JP5045613B2 - Power module substrate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a power module substrate used in a semiconductor device that controls a large current and a high voltage, and a method for manufacturing the same.

In general, a power module for supplying power among semiconductor elements has a relatively high calorific value, and as a power module substrate, for example, as shown in Patent Document 1 and Patent Document 2, metal is formed on both surfaces of a ceramic substrate. A plate in which a circuit having a desired pattern is formed on a metal plate on the surface side by etching is used.
In this case, in the power module substrate described in Patent Document 1, an aluminum plate is bonded to a ceramic substrate made of AlN, Al ₂ O ₃ , Si ₃ N ₄ , SiC, or the like via an Al—Si based brazing material. On the other hand, in the power module substrate described in Patent Document 2, a copper plate is bonded to an AlN ceramic substrate by a brazing material of Ti—Ag—Cu. In addition, each power module substrate is formed so that the metal plate on the back side is thicker than the metal plate (surface side metal plate) on which the circuit pattern is formed. Warping that may occur with the release of stress is prevented.

JP 2004-356502 A JP-A-5-170564

  By the way, when manufacturing such a power module substrate, a metal plate is brazed and bonded to both surfaces of the ceramic substrate before forming a circuit pattern by etching. This brazing step is a process in which both metal plates are brought into contact with both surfaces of the ceramic substrate, for example, with a brazing material foil interposed therebetween, and heated in a pressurized state. For this reason, if the plate thickness of the metal plates on both sides of the ceramic substrate is different as in the power module substrates described in both patent documents, warping is prevented in the final product, but in the intermediate after brazing and joining Warpage with a convex surface is likely to occur.

  In this case, when a circuit pattern is formed to obtain a final product, an etching process is performed after screen-printing a resist film in a desired pattern on a metal plate on the front side. At this time, if the intermediate body after the previous brazing process is warped, there is a problem that the resist film is not printed accurately. Further, when this resist film is screen-printed, the ceramic substrate is pressed with a squeegee so as to push back the warp, so that there is a possibility that cracking or the like may occur.

  The present invention has been made in view of such circumstances, such as a state in which there is no warp not only when the final product is printed but also when a resist film is printed, or a slight warp is caused as necessary. An object of the present invention is to provide a power module substrate in which warpage is controlled and a method for manufacturing the same.

The power module substrate according to the present invention, together with the metal plate on both surfaces of the ceramic substrate is brazed, a power module substrate on which a circuit pattern is formed on the metal plate of the surface side, the surface The metal plate on the side is made of pure aluminum or an aluminum alloy, the metal plate on the back side is made of pure aluminum having a purity of 99.0% by mass or more, and the metal plate on the front side and the metal plate on the back side are almost the same thickness is set to only the surface of the front Symbol surface side of the metal plate of the two metal plates, Ni-P electroless plating film for warpage thickness control 4μm~6μm in which the internal stress and the compression stress is formed It is characterized by that.

That is, by forming a warp controlling plating film, a compressive stress can be applied to the surface on which the plating film is formed. As a result, if warping occurs so that the back side is concave in the stage before forming this plating film, this warpage control plating film is formed on the surface side to correct the warpage. Can be made flat. In addition, when the flat state without warping is formed before the plating film is formed, a warp control plating film may be formed to cause the back surface to be slightly convex. I can .

In the power module substrate of this, since the front and back surfaces of the metal plate is substantially the same thickness, no warpage at the stage after the joining brazing. Therefore, resist printing can be performed in a flat state. However, after the etching process, the stress is released by the amount deleted by the pattern formation, so some warping occurs, but the warping is corrected and the final product is made flat by the subsequent warp control plating film formation. can do.

The power module substrate according to the present invention may have a configuration in which warpage occurs so that the back surface side is convex.
When assembling this power module substrate with a heat sink or the like coming into contact with the back surface, the back surface is pressed so as to return the warp while contacting the convex surface on the back surface. Can be assembled closely without forming.

In the method for manufacturing a power module substrate according to the present invention, a metal plate having substantially the same thickness is brazed to both the front and back surfaces of the ceramic substrate, and a circuit pattern is formed on the metal plate on the surface side. A power module substrate manufacturing method comprising the steps of brazing a metal plate made of pure aluminum or an aluminum alloy on the surface of the ceramic substrate and a pure aluminum metal plate having a purity of 99.0% by mass or more on the back surface. after forming a circuit pattern on the metal plate of the surface side, before SL only on the surface of the surface side of the metal plate, Ni for warpage thickness control 4μm~6μm in which the internal stress and the compression stress of the two metal plates A -P electroless plating film is formed.

