JPH11103169A - Glass ceramic wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass ceramic wiring board, which is provided with a copper conductor conductor layer formed on the surface of the wiring board with a stable bonding strength and a high adhesion, even if the glass ceramic wiring board is dipped into an acid or an alkaline etching liquid, a cleaning liquid, a plating solution or the like and has airtightness and high reliability. SOLUTION: In a conductor layer, which is formed by firing simultaneously with a glass ceramic porcelain and contains copper as its main component, the thickness of an internal conductor layer in a wiring board is 7 to 15 μm, the thickness of a surface conductor layer on the wiring board is 12 μm or thicker and the ratio of the thickness of a coated layer formed by coating on the surface conductor layer to the thickness of the surface conductor layer and the ratio of the thickness of the coated layer to the thickness of the surface conductor layer are 0.3 or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass-ceramic wiring board applied to various circuit boards or high-frequency multilayer wiring boards having a conductor layer made of a low-resistance copper conductor.

[0002]

2. Description of the Related Art Conventionally, as an insulating base for various kinds of wiring boards such as a semiconductor element housing package for housing a semiconductor element and a hybrid integrated circuit device mounted with various electronic components in addition to the semiconductor element, an electric insulating property and a chemical insulating property are known. Alumina ceramics having excellent properties such as mechanical stability have been widely used.

However, in recent years, wiring boards frequently used in the high frequency range of 1 to 10 GHz in the communication field typified by mobile phones have been further reduced in conductor loss and reduced in size compared to the insulating base made of alumina ceramics. Therefore, copper (Cu) or gold (A) is used as a low-resistance conductor.
u), a glass-ceramic wiring board having a conductor layer formed of silver (Ag) and having a dielectric constant similar to that of alumina ceramics has been attracting attention as a wiring board for the communication field.
Application to power amplifier modules and the like of mobile phones is being studied.

As a low-resistance conductor constituting such a glass-ceramic wiring board, gold has the disadvantage that the cost is high, while silver can be fired in the air, and the wiring conductor formed on the surface of the insulating substrate is coated with a metal coating. Although wire bonding is possible even without performing this method, it is advantageous in terms of cost, but the silver wiring conductor has a disadvantage that it is inferior in reliability due to migration and solder erosion. Addition of palladium or the like is performed, but in that case, the conductor resistance becomes high, and there is a problem that it cannot be applied particularly to a wiring board used in the high frequency region.

Accordingly, although the low-resistance conductor must be fired in a non-oxidizing atmosphere and the wiring conductor on the surface of the insulating substrate needs to be coated with a metal, copper which can ensure high reliability can be obtained. The wiring of conductors has been intensively researched and developed.

A glass ceramic wiring board using copper as a wiring conductor is formed, for example, by forming a slurry prepared using glass ceramic raw material powder and an organic binder into a sheet, and then forming a via hole or the like in the obtained glass ceramic green sheet. And the via hole is filled with a conductive paste containing copper as a main component and a glass powder, and a predetermined wiring pattern is formed on the green sheet using a conductive paste made of the same copper metallized composition. After a plurality of these are aligned and pressure-laminated, they are generally produced by heating the laminated body in a non-oxidizing atmosphere composed of a nitrogen atmosphere containing water vapor to remove the binder and fire. (See Japanese Patent Application Laid-Open No. 5-243700).

[0007]

However, since the fired copper conductor obtained in the above proposal contains a glass component, the surface of the conductor layer made of the copper conductor is made of Ni-A.
When applying metal coating such as u plating or Cu-Au plating,
The glass-ceramic wiring substrate must be immersed in an acidic or alkaline etching solution or cleaning solution in order to remove the glass on the copper conductor surface in advance, and the glass-ceramic wiring substrate must be immersed in an acidic or alkaline plating solution in the plating process. Is soaked,
The etching solution, the cleaning solution, the plating solution or the like penetrates into the fine voids in the copper conductor, or the glass component in the copper conductor is eluted, whereby the interface structure between the copper conductor and the glass ceramic porcelain is eroded. There has been a problem that the bonding strength with a conductor layer made of a copper conductor is deteriorated.

