiconductor chips and electrode terminals are integrally bonded and mounted on the surface of a metal circuit material by a bonding method such as soldering or brazing.

  As a method of joining the ceramic material and the metal circuit material, there is conventionally used a simultaneous firing method in which a high melting point metal paste such as Mo or W, which becomes a circuit layer, is printed on the surface of a ceramic sheet-like molded body and sintered. Direct bonding method (DBC method) that directly bonds the circuit layer (Cu circuit board) directly to the surface of the ceramic substrate using the eutectic reaction of copper and oxygen as circuit components without the use of ceramics. The DBA method for directly bonding a substrate and an Al plate by heat treatment, and the active metal method using a brazing material containing an active metal such as Ti as a bonding material (brazing material layer) between a metal circuit layer and a ceramic substrate are widely used. in use.

Moreover, as a ceramic substrate constituting the ceramic circuit board, a sintered body such as aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ) or the like has been conventionally used.

  For example, an aluminum nitride substrate has a thermal conductivity of 160 W / m · K or higher, and has a higher thermal conductivity than other ceramic substrates, and therefore has particularly excellent heat dissipation. Further, since the silicon nitride substrate has a three-point bending strength (room temperature) of 600 MPa or more, when used as a ceramic substrate constituent material, the strength of the circuit substrate can be improved. In contrast, the aluminum oxide substrate has a thermal conductivity of about 20 W / m · K, and a three-point bending strength of about 360 MPa. Therefore, in order to obtain particularly high heat dissipation and structural strength, it can be said that it is preferable as a circuit board to use a nitride ceramic substrate rather than an oxide ceramic substrate.

  On the other hand, when attention is paid to the bonding strength between the ceramic substrate and the metal circuit board, the active metal method is preferable among the above-described bonding methods. In the active metal method, a metal foil containing at least one of active metals such as Ti, Hf, Zr, and Nb, or a paste obtained by adding these active metals to an Ag—Cu brazing material is interposed between a ceramic substrate and a metal circuit board. In this method, both members are joined together by heat treatment after coating. When joining by an active metal method using a nitride-based ceramic substrate, a joining layer made of the nitride of the active metal is formed after the heat treatment, and a stronger joining state is formed. As described above, the joined body of nitride ceramics and metal member by the active metal method satisfies the characteristics required for a circuit board, and is widely used as an electronic circuit board such as a semiconductor module board on which a power semiconductor element is mounted. ing.

As a conventional ceramic circuit board, for example, a ceramic circuit board 1 as shown in FIG. 4 is generally used. This ceramic circuit board 1 has a ceramic substrate 2 made of a sintered body such as aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), etc. It is formed by integrally joining metal circuit boards 4 made of a conductive material such as copper (Cu). Further, in order to prevent warping of the ceramic substrate 2 and to enhance the bonding property with the mounting device, the back metal plate 5 is also bonded to the back side of the ceramic substrate 2 via the brazing material layer 3. . Further, a mounting part 6 such as a semiconductor chip, an electrode terminal, a capacitor, a thermistor for measuring a temperature rise of the circuit board, and a resistor are integrally joined to a predetermined position of the metal circuit board 4 by using a brazing material such as solder. .

  According to the ceramic circuit board with the above configuration, the electrode joint, circuit and wiring layer are formed with a thick metal circuit board with low resistance and large current carrying capacity, so it is used especially for mounting high-power transistors and power modules. It is suitable as a ceramic circuit board.

  However, in the assembling process of the conventional ceramic circuit board 1 as shown in FIG. 4, when a mounting component such as the semiconductor element 6 is to be joined with a brazing material such as solder, means for regulating the position of the mounting component is provided on the joining surface. Since it does not exist, the mounting components are likely to be misaligned, and the wiring positions and bonding positions are also misaligned, resulting in a decrease in the manufacturing yield of the semiconductor device. Also, depending on the bonding temperature, solder and brazing material flow out and short circuit with the adjacent circuit layers, so that there is a problem that the product yield is greatly reduced in any case.

  Therefore, a solder resist made of resin such as epoxy is printed on the circuit portion in advance as a conventional ceramic circuit board to eliminate misalignment and solder flow of various mounted components during joining by soldering as described above. It has been proposed.

