JP2001085808A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and stable circuit board which is suitable for a power module by connecting a ceramic board and an Al circuit formed of Al or Al alloy through a layer which is mainly composed of Al and Cu. SOLUTION: A layer containing Al and Cu is installed and an Al circuit or an Al alloy circuit (called as 'Al circuits' hereinafter) is formed in at least one face of a ceramic substrate. Namely, an Al substrate is connected to at least one face of the ceramic board by using Al-Cu alloy or mixture containing Al and Cu. The circuit board can be manufactured by a method for heating/ connecting the Al board or an Al alloy board and the ceramic board by using Al-Cu alloy and etching them and a method for connecting the pattern of the Al circuit punched from the Al board or the Al alloy board or a heating board to the ceramic board by using Al-Cu alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable circuit board used for a power module or the like.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor device used for a power module or the like, Cu, Al, alloys containing these metals as components, etc. are formed on the front and back surfaces of a ceramic substrate such as alumina, beryllia, silicon nitride, and aluminum nitride. A circuit board formed with the above circuit and a heat sink is developed (for example, US Pat. No. 5,354,415) and put into practical use. Such a circuit board is characterized in that higher insulating properties can be obtained more stably than a resin board and a metal board composite board or a resin board.

[0003] As a method of joining a ceramic substrate and a circuit or a heat radiating plate, there are roughly a brazing method using a brazing material and a method using no brazing material. As the latter typical method, a DBC method in which a tough pitch copper plate and alumina are joined using a eutectic point of Cu-O is known.

However, when the material of the circuit is Cu, the generation of thermal stress due to the difference in thermal expansion between the ceramic substrate and the solder is unavoidable, and cracks occur in the ceramic substrate and the solder due to repeated heat history. High reliability is not enough. On the other hand, thermal conductivity and electrical conductivity are slightly C
Although Al is inferior to u, if Al is selected for the circuit material, it is easily plastically deformed even when subjected to thermal stress, so that the stress applied to the ceramic substrate and solder is alleviated, and the reliability is dramatically improved.

[0005]

However, a problem with the Al circuit is that it is expensive. The reason is A
To form a circuit, (1) a molten aluminum method (for example, a method in which molten aluminum is brought into contact with a ceramic substrate to produce a joined body by contacting and cooling the ceramic substrate, and then mechanically ground to adjust the thickness of the Al plate, followed by etching); JP-A-7-193358,
JP-A-7-27262) and (2) a method of brazing and etching an Al foil or an Al alloy foil (for example, JP-A-3-125463).
Since the cost is about 2 to 5 times that in the case of forming a u circuit, it is unlikely to be widely used for purposes other than special purposes.

[0006] Apart from the molten metal method, which has a low production efficiency, the main reason why the cost of the Al circuit of the brazing method is higher than that of the Cu circuit is that the bonding conditions are very narrow. That is, the melting temperature of Al (660 ° C.) and the joining temperature (about 650 ° C. in the case of Al—Si system, which is the most common brazing material)
, Al melts locally and the soldering defect (A
In this case, a great deal of skill and labor is required to prevent the occurrence of the insect-eating phenomenon which occurs in the 1-circuit.

[0007] Al, Al undergoes plastic deformation, and its size depends on the magnitude of the thermal stress and the portion subjected to the thermal stress. Solder cracks may occur. Therefore, it is necessary to achieve a trade-off between maintaining a sufficient stress relaxation effect on the ceramic plate and suppressing solder cracks.

[0008] The present invention has been made in view of the above, and if an inexpensive Al-Cu-based alloy, which has not been omitted so far, is used as a bonding material and is bonded under specific conditions, Al-Cu
It has been found that the circuit can be easily formed on the ceramic substrate, and that in a circuit board having a heat sink formed on the back surface, the volume ratio between the Al circuit and the heat sink should be optimized.
The present invention has been completed.

An object of the present invention is to provide a ceramic substrate with Al.
Another object of the present invention is to provide a circuit board on which an Al alloy circuit is formed, or a circuit board on which a heat radiating plate is further formed on a surface of a ceramic substrate opposite to the Al circuit, while maintaining its high reliability at a low cost. In particular, it is an object of the present invention to provide a highly reliable circuit board in which not only cracks in solder and ceramic substrates but also peeling of bonding wires and plating are significantly prevented.

