JP2003152141A - Ceramic heat dissipation circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve solder wettability by preventing any solder flow and solder void from being formed upon a printed circuit board and a heat dissipation member being joined with a solder. SOLUTION: A ceramic heat dissipation circuit board is adapted such that it comprises a ceramic insulating board 2 to one side of which there is joined a Cu or Al circuit board 3 on which a semiconductor chip is mounted, and to the other side of which a Cu or Al plate 4 is joined, and a heat dissipation member 6 of an Al-SiC composite having an Al coating film 60 on the surface thereof, and a junction layer 64 is formed on the Al coating film of the heat dissipation member 6, and further the junction layer 64 and the Cu or Al plate 4 of the ceramic insulating substrate are joined with a solder 7. In the ceramic heat dissipation circuit board, the junction layer 64 is formed into a layer chiefly comprising Ni, and average surface roughness (Ra) of the surface 65 along a central line of the same is set to range from 0.2 to 1.5 μm with the thickness thereof set to range from 3 to 15 μm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composite of silicon carbide and aluminum (Al--, which is formed by impregnating a porous body mainly composed of silicon carbide (SiC) with a metal containing aluminum (Al) as a main component. The present invention relates to a ceramic heat dissipation circuit board in which a (SiC composite) and a ceramic insulating board made of silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ) or the like are joined using solder. .

[0002]

2. Description of the Related Art In recent years, in the field of industrial equipment, development of a high power module device for efficiently exchanging and controlling a large power to an optimum power by using a semiconductor switching device has been advanced. For example, high voltage as an inverter for electric vehicles,
There is an insulated gate bipolar transistor (IGBT) module capable of high current operation. The heat generated from the semiconductor chip is also increasing in accordance with such a high power module. The semiconductor chip is vulnerable to heat, and if the heat generation increases, malfunction or destruction of the semiconductor circuit will be caused. Therefore, a heat dissipation member such as a heat sink is provided on the back surface of the circuit board for mounting electronic components such as semiconductor chips, and the heat generated from the semiconductor chips is radiated to the outside via the heat dissipation components to stabilize the operation of the semiconductor circuit. Is being done. As a circuit board for mounting electronic parts, a ceramic insulating substrate such as silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ) is mainly used. A Cu plate or an Al plate is joined to the surface of the insulating substrate via a brazing material to form a circuit board.

As a circuit board of this type, a copper (Cu) circuit board is bonded onto a ceramics insulating board made of aluminum nitride (AlN) having good thermal conductivity, a circuit is formed, and then plating is performed to form a semiconductor. Some have a chip mounted. The AlN substrate and the Cu circuit board are joined to each other by an active metal brazing method in which a brazing material containing an active metal is interposed between the AlN substrate and the Cu substrate to perform heat treatment, or AlN whose surface is oxidized.
DBC (Direct Brazing Copper) that heat-bonds the substrate and Cu circuit board below the melting point of Cu and above the eutectic temperature of Cu-O
There are laws etc. In the board to which this Cu circuit board is joined,
Since the difference in thermal expansion between the circuit and the silicon semiconductor chip die-bonded to the surface of the circuit by solder is large, the solder is likely to crack immediately below the chip due to thermal stress repeatedly applied during the operation of the circuit. Also, Cu circuit board and Al
Since the difference in thermal expansion of the N substrate is large, there are problems that peeling may occur at the joint portion and cracks may occur in AlN.