Specifically, a photosensitive epoxy resin is applied to the surface of the wiring board with a predetermined thickness, and an exposure mask having a hole formed only in the projection forming portion is placed on the photosensitive epoxy resin layer, and the photosensitive epoxy resin layer There is also proposed a wiring board in which positioning projections made of resin are formed by exposing the projections to only the projection formation portions of the substrate and then developing and removing excess resin to develop (for example, Patent Document 1). reference.).
Japanese Patent Laid-Open No. 10-12671 (Claim 1, FIG. 1)

  However, in recent years, higher output, higher density integration, and higher functionality of electronic devices have further progressed, and there is a demand for increased use of high output transistors and power modules and higher reliability of semiconductor manufacturing equipment. Below, in order to further increase the bonding strength of the mounted components, a bonding operation at a high temperature is required so as to melt the soldering material such as solder. In other words, by increasing the bonding temperature to reduce the viscosity of the brazing material and increasing its fluidity, bonding with the brazing material spread over the entire joint surface of the mounted component increases the bonding strength and improves the reliability of the semiconductor product. In addition, increasing the durability is a technical problem.

  However, solder resists that can withstand high temperatures that melt soldering materials such as solder and do not flow out or burn out are rare, especially solder resists that can be used for brazing joints at high temperatures of 400 ° C or higher. It has not been developed yet. For this reason, at present, it is necessary to prevent misalignment by joining the mounted components in a restrained state using a dedicated restraining jig made of carbon. However, the above-mentioned carbon-made exclusive restraint jig has the disadvantages of being expensive and low in durability, and a high-level and complicated mechanism is essential for restraining work of mounted parts, so the manufacturing cost of ceramic circuit boards has increased significantly. There was a problem to do.

  The present invention has been made to solve the above-described conventional problems, and in particular, mounting position accuracy of mounting components such as semiconductor chips, electrode terminals, thermistors, resistors, etc. is high, and the mounting components are joined to the conductive circuit layer. It is an object of the present invention to provide a ceramic circuit board capable of effectively preventing solder or brazing material as a bonding material from flowing out into an adjacent circuit layer or wiring layer.

In order to achieve the above object, a ceramic circuit board according to the present invention has a ceramic circuit board in which a metal circuit board is integrally joined to at least one surface of the ceramic board, and a mounting component is joined to the metal circuit board. a recess is formed on the metal circuit plate surface while the bottom surface of the mounting part is in recess within this recess Ru joint surfaces der mounting component, with the depth of the recess is 0.05mm or more, The gap between the side surface of the recess and the side surface of the mounting component mounted and fixed in the recess is 0.5 mm or less, and the thickness of the metal circuit board is 0.1 to 0.3 mm. .

The ceramic substrate constituting the ceramic circuit board according to the present invention is not particularly limited, and can be appropriately selected according to required characteristics such as insulation, heat dissipation, and strength characteristics. Specifically, oxidation of nitride ceramic sintered bodies such as aluminum nitride (AlN) and silicon nitride (Si ₃ N ₄ ), alumina (Al ₂ O ₃ ), and a compound of alumina and zirconia (ZrO ₂ ). It is preferably made of a physical ceramic sintered body. In particular, assuming use at high temperatures, silicon nitride, aluminum nitride, alumina, etc. excellent in heat dissipation characteristics and mechanical strength are desirable. Moreover, it is preferable to improve heat dissipation by using an aluminum nitride substrate having a high thermal conductivity for a circuit board on which a high-power semiconductor element is mounted.

  In the ceramic circuit board, the metal circuit board is preferably made of at least one metal selected from copper and aluminum. Since a metal circuit board requires a particularly high current carrying capacity as a circuit layer, it is formed of a metal circuit board having a small conductive resistance and a large thickness. However, Cu, Al and their alloys are particularly preferred from the viewpoint of conductivity and economy. It is desirable to make up with materials.

  In the ceramic circuit board, the brazing material for joining the ceramic substrate and the metal circuit board is preferably composed of at least one element selected from Ag, Cu, Ti, Zr, Si and Al. Specifically, an active metal brazing material composition comprising, by mass%, 15 to 35% of Cu, 1 to 10% of at least one element selected from Ti, Zr, Si and Al, and the balance substantially consisting of Ag. Things are illustrated. In particular, by using a Ti—Ag—Cu-based active metal brazing material containing Ti and Zr, which are active metals, it is possible to significantly increase the bonding strength of the metal circuit board.

  By brazing the brazing material paste prepared by dispersing the brazing material composition in an organic solvent onto the surface of the ceramic substrate, a brazing material layer for joining the metal circuit board to the ceramic substrate surface is formed.

  In the present invention, a recess having a predetermined width and depth is formed on the surface of the metal circuit board. The recess is formed to restrict the mounting position of the mounted component and to store molten solder and brazing material and prevent the outflow thereof. As a method for forming the recess, a processing method such as a die press or an etching process can be applied. Moreover, you may form a recessed part with the brazing material which joins a mounted component to a metal circuit board. Specifically, a method of joining a brazing material metal foil, in which a recess is formed in advance by a processing method such as the above-mentioned die press or etching process, to the surface of the ceramic substrate, or after joining the brazing material metal foil on the ceramic substrate, etching And a method of forming a recess by honing or the like.

