JP3308883B2 - Board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION An object of the present invention is to provide a highly reliable board (circuit board or heat radiating board) particularly suitable for a power module of an electronic component.

The substrate of the present invention is obtained by forming an aluminum (Al) circuit and / or a heat radiation Al plate on a ceramic substrate.
The one formed with the 1 plate is used as a circuit board, and the one formed with only an Al heat radiating plate is used as a heat radiating substrate.
The essential difference between the circuit board and the heat radiating board in the present invention is that only the Al circuit is not formed on the heat radiating board, and its purpose, manufacturing method, etc. are the same as those of the circuit board. The present invention will be described using a circuit board as an example.

[0003]

2. Description of the Related Art In recent years, power modules such as high-power and high-efficiency inverters have been changing with the advancement of the performance of industrial equipment such as robots and motors. I have. In order to efficiently dissipate this heat, various methods have conventionally been used for power module substrates. Especially recently, ceramic substrates with good thermal conductivity have become available,
A structure in which a copper plate is bonded on the substrate to form a copper circuit and then a semiconductor element is mounted as it is or after performing a process such as nickel plating is being adopted. In this case, there is also a structure in which a heat-dissipating copper plate is formed on the ceramic substrate surface opposite to the copper circuit.

[0004] Such modules were initially used for simple machine tools, but have been used for welding machines, train drives and electric vehicles in recent years, and have been used under more severe environmental conditions. Durability and further miniaturization have been required. Therefore, the ceramic substrate is also required to have an increased copper circuit thickness for increasing the current density, and to have improved durability against thermal shock and the like.

[0005]

Conventionally, a commonly used circuit board is formed by forming a copper circuit on an alumina substrate or an aluminum nitride substrate. However, in order to further improve the reliability with respect to heat cycle resistance. Recently, an aluminum nitride substrate having an Al circuit formed thereon has been proposed. However, since aluminum has inferior electrical properties such as current density to copper, such circuit boards have not been widely used. Moreover, as a method for joining aluminum and a ceramic substrate, Al is used.
Although there is a method of heating by interposing a -Si metal foil between the two, it is difficult to further improve the reliability with respect to heat cycle resistance.

An object of the present invention is to provide a ceramic substrate with Al
The object of the present invention is to further increase the reliability of the circuit and / or the heat-dissipating Al plate on the substrate formed with the heat-dissipating Al plate.

[0007]

That is, according to the present invention, a ceramic substrate and an aluminum circuit and / or a heat-dissipating aluminum plate are provided so that copper and silicon in a brazing material have grain boundaries in the aluminum circuit and / or the heat-dissipating aluminum plate. It is those liquid-phase diffusion to become joined, gold the brazing material
70-95 parts by weight of aluminum,
0.5 to 25 parts by weight of copper and 0.5 to 8 parts by weight of copper
The substrate is characterized in that titanium hydride is 1 to 30 parts by weight per 100 parts by weight .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

A high voltage and a high current of several hundred amperes and several thousand volts flow through the metal circuit portion of the circuit board.
Copper circuits are mainly used. However, since a thermal shock is repeatedly received due to a change in environment during use, heat due to switching, and the like, a problem arises in that a copper circuit is separated from an interface of a ceramic substrate due to thermal stress due to a difference in thermal expansion between copper and ceramic.

The magnitude of the thermal stress due to the difference in thermal expansion between copper and ceramics is determined not only by the coefficient of thermal expansion but also by the mechanical properties of the metal itself, mainly tensile strength and proof stress. Therefore, in order to reduce the thermal stress, a metal having lower tensile strength and proof stress than copper may be used, and aluminum is one of such metals having such characteristics. However, in the conventional joining method of a ceramic substrate and an aluminum plate with an Al-Si metal foil interposed therebetween, the joining form is a solid phase diffusion of a Si component to the aluminum plate. Cycleability requirements cannot be met.

The present invention solves this problem, and differs from the prior art in the form of bonding between the aluminum plate and the ceramics substrate. By diffusing copper and Si into the aluminum plate at the grain boundary liquid phase, the present invention provides an improved resistance. The reliability of the heat cycle is further improved.

[0012] Here, the grain boundary liquid phase diffusion means that a paste brazing material containing aluminum, copper, Si and titanium hydride is interposed between a ceramic substrate and an aluminum plate, and is then placed under a high vacuum. By the heat treatment, the liquid phase containing aluminum, copper and Si diffuses along the grain boundaries of the aluminum plate.

[0013] In the conventional solid-phase diffusion with an Al-Si metal foil interposed, the diffusion at the atomic level is such that the Si component is taken into the crystal lattice of the aluminum plate or replaces the lattice atoms. The board will deteriorate. On the other hand, in the liquid phase diffusion at the grain boundary, the brazing filler metal component is present at the grain boundaries of aluminum, so that the original properties of aluminum are not impaired. improves.

