JPH02209793A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To prevent an etching agent from spreading to an unetched metallic plate by coating the ceramics plate and the metallic plate of a laminated body on a conductive plate with an insulator liquidtightly, performing electrical connection only between the conductive plate and the metallic plate with a conductive substance, and making a current flow. CONSTITUTION:A metallic plate 2 is stuck to one face of a ceramics plate 1 to form a laminated body. Said laminated body is mounted on a conductive plate 20 and an electrically-insulating screen 11 which is made of a material not reacting to corrosion solvent 7 and has a pattern to be etched corresponding to a circuit pattern is tightly adhered to the surface of the metallic plate 2. The corrosion solvent 7 after pasting is applied to the metallic plate 2 through the pattern of the screen 11. An electrode 8 is installed on the face to which the pre-corrosion solvent 7 is applied. The ceramics plate 1 and the other metallic plate 3 of the laminated body on the conductive plate 20 are covered liquidtightly by an insulator 21. Electrical connection only between the conductive plate 20 and the metallic plate 2 is performed with a conductive substance 22, a current is caused to flow between the electrode 8 and the conductive plate 20, and electrolytic etching is performed.

Description

[Detailed Description of the Invention] <Industrial Field of Application> What has not yet been invented is a method for manufacturing a circuit board with excellent heat dissipation and heat resistance, which is formed by bonding a metal plate onto a ceramic plate having electrical insulation properties. Regarding improvements.

<Conventional technology> In recent years, power semiconductor modules used for power switches, power control circuits, motor control circuits, high-frequency oscillation output, broadband power amplification, etc. have been trending toward higher density integration and higher current control. The substrates used in these modules are required to have heat dissipation properties that quickly dissipate a large amount of heat emitted from the elements, and to have finer and more precise conductor circuit patterns to accommodate the high density integration of modules.

Conventionally, as shown in FIG. 4, such a semiconductor module substrate is made by bonding a metal plate 2 having a circuit pattern to one surface of a ceramic plate 1 having electrical insulation properties, and mounting an element 4 on the metal plate 2. A mechanism is used in which the generated heat is conducted from the metal plate 2 through the ceramic plate 1 and dissipated to the heat sink 5 via the metal plate 3 bonded to the other side.
For example, a copper plate cut out in a predetermined pattern as a metal plate can be used as an insulating ceramic.
A product bonded using Al203 using the so-called eutectic method in which CuO eutectic is generated by heating has been commercialized.

As a means of improving the heat dissipation properties of semiconductor module substrates, there is a tendency to improve the thermal conductivity of ceramics, and attempts have been made to use materials with higher thermal conductivity such as BeO and A42N in place of Al2203. ing. For some of these new materials, it is difficult to directly apply the method of bonding patterned copper plates using the eutectic method.For example, although AuN has a thermal conductivity inferior to that of BeO, No need to worry about toxicity
Although it is a promising material, in order to apply the eutectic method,
The substrate is oxidized in advance and the surface is coated with Al120. It is necessary to form a layer. Therefore, attempts have been made to bond AJ2N to a copper plate using a brazing filler metal containing an active metal.

The laminate obtained by bonding the metal plate and the ceramic plate in this manner is subjected to etching to form a conductive circuit pattern on one of the metal plates. The important thing here is, first, to make electrical connections only to the metal plate to be etched, and second, to prevent the etching agent from getting to the metal plate that is not to be etched.

The first point is that since the metal plate itself is very thin, it is difficult to make electrical connections using lead wires or the like, and there is no material suitable for industrial use. The second point is that if the etching agent is a solution as in the past, it has a low viscosity and therefore tends to flow into the non-etched side, requiring complicated masking.

<Problems to be Solved by the Invention> On the other hand, as a means for achieving miniaturization and high precision of a conductor circuit pattern, there is a method of forming a pattern by photoetching after joining metal plates. In this case, etching is required to completely remove the bonding layer metal part and the metal plate, and the etching depth is the thickness of the metal plate (usually 0.1 to 0.4 mm) plus the bonding layer thickness. Since the etching ranges from 0.1 to 0.5 mm, it takes a long time to complete etching, and there is a possibility that problems such as side etching at the edges of the mask and damage to the mask may occur. Also, since the depth/width (=d/W) of such single-sided etching is d/w<0.5, the etching width is limited by the thickness of the metal plates to be joined, and for example, Plate thickness 0.2mm, bonding layer thickness 0
．． When the diameter is 0.05 mm, the minimum value of the gap that can be etched is 0.05 mm.
It will be 5mm.