Further, when the thickness of the internal conductor layer is increased, voids are easily generated on the green sheet laminating surface at the end of the internal conductor layer, so that the internal conductor layer is close to the outer peripheral portion of the glass ceramic wiring board. In this case, the gap is connected to the outer peripheral portion of the wiring board, and an etching solution, a cleaning solution, a plating solution, and the like penetrate, and the interface between the internal conductor layer and the glass ceramic porcelain is eroded, thereby reducing airtightness. There was also.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to stably bond a glass-ceramic wiring board to an acidic or alkaline etching solution, a cleaning solution, a plating solution, or the like. An object of the present invention is to provide a glass-ceramic wiring board having a conductor layer of a copper conductor formed with high strength and high adhesion, and having airtightness and high reliability.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the thickness of each conductor layer inside and on the surface of a glass ceramic wiring board, which is mainly composed of copper, and formed on the wiring board,
By controlling the thickness of the metal coating layer formed on the surface conductor layer to be within a certain range, the adhesion of the copper conductor to the conductor layer can be improved, and at the end of the internal conductor layer, The inventors have found that airtightness can be ensured by suppressing voids that are easily formed, and have led to the present invention.

That is, in the glass-ceramic wiring board of the present invention, the thickness of the internal conductor layer of the wiring board is 7 to 15 μm among the copper-based conductor layers formed by co-firing with the glass ceramic porcelain. The thickness of the surface conductor layer of the wiring board is 12 μm or more, and the ratio of the thickness of the coating layer formed on the surface conductor layer to the thickness of the surface conductor layer; The conductive layer has a thickness of 0.3 or less.

[0012]

According to the present invention, the thickness of the internal conductor layer mainly composed of copper in the glass ceramic wiring board is 7 to 15 μm.
m, the thickness of the surface conductor layer was increased to 12 μm or more, and the thickness of the metal coating layer formed on the surface conductor layer was set to 30% or less of the thickness of the surface conductor layer. In addition, in the pretreatment step, the treatment liquid suppresses the erosion of the interface structure between the surface conductor layer and the glass ceramic porcelain, and the interface structure can be maintained in a state after firing. Can stabilize the bonding strength.

Further, by limiting the thickness of the conductor layer mainly composed of copper inside the glass ceramic wiring board to 7 to 15 μm, a sufficiently low conductor resistance can be ensured, and a gap is formed at the end of the conductor layer. Can form a tissue that does not occur,
The airtightness of the wiring board can also be ensured.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The glass ceramic wiring board of the present invention will be described in detail below.

The copper-based conductor layer formed on the glass-ceramic wiring board of the present invention was formed into a paste with an organic binder and a solvent by adding a glass frit and, if necessary, a ceramic filler containing copper as a main component. It is formed using a copper conductor paste, and the copper conductor paste can be co-fired with glass ceramic porcelain.

The main component copper in the copper conductor paste is a spherical powder having an average particle diameter of 2 to 6 μm and a specific surface area of about 0.2 to 1.5 m ² / g. This is more preferable because it is difficult to generate voids by increasing the filling density of the copper powder in the copper conductor paste.

The glass frit to be added to the copper conductor paste has a glass transition point of 700 to 750 ° C. which can be co-fired with glass ceramic porcelain at a temperature of 700 to 1000 ° C. SiO ₂ -Al rapidly softened flowable at a temperature ₂ O ₃ -RO: 0.5 (R alkaline earth metal) -B ₂ O ₃ based glass is preferred, the amount added, the copper 100 parts by weight -5 parts by weight is preferred.

Further, ceramic powder can be added to the copper conductor paste in order to finely adjust the shrinkage behavior of the glass in the paste due to softening flow. Any material may be used as long as it does not easily react to form a compound, and examples thereof include Al ₂ O ₃ , SiO ₂ , and ZrO _{2. The} amount of the additive is 0.5 to 3 based on 100 parts by weight of the copper powder. It is desirable that the parts by weight be densely sintered.

On the other hand, the organic binder used for the copper conductor paste includes an acrylic resin, preferably methacrylic acid resin, which is excellent in thermal decomposability in a non-oxidizing atmosphere, and the solvent is dibutyl phthalate or the like. A general solvent for a conductive paste such as α-terpineol can be used, and a plasticizer can be added according to the characteristics of the organic binder.

Next, such a copper conductor paste is screen-printed on a green sheet containing glass ceramic raw material powder to form a conductor pattern in a predetermined pattern. After firing, a pattern to become an internal conductor layer of the glass ceramic wiring board is formed. If the thickness after printing is less than 7 μm, it is difficult to reduce the sheet resistance of the wiring conductor to 3 mΩ / □ or less, which is unsuitable for high frequency applications. Voids are likely to be generated on the sheet lamination surface, and when the pattern exists in a portion near the outer periphery of the wiring board, the voids are connected to the outer periphery of the wiring substrate, and the airtightness of the obtained glass ceramic wiring substrate is deteriorated. The length is limited to the range of 7 to 15 μm.

