JPH0715100A - Ceramic board having metallic circuit and production thereof - Google Patents

Abstract

PURPOSE:To form a circuit accurately by bonding a metallic circuit, obtained by removing the parts other than a circuit pattern from a detachable metal foil holding the circuit pattern, to the upper and lower surfaces of a ceramic board. CONSTITUTION:A metal foil 1, from which circuit patterns 2, 3 are punched by press, is fitted to the original position on the upper surface of an aluminium nitride board coated with a binder paste whereas a trimmed metal foil 5, from which a planar circuit pattern 6 is punched by press, is fitted to the original position on the lower surface of the board. It is then placed in a furnace thus producing a bonded body. The bonded body is then manually peeled off at the part not bonded with the aluminium nitride board, i.e., the part other than the circuit pattern, and then a copper circuit and a planar copper circuit are formed, respectively, on the upper and lower surfaces of the aluminium nitride board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate having a metal circuit used for a power module of electronic parts and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, along with the high performance of industrial equipment such as robots and motors, the transition of high power modules such as high power and high efficiency inverters is progressing, and the heat generated from semiconductor elements is also increasing. I am following. In order to efficiently dissipate this heat, various methods have been conventionally used in high power module substrates. In particular, recently, it has become possible to use a ceramic substrate having good heat conduction, so that a metal plate such as a copper plate is bonded onto the substrate, a circuit is formed, and the semiconductor substrate is processed as it is or after plating or the like. A structure for mounting an element is also being adopted. Inverters using such high power module boards are used for various machine tools, railways, robots, motors, etc.
It is expected to expand to the field of elevators and, in the future, electric vehicles.

Conventionally, such a metal circuit of a high-power module substrate is formed by bonding a metal foil circuit, which has been punched out or formed by etching, to a ceramics substrate with a fixing agent (hereinafter referred to as "pattern mounting method"). Alternatively, a metal foil on which no circuit is formed is fixed to the upper and lower surfaces of the ceramic substrate, and an etching resist is printed in a circuit pattern on the upper and lower surfaces to remove unnecessary portions (hereinafter, referred to as "etching method"). It was formed by. Furthermore, recently
It has also been proposed to remove a portion other than the circuit pattern from the metal foil on which the removable circuit pattern is held to form a circuit (Japanese Patent Laid-Open No. 3-102891).
WO 91/16805).

There are various methods for joining metal and ceramics, but from the viewpoint of manufacturing a circuit board, Mo--Mn is used.
Method, active metal brazing method, copper sulfide method, DBC method, copper metallizing method and the like.

[0005]

According to the pattern mounting method, the parts of the metal foil circuit pattern are previously made of gypsum, epoxy resin, or the like in order to position the adhesive pattern and the metal foil circuit pattern on the ceramic substrate. Since it is carried out by fitting it into a mold of a circuit pattern shape made of metal or the like and receiving it, there is a drawback in that it takes time to mount the circuit, handling is extremely precise, and the circuit moves even with slight vibration. On the other hand, the etching method has the advantage of being able to handle complex circuits, but it takes a long time to etch because the metal foil becomes thicker on circuit boards intended for large currents, and depending on the etching solution, the circuit may form a trapezoidal shape. As a result, this technique required a high degree of skill.

Furthermore, the etching method using an active metal brazing material for a ceramic substrate such as alumina and aluminum nitride is a DBC contact for metallizing the alumina surface with a copper foil whose surface is only copper oxide. Unlike the legal method (Japanese Patent Laid-Open No. 59-121175), when bonding the ceramic substrate and the metal foil, a conductive adhesive (brazing material) paste is applied to the entire surface of the ceramic substrate to manufacture a bonded body. Therefore, when etching the metal foil, it is necessary to pattern print the resist again, and since the unnecessary fixing agent also had to be etched with a chemical solution such as hydrofluoric acid, the etching solution for the metal foil and the chemical solution were Extremely strict control is required to prevent mixing, and it cannot be said that mass productivity is excellent.

At the present time when advanced power modules such as IGBTs have been developed, expectations for power modules that have been made more intelligent are increasing in the future, but as a circuit board for such applications, It is conceivable to change the surface thickness of the circuit in the controller and the driver. Further, it is considered desirable to partially provide a non-bonding portion between the circuit and the ceramic substrate by changing the thickness of the back surface of the circuit. However, it is difficult to change the thickness on the back surface of the circuit by the etching method, and even if the thickness of the circuit surface is changed, it is necessary to apply the half-etching method and the resist film twice, which makes it difficult to control the thickness. Therefore, in order to obtain a uniform product, the production efficiency was remarkably inferior and it was not a practical process.