Furthermore, when joining metal plates using a brazing filler metal containing the above-mentioned active metal, this conventional method of removing the metal plate portion and forming a pattern by photo-etching is a method for bonding the metal plates and the brazing filler metal. It is necessary to change the etching solution, which may complicate the process, and problems may occur, such as the active metal forming a stable compound with the ceramic and increasing the etching load.

For example, in the case of a board made by bonding a copper plate to AλN ceramics using an Ag-Cu brazing filler metal containing Ti as an active metal, the iron chloride-based etching solution used to etch the copper plate does not completely remove the brazing filler metal, and the nitric acid It is necessary to change the liquid to the system. Also, at this time, a conductive and stable compound (TjN) is formed at the interface between the AuN and the brazing metal, and to completely remove it, a highly active etching solution such as hydrofluoric nitric acid must be used. It won't happen.

The present invention aims to solve the above-mentioned problems that occur in the conventional photoetching process when etching 70,000 gold plates bonded to a ceramic plate to form a conductive circuit pattern. To provide a method for manufacturing a circuit board, especially for high power, which can electrically connect only the board and prevent etching agent from going around to a metal plate that is not etched, in a simple manner and suitable for mass production.

Means for Solving the Problems According to the present invention, a laminate is formed by bonding a metal plate to at least one side of an electrically insulating ceramic plate, and has a conductive circuit pattern on the metal plate. When manufacturing a circuit board, this laminate is placed on a conductive plate, and an etched plate is formed on the surface of the metal plate, which is made of a substance that has electrical insulation properties and does not react with a corrosive solvent, and corresponds to the circuit pattern. A mask having a pattern to be applied is placed in close contact with the metal plate, a corrosive solvent made into a paste is applied onto the metal plate through the pattern of the mask, an electrode is installed on the surface coated with the corrosive solvent, and then the conductive plate is The ceramic plate of the upper laminate and the other metal plate are liquid-tightly coated with an insulator, and only the conductive plate and the metal plate are electrically connected by a conductive substance, and the electrode and the conductor are electrically connected only between the conductive plate and the metal plate. Electricity is applied between the electrode and the metal plate to perform electrolytic etching through the corrosive solvent, and the metal plate is etched according to the pattern of the mask to form a conductor on the insulating ceramic plate. A method for manufacturing a circuit board is provided in which the special feature (J'2) is to form a circuit pattern.

The insulator is preferably a thermoplastic wax, and the conductive substance is preferably a conductive paste in which conductive particles are dispersed in a resin.

The ceramic plate and the metal plate are preferably bonded using a brazing filler metal containing an active metal in a vacuum or an inert atmosphere.

The pasting corrosion solvent contains at least 1 fffi acid selected from nitric acid, sulfuric acid, hydrochloric acid and hydrofluoric acid and/or
or at least one salt selected from ferric chloride and cupric chloride, alone or in combination, with water or sodium polyacrylate, sodium alginate, xanthan gum, silicon dioxide, alumina, and water glass. Preferably, the paste is prepared by adding at least one pasting agent.

Also, electrolytic etching can be performed with direct current or alternating current.

The invention will now be explained in more detail with reference to the accompanying drawings.

Figure 1 shows a method according to the present invention in which a conductive circuit pattern is formed by etching a metal plate of a laminate made by bonding metal plates 2 and 3 to the above-mentioned insulating ceramic plate 1. FIG. A screen 11 having a pattern to be etched, that is, a corrosive solvent permeable portion 11a and an impermeable portion 11b, is brought into close contact with the surface of the metal plate 2 to be etched. Solvent 7 is being applied.

6 is a fixed frame of the screen.

The ceramic plate 1 and the metal plate 2.3 may be joined using a commonly used Ag-Cu brazing filler metal.
An Ag-Cu-based brazing material containing an active metal such as Ti, Zr, or Hf that promotes bonding with ceramics may be used. The present invention is particularly suitable for etching a laminate bonded using a brazing material containing an active metal.

