JPH02209794A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To always use highly active etching liquid for improving the etching accuracy and the etching operatability by repeating processes of electrolyte etching with corrosion solvent and removal of said corrosion solvent used for the electrolytic etching. CONSTITUTION:Only parts, which are in contact with corrosion solvent 7 through parts 11a to be etched of a mask 11, of a metallic plate 2 is electrolytically etched by installing an electrode 8 on a face to which the corrosion solvent 7 is applied, connecting both said electrode 8 and the metallic plate 2 to a power supply 10 for electrolysis, and passing a current between the electrode 8 and the metallic plate 2 through the corrosion solvent 7 which has passed through the permeable parts 11a of the mask 11. Processes of thus causing a current to flow and removing corrosion solvent of decreased activity by suction or other means are repeated. The solvent of decreased activity can be removed, new corrosion solvent can be always used, and percolation to the mask part and clogging of the permeable parts of the mask, which are caused by the residue of the corrosion solvent, and side etch can be prevented by repeating said processes.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement in a method for manufacturing a circuit board with excellent heat dissipation and heat resistance, which is formed by bonding a metal plate to an electrically insulating ceramic plate. .

<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. 3, 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.
Products bonded using AILzO* using the so-called eutectic method in which Cu-0 eutectic is generated by heating have 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 it is recommended to use materials with higher thermal conductivity such as BeO and AβN instead of AJ22O. is being attempted. 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 AnN 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,
It is necessary to oxidize the substrate in advance to form an AJ2203 layer on the surface. Therefore, attempts have been made to bond Aj2N to a copper plate using a brazing filler metal containing an active metal.

<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 metal part of the bonding layer and the metal plate, and the etching depth is the thickness of the metal plate (usually 0.1 to 0.4 mm) plus the thickness of the bonding layer. Since the etching length is 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. In addition, 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. When the metal plate thickness is 0.2 mm and the bonding layer thickness is 0.05 mm, the minimum value of the gap that can be etched is 0.
．． 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. Problems arise, such as the need to change the etching solvent, which complicates the process, and the active metals forming stable compounds with the ceramics, increasing the etching load.

For example, a board made by bonding a copper plate to AjZN ceramics using an Ag-Cu brazing material containing Ti as an active metal,
The iron chloride-based corrosive solvent used to etch the copper plate does not completely remove the brazing material, and it is necessary to change the solution to a nitric acid-based one. Also, at this time, a conductive and stable compound (TiN) is formed at the interface between AflN and the brazing metal, and a highly active corrosive solvent such as nitric acid must be used to completely remove it. There must be.

The present invention aims to solve the above-mentioned problems that occur in the conventional photoetching process when etching a metal plate bonded to a ceramic plate to form a conductive circuit pattern. To provide a method for manufacturing a circuit board especially for high power use, in which the etching operation is simple and the etching accuracy can be improved even if the bonding is performed using a brazing material containing an active metal and the thickness thereof is increased. The purpose is to

In order to solve the above-mentioned problems, it is necessary to: ■ prevent the reaction between the brazing filler metal and active metal and ceramics when using a metal plate and joint, or a brazing filler metal containing an active metal; etching using a corrosive solvent that is effective against all the compounds formed during etching and that is always active; ■ using auxiliary means that promote corrosion, such as pressurization, rocking, and voltage application (electrolysis); The following three points are required: (1) The material of the mask and the method of attachment must be designed to withstand active corrosive solvents and corrosion accelerators.

According to the present invention, as satisfying these conditions,
When manufacturing a circuit board that is composed of a laminate formed by bonding a metal plate to at least one side of an electrically insulating ceramic plate and having a conductor circuit pattern on the metal plate, the surface of the metal plate is electrically insulated. A mask with a 41A to be etched, which is made of a material that has a chemical properties and does not react with a corrosive solvent, and corresponds to the circuit pattern is brought into close contact with the metal plate, and a corrosive paste is pasted on the metal plate through the pattern of the mask. After applying a corrosive solvent and further installing an electrode on the surface coated with the corrosive solvent, electrolytic etching is performed by passing an electric current between the electrode and the metal plate through the corrosive solvent, and then subjected to electrolytic etching. Manufacturing a circuit board characterized by repeating the cycle of removing a corrosive solvent and etching the metal plate according to the pattern of the mask to form a conductive circuit pattern on the insulating ceramic plate. A method is provided.

The joining of the ceramic plate and the metal plate is as follows:
It is preferable to carry out the process in vacuum or in an inert atmosphere using a brazing material containing an active metal.

The pasting 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. Alternatively, a paste is preferably 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.

Further, the electrolytic etching can be performed using direct current or alternating current.

