JPH0766507A - Circuit board - Google Patents

Abstract

PURPOSE:To provide a circuit board capable of avoiding any void during the soldering step onto a base copper plate furthermore having notable endurance to thermal shock and heat history. CONSTITUTION:The circuit board is provided with a metallic circuit on one surface of a ceramic substrate and a metallic heat sink on the other surface thereof and has thickness of the metallic circuit exceeding 0.3mm furthermore, the warp of the same heated at 250 deg.C not exceeding 200mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a circuit board composed of a ceramics substrate having a metal circuit and a metal heat dissipation plate, and is used for a power module of electronic parts.

In recent years, 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. . In order to efficiently dissipate this heat, various methods have been conventionally used for high power module substrates. Especially recently, since ceramic substrates having good thermal conductivity have become available,
A structure in which a metal plate such as a copper plate is joined to a substrate, a circuit is formed, and then a semiconductor element is mounted as it is or after being subjected to a treatment such as plating is being adopted.

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.

Particularly in high power module substrates, attention has been paid to aluminum nitride substrates having high thermal conductivity in place of conventional alumina. As a method for joining copper plates, an active metal may be contained between the copper plates and the aluminum nitride substrate. An active metal brazing method in which a material (hereinafter simply referred to as "brazing material") is interposed and heat-treated to form a joined body (for example, JP-A-60-177).
No. 634), or a DBC method (for example, Japanese Patent Laid-Open No. 56-163093) in which an aluminum nitride substrate whose surface is oxidized and a copper plate are heat-bonded at a temperature below the melting point of copper and above the eutectic temperature of Cu—O. There is.

The active metal brazing method has the following advantages over the DBC method. (1) Since the processing temperature for obtaining the bonded body is low, the residual stress caused by the difference in thermal expansion between the aluminum nitride substrate and the copper plate is small. (2) Since the brazing material is a ductile metal, it is highly durable against heat shock and heat cycles.

[0006]

However, even when the active metal brazing method is used, it cannot be said that it has sufficient durability against damage caused by heat shock such as heat shock or heat cycle, or heat history. A technology proposal was awaited. Therefore, the volume of the metal heat dissipation plate (usually provided on the lower surface of the ceramic substrate) is 50 to 90% of the volume of the metal circuit (usually provided on the upper surface of the ceramic substrate).
It is improved to some extent by adjusting the thickness of the metal heat sink to 50% or less of that of the metal circuit (Japanese Patent Laid-Open No. 5-170564). It was

However, in these techniques, since the metal circuit and the metal radiator plate are both made of copper, changing the volumes of both makes the balance of stress due to thermal expansion different. As a result, the thermal shock resistance of the joint itself became good, and the metal circuit or metal heat sink was less likely to peel off.However, when soldering the base copper plate to the metal heat sink and the semiconductor element to the metal circuit respectively, Due to such a rise in temperature, warp displacement of the bonded body becomes remarkable, and a gap is formed between the metal heat dissipation plate and the base copper plate, and there is a risk that the portion becomes a void after soldering.

The inventors of the present invention have conducted extensive studies in order to solve the above problems, and as a result, heat treatment is performed while applying a load to the bonded body or the circuit board, so that
The present invention has been completed by finding that the amount of warp when heated to 50 ° C. should be adjusted to 200 μm or less.

[0009]

That is, according to the present invention, a metal circuit is provided on one surface of a ceramic substrate and a metal heat dissipation plate is provided on the other surface, and the thickness of the metal circuit is 0. The circuit board is characterized by being larger than 3 mm and having a warp amount of 200 μm or less when heated to a temperature of 250 ° C.

The present invention will be described in more detail below. As the ceramic substrate used in the present invention,
Examples thereof include an aluminum nitride substrate, a beryllia substrate, and an alumina substrate. Among them, an aluminum nitride substrate is preferable, and its sintered density is preferably 95% or more in terms of mechanical strength and electrical characteristics. The thickness of the ceramic substrate is preferably about 0.4 to 0.7 mm.

On the other hand, copper, aluminum, tungsten, molybdenum or the like is used as the metal circuit and / or the metal heat dissipation plate, but copper is generally used. As the thickness of the metal circuit, in recent years, the current density has been increasing, the thickness is 0.3.
The thickness of the metal radiator plate is preferably 0.2 mm or less in order to reduce the thermal resistance.

A metal circuit is formed on one surface of the ceramic substrate,
As a method of providing a metal heat sink on the other surface, a method of etching a joined body of a ceramic substrate and a metal plate, a method of joining a metal circuit punched from the metal plate and / or a pattern of the metal heat sink to the ceramic substrate And the like. As a method for joining the metal plate or pattern to the ceramic substrate in these cases, an active metal brazing method, a DBC method, or the like can be adopted.

The metal component of the brazing filler metal in the active metal brazing method contains silver and copper as main components, and the active metal as a subcomponent for ensuring wettability with the ceramic substrate during melting. This active metal component reacts with the ceramic substrate to generate oxides and nitrides, and these products strengthen the bond between the brazing material and the ceramic substrate. Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium and compounds thereof. The ratio of these is 3 to 35 parts by weight of the active metal per 100 parts by weight of the total amount of 69 to 75 parts by weight of silver and 25 to 31 parts by weight of copper.