  The depth of the concave portion formed in the metal circuit board may be 0.05 mm or more from the viewpoint of the positioning stability of the mounted component and the ability to store and hold the amount of melt according to the solder and brazing material thickness. is necessary. When the depth of the recess is less than 0.05 mm, the effect of restricting the position of the mounted component due to the recess is not exhibited, the mounted component on the solder or brazing material is displaced, and the molten solder or brazing material is used. Since it cannot be stored and solder or the like protrudes to or flows out of the region outside the concave portion, a short circuit or the like occurs, which is inappropriate.

  In consideration of the thickness of the solder or brazing material, the depth of the recess is more preferably 0.1 mm or more. In addition, it is possible to increase the capability of storing and holding a molten material such as solder in proportion to the increase in the depth of the recess, but the effect of improving the positioning stability of the mounted component is small. Moreover, when the depth of the said recessed part shall be 0.5 mm or more, since it leads to the electricity supply area of a metal circuit board reducing, it is unpreferable.

  Further, the size of the opening of the concave portion is formed so as to have an area slightly larger than the cross-sectional area of the joint portion of the mounted component in order to ensure the stability of positioning of the mounted component. Specifically, the gap between the side surface of the recess and the side surface of the mounting component mounted and fixed in the recess is preferably 0.5 mm or less. That is, it is preferable to form a recess having a bottom surface protruding outward with an amount of protrusion of 0.5 mm or less from the outer periphery of the joint surface of the mounted component. However, when the overhang amount is less than 0.1 mm, the mounting component may not be inserted into the recess due to a finished dimensional error of the mounting component. Therefore, the gap is preferably in the range of 0.1 to 0.5 mm.

  If the gap between the side surface of the concave portion and the side surface of the mounting component mounted and fixed in the concave portion is excessively larger than 0.5 mm, the mounting component will be displaced in the gap range. The positional accuracy is lowered, the position of the wiring connected to the component and the bonding position are also shifted, and interference is caused with the adjacent wiring layer, both of which lead to a decrease in the operational reliability and manufacturing yield of the semiconductor product. This adverse effect has become a serious problem to be solved, particularly in the situation where the integration of semiconductor products has progressed in recent years and the circuit wiring width has become finer.

  The ceramic circuit board according to the present invention is manufactured, for example, by the following procedure. That is, a metal circuit board having a thickness of about 0.1 to 0.3 mm, in which a recess having a predetermined shape is formed by press molding or the like as described above, is prepared. On the other hand, a brazing material paste of Ag / Cu / Ti or the like is printed on at least one surface of the ceramic substrate by a screen printing method or the like to join the metal circuit board to a thickness of about 10 to 20 μm. A material layer is formed on the surface of the ceramic substrate, and then the metal circuit board is heat-treated in a vacuum atmosphere in a state of being bonded to the surface of the brazing material layer, and the metal circuit board is applied to the surface of the ceramic substrate through the printed brazing material layer. Join together. The metal circuit board to be bonded may be a metal circuit board in which a predetermined circuit pattern and a recess are formed in advance, but a resist is applied on the metal plate on the bonded flat plate, and then the predetermined circuit pattern and the recess are formed by etching. It may be formed.

  Next, the mounting portion of the mounting component is inserted into the concave portion formed in the metal circuit board, and is fixed via a bonding material such as solder or brazing material so that the bottom surface of the concave portion becomes the bonding surface of the mounting component, Thereafter, heat treatment is performed at a predetermined high temperature. At this time, the bonding material such as solder and brazing material is in a molten state with high fluidity due to high temperature and spreads uniformly over the entire bonding surface. Therefore, the mounted parts are integrally joined with high joining strength and positional accuracy. In this way, a ceramic circuit board free from defects such as misalignment of mounted components and solder flow can be easily manufactured with a high product yield.

  According to the ceramic circuit board of the present invention, the concave portion having a predetermined shape is formed on the surface of the metal circuit board, and the mounting component is inserted into the concave portion, and the bottom surface of the concave portion becomes the bonding surface of the mounting component. Therefore, when the mounting component is bonded and fixed via a bonding material such as solder or brazing material by heat treatment at a high temperature, the bonding position of the mounting component in the opposing surface direction is accurately regulated by the opposing side wall of the recess. For this reason, an effect of correcting a minute error in the mounting position, that is, a so-called self-alignment effect (self-position correcting effect) can be obtained, and a ceramic circuit board with high positional accuracy of the mounted components can be provided.

