JP3155885B2 - Circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board suitable for a power module for electronic components, particularly an intelligent power module.

2. Description of the Related Art In recent years, high-performance modules such as high-power and high-efficiency inverters have been transitioning along with high performance of industrial equipment such as robots and motors, and heat generated from semiconductor elements has been increasing steadily. . In order to efficiently dissipate this heat, various methods have conventionally been used for large power module substrates.

[0003] Recently, ceramic substrates made of aluminum nitride or the like having good heat conduction have become available, so that a metal plate such as a copper plate is bonded on the ceramic substrate to form a metal circuit, and then the metal circuit is directly or plated. The semiconductor element is mounted after the processing. In this case, a structure in which a heat-dissipating metal plate is provided on the surface opposite to the metal circuit surface for attachment to a heat sink is also employed.

[0004] On the other hand, there is a demand for further enhancement of functions, intelligence, and miniaturization. To meet the demand, a module having a structure in which a power unit and a control unit are combined has been studied, and some modules are commercially available. Its structure is a circuit board (hereinafter referred to as a “basic circuit board”) in which a copper circuit is formed on a ceramic substrate.
Power semiconductor element, power circuit,
A circuit board with a base terminal made of a glass epoxy or other base board separate from the basic circuit board for the purpose of detecting overcurrent and overvoltage, leaving a space for mounting the power section of the drive circuit etc. Hereinafter, these are referred to as “multi-purpose circuit boards”).

[0005] In such a two-stage circuit board, is it manufactured by soldering a multi-purpose circuit board while leaving a space for mounting a power portion on a copper circuit surface of a basic circuit board?
Alternatively, it has been proposed to bond with a rubber adhesive as described in the specification attached to Japanese Patent Application No. 6-22263.

However, this method has a problem that a considerable amount of labor is required for manufacturing and the cost is high. Furthermore, thermal stress is generated due to a difference in thermal expansion between the base substrate of the multi-purpose circuit board and the ceramic substrate of the basic circuit board due to a temperature cycle accompanying heat generation of the semiconductor element, and solder and the ceramic substrate are damaged, such as cracks. There is a problem that the reliability of the stepped circuit board is significantly reduced.

[0007]

As a result of various studies to solve the above-mentioned problems, the present inventors have provided portions having different thicknesses on the basic circuit board, and have exposed the metal circuit between the metal circuits.
The surface of the aluminum nitride substrate
Including 3ZrO ₂ · 2Y ₂ O ₃ by択的etching
The structure is such that a coating layer of an oxide layer is formed.
If this circuit board is provided with the function of a multi-purpose circuit board, the labor of joining the basic circuit board and the multi-purpose circuit board can be omitted, and
It has been found that generation of thermal stress due to difference in thermal expansion can be suppressed , and the present invention has been completed.

That is, the present invention provides 3ZrO ₂ · 2Y ₂
Aluminum nitride substrate and metal by bonding layer containing O ₃
The joined body formed by joining the plates is etched,
Aluminum substrate be one metal circuit or a metal circuit and the heat radiating metal plate has been formed, the different parts of the thicknesses present in the above aluminum nitride substrate <br/> and metal circuit, moreover the
Etching, aluminum nitride substrate between metal circuits 3
To be coated with an oxide layer containing ZrO ₂ .2Y ₂ O ₃
A circuit board characterized by being selectively performed , and an aluminum nitride-based circuit board in the circuit board.
Be present different portions of the thickness on only one surface of the plate, providing a rib on the aluminum nitride substrate, nitride Arumini
When the thickness of the metal substrate is A, the thickness of the metal circuit is B, and the thickness of the heat dissipating metal plate is C, A +
The value of B + C is constant, the power unit the thicker portion of the wall thickness of the metallic circuit, a circuit board, respectively, characterized by comprising a thin portion of the thick as a control unit consisting of a fine pattern.

Hereinafter, the present invention will be described in more detail.

The material of the ceramic substrate used in the present invention is aluminum nitride. As a method for allowing portions having different thicknesses to exist on the aluminum nitride substrate, aluminum nitride
There are a method of machining a minium sintered body, and a method of providing it at the stage of forming a green sheet by an extrusion molding method or the like.

FIG. 1 shows an example of the shape of an aluminum nitride substrate .
To 3. FIG. 1 shows a structure in which portions having different thicknesses are present on both surfaces of an aluminum nitride substrate , and the durability to a heat cycle is improved as compared with a structure in which it is present on only one surface. Figure 2 shows aluminum nitride
This is one in which portions having different thicknesses exist only on one side of the nickel substrate . The advantage of this shape is that it has
A metal plate can be easily attached .
FIG. 3 shows a structure in which ribs are provided in thin portions to reinforce the strength of the aluminum nitride substrate . The place where the rib is provided is not limited to the thin part, and may be the thick part or both.