  According to the present invention, when the warp control plating film is formed, the warp control to the front surface side occurs when the back surface side is warped in the stage before the plating film is formed. It can be flattened by forming a plating film, and when it is in a flat state without warping before the plating film is formed, it can cause warping so that the back side is slightly convex. The desired shape can be obtained. For this reason, it is possible not only to flatten the final product, but also to have a state without warping during printing of the resist film, so that productivity can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the overall configuration of a power module using the power module substrate according to the first embodiment of the present invention. A power module 1 shown in FIG. 1 includes a power module substrate 3 having a ceramic substrate 2, an electronic component 4 such as a semiconductor chip mounted on the surface of the power module substrate 3, and a power module substrate 3. It is comprised from the heat sink 5 joined to the back surface.

In the power module substrate 3, a circuit layer metal plate 6 for mounting the electronic component 4 is laminated on the front surface side of the ceramic substrate 2, and a heat dissipation layer metal plate 7 is laminated on the back surface side of the ceramic substrate 2. The heat sink 5 is attached to the metal plate 7 for heat dissipation layer.
Further, the ceramic substrate 2 is formed using, for example, a nitride ceramic such as AlN (aluminum nitride), Si ₃ N ₄ (silicon nitride), or an oxide ceramic such as Al ₂ O ₃ (alumina) as a base material. Yes. The circuit layer metal plate 6 is made of pure aluminum or an aluminum alloy, and the heat dissipation layer metal plate 7 is made of pure aluminum having a purity of 99.0 wt% or more. Moreover, in this 1st Embodiment, these both metal plates 6 and 7 are formed in the same thickness.

The ceramic substrate 2, the circuit layer metal plate 6, and the heat dissipation layer metal plate 7 are joined to each other by brazing. As the brazing material, Al-Si, Al-Ge, Al- Cu-based, Al-Mg-based, Al-Mn-based, or the like is used.
Of the two metal plates 6, 7, the circuit layer metal plate 6 is etched to form a desired circuit pattern. Further, the metal plate 6 for circuit layer has a plating film 8 formed on the surface thereof. Nickel is suitable as a material for the plating film, and Ni-1 to 13 wt% P and Ni-0.5 wt% B are used when electroless plating is used, and pure Ni is used when electrolytic plating is used.

And the electronic component 4 is joined on the metal plate 6 for circuit layers by solder materials, such as Sn-Ag-Cu type, Zn-Al type, or Pb-Sn type. Reference numeral 9 in the drawing indicates the solder joint layer. The electronic component 4 and the terminal portion of the circuit layer metal plate 6 are connected by a bonding wire (not shown) made of aluminum.
On the other hand, the heat sink 5 is formed by extrusion molding of an aluminum alloy, and is formed with a number of flow paths 10 for circulating cooling water along the length direction thereof. Joined by soldering, bolts, etc.

Next, a method for manufacturing the power module substrate 3 used in the power module 1 having such a configuration will be described.
First, a ceramic substrate 2 is manufactured, and a circuit layer metal plate 6 and a heat dissipation layer metal plate 7 having the same area and the same thickness are laminated on both surfaces of the ceramic substrate 2 with a brazing material foil (not shown) interposed therebetween. . Then, these laminates are heated in an inert gas atmosphere, a reducing gas atmosphere or a vacuum atmosphere in a state of being pressurized in the lamination direction, and the brazing material foil is melted, whereby a circuit layer as shown in FIG. The metal plate 6 and the heat dissipation layer metal plate 7 are joined to the ceramic substrate 2 respectively.
In the state in which the two metal plates 6 and 7 are joined by this brazing, since both the metal plates 6 and 7 have the same thickness (T ₁ = T ₂ ), no warp occurs.

Next, a resist film R having a desired pattern is printed on the circuit layer metal plate 6 as indicated by a chain line in FIG. At this time, since the surface of the circuit layer metal plate 6 is flat, the resist film R can be easily printed and is not deformed by pressing with a squeegee during screen printing.
After printing the resist film R, the circuit layer metal plate 6 is etched to form a circuit pattern. After the circuit pattern is formed, the area of the circuit layer metal plate 6 is reduced by the etching process, and the stress of the reduced part is released. Therefore, as shown in FIG. Warpage occurs so that the circuit layer metal plate 6 side, that is, the surface side is convex.

  Next, the plating film 8 is formed on the surface of the circuit layer metal plate 6 by electroless plating. Since the internal stress of the plating film 8 is a compressive stress, as shown in FIG. 1, by applying a compressive stress to the surface side of the power module substrate 3 so as to return the warpage shown in FIG. The power module substrate 3 is made flat.

