JP7334438B2 - Insulated circuit board manufacturing method and its insulated circuit board - Google Patents

Description

The present invention relates to a method for manufacturing an insulating circuit board used in a power module or the like for controlling high current and high voltage, and the insulating circuit board.

Insulated circuit substrates used in conventional power modules and the like include, for example, ceramic substrates made of AlN (aluminum nitride), Al ₂ O ₃ (alumina), Si ₃ N ₄ (silicon nitride), and one of the ceramic substrates. It has a circuit layer formed on one surface and a heat dissipation layer formed on the other surface of the ceramic substrate. A brazing material is generally used for joining these ceramic substrates and metal plates that serve as circuit layers or heat dissipation layers. When the metal plate is a copper or copper alloy plate, the brazing material used contains an active metal.

In the circuit board described in Patent Document 1, a circuit layer (copper circuit) made of copper is formed on one surface of the ceramic substrate, and a heat dissipation layer (heat dissipation copper plate) made of copper is formed on the other surface of the ceramic substrate. there is In this case, as a method of forming the copper layer of the circuit layer and the heat dissipation layer, there is a method of etching the periphery of the copper plate after bonding the ceramic substrate and the copper plate, and a method of bonding the copper plate punched in the shape of the circuit layer or the like to the ceramic substrate. method is mentioned. Also, for the joining, an active metal brazing method using Ag--Cu--Ti based brazing material is described.

JP-A-8-139420

By the way, when a circuit board having a copper layer bonded thereto is manufactured by bonding a copper plate for a circuit layer, which has been molded into a desired shape in advance, to a ceramic substrate without etching, the brazing material protruding from the copper plate at the time of bonding may be a part of the copper plate. There is a problem that a phenomenon occurs in which the copper layer creeps up to the surface along the side surface of the copper layer, and wax stains occur on the surface of the copper layer. If the copper layer is a circuit layer, solder stains on its surface will impair the adhesion of the plating film when plating on the circuit layer surface, hindering solder wettability and adhesion of bonding wires and sealing resin. There is a risk that it will be
Therefore, after bonding, the surface of the circuit layer is washed with persulfuric acid, iron chloride solution, or the like, but it is difficult to sufficiently remove the wax stain.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insulated circuit board that removes solder stains and has good solder wettability.

In the method for manufacturing an insulated circuit board of the present invention, a ceramic substrate and a copper plate made of copper or a copper alloy and having a predetermined pattern shape are bonded together via an Ag--Ti brazing filler metal or Ag--Cu--Ti brazing filler metal. a bonding step of bonding to form a copper layer on the surface of the ceramic substrate; a primary cleaning step of cleaning the surface of the copper layer on which wax stains are formed after the bonding step with iron chloride or an aqueous solution containing copper chloride; a secondary cleaning step of cleaning the surface of the copper layer after the primary cleaning step with an aqueous solution containing one or more of iron chloride and chlorides other than copper chloride, ammonia, cyanide, and thiosulfate; After the cleaning step, a tertiary cleaning step of cleaning the surface of the copper layer with an aqueous solution containing at least one of sulfuric acid, persulfate, and a mixed solution of sulfuric acid and hydrogen peroxide.

After bonding using a brazing filler metal, brazing stains can be removed by washing with an aqueous solution containing iron chloride or copper chloride, which is widely used as a copper etchant. However, when the copper is corroded by iron chloride or copper chloride, the copper chloride generated during the corrosion process or the copper chloride used for the primary cleaning tends to remain on the surface of the copper layer only with this primary cleaning. If this copper chloride remains, the surface tends to be discolored in a high-temperature environment. Since this copper chloride is difficult to dissolve in water, it cannot be completely removed by simply washing with water. Therefore, in the secondary cleaning step, cleaning is performed with an aqueous solution containing one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanides, and thiosulfates. Chloride ions and the like contained in these chlorides and the like form a complex with copper chloride to make it easier to dissolve.
After the copper chloride is washed by this secondary washing, the surface is washed with an aqueous solution containing at least one of sulfuric acid, persulfate, and a mixture of sulfuric acid and hydrogen peroxide to smooth the copper layer. It can be formed on the surface.

