JP2020161524A - Manufacturing method of insulated circuit board and its insulated circuit board - Google Patents

Abstract

To provide an insulated circuit board which removes wax stains and has good solder wettability and the like.SOLUTION: A manufacturing method of an insulated circuit board includes a joining step of joining a ceramic substrate and a copper plate made of copper or a copper alloy via a brazing material to form a copper layer on the surface of the ceramic substrate, a primary cleaning step of cleaning the surface of the copper layer with an aqueous solution containing iron chloride or copper chloride after the joining step, a secondary cleaning step of cleaning the surface of the copper layer with an aqueous solution containing one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanide, and thiosulfate after the primary cleaning step, and a tertiary cleaning step of performing the cleaning with an aqueous solution containing any one or more of sulfuric acid, persulfate, and a mixed solution of sulfuric acid and hydrogen peroxide after the secondary cleaning step.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing an insulated circuit board used for a power module or the like that controls a large current or a high voltage, and the insulated circuit board thereof.

The insulating circuit substrate used for the conventional power module or the like is, for example, a ceramic substrate made of AlN (aluminum nitride), Al ₂ O ₃ (alumina), Si ₃ N ₄ (silicon nitride), or one of the ceramic substrates. It includes a circuit layer formed on a surface and a heat radiating layer formed on the other surface of the ceramic substrate. Further, a brazing material is generally used for joining these ceramic substrates to these circuit layers or metal plates serving as heat dissipation layers. When the metal plate is copper or a copper alloy plate, a brazing material containing an active metal is used.

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

Japanese Unexamined Patent Publication No. 8-139420

By the way, in the case of producing a circuit board in which a copper plate for a circuit layer or the like molded into a desired shape is bonded to a ceramic substrate in advance without etching, the brazing material protruding from the copper plate at the time of bonding is a copper plate. A phenomenon occurs in which the copper layer crawls up to the surface along the side surface of the copper layer, causing wax stains on the surface of the copper layer. When the copper layer is a circuit layer, if wax stain occurs on the surface, the adhesion of the plating film is impaired when plating on the surface of the circuit layer, and the adhesiveness of the solder wettability and the adhesion of the bonding wire and the sealing resin are impaired. May be done.
For this reason, the surface of the circuit layer is washed with persulfuric acid, an aqueous iron chloride solution, or the like after bonding, but it is difficult to sufficiently remove the wax stain.

The present invention has been made in view of such circumstances, and an object of the present invention is to remove wax stains and provide an insulated circuit board having good solder wettability and the like.

The method for manufacturing an insulated circuit substrate of the present invention includes a joining step of joining a ceramic substrate and a copper plate made of copper or a copper alloy via a brazing material to form a copper layer on the surface of the ceramic substrate, and the copper after the joining step. A primary cleaning step of cleaning the surface of the layer with an aqueous solution containing iron chloride or copper chloride, and after the primary cleaning step, the surface of the copper layer is cleaned with chlorides other than iron chloride and copper chloride, ammonia, cyanide, and thiosulfate. A secondary cleaning step of washing with an aqueous solution containing any one or more of the above, and after the secondary cleaning step, an aqueous solution containing any one or more of a mixed solution of sulfuric acid, persulfate, and sulfuric acid and hydrogen peroxide. It has a tertiary cleaning step of cleaning.

After joining with a brazing material, the wax stain can be removed by washing with an aqueous solution containing iron chloride or copper chloride, which is widely used as an etching solution for copper. However, with only this primary cleaning, when copper is corroded by iron chloride or copper chloride, copper chloride generated in the process of corrosion and copper chloride used for the primary cleaning tend to remain on the surface of the copper layer. If this copper chloride remains, discoloration is likely to occur on the surface in a high temperature environment or the like. Since this copper chloride is difficult to dissolve in water, it cannot be completely removed by simply washing with water. Therefore, it is washed with an aqueous solution containing any one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanide, and thiosulfate by a secondary washing step. Copper chloride is complexed with chloride ions and the like contained in these chlorides and the like to make it easier to dissolve.
Then, after the copper chloride is washed by this secondary washing, the surface is washed with an aqueous solution containing any one or more of sulfuric acid, persulfate, and a mixed solution of sulfuric acid and hydrogen peroxide to smooth the copper layer. It can be formed on the surface.

The insulating circuit board of the present invention is an insulating circuit board in which a copper layer is brazed to the surface of a ceramics 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. The chlorine / copper concentration ratio on the surface of the copper layer is 0.45 or less.