As for the thickness of the aluminum nitride substrate, the thickness of the thick portion is 0.5 mm or more, particularly 0.6 mm or more, and the thickness of the thin portion is 0.3 to less than 0.5 mm. It is preferably 0.5 mm. Nitride
If the thickness of the thin portion of the aluminum substrate is too small, the strength is weakened, and if the thickness of the thick portion is too large, the heat resistance is disadvantageous.

The metal material of the metal circuit or the radiating metal plate used in the present invention is not particularly limited, and copper, nickel, a copper alloy or a nickel alloy is used. Is optimal. Also, there is no limitation on the thickness of the metal circuit, and it is desirable that the thickness be in the range of 0.1 to 0.5 mm. If the thickness of the metal circuit is too thin, the current capacity becomes small, and the capability of the circuit is limited. On the other hand, if the thickness of the metal circuit is too large, thermal stress due to the difference in thermal expansion is applied to the substrate, so that the durability of the circuit substrate is reduced. Since the portion requiring the current capacity is limited in the circuit board, only the portion requiring the current capacity is thickened. The thickness is desirably 0.3 to 0.5 mm, and the portion that does not require a current capacity may have the minimum necessary thickness, and about 0.1 to 0.2 mm is sufficient.

Circuit board [0014] The present invention is targeted, nitride
The metal circuit is formed on one surface of the aluminum substrate , and the heat dissipating metal plate formed on the other surface is arbitrary. When the heat-dissipating metal plate is provided, its thickness is suitably from 0.15 to 0.25 mm.

[0015] To form a metal circuit or a heat radiating metal plate is an aluminum nitride substrate, a brazing method using the brazing material containing an active metal bonding method using an organic adhesive, even by DBC method if metals are copper A method of manufacturing a joined body of an aluminum nitride substrate and a metal plate and etching the metal is preferable. When the thickness of the metal circuit or the heat radiating metal plate is small, it can be formed by a thin film metallization method, a thick film metallization method, a high melting point metallization method, or the like.

The active metal brazing method has an advantage that the durability against a heat cycle is large as compared with the DBC method. The metal component of the brazing material in the active metal brazing method is
An active metal is used as a secondary component in order to secure wettability with the aluminum nitride substrate at the time of melting, with silver and copper as main components. This active metal component reacts with the aluminum nitride substrate to form mainly nitrides, and these products form a brazing filler metal and an aluminum nitride.
Strengthen the bond with the minium substrate . Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium and compounds thereof. The proportion of the active metal is 3 to 35 parts by weight per 100 parts by weight of the total of 69 to 75 parts by weight of silver and 25 to 31 parts by weight of copper.

FIGS. 4 to 6 show an example of a joined body of an aluminum nitride substrate and a metal plate, and FIGS. 7 to 9 show an example of a circuit board manufactured from the joined body by an etching method. In the present invention, when the thickness of the aluminum nitride substrate is A, the thickness of the metal circuit is B, and the thickness of the heat-dissipating metal plate is C, the structure is such that the value of A + B + C is constant in any portion, thereby achieving a metal structure. There is an advantage that the work of applying an etching resist when forming a circuit and the work of wire bonding when assembling a circuit board into a module can be performed on the same plane.

As a method for forming a metal circuit, a method in which an etching resist is applied to a metal plate of a joined body and then etched is preferable. Examples of the etching resist include an ultraviolet curing type and a thermosetting type. When the metal plate is a copper plate or a copper alloy plate, a solution such as a ferric chloride solution, a cupric chloride solution, sulfuric acid, or a hydrogen peroxide solution is used as the etching solution. Preferably, they are a ferric chloride solution and a cupric chloride solution. On the other hand, when the metal plate is made of nickel or a nickel alloy, a ferric chloride solution is used.

Also, in the present invention, the exposure
The surface of the aluminum nitride substrate which issued 3ZrO ₂ · 2Y
_By coating with an oxide layer containing ₂ O ₃ , durability against a heat cycle can be further improved, and even if a thermal stress is generated in a circuit board, a crack that propagates to an aluminum nitride substrate can be prevented.

[0020] To coat the aluminum nitride substrate between the metal circuits at the oxide layer containing such 3ZrO ₂ · 2Y ₂ O _3, further 3ZrO ₂ · 2Y to brazing material containing an active metal
Aluminum nitride using ₂ O ₃ powder
3ZrO2 2Y2O is used for the bonding layer of the bonded body of the substrate and the metal plate.
3 or Y on the aluminum nitride substrate .
2O3 using a brazing material containing zirconium or zirconium compound as the active metal component if it contains, 3ZrO ₂ · 2Y ₂ to the bonding layer by reacting them in joining the aluminum nitride substrate and the metal plate O ₃ is generated, and in any case, 3ZrO ₂ .2 is used in a step of removing unnecessary brazing material existing between metal circuits.
It can be performed by performing a treatment such that Y ₂ O ₃ selectively remains. The processing method is as follows.

