JP2000349405A - Circuit board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide a highly reliable circuit board at a low cost, in which a circuit and a radiating plate composed of Al or Al alloy are formed on an aluminum nitride board. SOLUTION: In a circuit board, in which a circuit is formed on one surface of an aluminum nitride board and a radiating plate is formed on the other surface, thermal conductivity of the aluminum nitride board is 130 W/mK or higher, and the X-ray peak intensity ratio of the surface by CuKα is 3<=Y2 O3.Al2O3/AlN<=18, 2Y2O3.Al2O3/AlN<=3. The material of the circuit and the radiating plate is Al and/or Al alloy. The circuit and the radiating plate are bonded to the aluminum nitride board by heat treatment of a metal powder paste containing Al, Si and Mg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 used. Such a circuit board is characterized in that higher insulating properties can be obtained more stably than a resin-metal 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 two methods: a brazing method using a brazing material and a method using no brazing material. A typical method of the latter is a DBC method in which a tough pitch copper plate and alumina are joined using a eutectic point of Cu-O.

However, when the material of the circuit or the heat radiating plate is Cu, the generation of thermal stress due to the difference in thermal expansion between the ceramic substrate and the solder is unavoidable. Occurs and the high reliability is not sufficient. On the other hand, although Al is slightly inferior in heat conductivity and electric conductivity to Al, if Al is selected as a material of a circuit and a heat sink (hereinafter, both the circuit and the heat sink are also referred to as “circuits”), Even if it receives a thermal stress, it is easily plastically deformed, so that the stress applied to the ceramic substrate and the solder is alleviated, and the reliability is dramatically improved.

[0005]

However, a problem with Al is that it is expensive. A method of forming a circuit or the like using Al includes (1) a molten metal method in which molten aluminum is brought into contact with a ceramic substrate and cooled to produce a joined body thereof, and then the Al plate is mechanically ground to adjust its thickness, and then etched. (2) There is a method of etching after brazing an Al foil or an Al alloy foil, but in both cases, the cost is about 2 to 5 times that in the case of forming a circuit or the like using ordinary Cu. At such a high cost, it is unlikely that the product will be widely used for purposes other than special purposes.

[0007] Apart from the molten metal method, which has low production efficiency, the main cause of the increase in the cost of the Al circuit or the like over the Cu circuit or the like by the brazing method is that the bonding conditions are extremely narrow. That is, the melting temperature of Al (660 ° C.) and the joining temperature (for example,
In the case of Al-Si system, which is the most common brazing material, 63
(About 0 to 650 ° C.), so that Al is locally melted and a brazing defect (that is, an insect-eating phenomenon that has occurred in a circuit or the like) is likely to occur. Requires labor.

Another problem is that it is difficult to obtain a thin alloy foil. Many of the techniques proposed so far use alloy foils in their embodiments, but there is no commercially available thin alloy foil of about several tens of μm that can be used for bonding circuit boards. To obtain this, a special order of 1 ton or more is required, and it is difficult to consider the practical application.

[0008] The present invention has been made in view of the above, and uses an Al-Si-Mg-based metal powder, which has not been omitted so far, as a joining material, and has a specific thermal conductivity and surface characteristics. The inventors have found that an aluminum circuit and the like can be easily formed by applying pressure and bonding under specific conditions to form an Al circuit and the like, and the present inventors have made extensive studies and completed the present invention.

An object of the present invention is to provide a circuit board in which an aluminum or aluminum alloy circuit is formed on an aluminum nitride substrate while maintaining high reliability and at a low cost.

[0010]

That is, the present invention relates to a circuit board in which a circuit is formed on one surface of an aluminum nitride substrate and a radiator plate is formed on the other surface. / MK or more, the X-ray peak intensity ratio due to CuKα on the surface is 3 ≦ Y ₂ O _3.
Al ₂ O ₃ / AlN ≦ 18, 2Y ₂ O ₃ .Al ₂ O ₃ / AlN
≦ 3, and the material of the circuit and the heat sink is Al
And / or an aluminum alloy, wherein the bonding between the aluminum nitride substrate and the circuit and the heat sink is performed by heat treatment of a metal powder paste containing Al, Si and Mg. It is a substrate.

[0011] The present invention also provides a solid plate or pattern of Al and / or an Al alloy disposed on the front and back surfaces of the aluminum nitride substrate via the metal powder paste, and the solid plate or pattern is set at a temperature lower than the final bonding temperature by 10%. In a temperature range lower by about 30 ° C., the temperature is raised so as to be maintained for 15 minutes or more, the temperature is increased to the final bonding temperature, then cooled, and, if necessary, etched to form a circuit and a heat sink. A pressure of 10 to 100 kgf / cm ^{2 in} a direction perpendicular to the surface of the aluminum nitride substrate at least in a temperature range of 400 ° C. or higher.