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 be suppressed. Therefore, the adhesion of the plating film when forming the plating film on the surface of the copper layer and the solder wettability when soldering the semiconductor element are excellent, and the adhesion of the bonding wire, the resin, etc. is also good.
When the copper layer is patterned by etching after brazing, the peripheral portion is removed, so that the problem of brazing stain does not occur. If the thickness of the copper layer is large, etching takes time and it is uneconomical. Therefore, in the case of a circuit layer, it is more economical to join copper plates formed in a circuit pattern in advance. When the copper layer is not etched in this way, it is effective to use the present invention when the thickness of the copper layer is 0.1 mm or more, and it is more effective when the thickness of the copper layer is 0.5 mm or more.

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

It is a process drawing which shows one Embodiment of the manufacturing method of the insulated circuit board of this invention. It is a vertical sectional view of the insulation circuit board of one Embodiment. It is a vertical cross-sectional view which shows the state in the manufacturing process of the insulation circuit board of FIG.

Hereinafter, embodiments of the insulated circuit board of the present invention and the method for manufacturing the same 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. It has 13 and.

Ceramic substrate 11 is for preventing an electrical connection between the circuit layer 12 and the heat dissipation layer 13, aluminum nitride (AlN), silicon nitride _{(Si 3 N} 4), aluminum oxide _{(Al 2 O} 3) Etc. can be used, but silicon nitride is preferable because of its high strength. The thickness of the ceramic substrate 11 is set within the 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 having excellent electrical characteristics. The heat dissipation layer 13 is also made of copper or a copper alloy. The circuit layer 12 and the heat radiating layer 13 are formed, for example, by brazing and joining an oxygen-free copper plate having a purity of 99.96% by mass or more to the ceramic substrate 11 with, for example, an active metal brazing material. The thickness of the circuit layer 12 and the heat radiating layer 13 is set within the range of 0.1 mm or more and 5 mm or less.

Here, the wax stains on the circuit layer 12 and the heat radiating layer 13 have a width of 50 μm or less from the ends of the circuit layer 12 and the heat radiating layer 13. Since the width of the wax stain is 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. Further, the solder wettability is not deteriorated, and the adhesion of the bonding wire and the sealing resin is not impaired. Further, for example, even when the heat radiating layer 13 and the heat sink are soldered, the width of the wax stain is 50 μm or less, so that the wettability of the solder does not decrease and the solder bondability does not decrease.

Further, the chlorine / copper concentration ratio on the surfaces 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 by, for example, energy dispersive X-ray spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy) using a scanning electron microscope (SEM) in the circuit layer 12 or the heat dissipation layer 13. Characteristic X-rays emitted from the surface of the copper layer (hereinafter referred to as the copper layer when the circuit layer and the heat radiation layer are not particularly distinguished) are measured by elemental analysis. This chlorine / copper concentration ratio is due to the copper chloride remaining on the surface of the copper layer, and if it exceeds 0.45, the amount of copper chloride remaining increases, and discoloration is likely to occur in a high temperature environment or the like.

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 or the like manufacturing step, a joining step, a primary cleaning step, a secondary cleaning step, and a tertiary cleaning step. Hereinafter, the steps will be described in order.

(Copper plate manufacturing process)
Copper plates 12'and 13'for forming the circuit layer 12 and the heat dissipation layer 13 are punched and formed by press working or the like. In this case, the copper plate 12'which becomes the circuit layer 12 has a predetermined pattern shape as the circuit layer 12.
Further, a ceramic substrate 11 on which the circuit layer 12 and the heat radiating layer 13 are formed is prepared. Alternatively, a ceramic plate having a scribe line that can be divided into a plurality of ceramic substrates 11 is prepared. When a ceramic plate that can be divided into the plurality of ceramic substrates 11 is used, it is finally divided into individual ceramic substrates 11 having a circuit layer 12 and a heat dissipation layer 13, but the joining step and each cleaning step described later are performed. Since it is the same as that for a single ceramic substrate 11, it will be described below assuming 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 the ceramic substrate 11 via brazing materials 21 and 22, 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 foil, but may be formed by applying a brazing material paste to the ceramic substrate 11 by a screen printing method or the like.
In this case, it is preferable that each of the brazing members 21 and 22 is formed to have an outer shape that is the same as or slightly larger than the outer shape of the copper plates 12'and 13'to be joined. The thickness of these brazing materials 21 and 22 is 10 μm or more and 300 μm or less.

A laminate of the ceramic substrate 11 and the copper plates 12'and 13'laminated via the brazing materials 21 and 22 is installed in a heating furnace in a pressurized state, heated to a bonding temperature in a vacuum atmosphere, and then cooled. As a result, 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. In this case, the joining conditions include, for example, pressurizing the laminate with a pressing force of 0.1 MPa or more and 3.5 MPa or less, and 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. The bonding temperature is 1 to 60 minutes.