  In addition, since the bonding material such as solder and brazing material is in a molten state with high fluidity at high temperatures and uniformly spreads over the entire bonding surface, the mounted components can be integrally bonded with high bonding strength and positional accuracy. Furthermore, even when a bonding material such as solder or brazing material that is in a molten state with high fluidity at a high temperature is used, the bonding material such as solder is retained and retained by the recess and does not flow out of the recess. Therefore, a ceramic circuit board free from defects such as misalignment of mounted parts and solder flow can be easily manufactured with a high product yield.

  Hereinafter, embodiments of a ceramic circuit board according to the present invention will be described more specifically with reference to the accompanying drawings.

[Examples 1 to 6, 9, Reference Examples 7 and 8 and Comparative Example 1]
A large number of 0.635 mm thick aluminum nitride (AlN) substrates, silicon nitride (Si3N4) substrates and alumina (Al ₂ O ₃ ) substrates are prepared as ceramic substrates, and Ag / Cu / Ti is formed on the surface of these ceramic substrates. The brazing material paste of the system was applied by a screen printing method to form a brazing material layer having a thickness of 15 μm. Furthermore, an Ag / Cu / Ti-based brazing paste was applied to the back side of each ceramic substrate by a screen printing method to form a brazing filler metal layer having a thickness of 15 μm for joining the back metal plate.

Next, on both front and back surfaces of each ceramic substrate on which the brazing paste is printed, a circuit metal plate having a thickness of 0.25 to 0.3 mm as shown in Table 1 and a Cu plate or Al as a back metal plate The metal plate for metal circuit and the back metal plate are obtained by performing heat treatment at a temperature of 800 ° C. for 15 minutes in an atmosphere having a degree of vacuum of 1 × 10 ⁻⁴ torr or less in a state where the plates are pressed and contacted. A Cu-clad ceramic substrate and an Al-clad ceramic substrate were prepared by integrally bonding to a ceramic substrate.

  Thereafter, by etching the metal plate for circuit bonded to the surface side of each ceramic substrate, the depth D as shown in Table 1 is 0.03 to 0.15 mm, and the gap W with the mounted component is A recess having a thickness of 0.08 to 0.5 mm was formed.

  On the other hand, as Comparative Example 1, a ceramic circuit board in which a protrusion for preventing solder flow was formed by printing an epoxy resin solder resist on the surface of the ceramic board without forming the concave portion was produced.

Next, an Ag—Cu-based brazing foil (BAG-18) having a thickness of 0.05 mm is disposed in the recesses of the various ceramic circuit boards prepared as described above, and further on the upper surface of the brazing foil. Then, by pressing a Cu electrode terminal as a mounting component having a bonding cross section of 5 mm square, the electrode terminal is heated to a temperature of 730 ° C. with the electrode terminal fitted into the recess, and the bottom surface of the recess is bonded to the mounting component. The electrode terminal was brazed and joined so as to be a surface. Thus, ceramic circuit boards according to the respective examples , reference examples, and comparative examples were manufactured.

  As shown in FIGS. 1 and 2, the ceramic circuit board 1 a according to each example prepared in this manner has a metal circuit board 4 a integrally bonded to the surface side of the ceramic board 2 via a brazing material layer 3. The electrode terminals as the mounting components 6 are brazed and joined to the recesses 7 formed on the surface portion of the metal circuit board 4a, and the back metal side of the ceramic substrate 2 is connected to the back metal via the brazing material layer 3. The plate 5 has a structure joined together.

In order to evaluate the ceramic circuit boards according to the examples , reference examples, and comparative examples prepared as described above, the displacement of the electrode terminals fitted and joined to the recesses 7 is 0.25 mm or more from the predetermined position for each circuit board. The occurrence rate of the circuit board was measured. Moreover, the joint part of the electrode terminal was visually observed, the number of circuit boards in which the solder flowed out from the recesses 7 and the number of circuit boards in which a short circuit occurred were counted, and the occurrence rate was measured. The measurement results are shown in Table 1 below.