[0010]

That is, the present invention relates to the following circuit board. (Claim 1) A circuit board comprising a ceramic substrate and an Al circuit made of Al or an Al alloy joined through a layer mainly composed of Al and Cu. (2) The circuit board according to (1), wherein the proportion of Cu in the layer mainly composed of Al and Cu is 1 to 6% by weight. (Claim 3) The circuit board according to claim 1, wherein the layer mainly composed of Al and Cu contains Mg. (Claim 4) A circuit characterized in that a ceramic substrate and an Al circuit made of Al or an Al alloy are joined using a joining material made of an Al-Cu alloy and / or a mixture containing Al and Cu. substrate. (Claim 5) The circuit board according to claim 4, wherein the joining material is an Al-Cu alloy foil. (Claim 6) The composition of the bonding material is at least 86% by weight of Al,
The circuit board according to claim 5, further comprising u1 to 6% by weight and Mg 3% by weight or less (excluding 0). (Claim 7) A heat radiation plate made of Al or an Al alloy is formed on the opposite surface (back surface) of the ceramic substrate on which the Al circuit is formed. The described circuit board. (Claim 8) The circuit board according to claim 7, wherein a volume ratio of the Al circuit to the heat sink (circuit volume / heat sink volume) is 0.80 to 1.2. (Claim 9) The Vickers hardness of the Al circuit is 16 kgf /
^{mm 2 (157MPa, 1kgf / mm} 2) or less, the circuit board according to claim 7 or 8, wherein the Vickers hardness of the heat sink is characterized in that it is a 19~30kgf / mm ^2. (Claim 10) The ceramic substrate is an aluminum nitride substrate or a silicon nitride substrate.
10. The circuit board according to any one of claims 9 to 9. (Claim 11) The ceramic substrate has a thermal conductivity of 70 W /
The circuit board according to claim 10, wherein the circuit board has a mK or more. (Claim 12) An Al circuit comprising Al or an Al alloy,
The circuit board according to any one of claims 1 to 9, wherein the circuit board is formed using Al having a purity of 99.85% or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

A major feature of the present invention is that an Al circuit or an Al alloy circuit (hereinafter collectively referred to as "Al circuit") is formed on at least one surface of a ceramic substrate with a layer containing Al and Cu interposed. It is formed. In other words, the Al circuit is bonded to at least one surface of the ceramic substrate using an Al-Cu-based alloy or a mixture containing Al and Cu. The circuit board of the present invention may have a structure in which the opposite surface (back surface) of the ceramic substrate on which the Al circuit is formed is joined to a heat sink.

Until now, Al-Si alloys have been most frequently used to join Al circuits.
Studies have also been made on Si-Mg, Al-Ge, Al-Si-Ge, and the like. However, no prior art for joining using an Al-Cu alloy has been found. The reason is that Al-Cu based alloys containing a large amount of Cu are relatively hard and brittle, and are prejudiced that they are disadvantageous to plastic deformation that releases the thermal stress of the circuit board, and cannot be omitted. It is presumed that it was.

However, Al-Cu alloys are
Compared with Si-based, Al-Ge-based or Mg-based systems, Cu is more easily diffused into Al than Si or Ge, so that local melting occurs or extra joining material is used. This is advantageous in that protrusion does not easily occur and stable bonding of the Al circuit can be performed in a relatively short time. Also,
In the case of Al-Si or Al-Ge, it is necessary to add a relatively large amount of Si or Ge in order to lower the melting point. The composition will be selected. As a result, the melting point is close to that of Al, and bonding is difficult at 620 ° C. or lower. On the other hand, in an Al-Cu alloy, for example, even if the addition amount of Cu is about 4% by weight, bonding can be performed at a low temperature of about 600 ° C. by taking measures such as pressurization.
Al-Si or Al-G
It is advantageous as compared with the e system.

Al-Cu based alloys have an AA symbol of 2000
As an alloy of the series, it is widely used as a high-strength Al alloy or a heat-resistant Al alloy, and it is advantageous in terms of cost because it is easily formed into a foil.

In the circuit board of the present invention, the ceramic substrate and the Al circuit are joined together with a layer containing Al and Cu as main components. In addition to the two components described above, the composition may further contain a third component. Examples of the third component include, but are not limited to, Mg, Zn, In, Mn, Cr, and T.
i, Bi and the like, among which Mg is particularly preferable.

The above-mentioned layer containing Al and Cu as main components is obtained by arranging an Al-Cu alloy, Al or Al alloy plate, pattern, or both on a ceramic substrate in order, and then performing heat bonding while applying pressure. Thereby, it can be formed.