In the power module substrate 10 manufactured in this manner, the ceramic substrate 11 and the circuit layer 12 and the heat radiating layer 13 are joined by brazing.
The wax stain described above is caused by the molten 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. It is formed on the surfaces of the circuit layer 12 and the heat radiating layer 13 by crawling up along the side surface of ′, and most of it is removed by the cleaning step described later.

(Primary cleaning process)
The surface of the copper layer (circuit layer 12 and heat dissipation layer 13) of the power module substrate 10 after the joining step is cleaned with the primary cleaning liquid.
As the primary cleaning liquid, an aqueous solution of iron chloride or copper chloride is used. As the iron chloride, it is preferable to use iron (III) chloride (FeCl ₃ ). It is preferable to use copper (II) chloride (CuCl ₂ ) as the copper chloride.
Further, although not capacity ratio and the like is limited, as the aqueous solution of iron chloride, for example, 30 wt% to 45 wt% of FeCl ₃ aqueous solution, the aqueous solution of copper chloride, for example, the following 15 wt% to 25 wt% A mixed aqueous solution of CuCl ₂ and 3% by mass or more and 15% by mass or less of HCl is used.
The primary cleaning liquid is maintained at a temperature of 30 ° C. or higher and 60 ° C. or lower, and the power module substrate 10 is immersed for 0.5 minutes or longer and 10 minutes or shorter.
By this primary cleaning, the surface of the copper layer is cleaned, and all or most of the wax stains formed on the surfaces of the circuit layer 12 and the heat radiating layer 13 are removed. Although solidified brazing material is present on the side surfaces of the circuit layer 12 and the heat radiating layer 13, a part of the solidified brazing material remains even after the primary cleaning step because the solidified brazing material is formed thick. It may be, but it has no effect.

(Secondary cleaning process)
After the primary cleaning step, the surface of the copper layer is cleaned with a secondary cleaning solution.
As the secondary cleaning solution, an aqueous solution containing any one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanide, and thiosulfate is used.
As the chloride other than iron chloride and copper chloride, chloride of a metal element or hydrochloric acid can be used. As the chloride of the metal element, for example, chlorides of Li, Na, K, Be, Mg, Ca, Sr, Ba and Al can be used.
Examples of the cyanide include sodium cyanide, potassium cyanide, calcium cyanide, magnesium cyanide and the like.
Examples of the thiosulfate include sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate and the like.
Although the volume ratio is not limited, for example, hydrochloric acid of 1% by mass or more and 35% by mass or less, an aqueous solution of potassium chloride of 1% by mass or more and 30% by mass or less, and an aqueous solution of ammonia of 1% by mass or more and 30% by mass or less. Etc. are used.
The secondary cleaning liquid is maintained at a temperature of 15 ° C. or higher and 40 ° C. or lower, and the power module substrate 10 is immersed for 0.5 minutes or longer and 10 minutes or shorter.
After the primary cleaning, copper chloride, especially copper (I) chloride, generated in the process of oxidizing the copper on the surface of the copper layer by the cleaning liquid, iron chloride or copper chloride, may remain on the surface of the copper layer. This copper chloride is difficult to dissolve in water. Therefore, by the secondary cleaning, the copper chloride remaining on the surface of the copper layer is complexed and easily dissolved.

(3rd cleaning process)
After the secondary cleaning, the surface of the copper layer is cleaned with a tertiary cleaning solution.
As the tertiary cleaning solution, an aqueous solution containing any one or more of sulfuric acid, persulfate, and a mixed solution of sulfuric acid and hydrogen peroxide is used. Examples of the persulfate include sodium persulfate, potassium persulfate, ammonium persulfate and the like. The volume ratio is not limited, but a sulfuric acid aqueous solution of 3% by mass or more and 30% by mass or less, a persulfate aqueous solution of 3% by mass or more and 30% by mass or less, and a hydrogen peroxide of 1% by mass or more and 15% by mass or less. A mixed aqueous solution of water and sulfuric acid of 3% by mass or more and 20% by mass or less is used.
The tertiary cleaning liquid is maintained at a temperature of 15 ° C. or higher and 40 ° C. or lower, and the power module substrate 10 is immersed for 0.5 minutes or longer and 10 minutes or shorter.
By this tertiary cleaning step, a copper layer (circuit layer 12 and heat radiating layer 13) is formed 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 which has been completed up to the third cleaning in this way, neither the circuit layer 12 nor the heat radiation layer 13 has a wax stain on the surface, and no chloride due to the cleaning liquid used for removing the wax stain remains. Therefore, the adhesion of the plating film is excellent when the plating film is formed on the surface. In addition, the solder wettability and the adhesion of the bonding wire and the sealing resin are also improved.