Instead of this, for example, Japanese Patent Laid-Open No. 10-65
No. 296 discloses a ceramics circuit board in which an Al circuit board is joined to both surfaces of a Si ₃ N ₄ board via an Al—Si brazing material. In the Al circuit board in which the circuit board is replaced with Cu and made of Al, the deformation resistance of Al is smaller than that of Cu, so that the stress acting on the joint between the circuit and AlN can be suppressed to a low level. Further, in the die bonding portion with the silicon semiconductor chip, the plastic deformation of Al causes the expansion amount of the circuit surface to be close to that of AlN, and the stress applied to the solder can be reduced. Therefore, the joint portion between the Al circuit and the AlN substrate is less likely to be peeled off, and the joint reliability is high. Further, since the specific gravity of Al is 2.7 g / cm ^{3 and} is about 1/3 of the specific gravity of Cu which is 8.9 g / cm ³ , there is also an advantage that the weight of the circuit board can be reduced to less than half that of the conventional one. However, on the other hand, the specific resistance of Al is 2.66 × 10 ⁻⁶ Ωcm and the specific resistance of Cu is 1.67.
It is about 1.6 times larger than × 10 ^-6 Ωcm, and cannot withstand high withstand voltage and large current, and there is a problem that the usage range of the electric capacity is limited. For this reason, when it is used in a power module with high withstand voltage and large current, it is necessary to enlarge the volume of the circuit portion, which increases the thickness of the entire circuit board and causes the module to be large. As described above, Cu
Both the plate and the Al plate have merits and demerits, and when used as a circuit board, they are selected according to the application.

On the other hand, as the heat radiating member, there is conventionally one using a material such as copper, molybdenum, or tungsten.
However, the heat dissipation component made of molybdenum or tungsten is expensive, and the specific gravity of the metal is large, so that the weight of the heat dissipation component becomes heavy, which is not preferable. Further, since the heat dissipation member made of copper or copper-molybdenum alloy, copper-tungsten alloy has a large difference in coefficient of thermal expansion from the ceramics insulating substrate, when the heat dissipation member and the ceramics insulating substrate are joined by soldering, Due to the thermal cycle during use, the solder layer is likely to be broken, the heat dissipation path is blocked, and the ceramic insulating substrate is cracked. Therefore, an Al-SiC composite having low thermal expansion and high thermal conductivity, in which SiC is dispersed in Al or Al alloy, has been attracting attention as a heat dissipation member replacing the above conventional material (Japanese Patent Publication No. 7-26174, Kaisho 6
4-83634 etc.). The Al-SiC composite is, for example, a molten metal impregnation obtained by impregnating a porous body (preform) formed of SiC powder or SiC fibers with Al or Al alloy that is heated and melted under pressure or without pressure in a nitrogen atmosphere. There is a composite material made by the method. According to this, the content of SiC can be selected in the range of 20 to 90% by volume and the thermal expansion coefficient can be controlled. In addition, SiC
The porous body has a high degree of freedom in the shape, and has an advantage that a product having a complicated shape can be molded by near net shape molding.

From the above, Si ₃ N ₄ , AlN, Al
A ceramic heat dissipation circuit board is known in which a circuit board in which a Cu plate or an Al plate is joined to a ceramics insulating substrate made of ₂ O ₃ or the like via a brazing material and a heat dissipation member made of an Al-SiC composite are joined by soldering. There is. An example of such a ceramic heat dissipation circuit board is shown in FIG. The ceramic substrate 2 is an insulating substrate made of AlN, Al ₂ O _3, Si ₃ N _4, or the like. Ag is on the upper surface of the ceramics insulating substrate 2.
A Cu circuit board 3 and a Cu board 4 are joined to each other using a —Cu—Ti based brazing material. When Al is used for the circuit board 3, it is bonded to the ceramic insulating substrate 2 by using an Al-Si brazing material. A plurality of semiconductor chips 5 are mounted on the upper surface of the Cu circuit board 3 by solder and wired by wires. On the other hand, the heat dissipation member 6 is made of Al-SiC.
It is made of a composite and has an Al film on its surface. A bonding layer is formed on the Al film to have solder wettability, and the Cu plate 4 is bonded via the solder 7. In addition, a heat sink 8 having, for example, heat radiation fins is fastened with bolts 10 on the lower surface of the heat radiation member 6 with high thermal conductive grease or the like interposed. In such a ceramic circuit board 1, the heat generated from the semiconductor chip 5 or the like causes the Cu circuit board 3, the ceramics insulating substrate 2, the Cu plate 4, the solder 7,
And it is radiated from the surface of the heat sink 8 via the heat dissipation substrate 6.