The layer mainly composed of Al and Cu is in contact with the ceramic substrate, and preferably has a thickness of up to 100 μm from the surface. There may be another layer between the layer mainly composed of Al and Cu and the Al circuit.

In order to obtain a highly reliable circuit board, a preferable composition of the bonding material is one containing 86% by weight or more of Al, 1 to 6% by weight of Cu, and 3% by weight or less of Mg (not including 0). If the Cu content is less than 1% by weight, the joining temperature increases and approaches the melting point of Al, and if it exceeds 6% by weight, Cu diffuses into the Al circuit after joining to reduce the thermal history of the circuit board. Due to disadvantages, the Cu content is preferably 1.5 to 5% by weight.

The Cu content of the layer mainly composed of Al and Cu is substantially determined by the Cu content of the bonding material used for bonding.

Mg makes use of the characteristics of the Al-Cu system and improves the adhesion between the ceramic substrate and the Al circuit. The detailed mechanism of the manifestation of the effect of Mg is not clear, but Mg reacts with the oxide film on the Al surface to form MgO, thereby removing the film, forming MgN _{2 on the} ceramic substrate surface and improving wettability. It is presumed to be. If the Mg content exceeds 3% by weight, problems such as a large amount of Mg being volatilized during the joining operation and damaging the Al circuit and the like, and a large amount of Mg being diffused into the Al circuit and hardening of the Al become remarkable. is there. If the amount of Mg is too small, the effect of improving the adhesion will not be remarkable. The Mg content is preferably from 0.2 to 2.0% by weight.

Further, the bonding material is Zn, In, Mn, C
A fourth component such as r, Ti, Bi, B, Fe, etc., may contain about 5% by weight or less in total. By using a bonding material having such a composition, a circuit board can be supplied more stably and at low cost.

As the joining material, an Al-Cu alloy or a mixture containing Al and Cu is used. Among them, Al-
Cu-based alloy foils are preferred.

In particular, the Al-Cu alloy foil preferably has a thickness of 1/10 to 1/50 of the thickness of the Al circuit. If the thickness is less than 1/50, it is difficult to achieve sufficient bonding. If the thickness is more than 1/10, alloy components diffuse into Al, and
The circuit becomes hard and causes a decrease in reliability against the thermal history of the circuit board. Particularly preferably, the thickness is 100 μm or less, and more than 1/12 to the thickness of the Al circuit.
The thickness is 1/40. Usually 0.4 to 0.6 mm thick
Is used, the thickness of the bonding material is 10 to 5
0 μm, especially about 15 to 30 μm.

Further, it is also possible to use a powder of the alloy or a metal mixture having the same composition as the alloy, which is made into a paste with an organic binder and a solvent. In this case, sufficient attention must be paid to oxidation, and the amount of oxygen in the powder is adjusted to 1% by weight or less, particularly 0.8% by weight or less. Further, in order to maintain the thickness relationship with the Al circuit as described above, the thickness is converted into a thickness equivalent to an alloy foil. That is, the paste layer 100 having a packing density of 50% by weight.
In the case of μm, it is equivalent to 50 μm of the alloy foil.

Specific examples of the joining material (commercially available alloy) are as follows.
201 containing an Al—Cu alloy having a Cu content of 1 to 6% by weight, about 4% by weight of Cu, and about 0.5% by weight of Mg
8 alloy, further containing about 0.5% by weight of Mn 201
7 and the like, and further, JIS alloys 2001 and 20
03, 2005, 2007, 2011, 2014, 20
24, 2025, 2030, 2034, 2036, 20
48, 2090, 2117, 2124, 2218, 22
24, 2324, 7050 and the like.

Next, the Al circuit will be described.

As the material of the Al circuit, not only 1000 series pure Al, but also 4000 series Al-Si series alloy or 6000 series Al-Mg-Si series alloy which can be easily joined can be used. Above all, high-purity Al having a low yield strength (purity 9
9.85% or more). Such an Al plate is composed of 1
It is commercially available as 085, 1N85 material. Also, 9
9.9% (3N) product, 99.99% (4N) product, 99.
Even 999% (5N) products can be used because they are not so expensive.