The material of the ceramic substrate used in the present invention is, for example, silicon nitride, aluminum nitride, or alumina. Aluminum nitride is suitable for an electric vehicle module. As the thickness of the ceramic substrate,
If the thickness is too large, the thermal resistance increases, and if the thickness is too small, the durability is lost. Therefore, the thickness is preferably about 0.5 to 0.8 mm.

The surface properties of the ceramic substrate are important, and minute defects and dents have an adverse effect when joining an Al circuit, a heat-radiating Al plate, or an Al plate that is a precursor thereof to the ceramic substrate. It is desirable that Therefore, it is preferable that the ceramic substrate has been subjected to a honing process or a polishing process such as machining.

The aluminum purity of the Al circuit and the heat radiation Al plate is preferably 99.5% or more, and the thickness is 100 to 5%.
00 μm is preferred.

As a method of forming an Al circuit and / or a heat radiation Al plate on a ceramic substrate, there are a method of etching a joined body of a ceramic substrate and an aluminum plate, an Al circuit punched from an aluminum plate and / or a heat radiation A plate.
The l-plate pattern can be joined to the ceramic substrate by a method or the like. In these cases, the joining is performed by grain boundary liquid phase diffusion by an active metal brazing method using a paste brazing material.

The active metal brazing method is described in, for example, JP-A-60-177634. The metal component of the brazing filler metal in the active metal brazing method is mainly composed of aluminum, 4b metal such as silicon, tin, lead and germanium, preferably silicon, and 1b metal such as copper, silver and gold, preferably copper. An active metal is used as a secondary component in order to ensure wettability with the ceramic substrate during melting. Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium and the like and compounds thereof. Among them, titanium hydride is preferable. In the present invention, the ratio of titanium hydride to titanium 1-3 per 100 parts by weight of 70 to 95 parts by weight of aluminum, 0.5 to 25 parts by weight of silicon and 0.5 to 8 parts by weight of copper is used.
0 parts by weight. The bonding temperature is desirably 560 to 640 ° C., and the heat source is preferably near infrared rays. However, the heat source is not limited to this, and a conventional resistance heating method may be used.

[0019]

The present invention will be specifically described below with reference to examples and comparative examples.

Examples 1 to 4 25 parts by weight of terpineol were mixed with 100 parts by weight of the brazing material composition shown in Table 1, and a terpineol solution of polyisobutyl methacrylate was added and kneaded to prepare a brazing material paste. This brazing material paste is applied to an aluminum nitride substrate (size: 60 mm × 36 mm × 0.65 mm, bending strength: 40 kg / mm ² thermal conductivity: 135 W / mK)
Was applied in the form of a circuit pattern on both sides by screen printing. The coating amount (after drying) at that time was 3 mg / cm ² .

Next, an aluminum plate (purity 99.5%, 56 mm × 32 mm ×
0.3 mm) pattern, and the degree of vacuum was 1
Under vacuum of ^10-5 Torr or less at 620-630 ° C.
After heating by infrared rays for 0 to 30 minutes, the circuit board was manufactured by cooling at a temperature lowering rate of 2 ° C./min. At this time, it was confirmed from the results of observation of the cross section of the aluminum plate by a scanning electron microscope that the bonding between the aluminum plate and the aluminum nitride was in the form of grain boundary liquid phase diffusion.

COMPARATIVE EXAMPLE 1 Aluminum 80% on both surfaces of an aluminum nitride substrate
Metal foil made of 20% silicon (56 mm x 32 mm x
0.05mm) and an aluminum plate (purity 9)
9.5%, 56 mm × 32 mm × 0.3 mm) and placed under a vacuum of 1 × 10 ⁻⁵ Torr or less.
After near-infrared heating at 630 ° C. for 30 minutes, the circuit board was manufactured by cooling at a temperature lowering rate of 2 ° C./min. In this case, the bonding between the aluminum plate and the aluminum nitride substrate was in the form of solid phase diffusion.

With respect to the circuit board manufactured above, in air, -40 ° C. × 15 minutes, 25 ° C. × 15 minutes, 125 ° C. × 1
A heat cycle test was performed with 0 minute and 25 ° C. × 15 minutes as one cycle, and the number of cycles at which the Al circuit or the heat-dissipating Al plate was peeled was measured. Table 1 shows the results.

[0024]

[Table 1]

[0025]

According to the present invention, a highly reliable board (circuit board, heat dissipation board) having excellent heat cycle resistance is provided.

Continuation of the front page (56) References JP-A-7-45915 (JP, A) JP-A-9-262691 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 3 / 38 H05K 1/02 H01L 23/13 C04B 37/02

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the ceramic substrate and the aluminum circuit and / or the heat dissipating aluminum plate are made of copper and silicon in the brazing material.
Met Con those, which are bonded by diffusing grain boundary liquid phase in the aluminum circuit and / or dissipating aluminum plate in
The ratio of the metal component of the brazing material is aluminum 70
To 95 parts by weight, 0.5 to 25 parts by weight of silicon, and 0.1 part by weight of copper.
5 to 8 parts by weight of total 100 parts by weight of titanium hydride
1 to 30 parts by weight of a substrate.