In the power module substrate 3 manufactured in this way, the metal plates 6 and 7 on both sides of the ceramic substrate 2 have the same thickness, and therefore, after the metal plates 6 and 7 are brazed and joined, FIG. As shown in FIG. 2, the flat state can be obtained, and the subsequent printing operation of the resist film R can be easily and accurately performed. Moreover, although some curvature arises by an etching process, a final product can be finished flat by a subsequent plating process.
That is, in the case of the first embodiment, the plating film 8 formed on the surface of the circuit layer metal plate 6 is used as a warp control plating film. The thickness of the plating film 8 is, for example, 4 to 6 μm in the case of a Ni—P electroless plating film. The compressive stress in the plating film can be measured using, for example, a stress measurement method using X-ray diffraction.

  The power module substrate 3 is soldered with the electronic component 4 as described above. However, when the power module substrate is a conventional power module substrate, the warp generated in the previous stage is promoted by heat during soldering. And the warping is even greater. In the case of the power module substrate 3 of the present embodiment, it is in a flat state without warping, and even when heated during soldering, the flat state can be maintained and the bonding reliability of the electronic component 4 is improved. Can do.

FIG. 3 shows a second embodiment of the present invention. In the power module substrate 21 of the second embodiment, as shown in the final product in FIG. 3A, metal plates 6 and 7 having the same thickness are brazed and joined to both surfaces of the ceramic substrate 2. Is the same as that of the first embodiment, but the plating films 22 and 23 are formed on both of the metal plates 6 and 7 on both sides of the ceramic substrate 2, and these plating films 22 and 23 are the metal plates for circuit layers. 6, the thickness t ₁ of the plating film 22 is formed to be thicker than the thickness t ₂ of the plating film 23 of the metal plate 7 for heat dissipation layer.

When the power module substrate 21 is manufactured, the metal plates 6 and 7 having the same thickness are brazed and joined to both surfaces, and the circuit pattern is formed on the circuit layer metal plate 6 on the surface side by etching. The process is the same as the process shown in FIGS. 2A and 2B of the first embodiment. Then, electroless plating films 22A and 23 are formed on these metal plates 6 and 7 by electroless plating as shown in FIG. These electroless plating films 22A and 23 are formed to have the same thickness. Next, the electrolytic plating film 22B is formed on the electroless plating film 22A of the circuit layer metal plate 6 by selectively performing an electrolytic plating process on the circuit layer metal plate 6 on the surface side. Accordingly, the film thickness of the electroplating minute film 22B, FIG plating film 22 thickness t ₁ of it is the heat dissipation layer for the metal plate 7 of the plated film 23 of the circuit layer metal plate 6 as shown in (a) than it is thicker than t _2. Then, the compressive stress on the side of the metal plate for circuit layer 6 becomes larger than that on the side of the metal plate for heat radiation layer by the thickened electroplating film 22B, and the metal plate for circuit layer is similar to the example shown in FIG. The warp generated so that the 6 side is convex is returned and finished to a flat power module substrate 21.

  In the case of the second embodiment, the thick plating film 22 formed on the surface of the circuit layer metal plate 6 or the electroplating film 22B laminated on the electroless plating film 22A is used as the warp control plating film. The In this case, the thicknesses of the plating films 22 and 23 are, for example, a Ni-P electroless plating film, the plating film 23 of the heat dissipation layer metal plate 7 is 1 to 3 μm, and the plating film 22 of the circuit layer metal plate 6. 5 to 9 μm.

  FIG. 4 shows a third embodiment of the present invention. The power module substrate 31 of the third embodiment is also the same as the first and second embodiments in that the metal plates 6 and 7 having the same thickness are brazed to both surfaces of the ceramic substrate 2. Also in the third embodiment, the plating films 32 and 33 are formed on both the metal plates 6 and 7 on both surfaces of the ceramic substrate 2, but the plating film 32 of the circuit layer metal plate 6 radiates heat. The layer metal plate 7 is formed to have a larger area than the plating film 33. For example, when both plating films 32 and 33 are Ni-P electroless plating films having a thickness of 5 μm, the plating of the heat radiation layer metal plate 7 is performed with respect to the total area of the plating film 32 of the circuit layer metal plate 6. The area of the coating 33 is 70%.

That is, similar to the example shown in FIGS. 2A and 2B, the metal plates 6 and 7 are brazed and bonded to both surfaces of the ceramic substrate 2, the circuit pattern is etched, and then the heat radiation layer on the back side. The plating film 32 of the circuit layer metal plate 7 is formed in a larger area than the plating film 33 of the heat dissipation layer metal plate 7 by partially masking the metal plate 7 for application and performing electroless plating treatment on both sides. To do. For this reason, the compressive stress on the circuit layer metal plate 6 side becomes larger than that on the heat dissipation layer metal plate 7 side, and the warp generated in the same manner as in the example shown in FIG. Is returned to a flat power module substrate 31.
In the case of this third embodiment, the plating film 32 having a large area formed on the surface of the circuit layer metal plate 6 is used as a warp control plating film.