[0007]

The ceramic heat dissipation circuit board described above has a circuit board 9 (in the present invention, a ceramic circuit board 2 and a Cu circuit board 3 or a Cu board 4 joined together) and Al-. The SiC heat dissipation member 6 and the SiC heat dissipation member 6 are first fired under the respective conditions, and then the plate-shaped low melting point solder 7 is interposed therebetween. Here, normally, the semiconductor chip 5
Since the circuit board 9 and the heat dissipating member 6 are joined together, it is necessary to join the circuit board 9 and the heat dissipating member 6 with the solder 7 having a melting point lower than that of the brazing material used for bonding the semiconductor chip 5. Therefore, there is no choice but to use Pb-Sn-based solder, Pb-Sb-based solder, or the like whose composition is restricted. Then, after that, a soldering process at about 240 ° C. for about 10 minutes is performed in an H ₂ atmosphere so that the circuit board 9 and the heat dissipation member 6 are
We manufacture a ceramics heat dissipation circuit board that integrates and.

Here, the following problems occur. That is, in this soldering process, the solder is the Al-SiC heat dissipation member 6
It may flow to the area around. If this solder flow spreads the solder near the bolt holes at the corners of the heat dissipation member 6, the insulation between the semiconductor chip 5 and the Al—SiC heat dissipation member 6 cannot be maintained, and the function of the IGBT is impaired. In addition, there is a problem that it interferes with the assembly process of the heat sink 8 after soldering. Furthermore, when a solder flow occurs, cavities are easily formed between the layers of the solder, and a so-called solder void occurs. If the rate of occurrence of solder voids exceeds about 3%, there is also a problem that the joint strength and the thermal conductivity are significantly reduced and the function of the IGBT is impaired.

Therefore, the present invention has an object to prevent a solder flow generated when the circuit board and the heat dissipation member are joined by solder, and further, to reduce solder voids and improve solder wettability. It is intended to provide a substrate.

[0010]

According to the present invention, a Cu or Al circuit board on which a semiconductor chip is mounted is provided on one side and a Cu or Al circuit board is provided on the other side.
Alternatively, it is composed of a ceramics insulating substrate to which Al plates are respectively joined, and a heat dissipation member of an Al-SiC composite having an Al film on the surface, and a joining layer is formed on the Al film of the heat dissipation member. Cu of ceramics insulating substrate
Alternatively, in a ceramics heat dissipation circuit board formed by joining an Al plate with solder, the joining layer is a layer containing Ni as a main component, and the center line average surface roughness (Ra) of the surface is 0.2 to 1. It is a ceramic heat dissipation circuit board having a thickness of 5 μm. A more desirable center line average surface roughness (Ra) is 0.
It is 5 to 1.0 μm.

In the ceramic heat dissipation circuit board of the present invention, the thickness of the bonding layer is preferably 3 to 15 μm, more preferably 4 to 8 μm. Further, it is preferable that the bonding layer is composed of two layers, the underlayer is Ni—P plating, and the surface layer is Ni—B plating.