On the other hand, if the thickness of a pattern to be a conductor layer for depositing a metal coating layer on the surface of a glass ceramic wiring board after firing is less than 12 μm after firing, the wiring conductor and the glass during the plating process are required. There is a problem that the bonding strength of the wiring conductor is not stable due to the erosion of the interface structure of the ceramic porcelain. For example, when a copper conductor paste using a copper powder having a particle size of 6 μm is printed, the thickness direction of the copper conductor paste is reduced. This also means that two or more copper powders are required.

The thickness of the surface conductor layer is desirably about 30 μm or less from the viewpoint of workability in the screen printing process and that pressure is applied to portions other than the conductor portion when the green sheets are pressed and laminated.

Next, a plurality of green sheets on which the internal conductor layers are formed are laminated, and the green sheets on which the surface conductor layers are formed are laminated on both surfaces of the laminate, respectively.
After decomposing and removing organic binders, plasticizers, solvents, etc. contained in a nitrogen atmosphere containing water vapor at 500 ° C., the nitrogen atmosphere containing water vapor is also used as a firing atmosphere, and the firing temperature is set according to the composition of the glass ceramic material used. 800
The temperature is selected within the range of -1000 ° C. to be integrated by firing.

The thus obtained wiring board having a conductor layer containing copper as a main component inside and on the surface is made of Ni-Au in order to prevent oxidation of the wiring conductor on the surface and to improve the wettability of solder and brazing material. Alternatively, a metal coating layer made of Cu-Au or the like is applied.

Prior to the formation of the metal coating layer, a glass component on the copper conductor surface is removed by etching to improve the adhesion of the metal coating layer. Immersion in an acidic cleaning solution, the immersion conditions being appropriately selected depending on the glass ceramic porcelain and the copper conductor.

The plating solution for forming the metal coating layer depends on the kind, but since a strongly acidic or strongly alkaline solution is generally used, first, the thickness of the surface conductor layer is set as described above. And the ratio of the thickness of the metal coating layer to the thickness of the surface conductor layer satisfies the relationship of 0.3 or less between the thickness of the metal coating layer and the thickness of the surface conductor layer. is necessary.

That is, if the ratio exceeds 0.3, the bonding strength between the surface conductor layer and the glass ceramic porcelain decreases due to the elution of the copper conductor of the surface conductor layer by the plating solution and the residual stress caused by the plating film. And the adhesion becomes unstable.

As described above, it is possible to obtain a glass-ceramic wiring board having a conductor layer containing copper as a main component inside and on the surface of the substrate and having the metal coating layer formed on the surface conductor layer. it can.

[0029]

EXAMPLES The glass ceramic wiring board of the present invention was evaluated as follows.

First, SiO ₂ —Al ₂ O ₃ —RO (R: alkaline earth metal) having a glass transition point (Tg) of 720 ° C. with respect to 100 parts by weight of copper powder having an average particle size of 5 μm.
-B ₂ O ₃ based glass frit and Al ₂ O ₃ powder as filler, respectively 2 parts by weight, 0.1 parts by weight,
An organic binder and a solvent were added to the mixture and kneaded to prepare a copper conductor paste.

On the other hand, 44% by weight of SiO ₂ and Al ₂ O ₃
There 28 wt%, MgO 11 wt%, ZnO 8% by weight, B ₂ O ₃ is 9% by weight of a crystalline glass powder 61 wt% with the composition, powdered calcium 21 wt% zirconate, strontium titanate powder 16% by weight, Al ₂ O
_{(3) To a} glass ceramic raw material powder composed of 2% by weight of powder, 12% by weight of solid content of isobutyl methacrylate resin as an organic binder and 6% by weight of dibutyl phthalate as a plasticizer, and toluene and ethyl acetate as solvents are added. The mixture was mixed by a ball mill for 40 hours to prepare a slurry.

A glass ceramic green sheet having a thickness of 0.4 mm was formed from the obtained slurry by a doctor blade method.

