JP2555770B2 - Copper thick film circuit substrate and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a copper thick film circuit substrate and a method for manufacturing the same, and more specifically, a substrate used for a thick film hybrid IC, in which copper is deposited on a ceramic substrate such as alumina. The present invention relates to a copper thick film circuit substrate having a wiring pattern formed as a conductor, and a method for manufacturing the same.

2. Description of the Related Art In general, when manufacturing a copper thick film circuit board using a copper paste whose main component is metallic copper powder, first, a circuit pattern of the copper paste is printed on the ceramic substrate by a method such as screen printing, and then nitrogen. After the binder removal step in a firing furnace in an atmosphere, firing is performed at a high temperature of 850 to 950 ° C.

When a circuit pattern is printed on a ceramic substrate using copper paste, the printed film thickness must be about 17 μm or more after firing in order to secure the adhesive strength of the copper thick film conductor. , And volume shrinkage during firing are taken into consideration.

Further, the binder removal step is performed to remove organic substances such as polymer resin contained as a binder component in the copper paste, and is maintained at a relatively low temperature (about 450 to 700 ° C) in the firing furnace. 10pp in the removed binder process section
It is performed by adding a very small amount of oxygen of about m or less.

However, it is difficult to control the addition of a small amount of oxygen, and uncertain binder removal processing or copper component oxidation is likely to occur. The uncertain binder removal process causes deterioration of the adhesive strength of the copper thick film conductor, while the oxidation of the copper component deteriorates the solder wettability and the conductive resistance value.

As a method for preventing the oxidation of the copper, there is a method of firing the copper paste at a high temperature in air or an atmosphere containing oxygen, and then performing a reduction treatment in a hydrogen atmosphere at a temperature range of 300 to 500 ° C for 1 to 10 minutes. It has been disclosed (Japanese Patent Laid-Open No. 63-1174).
90 publication).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-described conventional method for manufacturing a copper thick film circuit substrate, the film thickness after firing is required to be about 17 μm or more in order to secure the adhesive strength of the copper thick film conductor. However, with a film thickness of about 17 μm or more, the line width and the distance between lines of the wiring pattern remain at a minimum of about 150 μm, and there is a problem that it is difficult to achieve higher density wiring with the current manufacturing technology.

Even if the line width could be reduced to less than 150 μm with a film thickness of about 17 μm by improving printing technology, the adhesive strength of the copper thick film conductor will decrease in proportion to the decrease in the contact area with the substrate. With the bonding strength that has been realized, there is a problem that the bonding strength of the thin line portion is significantly insufficient, and the reliability becomes low.

Furthermore, when a small amount of oxygen is added in the binder removal step, it is difficult to control the addition of a small amount of oxygen, and thus the incomplete binder removal process is likely to occur. Incomplete debinding process causes deterioration of the adhesive strength of the copper thick film conductor. In addition, there is a problem that the oxidation of the copper component causes deterioration of the solder wettability and the conductive resistance value and the deterioration of the basic characteristics of the copper thick film conductor.

Further, as disclosed in JP-A-63-117490, the copper paste is fired in air and then 500 ° C.
Even if the reduction treatment is performed in a hydrogen atmosphere of a certain degree, since the copper oxide once formed is not sufficiently reduced,
Conductive resistance does not recover to the level of normal copper conductors.
Furthermore, regarding solder wettability, for example, if firing is performed in an atmosphere containing 5,000 ppm oxygen, then 500 ° C
Even if reduction treatment with hydrogen is performed to a certain degree,
After all, there was a problem that it did not recover sufficiently and was not satisfactory.

The present invention has been invented in view of the above-mentioned problems, and is a basic characteristic as a copper thick film circuit substrate, that is, a copper thick film that is satisfactory in all properties of adhesive strength, conductive resistance and solder wettability. An object is to provide a circuit board and a method for manufacturing the same.

Means for Solving the Problems In order to achieve the above object, a copper thick film circuit substrate according to the present invention is a copper thick film circuit substrate in which a copper thick film conductor is formed on a ceramic substrate. Lead tungstate is present at the interface between the copper thick film conductor and (1).

Further, the copper thick film circuit substrate according to the present invention has the above (1).
In the copper thick film circuit substrate described, lead tungstate is
It is characterized by being PbWO ₄ (2).

Further, the method for manufacturing a copper thick film circuit substrate according to the present invention,
In the method for producing a copper thick film circuit board according to (1) above, a copper paste containing metallic copper powder as a main component and containing PbO and W or WO ₃ is used in an atmosphere satisfying the conditions of the following formulas. Of the binder removal process and a high-temperature baking process continuously performed thereafter, and the following ~
It is characterized in that a treatment including a reduction treatment step is carried out in a hydrogen atmosphere or a carbon monoxide atmosphere satisfying the condition of the formula (3).