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

FIG. 1 shows a method according to the present invention in which a conductor 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. It is a diagram. A pattern to be etched on the surface of the metal plate 2 to be etched.
That is, a mask 11 having a corrosive solvent permeable portion 11a and an impermeable portion ib is brought into close contact with the mask 11, and the paste-formed corrosive solvent 7 is applied through this mask.
6 is a fixed frame of the mask.

Furthermore, an electrode 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. The part 1 of the mask 11 to be etched is etched in the metal plate 2 by passing an electric current through the corrosive solvent 7 that has passed through the transparent part 11a of the mask 11.
Only the portion that is in contact with the corrosive solvent 7 through 1a is electrolytically etched.

In the present invention, there is a step of passing this current through, a step of removing the corrosive solvent whose activity has become low due to electrolytic etching by a method such as suction, and, if further electrolytic etching is necessary, a step of removing the corrosive solvent through a mask again. The steps of applying and applying the corrosive solvent 7 and passing electric current are repeated.

By repeating the above process, the active solvent can be removed and a new corrosive solvent can be used at all times, thereby preventing side etching, leaching of corrosive solvent residue into the mask area, clogging of the mask transparent area, etc. can be prevented.

Particularly when the etching width is narrow compared to the deep etching depth, when the bonding surface between the ceramic plate 1 and the metal plate 2 or 3 is thick, or when the paste-formed corrosive solvent 7 has a high viscosity. For example, it is essential to use a highly active corrosive solvent, so this step is particularly effective.

This removal method can be carried out using any suitable method. For example, as a suction removal method, it is preferable to use an aspirator or a vacuum pump to suck in air from above the mask through a nozzle. At this time, the nozzle should be shaped so as not to damage the mask. For example, the shape is preferably such that the entire etching process can be suctioned parallel to the surface to be etched and the mask.

Depending on the type of mask, the corrosive solvent may be used to prevent clogging of the mesh if the corrosive solvent paste comes into contact with the etching surface through the mesh, such as a screen, or to corrode the etching surface, such as with a sealing tape. When the solvent paste comes into direct contact with the etching surface, it is recommended to replace it once or twice/every 5 minutes of electrolysis time, depending on the presence or absence of solid matter generated in the etching gap.

Further, in the present invention, the ceramic plate 1 and the metal plate 2
．． For bonding with 3, the Ag-Cu brazing material used in -a may be used, but Ag-Cu containing active metals that promote bonding with ceramics such as Ti, Zr, and Hf
A type of brazing filler metal may also 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, use an inert "JW" such as Ar, He, or N2 to prevent oxidation.
It is better to be careful. Alternatively, a vacuum may be used.

The mask 11 having the pattern to be etched may be a screen, a positive-type photomask, a negative-type photomask, or a film, as long as it is made of a material that has electrical insulation properties and does not react with corrosive solvents. More specifically,
The resist may be printed on a screen made of nylon, Tetron, polymostil, etc., which is used in ordinary screen printing, or a sheet made of nylon, PVC, Teflon, stainless steel, etc. may be stamped. However, when using stainless steel screens, it is necessary to apply a suitable anti-corrosion coating. This mask 11 is fixed to a suitable fixing frame 6, and it is desirable that the mask itself has appropriate elasticity without bending and can be tightly attached to the surface of the metal plate to be etched.

In addition, this paste-formed corrosive solvent includes nitric acid,
Acids such as sulfuric acid, hydrochloric acid, orbutic acid and/or ferric chloride,
Of course, it can be made into a paste by adding water to cupric chloride salts alone or in a mixture, but it can also be made into a paste by adding paste-forming agents such as sodium polyacrylate, xanthan gum, silicon dioxide, alumina, water glass, etc. Any paste manufactured by any method can be used as long as it is an additional paste.

By forming the corrosive solvent into a paste in this manner, its fluidity and reactivity can be adjusted as appropriate. Thus, during etching, unlike the prior art,
Even without providing a photoresist layer in close contact with the surface of the Q material, a clear etching pattern without side etching can be obtained by a simple method of bringing a patterned etching mask into close contact with the surface of the material.

The reactivity and fluidity of the corrosive solvent used in paste formation are determined by the material of the material to be treated, the material of the mask used, the size of the pattern and required accuracy, the mesh spacing of the mask, the processing time, the method of processing (continuous processing, , batch processing, etc.)
It can be selected as appropriate.

However, when bonding is performed using a brazing filler metal containing an active metal, it is preferable to use a paste-like corrosive solvent containing nitric acid, nitric acid, or the like.

Further, the viscosity of the paste is preferably about 5,000 to 50,000 cps.

Note that the electrodes may be fixed or movable.

