JP2001053404A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a circuit board by using metallic plates respectively composed of plural layers including Al and Cu layers for metallic circuits and metallic heat sinks, and bonding the Al layer to an aluminum nitride substrate with an Al-Si-Mg or Al-Cu-Mg bonding material. SOLUTION: A circuit board is formed in such a way that metallic plates are laid on both the front and rear surfaces of an aluminum nitride substrate and bonded to the substrate, by evenly perpendicularly pressing the metallic plates against the substrate at a temperature of 550-635 deg.C in a vacuum atmosphere by using a jig which presses the metallic plates against the substrate by thrusting carbon plates into the substrate. Then an etching resist is screen- printed and etching is performed with an FeCl3 solution. In addition, the resist is removed and electroless Ni-P plating is performed to the thickness of 3 μm. The circuit board thus formed has metallic heat sinks using metallic plates each composed of two or more layers including Al and Cu layers. The Al layer is bonded to the aluminum nitride substrate by using an Al-Si-Mg bonding material, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a 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 on which the circuit and the heat sink are formed is used. Such a circuit board is characterized in that high insulation properties can be obtained more stably than a composite board of a resin board and a metal board or a resin board.

When the material of the circuit and the heat radiating plate is Cu or Cu alloy, the generation of thermal stress due to the difference in thermal expansion between the ceramic substrate and the solder is inevitable, so that the long-term reliability is insufficient. On the other hand, since Al or an Al alloy is easily plastically deformed even when subjected to thermal stress, the stress is relieved, and the reliability is dramatically improved. On the other hand, Cu or Cu alloy is
Since it is superior in thermal conductivity and electrical conductivity, it is superior in essential characteristics required for a power module substrate. There is also a proposal of a technique for combining them to ensure long-term reliability without impairing thermal and electrical characteristics (for example, see Japanese Patent Application Laid-Open No.
No.-53076).

[0004]

However, Al and an Al alloy (hereinafter, both are collectively referred to as "Al etc.") and Cu or a Cu alloy (hereinafter, both are referred to as "C
u etc. " ), The method of combining Al
In order to avoid the formation of an Al-Cu-based brittle alloy due to the reaction between Cu and Cu, a barrier layer is required between the two, and in practice, three or more layers are stacked. Since these layers have different bonding temperatures for each material, it is difficult to completely bond all the layers. In particular, Al and the like have a low melting point, a low bonding temperature, and are materials that are difficult to bond with ceramics. Further, when the bonding is performed at a temperature close to the melting point, the bonding with the metal plate is improved, but partial melting occurs in Al and the like, and voids called “insect biting” occur. Conversely, if a low melting point brazing material is used to join the aluminum nitride substrate at a low temperature, the joining with the metal layer becomes insufficient. That is, there is a problem that satisfying the joining of the two at the same time is a trade-off.

The present invention has been made in view of the above, and has grasped that it is the oxide layer on the surface of Al or the like that controls the bonding between the metal plate and Al at a relatively low temperature. As a result of intensive studies on the composition of the bonding material between Al and the like and the aluminum nitride substrate in order to remove the influence, it was found that if a bonding material with a specific composition is used, the bonding of the metal plate with Al or the like can be sufficiently performed. This has been thoroughly pursued and the present invention has been completed.

An object of the present invention is to simultaneously apply Al or the like to an aluminum nitride substrate, or to simultaneously bond an Al or the like to a copper plate, thereby enabling a metal plate combining Cu and Al to be applied to an aluminum nitride substrate. It is to provide a circuit board incorporating the advantages of the above.

[0007]

That is, according to the present invention, an aluminum nitride substrate has a metal circuit on one surface and a metal radiator plate on the other surface, and the metal circuit and the metal radiator plate are made of Al and C.
u is made of two or more metal plates, and the Al layer is made of Al.
A circuit board, which is bonded to an aluminum nitride substrate using a Si-Mg-based or Al-Cu-Mg-based bonding material.

[0008]

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 Al-Si-Mg or Al-
That is, a Cu—Mg based bonding material is used. This enables joining at a relatively low temperature such that local melting does not occur in Al or the like, and also satisfies the joining between Al or the like and the metal plate.

Originally, Al is a material which can be pressed against almost all metal materials, and various clad materials including Al-Al alloys and Al-Cu are commercially available. On the other hand, it is relatively difficult to join Al and the aluminum nitride substrate. For example, an Ag brazing material having a high melting point cannot be used, and an Al-based low melting point joining material is used. Al-Si and Al-Zn are typical compositions.

It is important to remove the oxide on the surface of the Al material for the bonding between Al and the like and the metal, and the Nocolok method using a fluorine-based surface cleaning agent is well known. However, in this method, it is necessary to remove the residue after joining, and the process becomes complicated. On the other hand, when joining metals and ceramics, we ensure the wettability between the joining material and the aluminum nitride substrate.
An active metal method including an active metal such as Ti or Zr is often used. Active metals are often added in the form of hydrides because hydrides are easily formed and hydrides are relatively resistant to oxidation.However, these additives that decompose to generate hydrogen gas are also included. Has a cleansing action. However, since this addition simultaneously raises the melting point of the joining material, there is a problem that local melting is easily generated in the Al material.

In the present invention, in order to solve these problems at once, Al-Si-Mg or Al-C
u-Mg is used. An appropriate amount of Mg to be added is 0.1 to 6% by weight. If the amount exceeds 6% by weight, the diffusion portion hardens into the Al material to be joined, and the thermal stress buffering effect is reduced. If the amount is less than 0.1% by weight, the bondability to aluminum nitride or metal is inferior. Preferably, it is 0.2 to 3% by weight. Although the detailed mechanism of the effect of the addition of Mg is not clear, the metastable M
It is supposed that g ₂ N ₃ is generated to improve the wettability with the bonding material, and to form MgO on the metal to remove the oxide on the Al surface.

In the present invention, the Al layer to be bonded to the aluminum nitride substrate has a thickness of 50 to 200 μm. 50μ
If it is less than m, the effect of buffering thermal stress due to plastic deformation is insufficient and reliability is inferior. If it exceeds 200 μm, joining with the metal joined to the Al layer becomes insufficient. Particularly preferably 70
１５０150 μm. Although it is generally said that Mg acts on the bonding as vapor, from the above point, it is thought that it diffuses in Al or the like to reach the opposite end face, and removes the oxide film on the surface. Can be In fact, the diffusion of Mg in a layer of Al or the like is much faster than that of a metal such as Si, Cu or Zn.

As a bonding material component other than Al and Mg, S
i and Cu. Si has the lowest melting point at 12% by weight, but has a problem in that the Si content becomes brittle when the amount of Si is large.
10% by weight is preferred. If it is 3% by weight or less, the bonding temperature approaches the melting point of Al or the like, which causes the formation of defects such as Al. When Cu is used, 2 to 6% by weight is suitable. When Si and Cu are used simultaneously, Si 4 to 9
% By weight, and 0.5 to 3% by weight of Cu.

In the present invention, Al, Si, Cu, M
Addition of a third metal other than g is acceptable. Not to mention inevitable impurities, trace components mixed into the JIS alloy do not cause any problem. Also, In, Ge, Z having a melting point lowering action
Bi, Ti, etc. for improving the adhesion, such as n, can be positively added within a total range of 5% or less.

In the present invention, the metal bonded to Al or the like is a layer containing Cu. However, as described above, since Al and Cu form a brittle alloy, a barrier layer that prevents a reaction between them is used. Is preferably placed. The material of the barrier layer is preferably a material that facilitates the formation of a foil and that reacts slowly with Cu and Al at the bonding temperature.
Ti, Cr and alloys containing these as main components. A
Although l and the like and the barrier layer, Cu and the like may be separately laminated and bonded, the barrier layer may be plated in advance on the surface of Cu or the like or Al or formed into a clad. Three or more layers may be clad and used. Furthermore,
After joining and forming the circuit, another surface layer may be further provided by plating or the like.

As for Cu and the like, there are no particular restrictions on the material and the like as in the case of a normal ceramic circuit board.
The thickness is usually 0.1 to 0.5 mm. By providing this layer, the same electrical conductivity as that of a circuit board using Cu or the like can be ensured, and the heat dissipation of the composite board is improved as compared with the case where Al is used alone. Furthermore, although it is generally considered that electroless plating on Al or the like is more difficult than Cu or the like, in the present invention, since the layer of Al or the like has the same potential as the layer of Cu or the like joined, Plating can be performed in the same manner as plating on ordinary Cu.

As for the aluminum nitride substrate used in the present invention, an aluminum nitride substrate having a thermal conductivity of 130 W / mK or more and good insulating properties is selected in consideration of use as a circuit board for a power module.

The method of manufacturing a circuit board according to the present invention will be described. In order to form a metal circuit and a metal radiator plate on an aluminum nitride substrate, the patterns must be bonded or
There is a method in which a metal plate is bonded and then etched, or both are used in combination. The thickness of the joining material is 10 to 50 μm although it depends on the type. If the thickness is less than 10 μm, joining becomes difficult. If the thickness exceeds 50 μm, the hardened layer in Al formed by the diffusion of alloy components expands, which causes a decrease in reliability when subjected to thermal history. Preferably 15 to
35 μm. The bonding material is the aluminum nitride substrate side,
It may be arranged on either side of Al or the like.