5 ≤ x ≤ 5,000 ... 100 ≤ y ≤ 550 ... y ≤ 192.1 log ₁₀ x + 165.8 ... y ≥ 150.0 log ₁₀ x-4.845 ... where x: oxygen amount in the firing process (ppm) y: temperature in the reduction process (° C ), Respectively.

Further, the method for manufacturing a copper thick film circuit substrate according to the present invention,
In the method for producing a copper thick film circuit board according to (1) above, a copper paste containing metallic copper powder as a main component and containing PbO and W or WO ₃ is used in an atmosphere satisfying the conditions of the following formulas. Of the binder removal process and a high-temperature baking process continuously performed thereafter, and the following ~
It is characterized in that a treatment including a reduction treatment step is performed in a hydrogen atmosphere or a carbon monoxide atmosphere satisfying the condition of the formula (4).

15 ≤ x ≤ 5,000 ... 100 ≤ y ≤ 525 ... y ≤ 200 log ₁₀ x + 150 ... y ≥ 286.1 log ₁₀ x -308.4 ... y ≥ 115.3 log ₁₀ x + 84.7 ... where x: amount of oxygen in the firing process (ppm) y: reduction Each represents the temperature (° C) in the treatment step.

Further, the method for manufacturing a copper thick film circuit substrate according to the present invention,
In the method for manufacturing a copper thick film circuit substrate according to (3) or (4) above, the firing step and the reduction treatment step are performed in one firing furnace, and oxygen is supplied to the firing furnace part for performing the firing step. It is characterized in that hydrogen is supplied into the firing furnace section for performing the reduction treatment step (5).

Action As a result of various studies on manufacturing methods for obtaining stable characteristics by preventing deterioration of basic characteristics in copper thick film circuit boards,
The following facts were found.

The copper thick film circuit substrate on which the copper paste is printed is fired in a tunnel type continuous firing furnace. This firing process is performed in a relatively low temperature region (about 450 to 700
C)) (hereinafter referred to as the binder removal region) to remove the organic binder component by adding oxygen, and a high temperature region (about 850 to 950 ° C) in the continuous firing furnace that follows.
(Hereinafter, referred to as a high temperature firing region), a high temperature firing process for performing a sintering reaction of a metal powder or the like.

When the amount of added oxygen in the binder removal region is increased beyond the several ppm that has been generally adopted in the past, the adhesion strength of the copper thick derivative to the substrate increases.

Oxygen added in the binder removal area of the continuous firing furnace is consumed for removing organic substances in the paste, and also partially moves or diffuses to the high temperature firing area of the continuous firing furnace.

The oxygen in the high-temperature firing region of the continuous firing furnace is a part of the oxygen added in the binder removal region as described above moves or diffuses in the continuous firing furnace. Therefore, the oxygen concentration in the high temperature firing region is equal to or lower than the oxygen concentration in the binder removal region.

When the oxygen concentration during the high temperature firing process in the high temperature firing region is increased, the conductive resistance value and the solder wettability are deteriorated. However, both properties can be improved to some extent by the subsequent reduction process in the hydrogen atmosphere.

In addition, the reduction treatment temperature required to improve the deterioration of the solder wettability also increases as the oxygen concentration increases during the high temperature firing treatment.

Furthermore, the amount of copper oxide generated in the copper thick film conductor increases with the increase of oxygen concentration during the high temperature firing treatment, but porosity (pores) is generated by the reduction of copper oxide by the reduction treatment. , Changes to a more porous film quality than when fired.

If the oxygen concentration during high-temperature baking exceeds 5,000 ppm, the conductivity resistance will remain deteriorated and will not recover even if reduction treatment with hydrogen is performed at a high temperature of about 600 ° C. If less than 5,000 ppm, the conductive resistance value is improved by the reduction treatment.

Although the adhesive strength decreases as the temperature of the reduction treatment with hydrogen increases, the lower the rate of reduction of the adhesive strength as the amount of oxygen added during the high temperature firing treatment increases, the more stable the adhesive strength characteristics become.

In addition, the adhesive strength of the copper thick film conductor subjected to the firing / reduction treatment after the temperature cycle test is large, and the strength deterioration rate is small.

When firing a copper paste containing PbO and W or WO ₃ , if the amount of oxygen added is increased above the commonly used level of several ppm, PbWO ₄ is generated at the copper thick film conductor / substrate interface. The production amount also increases in proportion to the added oxygen amount.