The solder wettability is improved by forming a bonding layer mainly composed of Ni on the Al film formed on the surface of the Al-SiC composite, and further, the center line average surface of the bonding layer is improved. The flow of solder can be prevented by controlling the roughness Ra to 0.2 to 1.5 μm. Regarding the surface roughness of the bonding layer, the center line average surface roughness (Ra) is 0.
It is obtained by adjusting to 2 to 1.5 μm. That is, this is because the surface roughness of the Al film is reflected as it is in the surface roughness of the bonding layer. If the surface roughness exceeds 1.5 μm, solder flow easily occurs. On the other hand, if it is less than 0.2 μm, a sufficient anchor effect cannot be obtained, and a problem occurs in the bonding strength. Further, the formation of the joining layer is necessary for solder joining, and this thickness has a preferable range in order to control the surface roughness and also in terms of joining strength and heat conduction. That is, the thickness of the bonding layer must not exceed 15 μm in order to project the surface roughness of the Al film whose surface properties have been adjusted almost directly onto the surface of the bonding layer. On the other hand, if it is less than 3 μm, the adhesion strength and the film are deteriorated, which causes a problem. Further, the bonding layer preferably has a two-layer structure. By forming Ni-P plating on the underlayer, soldering can be performed on the Al coating, and Ni-
The solder wettability is improved by applying the B plating layer.
As described above, by providing the bonding layer having the predetermined surface roughness and thickness, it is possible to prevent the solder flow and to obtain the adhesion strength.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a ceramic heat dissipation circuit board, and FIG. 2 is a 900 times micrograph of an Al film and a bonding layer, which is a bonding portion between a circuit board of the present invention and a heat dissipation member. FIG. 3 is a diagram schematically showing the periphery of the bonding layer, which is an enlarged view of a part of FIG. 2 (however, the scale is ignored). The basic structure of the ceramic heat dissipation circuit board of the embodiment is the same as that of the circuit board and heat dissipation member of FIG. 1 described above. That is, the circuit board 9 including the ceramics insulating substrate 2 in which the Cu circuit board 3 and the Cu board 4 are joined, and the Al-SiC
The heat dissipation member 6 is made of a composite material, and the circuit board 9 and the heat dissipation member 6 are joined with the solder 7 and then the heat sink 8 is assembled with bolts. In the present invention, the combination of the circuit board and the heat dissipation member is called a ceramics heat dissipation circuit board, but a heat sink may be included. Here, the ceramics insulating substrate 2 of the embodiment is made of AlN, and the Cu circuit board 3 having a thickness of 0.3 mm is formed on the upper surface thereof by Ag-.
Bonded with a Cu-Ti-based brazing material, the bottom surface has a thickness of 0.
A 2 mm Cu plate 4 is joined via the same Ag—Cu—Ti based brazing material.

The heat dissipating member 6 is made of SiC powder in a preform of 37% by volume of pure Al by a molten metal impregnation method.
It is obtained by impregnation, and its surface is about 0.05-0.1 m.
It has an Al film 60 of about m. This Al film 60
A bonding layer 64 is formed on the upper surface as shown in FIGS. The bonding layer 64 of this example is formed by forming a first layer 62 (underlayer) having a thickness of about 4 to 5 μm by Ni—P electroless plating, and forming a second layer 63 by Ni—B electroless plating on the first layer 62 (base layer).
The (surface layer) is formed to have a thickness of about 1 to 2 μm. Ni-P
Layer mainly improves adhesion, and the Ni-B layer mainly improves solder wettability. In the present invention, either one bonding layer or two bonding layers may be used, but the total thickness of these bonding layers 64 is 3 to.
The thickness is controlled to 15 μm, preferably 4 to 8 μm. Furthermore, the center line average surface roughness (Ra) of the surface 65 is 0.2 to 1.5 μm, preferably 0.5 to
It is controlled to be 1.0 μm.

FIG. 3 schematically shows an enlarged cross section near the bonding layer. In this embodiment, the center line average surface roughness (Ra) is shown.
Was about 0.9 μm. 2 and 3, it can be seen that the surface roughness of the bonding layer appears and reflects the surface texture of the surface 61 of the Al film 60 almost as it is along the surface of the bonding layer 64. As a method of adjusting the surface texture, for example, a method of mechanically removing crystal grains by sandblasting, shot blasting, grid blasting, hydroblasting, or the like, or a method of eluting from the grain boundary phase by an acid etching treatment such as hydrochloric acid or sulfuric acid is used. is there. Here, sand blasting is preferable in view of manufacturing efficiency and cost. Therefore, the centerline average surface roughness (Ra) of the surface 61 of the Al coating surface-treated by the sandblasting conditions described below and the centerline average surface roughness (Ra) of the surface 65 of the bonding layer 64 formed on this Al coating film. Was measured with a stylus type surface roughness measuring device over a distance of 2.5 mm. The result is shown in FIG.
Here, (a) is the surface roughness Ra = 0.
987 μm, and (b) after that, the surface roughness Ra of the surface of the bonding layer 64 composed of the first layer 5 μm and the second layer 1 μm.
= 0.943 μm. In this way, the Al film 6
It was confirmed that the center line average surface roughness (Ra) of 0 and the bonding layer 64 were almost the same. Further, similarly, when the thickness of the bonding layer was variously changed and the difference was observed, when the total thickness of the bonding layer 64 exceeds 15 μm, it becomes difficult to reflect the surface texture of the Al film 60 and a solder flow occurs. Was also confirmed. It was also found that if the total thickness is less than 3 μm, there will be a problem in bonding strength.

