JPH0831229A - Copper paste - Google Patents

Abstract

PURPOSE:To provide a copper paste that does not deflect a wiring board greatly and enables a wiring conductor to be strongly bonded to an insulating base by using copper powders covered with aluminum oxide at their surfaces in the fabrication of the copper paste used for forming a wiring conductor. CONSTITUTION:This copper paste contains copper powders 5 covered with aluminum oxide 4 at their surfaces; an organic binder for caking the copper powders; and a solvent for setting the organic binder at a predetermined viscosity. Preferably 0.02 to 1.0 parts by weight of aluminum oxide are used for 100 parts by weight of copper powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper paste used for a wiring conductor of a wiring board.

[0002]

2. Description of the Related Art Conventionally, a wiring board used for a circuit wiring board on which a semiconductor element is mounted, a semiconductor element housing package for housing the semiconductor element, or the like, is made of an aluminum oxide sintered body excellent in electrical insulation. It is composed of a base and a wiring conductor made of a refractory metal powder such as tungsten or molybdenum deposited on the surface of the insulating base.

In general, such a conventional wiring board is prepared by first adding a suitable organic binder, a plasticizer and a solvent to a raw material powder made of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc. and mixing them to form a sludge. A ceramic green sheet (ceramic green sheet) is obtained by adopting conventionally known sheet forming techniques such as a doctor blade method and a calendar roll method, and then an organic binder, a plasticizer, and a suitable organic binder for high melting point metal powder such as tungsten and molybdenum. A ceramic green sheet in which a metal paste obtained by adding and mixing a solvent is printed and applied in a predetermined pattern on the surface of the ceramic green sheet by a thick film method such as screen printing, and finally the metal paste is printed and applied in a predetermined pattern. Is burned at a temperature of about 1600 ° C in a reducing atmosphere to remove aluminum oxide. It is manufactured by sintering and integrating the aluminum powder and the high melting point metal powder such as tungsten and molybdenum.

However, in recent years, semiconductor devices have been rapidly becoming highly integrated and operating at high speeds, and when the semiconductor devices are mounted on and housed in the wiring board, they have the following drawbacks.

That is, (1) the coefficient of thermal expansion of silicon constituting a semiconductor element and the coefficient of thermal expansion of an aluminum oxide sintered body used as an insulating substrate such as a package for storing a semiconductor element or a circuit wiring board are 3.0 ×, respectively. 10-6 / ℃ ~ 3.5 × 10-6 / ℃, 6.0 × 10-6
/ ° C to 7.5 × 10-6 / ° C, which is a big difference, and when heat generated when the semiconductor element is operated is applied to both, a large thermal stress is generated between them and The semiconductor element may be broken or peeled off from the insulating substrate due to the stress.

(2) An aluminum oxide sintered body used as an insulating base for a package for housing a semiconductor element or a circuit wiring board has a high relative permittivity of 9 to 10 (room temperature 1 MHz). The propagation speed of the signal propagating through the provided wiring conductor is slow, and therefore, the semiconductor element that requires the high speed propagation of the electric signal cannot be accommodated and mounted.

(3) Tungsten forming a wiring conductor,
Since molybdenum or the like has a high electric resistance value, the voltage drop of the electric signal transmitted through the wiring conductor is large, and therefore it is difficult to make the wiring conductor fine and to miniaturize the wiring board. It had a defect such as.

In order to solve the above-mentioned drawbacks, therefore, the insulating substrate is formed of a glass ceramic sintered body having a low relative permittivity and a coefficient of thermal expansion close to that of silicon, and the wiring conductor has an electric resistance. A wiring board formed of copper having a low value has been proposed.

A wiring board in which a wiring conductor made of copper is adhered to an insulating substrate made of such a glass-ceramics sintered body is generally prepared by adding and mixing an appropriate organic binder, a plasticizer and a solvent to the glass-ceramics powder, and then mixing this into a sheet. After a copper paste containing copper powder as a main component is printed and applied in a predetermined pattern on the glass-ceramic green sheet formed in the shape of a sheet, a plurality of glass-ceramic green sheets on which the copper paste is printed and applied are vertically laminated as necessary. Together with this, in a non-oxidizing atmosphere such as a nitrogen atmosphere, about 750-10
It is manufactured by firing at a temperature of 00 ° C. and sintering and integrating glass ceramics and copper powder.