The Al circuit may be a single unit or may be a laminate of two or three or more clads. Examples of the laminate include Al-Ni, Al-Ni-Cu, and Al-M.
o, Al-W, Al-Cu and the like. These are appropriately selected depending on the purpose of use and the joining method. Among them, it is preferable to use a rolled plate of Al alone having a purity of 99.99% or more, particularly a rolled plate having a rolling reduction of 10% or more.
The reason why the rolled Al plate is suitable is that uniform plastic deformation is more likely to occur since uniform rolling is repeatedly performed with a roll as compared with the above-described molten aluminum method.

The thickness of the Al circuit is usually 0.3 to 0.5 m
m. If the value deviates significantly from this range, the above relationship with the preferable thickness of the bonding material cannot be maintained. For example, for an Al circuit having a thickness of 3 mm, an alloy foil of 200 μm, which is 1/15 thick, does not have an appropriate thickness, and a hard layer disadvantageous to the heat history is formed.

In a structure in which a heat sink is formed on the opposite surface (back surface) of the ceramic substrate on which the Al circuit is formed,
Since the heat sink is soldered to almost the entire surface to fix it to the ceramic substrate, the thermal stress on the solder also increases,
The occurrence and progress of solder cracks govern heat dissipation. Thermal stress on the ceramic substrate is concentrated at the end of the circuit pattern. In many cases, “horizontal cracks” that occur at the end of the circuit and propagate into the inside of the pattern contribute to controlling the heat dissipation.

In the circuit board of the present invention, from these points,
It is desirable that the volume ratio of the Al circuit to the heat sink (circuit volume / heat sink volume) be close to 1, and the ratio be 0.8 to
1.2, especially 0.85-1.15, and even 0.9-1.
It is preferably set to 1. In this case, it is desirable that the thickness of the heat sink be equal to or less than the thickness of the circuit. If there is a remarkable difference in the volume ratio, the generated thermal stress will be biased, causing warpage or undulation, and it will not be possible to sufficiently prevent damage such as solder cracks and peeling of bonding wires and plating.

The volume of the Al circuit is calculated by (circuit area × circuit thickness), and the volume of the heat sink is calculated by (heat sink area × heat sink thickness).

The Vickers hardness of the Al circuit is 16 k.
gf / mm ² (157 MPa, where 1 kgf / mm ² =
9.8 MPa) or less and the heat sink has a Vickers hardness of 19
-30 kgf / mm ^2, and it is particularly preferable that the above-mentioned volume ratio relationship be satisfied and that this Vickers hardness relationship be satisfied.

The Vickers hardness specified here is the hardness of the Al circuit or the heat sink, and is different from the hardness of the Al plate before joining. Since the Al plate is joined to the ceramic substrate by heating at a temperature in the range of 500 to 640 ° C. using the joining material, the microstructure changes due to heat treatment, and the purity of Al decreases due to diffusion of the joining material. It is. Further, by performing a heat treatment after the bonding, the Al characteristics are changed. Therefore, it does not make sense to specify the hardness of the Al plate before joining.

Vickers hardness is widely used as a high-level measuring method for metals and ceramics. Since the measurement is performed by driving a fine indenter under a load, the value may be slightly different depending on the measurement conditions. In the present invention,
The measurement was performed under the conditions of a load of 1 kgf and a holding time of 15 seconds.

The Vickers hardness of the Al circuit is 16 kgf /
If it exceeds mm ² , plastic deformation due to thermal stress becomes non-uniform, and partial deformation increases, so that there is a possibility that peeling of the bonding wire or plating may occur. The hardness is preferably as small as possible, but if it is too soft, it is easily damaged, so it is preferably from 11 to 15 kgf / mm ² . On the other hand, if the Vickers hardness of the heat radiating plate exceeds 30 kgf / mm ² , plastic deformation becomes difficult, and cracks easily occur in both the ceramic substrate and the solder. 19kgf /
If it is less than mm ² , plastic deformation is easy, but solder cracks are likely to occur due to large deformation due to repeated thermal history. Therefore, a particularly preferred Vickers hardness of the heat sink is 20 to 28 kgf / mm ² .

The hardness of the Al circuit and the radiator plate can be adjusted by selecting the material and the heat treatment conditions. As for the material, the higher the purity of the Al plate after joining, the softer the material. Therefore, the material may be selected based on the purity. Usually pure Al
As 99.0% to 99.99%.
There is a considerable range of 9%, and there is a large difference in hardness. 9
With Al of 9.5% or less, the Vickers hardness after bonding is 16
kgf / mm ² or less is difficult, and 99.5%
With the above, it is difficult to increase the pressure to 19 kgf / mm ² or more after joining. That is, in the present invention, high-purity Al material is used for the Al circuit, and relatively low-purity Al or Al is used for the heat sink.
An alloy is used. Examples of the Al alloy include an Al-Mn alloy such as AA symbol 3003 and the like, and an Al-Mg alloy such as 5052 and the like.