Next, the copper conductor paste was used on a glass ceramic green sheet, and a pattern for bonding strength evaluation of 2 mm square was printed after firing for the surface conductor layer, and the line width was reduced after firing for the internal conductor layer. 2
A sheet resistance evaluation pattern printed with a thickness of 00 μm and a line length of 40 mm, and a pattern for evaluating the airtightness due to the opening of the laminated surface associated with the internal conductor layer, which is 60 mm square after firing as a pattern for evaluating the airtightness. Printed patterns were prepared.

In the glass ceramic green sheet for the surface conductor layer, via holes are formed at positions corresponding to both ends of the line of the internal conductor layer at the time of lamination, and a copper conductor paste is filled thereinto so that the inner surface of the substrate is filled with the copper conductor paste. The sheet resistance of the conductor layer was measured.

After sequentially stacking the green sheets thus obtained, each of the green sheets is placed one on each side of the vertical and horizontal sides of the airtightness evaluation pattern.
In order to remove organic components such as an organic binder in the laminate and carbon remaining after the organic components are decomposed, the laminate is cut at a temperature of 750 ° C. in a nitrogen atmosphere containing 55 mmHg of steam. After performing the heat treatment for holding for one hour, it was held at a temperature of 900 ° C. for one hour and sintered.

Thereafter, Ni plating and Au are applied on the surface conductor layer.
Plating was sequentially performed, and the thickness of the Au plating was all 1 μm, and a metal coating layer was formed thereon to form a glass ceramic wiring board for evaluation.

The cross section of the glass-ceramic wiring board for evaluation thus obtained is mirror-polished, and the cross section is photographed using a scanning electron microscope. From the photograph, the surface conductor layer, the inner conductor layer, and the metal coating layer are taken. Was measured for thickness.

Further, regarding the bonding strength of the surface conductor layer,
A copper lead wire was soldered to a 2 mm square surface conductor layer parallel to the substrate surface, the lead wire was bent in a direction perpendicular to the substrate surface, and a tensile test was performed at a speed of 10 mm / min, and the lead wire was peeled off. The load at that time was evaluated as the bonding strength.

Next, regarding the sheet resistance of the internal conductor layer, the resistance of the pad portion connected on the surface of the substrate through the via hole connected to the internal conductor layer was measured by a four-terminal method, and the sheet length was determined from the line length and line width. It was converted to resistance.

On the other hand, regarding the airtightness of the wiring board,
After pressurizing the plated glass-ceramic wiring board in He gas at 4 atm for 2 hours, leave it for 30 minutes, measure the leak amount with a leak detector, and measure 5 × 10 ⁻⁸ atm.
cc / secHe or less was determined to be good.

[0041]

[Table 1]

As is clear from the table, Sample No. 1, which is outside the scope of the present invention, has a large sheet resistance of 4.5 mΩ / □, Sample No. 6 has poor airtightness, and Sample No. 7, Nos. 13 and 16 each have a small bonding strength of 1.6 kg / 2 mm square or less between the surface conductor layer and the glass ceramic porcelain, and do not satisfy various characteristics required as a glass ceramic wiring board.

On the other hand, it can be seen that the glass ceramic wiring board according to the present invention satisfies the above-mentioned characteristics.

The present invention is not limited to the above-described embodiment.

[0045]

As described in detail above, in the glass ceramic wiring board of the present invention, the thickness of the internal conductor layer mainly composed of copper is 7 to 15 μm, and the thickness of the surface conductor layer is 12 μm or more. Since the thickness of the metal coating layer to be formed on the surface conductor layer is not more than 0.3 times the thickness of the surface conductor layer, when the metal coating layer is formed, Since the interfacial structure with the glass ceramic porcelain can be suppressed from being eroded, and the occurrence of voids at the lamination interface at the end of the inner conductor layer can be suppressed, the bonding strength of the surface conductor layer is stable and high with the glass ceramic porcelain. Adhesiveness can be obtained, and a glass-ceramic wiring board excellent in airtightness can be obtained.

Claims (1)

[Claims] 1. A glass-ceramic wiring board having a wiring conductor containing copper as a main component and formed by co-firing with a glass-ceramic ceramic, wherein the thickness of the internal conductor layer of the glass-ceramic wiring board is 7 to 15 μm. A thickness of the surface conductor layer of the glass ceramic wiring board is 12 μm or more, and a ratio of the thickness of the metal coating layer formed on the surface conductor layer to the thickness of the surface conductor layer (the thickness of the metal coating layer) (Thickness / thickness of surface conductor layer) is 0.3 or less.