When bonding a ceramic plate and a metal plate, Ar or He is used to prevent oxidation.

It is preferable to use an inert atmosphere such as N2.

Alternatively, a vacuum may be used.

The brazing material used may be a paste containing Ag%Cu or the like, or a foil containing Ag, Cu, etc. The brazing material may also contain the active metal.

If the screen 11 having the pattern to be etched is made of a material that is electrically insulating and does not react with corrosive solvents, it may be made of a material such as nylon, tetron, polyester, etc. used in ordinary screen printing. Even if a resist is printed on it, nylon, PVC,
A stamped sheet of Teflon, stainless steel, etc. may also be used. This screen 11 is fixed to a suitable fixed frame 6, without bending, and with the screen itself having appropriate elasticity.
It is desirable to be able to adhere closely to the surface of the metal plate to be etched.

Moreover, a tape can also be used in place of the screen. When a tape is used, a mechanical means such as a cutter may be used to form the pattern, or a laser beam may be used to form the pattern, which is simpler than a photo-etching method. If tape is used, it can be attached more closely to the metal plate than the screen, and it is inexpensive and disposable, making it suitable for prototyping.

The paste-formed corrosive solvent 7 can be prepared by adding water to a mixture of acids such as nitric acid, sulfuric acid, hydrochloric acid, butic acid, and/or salts such as ferric chloride and cupric chloride. Not only can it be made into a paste, but it can also be made by any method as long as it is made by adding a pasting agent such as sodium polyacrylate, sodium alginate, xanthan gum, silicon dioxide, alumina, or water glass. be able to.

By forming the corrosive solvent into a paste in this manner, its fluidity and reactivity can be adjusted as appropriate. Thus, during etching, it is possible to achieve clear etching without side etching by using a simple method of closely contacting a patterned etching screen or tape, without having to provide a photoresist layer that is in close contact with the surface of the material to be processed as in the prior art. You can get the pattern.

The reactivity and fluidity of the corrosive solvent used in pasting will depend on the material of the material to be treated, the material of the screen used, the size of the pattern and required precision, the mesh spacing of the screen,
It can be selected as appropriate depending on the processing time, method to be processed (continuous processing, batch processing, etc.).

However, when the active metal contains Ti%Zr, Hf, etc., it is preferable to use a paste-like corrosive solvent containing nitric acid, nitric acid, etc.

In addition, the viscosity of the paste is 5000 to 50000cp
It is best to keep it at around s.

As shown in FIG. 1, an electric fi 8 is installed on the surface to which the corrosive solvent 7 is applied so that it can be energized, and both the electrode 8 and the metal plate 2 are connected to an electrolytic power source 10 via lead wires 9, respectively. A screen 11 is provided between the electrode 8 and the metal plate 2.
By passing an electric current through the corrosive solvent 7 that has passed through the permeable portion 11a of the metal plate 2, the corrosive solvent 7 is passed through the etched portion 11a of the screen 11 in the metal plate 2.
Only the parts that are in contact with are electrolytically etched. The electrodes may be fixed or octagonal. FIG. 4 shows a circuit board manufactured according to the present invention.

In addition to copper, nickel, stainless steel, common steel, titanium, and other metals, carbon, conductive ceramic, and the like can be used for the electrode, and the shape can be arbitrarily selected according to the shape of the material to be treated.

As the power source, a normal electric power source, potentiostat, galvanostat, etc. can be used, and can be selected depending on the purpose.

At this time, the polarity and current pattern may be appropriately selected depending on the metal plate, corrosion, and solvent, but applying an alternating current may be effective in preventing side etching. When performing direct current electrolysis, it is preferable to use the metal plate to be etched as an anode and the counter electrode as a cathode.

The present invention will be explained in more detail with reference to FIG.

