JPH06275948A - Heat cycle resisting property improving method for junction body - Google Patents

Abstract

PURPOSE:To provide the title heat cycle resisting property improving method for a junction body, consisting of a copper plate and an aluminum nitride substrate, with which an aluminum nitride substrate, having a copper circuit on which the durability against thermal impulse and the thermal history, namely, heat-cycle resisting property and heat-shock resisting property are sharply improved. CONSTITUTION:The title heat cycle resisting property improving method for a junction body is the method in which the heat cycle resisting property of the junction body, consisting of an aluminum nitride substrate on which a copper plate is jointed on both surfaces, is improved by heat-treating the junction body at 500 to 700 deg.C in a non-oxidizing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving heat cycle resistance of a bonded body, more specifically, an aluminum nitride substrate having a copper circuit which is preferably used in a power module of electronic parts and the like (hereinafter referred to as "copper circuit nitriding"). Aluminum substrate "
Which is used for manufacturing a bonded body of a copper plate and an aluminum nitride substrate.

[0002]

2. Description of the Related Art 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 has progressed, and the heat generated from semiconductor elements has also continued to increase. ing. In order to efficiently dissipate this heat, various methods have been conventionally used for high power module substrates. Recently, ceramic substrates with good thermal conductivity have become available, so after joining a metal plate such as a copper plate on the ceramic substrate and forming a circuit, the semiconductor element is mounted as it is or after plating or other treatment. The structure that does is also being adopted.

There are various methods for joining metal and ceramics, but from the viewpoint of manufacturing circuit boards, the Mo-Mn method,
There are active metal brazing method, copper sulfide method, DBC method, copper metallizing method and the like. In particular, in high power module substrates, attention has been paid to aluminum nitride substrates having high thermal conductivity in place of conventional alumina, and as a method for joining copper plates to be copper circuits or back copper plates, a copper plate and an aluminum nitride substrate are bonded to each other. An active metal brazing method (for example, Japanese Patent Laid-Open No. 60-177634) in which a brazing material containing an active metal is interposed and heat treatment is performed, or an aluminum nitride substrate whose surface is oxidized and a copper plate have a melting point of copper. In the following, a DBC method (for example, Japanese Patent Laid-Open No. 56-163093) in which heat bonding is performed at a temperature higher than the eutectic temperature of Cu-O is adopted.

[0004]

Inverters using such high-power module substrates are used for various machine tools, railways, elevators, robots, motors, etc.
In the future, it is expected to spread to electric vehicles. Therefore, miniaturization and weight reduction of the module are increasingly demanded, and in order to meet the demand, the copper circuit aluminum nitride substrate must be necessarily miniaturized. However, there is a problem that the thickness of the copper circuit must be increased in order to achieve a current density equivalent to that of the conventional one by downsizing, and the area of the aluminum nitride substrate also becomes small. I also needed to reduce the thickness.

Conventionally, in this type of copper circuit aluminum nitride substrate, since the circuit is formed without any post-treatment after the joining of the copper plate and the aluminum nitride substrate is completed, When subjected to thermal shock such as during soldering or heat cycle, the warpage increases to about 1.5 to 2 times due to the effect of thermal stress based on the difference in thermal expansion coefficient between copper and aluminum nitride. There was a problem in durability because the circuit or the back copper plate was peeled off, or the aluminum nitride substrate was cracked. Therefore, as described above, if the thickness of the copper circuit is increased and the thickness of the aluminum nitride substrate is decreased to achieve miniaturization, the stress difference due to the difference in thermal expansion coefficient between the two becomes larger and the durability is further deteriorated. I was afraid to do it.

As a result of intensive studies to solve the above problems, the present inventors have manufactured a bonded body of a copper plate and an aluminum nitride substrate and then rapidly heat-treated it in a non-oxidizing atmosphere. For example, even if it receives a thermal shock, its warpage is 1.
The inventors have completed the present invention by finding that it can be suppressed to twice or less.

[0007]

That is, the present invention is characterized in that a bonded body in which copper plates are bonded to both surfaces of an aluminum nitride substrate is heat-treated at a temperature of 500 to 700 ° C. in a non-oxidizing atmosphere. It is a method for improving heat cycle resistance of a joined body of a copper plate and an aluminum nitride substrate.

The present invention will be described in more detail below. Usually, this type of copper circuit aluminum nitride substrate is
Since the copper plate thickness on the circuit side is thicker than the copper plate thickness on the back side (for example, Japanese Patent Publication No. 3-511119), when a heat cycle test is performed, the copper plate thickness on the circuit side varies depending on the difference in thermal expansion coefficient between copper and aluminum nitride. The tensile stress acts to generate a warp that makes the circuit side convex, and the warp increases with an increase in heat cycles, so that the copper plate on the circuit side is often peeled off.

On the other hand, as in the present invention, by heat-treating a bonded body of a copper plate and an aluminum nitride substrate at a temperature of 500 to 700 ° C. in a non-oxidizing atmosphere, an aluminum nitride substrate produced by thermal contraction of the copper plate Since the thermal stress can be relaxed, the increase in the amount of warp can be reduced, and the heat cycle resistance can be improved.

More specifically, first, copper plates are bonded to both surfaces of an aluminum nitride substrate to manufacture a bonded body. There is no problem with the active metal brazing method or the DBC method, but the active metal brazing method having a low bonding temperature is more preferable. The aluminum nitride substrate does not have to be a special one, and one having a thermal conductivity of 80 W / mK or more is preferably used, and a front copper plate for forming a copper circuit or a back copper plate for attaching a heat sink is the same as the conventional one. In addition, oxygen-free copper plate, tough pitch copper plate, etc. are preferably adopted.

The brazing filler metal paste used in the active metal brazing method comprises a metal component, an organic solvent and, if necessary, an organic binder, and a mixer such as a roll, a kneader, a Banbury mixer, a universal mixer or a ladle mixer. It can be adjusted by mixing with the like. As the metal component at that time,
The main component of the silver component and the copper component and one or more active metal components selected from titanium, zirconium, hafnium, niobium, tantalum, vanadium and the like and these compounds are used, and as the organic solvent , Methyl cellosolve, ethyl cellosolve, terpineol, isophorone, toluene and the like, and as the organic binder, ethyl cellulose, methyl cellulose, polymethyl methacrylate and the like are used. The brazing material paste is applied on an aluminum nitride substrate by a screen printing method, a roll coater method, or the like, and a copper plate is placed on the aluminum nitride substrate, followed by heat bonding.

The joined body particularly suitable for carrying out the heat treatment of the present invention is one in which the copper plate on the circuit side is warped so as to be concave. The greater this warp, the more durable the heat cycle test is, but if it is too large, voids will occur when the back copper plate of the copper circuit aluminum nitride substrate is soldered to the heat sink. The warp value is 400 μm or less (0 is not included), preferably 300 μm or less, particularly preferably 30 to 200 μm. The warp value can be measured by a slit gauge method, a dial gauge method, use of a surface roughness meter, or the like.

The thickness of the aluminum nitride substrate, the front copper plate, and the back copper plate depends on the production of the above-mentioned bonded body. For example, the aluminum nitride substrate has a thickness of 0.635.
When the thickness of the front copper plate on the circuit side is 0.3 to 0.5 mm, the thickness of the back copper plate is 0.1 to 0.25 mm.
When the thickness of the aluminum nitride substrate is thicker or thinner than 0.635 mm, the durability of the aluminum nitride substrate against deformation such as warpage and stress such as compression and tension changes. It is desirable to change the thickness.

In the present invention, the joined body of the front and back copper plates and the aluminum nitride substrate manufactured as described above is placed in a furnace and heat-treated at a temperature of 500 to 700 ° C. in a non-oxidizing atmosphere of nitrogen, hydrogen, argon or the like. Is to do. 500 ° C
If the temperature is less than 1, the effect of the heat treatment is insufficient, while if it exceeds 700 ° C, in the case of a joined body produced by the active metal brazing method, the melting point of the brazing filler metal forming the joining layer is The bonding layer deteriorates due to the approach, and in the case of the bonded body manufactured by the DBC method, stress is caused by the difference in thermal expansion between Cu ₂ O and the aluminum nitride substrate, which is slightly present between the copper plate and the aluminum nitride substrate. Occurs and adversely affects the aluminum nitride substrate. The heat treatment time is from 1 to
About 3 hours is preferable, and after the heat treatment, cooling is performed at a rate of about 2 ° C./minute.

The heat treatment of the present invention can also be carried out by joining a copper plate and an aluminum nitride substrate, and holding them for 1 to 3 hours at a temperature of 500 to 700 ° C. on the way to cooling to room temperature.

In order to form a copper circuit in the joined body which is heat-treated by the method of the present invention, it is desirable to etch the front copper plate with ferric chloride or cupric chloride. At this time, the etching speed, the processing temperature, and the chlorine ion concentration are changed according to the thickness of the copper plate. Regarding the shape of the copper circuit, it is desirable to shorten the length of the continuous pattern with respect to the length of the aluminum nitride substrate so as to minimize the difference in thermal expansion between the aluminum nitride substrate and the copper plate. Further, it is desirable that the length of the aluminum nitride substrate is as short as possible.

[0017]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Examples 1-7 Comparative Examples 1-10 75 parts by weight of silver powder, 25 parts by weight of copper powder, 20 zirconium powder
1 part by weight, 15 parts by weight of terpineol and 1.5 parts by weight of solid content of a toluene solution of polyisobutyl methacrylate as an organic binder were added and mixed well to prepare a brazing paste. This is an aluminum nitride substrate (75mm × 70mm ×
The entire surface was coated on both sides with a thickness of 0.635 mm by screen printing. The coating amount (after drying) at that time was 6 to 8 mg / cm ² .

Next, the front copper plate and the back copper plate having various thicknesses shown in Table 1 are placed in contact with each other, and then placed in a furnace and heated under high vacuum at a temperature.
After heating at 900 ° C. for 30 minutes, it was cooled to room temperature at a temperature decrease rate of 2 ° C./min to manufacture a joined body, and the warpage was measured with a dial gauge. Then put it in another furnace, under a nitrogen atmosphere,
After heat treatment at the temperature and time shown in Table 1, the temperature was cooled to room temperature at a rate of about 2 ° C./minute, and the warpage was measured again.

A UV-curing type etching resist is applied to the circuit pattern by screen printing on the surface copper plate of the joined body that has been heat-treated as described above, and then an etching treatment is performed using a cupric chloride solution to eliminate the copper plate unnecessary portion. Was removed by dissolution, and the etching resist was peeled off with a 5% caustic soda solution.

The copper circuit aluminum nitride substrate obtained as described above contains residual unnecessary brazing filler metal, active metal components, and reaction products of the aluminum nitride substrate between the copper circuit patterns. 10 in ammonium fluoride solution
It was immersed for a minute and removed.

For the copper circuit aluminum nitride substrate obtained by the above series of treatments, after measuring the warp, a heat cycle (thermal shock) test was conducted and the warp was measured again. Heat cycle test: After holding at -65 ℃ for 20 minutes in air
One cycle of holding at 150 ° C. for 20 minutes was performed.

For evaluation, 10 samples were prepared for each example, and a heat cycle test was immediately performed. Then, the state of each sample was observed every three cycles, and if there was one sample in which copper plate peeling occurred, the number of cycles at that time was taken as the copper plate peeling number. Each warp is shown as an average of 10 samples. The results are shown in Table 2.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

EFFECTS OF THE INVENTION By using the joined body produced by the present invention, an aluminum nitride substrate having a copper circuit having significantly improved durability against heat shock and heat history, that is, heat cycle resistance and heat shock resistance, is manufactured. be able to.

Claims (1)

[Claims] 1. A bonded body, in which a copper plate is bonded to both surfaces of an aluminum nitride substrate, in a non-oxidizing atmosphere at a temperature of 500.
A method for improving heat cycle resistance of a joined body of a copper plate and an aluminum nitride substrate, characterized by performing a heat treatment at ˜700 ° C.