JP6020256B2 - Manufacturing method of power module substrate with heat sink - Google Patents

Description

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

  Conventionally, a power module substrate is known in which a circuit layer is bonded to one surface of a ceramic substrate in a laminated state and a heat dissipation layer is bonded to the other surface in a stacked state. An electronic component such as a semiconductor chip (power element) is soldered and a heat sink is joined to the heat dissipation layer to provide a power module.

In such a power module substrate, as a method of joining a ceramic layer with a metal layer serving as a circuit layer or a heat dissipation layer in a laminated state, for example, in Patent Document 1, an Al—Si based or Al—Ge based brazing material is interposed. Then, the ceramic substrate and the aluminum metal layer are overlaid, and the laminate is pressurized and heated to melt the brazing material and join the ceramic substrate and the aluminum metal layer.
As a substrate for this type of power module, when the thickness and material of the metal layers on the both sides of the ceramic substrate are different, there is a problem that warping occurs due to thermal stress through a heat treatment for brazing.
As a method for eliminating this warp, the applicant described in Patent Document 2 that a plurality of ceramic substrates and metal layers are alternately stacked and joined, and then the metal layers are arranged in the plane direction in the middle of the thickness direction. The manufacturing method of the board | substrate for power modules by which the metal layer of predetermined thickness was formed on both surfaces of the ceramic substrate by the cutting | disconnection along, and the curvature was suppressed is proposed.

JP 2008-311296 A JP 2012-109457 A

  By the way, as described above, in the power module substrate, a heat sink is bonded to the heat radiation layer on one side of the ceramic substrate in order to dissipate heat from the electronic components in use. In this case, since heat treatment is performed, warping is likely to occur. This warp has a shape with a convex circuit layer side, which may impair the solderability of electronic components mounted thereon.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method capable of solving the problem of warpage and manufacturing a highly reliable power module substrate with a heat sink.

  The method for producing a power module substrate with a heat sink according to the present invention includes a circuit layer on one surface of a ceramic substrate, a heat dissipation layer bonded to the other surface, and a heat module with a heat sink bonded to the heat dissipation layer. A method for manufacturing a circuit board, wherein the ceramic substrate, the heat dissipation layer, and the heat sink are arranged in this order on both side surfaces of a metal plate having a thickness that is at least twice that of the circuit layer and made of the same material as the circuit layer. A bonding step of forming a laminated and bonded bonded body, and a cutting step of cutting the metal plate in the bonded body obtained in the bonding step along the surface direction at a midway position in the thickness direction. And

According to the present invention, in the joining process, the ceramic substrate, the heat radiation layer, and the heat sink are symmetrically arranged and laminated on both sides of the metal plate as a center, and the laminate is heated and joined. The stretch is equal on both sides of the metal plate. In addition, since the relatively hard heat sink is arranged on the outermost side, the overall rigidity is governed by this heat sink, and it becomes difficult to warp.
And after joining, it bisects from the middle position of the thickness direction of a center metal plate, and two sets of power module substrates with a heat sink are manufactured.
Since the warpage of the power module substrate with a heat sink is suppressed, the planar accuracy of the circuit layer is high, the semiconductor element mounting operation can be facilitated, and the bonding reliability can be improved.
The heat sink is a flat plate, one having a large number of fins on one side, or a top plate of a cooler as long as it has a bonding surface with a heat dissipation layer on one surface, and is combined with other members. Therefore, the shape of the water-cooled or air-cooled cooler is not limited.

  In the method for manufacturing a power module substrate with a heat sink according to the present invention, the circuit layer is made of copper, the heat dissipation layer is made of aluminum, and the bonding step includes placing the ceramic substrates one by one on both side surfaces of the metal plate. A first joining step for joining the metal plate and the ceramic substrate by heating in a laminated state, and laminating the heat dissipation layer on the outer surface of the ceramic substrate joined to the metal plate by the first joining step. A second bonding step in which the heat dissipation layer is bonded to the ceramic substrate by heating in a heated state, and a state in which the heat sink is laminated on the outer surface of the heat dissipation layer bonded to the ceramic substrate in the second bonding step. A third joining step for joining the heat dissipation layer and the heat sink by heating at It can be a way.