FIG. 2 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 ceramics, 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.

<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.
3 mm, diameter 20 mm) and 107 by the eutectic method.
A laminate was obtained by heating and bonding at 0°C.

This laminate was etched to a length of 10 mm and a width of 0.2 mm using conventional etching and the paste of the present invention having the following composition.
It is etched into a cross shape. The etching solution was removed three times and replaced with new etching solution once every 5 minutes of electrolysis. The results are shown in Table 1.

(1) Composition of conventional etching solution 20% by weight ferric chloride aqueous solution (2) Composition of paste in the present invention 20% by weight ferric chloride aqueous solution +3 weight sodium polyacrylate aqueous solution Electrolysis conditions when using baset Current 200mA Electric voltage 4v Electrolysis time: 15 minutes Number of times to replace etching solution 3 times (15 minutes each time) (Comparative example 1) Etching was performed by immersion in a conventional etching solution.

The results are shown in Table 1.

Table 1 (Example 2) Aluminum nitride (Aj!N) (
(thickness: 0.835 mm, diameter: 20 mm),
Copper plate (thickness 0.2 mm, diameter 20 mm) as a metal plate
A containing 1% by weight of active metal Ti as a brazing material
A laminate was obtained by bonding using g-Cu brazing material. The bonding conditions are as follows.

This laminate was heated in a vacuum furnace at 800°C for 1 minute to a length of 20 mm and a width of 0.2 m using a conventional etching solution with the following composition and the paste of the present invention.
A cross shape of m was etched. The results are shown in Table 2.

(1) Composition of conventional etching solution: 15% by weight HNO! +2% by weight) IF (2) Composition of paste in the present invention 15wt 1%HNO, +2wt%HF +10wt% Electrolytic conditions when using Aerosil paste Current: 200mA Voltage: 4■ Electrolysis time: 15 minutes Etching exchange frequency Etching was performed three times (15 minutes each time) (Comparative Example 2) using a conventional etching solution. The results are shown in Table 2.

Table 2 <Effects of the Invention> In the present invention, since a paste is used as an etching agent, the poor operability associated with conventional corrosive solvents is solved and the process is simplified.

Furthermore, by always using a highly active etching solution, it is possible to prevent side etching, seepage into the mask area, and clogging of the mask transmission area.

Furthermore, since a brazing filler metal containing an active metal that increases the bonding strength between the ceramic plate and the metal material is used, even if the etching load increases, the etching accuracy and etching operability are not impaired.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view showing an example of a method according to the present invention for etching a metal plate bonded to a ceramic plate. FIG. 2 is a sectional view showing a circuit board manufactured by the method according to the invention. FIG. 3 is a sectional view showing a conventionally used semiconductor module substrate. Explanation of symbols 1... Ceramic plate with insulation, 2... Metal plate with circuit pattern, 3... Metal plate, 4... Element, 5... Heat sink, 6... Mask Fixed frame, 7... Pasted corrosion solvent, 8... Electrode, 9... Lead wire, 10... Power supply, 11... Mask, 11a... Corrosion solvent permeable portion, 11b ... Corrosion solvent impermeable part FIG FIG.

Claims (4)

[Claims] (1) When manufacturing a circuit board that is composed of a laminate formed by bonding a metal plate to at least one side of an electrically insulating ceramic plate and has a conductor circuit pattern on the metal plate, the surface of the metal plate is A patterned mask to be etched that corresponds to the circuit pattern and is made of a substance that is electrically insulating and does not react with a corrosive solvent is brought into close contact with the metal plate, and paste is formed on the metal plate through the pattern of the mask. After applying the corrosive solvent and further installing an electrode on the surface coated with the corrosive solvent, electrolytic etching is performed by passing an electric current through the corrosive solvent between the electrode and the metal plate, and then electrolytic etching is performed. A circuit board characterized in that a conductor circuit pattern is formed on the insulating ceramic plate by repeating the cycle of removing the applied corrosive solvent and etching 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 ceramic plate and the metal plate are joined together in a vacuum or an inert atmosphere using a brazing material containing an active metal. (3) The pasting corrosion solvent is at least one acid selected from nitric acid, sulfuric acid, hydrochloric acid, and hydrofluoric acid, and/or at least one acid selected from ferric chloride and cupric chloride. 2. A paste made by adding water or at least one pasting agent selected from sodium polyacrylate, sodium alginate, xanthan gum, silicon dioxide, alumina, and water glass to salts alone or in combination. 2. The method for manufacturing a circuit board according to 2. (4) The method for manufacturing a circuit board according to any one of claims 1 to 3, wherein the electrolytic etching is performed using direct current or alternating current.