Next, regarding the heat treatment conditions, when the circuit board of the present invention is manufactured, the bonding temperature between the Al plate and the ceramic substrate is higher than the annealing temperature of Al of 300 to 350 ° C. Cooling conditions are important. If the cooling is performed at a temperature higher than the annealing temperature of Al at a rate of 2 ° C./min or less, the hardness decreases, and at a rate of 5 ° C./min or more, the hardness relatively increases.

Next, the ceramic substrate will be described.

As for the material of the ceramic substrate, aluminum nitride or silicon nitride having a thermal conductivity of at least 70 W / mK is preferably used, considering that it is used for a power module requiring high reliability. Materials such as silicon carbide and beryllium oxide may be used, but are inferior in insulation and safety.

Such a ceramic substrate is prepared by adding yttria, alumina, magnesia,
A sintering aid such as a rare earth element oxide is blended in an amount of about 0.5 to 10% by weight, molded using an organic binder such as butyral or methyl cellulose, and then debindered.
In a non-oxidizing atmosphere such as nitrogen or argon, temperature 1700
It can be manufactured by holding at 1900 ° C. for about 1 to 12 hours. Such production methods are known,
There are also commercial products.

The thickness of the ceramic substrate is usually 0.63
It is 5 mm, but can be changed according to required characteristics.
For example, when thermal resistance is important and insulation at a high voltage is not so important, a thin substrate of 0.5 to 0.3 mm can be used. Is important, a thickness of 1 to 3 mm is used.

Next, a method of manufacturing a circuit board according to the present invention will be described.

The circuit board of the present invention is, for example, a method in which an Al plate or an Al alloy plate and a ceramic substrate are heated and joined by using the above-mentioned Al-Cu alloy and then etched, and is punched from the Al plate or the Al alloy plate. It can be manufactured by, for example, a method of joining a pattern of an Al circuit or a heat sink to a ceramic substrate using the above Al-Cu alloy.

In any method, it is necessary to bond the ceramic substrate, the Al circuit, and, if necessary, the heat sink. As a joining method, there is a method that does not use a joining material as in a molten metal method. However, in the present invention, an Al—Cu-based alloy or Al
And a method of joining using a mixture containing Cu and Cu.

The bonding material may be arranged on either the ceramic side, the metal plate or the circuit pattern side. When an alloy foil is used, the bonding material may be clad with the metal plate or the circuit pattern in advance.

The joining temperature is in the range of 540 to 640 ° C., but the appropriate range varies depending on the composition of the joining material. When a relatively low melting point component such as Zn or In is added, or when the content of Cu or Mg is relatively large, 60
Even at 0 ° C. or less, sufficient bonding can be achieved. On the other hand, when the joining temperature is 64
If the temperature exceeds 0 ° C., a soldering defect (insect eating phenomenon generated in the Al circuit) is likely to occur at the time of joining, which is not preferable.

Conventionally, in the production of a circuit board, a weight has been placed on the metal plate and the ceramics substrate when the metal substrate and the ceramic substrate are joined, and the pressure is applied.
It is about f / cm ² (9800 Pa). At such a pressure, the metal plate can follow only a relatively gentle warpage or undulation of the ceramic substrate. On the other hand, in the present invention, an insanely high pressure of 1 to 100 kgf / cm ² is applied in the prior art. Therefore, the ceramic substrate can be used as it is at a normal level without requiring strict smoothness and flatness, thereby improving the productivity. Since the ceramic substrate has a high compressive strength, it is not damaged even if pressed to such an extent.
However, usually, since the ceramic substrate has some warpage or undulation, it exceeds 50 kgf / cm ² , especially 100 kgf / cm ^2.
Care must be taken because applying a pressure exceeding f / cm ² may cause cracks or the like.

Al or Al alloy itself is 300 to 350
As can be seen from annealing at a temperature of 500 ° C., the metal becomes very soft at a temperature of 500 ° C. or higher. Therefore, even if a brazing defect occurs at the time of joining, it is not crushed by applying a pressure of 1 to 100 kgf / cm ² . Therefore, when it is important to eliminate brazing defects, re-heating while applying pressure at a temperature of 400 ° C. or more after joining, or in a cooling process after joining, at least in a temperature range of 400 ° C. or more. Pressurize.

In the present invention, a particularly preferable joining condition is to use an Al—Cu alloy foil having a thickness of 15 to 35 μm,
Pressing at 590 ° C. or higher at 8 to 50 kgf / cm ² , and maintaining the heated and pressed state for at least 20 minutes. As a result, the Vickers hardness of the Al circuit can be easily reduced to 16 kgf / mm ² or less. More preferably,
Heat to 595-635 ° C and hold for 20-90 minutes.

Although the details of the mechanism of the Vickers hardness reduction effect in the present invention are not clear, in the present invention, since the bonding is performed in an insane high-temperature region higher than the normal annealing temperature of 300 to 350 ° C., Al is extremely low. It is thought that this may be because grain growth is suppressed by transmitting pressure uniformly.

In the present invention, for example, an alloy foil, a plate of Al or the like, a pattern, or the like is arranged on both surfaces of a ceramic substrate.
It is preferable to apply pressure in a direction perpendicular to the ceramic substrate. The pressing direction is a direction perpendicular to the ceramic substrate, and the method and the like are not particularly limited. A method of placing a weight, a method of mechanically sandwiching with a jig or the like, and the like are employed.

Next, the joined body is etched as necessary. When the pattern of the Al circuit or the heat sink is joined, etching is not particularly required. The etching can be performed by a usual resist and etching process. Further, surface treatment such as plating is also performed as needed.

[0055]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 to 6 Comparative Examples 1 to 3 The aluminum nitride substrates were as fired without post-processing such as surface grinding and re-warping, and had a thickness of 0.63.
5mm, 2 inch square, thermal conductivity 170W / m
K and those having a bending strength of 400 MPa were used. Also,
The Al plate for forming the Al circuit is JIS1090 (thickness of 0. 1).
5 mm, 99.9% Al purity).

First, an Al plate is placed on the front and back surfaces of an aluminum nitride substrate via a bonding material, and sandwiched between CC composite plates (thickness: 2 mm). 550-62 while pressing
Heated to 0 ° C. in vacuo or N ₂ .

The bonding material is (a) Al-9.5% by weight Si
-1 wt% Mg alloy foil, (b) Al-15 wt% Ge alloy foil, (c) Al-4.1 wt% Cu-0.5 wt% M
n alloy foil, (d) Al-2.8% by weight Cu alloy foil,
(E) A powder obtained by atomizing the above (c) in N ₂ to an average diameter of 10 μm and pasting it with an organic binder (PIBMA) and a solvent (terpineol) was used.

[0059] 100 bonded bodies were prepared under each condition.
Using soft X-rays, three times magnification was used to inspect for poor bonding and soldering defects. The lower detection limit is about 0.3 mmφ in diameter. Also, 10 samples were taken out, 2 mm of the periphery of the Al plate was etched with FeCl ₃ solution, electroless Ni-P plating was applied at 3 μm, and two 12.5 mm square silicon chips were eutectic at the center. Solder with solder, and the other side is Al /
It was soldered to a SiC heat sink. The solder thickness of both is 150 μm.

Thereafter, a thermal hysteresis test of 3,000 cycles and 5000 cycles was carried out at -40 ° C., 30 minutes → room temperature, 10 minutes → 125 ° C., 30 minutes → room temperature, 10 minutes, and the appearance such as swelling and peeling was observed. Check was performed to check for the occurrence of solder cracks by observing the cross section of three sheets. Further, the circuit portions of the seven circuit boards were melted, and the presence or absence of cracks was measured by an ink test method (red check). Table 1 shows the results.

Example 7 Comparative Example 4 In Example 2 or Comparative Example 2, a silicon nitride substrate (thickness: 0.635 mm, size: 2 inch square, thermal conductivity: 70 W / mK, flexural strength) was used instead of the aluminum nitride substrate. 800
A circuit board was manufactured in the same manner except that MPa) was used. Table 1 shows the results.

[0062]

[Table 1]

As is clear from Table 1, all of Examples 1 to 7 of the present invention showed a good bonding state, and a circuit board could be manufactured stably even in N ₂ , while Comparative Example 1 ~
In the case of No. 4, failures occurred frequently and productivity was poor. Moreover, surprisingly, all of the examples of the present invention were not inferior to the comparative examples in terms of characteristics.

The alloy foils (a) and (b) used in the comparative examples have the compositions shown in JP-A-3-125463, but as alloy foils, both are custom-ordered and generally commercially available. In contrast, the alloy foil (c) of the example was a commercially available product obtained by converting the 2017 alloy into a foil, and was easily and inexpensively available.

Examples 8 to 12 Aluminum nitride substrates (thickness: 0.635 mm, size: 2
Inch square, thermal conductivity 175W / mK, 3 point bending strength 4
A bonding material and an Al plate (purity: 99.20 MPa) on the front and back surfaces.
99% or more (thickness shown in Table 2), and a carbon plate was screwed into the aluminum nitride substrate and pressed uniformly against the aluminum nitride substrate using a jig that pressed the substrate against the substrate. Table 2 shows the joining conditions. The joining material is (f) Al-3.9 wt% Cu alloy foil, or (g) and (f) in N2 with an average diameter of 9
After atomizing to μm, those having a size of 45 μm or less were collected, and an organic binder and a solvent were added to form a paste. Table 3 shows the results.

[0066]

[Table 2]

[0067]

[Table 3]

As is clear from Tables 2 and 3, when the thickness of the Al circuit is 100 μm or more, the Vickers hardness is 15 kg.
By setting it to f / mm ² or less, even after 5000 cycles of the heat cycle test, there was no damage to the bonding wires and plating, and the occurrence of cracks in the solder or aluminum nitride substrate could be reduced. In particular, from the comparison between Examples 8, 10, and 11, and Examples 9 and 12, the thickness of the Al circuit was 150 to 300 μm, and the volume ratio of the Al circuit to the heat sink (circuit volume / heat sink volume) was 0.80 to 1. .
By setting to 2, this effect became remarkable.

Examples 13 to 18 Using the aluminum nitride substrate used in Example 1, a circuit board was manufactured in the same manner as in Example 1 except for the Al plate (commercially available), bonding materials and bonding conditions shown in Table 4. did. Table 5 shows the results.

[0070]

[Table 4]

[0071]

[Table 5]

As is clear from the comparison between Tables 4 and 5 and Table 1, the use of a bonding material of 86% by weight or more, 1 to 6% by weight of Cu, and 3% by weight or less of Mg (not including 0) is used. A good bonding state without voids was obtained, and even after 5000 cycles of the heat cycle test, a circuit board with almost no occurrence of solder cracks and aluminum nitride substrate cracks and having high durability against heat history could be manufactured.

Further, Embodiments 13 and 18 and Embodiments 14 to 1
As is clear from comparison with No. 7, when the Al purity of the Al plate was increased, the number of defects due to the occurrence of substrate cracks tended to decrease even after 5000 cycles of the heat cycle test. In particular, as can be seen from a comparison between Example 14 and Example 15, etc., the rolled Al having a purity of 99.99% or more was obtained.
This effect was remarkable when a plate was used.

The reason why the fifteenth embodiment shows the best effect is that the thickness of the bonding material is optimized. It can be said from the comparison between Examples 16 and 17 that, in Example 17, the thickness of the bonding material was large, which was a disadvantageous condition for the substrate crack, but the purity of the Al plate was high. That is to surpass 16.

Examples 19 to 22 Al plate for Al circuit / joining material / aluminum nitride substrate used in Example 8 / joining material / Al plate for heat radiating plate
The joining was performed under the joining conditions shown in Table 7. The bonding materials shown in Table 6 were used.

After bonding, the etching resist was screen-printed and etched with a FeCl ₃ solution. Al circuit surface,
The pattern of the heat radiating plate surface was a square (the corner R was 2 mm), which was formed in the center of the ceramic substrate, and the size thereof was changed to adjust the volume ratio of the Al circuit to the heat radiating plate at the ratio shown in Table 6. Then, after removing the resist,
Electroless Ni-P plating was applied to 3 μm to obtain a circuit board.

Using a part of the obtained circuit board, the Al circuit and the heat sink were peeled off and their Vickers hardness was measured. Table 7 shows the results.