The present invention is not limited to the configuration of the above embodiment, and various changes can be made to the detailed configuration without departing from the spirit of the present invention.
In the embodiment, it is assumed that copper layers are formed on both sides of the ceramic substrate, but at least a copper layer as a circuit layer may be formed.
Further, although the power module substrate is immersed in each cleaning liquid, it also includes the case where the cleaning liquid is supplied to the copper layer by spraying or the like.
Although described as a power module board in the embodiment, it can be applied to an insulated circuit board other than the power module board.

A copper plate (37 mm × 37 mm × 0.3 mmt) made of oxygen-free copper (OFC) having a purity of 99.99% by mass or more is placed on one surface of a ceramic substrate (40 mm × 40 mm × 0.32 mmt) made of Si ₃ N _4. Laminated via Ag-Ti brazing foil (37 mm x 37 mm x 0.05 mmt), held in a pressurized state with a pressing force 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 on the substrate.

The obtained bonded body was subjected to a primary cleaning step, a secondary cleaning step, and a tertiary cleaning step in order. The cleaning liquids used in each cleaning step are as shown in Table 1.
In the table, the cleaning liquids for the primary cleaning step and the tertiary cleaning step are as follows.
"Iron chloride": 42 mass% FeCl ₃ aqueous solution "Copper chloride": A mixed aqueous solution of 21 mass% CuCl ₂ and 9 mass% HCl "Sulfuric acid + hydrogen peroxide": 15 mass% sulfuric acid and 2 mass% hydrogen peroxide Aqueous solution of "sulfuric acid": 10% by mass of sulfuric acid "Sodium persulfate": 15% by mass of aqueous sodium persulfate In addition, the chemical solution described in each column of Table 1 was used in the secondary washing step. After each wash, the conjugate was washed with pure water.
In this cleaning step, the primary cleaning was performed at a temperature of 42 ° C. for 2 minutes, the secondary cleaning was performed at room temperature (25 ° C.) for 1 minute, and the tertiary cleaning was performed at room temperature (25 ° C.) for 1 minute. “-” In Table 1 indicates that the process was not washed.

The residual chlorine concentration was measured on the surface of the copper layer of the obtained bonded body, 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 the 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 at any 15 locations on the surface of the copper layer, and the average was calculated. Each of the 15 copper layers of the bonded body was measured under each condition, the average value was calculated, and the value was taken as the surface chlorine / copper concentration ratio.

The width W of the wax stain was measured as follows.
The surface of the copper layer is visually observed from above, and the black area (black part) is regarded as a wax stain, and the distance from the end of the copper layer to the boundary between the black part and the area other than the black part is measured for each side. It was measured. The place where the distance was the longest was defined as the width W of the wax stain, and 15 joints were measured under each condition and the average value was calculated. 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 bonded body was left in a constant temperature and humidity environment at a temperature of 60 ° C. and a humidity of 30% for 100 hours, and a dark brown region darker than the copper layer was observed on the surface of the copper layer, or white unevenness was observed. The observed case 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 the primary cleaning, the secondary cleaning, and the tertiary cleaning were performed in order, the chlorine / copper concentration ratio on the copper layer surface was 0.45 or less, there was no wax stain, and there was no discoloration. It did not occur.
On the other hand, in Comparative Example 1, since the secondary cleaning was not performed, the chlorine / copper concentration ratio on the surface of the copper layer exceeded 0.45, and discoloration occurred. In Comparative Example 2, since the primary cleaning was not performed, wax stain 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 plate 21 and 22 Wax layer

Claims (2)

A joining step of joining a ceramic substrate and a copper plate made of copper or a copper alloy via a brazing material to form a copper layer on the surface of the ceramic substrate, and a joining step in which the surface of the copper layer contains iron chloride or copper chloride after the joining step. A primary cleaning step of cleaning with an aqueous solution, and after the primary cleaning step, the surface of the copper layer is washed with an aqueous solution containing one or more of chlorides other than iron chloride and copper chloride, ammonia, cyanide, and thiosulfate. It is characterized by having a secondary cleaning step for cleaning, and after the secondary cleaning step, a tertiary cleaning step for cleaning with an aqueous solution containing any one or more of a mixed solution of sulfuric acid, persulfate, and sulfuric acid and hydrogen peroxide. Manufacturing method of insulated circuit board. An insulating circuit board in which a copper layer is brazed to the surface of a ceramics substrate, and the wax stain formed on the surface of the copper layer has a width of 50 μm or less from the end of the copper layer, and the copper layer has a width of 50 μm or less. An insulated circuit board having a surface chlorine / copper concentration ratio of 0.45 or less.

Images