The copper paste used for manufacturing the wiring board is, for example, a paste in which glass filler, organic binder, solvent, etc. are added and mixed to copper powder having an average particle size of about 2 to 5 μm. in use.

[0011]

However, in this conventional copper paste, the sintering start temperature of the copper powder is about 600 ° C., and the sintering start temperature of the glass ceramics serving as the insulating substrate (about 700 to 800 ° C.). ) Is much lower than For this reason, when a glass ceramic green sheet on which a copper paste is printed and applied is fired to produce a wiring board by sintering and integrating glass ceramics and copper powder, the copper paste is sintered and shrunk faster than the glass ceramics, As a result, a large amount of warpage was generated in the wiring board, and the adhesion strength of the wiring conductor to the insulating substrate was reduced, which caused defects.

Further, in this conventional copper paste, the sintering start temperature of the copper powder is 600 ° C., which is lower than the temperature (about 650 ° C.) at which the binder in the copper paste is completely thermally decomposed and scattered to the outside. Therefore, when a glass ceramic green sheet on which a copper paste is printed and applied is fired to produce a wiring board by sintering and integrating glass ceramics and copper powder, before the binder in the copper paste is completely decomposed and scattered. The sintering of the copper powder started, and as a result, the binder, which could not be decomposed and scattered, remained as carbon in the wiring conductor, causing blistering in the wiring conductor.

[0013]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object thereof is not to cause a large warp in a wiring board and to firmly attach a wiring conductor to an insulating substrate. It is to provide a new copper paste that can be used.

[0014]

The copper paste of the present invention comprises:
It is characterized by containing a copper powder whose surface is coated with aluminum oxide, an organic binder for binding the copper powder, and a solvent for setting the organic binder to have a predetermined viscosity.

Further, the copper paste of the present invention is characterized in that the aluminum oxide is 0.02 to 1.0 part by weight with respect to 100 parts by weight of the copper powder.

[0016]

According to the copper paste of the present invention, since the surface thereof contains the copper powder coated with aluminum oxide, the sintering start temperature is set to the glass ceramics starting temperature (700 to 80).
When the glass ceramic green sheet on which the copper paste is printed and applied is fired and the glass ceramic and copper powder are sintered and integrated, the wiring board is manufactured. The copper paste and the glass ceramics are sintered and shrunk at substantially the same time to flatten the wiring board, and the adhesion strength of the wiring conductor to the insulating substrate becomes extremely large.

Further, according to the copper paste of the present invention, since the surface of the copper paste contains the copper powder coated with aluminum oxide, the sintering start temperature is equal to or higher than the temperature (650 ° C.) at which the binder in the copper paste is completely decomposed and scattered. 700 to 800 ℃,
As a result, when a wiring board is manufactured by sintering and integrating glass ceramics and copper powder, the copper powder starts sintering after the binder in the copper paste is completely decomposed and scattered. In addition, a part of the binder does not remain as carbon, and therefore blister does not occur in the wiring conductor.

[0018]

The present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a wiring board manufactured by using the copper paste of the present invention, where 1 is an insulating substrate and 2 is a wiring conductor.

The insulating substrate 1 is made of a glass-ceramics sintered body. For example, silicon oxide 37% by weight, aluminum oxide 35% by weight, magnesium oxide 10% by weight, zirconium oxide 5% by weight, calcium oxide 2% by weight, oxide It is formed of a small amount of lithium, sodium oxide, potassium oxide and the like.

The insulating substrate 1 is made into a slurry by adding and mixing an appropriate organic binder, a plasticizer, a solvent, etc. to a glass ceramic raw material powder consisting of components such as silicon oxide, aluminum oxide, magnesium oxide and the like, and is well known in the prior art. The glass-ceramic green sheet is formed by using the sheet forming technology such as the doctor blade method and the calendar roll method, and then the glass-ceramic green sheet is appropriately punched, and the glass ceramic green sheet is subjected to a punching process in a nitrogen atmosphere at about 750 to 1000 ° C. It is manufactured by firing at a temperature of.

A wiring conductor 2 made of a copper sintered body is attached to the upper surface of the insulating base 1, and the semiconductor element 3 and the like are electrically connected to the wiring conductor 2.

The insulating substrate 1 having a wiring conductor adhered on the upper surface thereof has a low relative permittivity of 6 (room temperature 1 MHz) of the glass-ceramic sintered body constituting the insulating substrate 1, and therefore the wiring conductor is low.
It is possible to increase the propagation speed of the electric signal transmitted through the device 2, and as a result, it becomes possible to accommodate and mount the semiconductor element 3 that requires high-speed signal propagation on the insulating substrate 1.

In the pre-insulating substrate 1, the coefficient of thermal expansion of the glass ceramics sintered body constituting the same is 3.5 × 10 −6 / ° C. to 5.
0 × 10−6 / ° C., which is close to the thermal expansion coefficient (3.0 × 10−6 / ° C. to 3.5 × 10−6 / ° C.) of silicon composing the semiconductor element 3, so that the semiconductor element is formed on the insulating substrate 1. Even after the heat generated by the semiconductor element 3 is applied to both the insulating substrate 1 and the semiconductor element 3 after mounting 3, the large thermal stress does not occur between the two. Therefore, the semiconductor element 3 will not be broken or peeled off from the insulating substrate 1.

Further, the wiring conductor 2 adhered to the upper surface of the insulating base 1 serves as a conductive path for electrically connecting the semiconductor element 3 mounted and housed on the upper surface of the insulating base 1 to an external electric circuit or the like. It acts and is formed of a sintered copper body.

Since the wiring conductor 2 made of a sintered body of copper has a low electric resistance value of copper, the voltage drop of the electric signal propagating through the wiring conductor 2 is made extremely small. Can be miniaturized to achieve miniaturization and high density of the wiring board.

A wiring conductor 2 made of the above-mentioned copper sintered body
Is deposited on the upper surface of the insulating substrate 1 by applying a copper paste, which will be described later, to a glass ceramic green sheet to be the insulating substrate 1 in advance by applying a known pattern by a screen printing method in a predetermined pattern.

The copper paste forming the wiring conductor 2 is
As shown in FIG. 2, an organic binder, an organic solvent, etc. are added to and mixed with copper powder 5 having an average particle size of 2 to 10 μm and a BET value of 0.5 to 1.0 m ² / g whose surface is coated with aluminum oxide 4. It is formed by

The copper powder 5 whose surface is coated with aluminum oxide 4 has a function of imparting conductivity to the wiring conductor 2, and the aluminum oxide 4 coating the surface is sintered of the copper powder 5. Is suppressed, the sintering start temperature is approximated to the sintering start temperature of the glass ceramics sintered body, and the temperature is set to 700 to 800 ° C., which is higher than the temperature at which the binder is completely decomposed and scattered.

The copper paste was obtained by coating the surface of copper powder 5 with aluminum oxide 4 and setting the sintering start temperature to 700 to 800.
Since the temperature is set to 0 ° C., when the glass ceramic green sheet on which the copper paste is printed and applied is fired and the wiring substrate is manufactured by sintering and integrating the glass ceramics and the copper powder, the copper paste and the glass ceramics are It is possible to sinter and shrink substantially at the same time to make the wiring substrate flat, and to make the adhesion strength of the wiring conductor 2 to the insulating substrate 1 extremely large.

The copper paste is formed by coating the surface of copper powder 5 with aluminum oxide 4 and setting the sintering start temperature to 700 to
Since the temperature was set to 800 ° C, when the glass ceramic green sheet on which this copper paste was printed was fired and the glass ceramics and copper powder were sintered and integrated to produce a wiring board, the binder in the copper paste was Since the copper powder begins to sinter after being completely decomposed and scattered, a part of the binder does not remain as carbon in the wiring conductor, and thus a wiring board having no blisters on the wiring conductor can be obtained.

The copper powder 5 whose surface is coated with aluminum oxide 4 is, for example, copper powder made of aluminum sulfate,
After immersing in an aluminum salt solution such as aluminum chloride,
By subjecting this to a dry heat treatment, or after coating with an organic aluminate such as an alkyl aluminate,
It is formed by heat-treating this.

Further, the copper powder 5 whose surface is coated with aluminum oxide 4 is such that the amount of aluminum oxide 4 is 10
When adjusted to be in the range of 0.02 to 1.0 parts by weight with respect to 0 parts by weight, the sintering start temperature of the copper paste is very close to the sintering start temperature of the glass ceramics, which results in the glass ceramics and the copper powder. When the wiring board is manufactured by integrally sintering and, the wiring board can be made flat and the adhesion strength of the wiring conductor 2 to the insulating substrate 1 can be made extremely large. Therefore, in the copper powder 5 whose surface is coated with aluminum oxide 4, the amount of aluminum oxide is 0.05 to 1.0 with respect to 100 parts by weight of copper powder.
It is preferable to set the range of parts by weight.

Further, the copper paste may be aluminum oxide.
An organic binder for binding the copper powder 5 coated with 4 into a paste form is added.

As the organic binder, an organic polymer material such as ethyl cellulose, nitrocellulose, acrylic resin, etc. is used. If the addition amount is less than 0.5 parts by weight with respect to 100 parts by weight of copper powder, the copper paste is added to the glass ceramic green sheet. When printed and applied in a predetermined pattern on, the copper paste pattern tends to peel off more easily than the ceramic green sheet, and when it exceeds 10.0 parts by weight, the viscosity of the copper paste becomes high and the glass ceramic green sheet is screen-printed by the screen printing method. Printability when printing tends to deteriorate. Therefore, the organic binder is copper powder.
It is preferable to set it in the range of 0.5 to 10.0 parts by weight with respect to 100 parts by weight. Furthermore, a solvent for imparting fluidity to the copper paste is added to the copper paste.

As the solvent, butyl carbitol acetate, alpha terpineol, etc. are used, and copper powder 100
If the amount is less than 5.0 parts by weight, the fluidity of the copper paste becomes poor and the printability tends to deteriorate when the copper paste is printed in a predetermined pattern on the glass ceramic green sheet. If it exceeds, the fluidity of the copper paste becomes high, and when the copper paste is printed and applied in a predetermined pattern on the glass ceramic green sheet, bleeding or the like tends to occur in the pattern. Therefore, the solvent added to the copper paste is preferably in the range of 5.0 to 40.0 parts by weight with respect to 100 parts by weight of the copper powder.

The copper paste contains a filler having the same composition as that of the insulating substrate 1 in an amount of 1.0 to 15.0 parts by weight based on 100 parts by weight of copper powder.
It is possible to firmly connect the wiring conductor 2 to the insulating base 1 while keeping the electric resistance value thereof to be small. Therefore,
The copper paste contains a filler having the same composition as the insulating substrate in an amount of 1.0 to 15.0 with respect to 100 parts by weight of the copper powder.
It is preferable to add it in the range of parts by weight.

Thus, the wiring board manufactured by using the above-mentioned copper paste of the present invention has the semiconductor element 3 on the wiring conductor 2.
Etc. are electrically connected, and the semiconductor element 3 is connected via the wiring conductor 2.
It functions as a circuit wiring board or a package for accommodating semiconductor elements by taking an electric signal in and out of the circuit.

Next, the operation and effect of the present invention will be described with reference to experimental examples described below.

Experimental Example First, the surface shown in Table 1 is 0.02 to
Average particle size 4 coated with 2.0 parts by weight of aluminum oxide
Prepare 6 kinds of copper powder with μm and BET value of 0.8 m ² / g, and add and mix 5 g of ethyl cellulose, 15 g of dibutyl phthalate, and 15 g of butyl carbitol acetate to 100 g of each copper powder and mix them to prepare a copper paste sample. Adjust.

The prepared copper paste sample was replaced with silicon oxide 37
% By weight, 35% by weight of aluminum oxide, magnesium oxide
10% by weight, zirconium oxide 5% by weight, calcium oxide
Warp measurement of 50 mm in length, 10 mm in width, and 20 μm in thickness by screen printing on a glass ceramics green sheet with a length of 65 mm, a width of 15 mm, and a thickness of 0.5 mm containing trace amounts of 2% by weight, lithium oxide, sodium oxide, potassium oxide, etc. Pattern and 2 mm diameter, 20 μm thick adhesion strength measurement pattern are applied by printing. After degreasing at 650 ° C or below, baking is performed at a temperature of 950 ° C to obtain 20 test pieces each. About the warp measurement pattern is measured in the length direction with a surface roughness meter, the amount of displacement in the height direction of the warp measurement pattern is divided by the measurement length, and the average value is used as the warp value. Solder one end of a copper wire with a diameter of 0.5 mm and a length of 20 mm to the adhesion strength measurement pattern, pull the other end of the copper wire perpendicular to one side of the test, and measure the adhesion strength at one end of the soldered conductor wire. When you remove it from the test piece with the pattern The average of the values obtained by dividing the tensile force by the area of the adhesion strength measurement pattern is taken as the adhesion strength of the wiring conductor, and the warp measurement pattern and the adhesion strength measurement pattern of the test piece are binocular with a magnification of 10 times. The presence or absence of blisters was confirmed by observing with a microscope.

The sintering start temperature of the copper powder in each sample shown in Table 1 was determined by heating and drying each sample at a temperature of about 80 ° C.
The butyl carbitol acetate contained in each copper paste sample was scattered and made into a powder, which was press-formed with a press molding machine to form a rod shape with a length of 10 mm and a diameter of 5 mm, which was then analyzed by a thermomechanical analyzer. Installed inside and from room temperature to approx.
The temperature at which contraction started after heating to a temperature of 1000 ° C. was measured as the contraction start temperature of the copper powder.

In Table 1, Sample No. 1 is a conventional copper paste in which copper in the copper paste is not coated with aluminum oxide.

The above results are shown in Table 1.

[0045]

[Table 1]

As can be seen from Table 1, the copper paste containing the copper powder coated with aluminum oxide of the present invention covers the test piece of the pattern more than the conventional copper paste in which copper is not coated with aluminum oxide. The adhesion strength is strong and the warp of the test piece is also small. In particular, when a copper paste containing copper powder in an amount of 0.02 to 1.0 parts by weight of aluminum oxide coating the copper powder is used, the warp of the test piece is extremely small at 50 μm or less, and the test piece of the copper metal layer is not covered. The adhesion strength is also extremely strong at 2.5 kg / mm ² . No blistering was observed in the case where the copper paste containing the copper powder coated with aluminum oxide of the present invention was used.

[0047]

EFFECTS OF THE INVENTION According to the copper paste of the present invention, since the surface thereof contains the copper powder coated with aluminum oxide, the sintering starting temperature is the glass ceramics starting temperature (about 700 to 800 ° C.). And the temperature of the binder contained in the copper paste is 700 to 800 ° C, which is higher than the temperature (650 ° C) at which the binder contained in the copper paste is completely decomposed and scattered. As a result, the glass-ceramic green sheet on which the copper paste is printed and applied is fired, When a wiring board is manufactured by sintering and integrating ceramics and copper powder, the binder contained in the copper paste is completely decomposed and scattered, and then the copper paste is sintered and shrunk at substantially the same time as the glass ceramics. The substrate becomes flat, the adhesion strength of the wiring conductor to the insulating base becomes extremely large, and the wiring conductor is free from blister.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a wiring board manufactured using the copper paste of the present invention.

FIG. 2 is a view for explaining a copper powder whose surface is coated with aluminum oxide, which is used in the copper paste of the present invention.

[Explanation of symbols]

 1 ... Insulating substrate 2 ... Wiring conductor 3 ... Semiconductor element 4 ... Aluminum oxide 5 ... Copper powder

Claims (2)

[Claims] 1. A copper paste comprising a copper powder whose surface is coated with aluminum oxide, an organic binder that binds the copper powder, and a solvent that makes the organic binder have a predetermined viscosity. 2. The copper paste according to claim 1, wherein the amount of aluminum oxide is 0.02 to 1.0 part by weight with respect to 100 parts by weight of copper powder.