The insulated circuit board of the present invention is an insulated circuit board in which a copper layer is brazed to the surface of a ceramic substrate, and the wax stain formed on the surface of the copper layer has a width of 50 μm from the end of the copper layer. and the chlorine/copper concentration ratio on the surface of the copper layer is 0.45 or less (excluding 0) .

Since the wax stain on the surface of the copper layer has a width of 50 μm or less and the chlorine/copper concentration ratio on the surface of the copper layer is 0.45 or less, discoloration of the surface due to corrosion can also be suppressed. Therefore, the adhesion of the plating film when forming the plating film on the surface of the copper layer, the solder wettability when soldering the semiconductor element are excellent, and the adhesion of the bonding wire, resin, etc. is also good.
It should be noted that when the copper layer is patterned by etching after brazing, the problem of brazing does not occur because the peripheral edge is removed. If the thickness of the copper layer is too large, etching takes a long time and is uneconomical. Therefore, in the case of the circuit layer, it is more economical to join a copper plate having a circuit pattern formed in advance. As for the case where the copper layer is not etched, the present invention is effective when the thickness of the copper layer is 0.1 mm or more, and is more effective when the thickness is 0.5 mm or more.

According to the present invention, it is possible to provide an insulated circuit board which is excellent in adhesion of a plating film, solder wettability, etc., by removing wax stains.

It is process drawing which shows one Embodiment of the manufacturing method of the insulated circuit board of this invention. 1 is a longitudinal sectional view of an insulated circuit board according to one embodiment; FIG. FIG. 3 is a vertical cross-sectional view showing a state in the middle of manufacturing the insulated circuit board of FIG. 2 ;

Hereinafter, embodiments of an insulated circuit board and a method for manufacturing the same according to the present invention will be described.
The insulated circuit board of this embodiment is a power module board used in a power supply circuit. As shown in FIG. 2, the power module substrate 10 includes a ceramic substrate 11, a circuit layer 12 formed on one surface of the ceramic substrate 11, and a heat dissipation layer formed on the other surface of the ceramic substrate 11. 13 and .

The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the heat dissipation layer 13 _, and is made of aluminum nitride (AlN), silicon nitride ( _Si3N4 ), aluminum oxide ( _{Al2O3 )} . etc. can be used, but among them, silicon nitride is preferred because of its high strength. The thickness of the ceramic substrate 11 is set within a range of 0.2 mm or more and 1.5 mm or less.

The circuit layer 12 is made of copper or a copper alloy with excellent electrical properties. Moreover, the heat dissipation layer 13 is also made of copper or a copper alloy. The circuit layer 12 and heat dissipation layer 13 are formed by brazing, for example, a copper plate of oxygen-free copper with a purity of 99.96% by mass or more to the ceramic substrate 11 with, for example, an active metal brazing material. The thicknesses of the circuit layer 12 and the heat dissipation layer 13 are set within a range of 0.1 mm or more and 5 mm or less.

Here, the wax stains on the circuit layer 12 and the heat dissipation layer 13 have a width of 50 μm or less from the end of the circuit layer 12 and the heat dissipation layer 13 . Since the width of the solder stain is set to 50 μm or less, for example, when the circuit layer 12 is plated with Ni plating or the like, the adhesion of the plating film is not impaired. In addition, the wettability of the solder does not deteriorate, and the adhesion of the bonding wires and the sealing resin is not hindered. Furthermore, for example, even when the heat dissipation layer 13 and the heat sink are soldered, the width of the braze stain is 50 μm or less, so the wettability of the solder does not deteriorate, and the solderability does not deteriorate.

Further, the surface chlorine/copper concentration ratio of the circuit layer 12 and the heat dissipation layer 13 is set to 0.45 or less. This chlorine/copper concentration ratio is determined, for example, by Energy Dispersive X-ray Spectroscopy (EDX) using a Scanning Electron Microscope (SEM). A characteristic X-ray emitted from the surface of a copper layer (hereinafter referred to as a copper layer when the circuit layer and heat dissipation layer are not particularly distinguished) is measured by elemental analysis. This chlorine/copper concentration ratio is due to the copper chloride remaining on the surface of the copper layer.

A method of manufacturing the power module substrate 10 configured in this way will be described.
As shown in FIG. 1, the power module substrate 10 is manufactured in the order of a copper plate manufacturing process, a bonding process, a primary cleaning process, a secondary cleaning process, and a tertiary cleaning process. The order of steps will be described below.

