JP2001053199A - Circuit board manufacturing method - Google Patents

Abstract

(57) [Problem] To provide a highly reliable circuit board capable of remarkably reducing not only the occurrence of cracks in a solder or an aluminum nitride substrate but also the peeling damage of bonding wires and plating. An aluminum nitride substrate has Al-
An Al plate is arranged via a joining material of a Cu-Mg alloy foil,
This is a method of forming an Al circuit on one surface of an aluminum nitride substrate and forming an Al radiator plate on the other surface by etching after producing a joined body by heat-treating the joined body.
The plate is a rolled Al plate having a thickness of 0.2 mm or more, a rolling reduction of 10% or more, and not subjected to a softening heat treatment after cold working, and the aluminum nitride substrate has an X-ray diffraction peak intensity ratio of 3Y ₂ O ₃ · 5Al ₂ O ₃ × 100 / AlN ≦
3. A method of manufacturing a circuit board, wherein 2Y ₂ O ₃ .Al ₂ O ₃ × 100 / AlN ≦ 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing 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, a Cu or Al circuit and a heat sink are formed on the front and back surfaces of a ceramic substrate such as alumina, beryllia, silicon nitride, and aluminum nitride, respectively. Circuit board 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.

[0003] The material of the circuit and the heat sink is made of Al rather than Cu.
The advantage is that in Cu, the generation of thermal stress due to the difference in thermal expansion between the ceramic substrate and the solder is inevitable,
While long-term reliability is insufficient, Al is slightly inferior to Cu in thermal conductivity and electrical conductivity, but easily undergoes plastic deformation even when subjected to thermal stress, so the stress is relaxed, The reliability is to be dramatically improved.

[0004]

However, the above-mentioned plastic deformation of Al significantly differs depending on the type of Al. In particular, when the plastic deformation is concentrated on a part of the circuit or the heat radiating plate, plating or peeling of the bonding wire occurs. In order to avoid this, if Al having high hardness is used, the stress relaxation effect naturally decreases. Therefore, there is a problem that it is necessary to achieve the trade-off between plastic deformation to such an extent that it can be used without trouble as a circuit and a heat sink while sufficiently maintaining the stress relaxation effect.

In order to solve this problem, conventionally, a plating composition (Japanese Patent Application Laid-Open No. 8-260187), a surface modification of a ceramic substrate (Japanese Patent Application Laid-Open No. 8-260186), and a particle size regulation of an Al plate (Japanese Patent Application Laid-Open No. 156330), but they have not been fully satisfactory. That is, cracks often occur in the solder or ceramic substrate, and the bonding wires and plating often peel off.

As a result of various studies in view of the above, the present inventor has found out of many Al materials, an Al material which is relatively easy to cause plastic deformation due to thermal stress relatively uniformly, and at the same time, has specified a ceramic substrate. The present inventors have found that the above problem can be solved to a high degree by using an aluminum nitride substrate having an agent phase and bonding both using a bonding material of a specific component, thereby completing the present invention.

An object of the present invention is to provide a highly reliable circuit board which not only prevents cracks in solder and ceramic substrates but also significantly prevents peeling of bonding wires and plating.

[0008]

That is, according to the present invention, an Al plate is arranged on the front and back surfaces of an aluminum nitride substrate via a bonding material of an Al-Cu-Mg alloy foil, and the Al plate is heated and bonded. A method of forming an aluminum circuit on one surface of an aluminum nitride substrate and forming an aluminum radiator on the other surface, wherein the aluminum plate has a thickness of 0.2 mm or more and a rolling reduction of 10 mm. % Or more and not subjected to a softening heat treatment after cold working, and the aluminum nitride substrate has an X-ray diffraction peak intensity ratio of 3Y ₂ O ₃ .5Al ₂ O ₃ × 100 / AlN ≦ 3 and 2Y ₂ O ₃ .Al ₂ O ₃ × 100 / AlN ≦ 1.

[0009]

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

A feature of the present invention is that, by optimizing the workability of an aluminum nitride substrate and an Al plate to be joined and a joining material, plastic deformation of the Al plate is relatively uniformly generated and the aluminum plate is firmly joined. Thus, the peeling of the plating and bonding wires and the generation of cracks in the solder and the ceramic substrate are significantly reduced.

The first measure taken by the present invention is to define the working ratio of the Al plate, and to use a rolled Al plate which is not subjected to softening heat treatment after cold working at a rolling reduction of 10% or more. is there.

The Al material has dozens of temper levels even if it is specified only in JIS, and has different physical properties such as hardness, tensile strength and moldability. This is due to the fact that the orientation, distortion, defects, and the like of the crystal of the Al material are easily changed by the cross-sectional reduction rate during rolling and the heat treatment. When used for a circuit board, the characteristics of the raw material Al plate have a strong effect even after bonding at a high temperature, so that the characteristics must be used after fully understanding these characteristics. Therefore, for example, the molten metal method of directly joining a molten Al material (for example, Japanese Patent Application Laid-Open No. 8-208359) is not suitable because the tempering of the Al material is difficult.