The sandblasting conditions are as follows:
It was Processing speed: 0.35 seconds / cm^Two Distance with nozzle: 100mm Nozzle ejection pressure: 0.3MPa Jet angle to substrate surface: 45 ° Abrasive: Alumina # 240 Sandblast conditions mentioned above (processing speed, distance from nozzle
Separation, jet pressure of nozzle, jet angle to substrate surface, grinding
The center line of the Al film can be adjusted by adjusting the type and size of the grains.
The average surface roughness and thus the surface roughness of the bonding layer can be controlled.
Center line average surface roughness (Ra) is in the range of 0.2 to 1.5 μm
Control, for example, to reduce the roughness
Of the last conditions, it is better to lower the ejection pressure, but conversely
It can be adjusted by increasing the jet pressure. Ra is
If it exceeds 1.5 μm, solder flow easily occurs. other
On the other hand, if it is less than 0.2 μm, a sufficient anchor effect can be obtained.
However, a problem occurs in the bonding strength.

FIG. 5 shows the center line average surface roughness (R
Characteristic data in which a) is plotted on the horizontal axis and the solder spreading coefficient is plotted on the vertical axis. The solder spread coefficient is the initial solder diameter (Dm
m) and the difference between the solder height (Hmm) when heated and the solder diameter D ((D−H) × 100 / D) are expressed by the spread rate (%) (see JISZ3197 spread test method). ). In the test, a test plate plated with a bonding layer was provided on a hot plate in the atmosphere, and the solder was melted at 250 ° C. and heated for 30 seconds for measurement. From this result, it has a spread coefficient of 75 or more which is a pass judgment in the range of Ra of approximately 0.2 to 1.5 μm. About 0.8 ~
A spread coefficient of 80% or more is shown in the range of 1.5 μm. The higher the spreading coefficient is, the better the solder wettability is. However, the spreading coefficient is preferably 75 to 85% because the solder spreading can be conducted even if the spreading coefficient is excessive. Further, when Ra is 1.5 μm or more, the expansion coefficient is 88 or more, and solder flow is observed.

(Example) Length 187 mm x width 137 mm x
On the Al-SiC heat dissipation member 6 having a thickness of 3 mm, a length of 55.
6 circuit boards 9 of 4 mm x width 57 mm x thickness 0.6 mm
The following tests were conducted on the individually arranged ceramics heat dissipation circuit boards. The center line average surface roughness (Ra) of the surface 61 of the Al coating 60 of the Al-SiC heat dissipation member 6 and the materials and thicknesses of the first plating layer 62 and the second plating layer 63 of the bonding layer 64 are changed variously. Sample Nos. 1 to 10 were produced. As the solder, a low melting point solder having a length of 54.9 mm, a width of 56.5 mm and a thickness of 0.2 mm is used, and the circuit board 9 is set to 325 in an H ₂ atmosphere.
℃ × 10 minutes, heat dissipation member 6 in H ₂ atmosphere 260 ℃ × 10
After baking for 5 minutes, the solder plate was interposed between the circuit board 9 and each of the heat radiating members, and soldering was performed at 250 ° C. for 10 minutes. The presence or absence of solder flow, the occurrence rate of solder voids (%), and the bonding strength were evaluated for these.
The void generation rate was obtained by averaging the generation rate of void areas per total area of the circuit board using an ultrasonic image. Regarding the bonding strength, a tensile test was performed and it was judged whether the plating layer was peeled off or not. Further, as comparative examples, sample Nos. 11 to 15 in which the center line average surface roughness (Ra) and the material and thickness of the bonding layer were changed were prepared, and the same evaluation was performed.
The other circuit board configurations are shown in FIG.
The structure shown in was used. Table 1 shows the above evaluation results.