  FIG. 5 shows a fourth embodiment of the present invention. The power module substrate 41 of the fourth embodiment has the same member configuration as that of the first embodiment. However, the heat radiation layer on the back side is formed by the compressive stress of the plating film 42 formed on the circuit layer metal plate 6. A slight warp is generated so that the metal plate 7 side is convex. That is, the plating film 42 formed on the surface of the circuit layer metal plate 6 serves as a warp control plating film.

When the power module substrate 41 is attached to the heat sink 5, the convex side is brought into contact with the heat sink 5, and the power module substrate 41 is returned so as to return its warp as shown by an arrow in FIG. While being deformed, the power module substrate 41 is flattened and fixed to the heat sink 5 with screws 43 as shown in FIG. Accordingly, it is possible to prevent the heat radiation layer metal plate 7 of the power module substrate 41 from being pressed into contact with the heat sink 5 and to prevent a gap from being formed between them, and heat is quickly transferred from the power module substrate 41 to the heat sink 5. Therefore, the heat dissipation effect can be enhanced.
In the process of manufacturing the power module substrate 41, the two metal plates 6 and 7 are flat as shown in the example shown in FIG. In the state where the pattern is formed on the circuit layer metal plate 6 as in the example shown, the slight warpage is generated so as to protrude toward the circuit layer metal plate 6 as in the above embodiments. is there.

As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.
For example, the thicknesses of the two metal plates do not necessarily have to be exactly the same as long as the resist film after brazing can be printed in a flat state, and may be the same as each other.
In addition, the plating film is suitable for nickel plating when the soldering of electronic parts is planned in the later process or when corrosion resistance is required, but other cases such as when soldering is not performed. Materials may be used.

It is a longitudinal cross-sectional view which shows the example of whole structure of the power module using the board | substrate for power modules of 1st Embodiment of this invention. The process for manufacturing the power module substrate of FIG. 1 is shown in the order of steps, in which (a) is a longitudinal sectional view showing a state after a metal plate is brazed to both surfaces of a ceramic substrate, and (b) is a circuit layer. It is a longitudinal cross-sectional view which shows the state after forming a pattern in the metal plate for operation. The 2nd Embodiment of this invention is shown, (a) is a longitudinal cross-sectional view which shows the board | substrate for power modules, (b) is a longitudinal cross-sectional view which shows the step in the middle of the manufacture. It is a longitudinal cross-sectional view which shows the board | substrate for power modules of 3rd Embodiment of this invention. The 4th Embodiment of this invention is shown, (a) is a longitudinal cross-sectional view which shows the board | substrate for power modules, (b) is a longitudinal cross-sectional view which shows the state which attached the board | substrate for power modules to the heat sink.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power module 2 Ceramic substrate 3 Power module substrate 4 Electronic component 5 Heat sink 6 Metal plate for circuit layer 7 Metal plate for heat radiation layer Plating film (plating film for warpage control)
9 Solder joint layer 10 Flow path 21 Power module substrate 22 Plating film (Plating film for warpage control)
23 plating film 22A electroless plating film 22B electrolytic plating film 31 power module substrate 32 plating film (plating film for warpage control)
33 Plating coating 41 Power module substrate 42 Plating coating (plating coating for warpage control)
43 Screw R Resist film

Claims (3)

A power module substrate in which a metal plate is brazed and bonded to both the front and back surfaces of a ceramic substrate, and a circuit pattern is formed on the metal plate on the surface side,
The metal plate on the front side is made of pure aluminum or an aluminum alloy, and the metal plate on the back side is made of pure aluminum having a purity of 99.0% by mass or more.
The metal plate on the front side and the metal plate on the back side are set to substantially the same thickness,
Only on the surface of the front Symbol surface side of the metal plate of the two metal plates, and characterized in that warp control Ni-P electroless plating film having a thickness of 4μm~6μm in which the internal stress and the compression stress is formed Power module substrate. The power module substrate according to claim 1, wherein a warp is generated so that the back surface side is convex. A method for producing a power module substrate in which a metal plate having substantially the same thickness is brazed and bonded to both front and back surfaces of a ceramic substrate, and a circuit pattern is formed on the metal plate on the surface side,
A metal plate made of pure aluminum or an aluminum alloy is brazed on the surface of the ceramic substrate, and a pure aluminum metal plate with a purity of 99.0% by mass or more is brazed to form a circuit pattern on the metal plate on the surface side. after, characterized in that only the surface of the front Symbol surface side of the metal plate of the two metal plates to form a Ni-P electroless plating film for warpage thickness control 4μm~6μm in which the internal stress and compressive stress A method for manufacturing a power module substrate.

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