That is, even if an unnecessary portion of the metal is removed from the joined body manufactured by the active metal brazing method by etching, the brazing material originally applied between the metal circuits, its alloy layer / nitride layer, or the metal circuit is removed. Unnecessary brazing material protruding outside the pattern remains. Therefore, it is necessary to remove the unnecessary brazing material, NH ₄ F solution as the first treatment liquid when the sulfate as a second treatment liquid, an aqueous solution containing an inorganic acid such as nitric acid and hydrogen peroxide used The concentration of the aqueous NH ₄ F solution in the first treatment liquid is 0.1 to 10% by weight, the temperature is 40 to 60 ° C., the concentration of the inorganic acid, preferably sulfuric acid, in the second treatment liquid is 2 to 4% by weight and the concentration of hydrogen peroxide When treated at 0.5 to 1% by weight and a treatment temperature of 40 to 60 ° C., 3ZrO _2.
Unnecessary brazing material can be removed by leaving 2Y ₂ O ₃ . The above-described first processing and second processing can be performed simultaneously.

[0022] Preferably 2~10μm as coating thickness of the oxide layer containing 3ZrO ₂ · 2Y ₂ O _3. If it is less than 2 μm, the effect is small, and if it exceeds 10 μm, the effect is not so much improved but spots and the like are generated, which is not preferable in appearance. 3ZrO ₂ · 2Y ₂ O _{3 in the} oxide layer can be confirmed by a peak of the (211) plane or the (003) plane by X-ray diffraction.

The function of a conventional two-stage circuit board can be provided by making the thick part of the metal circuit of the circuit board of the present invention a power part and the thin part a control part composed of a fine pattern.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Comparative Example 1 96 parts by weight of aluminum nitride powder, 4 parts by weight of a sintering aid (yttria), 6 parts by weight of polyvinyl butyral, 3 parts by weight of butyl phthalate, 1 part by weight of glycerin triolate and 60 parts by weight of toluene were placed in a nylon pot. For 24 hours. The obtained slurry was spread on a PET film by a doctor blade method, air-dried, and then dried at 120 ° C. for 3 hours to form a green sheet having a predetermined thickness.

The green sheets were punched into a size of 60 × 35 mm and 20 × 35 mm, and ten sheets of green sheets of the respective sizes were temporarily fixed by thermocompression bonding and integrated, and a tungsten weight was placed thereon. 1 at 500 ° C
After heating and degreasing for an hour, normal pressure sintering was performed in a nitrogen atmosphere at 1900 ° C. for 1 hour to produce an aluminum nitride substrate shown in FIG.

75 parts by weight of silver powder, 25 parts by weight of copper powder, 15 parts by weight of zirconium powder, 15 parts by weight of terpineol, and 1 part by weight of a toluene solution of polyisobutyl methacrylate are added and kneaded well to contain an active metal. The material paste was adjusted. This brazing material paste was applied to the entire front and back surfaces of the aluminum nitride substrate produced by the above method. The coating amount (after drying) at that time is 6 to 8 mg / cm
^{And 2} .

Next, copper plates are placed in contact with both sides of the aluminum nitride substrate on which the brazing material paste has been applied, and then heated at 900 ° C. under a vacuum of 1 × 10 ⁻⁵ Torr or less.
After heating for 0 minutes, the assembly was cooled at a temperature reduction rate of 2 ° C./min to produce a joined body shown in FIG.

An etching resist of a UV effect type is applied on the copper plate of the obtained joined body by screen printing, and then an etching process is performed using a cupric chloride solution to dissolve and remove unnecessary portions of the copper plate. Peeled off with 5% caustic soda solution. Since this is joined body after the etching treatment, there is a reaction between the residual unnecessary brazing material and active metal component and the aluminum nitride substrate between the copper circuit, to remove it, temperature 60 ℃, 10% NH ₄ F solution For 10 minutes to produce a circuit board shown in FIG.

Comparative Example 2 96 parts by weight of aluminum nitride powder and 4 parts by weight of yttria powder were premixed in a ball mill for 30 minutes, and then 1 part by weight of oleic acid was added and mixed for another 30 minutes. After adding 8 parts by weight of methylcellulose to this mixture and mixing with a high-speed mixer for 1 minute, a mixed solution of 3 parts by weight of glycerin and 12 parts by weight of water was added while stirring the mixer, and mixed for 2 minutes to obtain a granulated product. .