(Copper plate manufacturing process)
Copper plates 12' and 13' for forming the circuit layer 12 and the heat radiation layer 13 are punched by press working or the like. In this case, the copper plate 12 ′ that becomes the circuit layer 12 has a predetermined pattern shape as the circuit layer 12 .
Also, the ceramic substrate 11 on which the circuit layer 12 and the heat dissipation layer 13 are formed is prepared. Alternatively, a ceramic plate having scribe lines that can be divided into a plurality of ceramic substrates 11 is prepared. When a ceramic plate that can be divided into a plurality of ceramic substrates 11 is used, the ceramic substrates 11 are finally divided into individual ceramic substrates 11 each having a circuit layer 12 and a heat dissipation layer 13. Since the process is the same as that for a single ceramic substrate 11 , the following description will be made on the assumption that the circuit layer 12 and the heat dissipation layer 13 are formed on the ceramic substrate 11 .

(Joining process)
As shown in FIG. 3, copper plates 12' and 13' are arranged on both sides of a ceramic substrate 11 with brazing materials 21 and 22 interposed therebetween, and these are laminated. As the brazing materials 21 and 22, a brazing material made of Ag--Ti or Ag--Cu--Ti is used. The brazing materials 21 and 22 are supplied in the form of foils, but may be formed by applying a brazing material paste to the ceramic substrate 11 by screen printing or the like.
In this case, the brazing filler metals 21 and 22 are preferably formed to have the same outer shape as or slightly larger than the outer shape of the copper plates 12' and 13' to be joined. The thickness of these brazing filler metals 21 and 22 is set to 10 μm or more and 300 μm or less.

The laminated body of the ceramic substrate 11 and the copper plates 12' and 13' laminated via the brazing materials 21 and 22 is placed in a heating furnace under pressure, heated to the bonding temperature in a vacuum atmosphere, and then cooled. Thus, the circuit layer 12 is formed on one surface of the ceramic substrate 11, and the heat dissipation layer 13 is formed on the other surface. As the bonding conditions in this case, for example, the laminated body is pressed with a pressure of 0.1 MPa or more and 3.5 MPa or less, in a vacuum atmosphere of 10 ^-6 Pa or more and 10 ^-3 Pa or less, for example 790 ° C. or more and 850 ° C. or less. , and the heating time is 1 to 60 minutes.

In the power module substrate 10 manufactured in this manner, the ceramic substrate 11, the circuit layer 12 and the heat dissipation layer 13 are joined by brazing.
The above-mentioned brazing stain is caused by the melted brazing material protruding from between the ceramic substrate 11 and the copper plates 12' and 13' when the power module substrate 11 and the copper plates 12' and 13' are joined to each other. It is formed on the surfaces of the circuit layer 12 and the heat dissipation layer 13 by creeping up along the side surface of ', and most of it is also removed by the washing process described later.

(Primary washing process)
The surface of the copper layer (circuit layer 12 and heat dissipation layer 13) of the power module substrate 10 after the bonding step is washed with a primary cleaning liquid.
An aqueous solution of iron chloride or copper chloride is used as the primary cleaning liquid. As iron chloride, it is preferable to use iron chloride (III) (FeCl ₃ ). Copper chloride (II) (CuCl ₂ ) is preferably used as the copper chloride.
In addition, although the volume ratio and the like are not limited, the iron chloride aqueous solution is, for example, an _FeCl3 aqueous solution of 30% by mass or more and 45% by mass or less, and the copper chloride aqueous solution is, for example, 15% by mass or more to 25% by mass or less. A mixed aqueous solution of CuCl ₂ and 3 mass % or more and 15 mass % or less of HCl is used.
The power module substrate 10 is immersed in the primary cleaning liquid at a temperature of 30° C. or more and 60° C. or less for a time of 0.5 minutes or more and 10 minutes or less.
By this primary cleaning, the surface of the copper layer is cleaned, and all or most of wax stains formed on the surfaces of the circuit layer 12 and the heat dissipation layer 13 are removed. Although the solidified brazing material is present on the side surfaces of the circuit layer 12 and the heat dissipation layer 13, the solidified brazing material is thickly formed, so that a part of the solidified brazing material remains even after the primary cleaning process. There may be some, but it has no effect.