[0012]

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

The most important feature of the present invention is that an aluminum nitride substrate having a specific thermal conductivity and surface characteristics,
-Heat treatment with Mg-based metal powder under specific conditions,
The point lies in joining Al or an Al alloy.

In the past, in the case of Al or Al alloy bonding, there has been a report that a paste is used for metal-metal bonding, but in ceramic-metal bonding, Al-Si is used.
System, Al-Si-Mg system, Al-Ge system, Al-Si-
Ge-based alloy foils have been used. However, the alloy powder itself has a well-established production method as a so-called atomized powder, and its composition can be selected relatively freely.
There is an advantage that it can be easily obtained in units of g to several tens of kg, and that a third metal can be added.

The first feature of the present invention is to use a metal powder having such an advantage, particularly an Al-Si-Mg alloy powder. The use of Al-Si-Mg as a brazing material itself is described in JP-A-4-12554, but it is an alloy foil, not a metal powder.

In a circuit board on which a Cu circuit or the like, which is currently the mainstream, is formed, the formation of the Cu circuit or the like is almost always performed using a metal powder paste. The method is advantageous in terms of process. For example, since pattern printing can be performed, there is an advantage in that handling inconvenience unlike alloy foil can be eliminated, a size and a shape can be selected, and a non-joined portion (a portion where a circuit is floated without intentionally joining) is easily provided. .

The metal powder used in the present invention is, by weight percentage in the metal powder, 4 to 13% of Si, 0.5 to 8% of Mg,
Al is preferably 85 to 95%. If Si is not within this range, the melting point will be high, making it difficult to perform uniform melting upon joining. Mg is a bonding promoter,
In particular, it is possible to improve the adhesion to the aluminum nitride substrate and to perform stable bonding. Mg is 0.5%
If it is less than 8%, the effect will be insufficient, and if it exceeds 8%, it will diffuse into Al and Al alloy and harden, and the resistance of the circuit board to the thermal history will decrease. Particularly preferably, Si5
11%, Mg 1 to 6%, and Si ≧ Mg.

In the present invention, the addition of a third metal other than Al-Si-Mg is permissible. Not to mention inevitable impurities, trace components mixed into the JIS alloy do not cause any problem. In addition, Bi, Ti, and the like for improving adhesion, such as Ge and Zn, which have a melting point lowering action, can be positively added within a total range of 5% or less.

The particle size of the metal powder is preferably 44 μm, and the average diameter is preferably several μm to 20 μm. Further, it is preferable that the mixed oxygen amount of the metal powder is as low as possible,
1% or less, preferably 0.7% or less, particularly preferably 0.1% or less.
5% or less.

The metal powder may be a mixed powder of a single metal powder or an alloy powder. However, Mg alone is very easily oxidized and difficult to handle, so that an alloy with Al and / or Si is used. It is preferable to use them.

The metal powder paste can be prepared by adding an organic binder, a solvent, and, if necessary, a reducing agent or a cleaning agent to the metal powder and mixing them. A typical example of the organic binder is an acrylic polymer that decomposes monomers, and examples of the solvent are isophorone and terpineol. Further, as a reducing agent or a cleaning agent, NaCl, KCl, LiCl, ZnCl ₂ ,
Chloride such as KF and AlF ₃ , fluoride and titanium hydride are well known.

The application of the metal powder paste can be performed by screen printing, roll coating, or the like.
The metal powder paste can be applied to the aluminum nitride substrate side, Al or Al alloy side, or both.

The second feature of the present invention is that the ceramic substrate has a thermal conductivity of 130 W / mK or more and the surface has an X-ray peak intensity ratio of 4 ≦ Y ₂ O ₃ due to CuKα.
・ Al ₂ O ₃ / AlN ≦ 20, 2Y ₂ O ₃ .Al ₂ O ₃ / Al
An aluminum nitride substrate having a surface characteristic of N ≦ 3 is used. Accordingly, the aluminum nitride substrate having high thermal conductivity can be bonded to Al or an Al alloy with a sufficient size without performing complicated surface treatment such as oxidation treatment.

The aluminum nitride substrate used in the present invention is a substrate fired using Y ₂ O ₃ as a sintering aid, and has a surface phase of Y ₂ O ₃ —Al ₂ O ₃ system other than AlN. 2Y
₂ O ₃ · Al ₂ O ₃ , Y ₂ O ₃ · Al ₂ O ₃ , 3Y ₂ O ₃ · 5Al
₂ O _{3 and the} like. Of these, Y ₂ O ₃ · Al ₂ O ₃ , 3Y ₂ O ₃ · 5
An _{Al 2 O 3, 2Y 2 O} 3 · Al 2 O 3 has a not very good wettability with the brazing material. On the other hand, if the amount of Y ₂ O ₃ .Al ₂ O ₃ is too large, the transverse rupture strength decreases, so that 3 ≦ Y ₂ O _3.
Al ₂ O ₃ / AlN ≦ 18, 2Y ₂ O ₃ .Al ₂ O ₃ / Al
N ≦ 3, preferably 4 ≦ Y ₂ O ₃ .Al ₂ O ₃ / AlN ≦
In 16 it is important that 2Y ₂ O ₃ .Al ₂ O ₃ / AlN ≦ 2.

In the present invention, the intensity ratio of X-rays by CuKα is expressed as AlN (101) plane, 2Y ₂ O ₃ .Al ₂ O ₃ (2
01) plane, Y ₂ O ₃ .Al ₂ O ₃ (121) plane, 3Y ₂ O _3.
A value obtained by multiplying the diffraction line intensity ratio of the 5Al ₂ O ₃ (321) plane by 100 is adopted. Specific methods for keeping these values within the above range include (a) the composition ratio of Al ₂ O _{3 component} and Y ₂ O _{3 component} in the raw material powder, and (b) oxygen before firing (after degreasing). Increase amount,
(C) firing temperature and the like.

For example, 2Y_TwoO_Three・ Al_TwoO_ThreeWhen there are many
Is relatively Al_TwoO_ThreeYou only need to increase the amount
Use a lot of raw material AlN_TwoO_ThreeOr add
Y_TwoO_ThreeTake measures such as reducing the minutes. On the other hand, Y_TwoO_Three・ Al
_TwoO_ThreeIf there are many, Y_TwoO _ThreeReduce the amount of addition or baking
Decrease temperature. In addition, if degreasing is performed in air, Al_TwoO_Three
Minutes can be increased.

The third feature of the present invention is a heat treatment condition, which is performed under specific conditions while applying pressure. That is,
In a temperature range of 10 to 30 ° C. lower than the final bonding temperature, the temperature is raised to the final bonding temperature while maintaining the temperature for at least 15 minutes, and then cooled. The final joining temperature is
It depends on the alloy composition of the paste, the type of Al or Al alloy, the size and shape of the circuit board, etc.
610 ° C.

In the present invention, Al-
Since the Si-Mg-based metal powder is used, in order to sufficiently exert the above-described bonding promoting action of the Mg component, the state may be maintained or passed slowly in a temperature range where the vapor pressure of Mg is high. . However, at very high temperatures, M in Al
Since the diffusion of g progresses and the curing becomes remarkable, it is appropriate to hold for 15 minutes or more, preferably 15 to 90 minutes, particularly 15 to 60 minutes in a temperature range 10 to 30 ° C. lower than the final bonding temperature.

In this case, it is particularly important to apply a pressure of 10 to 100 kgf / cm ^{2 in} a direction perpendicular to the aluminum nitride substrate surface at least in a temperature range of 400 ° C. Al or Al alloy is 300-350 ° C
As can be seen from the fact that the metal is annealed at a temperature of 500 ° C. or more, it becomes a very soft metal. Therefore, even if the above-mentioned soldering defect occurs, the defect is not crushed by applying pressure in this temperature range.

Usually, in the manufacture of a circuit board, a metal plate and
Applying weight and pressing when joining ceramic substrates
The pressure is at most 0.1 kgf /
cm ^TwoIt is about. At this level of pressure, ceramics
The metal plate follows only the relatively gentle warpage and undulation of the substrate
Can not. In contrast, in the present invention, 10 to 10
0kgf / cm^TwoAnd insane high pressure with conventional technology
I can. This makes the aluminum nitride substrate particularly stringent.
Without the need for smoothness and flatness,
It can be used as it is, and joining and productivity
improves.

The pressing direction is a direction perpendicular to the aluminum nitride substrate, and the method and the like are not particularly limited. As described above, a method of placing a weight, a method of mechanically sandwiching with a jig or the like, and the like are adopted.

In the present invention, there is no particular limitation on the steps after joining Al or Al alloy. When a solid plate of Al or Al alloy is joined, a normal resist,
A circuit or the like is formed by an etching process. On the other hand, when a pattern such as a circuit of Al or an Al alloy is joined, a circuit or the like is formed on the aluminum nitride substrate at the stage of joining, so that no special treatment is required.

According to the above method, in a circuit board in which a circuit is formed on one surface of the aluminum nitride substrate and a heat sink is formed on the other surface, the aluminum nitride substrate has a thermal conductivity of 130 W / mK or more. When the X-ray peak intensity ratio of CuKα on the surface is 3 ≦ Y ₂ O ₃ .Al ₂ O ₃ / AlN ≦
Is of _{18,2Y 2 O 3 · Al 2 O} 3 / AlN ≦ 3,
The material of the circuit and the heat sink is Al and / or an Al alloy, and the bonding between the aluminum nitride substrate and the circuit and the heat sink is performed by heat treatment of a metal powder paste containing Al, Si, and Mg. , The circuit board of the present invention.

[0034]

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

Examples 1-4, Comparative Examples 1-3

The aluminum nitride substrate used had a thickness of 0.635 mm and a size of 2 inch square. That X
Table 1 shows the surface phases obtained by the line diffraction. Metal plate is Al plate 1
085 material of 0.5 mm. Bonding is 10 ^-3 Pa in vacuum
I went in. Other conditions are shown in Table 1.

For each sample, an Al plate was arranged on the front and back surfaces of the aluminum nitride substrate via a bonding material, and the aluminum plate was uniformly pressed in a vertical direction on the aluminum nitride substrate by a hot press device.

The bonding material is (a) Al-9.5% Si-1
% Mg alloy foil (50 μm thick), (b) Al-15% Ge
Alloy foil (50 μm thick), (c) Al-10% Si-5% M
g of N ₂ metal powder atomized to an average diameter of 10μm in the paste, (d) Al-7% Si-4% Mg average diameter 8μm the atomized metal powder paste in N _2,
(E) A metal powder obtained by atomizing Al-3.3% Mg to an average diameter of 20 μm in N ₂ was mixed with a Si powder having an average diameter of 5 μm,
This is a metal powder paste blended to be 1-6% Si-3% Mg.

The bonded bodies were manufactured 100 by 100, and three times enlarged using soft X-rays to detect poor bonding and brazing defects. The lower limit of detection is about 0.3 mmφ.

Further, 10 sheets of each of the joined bodies were extracted, and the surrounding 2 mm was etched with a FeCl ₃ solution to form an electroless Ni—
P plating is performed at 5 μm to form a circuit board.
A heat history test of 3000 cycles was performed with one cycle of minutes → room temperature, 10 minutes → 125 ° C., 30 minutes → room temperature, 10 minutes. After checking the appearance abnormality such as swelling and peeling of the circuit board after the test, the circuit and the radiator plate were dissolved and removed, and the occurrence of cracks in the aluminum nitride substrate was examined by an ink test method (red check). Table 2 shows the results.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from Tables 1 and 2, all of the examples of the present invention exhibited a good bonding state, whereas the comparative example had many failures and was unstable with low productivity. It was a good joint. In addition, surprisingly, all of the examples of the present invention were superior to the comparative example using the alloy foil.

[0044]

According to the present invention, it is possible to obtain a highly reliable circuit board in which an aluminum or aluminum alloy circuit and a radiator plate are formed on an aluminum nitride substrate stably at low cost.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihiko Tsujimura 1 Shinkaicho, Omuta-shi, Fukuoka Denki Kagaku Kogyo Co., Ltd. Inside the Omuta plant (72) Inventor Katsunori Terano 1 Shinkaicho, Omuta-shi Fukuoka 1 Denki Kagaku Kogyo Co., Ltd. F-term in Omuta factory (reference) 4E351 AA09 BB01 BB31 BB38 CC11 CC22 CC31 CC40 DD10 DD28 DD52 DD60 GG04 4G026 BA16 BB27 BF31 BF33 BF44 BG02 BG03 BG06 BH07 5E338 AA18 BB63 BB71 BB75 EE02 EE31

Claims (2)

[Claims] 1. The method according to claim 1, further comprising the step of:
Circuit board with a heat sink formed on the other side
The aluminum nitride substrate has a thermal conductivity of 130 W /
Above mK, X-ray peak intensity of CuKα on the surface
The ratio is 3 ≦ Y_TwoO _Three・ Al_TwoO_Three/ AlN ≦ 18,2Y_TwoO_Three
・ Al_TwoO_Three/ AlN ≦ 3.
The material of the hot plate is Al and / or an Al alloy, and
Contact between the aluminum nitride substrate and the circuit and heat sink
When the heat of the metal powder paste containing Al, Si and Mg
Characterized by being performed by processing
Circuit board. 2. The method according to claim 1, wherein the metal powder paste is provided on the front and back surfaces of the aluminum nitride substrate according to claim 1.
Placing a solid plate or pattern of l and / or Al alloy,
In a temperature range of 10 to 30 ° C. lower than the final bonding temperature, the temperature is raised so as to be maintained for 15 minutes or more to raise the temperature to the final bonding temperature, then cooled, and if necessary, etched to perform circuit etching. And a method of forming a heat sink, wherein a pressure of 10 to 100 kgf / cm ² is applied in a direction perpendicular to the aluminum nitride substrate surface at least in a temperature range of 400 ° C. or more.