After the granulated product is kneaded with a roll, it is molded by an extruder while performing vacuum degassing, dried in a belt-type drying furnace at 80 ° C. for 20 minutes, and then cut to obtain aluminum nitride. Green sheets were manufactured. Thereafter, the same operation as in Comparative Example 1 was performed to produce the aluminum nitride substrate shown in FIG. 2, and the circuit board shown in FIG. 8 was produced through the joined body shown in FIG. 5.

Example 1 Removal of unnecessary brazing material was carried out at a temperature of 60 ° C. for 5 minutes in a 5% aqueous solution of NH ₄ F, and then at a temperature of 50 ° C. for 5 minutes in a mixed aqueous solution of 3% sulfuric acid and 0.7% hydrogen peroxide. A circuit board was manufactured in the same manner as in Comparative Example 1 except that the circuit board was immersed. It was confirmed by X-ray diffraction and the like that the surface of the aluminum nitride substrate between the copper circuits of the obtained circuit substrate was covered with an oxide layer containing 3ZrO ₂ .2Y ₂ O ₃ .

[0033] except that the removal of the Example 2 unnecessary brazing material was performed under the conditions of Example 1 were manufactured circuit board in the same manner as in Comparative Example 2. It was confirmed by X-ray diffraction and the like that the surface of the aluminum nitride substrate between the copper circuits of the obtained circuit substrate was covered with an oxide layer containing 3ZrO ₂ .2Y ₂ O ₃ .

A heat cycle (thermal shock) test was performed on the circuit boards manufactured through these series of processes.
The heat cycle test was performed in the air, after holding at -40 ° C for 30 minutes, leaving at 25 ° C for 10 minutes, and further holding at 125 ° C for 30 minutes, then leaving at 25 ° C for 10 minutes as one cycle. The number of heat cycles at which the copper plate was first peeled off from at least one sheet was measured as the number of copper plate peeling starts.

[0035] As a result, Comparative Example 1 is 3000 times, Comparative Example
2 2800 times, Example 1 3500 times, Example 2 3
It was 300 times.

[0036]

According to the present invention, a power part such as a power semiconductor element, a power supply circuit, a drive circuit, and the like, a relay terminal for an extraction electrode, or a part for detecting overcurrent and overvoltage, etc., coexist. In addition, it is possible to provide a circuit board, for example, an intelligent power module board, which can sufficiently cope with demands for high functionality and miniaturization and has high durability against heat cycles, at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an aluminum nitride substrate used in the present invention.

FIG. 2 is a perspective view showing an example of an aluminum nitride substrate used in the present invention.

3 is a perspective view showing an example of the aluminum nitride base plate used in the present invention.

FIG. 4 is a perspective view showing an example of a joined body of an aluminum nitride substrate and a metal plate used in the present invention.

FIG. 5 is a perspective view showing an example of a joined body of an aluminum nitride substrate and a metal plate used in the present invention.

FIG. 6 is a perspective view showing an example of a joined body of an aluminum nitride substrate and a metal plate used in the present invention.

FIG. 7 is a perspective view showing an example of a circuit board of the present invention.

FIG. 8 is a perspective view showing an example of a circuit board of the present invention.

FIG. 9 is a perspective view showing an example of the circuit board of the present invention.

[Explanation of symbols]

1 Aluminum nitride substrate 2 Metal plate 3 Metal circuit 4 Heat dissipation metal plate The dimensions in the figure are mm.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-250191 (JP, A) JP-A-5-121589 (JP, A) JP-A-5-102629 (JP, A) JP-A-2- 165688 (JP, A) Fully open sho 59-185864 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 1/02 H05K 1/05

Claims (5)

(57) [Claims] 1. A bonding layer containing 3ZrO ₂ · 2Y ₂ O ₃
Therefore, the aluminum nitride substrate and the metal plate are not
A metal circuit or a metal circuit and a heat-dissipating metal plate are formed on the aluminum nitride substrate, and the aluminum nitride substrate and the metal circuit have portions having different thicknesses. Moreover, the above-mentioned etching
Aluminum nitride substrate between circuits is 3ZrO ₂ · 2Y ₂ O
Selectively to be coated with an oxide layer containing ₃
Circuit board, characterized in that the shall. 2. The circuit board according to claim 1, wherein a portion having a different thickness exists only on one surface of the aluminum nitride substrate. 3. The circuit board according to claim 1, wherein a rib is provided on the aluminum nitride substrate. 4. When the thickness of the aluminum nitride substrate is A, the thickness of the metal circuit is B, and the thickness of the heat dissipating metal plate is C,
2. The circuit board according to claim 1, wherein the value of A + B + C is constant in any part. 5. The power circuit according to claim 5, wherein the thick part of the metal circuit is a power part.
2. The circuit board according to claim 1, wherein the thin part is used as a control unit composed of a fine pattern.