The brazing material paste used in the active metal brazing method is prepared by adding an organic solvent and, if necessary, an organic binder to the metal components of the brazing material described above, a roll, a kneader, a Banbury mixer, a universal mixer, and a raider. It can be adjusted by mixing with a machine or the like. Methylcellosolve, terpineol, isophorone, toluene and the like are used as the organic solvent, and ethylcellulose, methylcellulose, polymethylmethacrylate and the like are used as the organic binder. When the material of the metal circuit or the metal radiating plate is aluminum, it is not necessary to use the brazing material described above, and for example, a material containing aluminum and silicon as metal components is sufficient.

According to the present invention, in such a circuit board,
The amount of warpage when heated to a temperature of 250 ° C is 200μ
A major feature is that the thickness is set to m or less. In the prior art, oxygen-free copper or tough pitch copper mixed with a slight amount of oxygen is preferably used as the material of the metal circuit or the metal heat sink in terms of electrical conductivity. The coefficient of thermal expansion of such copper is almost the same as the literature value.
Since it was 10 ⁻⁶ / ° C., which was larger than 4.5 × 10 ⁻⁶ / ° C. of a ceramic substrate, for example, an aluminum nitride substrate, thermal stress was generated when heat was applied to the circuit substrate.

In addition, in the method of changing the volume ratio of the metal circuit and the metal heat sink, when manufacturing the bonded body of the metal plate and the ceramics board, when mounting the obtained circuit board on the base copper plate, As described above, there were many occasions when thermal stress was applied due to thermal shock caused by a temperature difference during use.

However, the thickness of the metal circuit tends to become thicker in the future in order to maintain the current capacity, and it is desirable that the metal radiator plate be thin from the viewpoint of reducing the thermal resistance. Therefore, according to the present invention, even in the case of the circuit board having such a structure, in order to prevent thermal stress from being transmitted to the ceramics substrate as much as possible, after the bonded body or the circuit board is manufactured, 0.3 to 10 kg / cm ² 1 to 2 at a temperature of 100 to 200 ° C. under an inert atmosphere such as nitrogen while applying the load of
After holding for 4 hours, by removing the load and cooling,
The amount of warpage of the circuit board when heated to a temperature of 250 ° C. is set to 200 μm or less.

[0018]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Examples 1 to 3 Comparative Examples 1 to 7 75 parts by weight of silver powder, 25 parts by weight of copper powder, 5 parts by weight of zirconium powder, 15 parts by weight of terpineol and a toluene solution of polyisobutyl methacrylate as an organic binder in a solid content of 1. 5 parts by weight were added and kneaded well to prepare a brazing material paste. This brazing paste is 60x30x
Both sides of a 0.65 mm aluminum nitride substrate were applied to the entire surface by screen printing. The coating amount (after drying) at that time was 6 to 8 mg / cm ² .

Next, a 60 × 30 × 0.5 mm copper plate is placed on the front surface of the aluminum nitride substrate coated with the brazing material paste, and a 60 × 30 × 0.2 mm copper plate is placed on the back surface thereof, respectively. From the above, the load shown in Table 1 was applied to the furnace, heated in a high vacuum at a temperature of 900 ° C. for 30 minutes, and then cooled at a rate of 2 ° C./minute to manufacture a joined body.

A UV-curing type etching resist is applied to the circuit pattern by screen printing on the copper plate of the obtained joined body, and then an etching treatment is carried out using a cupric chloride solution to dissolve and remove unnecessary portions of the copper plate. The etching resist was stripped with a 5% caustic soda solution. On the circuit board after this etching treatment, there is a residual unnecessary brazing material or a reaction product of the active metal component and the aluminum nitride substrate between the copper circuits. Immerse in the solution for 10 minutes. The obtained circuit board was heat-treated under the conditions shown in Table 1, then the load was removed, and the circuit board was cooled to room temperature.

A heat cycle (thermal shock) test was conducted on the circuit board manufactured as described above. The heat cycle test is carried out in the air at −40 ° C. for 30 minutes, then at 25 ° C.
× 10 minutes, 125 ° C × 30 minutes, then 25
The cycle of 10 minutes at ℃ × 10 was performed as one cycle, and the number of heat cycles at which copper started to peel was measured. Also, the temperature is 25
The amount of warpage of the circuit board when heated in 0 ° C. air for 5 hours was measured by a non-contact laser displacement meter. Furthermore, after soldering the circuit board to a base copper plate having a thickness of 4 mm in a reflow furnace at a temperature of 250 ° C. with no load, the voids are measured with an ultrasonic probe, and the void generation rate (%) is area/
The area was calculated as (circuit board area) × 100. The results are shown in Table 1.

[0022]

[Table 1] (Note) The direction of warpage of the circuit board is indicated as + when the circuit surface is concave.

[0023]

Since the circuit board of the present invention has a significantly small warp displacement due to temperature change, the occurrence of voids when soldering the circuit board to the base copper plate is reduced, and the durability against thermal shock and thermal history, that is, Heat cycle resistance is improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Miyuki Nakamura 1 Shinkaimachi, Omuta City, Fukuoka Prefecture Omuta Plant, an electric chemical industry company

Claims (1)

[Claims] 1. A ceramic substrate having a metal circuit on one surface thereof and a metal heat radiating plate on the other surface thereof, the metal circuit having a thickness of more than 0.3 mm and a temperature of 250 ° C. A circuit board having a warp amount of 200 μm or less when heated.