On the other hand, in the method of forming a circuit using a metal foil having a removable circuit pattern held therein, in order to avoid contact and fixation between the metal foil other than the circuit pattern and the adhesive agent, the adhesive agent is used. Since it was necessary to print the same in the same shape as the circuit pattern, the work became complicated, and it could not be said that it was excellent in mass productivity. Moreover, since the front surface and / or the back surface of the metal circuit formed by this method is a uniform plane, it has not been possible to sufficiently cope with the power module which has advanced the above-mentioned intelligentization.

An object of the present invention is to solve the above-mentioned drawbacks, and it is possible to form a circuit with high accuracy, eliminate a positional deviation of a circuit pattern, and to provide a ceramic substrate having a metal circuit excellent in mass productivity. A manufacturing method is provided. Another object of the present invention is to provide a ceramics substrate having a metal circuit that can be mass-produced, as a circuit substrate for a power module that has been made more intelligent.

[0010]

That is, the present invention provides a metal obtained by removing a portion other than a circuit pattern from a metal foil having removable circuit patterns held on the upper and lower surfaces of a ceramic substrate. A circuit is joined, and at least one of the combinations of the metal circuit parts forming the metal circuit has a thickness difference, or a metal forming the metal circuit. A ceramic substrate having a metal circuit, characterized in that at least one of the circuit portions has a thickness difference provided on the front surface and / or the back surface thereof, and a ceramic substrate having the metal circuit. As an applicable method, a removable circuit pattern is held after applying the adhesive to the entire upper and lower surfaces of the ceramic substrate. After stacking the metal foils formed by the above, after heating and joining, peel off parts other than the circuit pattern of the metal foils to form metal circuits on the upper and lower surfaces of the ceramic substrate, and then remove unnecessary adhesive with a chemical solution. In the method for manufacturing a ceramic substrate having a metal circuit characterized by, and the manufacturing method, the metal foil has a thickness difference in at least one of the combinations between the circuit pattern portions, or at least one of A method of manufacturing a ceramic substrate having a metal circuit, characterized in that the front surface and / or the back surface of a circuit pattern portion has a thickness difference.

The present invention will be described in more detail below. The metal foil used in the present invention also includes a metal plate usually called a metal plate having a large thickness, for example, copper, iron, nickel, aluminum, brass, stainless steel. It may be a metal foil of steel or the like, which may be partially or entirely plated with an alloy of these or a dissimilar metal. For example, in order to facilitate wire bonding after mounting a semiconductor on a circuit board, nickel foil or gold plated copper foil may be used.

As a method for obtaining a metal foil having a removable circuit pattern bonded to the upper surface of a ceramic substrate, a method of removing the portion corresponding to the circuit pattern from the metal foil and then returning it to the original state is described. Alternatively, it is possible to employ a method in which most of the circuit pattern is separated and a groove is formed until just before part of the circuit pattern falls off. The former can be performed by a press punching die, a profile saver, a profile milling machine, and the latter can be performed by chemical etching using iron chloride or the like. Of these, the method suitable for the present invention is press punching, which increases the mass productivity and allows the ceramic substrate to be marked, so that the positioning becomes easy. Press punching
All circuit patterns may be punched by one press, or so-called progressive press punching may be performed in which the circuit patterns are partially punched in several times.
These are properly used depending on the complexity of the circuit pattern, the method of holding the metal foil, and the thickness of the metal foil.

On the other hand, a metal foil holding a removable circuit pattern bonded to the lower surface of the ceramic substrate can be manufactured in the same manner as above.
The circuit pattern formed by this metal foil is usually
It is a planar circuit pattern that is trimmed from the end of the ceramic substrate by about 0.1 to 5 mm, preferably about 0.1 to 1 mm, and is attached to the heat sink. In the present invention, it is not limited to such a planar circuit pattern, and any circuit pattern may be drawn.

As in the present invention, at least one of the combinations of the metal circuit parts forming the metal circuit has a thickness difference, or at least the metal circuit parts forming the metal circuit. In order to provide a thickness difference on the front surface and / or the back surface of one metal circuit portion, in the metal foil holding the removable circuit pattern, at least one of the combinations of the circuit pattern portions has a thickness difference. This can be done by using a metal foil provided with the metal foil or by using a metal foil having a thickness difference on the front surface and / or the back surface of at least one circuit pattern portion. In the latter case, it is desirable that the thickness difference be extremely changed by providing a step rather than continuously changing it, and the step is provided on one surface and / or on both surfaces by one or more.

Further, in the present invention, in order to avoid contact between a ceramic substrate and a circuit portion having a large coefficient of thermal expansion such as a soldered portion, a part of the circuit portion is bent to form a ceramic substrate. The non-contact portion can also be formed.

Since the back surface of the metal foil holding the removable circuit pattern used in the present invention is not on the same plane and there is a step between the circuit pattern portion and the other portion, the ceramic substrate has When bonding this, there is a feature that parts other than the circuit pattern can be floated from the ceramic substrate to avoid contact with the adhesive agent and be bonded.

Examples of the ceramic substrate used in the present invention include alumina, silicon carbide, aluminum nitride, beryllia and the like. Further, as the fixing agent, as a metal component, Ag and Cu as a main component and T
An active metal foil (for example, JP-A-58-140381) or a paste of active metal powder (for example, JP-A-56-163093) containing an active metal such as i or Zr as a subcomponent is preferable, and Ag69 to 75 is particularly preferable. Parts by weight and Cu 25-31
A paste containing 3 to 35 parts by weight of Zr per 100 parts by weight of the total weight is suitable. To prepare the paste, an organic solvent and an organic binder as necessary are used, and as the organic solvent, methylcellosolve, ethylcellosolve, terpineol, isophorone, toluene, etc., and as an organic binder, Ethyl cellulose, methyl cellulose, polymethyl methacrylate, etc. are used.

In order to form a metal circuit on the upper and lower surfaces of the ceramic substrate, the adhesive is applied to the entire upper and lower surfaces of the ceramic substrate in an amount of 5 to 10 mg / cm ² (after drying), and then removable. If necessary, at least one of the circuit pattern portions may have a thickness difference, or a metal foil having a circuit pattern held on the top surface and / or the back surface of the circuit pattern portion may have a thickness difference between the top surface thereof. After arranging them on the lower surface and keeping them under a high vacuum of 10 ^-4 Torr or less at a temperature of 880 to 950 ° C. for about 0.3 to 3 hours to join them, peel off parts other than the circuit pattern by hand or the like. Can be done by
Then, the unnecessary adhesive agent remaining between the metal circuits is hydrofluoric acid alone, or a mixed acid of inorganic acid such as nitric acid, sulfuric acid, hydrochloric acid and hydrofluoric acid, or aqua regia, sodium hydroxide solution, ammonium fluoride solution. Dip in a chemical solution such as hydrogen peroxide solution or shower to remove. In this case, add 40 to 80
It is effective to warm it to ℃.

[0019]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Example 1 Ag powder 75 parts by weight, Cu powder 25 parts by weight, Zr powder 2
A binder solution was prepared by adding 0 parts by weight, 15 parts by weight of terpineol and 1.5 parts by weight of a solid solution of a toluene solution of polyisobutyl methacrylate as an organic binder and mixing them well. This has a size of 75 × 70 mm and a thickness of 0.
The entire upper and lower surfaces of a 635 mm aluminum nitride substrate were applied by screen printing. The coating amount (after drying) at that time was 6 to 8 mg / cm ² .

Next, on the upper surface of the aluminum nitride substrate coated with the adhesive paste, a size of 75 × 70 m is formed.
m, a thickness of 0.3 mm, and the metal foil 1 shown in FIG. 1 in which the circuit patterns 2 and 3 were once removed by press punching and then fitted in the original position, and the lower surface, FIG. 2 shows a copper foil having a size of 75 × 70 mm and a thickness of 0.25 mm, in which the planar circuit pattern 6 having a 1 mm edge from the end is once removed by press punching and then fitted in the original position. Metal foil 5
It was charged into the furnace from the superposed respectively, 1 × 10 ^-5 T
After heating in a high vacuum of orr at a temperature of 900 ° C. for 30 minutes, the bonded body was manufactured by cooling at a temperature decrease rate of 2 ° C./minute.

With respect to the obtained joined body, the copper foil on the portion not joined to the aluminum nitride substrate, that is, the portion other than the circuit pattern is peeled off by hand, and the copper circuit is formed on the upper surface of the aluminum nitride substrate and the copper foil is formed on the lower surface. Formed a planar copper circuit. Next, in order to remove unnecessary adhesives and active metal components remaining between the copper circuits and the reaction product with the aluminum nitride substrate, the temperature is kept at 60 ° C. and 10%.
It was immersed in an ammonium fluoride solution for 10 minutes.

The peel strength of the copper circuit portion of the obtained ceramic substrate having a copper circuit was measured by a push-pull gauge to be 10 kg / cm.

Further, the heat cycle (thermal shock) test was carried out by holding in air at −40 ° C. for 30 minutes, then leaving at 25 ° C. for 10 minutes, further holding at 125 ° C. for 30 minutes, then leaving at 25 ° C. for 10 minutes. It went as a cycle. The test was conducted on 10 samples, and the state of the sample was observed every 3 cycles. If any of the samples had copper plate peeling, the number of cycles at that time was measured as the copper plate peeling start frequency. The result was 300 times.