[0019]

[Table 1]

From the above, solder having no center line average surface roughness (Ra) of 0.2 to 1.5 μm has no solder flow and the void generation rate is suppressed. As a result, all the bonding strengths also passed. Further, when the thickness of the bonding layer is in the range of 3 to 15 μm, the surface roughness is reflected, and there is no solder flow,
The void generation rate was low and the bonding strength was sufficient. Actually, it is necessary to satisfy both conditions of surface roughness and bonding layer thickness. For example, it can be seen from Example 8 that the occurrence rate of voids increases as the surface roughness decreases. In Comparative Example 1, the strength is insufficient because the thickness of the bonding layer is small. On the contrary, in Comparative Example 2, it is considered that the solder flow occurs because the surface roughness is large. From Comparative Examples 2 and 3, it is considered that, in addition to the surface roughness, the difference in the thickness of the bonding layer affects the plating film strength, which appears in the difference in the bonding strength pass / fail. Further, it is considered that the generation of voids is affected by the solder wettability.

[0021]

According to the present invention, the center line average surface roughness (Ra) of the bonding layer formed on the Al coating of the heat dissipation member made of an Al-SiC composite is 0.2 to 1.5 μm. ,
And by setting the thickness of the bonding layer to 3 to 15 μm,
It is possible to prevent a solder flow that occurs when the circuit board and the heat dissipation member are joined by solder. Further, it is possible to reduce the generation of solder voids and improve the solder wettability. Therefore,
It was possible to provide a ceramics heat dissipation circuit board with stable bonding strength and thermal conductivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a ceramics heat dissipation circuit board.

FIG. 2 is an electron micrograph showing the vicinity of the bonding layer between the circuit board of the present invention and the heat dissipation member.

3 is a schematic cross-sectional view in the vicinity of a bonding layer in FIG.

FIG. 4 is a surface roughness (a) of an Al film according to an embodiment of the present invention.
And the surface roughness (b) of the bonding layer.

FIG. 5 is a characteristic diagram showing a relationship between a centerline average surface roughness and a solder spreading coefficient according to an example of the present invention.

[Explanation of reference numerals] 1: Ceramic heat dissipation circuit board, 2: AlN board, 3:
Cu circuit board, 4: Cu plate, 5: Semiconductor chip, 6: Al
-SiC heat dissipation member, 7: solder, 8: heat sink, 9:
Circuit board, 10: Fastening member, 60: Al film, 61: A
l coating surface, 62: first plating layer (base layer), 6
3: second plating layer (surface layer), 64: bonding layer, 65:
Bonding layer surface

[Procedure amendment]

[Submission date] November 28, 2001 (2001.11.
28)

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G026 BA03 BA16 BA17 BB14 BB27                       BB31 BC01 BC02 BD02 BD06                       BD12 BD14 BF11 BF18 BF42                       BF46 BG02 BG28 BH07                 5E338 AA01 AA18 BB63 EE02                 5F036 AA01 BA23 BB05 BB08

Claims (3)

[Claims] 1. A heat dissipating member of an Al--SiC composite having a ceramic insulating substrate on which a semiconductor chip is mounted on one side and a Cu or Al plate on the other side, respectively, and an Al film on the surface. And a bonding layer is formed on the Al film of the heat dissipation member, and the bonding layer and the Cu or Al plate of the ceramics insulating substrate are bonded by soldering. And a center line average surface roughness (Ra) of the surface thereof is 0.2 to 1.5 μm. 2. The ceramic heat dissipation circuit board according to claim 1, wherein the bonding layer has a thickness of 3 to 15 μm. 3. The bonding layer is composed of two layers, and the underlayer is N
3. The ceramic heat dissipation circuit board according to claim 1, wherein the plating layer is iP and the surface layer is NiB.