As is clear from the results shown in Table 1, the depth D to the metal circuit plate 4a surface is not less 0.05 m m or more, the gap W between the concave side and the mounting part side of 0.1~0.5mm According to the ceramic circuit boards 1a according to Examples 1 to 6 in which the concave portion 7 having a predetermined shape as a range is formed, the electrode terminal as the mounting component 6 is fitted into the concave portion 7, and the bottom surface of the concave portion 7 is the bonding surface of the electrode terminal. Therefore, when the mounting component 6 is bonded and fixed via a bonding material such as solder or brazing material by high-temperature heat treatment, the electrode terminal as the mounting component 6 faces the side wall facing the recess 7. Since the joint position in the opposing surface direction is accurately regulated by the above, an effect of correcting a fine attachment position error, that is, a so-called self-alignment effect (self-position correction effect) is obtained, and the fixed position accuracy of the mounting component 6 is high. Ceramics It was able to provide the road board. Of course, in any case of the used AlN substrate, Si ₃ N ₄ substrate, Al ₂ O ₃ substrate, or the like, the difference in the above effects based on the difference in the type of the ceramic substrate was not observed.

  In addition, since bonding materials such as solder and brazing material are in a molten state with high fluidity due to high temperature and are uniformly distributed over the entire bonding surface, the electrode terminals as the mounting components 6 should be integrally bonded with high bonding strength and positional accuracy. Became possible. Furthermore, even when a bonding material such as solder or brazing material that is in a molten state with high fluidity at high temperatures is used, the bonding material such as solder is retained and retained by the recess 7 and does not flow out of the recess 7. . Therefore, the ceramic circuit board 1a free from defects such as misalignment of electrode terminals and solder flow as a mounting component can be easily produced at a high product yield.

However, in the ceramic circuit boards according to Reference Example 7 and Reference Example 8 in which the depth D is too small even when the recess 7 is formed, the self-alignment effect of the mounted component and the solder flow prevention effect by the recess 7 However, the occurrence rate of deviation and the occurrence rate of short circuit due to the solder flow were relatively increased.

  On the other hand, in the ceramic circuit board according to Comparative Example 1 in which an epoxy resin solder resist is printed on the surface of the ceramic substrate 2 without forming the recesses 7 and the protrusions for preventing solder flow are formed, the printed solder It was reconfirmed that the resist burned out when the bonding treatment was performed at a high temperature, the electrode terminal positioning effect and the solder flow prevention effect were not sufficiently obtained, and the defect occurrence rate increased.

  Moreover, according to the ceramic circuit board according to the present embodiment, the volume obtained by subtracting the volume of the joint portion of the mounting component 6 inserted into the recess 7 from the total volume of the recess 7 to be formed is the maximum of the molten brazing material. It can be easily calculated as the amount of storage. Therefore, it becomes unnecessary to strictly control and control the amount of solder so as not to cause solder flow as before, and a remarkable operational effect is achieved in which manufacturing management is greatly simplified.

  In the above embodiment, as shown in FIG. 1, a square-shaped recess 7 having a bottom surface slightly protruding outward from the joint surface of the mounting component 6 is formed in the surface region of the metal circuit board 4a. Although an example is shown, the present invention is not limited to this configuration. For example, as shown in FIG. 3, a groove-like recess 7a is formed so as to penetrate the surface region of the metal circuit board 4b, and a plurality of recesses 7a are formed in the recess 7a. Even when the semiconductor chip or the electrode terminal as the mounting parts 6 and 6 is inserted and brazed and joined, it is confirmed that the same effect as the above-described embodiment can be obtained.

The top view which shows one Example of the ceramic circuit board based on this invention. Sectional drawing of the ceramic circuit board shown in FIG. The top view which shows the other Example of the ceramic circuit board based on this invention. Sectional drawing which shows the structural example of the conventional ceramic circuit board.

Explanation of symbols

1, 1a, 1b Ceramic circuit board 2 Ceramic board 3 Brazing material layer 4 Metal circuit board (metal circuit layer, copper circuit board)
5 Back metal plate 6 Mounting parts (semiconductor chip, electrode terminal, resistor, capacitor, thermistor, etc.)
7, 7a Concave part D Depth depth W Clearance between the concave part side surface and the mounted component side

Claims (4)

In the ceramic circuit board in which the metal circuit board is integrally joined to at least one surface of the ceramic substrate and the mounting component is joined to the metal circuit board, a recess is formed on the surface of the metal circuit board. while the bottom surface of the mounting part is fitted recess Ru joint surfaces der mounting component, with the depth of the recess is 0.05mm or more, and a side surface of the recess, side surfaces of the mounting fixed mounting component in the recess A ceramic circuit board , wherein the metal circuit board has a thickness of 0.1 to 0.3 mm . 2. The ceramic circuit board according to claim 1, wherein the recess is formed by die press molding . 2. The ceramic circuit board according to claim 1, wherein the recess is formed by an etching process . 2. The ceramic circuit board according to claim 1, wherein the ceramic substrate is an AlN substrate or Si. ₃ N ₄ A ceramic circuit board characterized by being a substrate.

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