Also, 13 is provided at the center of another circuit board.
A heat cycle test was performed after soldering the Si chip of mm square. The heat cycle test was performed at -40 ° C and 30 ° C.
Minutes → room temperature, 10 minutes → 125 ° C., 30 minutes → room temperature, 10 minutes as one cycle, and after 3000 cycles and 5000 cycles of heat cycle test, the number of defective substrates is counted by external appearance observation, and ultrasonic depth The bonding state between the chip solder and the solder under the board was examined by a scratch device (SAT). Diameter 1
When a non-joined portion of not less than 1 mm or a non-joined area portion of not less than 1% could be confirmed, it was regarded as poor joining. Table 8 shows the results.
Shown in

[0079]

[Table 6]

[0080]

[Table 7]

[0081]

[Table 8]

As is clear from the comparison between Examples 19 to 21 and Example 22, the Vickers hardness of the Al circuit was 16 k.
gf / mm ² or less, and the heat sink has a Vickers hardness of 19 to
By setting the pressure at 30 kgf / mm ² , the occurrence of solder cracks and substrate cracks could be significantly suppressed even after 5000 cycles. This effect was particularly remarkable in a circuit board having a volume ratio of the Al circuit to the heat sink of 0.80 to 1.2.

In Examples 13 to 22, the Cu content of the layer mainly containing Al and Cu in each bonding layer was 1%.
６6% by weight was confirmed by quantifying the peak ratio of elemental analysis by cross-sectional observation.

[0084]

According to the present invention, a highly reliable circuit board which is inexpensive, stable and suitable for a power module is provided.

According to the present invention, there is provided a highly reliable circuit board in which the occurrence of solder cracks and cracks in the ceramics substrate can be significantly reduced, and peeling of bonding wires and plating is also significantly prevented.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H05K 1/03 610 H05K 3/38 E 3/38 H01L 23/36 C (72) Inventor Yoshihiko Tsujimura Shinkai, Omuta-shi, Fukuoka Town 1 Denki Kagaku Kogyo Co., Ltd. Omuta Plant (72) Inventor Katsunori Terano 1 Shinkaicho, Omuta-shi, Fukuoka Prefecture Denki Kagaku Kogyo Co., Ltd. Omuta Plant (72) Inventor Takeshi Goto 1 Shinkaicho, Omuta-shi, Fukuoka Electrochemical In the Omuta Plant of Industrial Co., Ltd. (72) Nobuyuki Yoshino, 1 Shinkaicho, Omuta-shi, Fukuoka Prefecture In the Omuta Plant of Electrochemical Industry Co., Ltd. (72) Isao Sugimoto, 3-5-1 Asahimachi, Machida-shi, Tokyo Electrochemistry Industrial Research Institute Central Research Laboratory

Claims (12)

[Claims] 1. A circuit board comprising a ceramic substrate and an Al circuit made of Al or an Al alloy joined via a layer mainly composed of Al and Cu. 2. The circuit board according to claim 1, wherein the proportion of Cu in the layer mainly composed of Al and Cu is 1 to 6% by weight. 3. The circuit board according to claim 1, wherein the layer mainly containing Al and Cu contains Mg. 4. A ceramic substrate and an Al circuit made of Al or an Al alloy are made of an Al—Cu-based alloy and / or an Al circuit.
A circuit board, which is joined by using a joining material made of a mixture containing Cu and Cu. 5. The circuit board according to claim 4, wherein the bonding material is an Al—Cu alloy foil. 6. The composition of the bonding material is at least 86% by weight of Al.
6. The circuit board according to claim 5, comprising 1 to 6% by weight of Cu and 3% by weight or less of Mg (not including 0). 7. A heat radiation plate made of Al or an Al alloy is formed on an opposite surface (back surface) of a ceramic substrate on which an Al circuit is formed.
The circuit board according to any one of the above. 8. The circuit board according to claim 7, wherein the volume ratio of the Al circuit to the heat sink (circuit volume / heat sink volume) is 0.80 to 1.2. 9. The Vickers hardness of the Al circuit is 16 kgf.
/ Mm ² (157 MPa, but 1 kgf / mm ² = 9.8
The Vickers hardness of the heat sink is 19 to
The circuit board according to claim 7, wherein the circuit board has a weight of 30 kgf / mm ² . 10. The circuit board according to claim 1, wherein the ceramic substrate is an aluminum nitride substrate or a silicon nitride substrate. 11. A ceramic substrate having a thermal conductivity of 70 W
The circuit board according to claim 10, wherein the value is not less than / mK. 12. The circuit board according to claim 1, wherein the Al circuit made of Al or an Al alloy is formed using Al having a purity of 99.85% or more.