In any of the joining steps from the first joining step to the third joining step, the metal plate is symmetrically laminated and the laminated body is heated and joined. Therefore, the power with heat sink obtained by cutting the metal plate The module substrate is capable of suppressing warpage despite the fact that metal layers of different materials are provided on both sides of the ceramic substrate, ensuring high bonding reliability to electronic components with a copper circuit layer, and aluminum Even when used in a heat cycle environment due to the heat dissipation layer, cracking of the ceramic substrate, peeling of the joints, and the like are unlikely to occur, and good quality can be maintained.
In this case, when the metal plate has a thickness of 2 mm or more and 8 mm or less and the heat dissipation layer has a thickness of 0.5 mm or more and 2 mm or less, the power with a heat sink by the copper circuit layer and the aluminum heat dissipation layer Warpage can be effectively suppressed in the module substrate.

In the method for manufacturing a power module substrate with a heat sink according to the present invention, the heat sink may be a JIS 7000 series aluminum alloy.
Aluminum alloys in the JIS 7000 range have high yield strength and can suppress warpage to a smaller extent.

  According to the method for manufacturing a power module substrate with a heat sink of the present invention, warpage due to heat at the time of joining can be suppressed, so that a highly reliable power module substrate with a heat sink can be manufactured.

It is sectional drawing which showed typically the process of joining a ceramic substrate to both surfaces of a metal plate in one Embodiment of the manufacturing method of the board | substrate for power modules with a heat sink of this invention. It is sectional drawing which showed typically the process of joining a thermal radiation layer to the outer surface of both ceramic substrates after the process shown in FIG. It is sectional drawing which showed typically the process of joining a heat sink to the outer surface of both heat radiating layers after the process shown in FIG. It is sectional drawing which showed typically the process of cut | disconnecting the center part of the thickness direction of a metal plate after the process shown in FIG. It is sectional drawing of the board | substrate for power modules with a heat sink obtained by the method of one Embodiment. It is sectional drawing which showed typically the process of joining the heat sink which has a pin-shaped fin in the method of other embodiment of this invention.

Hereinafter, the manufacturing method of the board | substrate for power modules with a heat sink which concerns on embodiment of this invention is demonstrated.
First, a power module substrate with a heat sink manufactured by the manufacturing method of one embodiment will be described. As shown in FIG. 5, the power module substrate with a heat sink 10 includes a ceramic substrate 20 and one of the ceramic substrates 20. A circuit layer 30 bonded to the surface of the ceramic substrate 20, a heat dissipation layer 40 bonded to the other surface of the ceramic substrate 20, and a heat sink 50 bonded to the surface of the heat dissipation layer 40 opposite to the ceramic substrate 20. . In this case, the heat dissipation layer 40 is formed in a rectangular flat plate shape, but the circuit layer 30 is formed in a desired circuit pattern by etching or the like.

  Then, as shown by a two-dot chain line in FIG. 5, an electronic component 101 such as a semiconductor chip is joined to the circuit board 30 by a solder layer 102 on the power module substrate 10 with a heat sink. The power module is configured by connecting the layer 40 with a bonding wire (not shown). Further, the whole is sealed with a mold resin (not shown) as necessary. The solder layer 102 is formed of solder such as Sn—Cu, Sn—Ag—Cu, Zn—Al, or Pb—Sn.