A laminate consisting of ceramic plate 1 and metal plate 2.3 is placed on a conductor 20 such as a metal plate, and first, the entire circumferential surface of ceramic plate 1 and metal plate 3 is covered with insulator 21.
Next, a conductive substance 22 is inserted between the metal plate 2 and the conductor 20.
Connect with. Then, a mask such as a screen or tape having a pattern corresponding to a conductive circuit pattern is brought into close contact with the metal plate 3, the above-mentioned paste 7 is supplied through the mask, and an electrode 8 is arranged on this paste 7, A voltage is applied between the electrode 8 and the conductor 20 by a power source 10 to perform electrolytic etching.

At this time, when using a screen as a mask,
The screen 11 and the metal plate 2 must be brought into close contact over the entire area in order to perform complete etching. For this purpose, the conductor 22 must be at a lower level than the level of the metal plate 22. As a result, the screen is brought into close contact with the entire surface of the metal plate 2, so that it does not float off the metal plate 2, and the etching is performed well on the entire metal plate.

When using tape as a mask, the tape is attached to a metal plate, so it is not necessarily necessary to do so as in the case of a screen.

As the conductor, a copper plate, an iron plate, a stainless steel plate, etc. can be used.

The above-mentioned insulator is preferably a plastic one, such as a flexible wax that is usually used for temporary fixing of cut samples, and which does not react with the material that makes up the 4B of the laminate, such as a hot plate, etc. It is preferable to use an adhesive that can be easily attached and removed without deteriorating the laminate at a low temperature of 200 DEG C. or lower, such as Green Wax manufactured by Malto Aji.

In addition, as the conductive substance, it is convenient to use a conductive paste, which is made by dispersing conductive particles such as metal powder in a resin, and which hardens and develops conductivity by drying a solvent at room temperature. It is preferable to use a room-temperature curing conductive paste (trade name: Dotite, manufactured by Takura Kasei).

<Example> The present invention will be specifically described below based on Examples.

(Example 1) Alumina (thickness 0.635 mm,
A copper plate (thickness 0.2 mm) was used as the metal plate.
mm, diameter 20 mm) and 1070 mm by the eutectic method.
A laminate was obtained by heating and bonding at ℃. The bonding conditions are as follows.

The laminate was heated to a length of 20 mm% and a width of 0.2 m using a conventional etching solution having the composition shown below and the paste of the present invention in an N2-0° (0.2%) mixed gas atmosphere of 7 atmospheres and held at 1070°C for 5 minutes.
A cross shape of m was etched. Electrolytic etching was carried out as shown in FIG. 3 using a stainless steel plate as a conductor, green wax manufactured by Malto Aji as an insulator, and dotite manufactured by Nokura Kasei as a conductive paste. As a result, when a paste-like corrosive solvent (paste) is used, by adjusting the viscosity of the paste, the paste stays in the transparent part of the screen or mask, allowing for efficient etching.The etching width is 0.3 mm on the copper plate surface. Although a substrate interface of 0.17 mm was obtained, using a conventional etching solution, the etching solution seeped under the screen or mask, corroding the copper plate in areas that were not intended to be etched.

(1) Composition of conventional etching solution 20wt% ferric chloride aqueous solution (2) Composition of paste in the present invention 20+vt% S2 iron chloride aqueous solution + 3wt% sodium polyacrylate aqueous electrolytic condition current when using paste 200 mA Voltage: 4v Time: 15 minutes (Example 2) An Al1N plate (thickness: 0.635 mm) was used as the ceramic plate.
, diameter 20 mm), and a copper plate (thickness 0.2 mm) as the metal plate.
2 mm, diameter 20 mm), and Ag-Cu brazing material 72Ag-27Cu-IT containing active metal Ti as a brazing material.
A laminate was obtained by bonding copper plates to both sides of the ceramic plate using i. The bonding conditions are as follows.

Vacuum furnace: Hold at 800°C for 5 minutes. Vacuum level: 5 x 10-5 Torr when reaching 800°C. This laminate was etched into a length of 20 mm and a width of 0.2 mm using a conventional etching solution with the following composition and the paste of the present invention.
A cross shape is etched on the surface. A stainless steel plate was used as the conductor, and as the insulator, a sample cutting adhesive manufactured by Marutami Co., Ltd. (trade name) Adfiltus was used as a conductive paste (trade name), a room temperature curing conductive paste manufactured by Fujikura Kasei ■ (trade name: Dotite) was used, as shown in Figure 3. Electrolytic etching was performed as shown.