[0013] That is, the Al material obtained by the molten metal method is as-cast and has not been rolled. In such an Al material, plastic deformation is likely to be unevenly generated when subjected to thermal stress, and partial deformation is increased, causing plating, bonding wire peeling, and damage such as solder cracks. growing.

On the other hand, although the detailed mechanism is unknown,
Even if the circuit board is manufactured using an Al plate annealed like an O material or an Al plate with a very low workability such as an extruded or as-cast F material, heat shock or heat When subjected to the cycle, the plastic deformation is partially concentrated, causing similar disadvantages. The reason for this is that when joining an Al plate to an aluminum nitride substrate using a joining material, heat treatment is performed at a temperature higher than the softening temperature of Al, so that the joining material diffuses into the Al plate up to about 0.1 mm. It is thought to be related to that.

On the other hand, as in the present invention, a rolling reduction of 10
% Or more, and if a rolled Al plate that has not been subjected to softening treatment after cold working is used, since it is repeatedly rolled uniformly by a roll, relatively uniform plastic deformation is caused. Significantly reduced. The higher the rolling ratio of the Al plate, the more preferable it is because it causes uniform plastic deformation, but on the other hand, an excessively high rolling ratio limits the selection of materials and lacks stable supply.

If the Al plate used in the present invention is represented by a JIS symbol, it is H12 to H18, particularly preferably H14.
To H18. However, since the JIS symbol is defined by the tensile strength, it is not limited to this.
For example, a H24 material that has been softened and heat-treated may be purchased, and then rolled and used by 10% or more.

Regarding the thickness of the Al plate, it is necessary to ensure conductivity sufficient to cope with a large current for a power module application, and to ensure that the bonding material has a maximum thickness of 0.1 mm in the Al plate during the heat treatment.
Considering diffusion to about 1 mm, at least 0.
2 mm is required.

The higher the purity of the Al plate, the better the electrical and thermal characteristics, but the higher the purity, the higher the price. A commonly available product of about 99.85% by weight is sufficient.

A second measure taken by the present invention is the provision of an aluminum nitride substrate. The nitrided ceramic substrate used in the present invention is a substrate fired using Y ₂ O ₃ as a sintering aid, and the surface has an X-ray diffraction peak intensity ratio due to CuKα of 3Y ₂ O ₃ .5Al ₂ O _3. × 100 / AlN ≦ 3 and 2Y ₂ O ₃ .Al ₂ O ₃ × 100 / AlN ≦ 1. The aluminum nitride substrate having such surface characteristics can be used without performing complicated surface treatment such as oxidation treatment.
Using the Al-Cu-Mg alloy foil described below,
It can be joined with a board with sufficiently strong strength. The thermal conductivity of the aluminum nitride substrate is preferably 130 W / mK or more.

The auxiliary phase on the surface of the aluminum nitride substrate
Strongly affects compatibility, 2Y_TwoO_Three・ Al _TwoO_ThreeIf there are many joints
It will be difficult. On the other hand, 3Y_TwoO_Three・ 5Al_TwoO_ThreeMostly nitrided
Low thermal conductivity of luminium substrate for power modules
As inappropriate. Therefore, the present invention
In this case, both auxiliary phases are restricted as described above.

Adjustment of surface characteristics of aluminum nitride substrate
Represents Al in the raw aluminum nitride powder _TwoO_ThreeMinute and Y_TwoO_ThreeMinute
Composition ratio, (B) increased oxygen amount before degreasing and before firing, (C)
It can be performed depending on the firing temperature or the like. For example, 2Y_Two
O_Three・ Al_TwoO_ThreeWhen there are many, relatively Al_TwoO_ThreeMinutes
Aluminum nitride powder with high oxygen content
Use raw material or Al_TwoO_ThreeTo add Y_TwoO_ThreeReduce minutes
You. On the other hand, Y_TwoO_Three・ Al_TwoO_ThreeIf there are many, Y_TwoO_Threeof
Reduce the amount added or lower the firing temperature. In addition, degreasing
Al in air_TwoO_ThreeMinutes can be increased.

A third means adopted in the present invention is that an aluminum nitride substrate and a rolled Al plate are joined by using an Al-Cu-Mg alloy foil joining material. The reason is that the Al-Cu-Mg based alloy is a high-strength Al alloy or heat-resistant A
It is widely used as an alloy and is easy to make into a foil, which is advantageous in terms of cost. In addition, the Al-Cu-Mg-based alloy has Cu and Mg more uniformly in Al than Si or Ge. Due to easy diffusion, local melting occurs, excess bonding material is extruded and extrusion does not easily occur, and stable bonding can be performed in a relatively short time.