As a joining material, there is a method using an alloy foil.
In circuit boards on which circuits such as Cu, which are the current mainstream, are formed, the paste method is more process-intensive as can be understood from the fact that it is almost always performed using a metal powder paste. It is advantageous. For example, since pattern printing can be performed, there is an advantage 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. .

When the paste method is used, the bonding material metal powder is used by being mixed with an organic binder or an organic solvent.
Typical examples of the organic binder include acrylic polymers, and examples of the solvent include isophorone and terpineol.

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,
It is at most 1%, preferably at most 0.7%, particularly preferably at most 0.5%.

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 may be used. It is preferable to use them.

In the present invention, a plate, a pattern, or both of each metal layer is disposed on both sides of an aluminum nitride substrate via the above-mentioned bonding material, and is placed in a direction perpendicular to the aluminum nitride substrate at a pressure of 15 to 100 kgf / cm ² . Is preferably applied. Pressing can be performed by placing a weight on the laminate, mechanically sandwiching it with a jig or the like, or the like.

Conventionally, in the manufacture of a circuit board, when a metal plate and a ceramics substrate are joined together, a weight is placed on them and pressurized.
It is about 1 kgf / cm ² . With such a pressure, the metal plate can follow only a relatively gentle warpage or undulation of the ceramic substrate. In contrast, 15-1
When a high pressure of 00 kgf / cm ² is applied, sufficient bonding can be stably obtained, and plastic deformation of Al or the like occurs relatively uniformly, so that a highly reliable circuit board can be manufactured. Preferred pressure is 20 to 80 kgf / c.
m ² .

Next, the joined body is etched as necessary. Etching is not particularly necessary when the circuit or heat sink pattern is joined. The etching can be performed by a usual resist and etching process.

[0027]

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

Examples 1 to 4 Comparative Examples 1 to 3 The aluminum nitride substrates used were commercial products, each having a thickness of 0.635 mm, a size of 2 inches square, and a thermal conductivity of 180 W / mK by a laser flash method. The three-point bending strength is 430 MPa. Table 1 shows the bonding materials. For each metal plate, a combination of each type and thickness shown in Table 2 was used for the circuit surface and the heat radiation surface.

A metal plate was placed on the front and back surfaces of the aluminum nitride substrate, and a carbon plate was screwed on and pressed uniformly against the aluminum nitride substrate using a jig pressed against the substrate. Bonding is performed in a vacuum atmosphere at a temperature of 550 to 63
The test was performed while applying pressure at 5 ° C. Table 1 shows the joining conditions.

After bonding, the etching resist was screen-printed and etched with a FeCl ₃ solution. Next, after the resist was peeled off, electroless Ni-P plating was applied at 3 μm to obtain a circuit board.

The obtained circuit board is -40 ° C. × 30 minutes →
A heat cycle test of 3000 cycles was performed with room temperature × 10 minutes → 125 ° C. × 30 minutes → room temperature × 10 minutes as one cycle. After the heat cycle test, the appearance of the substrate such as pattern peeling was checked for damage to the substrate. The metal circuit and the metal radiator plate were dissolved with hydrochloric acid, and the aluminum nitride substrate was observed for cracks. Table 3 shows the results.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

As is clear from Tables 1 to 3, in each of the examples of the present invention, the occurrence of cracks on the substrate was significantly reduced even after 3000 cycles of the heat cycle test.
In contrast, in the comparative example, since the bonding material composition and the thickness of Al and the like were out of the range of the present invention, cracks frequently occurred on the aluminum nitride substrate after heat cycling, and pattern peeling was observed. However, it was insufficient for a flexible circuit board.

[0036]

According to the present invention, it is possible to provide a highly reliable circuit board combining Cu or the like and Al or the like.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihiko Tsujimura 1 Shinkaicho, Omuta-shi, Fukuoka Prefecture Inside the Omuta Plant, Inc. Omuta factory F-term (reference) 4E351 AA09 BB01 BB33 BB35 BB38 BB50 CC18 CC21 DD04 DD10 GG03 GG04

Claims (1)

[Claims] 1. An aluminum nitride substrate having a metal circuit on one surface and a metal radiator plate on the other surface, wherein the metal circuit and the metal radiator plate comprise two or more metal plates containing Al and Cu,
And the Al layer has a thickness of 50 to 200 μm and is made of Al-Si-M
A circuit board, which is bonded to an aluminum nitride substrate using a g-based or Al-Cu-Mg-based bonding material.