The ceramic substrate 20 is formed in a rectangular shape using, for example, a nitride ceramic such as AlN (aluminum nitride) or Si ₃ N ₄ (silicon nitride) or an oxide ceramic such as Al ₂ O ₃ (alumina) as a base material. ing. The thickness of the ceramic substrate 20 is 0.3 mm to 1.0 mm.
The circuit layer 30 is formed of pure copper such as oxygen-free copper or tough pitch copper, or a copper alloy (simply referred to as copper in the present invention), and is etched by stamping the plate material with a press or bonding the plate material to the ceramic substrate 20. Thus, a desired circuit pattern is formed. The thickness of the circuit layer 30 is 1 mm to 4 mm.
The heat radiation layer 40 is formed of pure aluminum or aluminum alloy having a purity of 99.90% or more (in the present invention, simply referred to as aluminum), has a thickness of 0.5 mm to 2 mm, and is generally a rectangular flat plate smaller than the ceramic substrate 10. Formed.
The heat sink 50 is formed to a thickness of 3 mm to 5 mm by an aluminum alloy such as JIS 6000 series and 7000 series which is harder than the circuit layer 30 and the heat dissipation layer 40. In the illustrated example, it is formed in a flat plate shape.

Next, a manufacturing method of the power module substrate 10 with a heat sink configured as described above will be described.
First, for the circuit layer 30, a metal plate 31 having the same thickness as that of the same material is prepared. Specifically, the metal plate 31 has a thickness obtained by adding a cutting allowance described later to two circuit layers 30. The ceramic substrate 20, the heat radiation layer 40, and the heat sink 50 are prepared with product thickness. The metal plate 31, the ceramic substrate 20, the heat radiation layer 40, and the heat sink 50 are joined in three steps as follows.

(First joining process)
As shown in FIG. 1, the ceramic substrates 20 are laminated on both surfaces of the metal plate 31 via a bonding material 61. In the example shown in FIG. 1, the bonding material 61 is composed of a paste, and is applied to one side of the ceramic substrate 20 by screen printing and dried. For joining the metal plate 31 and the ceramic substrate 20, an active metal brazing method using an active brazing material such as Ag—Ti or Ag—Cu—Ti as the joining material 61 is applied. A bonding material (active brazing material) 61 is disposed between the metal plate 31 and the ceramic substrate 20, and these are sandwiched between a pair of contact plates 71 and heated in a vacuum while being pressed in the stacking direction as indicated by arrows. As a result, Ti, which is an active metal in the brazing material, reacts with N, O, or C contained in the ceramic substrate 20 to form nitrides, oxides, carbides, and the like on the surface of the ceramic substrate 20, and Ag. Forms a molten metal layer by eutectic reaction of the metal plate 31 with Cu, and is cooled and solidified to bond the copper metal plate 31 and the ceramic substrate 20 via the Ag-Cu eutectic layer.

Specifically, a joining material 61 containing Ag, Ti, a dispersant, a plasticizer, and a reducing agent is used, and a laminate of the metal plate 31, the joining material 61, and the ceramic substrate 20 is 10 N / mm ² (1 kgf) in the laminating direction. / Mm ² ) to 334 N / mm ² (35 kgf / mm ² ). The backing plate 71 is made of carbon so that it does not adhere to the laminate during this joining step. And in this pressurization state, the whole is inserted into a vacuum heating furnace, heated at 790 ° C. to 850 ° C. and cooled.
The brazing material may be used in the form of a foil in addition to the paste.
By this first bonding step, a first bonded body 71 in which the ceramic substrate 20 is bonded to both surfaces of the metal plate 31 is manufactured.

(Second joining process)
As shown in FIG. 2, the heat dissipation layer 40 is laminated on both sides of the first bonded body 81, that is, on the outer surface of the ceramic substrate 20 via a bonding material 62. As the bonding material 62 in this case, a brazing material such as Al—Si, Al—Ge, Al—Cu, Al—Mg, or Al—Mn is used, but contains Si which is a melting point lowering element. The Al—Si brazing material is suitable and is used in the form of a foil having a thickness of 5 μm to 50 μm. As a bonding method, a bonding material (brazing material foil) 62 is interposed between the heat dissipation layer 40 and the ceramic substrate 20 and laminated, or the bonding material 62 is temporarily attached to an aluminum plate for forming the heat dissipation layer 40. The heat dissipation layer 40 temporarily bonded with the bonding material 62 is formed by punching with a press, and the bonding material 62 side of the heat dissipation layer 40 is stacked on the ceramic substrate 20 and stacked. be able to.