(Secondary washing process)
After the primary cleaning step, the surface of the copper layer is cleaned with a secondary cleaning liquid.
As the secondary cleaning liquid, an aqueous solution containing one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanides, and thiosulfates is used.
Chlorides of metal elements and hydrochloric acid can be used as chlorides other than iron chloride and copper chloride. As chlorides of metal elements, for example, chlorides of Li, Na, K, Be, Mg, Ca, Sr, Ba, and Al can be used.
Cyanide includes sodium cyanide, potassium cyanide, calcium cyanide, magnesium cyanide and the like.
Thiosulfates include sodium thiosulfate, potassium thiosulfate and ammonium thiosulfate.
Although the volume ratio is not limited, for example, hydrochloric acid of 1% by mass to 35% by mass, potassium chloride aqueous solution of 1% by mass to 30% by mass, and ammonia aqueous solution of 1% by mass to 30% by mass. etc. are used.
The power module substrate 10 is immersed in the secondary cleaning liquid at a temperature of 15° C. or higher and 40° C. or lower for a period of 0.5 minutes or longer and 10 minutes or shorter.
After the primary cleaning, copper chloride generated during the process of oxidation of copper on the surface of the copper layer by the cleaning liquid iron chloride or copper chloride, especially copper (I) chloride, may remain on the surface of the copper layer. This copper chloride is sparingly soluble in water. For this reason, the copper chloride remaining on the surface of the copper layer is complexed by the secondary cleaning to make it easier to dissolve.

(Tertiary cleaning process)
After the secondary cleaning, the surface of the copper layer is cleaned with a tertiary cleaning liquid.
As the tertiary cleaning liquid, an aqueous solution containing at least one of sulfuric acid, persulfate, and a mixture of sulfuric acid and hydrogen peroxide is used. Examples of persulfates include sodium persulfate, potassium persulfate and ammonium persulfate. Although the volume ratio and the like are not limited, an aqueous sulfuric acid solution of 3% by mass to 30% by mass, an aqueous persulfate solution of 3% by mass to 30% by mass, and hydrogen peroxide of 1% by mass to 15% by mass. A mixed aqueous solution of water and 3% by mass or more and 20% by mass or less of sulfuric acid is used.
The power module substrate 10 is immersed in the tertiary cleaning solution at a temperature of 15° C. or more and 40° C. or less for a time of 0.5 minutes or more and 10 minutes or less.
This tertiary cleaning process forms the copper layer (circuit layer 12 and heat dissipation layer 13) on a smooth surface.

After each cleaning step, the power module substrate 10 is washed with water in order to wash off the cleaning liquid.
In the power module substrate 10 that has undergone the third cleaning in this way, both the circuit layer 12 and the heat dissipation layer 13 have no waxy stains on the surface, and no chlorides caused by the cleaning liquid used to remove the waxy stains remain. Therefore, when a plating film is formed on the surface, the adhesion of the plating film is excellent. Solder wettability and adhesion of bonding wires and sealing resin are also improved.

The present invention is not limited to the configurations of the above-described embodiments, and various modifications can be made to the detailed configurations without departing from the scope of the present invention.
In the embodiment, copper layers are formed on both sides of the ceramic substrate, but at least copper layers as circuit layers may be formed.
Moreover, although the power module substrate is immersed in each cleaning liquid, the case of supplying the cleaning liquid to the copper layer by spraying or the like is also included.
Although the power module board has been described in the embodiment, it can be applied to an insulated circuit board other than the power module board.

A copper plate (37 mm x 37 mm x 0.3 mmt) made of oxygen-free copper (OFC) with a purity of 99.99% by mass or more is placed on one side of a ceramic substrate (40 mm x 40 mm x _0.32 mmt) made of _Si3N4 . Laminated via Ag-Ti brazing material foil (37 mm × 37 mm × 0.05 mmt), held in a pressurized state with a pressure of 0.6 MPa, held in a vacuum atmosphere at a heating temperature of 820 ° C. for 30 minutes, and ceramics A copper layer was formed over the substrate.