The PbWO ₄ formed between the copper thick film conductor and the substrate is stable and does not change even if hydrogen reduction is performed after firing.

Based on these facts, various experiments will be further conducted to propose the best method for the copper thick film circuit substrate and its manufacturing method.

If the oxygen concentration in the binder removal area during firing is less than 5 ppm, it becomes difficult to completely remove the binder component in the copper paste, and it becomes impossible to secure the adhesive strength. 2 and 3 show the amount of oxygen in the binder removal area during firing.
The result of analysis by X-ray diffraction of a sample that was reduced to 3 ppm or 500 ppm and then further reduced in a hydrogen atmosphere at 500 ° C shows that the oxygen concentration in the binder removal region is less than 5 ppm, copper thickness PbWO _{4 at the} membrane conductor / substrate interface
Was confirmed not to be generated.

Further, from the above, the oxygen concentration during the high temperature firing treatment was set to 5000 ppm or less as a range in which good solder wettability and a conductive resistance value are secured by the reduction treatment after firing.

Also, the temperature y in the reduction process is set to be 5 p
When it is set within the range of pm or more and 100 ppm or less to satisfy the above formula, the adhesive strength does not deteriorate. this is,
It is considered that the production amount of the oxide exhibiting the adhesive strength in the copper thick film circuit substrate can be secured even when the reduction treatment with hydrogen is performed. In addition, the reduction treatment temperature y is
When the temperature exceeds 550 ° C, the reducing power becomes extremely large, and the adhesive strength is extremely reduced.

Furthermore, when the reduction treatment is performed in a temperature range lower than the reduction treatment temperature y represented by the above formula, the solder wettability does not recover to a practical level. This is because the reduction reaction on the copper thick film conductor surface, that is, the reaction represented by Cu ₂ O + H ₂ → 2Cu + H ₂ O does not proceed sufficiently in the temperature range lower than y expressed by the above formula, and the amount of unreduced Cu ₂ O is large. Exists,
This hinders solder wettability.

Based on the above consideration, the conditions represented by the above formulas (Fig. 1) were set.

Furthermore, within the range represented by the above formula (FIG. 1), the range represented by the above formula (FIG. 1) was proposed as a range in which the adhesive strength and the like are particularly excellent. In this range, particularly excellent characteristics as a copper thick film circuit substrate are obtained, as will be demonstrated by the examples described later.

Further, in the above-described method for manufacturing a copper thick film circuit substrate, the firing step and the reduction treatment step are performed in one firing furnace, and oxygen is supplied into the firing furnace portion for performing the firing step, and the reduction treatment step is performed. By supplying hydrogen or carbon monoxide into the firing furnace portion to be performed, a copper thick film circuit substrate having excellent characteristics can be continuously and efficiently manufactured.

Further, in a copper thick film circuit substrate in which a copper thick film conductor is formed on a ceramic substrate, the presence of lead tungstate at the interface between the ceramic substrate and the copper thick film conductor, The adhesive strength with the copper thick film conductor is improved.

It was also confirmed that the lead tungstate was present in the form of PbWO ₄ , for example.

Furthermore, in the copper thick film circuit substrate described above, a copper paste containing metallic copper powder as a main component and containing PbO and W or WO ₃ is used, and a firing step in an atmosphere satisfying the conditions of the above formulas, and By including a reduction treatment step in a hydrogen atmosphere or a carbon monoxide atmosphere satisfying the above conditions (1) to (3), the adhesive strength between the substrate and the copper thick film conductor is further improved, and even after a temperature cycle test. Thus, a copper thick film circuit substrate having stable adhesive strength, particularly excellent adhesive strength, and also excellent in conductive resistance value and solder wettability is manufactured.

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of the copper thick film circuit substrate and the manufacturing method thereof according to the present invention will be described below.

First, an alumina substrate having a predetermined shape is prepared, and a copper paste containing a metallic copper powder as a main component, Pb, W, and a binder component made of a polymer resin is used on the surface of the alumina substrate by screen printing. Was applied. After that, the binder removal area (450
(About 700 ° C.), the binder removal treatment was performed by adjusting the oxygen addition amount to 3 to 8000 ppm.

After that, high temperature firing treatment was performed in a firing temperature range of 850 to 950 ° C. in a high temperature firing region in a belt conveyor type continuous firing furnace.

After that, reduction treatment was performed at a reduction temperature of 200 to 600 ° C. in a reduction treatment section in a hydrogen atmosphere or a carbon monoxide atmosphere.