Then, the brazing material is heated in a vacuum heating furnace in a state where the laminated body in which the heat radiation layer 40 is laminated through the bonding material 62 is pressurized in the laminating direction indicated by the arrow through the carbon backing plate 71. The aluminum layer 62 and a part of the aluminum layer 40 are melted and cooled and solidified to bond the heat dissipation layer 40 to the ceramic substrate 20. Pressure is ^{10N / mm 2 (1kgf / mm} 2) ~334N / mm 2 (35kgf / mm 2), the heating temperature is set to 550 ° C. to 650 ° C.. The pressing plate made of carbon is used during the pressurization, as in the first joining step.
By this second bonding step, the ceramic substrate 20 is bonded to both surfaces of the metal plate 31, and the second bonded body 82 in which the heat dissipation layer 40 is bonded to the outer surface of the ceramic substrate 20 is obtained.

(Third joining step)
As shown in FIG. 3, heat sinks 50 are laminated on both sides of the second bonded body 82, that is, on the outer surface of the heat dissipation layer 40 via bonding materials 63. In this case, the bonding material 63 can be the same type of brazing material as that used in the second bonding step, and an Al—Si based brazing material is particularly suitable and is used in the form of a foil having a thickness of 5 μm to 50 μm. .
Then, the brazing material 63 and the heat dissipation layer are heated by heating the laminated body in which the heat sink 50 is laminated through the bonding material 63 in a vacuum heating furnace in a state of being pressed in the laminating direction indicated by the arrow through the contact plate 71. The heat sink 50 is joined to the heat dissipation layer 40 by melting a part of aluminum of the heat sink 40 and the heat sink 50 and solidifying by cooling. Pressure is ^{10N / mm 2 (1kgf / mm} 2) ~334N / mm 2 (35kgf / mm 2), the heating temperature is set to 550 ° C. to 650 ° C..
In this second bonding step, as shown in FIG. 4, the ceramic substrate 20 is bonded to both surfaces of the metal plate 31, the heat dissipation layer 40 is bonded to the outer surface of the ceramic substrate 20, and the heat sink 50 is bonded to the outer surface of the heat dissipation layer 40. A third joined body 83 is obtained.

(Cutting process)
The center position in the thickness direction of the metal plate 31 disposed in the center of the third joined body 83 is cut in the surface direction as indicated by a one-dot chain line C in FIG. In order to cut with high precision and a small cutting margin, it is preferable to apply cutting means used for silicon wafers such as a dicing saw and a wire saw. For example, the thickness of the cutting allowance of a silicon wafer cutting dicing blade is generally about 100 μm.
By this cutting step, the metal plate 31 is separated at the center position in the thickness direction to form two circuit layers 30, and two sets of power module substrates 10 with heat sinks having the circuit layers 30 are manufactured.

  The power module substrate 10 with a heat sink manufactured in this way has the ceramic substrate 20, the heat dissipation layer 40, the heat sink on both sides with the metal plate 31 as the center in both the first joining step, the second joining step, and the third joining step. Since 50 are joined in a symmetrically arranged state, thermal expansion and contraction generated on both surfaces of the metal plate 31 is equal, and warpage due to the influence of heat can be suppressed. In the final third joining step, since the hard heat sink 50 is disposed on both sides, the overall rigidity is increased, the bending is less likely, and the warpage is less likely to occur.

  In addition, after cutting the metal plate 31 to obtain the power module substrate 10 with the heat sink, the circuit layer 30 is deburred using, for example, a polishing brush, and then the surface of the circuit layer 30 is processed by surface treatment. A process of removing distortion and smoothing may be performed. As the surface treatment, for example, alkali etching immersed in a 5% aqueous solution of sodium hydroxide for 80 seconds to 160 seconds, or acid treatment immersed in a 30% aqueous solution of nitric acid for 20 seconds to 40 seconds can be applied.

As described above, according to the method for manufacturing a power module substrate with a heat sink, the members arranged symmetrically around the metal plate 31 are joined in each joining step, and thus warpage occurs due to the difference in thermal expansion and contraction between the members. By cutting the metal plate 31 last, a highly reliable power module substrate 10 with a heat sink in which warpage is suppressed can be manufactured.
In this case, by appropriately setting the thickness and cutting position of the metal plate 31, it is also possible to manufacture a power module substrate with a heat sink in which the circuit layer and the heat dissipation layer have different thicknesses. In the process, a symmetrical joined body is formed on both sides of the metal plate, so that a power module substrate with a heat sink with less warpage can be manufactured.

FIG. 6 shows another embodiment of the present invention. The same elements as those in the above-described embodiment are denoted by the same reference numerals to simplify the description.
The first joined body and the second joined body have the same configuration as that of the embodiment, and are formed in the same manner as described above. FIG. 6 shows a process of joining the heat sink 55 to the second joined body 82. In this heat sink 55, a plurality of mutually parallel pin-shaped fins 57 are integrally formed on one surface of the flat plate portion 56, and the surface opposite to the side where these fins 57 are formed is joined to the heat dissipation layer 40. Is done.
For this reason, as shown by a two-dot chain line, the backing plate 75 used when joining the heat sink 55 to the heat radiation layer 40 is a plurality of fins 57 into which the fins 57 can be inserted so as to avoid the fins 57 and press the flat plate portion 56. The hole 76 is formed.
As described above, the heat sink has a flat plate shape as in the embodiment, has a pin-shaped fin 56 as shown in FIG. 6, has a fin other than the pin shape, or is combined with other members. Various shapes such as those for forming a flow path for air cooling or water cooling can be applied, and it is only necessary to have a surface for joining to the heat dissipation layer 40.

As an example, a 31 mm square x 2 mm thick copper circuit layer, a 33 mm square x 0.635 mm aluminum nitride ceramic substrate, a 31 mm square x 1.6 mm thick aluminum heat dissipation layer, a 50 mm square x 3 mm thick The warp in the case of manufacturing a power module substrate with a heat sink having a flat heat sink made of JIS standard A6063 aluminum alloy was obtained by simulation. After using a metal plate having a thickness of 4.5 mm as a cutting allowance of 0.5 mm for two copper circuit layers, the metal plate is bonded to the copper circuit layer in three steps as described in the previous embodiment. Cutting was performed so that the thickness was 2 mm.
As a comparative example, except for the metal plate, the same ceramic substrate, heat dissipation layer, and heat sink as in the example were used. First, a circuit layer and a ceramic substrate having a thickness of 2 mm were laminated and bonded one by one, and then the opposite of the ceramic substrate. Warpage was also obtained for a power module substrate with a heat sink manufactured by a conventional bonding method in which a heat dissipation layer was bonded to the surface and a heat sink was bonded to the heat dissipation layer.
As a result, the warpage of the lower surface of the heat sink was 750 μm in the conventional example, but was suppressed to 250 μm in the present example.

In order to investigate the influence of the difference in the thickness of the metal plate, the heat dissipation layer, the ceramic substrate and the heat sink have the same dimensions as the previous embodiment, and the planar shape of the circuit layer is the same as the previous embodiment. There are four types of thicknesses: 1 mm (metal plate thickness 2 mm), 2 mm (metal plate thickness 4 mm), 3 mm (metal plate thickness 6 mm), 4 mm (metal plate thickness 8 mm). After joining in the same manner, the warp was obtained by cutting at the center of the thickness of the metal plate.
The results are shown in Table 1.

  As shown in Table 1, when the thickness of the circuit layer is 1 mm, all the warpages are 250 μm except for the warpage of 270 μm.

In addition, the circuit layer, the ceramic substrate, and the heat sink have the same dimensions as the previous examples, and the thickness of the heat dissipation layer is changed to 0.5 mm, 1.0 mm, 1.6 mm, and 2.0 mm. We investigated the effect of warpage on warpage. In all cases, the planar shape was the same as in the previous example.
The results are shown in Table 2.

As shown in Table 2, although the warpage was slightly different depending on the thickness of the heat dissipation layer, it can be said that it does not greatly affect the warp in practice.