As a result, when a paste-like corrosive solvent (paste) is used, by adjusting the viscosity, the paste stays in the transparent area of the screen or mask, making it possible to perform etching with good workability.
0.18 mm was obtained at the 2 mm substrate interface.

However, the conventional etching solution flowed out under the screen and mask, not only corroding the copper plate in areas that were not intended to be etched, but also reaching the conductive paste and the stainless steel plate, which is a conductor, and corroding it. .

(1) Composition of conventional etching solution 20 wt% ferric chloride aqueous solution (2) Composition of paste in the present invention 20 wt% ferric chloride aqueous solution + 3 wt% sodium polyacrylate water (electrolytic conditions when using 8-part paste) Current: 200 mA Voltage: 4 V Time: 15 minutes (Effects of the Invention) In the present invention, since a paste is used as the etching agent, the poor operability of conventional etching solutions is solved and the process is simplified.

Furthermore, etching precision and etching operability can be improved by using a brazing material containing an active metal that increases the bonding strength between the ceramic plate and the metal material.

Furthermore, only the metal plates to be etched are electrically connected, and the paste is prevented from getting around to the metal plates that are not to be etched, so the metal plates that are not to be etched do not deteriorate and a high-quality circuit board is produced. can get.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a method of etching a metal plate bonded to a ceramic plate according to the method of the present invention. FIG. 2 is a sectional view showing a circuit board manufactured by the method according to the invention. FIG. 3 is a diagrammatic sectional view showing a specific example of carrying out the method of the present invention. FIG. 4 is a sectional view showing a conventionally used semiconductor module substrate. 6... Screen fixing frame, 7... Pasted solvent for corrosion, 8... Electrode, 9... Lead wire, 10... Power supply, 11... Screen, +1a... For corrosion Solvent permeable portion, 11b...Corrosion solvent impermeable portion 20...Conductor, 21...Insulator, 22...Conductive substance Explanation of symbols 1...Ceramic plate having insulation properties, 2 ... Metal plate having a circuit pattern, 3... Metal plate, 4... Element, 5... Heat sink, FI G, 1 FIG, 3 No.

Claims (6)

[Claims] (1) Consisting of a laminate formed by bonding a metal plate to at least one side of an electrically insulating ceramic plate, when manufacturing a circuit board having a conductive circuit pattern on the metal plate, the laminate is conductive. A mask made of a material that has electrical insulation properties and does not react with corrosive solvents and has a pattern to be etched corresponding to the circuit pattern is brought into close contact with the surface of the metal plate. After applying a pasted corrosive solvent onto the plate through the pattern of the mask and further installing an electrode on the surface coated with the corrosive solvent, the ceramic plate of the laminate on the conductive plate and the other metal plate are applied. is liquid-tightly covered with an insulator, and only the conductive plate and the metal plate are electrically connected by a conductive substance, and current is passed between the electrode and the conductor to connect the electrode and the metal plate. A circuit board characterized in that a conductor circuit pattern is formed on the insulating ceramic plate by electrolytically etching the metal plate through the corrosive solvent between the plate and the metal plate according to the pattern of the mask. manufacturing method. (2) The method for manufacturing a circuit board according to claim 1, wherein the insulator is a thermoplastic wax. (3) The method for manufacturing a circuit board according to claim 1 or 2, wherein the conductive substance is a conductive paste in which conductive particles are dispersed in a resin. (4) The method for manufacturing a circuit board according to any one of claims 1 to 3, wherein the ceramic plate and the metal plate are bonded together in a vacuum or in an inert atmosphere using a brazing material containing an active metal. (5) The paste-forming corrosion solvent contains at least one acid selected from nitric acid, sulfuric acid, hydrochloric acid, and hydrofluoric acid and/or at least one salt selected from ferric chloride and cupric chloride. or a paste obtained by adding water or at least one pasting agent selected from sodium polyacrylate, sodium alginate, xanthan gum, silicon dioxide, alumina, and water glass to the mixture. The method for manufacturing a circuit board according to the invention. (6) The method for manufacturing a circuit board according to any one of claims 1 to 5, wherein the electrolytic etching is performed using direct current or alternating current.