The evaluation test of the copper thick film circuit substrate formed on the ceramic substrate was performed as follows.

First, the adhesive strength test is conducted by soldering an annealed copper wire with a diameter of 1.2 mm to the center of the land of a 2 × 2 mm thick copper conductor formed on a 96% alumina substrate, and then pulling it with an initial strength of 150 The adhesive strength after aging at 1000 ° C. for 1000 hours and the adhesive strength after the temperature cycle test were measured. The temperature cycle test was carried out for 500 cycles at a temperature from −55 ° C. to + 150 ° C. The case where the initial strength was less than 18 kgf and the case after aging was less than 12 kgf were judged as poor strength.

In addition, the solder wettability test was conducted with a 230 mm 2 × 2 mm land.
It was carried out by immersing it in eutectic solder (63% Sn-37% Pb) in a molten state at ± 10 ° C for about 5 seconds, then pulling it up, and measuring the area ratio of the well-wetted portion in the land portion. . The solder wettability was determined to be good when the solder wettability of the land portion was 90% or more.

Further, the conductive resistance value is L (length) / W (width) formed =
The conductive resistance value of the measurement conductor pattern having a ratio of 150 was measured, and then the film thickness was measured and converted into a value at a film thickness of 10 μm. The case where the conductive resistance value exceeds 2.8 mΩ was determined to be defective.

Table 1 shows the test results of Examples and Comparative Examples. Among the evaluations of ○, the adhesive strength is 20 kgf or more, which is particularly excellent, and the solder wettability is also excellent.

FIG. 1 is a graph in which the data shown in Table 1 is plotted, and FIG. 1 also shows the range of the above formulas and the range of the formulas. All of the evaluations of ∘ are within the range shown by the above formulas. Moreover, all the evaluations of ⊚ are within the range shown by the above formulas.

An example of good solder wettability and bad solder wettability is shown in FIG. FIG. 4 (a) (Sample No. 8) shows a good case, and most of the land 1 is covered with the solder 2. FIG. 4B (Sample No. 7) shows a case where the solder wettability is poor, and a considerable portion of the land 1 is exposed without being covered with the solder 2.

Further, when treated under the conditions within the scope of the present invention, sample N
Even if the film thickness is thin as in O.14 to 16, the adhesive strength is strong,
On the other hand, when treated under a condition outside the scope of the present invention, the adhesive strength is remarkably reduced in the case where the film thickness is thin (Sample No. 17), which is unreliable and unsuitable for use for high-density wiring. .

In addition, the sample N when treated under the conditions within the scope of the present invention
In both o.19 and No.20, the adhesive strength is good even after the cycle test, but when treated under the conditions outside the scope of the present invention, after the cycle test like No.21 and No.22. It can be seen that the adhesive strength is greatly reduced.

Further, when treated under the conditions within the range of the present invention, all show good initial adhesive strength, especially when treated under the conditions within the range shown by the above formulas marked with ⊚, the initial adhesive strength, The adhesive strength after aging and the cycle test shows even better adhesive strength.

Furthermore, when the reduction temperature is too high as in sample No. 11, sufficient adhesive strength cannot be obtained, and conversely, in tests No. 7 and No. 2
When the reduction temperature is too low as in the case of 3, the practical solder wetting performance is insufficient, so that it is not suitable as a manufacturing condition.

As described above, according to the copper thick film circuit board and the method for manufacturing the same according to the present embodiment, it is possible to secure sufficient adhesive strength even when the film thickness is reduced, and to keep the line width and the line interval of 150 μm or less. It is possible to manufacture the one suitable for forming the high-density wiring pattern possessed. Moreover, it has a sufficient effect on the improvement of the adhesive strength of the copper thick film conductor after the temperature cycle test, and the basic characteristics of the copper thick film circuit board are the adhesive strength, the conductive resistance value and the solder wettability. It is possible to manufacture a copper thick film circuit board that is satisfactory in all characteristics.

EFFECTS OF THE INVENTION As is clear from the above description, according to the copper thick film circuit substrate and the method for manufacturing the same according to the present invention, these include a firing step and a reduction treatment step in a hydrogen atmosphere or a carbon monoxide atmosphere. By performing each step by satisfying the conditions of the above formula, it is possible to obtain excellent in all the characteristics of the adhesion strength, the conductive resistance value and the solder wettability, which are the basic characteristics of the copper thick film circuit board. .

Further, by adopting the treatment steps satisfying the above conditions (1) to (4), it is possible to manufacture a copper thick film circuit board which is particularly excellent in adhesive strength and has sufficiently satisfactory values for other characteristics.