The circuit layer, the ceramic substrate, and the heat dissipation layer used had the same planar shape and dimensions as the previous examples, and the warp was obtained by changing the heat sink to a JIS standard A7001 aluminum alloy.
As a result, the warpage was reduced to 220 μm. The proof stress of A6063 aluminum alloy is 50 MPa, whereas the proof stress of A7001 aluminum alloy is 150 MPa, and it can be seen that the effect of reducing warpage is great by using this 7000 series aluminum alloy with high proof strength.

In addition, this invention is not limited to the thing of the structure of the said embodiment, In a detailed structure, it is possible to add a various change in the range which does not deviate from the meaning of this invention.
For example, although the circuit layer is made of copper, it can also be applied to an aluminum circuit layer. In that case, since 99.90% or more of pure aluminum is used as the circuit layer, the circuit layer and the heat dissipation layer are made of the same kind of material. Therefore, an aluminum metal plate having a thickness more than twice that of the circuit layer, ceramics It is possible to bond the substrate and the heat dissipation layer at once through the bonding material made of the brazing material such as Al-Si, Al-Ge, Al-Cu, Al-Mg, or Al-Mn. is there.
For heat sinks, when using JIS 6000 or 7000 series aluminum alloys, the melting point is lower than that of pure aluminum, so it is better to join the circuit layer and heat dissipation layer in a separate process. When the layers, the heat dissipation layer, and the heat sink are made of similar materials, the circuit layer, the heat dissipation layer, and the heat sink can be joined at once by a brazing material.
Further, in the embodiment, the case where two sets of power module substrates with heat sinks are manufactured has been described. However, by multiply stacking two sets each, four sets or even six sets or more sets of power module substrates with heat sinks are formed. You may make it manufacture. In that case, it is good to laminate | stack in the state which interposed the contact plate which consists of carbon between each group, and to pressurize and heat.

10 Power Module Substrate with Heat Sink 20 Ceramic Substrate 30 Circuit Layer 31 Metal Plate 40 Heat Dissipation Layers 50 and 55 Heat Sink 56 Pin-shaped Fins 61 to 63 Bonding Material 71 Patch Plate 75 Patch Plate 76 Hole 81 First Bonded Body 82 Second Bond Body 83 Third bonded body 101 Electronic component 102 Solder layer

Claims (4)

A method for producing a power module substrate with a heat sink, wherein a circuit layer is bonded to one surface of a ceramic substrate, a heat dissipation layer is bonded to the other surface, and a heat sink is bonded to the heat dissipation layer,
The ceramic substrate, the heat dissipation layer, and the heat sink are respectively laminated in this order on both side surfaces of a metal plate having a thickness more than twice that of the circuit layer and made of the same material as the circuit layer to form a joined body. A joining process to perform,
And a cutting step of cutting the metal plate in the joined body obtained in the joining step along the plane direction at a midway position in the thickness direction. The circuit layer is made of copper, and the heat dissipation layer is made of aluminum.
The joining step includes a first joining step of joining the metal plate and the ceramic substrate by heating in a state where the ceramic substrates are laminated one by one on both side surfaces of the metal plate, and the first joining step A second bonding step of bonding the heat dissipation layer to the ceramic substrate by heating in a state where the heat dissipation layer is laminated on the outer surface of the ceramic substrate bonded to the metal plate; and the ceramic in the second bonding step. 2. A third joining step for joining the heat-radiating layer and the heat sink by heating in a state where the heat sink is laminated on the outer surface of the heat-radiating layer joined to the substrate. Of manufacturing a power module substrate with a heat sink.   The method of manufacturing a power module substrate with a heat sink according to claim 2, wherein the metal plate has a thickness of 2 mm or more and 8 mm or less, and the heat dissipation layer has a thickness of 0.5 mm or more and 2 mm or less.   The said heat sink is a JIS7000 series aluminum alloy, The manufacturing method of the board | substrate for power modules with a heat sink as described in any one of Claims 1-3 characterized by the above-mentioned.

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