Comparative Example 1 In the same manner as in Example 1, the adhesive paste was applied to the upper and lower surfaces of the aluminum nitride substrate, a copper plate having a thickness of 0.3 mm was formed on the upper surface, and a copper plate having a thickness of 0.25 mm was formed on the lower surface. After placing them in contact with each other, they are put into a furnace, and 1 × 10 ⁻⁵ T
After heating in a high vacuum of orr at 900 ° C for 30 minutes, 2
A joined body was manufactured by cooling at a temperature falling rate of ° C / min.

Next, a UV curing type etching resist is screen-printed on the upper surface and the lower surface of the joined body by screen printing as shown in FIG.
After applying the circuit pattern shown in FIG. 2, an etching treatment was performed using a cupric chloride solution to dissolve and remove unnecessary portions of the copper plate, and the etching resist was stripped with a 5% caustic soda solution. In the bonded body after this etching treatment, there is a reaction product between the aluminum nitride substrate and the unnecessary adhesive agent or active metal component remaining between the copper circuits or the like. % Ammonium fluoride solution for 10 minutes.

The number of times of initiation of peeling of the copper plate of the obtained ceramic substrate having a copper circuit was 200 times.

Example 2 In Example 1, as the metal foil 1, the circuit pattern 2 had a thickness of 0.5 mm and the circuit pattern 3 had a thickness of 0.3 m.
When a ceramic substrate having a copper circuit was manufactured in the same manner as in Example 1 except that the m substrate was used,
The peel strength of the copper circuit portion was 10 kg / cm, and the copper plate peeling start number was 300 times.

Example 3 In Example 1, although there was no difference in the thickness of the back surface of the metal foil 1, the circuit pattern 2a had a thickness of 0.5 mm and the circuit pattern 2b had a thickness of 0.3 mm. A ceramic substrate having a copper circuit was produced in the same manner as in Example 1 except that the one having a thickness of 0.3 mm was used, and the peel strength of the copper circuit portion was 10 kg /
cm, and the number of times of peeling of the copper plate was 300 times.

[0029]

According to the present invention, it is possible to manufacture a ceramic substrate having a metal circuit that has a high processing accuracy of a metal circuit, does not have a positional deviation of a circuit pattern, and can flow a target rated current in a stable manner. You can Further, as compared with the conventional pattern mounting method and etching method, the manufacturing process is simple and the manufacturing can be performed in a short time, so that it is excellent in mass productivity.

Furthermore, the ceramic substrate having a metal circuit of the present invention is industrially used when it is used as an intelligent hybrid integrated circuit substrate with a close packing and a large current capacity in which a control unit and a driving unit coexist. The value is extremely large.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a metal foil that holds a removable circuit pattern bonded to the upper surface of a ceramic substrate.

FIG. 2 is a plan view showing an example of a metal foil holding a removable circuit pattern bonded to the lower surface of a ceramic substrate.

[Explanation of symbols]

1 Metal foil holding removable circuit pattern 2 Circuit pattern 3 Circuit pattern 4 Part other than circuit pattern 5 Metal foil holding removable circuit pattern 6 Circuit pattern 7 Part other than circuit pattern

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Terano 1 Shinkai-cho, Omuta-shi, Fukuoka Electric Chemical Industry Co., Ltd. Omuta Factory

Claims (3)

[Claims] 1. A metal circuit obtained by removing a portion other than a circuit pattern from a metal foil having a removable circuit pattern held on the upper surface and the lower surface of a ceramic substrate. , At least one of the combinations between the metal circuit parts forming the metal circuit has a thickness difference, or at least one metal circuit part among the metal circuit parts forming the metal circuit A ceramic substrate having a metal circuit, wherein a thickness difference is provided on the front surface and / or the back surface of the ceramic substrate. 2. A metal foil having a removable circuit pattern, which is applied to the entire upper and lower surfaces of a ceramics substrate, is superposed on each other, and after heating and bonding, other than the circuit pattern of the metal foil. A method for manufacturing a ceramic substrate having a metal circuit, comprising the steps of peeling off a portion to form a metal circuit on the upper and lower surfaces of the ceramic substrate, and then removing unnecessary adhesive with a chemical solution. 3. The metal foil has a thickness difference in at least one of the combinations between the circuit pattern portions, or has a thickness difference in the front surface and / or the back surface of at least one circuit pattern portion. The method for producing a ceramic substrate having a metal circuit according to claim 2, wherein