Further, oxygen is supplied into the firing furnace section for performing the firing step, and hydrogen or carbon monoxide is supplied to the firing furnace section for performing the reduction treatment step.
By carrying out the treatment step satisfying the conditions of the formulas or to, it is possible to continuously and efficiently manufacture the copper thick film circuit substrate having excellent characteristics.

Further, in a copper thick film circuit substrate in which a copper thick film conductor is formed on a ceramic substrate, when lead tungstate is present at the interface between the ceramic substrate and the copper thick film conductor, the substrate It becomes possible to improve the adhesive strength between the copper thick film conductor and PbWO.
_When it is ₄ , the adhesive strength between the substrate and the copper thick film conductor can be further improved.

Further, in the above-mentioned method for manufacturing a copper thick film circuit substrate, a copper paste containing metallic copper powder as a main component and containing PbO and W or WO ₃ is used, and firing is performed in an atmosphere satisfying the conditions of the above expressions. In the case of including a step and a reduction treatment step in a hydrogen atmosphere or a carbon monoxide atmosphere satisfying the above conditions (1) to (4), the adhesive strength between the substrate and the copper thick film conductor is stable even after a temperature cycle test. In particular, it is possible to manufacture a copper thick film circuit board having excellent adhesive strength and excellent basic characteristics such as a conductive resistance value and solder wettability. Therefore, it becomes possible to form a high-density wiring pattern having a fine line width and a distance between lines.
Moreover, it is possible to provide a highly reliable copper thick film circuit substrate.

[Brief description of drawings]

FIG. 1 is a diagram showing the range of the method according to the present invention with the oxygen addition amount in the firing process and the reduction temperature in the reduction treatment process as parameters, and a diagram in which the execution conditions of Examples and Comparative Examples are also plotted. Figure 2 (a) shows the oxygen content during firing.
The figure which shows the analysis result by the X-ray diffraction of the board | substrate for copper thick film circuits after baking at 3 ppm, FIG.2 (b) is the figure which shows the analysis result after reduction of FIG.2 (a), Figure (a) is a diagram showing the analysis results by X-ray diffraction of the copper thick film circuit board after firing when the amount of oxygen during firing is 500 ppm, and Figure 3 (b) is the reduction of Figure 3 (a). Fig. 4 (a) showing the subsequent analysis results
(B) is a figure showing an example of a test result of solder wettability.

Claims (5)

(57) [Claims] 1. A copper thick film circuit substrate having a copper thick film conductor formed on a ceramic substrate, wherein lead tungstate is present at an interface between the ceramic substrate and the copper thick film conductor. A copper thick film circuit board. 2. The lead tungstate is PbWO _4.
The copper thick film circuit substrate described. 3. A debindering treatment in an atmosphere satisfying the following expressions (1) to (4) is continuously performed using a copper paste containing metallic copper powder as a main component and containing PbO and W or WO _3. 2. The copper thick film circuit according to claim 1, wherein a baking treatment comprising a high temperature baking treatment and a treatment including a reduction treatment step in a hydrogen atmosphere or a carbon monoxide atmosphere satisfying the following expressions (1) to (4) are performed. Substrate manufacturing method. 5 ≤ x ≤ 5,000 ... 100 ≤ y ≤ 550 ... y ≤ 192.1 log ₁₀ x + 165.8 ... y ≥ 150.0 log ₁₀ x-4.845 ... where x: oxygen amount in the firing process (ppm) y: temperature in the reduction process (° C ), Respectively. 4. A binder paste containing metal copper powder as a main component and containing PbO and W or WO ₃ in a atmosphere satisfying the conditions of the following expressions (1) to (4), followed by continuous debinding. The copper thick film circuit according to claim 1, wherein a treatment including a firing step consisting of a high temperature firing treatment and a reduction treatment step in a hydrogen atmosphere or a carbon monoxide atmosphere satisfying the following conditions (1) to (4) is performed. Substrate manufacturing method. 15 ≤ x ≤ 5,000 ... 100 ≤ y ≤ 525 ... y ≤ 200 log ₁₀ x + 150 ... y ≥ 286.1 log ₁₀ x -308.4 ... y ≥ 115.3 log ₁₀ x + 84.7 ... where x: amount of oxygen in the firing process (ppm) y: reduction Each represents the temperature (° C) in the treatment step. 5. A firing step and a reduction treatment step are performed in one firing furnace, oxygen is supplied into the firing furnace section for performing the firing step, and hydrogen is supplied to the firing furnace section for performing the reduction treatment step. A method for manufacturing a copper thick film circuit substrate according to claim 3 or 4.