The resulting joined body was subjected to a primary cleaning process, a secondary cleaning process, and a tertiary cleaning process in this order. The washing liquid used in each washing step is as shown in Table 1.
In the table, the washing solutions in the primary washing process and the tertiary washing process were as follows.
“Iron chloride”: 42 mass% _FeCl3 aqueous solution “Copper chloride”: mixed aqueous solution of 21 mass% _CuCl2 and 9 mass% HCl “Sulfuric acid + hydrogen peroxide”: 15 mass% sulfuric acid and 2 mass% hydrogen peroxide "Sulfuric acid": 10% by mass aqueous solution of sulfuric acid "Sodium persulfate": 15% by mass aqueous solution of sodium persulfate In the secondary cleaning step, the chemicals listed in each column of Table 1 were used. After each wash, the conjugate was washed with pure water.
In this washing process, the first washing was performed at a temperature of 42° C. for 2 minutes, the second washing was performed at normal temperature (25° C.) for 1 minute, and the tertiary washing was performed at normal temperature (25° C.) for 1 minute. "-" in Table 1 indicates that washing was not performed in that step.

On the surface of the copper layer of the obtained joined body, the residual chlorine concentration was measured, and the degree of wax stain and discoloration was evaluated.
The concentration of chlorine and copper on the surface of the copper layer is measured by elemental analysis of characteristic X-rays emitted from the surface of the copper layer by energy dispersive X-ray spectroscopy (EDX) using a scanning electron microscope (SEM). It was measured. The ratio (Cl/Cu) of the quantitative values (at %) of Cu and Cl was measured for 15 arbitrary points on the surface of the copper layer, and the average was obtained. The copper layers of 15 bonded bodies were measured for each condition, the average value was obtained, and the value was taken as the surface chlorine/copper concentration ratio.

Width W of wax stain was measured as follows.
Visually observe the copper layer surface from above, consider the black area (black part) as wax stain, and measure the distance from the edge of the copper layer to the boundary between the black part and the area other than the black part for each side It was measured. The width W of the wax stain was defined as the point with the longest distance, and the width was measured for 15 joined bodies under each condition, and the average value was obtained. When the width was 50 μm or less, it was evaluated as “A”, and when it exceeded 50 μm, it was evaluated as “B”.
Regarding discoloration, the joined body was left in a constant temperature and humidity environment with a temperature of 60° C. and a humidity of 30% for 100 hours. The case where it was observed was evaluated as "B", and the other cases were evaluated as "A".
These results are shown in Table 2.

As shown in Table 2, in the examples in which primary cleaning, secondary cleaning, and tertiary cleaning were performed in this order, the chlorine/copper concentration ratio on the surface of the copper layer was 0.45 or less, and there was no wax stain or discoloration. did not occur.
On the other hand, in Comparative Example 1, since the secondary cleaning was not performed, the chlorine/copper concentration ratio of the copper layer surface exceeded 0.45, and discoloration occurred. Since Comparative Example 2 was not subjected to primary cleaning, wax stains occurred.

10 Power module board (insulated circuit board)
11 ceramic substrate 12 circuit layer (copper layer)
13 heat dissipation layer (copper layer)
12', 13' Copper plates 21, 22 Brazing material layer

Claims (2)

A copper layer is formed on the surface of the ceramic substrate by joining a ceramic substrate and a copper plate made of copper or a copper alloy and having a predetermined pattern through an Ag--Ti brazing material or an Ag--Cu--Ti brazing material. a bonding step of forming, a primary cleaning step of cleaning the surface of the copper layer on which the wax stain is formed after the bonding step with an aqueous solution containing iron chloride or copper chloride, and after the primary cleaning step, cleaning the surface of the copper layer, A secondary cleaning step of cleaning with an aqueous solution containing one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanide, and thiosulfate, and after the secondary cleaning step, sulfuric acid, persulfate, A method for manufacturing an insulated circuit board, comprising a tertiary cleaning step of cleaning the surface of the copper layer with an aqueous solution containing at least one of a mixture of sulfuric acid and hydrogen peroxide. An insulated circuit board in which a copper layer is brazed to the surface of a ceramic substrate with an Ag--Ti brazing material or an Ag--Cu--Ti brazing material , wherein the brazing stain formed on the surface of the copper layer is the copper layer. is 50 μm or less, and the chlorine/copper concentration ratio of the surface of the copper layer is 0.45 or less (excluding 0).

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