The thickness of the Al—Cu—Mg based alloy foil is set to 0.1.
It is preferably from 015 to 0.040 mm. If the thickness is less than 0.015 mm, joining becomes difficult, and 0.04 mm or less.
If the thickness exceeds 0 mm, the hardened layer in Al generated by diffusion of Cu and Mg expands, which causes a decrease in reliability when subjected to a thermal history. The Al-Cu-Mg-based alloy foil may be disposed on either the aluminum nitride substrate side or the Al plate side, or may be clad with the Al plate in advance.

In the method for manufacturing a circuit board according to the present invention,
First, an Al-Cu-Mg-based alloy foil is disposed between an aluminum nitride substrate and an Al plate, and heat-treated to produce a joined body. The bonding is performed by holding the substrate at a temperature of 580 to 650 ° C. for about 10 to 100 minutes in a non-oxidizing atmosphere such as nitrogen or a vacuum atmosphere. In this case, from 15 to 100 kgf /
It is preferable to apply a pressure of ² cm ² , particularly 20 to 80 kgf / cm ² , so that sufficient joining can be stably obtained, and plastic deformation of the Al plate occurs relatively uniformly. Pressing can be performed by placing a weight on the laminate, mechanically sandwiching it with a jig or the like, or the like.

In the present invention, instead of the Al plate, Al
The pattern of the plate may be heated and joined using the pattern instead of the Al-Cu-Mg alloy foil.
In this case, the post-etching process can be omitted in many cases.

Next, the joined body is etched, and a circuit having a desired shape and a heat sink are formed on the front and back surfaces of the aluminum nitride substrate. The etching can be performed by a normal process using a normal resist. Further, a surface treatment such as plating is performed on the formed circuit and the heat radiation plate as needed.

[0027]

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

Examples 1 to 3 Comparative Examples 1 to 5 All of the aluminum nitride substrates used were 2 inches square and had a thermal conductivity (n
Table 3 shows the three-point bending strength (average of n = 5) and the auxiliary phase (average of n = 3) by X-ray diffraction.

An aluminum plate is placed on the front and back surfaces of the aluminum nitride substrate via a bonding material, and heat treatment is performed while uniformly pressing the aluminum nitride substrate in the vertical direction using a jig into which a carbon-made pressing plate can be screwed. Was. Table 2 shows the Al plates and the joining materials used. The Al material used was not softened after cold working. Table 3 shows the joining conditions.

An etching resist was screen-printed on the obtained joined body, and was etched with a FeCl ₃ solution. Next, after the resist was stripped, electroless Ni-P plating was performed for 3 hours.
μm to produce a circuit board.

After bonding an Al wire to the circuit board by ultrasonic waves, a 13 mm square Si chip was soldered to the center. This was subjected to a heat cycle test for every ten sheets. Heat cycle test: -40 ° C x 30 minutes → room temperature x
3000 cycles were performed with 10 minutes → 125 ° C. × 30 minutes → room temperature × 10 minutes as one cycle. After the heat cycle test, after examining for damage such as peeling of bonding wires and solder cracks, dissolve the circuit and heat sink with hydrochloric acid,
The presence or absence of cracks in the aluminum nitride substrate was observed. Table 4 shows the results.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

As is clear from Tables 1 to 4, in each of the examples of the present invention, even after 3000 cycles of the heat cycle test, there was no damage to the bonding wires and plating, and cracks were significantly generated in the solder and aluminum nitride substrate. There were few. On the other hand, in Comparative Example 1 using a bonding material different from the present invention and Comparative Examples 4 and 5 in which the aluminum nitride substrate was out of the range of the present invention, the circuit pattern was peeled off after the heat cycle. In Comparative Example 3 in which the Al material was not within the scope of the present invention, peeling of the bonding wires and plating was observed, and cracks occurred in the solder and aluminum nitride substrates. Was something.

[0037]

According to the present invention, it is possible to manufacture a high-reliability circuit board which not only generates cracks in the solder or aluminum nitride substrate but also significantly reduces peeling damage of bonding wires and plating.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Katsunori Terano 1 Shinkaicho, Omuta-shi, Fukuoka Prefecture Inside the Omuta Plant of Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] An aluminum nitride substrate is provided with Al
-Place an Al plate via a joining material of a Cu-Mg alloy foil, heat-treat it to produce a joined body, perform etching, and perform an Al circuit on one surface of the aluminum nitride substrate;
A method of forming an Al heat radiating plate on the other surface, wherein the Al plate has a thickness of 0.2 mm or more, a rolling reduction of 10% or more, and is not subjected to softening heat treatment after cold working.
And the aluminum nitride substrate is 3Y ₂ O ₃ .5Al ₂ O ₃ × 100 / Al in X-ray diffraction peak intensity ratio.
N ≦ 3 and 2Y ₂ O ₃ .Al ₂ O ₃ × 100 / AlN ≦ 1
A method for manufacturing a circuit board, comprising: